The technique, method and apparatus described below can be used in various wireless access technologies such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. The wireless access technologies can be implemented with various wireless communication standard systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with a radio technology such as Global System for Mobile communications (GSM)/ General Packet Radio Service (GPRS)/ Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented with a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, E-UTRA (Evolved-UMTS Terrestrial Radio Access) etc. 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved-universal mobile telecommunications system (E-UMTS). The 3GPP LTE employs the OFDMA in downlink and employs the SC-FDMA in uplink. LTE-advance (LTE-A) is an evolution of the LTE.

For clarity, the following description will focus on the 3GPP LTE/LTE-A. However, technical features of the present invention are not limited thereto.

The technique, method and apparatus described below can be applied to a frequency division duplex (FDD) system or time division duplex (TDD) system. In the FDD system, uplink transmission and downlink transmission may use same time but different frequency bands. In the TDD system, uplink transmission and downlink transmission may use same frequency bands but different time.

FIG. 1 shows a wireless communication system. A wireless communication system 10 includes at least one base station (BS) 11. The BSs 11 provide communication services to specific geographical regions (generally referred to as cells) 15a, 15b, and 15c. The cell can be divided into a plurality of regions (referred to as sectors). A user equipment (UE) 12 may be fixed or mobile, and may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device, etc. The BS 11 is generally a fixed station that communicates with the UE 12 and may be referred to as another terminology, such as an evolved node-B (eNB), a base transceiver system (BTS), an access point, etc.

Hereinafter, a downlink denotes a communication link from the BS to the UE, and an uplink denotes a communication link from the UE to the BS. In the downlink, a transmitter may be a part of the BS, and a receiver may be a part of the UE. In the uplink, the transmitter may be a part of the UE, and the receiver may be a part of the BS.

FIG. 2 shows a structure of a TDD radio frame in a 3GPP LTE system. This may be found in section 4.2 of 3GPP TS 36.211 V8.2.0 (2008-03) "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)". One radio frame has a length of 10 milliseconds (ms) and consists of two half-frames each having a length of 5 ms. One half-frame consists of five subframes each having a length of 1 ms. Each subframe is used as any one of an uplink (UL) subframe, a downlink (DL) subframe, and a special subframe. One radio frame includes at least one UL subframe and at least one DL subframe.

The special subframe is a specific period positioned between the UL subframe and the DL subframe to separate uplink and downlink. One radio frame includes at leas one special subframe. The special subframe includes a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). The DwPTS is used for initial cell search, synchronization, or channel estimation. The UpPTS is used for channel estimation in a base station (BS) and uplink transmission synchronization of a user equipment (UE). The GP is positioned between uplink and downlink and is used to remove interference that occurs in uplink due to a multi-path delay of a downlink signal.

Table 1 shows a structure of a configurable frame according to arrangement of the UL subframe and the DL subframe in a 3GPP LTE TDD system. In configurations 0, 1, 2, and 6, uplink and downlink are switched with a switching point period of 5 ms. In configurations 3, 4, and 5, uplink and downlink are switched with a switching point period of 10 ms. Herein, 'D' denotes a DL subframe, 'U' denotes a UL subframe, and 'S' denotes a special subframe.

Table 1

FIG. 3 shows a structure of a DL subframe. A subframe includes two slots and 14 OFDM symbols. Each slot includes 7 OFDM symbols. A time for transmitting one subframe is defined as a transmission time interval (TTI). For example, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms. The number of OFDM symbols included in the subframe may change according to a length of a cyclic prefix (CP) or according to a system. For example, a subframe of a normal CP may include 14 OFDM symbols whereas a subframe of an extended CP may include 12 OFDM symbols. The OFDM symbol is for expressing one symbol period since the 3GPP LTE uses OFDMA in downlink. According to a system, the OFDM symbol may be referred to as an SC-FDMA symbol or a symbol duration. A resource block (RB) is a resource allocation unit, and includes 12 consecutive subcarriers.

A maximum of three OFDM symbols located in a front portion of a first slot within the subframe correspond to a control region to be assigned with control channels. The remaining OFDM symbols correspond to a data region to be assigned with a physical downlink shared channel (PDSCH).

