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Title:
UPLINK CONTROL SIGNALING FOR JOINT FDD AND TDD CARRIER AGGREGATION
Document Type and Number:
WIPO Patent Application WO/2014/209959
Kind Code:
A1
Abstract:
In described examples, a connection is established to a first serving cell (101) designated as a primary serving cell (PCell), and a connection is established to a second serving cell (105) designated as a secondary serving cell (SCell). The SCell (105) uses a different duplex mode than the PCell (101). The PCell (101) and SCell (105) duplex modes are selected from FDD and TDD modes. A mobile device receives subframe scheduling messages for the SCell (105) in a downlink subframe and selects an uplink subframe to send a scheduling message acknowledgement based upon the duplex mode of the PCell (101).

Inventors:
EKPENYONG, Anthony, Edet (2001 Westheimer Road, Apt. 508Houston, TX, 77098, US)
Application Number:
US2014/043805
Publication Date:
December 31, 2014
Filing Date:
June 24, 2014
Export Citation:
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Assignee:
TEXAS INSTRUMENTS INCORPORATED (P.o. Box 655474, Mail Station 3999Dallas, TX, 75265-5474, US)
TEXAS INSTRUMENTS JAPAN LIMITED (24-1, Nishi-shinjuku 6-chomeShinjuku-ku, 160-8366, JP)
International Classes:
H04J4/00; H04L1/16; H04L5/14
Domestic Patent References:
WO2012109195A22012-08-16
WO2012108718A22012-08-16
Other References:
"LTE Carrier Aggregation between TDD and FDD. Discussion and Decision", 13.1. 3GPP TSG RAN MEETING #59, 2 February 2013 (2013-02-02) - 1 March 2013 (2013-03-01), VIENNA, AUSTRIA, Retrieved from the Internet
Attorney, Agent or Firm:
DAVIS, Michael, A. et al. (Texas Instruments Incorporated, International Patent ManagerP.o. Box 655474, Mail Station 399, Dallas TX, 75265-5474, US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A method of operating a mobile device, the method comprising:

establishing a connection to a first serving cell designated as a primary serving cell (PCell);

establishing a connection to a second serving cell designated as a secondary serving cell (SCell), wherein the SCell uses a different duplex mode than the PCell;

receiving subframe scheduling messages for the SCell in a downlink subframe; and selecting an uplink subframe to send a scheduling message acknowledgement based upon the duplex mode of the PCell;

wherein the PCell and SCell duplex modes are selected from a frequency division duplex (FDD) mode and a time division duplex (TDD) mode.

2. The method of claim 1, wherein the primary serving cell operates in FDD mode, and the secondary serving cell operates in TDD mode.

3. The method of claim 2, wherein a downlink control information (DCI) format scheduling downlink assignments or uplink grants on the TDD SCell does not include information in a downlink assignment index (DAI) field.

4. The method of claim 1, wherein a downlink control information (DCI) format scheduling an uplink grant on a first serving cell operating in FDD mode contains information in a downlink assignment index (DAI) field indicating the cumulative number of scheduling message acknowledgements required for a second serving cell operating in TDD mode.

5. The method of claim 1, wherein the mobile device is capable of only half-duplex operation.

6. The method of claim 5, wherein the primary serving cell operates in TDD mode, and the secondary serving cell operates in FDD mode, the method further comprising:

configuring the mobile device to apply the same uplink/downlink configuration of the TDD PCell for hybrid automatic repeat request (HARQ) acknowledgements corresponding to downlink assignments on a physical downlink shared channel (PDSCH) of the FDD SCell.

7. The method of claim 1, wherein the mobile device is FDD-only and is operated on a TDD carrier, the method further comprising:

configuring the mobile device with a restricted set of subframes to monitor for downlink control information scheduling downlink assignments on the TDD carrier.

8. The method of claim 7, further comprising:

indicating to the mobile device a set of subframes where a detected DL assignment on the PDSCH contains fewer than a maximum number of OFDM symbols in a subframe.

