METHOD AND APPARATUS FOR WIRELESS RESOURCE

ALLOCATION

Field of the Technology

The present invention generally relates to orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) communication systems. More particularly, the present invention relates to novel and improved methods of allocating radio resources for transmission in a wireless communication system.

Background of the Invention

Demand for wideband wireless high-speed data services are on the rise. In a wideband wireless communications system, the signal tends to suffer from the frequency selective fading due to multi-path. Orthogonal Frequency Division Multiplexing (OFDM) systems have been proposed to combat the frequency selective fading by dividing the total bandwidth into a plurality of subcarriers where the bandwidth on each of multiple subcarriers is sufficiently narrow to enable the data modulation symbols carried by that subcarrier to experience relatively flat fading.

Orthogonal Frequency Division Multiple Access (OFDMA) systems use the OFDM modulation technique to multiplex the traffic data of a plurality of mobile stations (MS) in frequency and time. FIG. IA illustrates that in an OFDMA system, the available radio resource 100 over one time interval (frame) for traffic data, which may or may not include the radio resource occupied by the guard band, the control channels, the pilot or other overhead channels, is divided in time and frequency. The smallest bin 110 is one subcarrier in frequency over one OFDM symbol period in time. The forward shared scheduling channels (F-SSCH) transmit assignment messages that communicate which mobile station (MS) is assigned with which bin or group of bins for data transmission. In order to reduce the overhead of the F-SSCH, a plurality of subcarriers over a period of one frame, consisting of a plurality of OFDM symbols in time, are assigned to a mobile station for data transmission.

In a cellular network or an ad hoc network, some mobile stations may be moving at fast rate of speed with respect to the base station, while other mobile stations are more stationary when they transmit or receive data. Some mobile stations experience severe multi-path while others have a near line-of-sight channel with the base station antenna. Therefore, two types of assignment strategies have been proposed for an OFDMA-based wireless communications system.

Referring to FIG. IA as an illustrative example, the total radio resource 100 over one frame is divided up for four different assigned mobile stations, indicated by different patterns 115, 120, 125, 130, respectively. The radio resource assigned for a particular mobile station in FIG. IA is disjoint in frequency with equal spacing between the adjacent assigned subcarriers and disjoint in time with frequency offset hopping from OFDM symbol to OFDM symbol. This type of assignment is called distributed assignment. In general, the radio resource assigned to a user (mobile station) via a distributed assignment is disjointed in either time or frequency or both.

Referring to FIG. IB as another illustrative example, the total radio resource 150 is divided up for four different assigned mobile stations, indicated by shade patterns 160, 165, 170, 175, respectively. The radio resource assigned for a particular mobile station in FIG. IB is contiguous in both frequency and time. This type of assignment is called localized assignment.

In order to optimize the utilization of the radio resource in an OFDMA-based wideband wireless communications system, a method is needed to multiplex the data packets of multiple mobile stations with different channel fading conditions using minimal control overhead.

Summary of the Invention

It is an objective of the present invention to provide a radio resource assignment method and apparatus that gives the base station the flexibility to divide and assign the radio resource in time only, in frequency only, or in both time and frequency to each of a

plurality of mobile stations on a dynamic frame-by-frame basis in a wireless communication system using OFDMA.

It is another objective of the present invention to provide a method and apparatus for the base station to communicate the assignments to the mobile stations reliably, while minimizing the signaling overhead.

It is yet another objective of the present invention to provide a method and apparatus for the mobile station to detect the assignment from the base station reliably.

It is yet another objective of the present invention to provide a novel method and apparatus of inter-cell interference mitigation in a cellular system, preferably in an OFDMA-based wireless communication system.

It is yet another objective of the present invention to provide a method and apparatus for the base station to indicate the assignments to the mobile stations reliably meanwhile minimizing the signaling overhead.

It is yet another objective of the present invention to provide a method and apparatus for the mobile station to detect the assignment from the base station reliably.

It is yet another objective of the present invention to provide a method of transmitting the HARQ re-transmission in an adaptive manner in a wireless communication system.

In accordance with one aspect of the present invention, there is a first type of assignment that can be used to assign the radio resource of a frame in frequency only.

This first type of assignment is provided by dividing the total radio resource of a frame into frequency subcarriers such that each possible assignment unit contains subcarriers that are contiguous in both time and frequency. A second type of assignment can be used to assign the radio resource of a frame in time only or in both time and frequency. This second type of assignment is provided by dividing the total radio resource of a frame in time only such that the smallest assignment unit is one OFDM symbol in time and then

further dividing the radio resource into frequency subcarriers such that the assignment units are a group of disjoint subcarriers (not contiguous in frequency or time).

In accordance with another aspect of the present invention, a method is provided to multiplex the first and second types of assignments in the same frame by dividing the frame into a first zone and a second zone, wherein all of the first type of assignments are assigned to be in the first zone and all of the second type of assignments are assigned to be in the second zone. The demarcation between the first zone and the second zone is implicitly communicated via the signaling for the individual assignments. Based on the traffic loading conditions of the first and second types of assignments in a frame, the base station can choose one of two demarcation strategies to use, on a dynamic frame-by- frame basis. In the first demarcation strategy, the demarcation between the first zone and second zone is implicitly indicated by the last assignment of the second type of assignment (the distributed, non-contiguous assignment). In the second demarcation strategy, the demarcation between the first and second zones is implicitly indicated through all of the first type of assignments. Which demarcation strategy is being used is implicitly indicated through the last assignment of the second type of assignment.

In accordance with yet another aspect of the present invention, methods are provided to identify the last assignment of the second type of assignment. In one embodiment, the last assignment of the second type of assignment is identified by the position of the resource assigned by the last assignment of the second type of assignment in a resource denotation table. In another embodiment, the last assignment of the second type of assignment, if it exists in a frame, is transmitted only on a first forward shared scheduling channel (F-SSCH) among multiple such channels. An assignment that is not the last assignment of the second type of assignment can be transmitted on the first F-SSCH if and only if the last assignment of the second type of assignment does not exist in the same frame. Therefore, the last assignment of the second type of assignment can be identified by the 'Assignment Type' field in the assignment carried by the first F-SSCH. The first F-SSCH can be distinguished from the other F-SSCHs by using a special orthogonal code, scrambling code, frequency subband, sub-field within a long field of assignment message, time, or time-frequency bin, which is specified by the individual

base station. The F-SSCH is communicated to all mobile stations by signaling messages. In a system where the forward link and reverse link share the same F-SSCH pool, the first F-SSCH for the forward link transmission can be a different F-SSCH than the first F- SSCH for the reverse link transmission.

In yet another embodiment, the last assignment of the second type of assignment can be identified by using a second scrambling method on the F-SSCH that carries the last assignment of the second type of assignment, while the first scrambling method is used to scramble any F-SSCH that does not carry the last assignment of the second type of assignment. The first and second scrambling methods can differ in the PN register structure or in the scrambling seed, for example, by adding a field of 'Scrambling Type' in the scrambling seed.

In accordance with yet another aspect of the present invention, a method is provided to confirm to the mobile stations that are scheduled with the second type of assignment that there is no first type of assignment in the same frame. This method includes transmitting the last assignment message of the second type of assignment on the first F- SSCH and scrambling it with the first scrambling method (if there is at least one assignment of the first type of assignment in the same frame) or scrambling it with the second scrambling method (if there is no assignment of the first type of assignment in the same frame).

In accordance with yet another aspect of the present invention, a method and apparatus is provided for indicating the assignment type implicitly by the size of the resource assigned, eliminating the need for an 'Assignment Type' field in the assignment message and minimizing the signaling overhead.

In accordance with yet another aspect of the present invention, to combat the inter- cell interference in a cellular system, the system may employ a method and apparatus disclosed in this application: a frequency reuse scheme, a time reuse scheme, a soft time reuse scheme, a group frequency hopping scheme, a group time hopping scheme, a subcarrier time hopping scheme, or a combination of. The present invention discloses a novel method and apparatus of inter-cell interference mitigation in a cellular system,

preferably in an OFDMA-based wireless communication system. The method and apparatus first dividing a frame from a base station to a mobile station into a plurality of subcarriers based on certain time and frequency intervals, then dividing the plurality of subcarriers into two zones, where one of the two zones is designated for a dynamic radio resource assignment. Further a time reuse parameter or a frequency reuse parameter, or a combination of the two such parameters are defined to establish a plurality of schemes for dynamically loading the subcarriers within one of the designated zones. As a result, the inter-cell interference may be avoided or mitigated in a cellular system. Therefore, in accordance with the previous summary, objects, features and advantages of the present disclosure will become apparent to a person of the ordinary skill in the art from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.

In accordance with yet another aspect of the present invention, a method and apparatus of signaling radio resource allocation in a wireless communication system is disclosed. The method comprises, dividing the radio resource into a first type of assignment units; dividing the radio resource into a second type of assignment units; using the first type of assignment units for the first type of assignment; using the second type of assignment units for the second type of assignment; multiplexing the first type and the second type of assignments in the same frame; indicating the multiplexing mode to each of the plurality of mobile stations by the base station using the last assignment message of the second type of assignments; indicating the assignment for each of a plurality of mobile stations by a base station; indicating the overlapped region using the last assignment message of the second type of assignments so that all mobile stations scheduled with the first type of assignment avoid using the overlapped region when the first multiplexing mode is used; and indicating the overlapped region using all the first type of assignment message so that all mobile stations scheduled with the second type of assignment avoid using the overlapped region when the second multiplexing mode is used.

In accordance with yet another aspect of the present invention, a method of transmitting the HARQ re-transmission in an adaptive manner in a wireless

communication system is disclosed. The method comprises, scheduling the retransmission based on the decoding results from the receiver; determining the size and location of the frequency-time resource, the assignment type, the multiplexing mode in the frame, for the retransmission in a adaptive manner; sending the assignment message for the re-transmission that requires so; using the NodeID field in the assignment message for the retransmission to indicate the change of subcarrier-time resources in an absolute manner or incremental manner; using the Assignment Type in the assignment message for the re-transmission to indicate the change of assignment type for the re-transmission; using the PF field in the assignment message for the re-transmission to indicate the assignment message is for a re-transmission; using the MACID field in the assignment message for the retransmission to indicate the target mobile station for the retransmission; transmitting data packet for the retransmission; using the decoding result from the receiver to determine any further need of re-transmission. The present invention also discloses a procedure for the base station to determines if the base station needs to send the assignment message for the re-transmission and the procedure regarding how the base station should put the transmit power on the channel that carries the assignment message for the re-transmission.

Brief Description of the Drawings

FIGS. IA and IB together illustrate the radio resource in an OFDMA system and two conventional resource assignment methods.

FIGS. 2A and 2B together illustrate two alternative tree structures of combining of smaller resource assignment units into a bigger resource assignment unit and the denotation of the tree nodes.

FIG. 3 provides a block diagram of an exemplary control channel for the communication of assignment messages.

FIG. 4 provides an exemplary embodiment of multiplexing two types of resource assignment in the same data frame by providing a demarcation line between two types of assignment zones with each zone having only one type of resource assignment.

FIG. 5 provides a flowchart for the procedure of an exemplary base station in sending assignment messages and data packets.

FIG. 6 provides a flowchart for the procedure of exemplary mobile station in detecting the assignment messages and data packets, where the mobile station identifies the Last Distributed Assignment by the position of the NodeIDs in each decoded distributed assignment message.

FIG. 7 provides a flowchart for the procedure of an improved mobile station in detecting the assignment messages and data packets, wherein the mobile station identifies the Last Distributed Assignment only on the first F-SSCH.

FIG. 8 provides a flowchart for a second demarcation strategy for multiplexing two types of resource assignments in the same data frame.

FIG. 9 illustrates a preferred embodiment of the base station procedure for sending the assignment messages and data packets.

FIG. 10 illustrates a preferred embodiment of the mobile station procedure for detecting the assignment messages and data packets.

FIG. 11 shows a frequency reuse scheme among a plurality of cells in a cellular system.

FIG. 12 shows a time reuse scheme among a plurality of cells in a cellular system.

FIG. 13 shows a fractional frequency reuse scheme among a plurality of adjacent cells in a cellular system.

FIG. 14 shows a soft frequency reuse scheme among a plurality of adjacent cells in a cellular system.

FIGS. 15A, 15B and 15C together illustrate an embodiment of interference avoidance according to the present invention.

FIGS. 16A, 16B and 16C together illustrate another embodiment of interference avoidance according to the present invention.

FIGS. 17A, 17B and 17C together illustrate yet another embodiment of interference avoidance according to the present invention.

FIGS. 18A and 18B together illustrate an exemplary embodiment of soft time reuse in a cellular system according to the present invention.