Examples of downlink control channels include a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid-ARQ indicator channel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of a subframe and carries information regarding the number of OFDM symbols used to transmit control channels within the subframe. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI transmits uplink or downlink scheduling information or includes an uplink transmit (Tx) power control command for arbitrary UE groups. Further, the PDCCH includes resource allocation information for a system information block (SIB).

The PDCCH can carry a transport format and a resource allocation of a downlink shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information on a paging channel (PCH), system information on the DL-SCH, a resource allocation of an upper-layer control message such as a random access response transmitted on the PDSCH, a set of Tx power control commands on individual UEs within an arbitrary UE group, a Tx power control command, activation of a voice over IP (VoIP), etc. A plurality of PDCCHs can be transmitted within a control region. The UE can monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate based on a state of a radio channel. The CCE corresponds to a plurality of resource element groups. A format of the PDCCH and the number of bits of the available PDCCH are determined according to a correlation between the number of CCEs and the coding rate provided by the CCEs.

The BS determines a PDCCH format according to a DCI to be transmitted to the UE, and attaches a cyclic redundancy check (CRC) to control information. The CRC is masked with a unique identifier (referred to as a radio network temporary identifier (RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UE may be masked to the CRC. Alternatively, if the PDCCH is for a paging message, a paging indicator identifier (e.g., paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is for system information (more specifically, a system information block (SIB) to be described below), a system information identifier and a system information RNTI (SI-RNTI) may be masked to the CRC. To indicate a random access response that is a response for transmission of a random access preamble of the UE, a random access-RNTI (RA-RNTI) may be masked to the CRC. Table 2 below shows an example of identifiers masked to the PDCCH.

Table 2

The wireless communication system can support uplink or downlink hybrid automatic repeat request (HARQ).

FIG. 4 shows uplink HARQ. A BS receives uplink data 101 from a UE on an physical uplink shared channel (PUSCH), and thereafter transmits an acknowledgement (ACK)/not-acknowledgement (NACK) signal 102 on a PHICH. The ACK/NACK signal 102 corresponds to an ACK signal when the uplink data 101 is successfully decoded, and corresponds to a NACK signal when the uplink data 101 fails in decoding. Upon receiving the NACK signal, the UE can transmit retransmission data 111 for the uplink data 101 until ACK information is received or until retransmission is performed up to a maximum number of retransmission attempts. The BS can transmit an ACK/NACK signal 112 for the retransmission data 111 on the PHICH.

Now, a PHICH configuration in the 3GPP LTE is described.

FIG. 5 is a flowchart showing the PHICH configuration. This may be found in section 6.9 of 3GPP TS 36.211 V8.2.0 (2008-03). Since the 3GPP LTE system does not support single user-multiple input multiple output (SU-MIMO) in uplink, the PHICH carries a 1-bit ACK/NACK signal corresponding to a PUSCH for one UE. In step S110, the 1-bit ACK/NACK signal is subjected to channel coding by using repetition coding having a code rate of 1/3. In step S120, an ACK/NACK signal coded with a 3-bit codeword is mapped to three modulation symbols by binary phase shift keying (BPSK). In step S130, the modulation symbols are spread using a spreading factor (SF) N ^PHICH _SF and an orthogonal sequence. To apply I/Q multiplexing, the number of orthogonal sequences used for spreading is twice of N ^PHICH _SF . 2N ^PHICH _SF PHICHs are spread using 2N ^PHICH _SF orthogonal sequences and are defined with one PHICH group. The PHICHs belonging to the same PHICH group are identified with different orthogonal sequences. In step S140, the spread symbols are subjected to layer mapping according to a rank. In step S150, the layer-mapped symbols are respectively mapped to resource elements.