9. A user equipment device, comprising:

a processor circuit configured to:

establish a connection to a first serving cell operating in a frequency division duplex (FDD) mode, the first serving cell designated as a primary serving cell (PCell); and

establish a connection to a second serving cell operating in a time division duplex (TDD) mode, the second serving cell designated as a secondary serving cell (SCell);

a receiver circuit configured to receive downlink subframe scheduling messages for the SCell; and

a transmitter circuit configured to transmit acknowledgment messages on one of: a physical uplink control channel of the PCell; and a physical uplink shared channel; wherein the acknowledgement messages correspond to the downlink subframe scheduling messages received for the SCell.

10. The device of claim 9, wherein the subframe scheduling messages include a downlink data assignment, and wherein the acknowledgement messages include a positive or negative hybrid automatic repeat request acknowledgment (HARQ-ACK) for a physical downlink shared channel (PDSCH) transmitted on the TDD SCell, and wherein the HARQ-ACK message follows a HARQ-ACK timing format of the FDD PCell.

11. The device of claim 9, wherein when the receiver circuit detects a downlink assignment for the physical downlink shared channel (PDSCH) on the TDD SCell in a subframe n, the transmitter circuit is configured to transmit a hybrid automatic repeat request positive or negative acknowledgment (HARQ-ACK) on one of: the PUCCH of the FDD PCell; and a UL grant in subframe n+4.

12. The device of claim 9, wherein when the receiver circuit detects a downlink control information (DO) format scheduling an uplink grant on the FDD PCell, the transmitter circuit is configured to transmit one or more positive or negative acknowledgments according to the information contained in a downlink assignment index (DAI) field of the DCI format.

13. A user equipment device, comprising:

a processor circuit configured to:

establish a connection to a first serving cell operating in a time division duplex (TDD) mode, the first serving cell designated as a primary serving cell (PCell); and

establish a connection to a second serving cell operating in a frequency division duplex (FDD) mode, the second serving cell designated as a secondary serving cell (SCell); a receiver circuit configured to receive a physical downlink shared channel (PDSCH) message in a downlink subframe on the SCell; and

a transmitter circuit configured to transmit an acknowledgment message corresponding to the received PDSCH message in a selected uplink subframe.

14. The device of claim 13, wherein the transmitter circuit is configured to transmit acknowledgment messages on the PUCCH of the PCell.

15. The device of claim 13, wherein the downlink subframe is subframe n, and the selected uplink subframe is subframe n+k, where k>4, and n+k is the first valid uplink subframe following the downlink subframe.

16. The device of claim 13, wherein the transmitter circuit is configured to transmit simultaneous physical uplink control channel (PUCCH) transmissions on both the PCell and SCell.

17. The device of claim 13, wherein the transmitter circuit is configured to transmit time -multiplexed physical uplink control channel (PUCCH) transmissions on the PCell and SCell.

18. The device of claim 17, wherein the transmitter circuit is configured to transmit on PUCCH of the FDD SCell only if an uplink subframe on the FDD SCell corresponds to a downlink subframe on the TDD PCell.

19. The device of claim 17, wherein the transmitter circuit is configured to transmit on PUCCH of the TDD PCell if the subframe is an uplink subframe on the TDD PCell.

Description:
UPLINK CONTROL SIGNALING FOR JOINT FDD AND

TDD CARRIER AGGREGATION

[0001] This relates in general to wireless communication, and in particular to wireless telephony.

BACKGROUND

[0002] A cellular wireless network includes multiple base stations. Each base station transmits to (downlink or DL) and receives from (uplink or UL) mobile users in its coverage area. The explosion in data traffic in wireless cellular networks has created a need for rapid expansion of network capacity to cope with increasing user demand. Carrier aggregation provides one method to increase network capacity. With carrier aggregation, a base station simultaneously transmits data to, or receives data from, mobile user equipment (UE) on multiple carriers in the same or different RF bands. For example, in a cellular system complying with the third generation partnership project (3GPP) long term evolution (LTE) standards, carrier aggregation has been standardized in LTE Releases 10 and 11 for both intra-band and inter-band operation. The cost of mobile UEs is strongly dependent upon the cost of the RF front end, including the mixers, oscillators and radio amplifier, which is designed to work in a specific RF band(s). To maximize return on investment, mobile UE vendors strive for equipment that can be used in both frequency division duplex (FDD) and time division duplex (TDD) modes, as well as in the most widely deployed RF bands across all geographic regions.