FIGS. 19A, 19B, 19C and 19D together illustrate an embodiment of interference randomization according to the present invention.

FIGS. 2OA, 2OB, 2OC and 2OD together illustrate another embodiment of interference randomization according to the present invention.

FIGS. 21A and 21B together illustrate yet another embodiment of interference randomization according to the present invention.

FIGS. 22A and 22B illustrate two existing modes of multiplexing two types of radio resource assignments in one frame.

FIG. 23 illustrates an embodiment of the base station procedure for sending the assignment messages and data packets according to the present invention.

FIG. 24 illustrates an embodiment of the mobile station procedure for detecting the assignment messages and data packets according to the present invention.

FIG. 25A illustrates the timing relationship for the forward link HARQ according to the present invention.

FIG. 25B illustrates the timing relationship for the reverse link HARQ according to the present invention.

Detailed Description of the Invention

Table 1 below provides an exemplary denotation of the radio resources assigned with a localized assignment method (the first type of assignment), according to one embodiment of the present invention. The total bandwidth of the exemplary system is 5 MHz with a sampling rate of 4.9152 Msps (million samples per second). The fast Fourier transformation (FFT) size is 512, which is also the total number of subcarriers (divisions of the total frequency bandwidth). The 512 subcarriers are divided into a minimum of 32 contiguous localized assignment units. Each localized assignment unit consists of 16 contiguous subcarriers to transmit a plurality of contiguous OFDM symbols within a frame.

In a system where the control channels, such as F-SSCH, that carry the assignment messages for each frame are frequency division multiplexed (FDM) with the data channels, some localized assignment units are used for the control channels and thus, cannot be used for the data channels. In a system where the control channels are time division multiplexed (TDM) with the data channels, which is the case illustrated in Table 1, some OFDM symbols in a frame (for example, OFDM Symbol 0) is used for the control channels, while OFDM Symbols 1 to 7 are used for the data channels. In addition, the solid-shaded area in Table 1 may be used for Guard Band and therefore, is not available for data. The Guard Band in the example given in Table 1 corresponds to subcarriers 224 to 287. Subcarrier 0 is the Direct Current (DC) tone of the baseband signal.

Table 1

As shown in Table 1 above, a localized assignment unit (the first assignment type) s denoted as L _k ^N , representing the kth divided assignment unit if the total available

resource is divided into N equal-sized localized assignment units. As shown in Table 1, two smaller localized assignment units with the same size and certain relationship in their indices can be combined into a larger localized assignment unit.

FIG. 2A further illustrates, with an exemplary tree structure, how two smaller localized assignment units with the same size and certain relationship in their indices can be combined into a larger localized assignment unit. Each circle, called a tree node, in

FIG. 2A represents a localized assignment unit. Each tree node can be represented by a combination of N and k as defined above. To reduce the signaling overhead, the representation of a tree node can be simplified as one number, called a Node Index (NodelD), which is above each circle as shown in FIG. 2A. The generalized rule of combining two smaller localized assignment units into a larger localized assignment unit is as follows:

T N _ T 2N , T 2N /i s

Lk - Lk + Lk+N (1)

Table 2 below shows an exemplary denotation of the radio resources with the distributed assignment (the second assignment type) for the same 5 MHz system, according to one embodiment of the present invention. In the example shown in Table 2, one frame consists of 8 OFDM symbols and each OFDM symbol is divided in frequency into 4 minimum distributed assignment units. Each minimum distributed assignment unit consists of 128 disjoint and evenly spaced subcarriers. In a system where the control channels are frequency division multiplexed with the data channels, some subcarriers are assigned for the control channels and cannot be used for the data channels. In a system where the control channels are time division multiplexed with the data channels, some OFDM symbols in a frame (for example, OFDM Symbol 0), as indicated by the solid- shaded area in Table 2, is used for the control channels, while OFDM Symbols 1 to 7 are used for the data channels. In addition, the grid-shaded area in Table 2 may be used as Guard Band and therefore, not available for the data channels. The Guard Band in the example given in Table 2 corresponds to subcarriers 224 to 287. Subcarrier 0 is the Direct Current (DC) tone of the baseband signal.

As shown in Table 2 above, a distributed assignment unit is denoted as Dk ^N , representing the kth divided assignment unit if the total available resource is divided into N equally-sized distributed assignment units. In Table 2, two smaller distributed assignment units with the same size and certain relationship in their indices can be combined into a larger distributed assignment unit. The same tree structure and denotation of tree nodes as shown in FIG. 2A can be used to illustrate the combining of the distributed assignment units. The generalized rule of combining two smaller distributed assignment units into a larger distributed assignment unit is as follows:

D _k - Dk + D _k +N (2)

Unlike the conventional distributed resource assignment method illustrated in FIG. IB, the novel and improved method disclosed in the present invention for distributed resource assignment provides the benefits of both OFDMA and time division multiple access (TDMA). As shown in Table 2 above, the total radio resource within a frame is first divided only in time into two groups of contiguous OFDM symbols. Then, each group of OFDM symbols is further divided only in time into two smaller groups of contiguous OFDM symbols. The division continues until each divided distributed assignment unit covers one OFDM symbol. Then, each of the distributed assignment units is further divided only in frequency, into two smaller distributed assignment units that are interlaced in frequency subcarriers. Then, the division continues until reaching the size of the minimum distributed assignment unit. Therefore, the novel and improved distributed assignment method disclosed above allows multiple small data packets to share a wideband channel by multiplexing them in frequency (i.e. OFDMA) in a distributed fashion to explore the performance gain from frequency diversity. This strategy especially benefits the delay-sensitive and low data rate applications such as Voice over Internet Protocol (VoIP). When the data packets from different mobile stations are large enough to fill up one OFDM symbol, these data packets can be time division multiplexed (TDM). In this case, if the channel response is frequency-selective, each data packet still enjoys the performance gain from frequency diversity. Meanwhile, if the channel response is relatively flat for at least some mobile stations, the ability to

time division multiplex data packets from different mobile stations within a frame can help the base station scheduler take advantage of multi-user scheduling gain with the channel feedbacks from these mobile stations.

Furthermore, the smallest bin in Table 2 can correspond to a group of contiguous 5 subcarriers, called a tile, instead of corresponding to one subcarrier as described in Table 2. This is especially useful for the reverse link where individual pilot tones are needed within each tile for channel estimation and coherent demodulation.

Alternatively, Table 3 below can replace Table 1 with a different denotation of the radio resource with the localized assignment, Table 4 below can replace Table 2 with a io different denotation of the radio resource with the distributed assignment, and the tree structure and denotation of the tree nodes shown in FIG. 2 A can be replaced by those in FIG. 2B, where the letter "X" can be "L" or "D". In this alternative denotation scheme, the generalized rule of combining two smaller assignment units of the same type into a larger assignment unit of the same type is as follows: i _c v N _ _v 2N , Y 2N /o\

15 Xk - A ₂ k + X ₂ k+1 (-3)

where "X" can be "L" or "D".

Table 3

FIG. 3 illustrates an exemplary channel structure for the forward shared scheduling channel (F-SSCH) that sends the assignment messages to the mobile stations. The assignment message contains at least a field of Media Access Control Index (MACID) to identify the intended mobile station, a field of Node Index (NodelD) to identify the assigned radio resource in time and frequency, a field of Assignment Type to identify whether the assignment is a localized assignment or a distributed assignment, a field of Packet Format (PF) to identify the encoder packet size, modulation level, and code rate of the data packet. In addition, the assignment message may contain fields for message type, multiple antenna mode, etc.

The field of Assignment Type in the F-SSCH can be eliminated in a simplified scheme by limiting the localized assignment units to those with a first set of sizes and limiting the distributed assignment units to those with a second set of sizes, wherein none of the sizes in the first set exists in the second set and none of the sizes in the second set exists in the first set. For example, in the 5MHz system illustrated above, the localized assignment units can be limited to L ₀ ¹ , L ₁ ² , L _j ⁴ , and L _m ⁸ , where i, j, and m are integers, and O≤i≤l, 0<j<3, 0<m<7. Meanwhile, the distributed assignment units can be limited to D _x ¹⁶ and D _y ³² , where x and y are integers, and 0<x<15, 0<y<31. Therefore, the assignment size implies which assignment type is used, and there is no need to have an explicit field of Assignment Type in the F-SSCH.

Referring to FIG. 3, in an embodiment of the present invention, the Cyclic

Redundant Check (CRC) bits are first added to the information bits of the assignment message by CRC element 310. The encoder 315 adds forward error correction (FEC) coding to the output sequence of CRC element 310. Then, a rate matching element 320 repeats and/or punctures the encoded bits from encoder 315 in order to match the rate on the F-SSCH to certain fixed rate. A scrambler 325 then scrambles the output sequence from the rate matching element 320 with a scrambling code that is generated from a scrambling code generator 330. The scrambling code generator 330 is a PN register that is seeded with the channel identity of the F-SSCH, the current frame number, and optionally, the scrambling type. The scrambled sequence is then interleaved by channel interleaver 335. The interleaved sequence is then modulated by modulator 340. The in-

phase (I) and quadrature (Q) outputs of modulator 340 are then gain-controlled by channel gain elements 345 and 350. The output complex signal is then multiplexed with the other channels by channel multiplexer 355 using Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), OFDMA, or any combination of the above.

Referring to FIG. 4, the frame is split into a localized assignment zone (the first zone) and a distributed assignment zone (the second zone). A number of consecutive OFDM symbols are used for the mobile stations with the localized assignment and the remaining OFDM symbols in the same frame are used for the mobile stations with the distributed assignment. Because the mobile stations with the distributed assignment may not be able to fill up the far-left OFDM symbol in their zone, the mobile stations with the localized assignment share the remaining subcarriers in that OFDM symbol. Therefore, the demarcation line 410 may be a straight line, or it may be a rectangular-pulse-shaped line.

In one embodiment of the present invention, the two assignment zones are time division multiplexed. The two assignment zones may share at most one OFDM symbol in time, during which time the two assignment zones do not overlap in frequency subcarriers. The preferred embodiment is that the localized assignment zone is transmitted before the distributed zone of the same frame. In an alternative embodiment, the distributed assignment zone is transmitted before the localized zone of the same frame.

In order for the mobile stations with the localized assignment to decode their data packet correctly, they need to know precisely where the demarcation line 410 is. A Layer 3 signaling message can be used to broadcast the demarcation information in a slow fashion (due to the long latency associated with Layer 3 messages). However, the lack of an ability to change the demarcation line 410 in a dynamic frame-by-frame fashion puts some constraints on the base station scheduler, therefore undermining the performance of the scheduler. A MAC Layer control message can be used to broadcast the demarcation information in a relatively fast fashion. However, it would require additional base station

transmit power and subcarriers, which would otherwise be available for the transmission of data packets.

A preferred embodiment of the present invention for indicating the demarcation line 410 between the localized assignment zone and the distributed assignment zone is described in the following sections.

In the example shown in FIG. 4, three different mobile stations, indicated by three different shade patterns, are assigned in the localized assignment zone. The resource assigned to each of them can have different sizes. Four different mobile stations, indicated by four other shade patterns, are assigned in the distributed assignment zone. The resource assigned to each of them can also have different sizes. We define the Last Distributed Assignment as the distributed assignment that is the farthest away from the beginning of the distributed assignment zone in time and the last in frequency location. In Table 2, the beginning of the distributed assignment zone is the end of the data frame. Therefore, the radio resource units for the distributed assignments are assigned from top to bottom in frequency first, then from left to right in time. The assignment message for the Last Distributed Assignment is sent with sufficient power such that the intended mobile station for the Last Distributed Assignment and all mobile stations that are scheduled with the localized assignment in the same frame can decode the Last Distributed Assignment message correctly. The Node Index field in the Last Distributed Assignment message indicates which radio resource in time and frequency is assigned to the mobile station that is intended for the Last Distributed Assignment, implying where the entire distributed assignment zone is. As a result, each mobile station that is scheduled with the localized assignment in the same frame will know the demarcation line 410 and be able to retrieve the modulation symbols for its data packet correctly.