As disclosed in section 6.9 of 3GPP TS 36.211 V8.2.0 (2008-03), a PHICH resource corresponding to the PUSCH is defined using a lowest physical resource block (PRB) index I ^lowest_index _{PRB_RA} of a resource used in the PUSCH and a cyclic shift n _DMRS of a data demodulation reference signal used in the PUSCH. The demodulation reference signal is a reference signal used to demodulate data transmitted on the PUSCH. More specifically, the PHICH resource is known by an index pair (n ^group _PHICH , n ^seq _PHICH ). n ^group _PHICH denotes a PHICH group number. n ^seq _PHICH denotes an orthogonal sequence index within a PHICH group, and is expressed by Equation 1 below:

MathFigure 1

where 'mod' denotes a modulo operation.

n ^group _PHICH has a value between 0 and (N ^group _PHICH -1). N ^group _PHICH denotes the number of PHICH groups and is expressed by Equation 2 blow in an FDD system:

MathFigure 2

where N ^DL _RB denotes a total number of resource blocks within a DL subframe, and corresponds to a DL bandwidth. A PHICH resource Ng satisfies Ng∈{1/6, 1/2, 1, 2}, and is obtained from a master information block (MIB) on a physical broadcast channel (PBCH). The PHICH resource may be defined as a parameter for obtaining the number of PHICH groups.

The MIB includes resource allocation information (i.e., the PHICH resource Ng and the PHICH duration m) for acquiring a resource region of a PHICH within a control region. The PHICH duration m denotes the number of OFDM symbols that can be allocated with the PHICH in one subframe. The PHICH duration configured puts lower limit on the size of the control region signaled by the PCFICH.

The resource allocation of the PHICH is included in the MIB because the UE has to know the resource region of the PHICH to receive the PDCCH. In the control region, the PDCCH is allocated to a region except for a resource region allocated with the PCFICH and the PHICH.

FIG. 6 shows an example in which resource regions of a PDCCH and a PHICH are allocated in a control region. It is assumed herein that a PHICH duration m is 3, and two PHICH groups exist. A UE first acquires an MIB that is system information, and then acquires a resource region of the PHICH by using resource allocation information, i.e., PHICH resource Ng and the PHICH duration m. Upon acquiring a resource allocation of the PHICH, a resource region of the PDCCH within the control region can be acquired. Thus, the PDCCH can be detected by monitoring the PDCCH within the resource region of the PDCCH. Monitoring implies attempting to decode each of the PDCCHs in the control region. When the decoding of the PDCCH is successful, the PDCCH is detected.

Now, transmission of system information in the 3GPP LTE is described.

System information is divided into the Master Information Block (MIB) and a number of System Information Blocks (SIBs). The MIB includes a limited number of most essential and most frequently transmitted parameters that are needed to acquire other information from the cell, and is transmitted on PBCH mapped to Broadcast Channel (BCH). SIBs are transmitted on PDSCH mapped to Downlink Shared Channel (DL-SCH).

There are various types of SIBs. SIBs other than SIB-1 (SIB Type1) may flexibly be configurable by scheduling information included in the SIB-1. SIB-1 contains information relevant when evaluating if a UE is allowed to access a cell and defines the scheduling of other SIBs. SIB-2 (SIB Type2) contains common and shared channel information. SIB-3 (SIB Type3) contains cell re-selection information, mainly related to the serving cell. SIB-4 (SIB Type4) contains information about the serving frequency and intra-frequency neighboring cells relevant for cell re-selection (including cell re-selection parameters common for a frequency as well as cell specific re-selection parameters). SIB-5 (SIB Type5) contains information about other E UTRA frequencies and inter-frequency neighbouring cells relevant for cell re-selection (including cell re-selection parameters common for a frequency as well as cell specific re-selection parameters). SIB-6 (SIB Type6) contains information about UTRA frequencies and UTRA neighbouring cells relevant for cell re-selection (including cell re-selection parameters common for a frequency as well as cell specific re-selection parameters). A single SI-RNTI may be used to address SIB-1 as well as other SIBs.

The MIB uses a fixed schedule with a periodicity of 40 ms and repetitions made within 40 ms. The MIB is scheduled in subframe #0 (first subframe) of radio frames. SIB-1 uses a fixed schedule with a periodicity of 80 ms and repetitions made within 80 ms. The SIB-1 is scheduled in subframe #5 (sixth subframe) of radio frames.