[0003] On the other hand, the cost of RF spectrum is a significant bottleneck in the deployment of ubiquitous and high data rate wireless communication systems. Cellular network operators acquire RF spectrum based on several factors, including the size of allocated spectrum chunks (where higher RF bands are better) and optimized coverage (where lower frequency bands provide better in-building penetration). Furthermore, widespread adoption of a particular band guarantees that mobile devices would support that band. Based on these factors, a network operator may own spectrum in both FDD and TDD bands and may want to configure carrier aggregation for a UE on both TDD and FDD component carriers. SUMMARY

[0004] In described examples, a connection is established to a first serving cell designated as a primary serving cell (PCell), and a connection is established to a second serving cell designated as a secondary serving cell (SCell). The SCell uses a different duplex mode than the PCell. The PCell and SCell duplex modes are selected from FDD and TDD modes. A mobile device receives subframe scheduling messages for the SCell in a downlink subframe and selects an uplink subframe to send a scheduling message acknowledgement based upon the duplex mode of the PCell.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a perspective view of a network system in a heterogeneous deployment scenario, where a base station operates in FDD mode and provides macro coverage in a macro cell site having three sectors.

[0006] FIG. 2 is a subframe diagram of a mobile device scheduled to transmit PUSCH on the FDD PCell in subframe 7 of radio frame ¾ + 1.

[0007] FIG. 3 is a subframe diagram of a scenario where a mobile device is configured with an FDD SCell and a TDD PCell employing TDD UL/DL Configuration 2.

[0008] FIG. 4 is a subframe diagram of using an FDD secondary serving cell for half-duplex TDD mobile devices employing TDD UL/DL Configuration 1.

[0009] FIG. 5 is a subframe diagram of using a TDD cell as a secondary serving cell for an FDD-only mobile device.

[0010] FIG. 6 is a block diagram of internal details of a mobile user equipment and a base station operating in a network system, such as the system of FIG. 1.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0011] A joint FDD and TDD design provides carrier aggregation in a wireless communication system. The signaling methodology described herein may be implemented in an orthogonal frequency-division multiplexing (OFDM)-based cellular system that operates in FDD and/or TDD modes, such as in an LTE cellular network.

[0012] In one embodiment, the PCell operates in FDD mode, and the SCell operates in TDD mode. In this configuration, the mobile device receives a physical downlink shared channel (PDSCH) from the TDD SCell in a subframe n and transmits a hybrid automatic repeat request acknowledgment (HARQ ACK) to the FDD PCell in subframe n+4. [0013] In another embodiment, the PCell operates in TDD mode, and the SCell operates in FDD mode. In this configuration, the mobile device receives PDSCH in a downlink subframe from the FDD SCell and transmits a HARQ ACK corresponding to the PDSCH to the TDD PCell in a selected uplink subframe. The selected uplink subframe may be the first valid uplink subframe following the downlink subframe. In one example, the downlink subframe carrying the PDSCH is subframe n, and the selected uplink subframe is subframe n+k, where k>4.

[0014] The mobile device may operate in a half-duplex TDD mode, in which case it uses an uplink/downlink subframe configuration for a TDD PCell when transmitting to an FDD SCell.

[0015] In a deployment scenario for joint FDD/TDD carrier aggregation, joint FDD/TDD operation is proposed when a cellular network operator owns both FDD and TDD spectrum in the same geographical area. For example, in a given geographical area, FDD spectrum at 800 MHz and TDD spectrum at 2.6 GHz may be available. FIG. 1 shows a heterogeneous deployment scenario, where base station 101 operates in FDD mode and provides macro coverage in a macro cell site having three sectors 102-104. Base stations 105 are low power nodes that operate in TDD mode in a higher frequency band and control small cells 106. Small cells 106 can be used as capacity boosters to increase throughput at hotspots within the macro-cell sectors. In other scenarios, the macro cell base station 101 may operate in TDD mode, and the hotspot base stations 105 may operate in FDD mode. Base stations 101 and 105 may be owned and controlled by a single network operator or by two or more different network operators in a radio access network (RAN) sharing arrangement.