As shown in FIG. 5, according to one aspect of the present invention, the base station (BS) first selects which mobile stations are to be scheduled for transmission in the next frame in step 500 and which type of assignment is used for each of those scheduled mobile stations (MS) in step 510. In step 520, the base station determines if there is at least one mobile station that is scheduled with the distributed assignment. If none is

selected, the base station sends the assignment messages and data packets for those mobile stations with the localized assignment in step 530. Then, the base station waits until the next frame. If there is at least one mobile station that is scheduled with the distributed assignment, the base station selects a mobile station that is scheduled with the distributed assignment to be the intended mobile station for the Last Distributed Assignment in step 540. For example, the base station can select the mobile station with the worst channel condition among all mobile stations that are scheduled with the distributed assignment to be the intended mobile station of the Last Distributed Assignment. This selection method can help to utilize the base station's transmit power more efficiently, but it should be obvious to those skilled in the art that other selection methods may be used. Next, the base station ranks the channel conditions of all mobile stations that are scheduled with the localized assignment based via their channel condition feedback and selects the worst one to compare with the channel conditions of the intended mobile station of the Last Distributed Assignment in step 550. In step 560, the base station determines if the channel condition of the intended mobile station of the Last Distributed Assignment is worse than the worst channel condition among all mobile stations that are scheduled with the localized assignment. If yes, the base station sends the Last Distributed Assignment message with the MACID of the intended mobile station in it and with sufficient power to ensure the intended mobile station of the Last Distributed Assignment can decode the Last Distributed Assignment message correctly in step 570. If no, the base station sends the Last Distributed Assignment message with the MACID of the intended mobile station in it and with sufficient power to ensure the mobile station with the worst channel conditions among all mobile stations that are scheduled with the localized assignment can decode the Last Distributed Assignment message correctly in step 580. The base station sends the other assignment messages and all data packets in step 530. Then, the base station waits until the next frame. It should be obvious to those skilled in the art that the term sufficient power throughout this description may or may not includes additional marginal power.

Referring to FIG. 6, the mobile station (MS) first detects all assignment messages in all F-SSCHs in step 600. Then the mobile station determines if self MACID has been found in any of those assignment messages in step 610. If no, the mobile station waits

until the next frame. If yes, the mobile station determines if its assignment type is the localized assignment in step 620. If no, the MS decodes the data packet according to the Node Index in his own assignment message in step 630 and waits until the next frame. If yes, in step 640, the mobile station determines if any distributed assignment message for another mobile station is detected on any F-SSCH. If no, the MS decodes the data packet according to the Node Index in his own assignment message in step 630 and waits until the next frame. If yes, in step 650, the mobile station maps all Node Indices that are decoded correctly from the distributed assignment messages onto the distributed resource denotation table that is being used by the base station, such as Table 2, and identifies the distributed assignment that is the farthest away from the beginning of the distributed assignment zone in time and the last in frequency location in Table 2 among all distributed assignments within the same OFDM symbol as the Last Distributed Assignment. In step 660, the mobile station uses the Node Index in the Last Distributed Assignment message to demarcate the two assignment zones and to retrieve the modulation symbols for itself. The mobile station decodes the data packet in step 630 and then waits until the next frame.

In the mobile station procedure illustrated in FIG. 6 and described above, a mobile station scheduled with the localized assignment may miss the detection of the true Last Distributed Assignment message and thus, the true demarcation of the two assignment zones, causing failure in decoding its data packet.

To enhance the robustness of the scheme of using the Last Distributed Assignment message to indicate the demarcation of the two assignment zones, novel methods are described below to distinguish the Last Distributed Assignment message from the other distributed assignment messages.

In one embodiment, if there is at least one distributed assignment in the frame, the

Last Distributed Assignment message is always carried on the first F-SSCH. The first F- SSCH can be distinguished from the other F-SSCH' s by using a special orthogonal code, scrambling code, frequency subband, sub-field within a long field of assignment message, time, or time-frequency bin, which is specified by the individual base station, can be

different from base station to base station, and is informed to all mobile stations by signaling messages. If there is no distributed assignment in the frame, the first F-SSCH can be used for carrying a localized assignment message. In this case, because all mobile stations that are scheduled with the localized assignment need to detect correctly that the first F-SSCH is carrying a localized assignment message, the first F-SSCH should be sent with sufficient power to ensure all mobile stations that are scheduled with the localized assignment can detect it correctly. Further, selecting the mobile station with the worst channel conditions among all mobile stations that are scheduled with localized assignment can help to utilize the base station's transmit power more efficiently.

Referring to FIG. 7, the mobile station first detects all assignment messages in all F-

SSCHs in step 700. Then, the mobile station determines if its own MACID has been found in any of those assignment messages in step 710. If no, the mobile station waits until the next frame. If yes, the mobile station determines if the assignment type for it is the localized assignment in step 720. If no, the MS decodes the data packet according to the Node Index in its own assignment message in step 730 and then waits until the next frame. If yes, in step 740, the mobile station further determines if a distributed assignment message is detected on the first F-SSCH. If no, the MS decodes the data packet according to the Node Index in its own assignment message in step 730 and then waits until the next frame. If yes, in step 750, the mobile station takes the distributed assignment message on the first F-SSCH as the Last Distributed Assignment message. In step 760, the mobile station uses the Node Index in the Last Distributed Assignment message to demarcate the two assignment zones and to retrieve the modulation symbols intended for it. The mobile station decodes the data packet in step 730, and then waits until the next frame.

In an alternative embodiment, the F-SSCH that carries the Last Distributed

Assignment message is scrambled by scrambler 325 as shown in FIG. 3 with a second scrambling method while the F-SSCHs for the other distributed assignment messages or for any localized assignment messages are scrambled by scrambler 325 with a first scrambling method. The two scrambling methods can differ in the PN register structure or differ in the scrambling seed, for example, by adding a field of Scrambling Type in the

scrambling seed. Another aspect of this embodiment is that when there is at least one localized assignment and no distributed assignment in the frame, at least one F-SSCH that carries a localized assignment message can be scrambled with the second scrambling method to indicate that there is no distributed assignment in the current frame, and it should be sent with sufficient power to ensure that all mobile stations that are scheduled with the localized assignment in the frame can decode it correctly. Because an F-SSCH can be scrambled in two possible ways, the mobile station needs to detect each F-SSCH with two possible de-scrambling methods before determining, in step 600, what message is carried on it. As a result, the detection performance on each F-SSCH can be potentially degraded. Therefore, further enhancement of this embodiment by limiting the two possible scrambling methods only on the first F-SSCH, which is the only F-SSCH that can carry the Last Distributed Assignment message, is preferable. However, it should be clear to those skilled in the art that other implementations are possible. We will describe how to use this preferred combination to provide more flexibility in multiplexing different type of assignments in the later sections.

If there are a large number of mobile stations that are scheduled with the distributed assignment with the demarcation strategy as described above and as shown in FIG. 4, the radio resources assigned for any mobile stations that are scheduled with the localized assignment in the same frame are dramatically reduced by the distributed assignment zone, and thus, the assignment efficiency becomes low. If there are only a few mobile stations scheduled with the localized assignment in the same frame, the base station can switch to a second demarcation strategy as shown in the example in FIG. 8, according to another aspect of the present invention.

Referring to FIG. 8, the radio resource 800 of the Last Distributed Assignment reaches the end of the potential distributed assignment zone, which is also the beginning of the data frame as well as the beginning of the localized assignment zone. In the second demarcation strategy, the demarcation line 810 between the two assignment zones becomes the frequency boundaries of the localized assignments based on the NodeIDs in those localized assignment messages and a localized resource denotation table such as Table 1, meanwhile the localized assignment zone stretches from the beginning of the

data frame to the end of the data frame. So, the two assignment zones becomes frequency division multiplexed (FDM), as opposed to TDM in the first demarcation strategy shown in FIG. 4. And in the second demarcation strategy, the signaling of the demarcation line is the NodeIDs in all localized assignment messages, as opposed to the NodeID in the Last Distributed Assignment message in the first demarcation strategy.

The communication of the switching between these two demarcation strategies in the example illustrated in FIG. 8 is based on whether the radio resource 800 of the Last Distributed Assignment reaches the end of the potential distributed assignment zone. In a more specific example using Table 2, considering that OFDM Symbol 0 is used for the F-SSCHs and the data frame begins from OFDM Symbol 1 to Symbol 7, a Last Distributed Assignment message with a NodeID corresponding to any of Do ¹ , D] ² , D ₃ ⁴ , D ₃ ⁸ , Di ₁ ¹⁶ , or D ₂₇ ³² indicates that the second demarcation strategy is used in the current frame and all scheduled mobile station should decode their data packet accordingly. In order for all of the scheduled mobile stations to understand that the second demarcation strategy is being used, the F-SSCH that carries the Last Distributed Assignment message should be sent with sufficient power to ensure that all scheduled mobile stations can decode it correctly. Using the Last Distributed Assignment message for the mobile station with the worst channel condition among all scheduled mobile station with the distributed assignment can help to utilize the base station transmit power more efficiently as mentioned before, but it is not required. In addition, in order for all mobile stations scheduled with the distributed assignment to understand where the demarcation line 800 is with the second demarcation strategy being used, any localized assignment message should be sent with sufficient power to ensure all the mobile stations that are scheduled with the distributed assignment to decode the localized assignment message correctly.

Furthermore, using the very end of the potential distributed assignment zone as the benchmark for switching between the two demarcation strategies may be too restrictive. For example, even if the Last Distributed Assignment message has a NodeID of D ₃ ¹⁶ in the specific example described above, there is not enough radio resource left to make any meaningful localized assignment. In this case, the base station can use the NodeID of Dn ¹⁶ instead of D ₃ ¹⁶ on the Last Distributed Assignment message so that the restrictive

benchmark is still met while leaving the radio resource on D ₃ ¹⁶ un-used. Or, a more relaxed benchmark can be used such that if the radio resource assigned for the Last Distributed assignment has reached certain a portion of the potential distributed assignment zone, the second demarcation strategy is used. Otherwise, the first demarcation strategy is used. The exact benchmark should be known to all mobile stations by default or by signaling messages. It should be clear to those skilled in the art that a variety of strategies can be used to decide upon when to switch to the second demarcation strategy.

In addition, when the second demarcation strategy is used and there is no localized assignment being scheduled in the same frame, a mobile station that is scheduled with the distributed assignment may not be able to tell whether it has missed the detection of any localized assignment messages or whether there is no localized assignment.

According to yet another aspect of the present invention, if there is at least one distributed assignment and at least one localized assignment in the frame, the Last Distributed Assignment message is sent on the first F-SSCH and scrambled with the first scrambling method. If there is at least one distributed assignment and no localized assignment, the Last Distributed Assignment message is sent on the first F-SSCH and scrambled with the second scrambling method.

A third scrambling method can be used to scramble the first F-SSCH when it carries the Last Distributed Assignment and the second demarcation strategy is being used in the frame. In this alternative method of indicating the switching of demarcation strategies, the signaling of the switching of the demarcation strategy is no longer based on whether the NodeID in the Last Distributed Assignment reaches the benchmark or not. It is based on whether the third scrambling method is used on the first F-SSCH or not. However, the former method is more preferable as it does not increase the number of detection hypnoses on the first F-SSCH and therefore, doesn't degrade the detection performance of the first F-SSCH.

As shown in FIG. 9, according to the preferred embodiment of the present invention, the base station (BS) first selects which mobile stations is to be scheduled for

transmission in the next frame in step 900 and which type of assignment is used for each of those scheduled mobile stations in step 905. In step 910, the base station determines if there is at least one mobile station (MS) that is scheduled with the distributed assignment. If there is no mobile station that is scheduled with the distributed assignment, the base station determines if there is at least one mobile station that is scheduled with the localized assignment in step 915. If no, the base station waits until the next frame. If yes, in step 920, the base station sends a localized assignment message on the first F-SSCH with the first scrambling method and with sufficient power for all scheduled mobile stations to decode it correctly. Then, the base station sends the other assignment messages and all data packets in step 925. Then, the base station waits until the next frame. If the base station determines that there is at least one mobile station that is scheduled with the distributed assignment in step 910, the base station selects a mobile station that is scheduled with the distributed assignment to be the intended mobile station for the Last Distributed Assignment in step 930. For example, the base station can select the mobile station with the worst channel condition among all mobile stations that are scheduled with the distributed assignment to be the intended mobile station of the Last Distributed Assignment. This selection method can help to utilize the base station's transmit power more efficiently, but it is not required. Next, in step 935, the base station determines if there is at least one mobile station that is scheduled with the localized assignment. If there is no mobile station scheduled with the localized assignment, the base station scrambles the first F-SSCH with the second scrambling method in step 940. Then, the base station sends the Last Distributed Assignment message on the first F-SSCH with sufficient power for all scheduled mobile stations to decode it correctly in step 945. Then, the base station sends the other assignment messages and all data packets in step 925. Then, the base station waits until the next frame. If the base station determines that there is at least one mobile station that is scheduled with the localized assignment in step 935, the base station scrambles the first F-SSCH with the first scrambling method in step 950. Then, in step 955, the base station determines which demarcation strategy is to be used in the frame. If the first demarcation strategy is to be used, the base station ensures the NodeID in the Last Distributed Assignment message does not meet the benchmark in step 960. If the second demarcation strategy is to be used, the base station ensures the NodeID

in the Last Distributed Assignment message meets the benchmark in step 970. Then, the base station sends the Last Distributed Assignment message on the first F-SSCH with sufficient power for all scheduled mobile stations to decode it correctly in step 945. The base station sends the other assignment messages and all data packets in step 925. Then, the base station waits until the next frame.