FIG. 7 is a flow diagram showing acquisition of system information. In step S210, a UE first acquires an MIB on a PBCH. The UE acquires information regarding a resource allocation of a PHICH from the MIB. On the basis of the resource allocation of the PHICH, the UE can acquire a resource region of the PHICH, and can receive a PDCCH. In step S220, the UE can receive an SIB-1 on a PDSCH indicated by the PDCCH which is CRC-masked using an SI-RNTI. In step S230, the UE can receive other SIBs by using scheduling information included in the SIB-1.

When the aforementioned method is used, PHICH allocation cannot be modified during a transmission period (i.e., 40 ms) of the MIB. This is because the UE can know the PHICH allocation after receiving the MIB. Further, the PHICH allocation is difficult to be carried out in every subframe. This is because there is a limit in an amount of information that can be included in the MIB. In particular, the PHICH allocation may need to be modified in every subframe in a TDD system of which the number of DL subframes within one radio frame is less than that of an FDD system.

Therefore, a method capable of acquiring resource allocation information of the PHICH in every subframe is proposed for more flexible resource allocation.

FIG. 8 shows an example of a method of acquiring a resource allocation according to an embodiment of the present invention. A UE receives an MIB 300 on a PBCH, and acquires a resource allocation of a PHICH included in the MIB 300. On the basis of the resource allocation of the PHICH, the UE acquires a resource region of the PHICH in a subframe at which an SIB-1 310 is transmitted. This implies that the resource allocation of the PHICH within the MIB 300 is information for acquiring the resource region of the PHICH in a specific subframe.

Since the UE can acquire the resource region of the PHICH in the subframe at which the SIB-1 310 is transmitted, the UE can receive a PDCCH in the subframe at which the SIB-1 310 is transmitted. Therefore, the SIB-1 310 is received on a PDSCH indicated by a PDCCH on which an SI-RNTI is CRC-masked. The SIB-1 includes a resource allocation of the PHICH in a subframe unit. The resource allocation of the SIB-1 may include a PHICH resource and/or a PHICH duration in each subframe. Alternatively, the resource allocation of the SIB-1 may include a variation amount of the resource allocation received using the MIB. The SIB-1 for resource allocation can contain information with a larger amount than the MIB, and thus the SIB-1 can include a resource allocation of the PHICH corresponding to each subframe.

The above method can apply to a TDD system. For example, when the downlink-uplink configuration of Table 1 is used, the resource allocation of the PHICH can be configured for each downlink subframe.

Although the MIB indicates the resource allocation of the PHICH for reception of the SIB-1 herein, this is for exemplary purposes only, and thus various embodiments are possible. For example, the SIB-1 may indicate the resource allocation of the PHICH for reception of an SIB-2. In this case, the SIB-2 may include another form of the resource allocation of the PHICH. It can be said that a first resource allocation of a control channel for reception of second system information is acquired from first system information, and a second resource allocation of the control channel is acquired from the second system information.

FIG. 9 is a flowchart showing a method of acquiring a resource allocation of a control channel according to an embodiment of the present invention. This procedure may be carried in a UE.

Referring to FIG. 9, in step S510, a UE receives a first resource allocation of a control channel on a first downlink channel in a first subframe. The control channel may be PHICH and the first downlink channel may be PBCH. The first resource allocation may be include in a MIB on the PBCH and may include a PHICH resource and a PHICH duration in a second subframe. The PHICH resource may be used to acquire the number of PHICH groups and the PHICH duration may indicate the number of OFDM symbols in which the PHICH is allocated.

In step S520, the UE acquires a resource region of the control channel in a second subframe based on the first resource allocation of the control channel. In step S530, the UE acquires a resource region of a second downlink channel in the second subframe based on the resource region of the control channel. The second downlink channel may be PDCCH. A subframe includes a plurality of OFDM symbols. The subframe may be divided into a control region and a data region. The control region may precede the data region. Both the control channel and the second downlink channel may be allocated in a control region of the second subframe. The resource region of the control channel may not be overlapped with the resource region of the second downlink channel in the control region of the second subframe.

In step S540, the UE receives a second resource allocation of the control channel on a third downlink channel in the second subframe. The third downlink channel may be PDSCH. In the second subframe, the PDSCH may be indicated by the second downlink channel, i.e. PDCCH, whose cyclic redundancy check (CRC) is masked with System Information-Radio Network Temporary Identifier (SI-RNTI).