[0016] Given this general deployment scenario, three modes of joint FDD/TDD operation are: a default single mode operation; carrier aggregation; and inter-node aggregation as explained below.

[0017] In carrier aggregation (CA), a UE may be configured to receive and transmit data on multiple component carriers (CCs). From the perspective of the MAC layer, data transmission in either DL-only or both DL and UL directions are scheduled per component carrier (CC). Accordingly, each component carrier may be considered as a serving cell each with its own MAC scheduler. In the LTE system, an anchor cell provides a mobility connection to the network and is called the primary serving cell (PCell). Depending on data traffic requirements, the base station may configure additional serving cells known as secondary serving cells (SCells). In one deployment configuration, all primary and secondary serving cells are collocated. In a different deployment configuration, an SCell may be deployed at a different location from the PCell with a backhaul connection 107 (preferably with low latency and high throughput) connecting the PCell and SCell locations.

[0018] For joint FDD-TDD carrier aggregation operation, the PCell (and possibly some SCells) may be FDD, while one or more SCells may be TDD or vice-versa. The requirements for joint FDD-TDD carrier aggregation include: UEs that are capable of multi-mode operation (as either TDD or FDD UEs); inter-band carrier aggregation capability; UL carrier aggregation joint operation, which also requires the UEs to support an independent UL timing advance for different component carriers; and determining the cell to which the UE transmits uplink control information (UCI).

[0019] For joint FDD-TDD carrier aggregation design, hybrid automatic repeat request (HARQ) scheduling and feedback considerations exist.

[0020] For an LTE system, some existing procedures and DL/UL signaling for carrier aggregation are agnostic about whether the configured serving cells operate in FDD or TDD modes. A key difference is the HARQ scheduling and HARQ feedback acknowledgments (HARQ-ACK) timelines. With the paired DL and UL carriers in FDD, a UE may be scheduled for DL assignments and/or UL grants with one-millisecond granularity (in any subframe). Correspondingly, the HARQ-ACK feedback for a DL assignment in subframe n is transmitted in subframe n+4 for normal HARQ operation. Similarly, the DL HARQ-ACK feedback for a UL grant in subframe n is transmitted on the physical HARQ indicator channel (PHICH) in subframe n+4.

[0021] By comparison, TDD divides a radio frame into DL and UL sub frames with a guard period to enable transition from DL to UL. This results in restricted opportunities for DL/UL transmission and HARQ-ACK feedback. The LTE system defines a Special subframe, which consists of a DL portion (the downlink pilot time slot or DwPTS), a guard period, and a UL portion (the uplink pilot time slot or UpPTS).

[0022] There are seven TDD UL/DL configurations defined in LTE Releases 8-11, as shown in Table 1. The choice of the TDD UL/DL configuration for a given cell depends on several factors, such as the DL and UL traffic rates observed in a cell, the need for good UL coverage (e.g., requiring a UL-heavy UL/DL configuration), and coexistence with other TDD wireless technologies such as time division synchronous code division multiple access (TD-SCDMA). Table 1

[0023] As shown in Table 1, when operating in TDD mode, limited UL subframes are available in which to transmit data or uplink control information, such as HARQ-ACK feedback, channel state information (CSI), and scheduling requests. In a UL subframe, the UE may be required to transmit HARQ-ACK feedback for a set of M DL subframes, which is referred to as the downlink association set.