Referring to FIG. 10, the mobile station first detects all assignment messages on all F-SSCHs in step 1000. Then, the mobile station determines if its MACID has been found in any of these assignment messages in step 1005. If no, the mobile station waits until the next frame. If yes, the mobile station determines if there is a distributed assignment message on the first F-SSCH in step 1010. If no, the mobile station further determines if the assignment for it is a localized assignment in step 1015. If no, there is a detection error and the mobile station waits until the next frame because the assignment for this mobile station cannot be a distributed assignment if the assignment on the first F-SSCH is not a distributed assignment. If the mobile station determines that the assignment for it is a localized assignment in step 1015, the mobile station uses the NodeID in its assignment message to retrieve the modulation symbols for its data packet and decodes that data packet in step 1020. Then, the mobile station waits until the next frame. If the mobile station determines that there is a distributed assignment message on the first F-SSCH in step 1010, this distributed assignment message is the Last Distributed Assignment message. The mobile station then determines if the first F-SSCH is scrambled with the first scrambling method in step 1025. If no, the mobile station then determines if the assignment for it is a localized assignment in step 1030. If yes, there is a detection error and mobile station waits until the next frame, because if the mobile station determines that the first F-SSCH is scrambled with the second scrambling method in step 1025, there is no localized assignment in the frame. If the mobile station determines that the assignment for itself is a localized assignment in step 1030, the mobile station uses the NodeID in its assignment message to retrieve the modulation symbols for its data packet and decodes that data packet in step 1020. Then, the mobile station waits until the next frame. If the mobile station determines that the first F-SSCH is scrambled with the first scrambling method in step 1025, the mobile station determines if the first demarcation strategy is used in the frame in step 1035. If yes, the mobile station then determines if the

assignment for it is a localized assignment in step 1040. If no, the mobile station uses the NodeID in its assignment message to retrieve the modulation symbols for its data packet and decodes that data packet in step 1020. Then, the mobile station waits until the next frame. If yes, the mobile station first uses the NodeID in the Last Distributed Assignment message to derive the demarcation line between the two assignment zones in step 1045. Then, the mobile station uses the NodeID in its assignment message and the demarcation line to retrieve the modulation symbols for its data packet and decodes that data packet in step 1020. Then, the mobile station waits until the next frame. If the mobile station- determines that the second demarcation strategy is used in the frame in step 1035, the mobile station then determines if the assignment for it is a localized assignment in step 1050. If yes, the mobile station uses the NodeID in its assignment message to retrieve the modulation symbols for its data packet and decodes that data packet in step 1020. Then, the mobile station waits until the next frame. If no, the mobile station first uses the NodeIDs in all localized assignment messages to derive the demarcation line between the two assignment zones in step 1055. Then, the mobile station uses the NodeID in its assignment message and the demarcation line to retrieve the modulation symbols for its data packet and decodes that data packet in step 1020. Then, the mobile station waits until the next frame.

The exemplary embodiments disclosed in the present invention are mostly described for the forward link (i.e. from the base station to the mobile station) for convenience. The same novel and improved methods and apparatus can be applied to the reverse link (i.e. from the mobile station to the base station). Some differences between the forward link and the reverse link include that for the reverse link, each distributed assignment unit shown in Table 2 or Table 4 consists of a number disjoint tiles and each tile consists of a number contiguous subcarriers since individual pilot tones are needed within each tile for channel estimation and coherent demodulation on the reverse link. In the reverse link, the mobile stations decipher the demarcation line according to the various embodiments described above, for the purpose of selecting the correct radio resource that has been scheduled by the base station to send the data packets such that the base station may decode it correctly and not for the purpose of decoding the data packet sent by the base station.

When the assignment messages for the forward link and the reverse link are sharing the same pool of F-SSCHs, the Last Distributed Assignment message for the forward link, if it exists in the frame, is sent only on the first F-SSCH, and the Last Distributed

Assignment message for the reverse link, if it exists in the same frame, is sent only on a second F-SSCH. The second F-SSCH is distinguished from the other F-SSCHs in a similar way that the first F-SSCH is distinguished from the other F-SSCHs (for example, by using a special orthogonal code, scrambling code, frequency subband, subfield within a long field of assignment message, time, or time-frequency bin, which is specified by the individual base station, can be different from base station to base station, and is informed to all mobile stations by signaling messages).

Table 5 below shows the rules of assigning messages to the first (1st) F-SSCH and the second (2nd) F-SSCH under various scenarios depending on the numbers of the distributed assignments (DA) and the localized assignments (LA) on the forward link and the reverse link. Table 5 shows that when there is no distributed assignment on the forward link, any remaining assignments on any link except the Last Distributed Assignment (LDA) message, if it exists, on the reverse link, can be sent on the first F- SSCH so that any mobile station that is scheduled with the localized assignment on the forward link can confirm that there is no distributed assignment on the forward link and thus, interpreting the demarcation strategy and demarcation line properly. When there is no distributed assignment on the reverse link, any remaining assignments on any link except the Last Distributed Assignment message, if it exists, on the forward link, can be sent on the second F-SSCH.

Table 6 below shows alternative rules of assigning messages to the first F-SSCH and the second F-SSCH under the same scenarios as shown in Table 5. The difference in Table 6 is that when there is no distributed assignment message on one link, the base station gives higher priority to the localized assignment messages on the same link than any remaining assignment messages on the opposite link. The method in Table 6 has benefits. However, as described before, it is always better from the base station power efficiency viewpoint to choose the eligible mobile station with the worst channel condition on the first F-SSCH or the second F-SSCH. The method in Table 5 does

increase the pool of eligible mobile stations to choose the worst channel condition from when there is no distributed assignment on one link and thus, may be preferred for a system where the power on the control channels is in great demand.

Table 5

Assignment Scenarios Forward Reverse Link

The 1st F-SSCH The 2nd F-SSCH Link (FL) (RL)

DA LA DA LA carry the FL LDA message carry the RL LDA message at least with the 1st scrambling with the 1st scrambling 1 at method method least 1 carry the FL LDA message carry the RL LDA message at least none with the 1st scrambling with the 2nd scrambling

1 method method carry the FL LDA message at least carry any remaining with the 1st scrambling assignment message with the 1 method 1st scrambling method none carry the FL LDA message carry any remaining none with the 1st scrambling assignment message with the at 1st scrambling method least- method

1 carry the FL LDA message carry the RL LDA message at least 1 with the 2nd scrambling with the 1st scrambling at method method least 1 carry the FL LDA message carry the RL LDA message none with the 2nd scrambling with the 2nd scrambling none method method carry the FL LDA message carry any remaining at least assignment message with the 1 with the 2nd scrambling method 1 st scrambling method none carry the FL LDA message carry any remaining none with the 2nd scrambling assignment message with the method 1st scrambling method carry any remaining carry the RL LDA message at least assignment message with with the 1st scrambling 1 non at the 1st scrambling method method e least 1 carry any remaining carry the RL LDA message none assignment message with with the 2nd scrambling at the 1st scrambling method method least-

1 at least carry any remaining carry any remaining assignment message with assignment message with the the 1st scrambling method 1st scrambling method none carry any remaining carry any remaining none assignment message with assignment message with the the 1st scrambling method 1st scrambling method RL LDA message at at least carry any remaining carry the assignment message with with the 1st scrambling least 1 1 none the 1st scrambling method method

carry any remaining carry the RL LDA message none assignment message with with the 2nd scrambling the 1st scrambling method method

, carry any remaining carry any remaining

₁ assignment message with assignment message with the the 1st scrambling method 1st scrambling method none Don't care Don't care

Table 6

Assignment Scenarios

none assignment message with the assignment message with the 1st scrambling method 1st scrambling method at carry any remaining carry the RL LDA message at least least assignment message with the with the 1st scrambling none 1 1 1st scrambling method method

carry any remaining carry the RL LDA message none assignment message with the with the 2nd scrambling 1st scrambling method method

, carry any remaining carry a RL localized

. assignment message with the assignment message with the 1st scrambling method 1st scrambling method none Don't care Don't care

Novel and improved methods and apparatus to allow the base station to multiplex different types of radio resource assignments in the same data frame have been disclosed in the present invention. There are several advantages of this methodology: The base station has more freedom with the time and frequency resource to multiplex data packets from different users; the base station transmission power on the control channel F-SSCHs is utilized more efficiently with the described methods; and the detection of the assignment messages by the mobile station is more robust.

Another benefit of the present invention is that it is not necessary to have the common pilot tones in the localized assignment zone. Instead, the dedicated pilot tones, which normally are more power-efficient, can be used in the localized assignment zone.

Yet another benefit of the present invention is that the mobile stations that are scheduled with the localized assignment only need to know where the demarcation line is and don't need to know where each distributed assignment occurs, whereas in the prior art, the mobile stations that are scheduled with the localized assignment need to know precisely where each distributed assignment occurs. Therefore, the present invention simplifies the hardware and software implementation at the mobile station receiver.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiment disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be implemented or performed directly in hardware, in a software

module executed by a processor, or in combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, or any other form of storage medium in the art.

An objective of the present invention is to minimize the inter-cell interference experienced by the mobile stations that are assigned with the distributed assignments, which tend to be disadvantaged mobile stations, thereby improving the cell coverage through interference avoidance by using the time reuse or a combination of time and frequency reuse within a frame.

Another objective of the present invention is to provide the above in two possible manners: 1) a static manner; and 2) a dynamic manner.

Yet another objective of the present invention is to provide the above with reliable and minimal signaling overhead.

Yet another objective of the present invention is to support macro diversity wherein more than one base station transmit antennas transmit the same signal waveform to the mobile station using the same frequency-time resource.

Yet another objective of the present invention is to support soft time re-use in the distributed assignment zone.

Yet another objective of the present invention is to randomize the inter-cell interference in the distributed assignment zone.

As aforementioned, methods are disclosed to multiplex two types of assignments in the same frame by dividing the frame into two zones, wherein all first type of assignments are assigned in the first zone and all second type of assignments are assigned in the second zone. The demarcation between the two zones is implicitly indicated through the signaling for the individual assignment in a dynamic frame-by-frame manner.

As aforementioned, there are two strategies for multiplexing and demarcating the two types of assignments. According to the first demarcation strategy, as shown in FIG. 4 as an illustrative example, the base station fills up the resource space with the distributed

assignments starting from the last OFDM symbol of the data frame, from the top to the bottom until all distributed assignments have been assigned, or until the last OFDM symbol of the data frame is filled up, then the base station starts to fill up the next OFDM symbol to the left with the distributed assignments. The base station continues in this manner until all distributed assignments have been assigned. That is where the distributed assignment zone ends. The remaining area of the data frame is the localized assignment zone. The localized assignment zone starts from the beginning of the data frame and ends at the demarcation line that is between the two zones. The distributed assignment zone starts from the end of the data frame and ends at the demarcation line. The two zones may share at most one OFDM symbol, during which time the two zones do not share the same frequency subcarriers. Therefore, the demarcation line 410 may be a straight line, or it may be a rectangular pulse-shaped line. The demarcation line is signaled by the base station implicitly by sending the Last Distributed Assignment message to all scheduled mobile stations. The Last Distributed Assignment is defined as the distributed assignment that is the farthest away from the beginning of the distributed assignment zone in time and the last in frequency location, for example using Table 2, among all distributed assignments within the same OFDM symbol. In this embodiment, the Last Distributed Assignment message is always sent on a first forward shared scheduling channel (F- SSCH) to eliminate any ambiguity and therefore improve the reliability of the signaling.

On the other hand, in the illustrative example shown in FIG. 8, the distributed assignment zone dominates the occupancy of the frame. Therefore, it would be very inefficient to assign any localized assignment according to the first strategy of multiplexing and demarcation as described above. In this case, according to the second strategy of multiplexing and demarcating the two types of assignments, the demarcation line becomes the boundaries of all the resource assigned with the localized assignments. Therefore, the signaling of the demarcation line is all the localized assignments.

As aforementioned, the signaling of which strategy of multiplexing and demarcation is used is whether the occupancy of the distributed assignment zone has exceeded a certain threshold, which can be derived from the Last Distributed Assignment message by the mobile stations.