The second resource allocation may include information on the size of the resource region of the control channel and the number of control channels in a subframe. More specifically, the second resource allocation may include PHICH resources or PHICH durations in each downlink subframe.

The first resource allocation of the control channel is included in a MIB and the second resource allocation of the control channel is includes in a SIB, e.g. SIB-1. The first subframe in which the MIB is transmitted may be a first subframe of a radio frame and the second subframe in which the SIB-1 is transmitted may be a sixth subframe of the radio frame.

This embodiment may be applied to a TDD system in which a radio frame includes a plurality of downlink subframe and at least one uplink subframe. The radio frame may use at least one configuration among downlink-uplink configurations shown in Table 1.

FIG. 10 is a flowchart showing a method of monitoring a control channel according to an embodiment of the present invention. This procedure may be carried in a UE.

Referring to FIG. 10, in step S610, a UE receives a first resource allocation of a control channel on a first downlink channel in a first subframe. The control channel may be PHICH and the first downlink channel may be PBCH. The first resource allocation may be include in a MIB on the PBCH and may include a PHICH resource and a PHICH duration in a second subframe. The PHICH resource may be used to acquire the number of PHICH groups and the PHICH duration may indicate the number of OFDM symbols in which the PHICH is allocated.

In step S620, the UE acquires a resource region of the control channel in a second subframe based on the first resource allocation of the control channel. In step S630, the UE acquires a resource region of a second downlink channel in the second subframe based on the resource region of the control channel. The second downlink channel may be PDCCH. A subframe includes a plurality of OFDM symbols. The subframe may be divided into a control region and a data region. The control region may precede the data region. Both the control channel and the second downlink channel may be allocated in a control region of the second subframe. The resource region of the control channel may not be overlapped with the resource region of the second downlink channel in the control region of the second subframe.

In step S640, the UE monitors the second downlink channel in the second subframe. The PDCCH may be detected when decoding of the PDCCH is successful since the CRC of the PDCCH is masked with SI-RNTI.

In step S650, the UE receives a second resource allocation of the control channel on a third downlink channel in the second subframe. The third downlink channel may be PDSCH. In the second subframe, the PDSCH may be indicated by the second downlink channel, i.e. PDCCH. The second resource allocation may include information on the size of the resource region of the control channel and the number of control channels in a subframe. More specifically, the second resource allocation may include PHICH resources or PHICH durations in each downlink subframe.

The first resource allocation of the control channel is included in a MIB and the second resource allocation of the control channel is includes in a SIB, e.g. SIB-1. The first subframe in which the MIB is transmitted may be a first subframe of a radio frame and the second subframe in which the SIB-1 is transmitted may be a sixth subframe of the radio frame.

This embodiment may be applied to a TDD system in which a radio frame includes a plurality of downlink subframe and at least one uplink subframe. The radio frame may use at least one configuration among downlink-uplink configurations shown in Table 1.

FIG. 11 is a block diagram showing an apparatus of wireless communication that may be used with the previously described embodiments. An apparatus 50 may be a part of UE. The apparatus 50 includes a processor 51, a memory 52, a transceiver 53, a display 54, and a user interface unit 55. The processor 51 may be configured to perform procedures shown in FIGs. 8-10. The memory 52 is coupled with the processor 51 and stores a variety of information to receive control channels. The display unit 54 displays a variety of information of the apparatus 50 and may use a well-known element such as a liquid crystal display (LCD), an organic light emitting diode (OLED), etc. The user interface unit 55 can be configured with a combination of well-known user interfaces such as a keypad, a touch screen, etc. The radio frequency (RF) unit 53 is coupled with the processor 51 and transmits and/or receives a radio signal.

The present invention can be implemented with hardware, software, or combination thereof. In hardware implementation, the present invention can be implemented with one of an application specific integrated circuit (ASIC), a digital signal processor (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, other electronic units, and combination thereof, which are designed to perform the aforementioned functions. In software implementation, the present invention can be implemented with a module for performing the aforementioned functions. Software is storable in a memory unit and executed by the processor. Various means widely known to those skilled in the art can be used as the memory unit or the processor.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.