[0024] Table 2 represents the HARQ-ACK DL association set K for TDD UL/DL configurations in an LTE system. The set of possible HARQ-ACK feedback states includes positive acknowledgement (ACK), negative acknowledgement (NACK), and discontinuous transmission (DTX). Accordingly, given a set of M elements, {k 0 , k l ., k M -i} the UE generates HARQ-ACK feedback in a UL subframe n corresponding to DL subframes {n-ko, n- k l ., n-kM-i}. The downlink control information (DCI) formats scheduling DL assignments or UL grants on a TDD serving cell contain a downlink assignment index (DAI) field, which indicates to the UE the number of DL subframes for which HARQ-ACK feedback is expected. For example, in a UL subframe n for which up to M DL subframes {n-ko, n- k l ., n-kM-i} may require HARQ-ACK feedback, the DAI field may indicate that fewer than M subframes were actually scheduled to the UE. A radio frame includes ten subframes labeled as subframes 0 to 9. In Table 2, the subframes in subsequent frames may be labeled as subframes 10 to 19, etc. in order to compute the subtraction n ¾ for i = 0 to M-l . Table 2

[0025] A design constraint for carrier aggregation in current LTE systems is that UCI is only transmitted on the physical uplink control channel (PUCCH) of the PCell. Accordingly, efficient FDD-TDD HAPvQ-ACK feedback in carrier aggregation depends on which duplex mode is operated on the PCell (FDD is full-duplex, and TDD is half-duplex). Certain design principles used in current LTE systems may be re -visited for more efficient FDD-TDD operation. These include: introduce no new TDD UL/DL configurations for joint FDD-TDD carrier aggregation operation; and transmit UCI only on the PUCCH of the PCell.

[0026] In the following sections, different HARQ-ACK feedback designs are considered for the cases where the PCell is operating in either FDD or TDD mode. Although these examples are described using the special case of a single SCell, the design may be generalized to carrier aggregation using multiple SCells.

[0027] In one scenario, the PCell operates in FDD mode, and the SCell operates in TDD mode. When the network includes a mix of FDD and TDD cells, one benefit of having the PCell operate in FDD mode is that all subframes of an FDD radio frame are valid UL subframes for UCI transmission. Accordingly, when an additional serving cell is configured for TDD, the HARQ-ACK feedback timeline for any TDD UL/DL configuration can be followed for HARQ-ACK feedback on PUCCH, because the set of UL subframes for the PCell is a superset of the TDD UL subframes. For single duplex mode carrier aggregation, an LTE Release 10 or Release 11 UE may be configured with one of the following PUCCH schemes: PUCCH Format lb with channel selection or PUCCH Format 3. The same PUCCH schemes may be configured for FDD-TDD CA as follows.

[0028] 1) If the UE detects a DL assignment on the physical downlink control channel (PDCCH) or enhanced physical downlink control channel (EPDCCH), scheduling PDSCH in a TDD SCell in any one of the M subframes associated with an uplink subframe.

[0029] a) When PUCCH Format 3 is configured, the PUCCH resource is indicated by the

Transmit Power Control (TPC) field of the PDCCH scheduling PDSCH on the SCell, where the TPC field indicates one out of four semi-statically configured resources.

[0030] b) When PUCCH Format lb with channel selection is configured for the case of a single SCell: (a) if the PDSCH on the SCell is cross-scheduled from the PCell, up to two resources may be indicated by dynamic PUCCH allocation based on the PDCCH/EPDCCH detected on the PCell; or (b) otherwise, if the PDSCH is self-scheduled on the SCell, the value of the TPC field of any PDCCH/EPDCCH scheduling PDSCH in any of the M DL subframes associated with the UL subframe indicates one of a set of four pairs of semi-statically configured PUCCH resources.

[0031] 2) If the UE does not detect a PDCCH/EPDCCH scheduling PDSCH in a TDD SCell in any one of the M subframes associated with an uplink subframe, then the UE transmits on the PUCCH of the FDD PCell in subframe n only if a PDSCH or PDCCH/EPDCCH indicating semi-persistent scheduling (SPS) release is detected in the PCell in subframe n-4.