The present invention provides unique methods for interference mitigation in an

OFDMA-based communication system. As illustrated in FIG. 4 and FIG. 8, a system is allowed to use frequency reuse, for example by assigning localized assignments using different frequency subbands by different base stations. In addition, the present invention also provides unique dynamic time division multiplexing (TDM) with the novel signaling of the distributed assignment zone. Based on this, the present invention also discloses two strategies of a method and apparatus for interference mitigation in a cellular communication system, namely "Interference Avoidance" and "Interference

Randomization". Each of the strategies is described in the following sections of the detailed description.

(1) Interference Avoidance

Referring to FIGS. 15A, 15B, and 15C, an embodiment of interference avoidance according to the present invention is disclosed. As shown in FIGS. 15A, 15B, and 15C, different base stations (BS), BS A, BS B, and BS C, use different time offsets for the beginning of the distributed assignment zone within a frame. BS A is fully loaded, BS B is lightly loaded, and BS C has more distributed assignments and distributed assignment zone in BS C wraps around the data frame. Therefore, the distributed assignment zones for the Base Stations A, B, and C benefit from less interference from the other two base stations respectively.

In one embodiment, the time offset for the beginning of the distributed assignment zone can be indicated by the signaling message in the superframe preamble, which happens once in each of a plurality of data frames. In another embodiment, the time offset for the beginning of the distributed assignment zone can be indicated by the First Distributed Assignment on a frame-by-frame base. The First Distributed Assignment is defined as the distributed assignment that occupies the very beginning of the distributed assignment zone, therefore the assignment message for the First Distributed Assignment signals where the distributed assignment zone begins. For example, as shown in FIG 15B, the distributed assignment zone begins from the sixth OFDM symbol in the frame, which is the OFDM Symbol 5 as denoted in Table 2 above. The Node Index in the First

Distributed Assignment message can be D ₂ ⁴ , D ₂ ⁸ , D ₂ ¹⁶ , or D ₂ ³² . Furthermore, to reduce the ambiguity of detecting the First Distributed Assignment, if the First Distributed Assignment exists in the frame, the First Distributed Assignment is always sent, in this embodiment, on the second F-SSCH, which is different from the first F-SSCH that carries the Last Distributed Assignment, except when there is only one distributed assignment in the frame. When there is only one distributed assignment in the frame, the First Distributed Assignment, which is also the Last Distributed Assignment, is sent on the first F-SSCH. Meanwhile the second F-SSCH carries one localized assignment message with sufficient power for all scheduled mobile stations to decode the second F-SSCH correctly if at least one localized assignment exists in the frame. The mobile stations interpret the absence of a distributed assignment message on the second F-SSCH as only one distributed assignment exists in the frame. As shown in FIGS. 15A, 15B, and 15C, the localized assignment zone begins after the beginning of the distributed assignment zone and continues until the demarcation line. If the localized assignment zone reaches the end of the data frame before reaching the demarcation line as shown in FIG. 15B, the localized assignment zone wraps around the data frame and continues from the beginning of the data frame until the demarcation line.

For those with ordinary skill in the art, it is obvious that the co-located sectors can use the same beginning of the distributed assignment zone in order to facilitate macro diversity transmission with the distributed assignments. In addition, if the multicast or broadcast service is supported in the distributed assignment zone by a plurality of base stations, at least some portion of the distributed assignment zone among these base stations is aligned in time.

Referring now to FIGS. 16A, 16B and 16C, another embodiment of interference avoidance according to the present invention is disclosed. As shown in FIGS. 16A, 16B, and 16C, when three base stations BS A, BS B, and BS C are lightly loaded, with some coordination among these three base stations through backhaul, not all OFDM symbols in the distributed assignment zones, which all begins from the end of the data frame, will be used by the distributed assignments from each of these three base stations BS A, BS B, and BS C. Therefore, inter-cell interference can be avoided through time reuse.

Furthermore, since the localized assignment zones are punctured by the virtually enlarged distributed assignment zones significantly, the second demarcation strategy can be used where the localized assignments puncture the distributed assignments. In the example illustrated in FIGS 16A and 16B, BS A and BS B send a dummy Last Distributed Assignment that occupies the end of the distributed assignment zone to indicate that the second demarcation strategy is used. A dummy Last Distributed Assignment message is sent on the first F-SSCH with a dummy MAC Index, which is used to identify a mobile station that does not exist. Referring to FIG. 16C, the Last Distributed Assignment sent by the BS C may be a dummy one or a real one.

Referring now to FIGS. 17A, 17B, and 17C, yet another embodiment of interference avoidance according to the present invention is disclosed. As shown in FIGS. 17A, 17B, and 17C, the distributed assignment zone always starts from the end of the data frame by default. This helps to facilitate the macro diversity transmission. After the first OFDM symbol in the distributed assignment zone, which is the last OFDM symbol in the data frame, the second OFDM in the distributed assignment zone may not necessarily be the OFDM symbol that is next to the first OFDM symbol in the distributed assignment zone. The second OFDM symbol in the distributed assignment zone hops to a different OFDM symbol for different base stations. The third OFDM symbol in the distributed assignment zone also does, and so on. In this way, the OFDM symbol sequence that the distributed assignment zone expends through is randomized between base stations, as shown in FIGS. 17 A, 17B, and 17C. The arrows in FIGS. 17A, 17B, and 17C show the hopping sequence of the OFDM symbols progressing through the distributed assignment zone. In this embodiment, the localized assignment zone starts from the first OFDM symbol in the frame that is not completely occupied by the distributed assignment zone and the localized assignment zone continues towards the end of the data frame, skipping all the OFDM symbols along the way that have been completely occupied by the distributed assignment zone.

For those with ordinary skill in the art, it is obvious that the co-located sectors can use the same OFDM symbol hopping sequence that the distributed assignment zone expends through in order to facilitate macro diversity transmission with the distributed

assignments. Moreover, if the multicast or broadcast service is supported in the distributed assignment zone by a plurality of base stations, at least some portion of the distributed assignment zone among these base stations will be aligned in time.

The interference avoidance schemes described above benefit a system that is lightly loaded. When a system becomes heavily loaded, i.e. when all the OFDM symbols in a frame are occupied by the traffic data among the adjacent base stations, the inter-cell interference may still exist. In this case, a technique called soft time reuse can be used on each of the interference avoidance schemes as described above. The soft time reuse technique is very similar to the soft frequency reuse technique. FIG. 18 illustrates an exemplary embodiment of soft time reuse in a cellular system according to the present invention. As shown in FIG. 18, each base station can transmit at full power over some

OFDM symbols which are mutually exclusive among the interfering base stations.

Additionally, each base station can transmit at limited power over the remaining OFDM symbols in the frame. Certain backhaul coordination among the interfering base stations may be needed.

For each of the reuse schemes described above, the reuse parameters can be either fixed or dynamically adjustable. If the reuse parameters are fixed, the spectrum efficiency may be low as the reuse parameters can not be adaptive to the changing channel conditions or traffic loading conditions. If the reuse parameters can be dynamically changed, a signaling mechanism is needed to indicate the reuse parameters in a dynamic and efficient manner.

(2) Interference Randomization

When two distributed assignments from two adjacent base stations overlap with each other in both time and frequency, the constant interference causes bursty transmission errors, which is difficult to be corrected by the error-correction coding. The embodiments according to another aspect of the present invention to randomize the inter-cell interference in the distributed assignment zone are described below, which can help avoid bursty transmission errors.

FIGS. 19A and 19B together illustrate an embodiment of interference randomization according to the present invention. As illustrated in FIG. 19A, the subcarriers of one particular minimum distributed assignment unit are evenly spaced. Every four contiguous subcarriers, which are indexed alphabetically with A, B, C, and D, within an OFDM symbol form a group. The group is further indexed numerically in sequence along the frequency axis starting from zero from the top. All the subcarriers numbered A in the first OFDM symbol in the distributed assignment zone form one minimal distributed assignment unit, and can be denoted, for example, as D ₀ ³² using Table 2 above. All the subcarriers numbered B in the first OFDM symbol in the distributed assignment zone form another minimal distributed assignment unit, and can be denoted, for example, as D ₈ ³² using Table 2 above. All the subcarriers numbered C in the first OFDM symbol in the distributed assignment zone form yet another minimal distributed assignment unit, and can be denoted, for example, as Dj ₆ ³² using Table 2 above. All the subcarriers numbered A and C in the first OFDM symbol in the distributed assignment zone can form a larger distributed assignment unit, and can be denoted, for example, as Do ¹⁶ using Table 2 above. The demarcation line 1110 is a regular pulse- shaped line.

According to one aspect of the present invention, as illustrated in FIG. 19B, the permutation of the four subcarriers within each group is randomized as a function of at least the Group Index, the OFDM Symbol Index, the Base Station Index, and the current frame number. The randomization of the permutation of the four subcarriers within each group is called group frequency hopping. Therefore, the subcarrier-time bins of one distributed assignment unit does not always overlap with the subcarrier-time bins of the same distributed assignment unit in an adjacent base station. The demarcation line 1120 becomes an irregular pulse-shaped line. As a result of the group frequency hopping, the interference is randomized among four possible resources and bursty transmission errors may be avoided. With group frequency hopping, the base station defines the Last Distributed Assignment based on the location of the resource of the distributed assignment before the group frequency hopping is applied to the distributed assignment. The mobile stations first determine which demarcation strategy is being used based on the Last Distributed Assignment, i.e. if the resource occupied by the Last Distributed

Assignment reaches a certain benchmark of the frame, the second demarcation strategy is being used, otherwise, the first demarcation strategy is being used. If the second demarcation strategy is being used and the mobile station is scheduled with a localized assignment, the mobile station interprets the demarcation line to mean the resource assigned to the mobile station based on the localized assignment of itself. If the second demarcation strategy is being used and the mobile station is scheduled with a distributed assignment, the mobile station interprets the demarcation line by all the localized assignment messages that the mobile station correctly decodes. Then the mobile station locates the subcarrier-time bins assigned to itself based on the distributed assignment message for itself, excluding the subcarrier-time bins occupied by the localized assignment zone and without applying the group frequency hopping. Then the mobile station applies the group frequency hopping to the located subcarrier-time bins to determine the final locations of all the subcarrier-time bins assigned to itself. If the first demarcation strategy is being used and the mobile station is scheduled with a distributed assignment, the mobile station first locates the subcarrier-time bins assigned to itself based on the distributed assignment message for itself without applying the group frequency hopping. Then the mobile station applies the group frequency hopping to the located subcarrier-time bins to determine the final locations of all the subcarrier-time bins assigned to itself. If the first demarcation strategy is being used and the mobile station is scheduled with a localized assignment, the mobile station first interprets the initial demarcation line based on the Last Distributed Assignment message without applying the group frequency hopping. If the demarcation line is a straight line, the mobile station then locates the subcarrier-time bins assigned to itself within the localized assignment zone based on the localized assignment message of itself. If the demarcation line is not a straight line, the mobile station first locates the subcarrier-time bins assigned to itself within the localized assignment zone based on the localized assignment message of itself without using the group frequency hopping. Then the mobile station applies the group frequency hopping to those subcarrier-time bins that are assigned to itself and that are in the same OFDM symbol shared by the distributed assignment zone to determine the final location of those subcarrier-time bins that are assigned to itself and that are in the same OFDM symbol shared by the distributed assignment zone.

Now referring to FIGS. 2OA, 2OB, and 2OC, another embodiment of interference randomization according to the present invention is disclosed. This embodiment discloses a method for randomizing inter-cell interference with group time hopping. Referring to FIG. 2OA, every four contiguous subcarriers within an OFDM symbol form a group. Each group has two indices. Along the frequency axis, each group is indexed numerically in sequence starting from zero from the top. This index is called a group frequency index. Along the time axis, each group is further indexed, for example with the number inside each bin as shown in FIG. 2OA, according to the OFDM Symbol Index of the OFDM symbol that the group is located at. This index is called a group time index. Since the group time hopping is not applied in the example shown in FIG. 2OA, the group time index shown in each subcarrier-time bin coincides with the OFDM Symbol Index of the OFDM symbol that the subcarrier-time bin is located at.

FIG. 2OB shows an example of a method to apply the group time hopping wherein each group may exchange its location in time with another group that has the same group frequency index. Therefore, the hopping happens only along the time axis.

FIG. 2OC shows another example where the groups in the OFDM symbol that is shared by both the distributed assignment zone and the localized assignment zone do not participate the group time hopping due to the fragmentation of that OFDM symbol. The permutation patterns of the each group among the groups that have the same group frequency index is a function of at least the group frequency index, the group time index, the base station index, the frame number, and the distributed assignment zone length along the time axis. As a result of the group time hopping, the interference is randomized among multiple possible resources and bursty transmission errors may be avoided. With group time hopping, the base station defines the Last Distributed Assignment based on the location of the resource of the distributed assignment before the group time hopping is applied to the distributed assignment. The mobile stations first determines which demarcation strategy is being used based on the Last Distributed Assignment as described above. If the second demarcation strategy is being used and the mobile station is scheduled with a localized assignment, the mobile station interprets the demarcation line to mean the resource assigned to the mobile station based on the localized assignment of

itself. If the second demarcation strategy is being used and the mobile station is scheduled with a distributed assignment, the mobile station interprets the demarcation line by all the localized assignment messages that the mobile station correctly decodes. Then the mobile station locates the subcarrier-time bins assigned to itself based on the distributed assignment message for itself, excluding the subcarrier-time bins occupied by the localized assignment zone and without applying the group time hopping. Then the mobile station applies the group time hopping rules to the located subcarrier-time bins to determine the final locations of all the subcarrier-time bins assigned to itself.

The group time hopping rules not only include the hopping function but also include whether the groups in the OFDM symbol that is shared by the two zones participate the group time hopping. If the first demarcation strategy is being used and the mobile station is scheduled with a distributed assignment, the mobile station first locates the subcarrier- time bins assigned to itself based on the distributed assignment message for itself without applying the group time hopping. Then the mobile station applies the group time hopping rules to the located subcarrier-time bins to determine the final locations of all the subcarrier-time bins assigned to itself. If the first demarcation strategy is being used and the mobile station is scheduled with a localized assignment, the mobile station determines the demarcation line based on the Last Distributed Assignment message without applying the group time hopping because the group time hopping does not change the demarcation line for the mobile stations that are scheduled with the localized assignments.

FIG. 2OD shows a modified time hopping scheme, called subcarrier time hopping, where the base station performs the time hopping along the time axis per the individual subcarrier, instead of per group of subcarrier. In this case, even the subcarriers that are in the distributed assignment zone and in the OFDM symbol that is shared by the two zones also participate the time hopping. There are now two lengths for the distributed assignment zone in the time axis. The base station will now apply the distributed assignment zone length according to each subcarrier in the function that calculates the time hopping pattern.

The group time hopping and the subcarrier time hopping described above also provide the time diversity as each distributed assignment unit spreads over multiple OFDM symbols but still within the distributed assignment zone. Furthermore, these hopping schemes can be combined to further randomize inter-cell interference. FIGS. 21A and 21B together illustrate yet another embodiment of interference randomization according to the present invention. FIG. 21A shows a scheme of combining the group frequency hopping as shown in FIG. 19B and the group time hopping as shown in FIG. 2OB. FIG. 21B shows a scheme of combining the group frequency hopping as shown in FIG. 19B and the subcarrier time hopping as shown in FIG. 2OD.

With the group frequency hopping and group or subcarrier time hopping as disclosed in the present invention, the subcarrier-time bins assigned by each distributed assignment spread over both frequency and time randomly but still within the distributed assignment zone, which is clearly separated from the localized assignment zone with a demarcation line, for example 1320 in FIG. 21A and 1330 in FIG. 21B. The mobile stations that are scheduled with the localized assignment only need to know where the demarcation line is and the mobile stations do not need to know where each distributed assignment occupies. While with the conventional distributed assignment where the subcarrier-time bins for each distributed assignment is spread over the entire data frame randomly, the mobile stations that are scheduled with the localized assignment need to know precisely where each distributed assignment occupies. Therefore the present invention simplifies the hardware and software implementation at the mobile station receiver.

For those with ordinary skill in the art, it is obvious that the co-located sectors can use the same group frequency hopping pattern and the same group time hopping pattern in order to facilitate macro diversity transmission with the distributed assignments. In addition, if the multicast or broadcast service is supported in the distributed assignment zone by a plurality of base stations, at least some portion of the distributed assignment zone among these base stations will use the same group frequency hopping pattern and the same group time hopping pattern.

Any interference avoidance scheme or a combination of as described in the present invention can be further combined with any interference randomization scheme or a combination of as described above.

Any interference avoidance scheme, or any interference randomization scheme, or a combination of can be used on the forward link (i.e. from the base station to the mobile station) or the reverse link (i.e. from the mobile station to the base station).

As aforementioned, two assignment methods have been proposed for an OFDMA- based wireless communications system. One assignment method, called localized resource channel (LRCH) assignment, assigns the subcarriers that are contiguous in both time and frequency to one mobile station. Another assignment method, called distributed resource channel (DRCH) assignment, assigns the subcarriers that are scattered in both time and frequency to one mobile station.

FIGS. 22A and 22B illustrate examples of two modes of multiplexing these two types of assignments in one frame. In the first multiplexing mode as shown in FIG. 22A, users, which are also known as mobile stations, A, B, C, and D are assigned with LRCH assignments. Users E and F are assigned with DRCH assignments. The subcarrier-time bins assigned to users E and F overlap with some but not all subcarrier-time bins assigned to users A, B, C, and D. In the first multiplexing mode, users A, B, C, and D don't use those overlapped subcarrier-time bins. In the second multiplexing mode as shown in FIG. 22B, only user C is assigned with the LRCH assignment. The other users, including users A and B, are assigned with the DRCH assignments. The subcarrier-time bins assigned to the users with DRCH assignments do not overlap with the subcarriertime bins assigned to user C. This is done by re-arranging the scattering pattern of the subcarrier-time bins assigned to the users with the DRCH assignments.

Now a signaling mechanism is needed for the base station to inform all mobile stations which multiplexing mode is used in the current frame. In addition, when the first multiplexing mode is used, the base station also needs to inform all mobile stations that are scheduled with the LRCH assignments about which subcarrier-time bins are assigned to the DRCH assignments so that the mobile stations that are scheduled with the LRCH

assignments avoid using those subcarrier-time bins. Furthermore, when the second multiplexing mode is used, the base station also needs to inform all mobile stations that are scheduled with the DRCH assignments about which subcarrier-time bins are assigned to the LRCH assignments so that the mobile stations that are scheduled with the DRCH assignments rearrange the scattering pattern and avoid using those subcarrier-time bins. It has been proposed that a common signaling channel called forward primary data control channel (F-PDCCH) performs the above functions.

In addition, a signaling mechanism is needed for the base station to inform each scheduled mobile station about what frequency-time resources, whether with LRCH or DRCH assignment type, are assigned to the mobile station. It has been proposed that a dedicated signaling channel called forward secondary data control channel (F-SDCCH) performs the above functions.

Table 3 shows an exemplary denotation of the radio resources assigned with the LRCH assignment according to one embodiment of the present invention, the total bandwidth of the exemplary system is 5 MHz with a sampling rate of 4.9152 Msps (million samples per second). The fast Fourier transformation (FFT) size is 512, which is also the total number of subcarriers in frequency. The 512 subcarriers are divided into 32 contiguous minimum localized assignment units in frequency. Each minimum localized assignment unit consists of 16 contiguous subcarriers over a plurality of contiguous OFDM symbols in time within a frame. In a system where the control channels, such as the F-SSCHs that carry the assignment messages for each frame, are frequency division multiplexed (FDM) with the data channels, some minimum LRCH assignment units are assigned for the control channels and can not be used for the data channels. In a system where the control channels are time division multiplexed (TDM) with the data channels, which is the case illustrated in Table 3, some OFDM symbols in a frame, for example, OFDM Symbol 0, is assigned for the control channels, while OFDM Symbols 1 to 7 are used for the data channels. In addition, the solid-shaded area in Table 3 may be used for Guard Band, therefore not available for the data channels. The Guard Band in the example given in Table 3 corresponds to subcarriers 224 to 287. Subcarrier 0 is the Direct Current (DC) tone of the baseband signal.

N

As shown in Table 3, an LRCH assignment unit is denoted as L _k , representing the kth divided assignment unit if the total available resource is divided into N equal-sized LRCH assignment units. In Table 3, two smaller LRCH assignment units with the same size and certain relationship in the indices of the LRCH assignment units can be combined into a larger LRCH assignment unit.

FIG. 2B further illustrates, with an exemplary tree structure, how two smaller LRCH assignment units with the same size and certain relationship in the indices of the two assignment units can be combined into a larger LRCH assignment unit. Replacing the letter "X" with "L", each circle, denoted tree node, in FIG. 2B represents an LRCH assignment unit. Each tree node can be represented by a combination of N and k as defined above. To reduce the signaling overhead, the representation of tree node can be simplified as one number, called Node Index (NodelD), which is above each circle as shown in FIG. 2B. The generalized rule of combining two smaller LRCH assignment units into a larger LRCH assignment unit is illustrated in the following equation:

N ₂ N 2N Lk = L _2k + L _2k+ i (3)

Table 7 below shows an exemplary denotation of the radio resources with the DRCH assignment for the same 5 MHz system according to one embodiment of the present invention. For the first OFDM symbol in the data frame, starting from subcarrier 0, which is the DC tone, every 32 contiguous subcarriers form a group, and the subcarriers within each group in the first OFDM symbol are denoted according the first column in Table 7 in a repeated manner. For the second OFDM symbol in the data frame, starting from subcarrier 0, every 32 contiguous subcarriers form a group, and the subcarriers within each of the 16 groups in the second OFDM symbol are denoted according the second column in Table 7, which is a cyclically rotated version of the first column with an offset of, for example, 4 subcarriers. The subcarriers in third OFDM symbol in the data frame are denoted in a similar cyclically rotated manner, so does the

N forth OFDM symbol and so on. The subcarriers denoted with the same N and k in Dk represent the kth divided assignment unit if the total available resource is divided into N equal-sized DRCH assignment units.

In Table 7, two smaller DRCH assignment units with the same size and certain relationship in their indices can be combined into a larger DRCH assignment unit. Replacing the letter "X" with "D", the same tree structure and denotation of tree nodes as shown in FIG. 2B can be used to illustrate the combining of the DRCH assignment units. The generalized rule of combining two smaller DRCH assignment units into a larger DRCH assignment unit is illustrated in the following equation:

In the example shown in Table 7, the incremental offset of the cyclic rotation in denoting a 32-subcarrier group is constant and regular. A person of the ordinary skill in the art will understand any irregular offset pattern can be used between the OFDM symbols.

Because the denotation of the subcarriers of one group is repeated 16 times in one OFDM symbol in the example, the subcarriers within the same DRCH assignment unit are evenly spaced in frequency and scattered across time. In another embodiment, the 16 groups within each OFDM symbol are further indexed from 0 to 15. And the offset of the cyclic rotation is not only a function of OFDM Symbol Index, the base station index, and the current frame number, but also a function of group index. In this embodiment, the subcarriers within the same DRCH assignment unit are no longer evenly spaced in frequency, and further interference randomization is achieved.

In yet another embodiment according the present invention, the denotation of a 32- subcarrier group is not a simple cyclically rotated version, but a randomly permutated version of the 32-subcarrier group in the first OFDM symbol as a function of OFDM Symbol Index, the base station index, and the current frame number. Then the permutation pattern is repeated 16 times for the 16 groups within an OFDM symbol. In this way, the subcarriers within the same DRCH assignment unit are evenly spaced in frequency and scattered across time. In yet another embodiment according to the present invention, the 16 groups within each OFDM symbol are further indexed from 0 to 15, and

the permutation pattern is a function of both the OFDM Symbol Index, the base station index, the current frame number, and the group index. In this embodiment, the subcarriers within the same DRCH assignment unit are no longer evenly spaced in frequency, and further interference randomization is achieved.

FIG. 3 illustrates an exemplary channel structure for the forward shared scheduling channel (F-SSCH) that sends the assignment messages to the mobile stations according to the present invention. The assignment message contains at least a field for Media Access Control Index (MACID) to identify the intended mobile station, a field for Node Index (NodelD) to identify the assigned radio resource in time and frequency, a field for Assignment Type to identify whether the assignment is the LRCH assignment or the DRCH assignment, a field of Packet Format (PF) to identify the encoder packet size, modulation level, and code rate of the data packet. A person of the ordinary skill in the art will understand, the assignment message may contain other fields including, but not limited to, fields for message type and multiple antenna mode or may not contain some of the fields as the information is either implicitly sent or is known to the mobile station.

The field of Assignment Type in the F-SSCH can be eliminated in a simplified scheme by limiting the localized assignment units to those with a first set of sizes and limiting the distributed assignment units to those with a second set of sizes, wherein none of the sizes in the first set exists in the second set and none of the sizes in the second set exists in the first set. For example, in the 5MHz system illustrated above, the localized assignment units can be limited to L ₀ ¹ , Lj ² , L _j ⁴ , and L _m ⁸ , meanwhile the distributed assignment units can be limited to D _x ¹⁶ and D _y ³² , where i, j, m, x, y are integers, and O≤i≤l, 0<j<3, 0<m<7, 0<x<15, and 0<y<31. Therefore, the assignment size implies which assignment type is used and no need to have an explicit field of Assignment Type in the F-SSCH.