[0032] HARQ-ACK feedback can be optimized for a TDD SCell when the PCell is operated in FDD mode. Specifically, the HARQ-ACK timing for the PDSCH transmitted on the TDD SCell follows the HARQ-ACK timing on the FDD PCell. Accordingly, the UE transmits HARQ-ACK feedback in the PUCCH of the PCell in subframe n for a PDSCH detected on a TDD SCell in subframe n-4. When PUCCH Format 3 is configured, the PUCCH resource is indicated by the TPC field of the PDCCH/EPDCCH scheduling PDSCH on the TDD SCell. Similarly, when PUCCH Format lb with channel selection is configured up to two PUCCH resources corresponding to SCell, PDSCH are indicated by the TPC field of the PDCCH/EPDCCH scheduling the PDSCH on the SCell. This scheme eliminates the need for a downlink association set (M = 1 for any UL/DL configuration). Accordingly, a DAI field is unnecessary in the DCI formats scheduling a DL assignment or UL grant on a TDD SCell when the PCell operates in FDD mode, because the HARQ-ACK timing follows the FDD PCell HARQ-ACK timing. [0033] Another consideration is how to multiplex the HARQ-ACK bits on PUSCH when the UE is transmitting on PUSCH. In LTE Release 11 TDD, the number of HARQ-ACK bits transmitted on PUSCH for a configured serving cell depends on the size of the DL association set M or the DAI value contained in the DL assignment or in the UL grant that is transmitted on the PDCCH/EPDCCH. Zero to nine subframes may be indicated by the DAI value in the PDCCH/EPDCCH. In contrast, for an FDD serving cell in LTE Release 11, the number of HARQ-ACK bits is based on the number of configured serving cells and the downlink transmission modes configured for each FDD serving cell.

[0034] FIG. 2 shows carrier aggregation with a PCell in FDD mode and an SCell in TDD UL/DL Configuration 2. In the TDD SCell, DL assignments for the SCell in DL subframes 4 and 5 of radio frame ¾ are acknowledged (HARQ-ACK feedback) by the UE in UL subframe 2 of radio frame ¾ + 1. The DL assignment for the SCell in Special subframe 1 of radio frame n f + 1 is acknowledged by the UE in UL subframe 7 of radio frame ¾ + 1. Conversely, in the FDD PCell, each DL subframe n can always be uniquely associated with a corresponding UL subframe that is four subframes later (n + 4), because the FDD PCell has a pair of CCs for DL and UL respectively. For example, a DL assignment in subframe 8 of radio frame n f is acknowledged in UL subframe 2 of radio frame n f +1. Furthermore, if a UL grant is transmitted in subframe 8 of radio frame n f in addition to the DL assignment, the UE transmits the HARQ-ACK feedback on PUSCH if the UE is not configured for simultaneous PUCCH and PUSCH transmission. A DAI field is unnecessary in FDD, because the feedback in a UL subframe n + 4 corresponds to the DL assignment transmitted on the PDSCH in DL subframe n.

[0035] For joint FDD-TDD carrier aggregation operation, HARQ-ACK feedback on PUSCH may need to take into account HARQ-ACK feedback for FDD cells. However, in current FDD-only carrier aggregation operation, the downlink control information (DO) formats have no DAI field. Two possible solutions are described below to efficiently support joint FDD-TDD carrier aggregation operation.

[0036] Solution 1 : maintain the current design in which DCI formats have no DAI field in an FDD cell.

[0037] 1) For PUSCH transmission on an FDD serving cell:

[0038] a) Arrange the HARQ-ACK bits according to the serving cell index, where 0 is for the PCell, 1 is the first SCell, etc. [0039] b) For an FDD cell, generate one or two HARQ-ACK bits, depending on whether the configured transmission mode supports one or two transport blocks, respectively.

[0040] c) For the c* TDD cell, generate either B^ L or 2B° L , depending on whether the configured transmission mode supports one or two transport blocks respectively, where

B c DL = M.

[0041] In an alternative embodiment, the UE determines the HARQ-ACK feedback for a TDD SCell based on the value of the DAI ( ) in the most recent detected PDCCH/EPDCCH scheduling PDSCH on the SCell for the DL aassociation set {n - k m ), m - 0, ...,M -1 . Accordingly, the number of generated HARQ-ACK bits for this TDD cell is B° L = .

[0042] d) FIG. 2 shows an example for an SCell using TDD UL/DL Configuration 2. In

UL subframe 2 of radio frame n f + 1, the UE transmits HARQ-ACK feedback corresponding to detected DL assignments in subframes 4 and 5 of the TDD SCell and subframe 8 of the FDD PCell in radio frame n f .