Referring again to FIG. 3, the Cyclic Redundant Check (CRC) bits are first added to the information bits of the assignment message by the CRC element 310. The forward error correction (FEC) element 315 adds error correction coding to the output sequence of the CRC element 310. Then a rate matching element 320 repeats and/or punctures the

encoded bits from the encoder in order to match the rate on the F-SSCH to a certain fixed rate. A scrambler 325 then scrambles the output sequence from the rate matching element 320 with a scrambling code that is generated from scrambling code generator 330. The scrambling code generator 330 is a PN register that is seeded with the channel identity of the F-SSCH, the current frame number, and optionally the scrambling type. The scrambled sequence is interleaved by channel interleaver 335. The interleaved sequence is then modulated by modulator 340. The in-phase (I) and quadrature (Q) outputs of modulator 340 are then gain-controlled by the channel gain elements 345 and 350 respectively. The complex output signal is then multiplexed with the other channels by the channel multiplexer 355 using Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), OFDMA, or any combination of the above.

According to one aspect of the present invention, at least one DRCH assignment and at least one LRCH assignment can be multiplexed in the same frame, and different DRCH assignment can have difference assignment size, and different LRCH assignment can have difference assignment size.

According to another aspect of the present invention, the base station assigns the DRCH assignments according to the sequence of the minimum DRCH assignment units that the DRCH assignments cover. For example in the 5MHz system illustrated in Table

8 16 32

7, the following three DRCH assignments, D ₀ , D ₂ , and D ₆ , leave no vacant

8 subcarriers in the resource assigned. But the following three DRCH assignments, D ₀ ,

16 32

D ₄ , and Di ₀ , would leave some vacant subcarriers in the resource assigned.

According to yet another aspect of the present invention, a Last DRCH Assignment is defined as the DRCH assignment that covers the minimum DRCH assignment unit, for

32 example D _k , with the largest index k among all DRCH assignments. Therefore, the NodeID field in the Last DRCH Assignment message implicitly indicates all the DRCH assignment units assigned to the mobile station that are scheduled with DRCH assignments. The assignment message for the Last DRCH Assignment is sent on the first F-SSCH with sufficient power by the Channel Gain elements 345 and 350 such that all

scheduled mobile stations can decode the Last DRCH Assignment message correctly. Therefore, in the first multiplexing mode, since each mobile station understands the group offset values or group permutation pattern as described above, as a result of the Last DRCH assignment message, each mobile station that is scheduled with the LRCH assignment in the same frame will recognize subcarrier-time bins that are assigned to the mobile station and are overlapped with the DRCH assignments. According to the first mode of multiplexing, the mobile stations that are scheduled with LRCH assignments will not use those overlapped subcarrier-time bins when retrieving the modulation symbols for each corresponding data packet.

The first F-SSCH can be distinguished from the other F-SSCHs by using a special orthogonal code, scrambling code, frequency subband, subfield within a long field of assignment message, time, or time-frequency bin, which is specified by the individual base station, can be different from base station to base station, and is informed to all mobile stations by signaling messages. If there is no DRCH assignment in the frame, the first F-SSCH can be used for carrying a LRCH assignment message. In this case, because all mobile stations that are scheduled with the LRCH assignment need to detect correctly that the first F-SSCH is carrying a LRCH assignment message, the first FSSCH should be sent with sufficient power by the Channel Gain elements 345 and 350 to ensure all mobile stations that are scheduled with the LRCH assignment can detect it correctly. Furthermore, selecting the mobile station with the worst channel condition among all mobile stations that are scheduled with LRCH assignment can help to utilize the base station transmit power more efficiently, but this is not required. In the first multiplexing mode, all DRCH assignment messages except the Last DRCH Assignment message and all LRCH assignment messages can be sent in a dedicated manner, i.e. be sent with sufficient power by the Channel Gain elements 345 and 350 to ensure the target mobile station can decode the assignment message correctly, for example, based on the channel quality feedback from the target mobile station.

[According to another aspect of the present invention, the Last DRCH assignment message also serves as the indicator of which multiplexing mode is used in the frame. More specifically, when the number of subcarriers assigned to the DRCH assignments

within each 32-subcarrier group exceeds a mode-switching threshold, an enhanced second multiplexing mode is used. Otherwise, the first multiplexing mode is used. In the enhanced second mode of multiplexing, the overlapped subcarrier-time bins are assigned to the mobile stations that are scheduled with the LRCH assignment, and the mobile stations that are scheduled with DRCH assignments can not use those overlapped subcarrier-time bins. In order for all the scheduled mobile stations to understand that the second mode is being used, the first F-SSCH that carries the Last DRCH Assignment message should be sent with sufficient power by the Channel Gain elements 345 and 350 to ensure all scheduled mobile stations can decode the Last DRCH Assignment message correctly. Using the Last DRCH Assignment message for the mobile station with the worst channel condition among all mobile station that are scheduled with the DRCH assignment can help to utilize the base station transmit power more efficiently as mentioned before, but it is not required. In addition, in the enhanced second mode of multiplexing, in order for all mobile stations scheduled with the DRCH assignment to understand which subcarrier-time bins are assigned for the LCRH assignments, any LRCH assignment message should be sent with sufficient power by the Channel Gain elements 345 and 350 to ensure all the mobile stations that are scheduled with the DRCH assignment to decode the LRCH assignment message correctly. In the second mode of multiplexing, all DRCH assignment messages except the Last DRCH Assignment message can be sent in a dedicated manner, i.e. besent with sufficient power by Channel Gain elements 345 and 350 to ensure the target mobile station can decode the assignment message correctly, for example, based on the channel quality feedback from the target mobile station.

In addition, when the enhanced second mode of multiplexing is used and there is no LRCH assignment being scheduled in the same frame, a mobile station that is scheduled with the DRCH assignment may not be able to recognize whether the mobile station has missed the detection of any LRCH assignment messages or there is no LRCH assignment indeed.

According to yet another aspect of the present invention, if there is at least one DRCH assignment and at least one LRCH assignment in the frame, the Last DRCH

Assignment message is sent on the first F-SSCH and scrambled with the first scrambling method. If there is at least one DRCH assignment and no LRCH assignment, the Last DRCH Assignment message is sent on the first F-SSCH and scrambled with the second scrambling method.

FIG. 23 illustrates an embodiment of the base station procedure for sending the assignment messages and data packets according to the present invention. As shown in FIG. 23, the base station first selects which mobile stations to be scheduled for transmission in the next frame in step 400 and which type of assignment is used for each of those scheduled mobile stations in step 405. In step 410, the base station determines if there is at least one mobile station that is scheduled with the DRCH assignment. If there is no mobile station that is scheduled with the DRCH assignment, the base station further determines if there is at least one mobile station that is scheduled with the LRCH assignment in step 415. If no, the base station waits until the next frame arrives. If yes, in step 420, the base station sends an LRCH assignment message on the first F-SSCH with the first scrambling method and with sufficient power for all scheduled mobile stations to decode it correctly. Then the base station sends the other assignment messages in a dedicated manner as described above and all data packets in step 425 and the based station waits until the next frame arrives. If the base station determines that there is at least one mobile station that is scheduled with the DRCH assignment in step 410, the base station selects a mobile station that is scheduled with the DRCH assignment to be the intended mobile station for the Last DRCH Assignment in step 430. For example, the base station can select the mobile station with the worst channel condition among all mobile stations that are scheduled with the DRCH assignment to be the intended mobile station of the Last DRCH Assignment. This selection method can facilitates the base station to transmit power more efficiently, but it is not required. Next in step 435, the base station further determines if there is at least one mobile station that is scheduled with the LRCH assignment. If there is no mobile station that is scheduled with the LRCH assignment, the base station scrambles the first F-SSCH with the second scrambling method in step 440. Then the base station sends the Last DRCH Assignment message on the first F-SSCH with sufficient power for all scheduled mobile stations to decode it correctly in step 445. Then the base station sends the other assignment messages in a

dedicated manner and all data packets in step 425 and the based station waits until the next frame arrives. If the base station determines that there is at least one mobile station that is scheduled with the LRCH assignment in step 435, the base station scrambles the first F-SSCH with the first scrambling method in step 450. Then in step 455, the base station further determines which multiplexing mode to be used in the frame. If the first multiplexing mode is to be used, the base station ensures that the NodeID in the Last DRCH Assignment message does not exceed the mode-switching threshold in step 460. If the second multiplexing mode is to be used, the base station ensures that the NodeID in the Last DRCH Assignment message exceeds the mode-switching threshold in step 470. Then the base station sends the Last DRCH Assignment message on the first F-SSCH with sufficient power for all scheduled mobile stations to decode it correctly in step 445. The base station sends the other assignment messages and all data packets in step 425 and the based station waits until the next frame arrives.

FIG. 24 illustrates an embodiment of the mobile station procedure for detecting the assignment messages and data packets according to the present invention. Referring to FIG. 24, the mobile station first detects all assignment messages on all F-SSCHs in step 500. Then the mobile station determines if the MACID of the mobile station has been found in any of these assignment messages in step 505. If no, the mobile station waits until the next frame arrives. If yes, the mobile station further determines if there is a DRCH assignment message on the first F-SSCH in step 510. If no, the mobile station further determines if the assignment for the mobile station is an LRCH assignment in step 515. If no, a detection error is shown and the mobile station waits until the next frame arrives, because the assignment for this mobile station can not be a DRCH assignment when the assignment on the first F-SSCH is not a DRCH assignment. If the mobile station determines that the assignment for the mobile station is an LRCH assignment in step 515, the mobile station uses the NodeID in the assignment message of the mobile station to retrieve the modulation symbols of data packet for the mobile station and decodes that data packet in step 520. Then the mobile station waits until the next frame arrives. If the mobile station determines that there is a DRCH assignment message on the first F-SSCH in step 510, this DRCH assignment message is the Last DRCH Assignment message. The mobile station then further determines if the first F-SSCH is scrambled

with the first scrambling method in step 525. If no, the mobile station then determines if the assignment for the mobile station is an LRCH assignment in step 530. If yes, a detection error is shown and mobile station waits until the next frame arrives, because if the mobile station determines that the first F-SSCH is scrambled with the second scrambling method in step 525, there is no LRCH assignment in the frame. If the mobile station determines that the assignment for the mobile station is an LRCH assignment in step 530, the mobile station uses the NodeID in the assignment message of the mobile station to retrieve the modulation symbols of the data packet for the mobile station and decodes that data packet in step 520. Then the mobile station waits until the next frame arrives. If the mobile station determines that the first F-SSCH is scrambled with the first scrambling method in step 525, the mobile station further determines if the first multiplexing mode is used in the frame in step 535. If yes, the mobile station then determines if the assignment for the mobile station is an LRCH assignment in step 540. If no, the mobile station uses the NodeID in the assignment message of the mobile station to retrieve the modulation symbols of the data packet for the mobile station and decodes that data packet in step 520. Then the mobile station waits until the next frame arrives. If yes, the mobile station first uses the NodeID in the Last DRCH Assignment message to determine overlapped subcarrier-time bins in step 545. Then the mobile station uses the NodeID in the assignment message of the mobile station excluding the overlapped subcarrier-time bins to retrieve the modulation symbols of the data packet for the mobile station and decodes the data packet in step 520. Then the mobile station waits until the next frame arrives. If the mobile station determines that the second multiplexing mode is used in the frame in step 535, the mobile station then determines if the assignment for the mobile station is an LRCH assignment in step 550. If yes, the mobile station uses the NodeID in the assignment message of the mobile station to retrieve the modulation symbols of the data packet for the mobile station and decodes the data packet in step 520. Then the mobile station waits until the next frame arrives. If no, the mobile station first uses the NodeIDs in all the LRCH assignment messages to determine the overlapped subcarriertime bins in step 555. Then the mobile station uses the NodeID in the assignment message of the mobile station excluding the overlapped subcarrier-time bins to retrieve the modulation symbols of the data packet for the mobile station and decodes

the data packet in step 520. Then the mobile station waits until the next frame arrives.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiment disclosed herein may be implemented or performed with, but not limited to, a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, and any combination thereof designed to perform the functions described herein.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be implemented or performed directly in hardware, in a software module executed by a processor, or in combination of the two. A software module may reside in, but not limited to, RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, and any other form of storage medium in the art.

The present invention provides a unique method and system for Adaptive Hybrid ARQ in An OFDMA Based Communication System. It is understood, however, that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components, signals, messages, protocols, and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to limit the invention from that described in the claims. Well known elements are presented without detailed description in order not to obscure the present invention in unnecessary detail. For the most part, details unnecessary to obtain a complete understanding of the present invention have been omitted inasmuch as such details are within the skills of persons of ordinary skill in the relevant art. Details regarding control circuitry described herein are omitted, as such control circuits are within the skills of persons of ordinary skill in the relevant art.

It is an objective of the present invention to provide a method and apparatus to support the HARQ retransmission in an adaptive manner in order to fit into the various multiplexing modes of two types of assignments in the frame during re-transmission.

It is another objective of the present invention to support the base station to do the above with minimum signaling overhead.

It is yet another objective of the present invention to provide a method for the base station to determine when it is necessary to send the assignment message for the re- transmission.

According to one aspect of the present invention, FIGS. 25A and 25B illustrate the processing steps and the timing relationship of HARQ for the forward link (FL) and the reverse link (RL), respectively. Referring to FIG. 25A, for the FL FIARQ operation, in step IA, the base station transmits the assignment messages to the scheduled mobile stations using the shared scheduling channel (SSCH) in the first OFDM symbol of a frame, and the mobile station decodes all the assignment messages and determines if 'an assignment message for the mobile station is detected. In step 2A, the base station transmits the data packets for the scheduled mobile stations according to the assignment messages using the data channel (DCH) for the rest of the data frame. And if there is multiple-input-multiple-output (MIMO) transmission, the base station may also include the assignment messages for the other layers of the MIMO transmission as a preamble of the data packet of the first layer transmission in the DCH in step 2A while the assignment message for the first layer is sent with the shared scheduling channel in step IA. If the mobile station determines an assignment message for the mobile station is detected in step IA, then in step 3A, the mobile station decodes the data packet for the mobile station. If the mobile station decodes the data packet correctly in step 3A, then the mobile station sends an ACK in step 4A, otherwise the mobile station sends a NACK in step 4A. In step 5A, the base station decodes the ACK/NACK signals from all previously scheduled mobile stations, detects the FL channel condition feedbacks from all mobile stations, and schedules the data transmissions including the HARQ retransmissions for the next frame. If the base station detects a NACK from a mobile station in step 5A, the base station may send an assignment message, in step 6A, to that mobile station for the re-transmission, depending on the procedure that will be described later in the present invention. Then in step 7A, the base station re-transmits the previously failed data packet according to the incremental redundancy or chasing combining.

Referring to FIG. 25B, for the RL HARQ operation, in step IB, the base station initially transmits the assignment messages to the scheduled mobile stations using the SSCH in the first OFDM symbol of a frame, and the mobile station decodes all assignment messages and determines if an assignment message for the mobile station is detected. If the mobile station determines an assignment message for the mobile station is detected in step IB, then the mobile station transmits the data packets according to the assignment message using the DCH for the rest of the data frame in step 2B. In step 3B, the base station decodes all data packets for the scheduled mobile stations. If the base station decodes the data packet for a mobile station correctly in step 3B, the base station sends an ACK to the mobile station in step 5B. Otherwise, the base station sends a NACK to the mobile station in step 5B. In step 4B, the base station detects the RL channel conditions for all mobile stations, and schedules the data transmissions on the RL including the HARQ re-transmissions for the next frame depending on at least, but not limited to, the RL channel condition and ACK/NACK situation of the previous transmission for each mobile station. If the base station sends a NACK to a mobile station in step 5B, the base station may also send an assignment message for the retransmission in step 5B, depending on the procedure that will be described later in the present invention. Then in step 6B, the mobile station re-transmits the previously failed data packet according to the incremental redundancy or chasing combining.

According to the embodiments illustrated in FIGS. 25A and 25B, the HARQ interlacing period is 5 frames. A person of the ordinary skill in the art will understand that other interlacing periods are possible.

According to another aspect of the present invention, the frame boundaries of the transmitted FL frame and the received RL frame at the base station antenna may be aligned or it may be offset by an integer number of OFDM symbols to support the HARQ timing for various cell sizes that may be encountered in the deployment. When the cell size is large and the round-trip propagation delay of the signal is longer than a certain threshold, the offset becomes necessary to allow the mobile station to have enough time to decode the ACK/NACK and/or assignment messages from the base station and to assemble the modulation symbols and waveforms accordingly in step IB, before

transmitting the waveforms in step 2B.

FIGS. 4 and 8 illustrate examples of two modes of multiplexing two types of assignments in one frame. An alternative embodiment of multiplexing two types of assignment with two possible modes is also disclosed in the present invention. In both disclosures, the base station assigns the distributed assignment units according to certain sequence such that the last distributed assignment implicitly indicates which resource units are used by the distributed assignments collectively.

According to yet another aspect of the present invention, the base station can retransmit a previously failed data packet using a different assignment type from the assignment type that is used for the previously failed transmission. For example, if the base station uses the distributed assignment for the initial transmission and the initial transmission fails, the base station can use the localized assignment for the retransmission. When the base station changes the assignment type for the retransmission, the base station will send an assignment message to the mobile station to inform the mobile station.

According to yet another aspect of the present invention, the base station can retransmit a previously failed data packet in the new frame using a different multiplexing mode from the multiplexing mode that is used in the frame of the previously failed transmission. For example, if the base station uses the first multiplexing mode in the frame of the initial transmission, no matter what assignment type the initial transmission uses, and the initial transmission fails, the base station can use the second multiplexing mode in the frame of the retransmission. When the base station changes the multiplexing mode in the frame of the re-transmission, the base station may need to send an assignment message to the mobile station to inform the mobile station according to Table 8 that will be described later in the present invention.

As aforementioned, each assignment message contains at least a field of Media Access Control Index (MACID) to identify the intended mobile station for the assignment message, a field of Node Index (NodelD) to identify the assigned radio resource in time and frequency, a field of Assignment Type to identify whether the

assignment is the localized resource channel (LRCH) assignment or the distributed resource channel (DRCH) assignment, a field of Packet Format (PF) to identify the encoder packet size, modulation level, and code rate of the data packet. A person of the ordinary skill in the art will understand, the assignment message may contain other fields including, but not limited to, fields for message type and multiple antenna mode. As aforementioned, the field of Assignment Type in the F-SSCH can be eliminated in a simplified scheme by limiting the localized assignment units to those with a first set of sizes and limiting the distributed assignment units to those with a second set of sizes, wherein none of the sizes in the first set exists in the second set and none of the sizes in the second set exists in the first set. For example, in the 5MHz system illustrated above,

1 2 4 8 the localized assignment units can be limited to L ₀ , Li , L _j , and L _m , meanwhile the

16 32 distributed assignment units can be limited to D _x and D _y , where i, j, m, x, y are integers, and O≤i≤l, 0<j<3, 0<m<7, 0<x<15, and 0<y<31. Therefore, the assignment size implies which assignment type is used and no need to have an explicit field of Assignment Type in the F-SSCH.

According to yet another aspect of the present invention, the base station may use different subcarriertime bins to re-transmit the failed data packet to the mobile station from the subcarrier-time bins assigned for the initial transmission. The base station may reduce the number subcarrier-time bins if the base station believes the earlier transmission is close to success and only a smaller number of redundant modulation symbols are needed for the re-transmission. The base station may increase the number subcarrier-time bins if the base station wants to transmit more redundant modulation symbols so that the HARQ re-transmission can be completed successfully before the target number or the maximum number of HARQ retransmission. The base station may change the location of the subcarrier-time bins for the re-transmission. In all the cases described above, the base station will send an assignment message to the mobile station to inform the mobile station about the changes.

In one embodiment of the HARQ re-transmission, the base station sends the assignment message with a new NodeID to indicate the changes in the subcarrier-time

bins for the re-transmission as described above. In this embodiment, the new NodeID will indicate the total subcarrier-time bins assigned for the re-transmission. The new NodeID may just indicate the change of the location of the subcarrier-time bins without changing the total number of the subcarriertime bins. In another embodiment, the new NodeID will be interpreted by the mobile station as the incremental change (i.e. adding to the existing resource assigned) or decremental change (i.e. removing from the existing resource assigned). In addition to the NodeID, the base station will indicate to the mobile station which way the mobile station should interpret the new NodeID.

According to yet another aspect of the present invention, when the base station sends the assignment message for the HARQ re-transmission, the PF field in that assignment message will be a special combination, for example "111111", to indicate that the data packet is for a re-transmission, while all the other combinations of the PF field indicate valid values for the packet format. In another embodiment, a first special combination, such as ""111111", in the PF field is used to indicate that the data packet is for a re- transmission and the modulation level on the DCH is maintained as the before, and a second special combination, such as "111110", in the PF field is used to indicate that the data packet is for a re-transmission and the modulation level on the DCH is reduced to one level below the previous modulation level, while all the other combinations of the PF field indicate valid values for the packet format. The modulation level on the DCH can be, in an ascending order of the modulation levels, Binary Phase Shift Keying (BPSK), Quadrature Phase Sift Keying (QPSK), 8-phase Phase Sift Keying (8PSK), 16-phase Quadrature Amplitude Modulation (16QAM), 32-phase Quadrature Amplitude Modulation (32QAM), or 64-phase Quadrature Amplitude Modulation (64QAM). In yet another embodiment, in addition to the first two specially combinations in the PF field as described above, a third special combination, such as "111101", in the PF field can be used to indicate that the data packet is for a re-transmission and the modulation level on the DCH is increased to one level above the previous modulation level, while all the other combinations of the PF field indicate valid values for the packet format.

In addition to the rules and procedures that determine if the base station needs to send assignment message for a re-transmission as described above, in some cases where

the base station does not change the modulation level, or the number of the subcarrier- time bins, or the location of the subcarrier-time bins, or the assignment type for the retransmission, the base station may still need to send the assignment message with the NodeID and Assignment Type of the previous transmission to inform the mobile stations that are scheduled for transmission in the same frame as the re-transmitted packet about which subcarrier-time bins will be used by the re-transmitted packet. Table 8 below illustrates various cases where the base station needs or does not need to send the assignment message with the SSCH for the re-transmission in the cases where even though the modulation level, the number of the subcarrier-time bins, and the assignment type for the retransmission do not change in the re-transmission. The Table 8 below also explains why the assignment message for the re-transmission is needed. Therefore, Table 8 can be used as the procedure regarding how the base station determines if the base station needs to send the assignment message with the SSCH for the re-transmission in the cases where the modulation level, the number of the subcarriertime bins, and the assignment type for the re-transmission do not change in the re-transmission and the procedure regarding how the base station should put the transmit power on the SSCH that carries the assignment message for the re-transmission.

Table 8

Old Frame New Frame

The Need and Reason for SSCH for

Cases Multiplexing Multiplexing Retransmission

Mode Mode

Yes. To inform all DRCH users in the new

2nd mode frame of the NodeID of the failed LRCH.

Initial 2nd mode

1st mode No. LRCH failed Yes. To inform all DRCH users in the new

2nd mode frame of the NodeID of the failed LRCH.

1st mode

1st mode No.

Yes if the new Last DRCH is the failed DRCH, to inform all users in the new frame of the multiplexing mode.

2nd mode

No if the new Last DRCH is not the failed DRCH.

2nd mode Yes if the new Last DRCH is the failed DRCH or has a smaller index than the failed DRCH. To inform all users in the new frame of the multiplexing mode if the new Last DRCH is the failed DRCH; or to re-locate the failed DRCH to be within the index of the new Last DRCH if the new Last DRCH has a smaller index than the failed DRCH.

1st mode

Initial No if the new last DRCH has a larger index

DRCH than the failed DRCH. failed Yes if the failed DRCH is the Last DRCH in the new frame, to inform all users in the new frame of the multiplexing mode .

2nd mode

No if the failed DRCH is not the Last DRCH in the new frame.

^{1 st mode} Yes if the new Last DRCH is the failed DRCH or the new Last DRCH has a smaller index than the failed DRCH. To inform all users in the new frame of the multiplexing mode if the new Last DRCH is the failed DRCH; or to relocate the failed DRCH to be within the index of the new Last DRCH if the new Last DRCH has a smaller index than the failed DRCH.

1 st mode No if the new Last DRCH has a larger index than the failed DRCH.

The various illustrative logical blocks, modules, and circuits described in connection

with the embodiment disclosed herein may be implemented or performed with, but not limited to, a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, and any combination thereof designed to perform the functions described herein.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be implemented or performed directly in hardware, in a software module executed by a processor, or in combination of the two. A software module may reside in, but not limited to, RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, and any other form of storage medium in the art.

The previous description of the disclosed embodiments is provided to enable those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art and generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.