[0043] 2) For PUSCH transmission on a TDD serving cell:

[0044] a) If the PUSCH transmission is not adjusted based on a detected

PDCCH/EPDCCH with DCI format 0/4, then follow the same bit ordering and number of generated bits as above for PUSCH transmission on an FDD serving cell with B° L = M .

[0045] b) If the PUSCH transmission is adjusted based on a detected PDCCH/EPDCCH conveying UL DCI format 0/4, then

[0046] i) For the c* TDD cell, 5 c m = W M , where ¾is the DAI value in the detected DCI format 0/4.

[0047] ii) In one embodiment, the bit ordering is determined according to the cell index as described above for PUSCH transmitted on an FDD serving cell.

[0048] iii) In another embodiment, the HARQ-ACK bits generated for one or more FDD serving cells are appended to the HARQ-ACK bits for the TDD serving cells (so they are the least significant bits). Accordingly, when a UL grant is detected for subframe n on a TDD serving cell, if no PDSCH or SPS release DCI was in subframe n-4 of the FDD serving cell, the bit mapping is the same as for TDD-only carrier aggregation.

[0049] Solution 2: add a DAI field for DCI formats in an FDD serving cell. The DAI field would indicate (to the UE) the total number of subframes requiring feedback for any configured TDD serving cell. This solution avoids any possible ambiguity between the base station and the UE, in case the UE misses all the scheduling assignments within the DL association set for a UL subframe n.

[0050] The length of the DAI field may be two bits, but in other embodiments a one-bit DAI field may be defined. The DAI field is used for indicating (to the UE) that feedback is required for at least one configured TDD serving cell with B° L = M . Other values are not precluded, because a primary goal is to inform the UE when transmitting PUSCH in an FDD cell to include HARQ-ACK feedback for TDD cells.

[0051] This solution is also applicable for a TDD PCell and an FDD SCell, because a UL grant for the FDD SCell may contain a DAI field to indicate the number of DL subframes of the TDD PCell that require HARQ-ACK feedback. Accordingly, the DAI field may exist for PDCCH/EPDCCH on an FDD serving cell whenever at least one TDD serving cell is configured for a UE.

[0052] Alternatively, the DAI field exists for only an FDD serving cell when the subframe is also a UL subframe corresponding to a linked DL association set for at least one of the configured TDD serving cells.

[0053] FIG. 2 shows that the UE is scheduled to transmit PUSCH on the FDD PCell in subframe 7 of radio frame nf + 1. Also, a DL assignment is in subframe 1 (Special subframe) of the TDD SCell in the same frame. Even if the UE misses this DL assignment, the value of the DAI field in the UL grant for UL subframe 7 indicates (to the UE) how many DL subframes required HARQ-ACK feedback. This mechanism enables the UE to determine that it failed to detect one or more DL assignments on the TDD serving cell.

[0054] An interesting deployment scenario occurs when the PCell is operating in TDD mode and at least one SCell is operating in FDD mode. If the design constraint that PUCCH transmission only occurs on the PCell is followed, this limits HARQ-ACK feedback opportunities for the FDD SCell. Essentially, it forces the FDD SCell to follow the TDD PCell HARQ-ACK feedback timeline. For the case of a DL-only FDD serving cell without a paired UL carrier, this is the default operation. However, when the FDD serving cell has a paired UL carrier, it makes sense to consider more efficient means for transmitting HARQ-ACK feedback corresponding to PDSCH on the FDD SCell. This consideration is even more imperative for the following scenario.

[0055] FIG. 3 shows the scenario where a UE is configured with an FDD SCell and a TDD PCell employing TDD UL/DL Configuration 2. Consider the case where a UE is scheduled for PDSCH reception in a DL subframe of the FDD SCell, but this subframe is a UL subframe according to the TDD UL/DL configuration of the PCell, as shown in FIG. 3. Following current FDD procedures, the UE should transmit the corresponding feedback in subframe 6, but subframe 6 is a Special subframe for the TDD PCell. One solution to this problem is to configure the UE to transmit HARQ-ACK feedback on the PUCCH of the SCell. Two possible implementations of this solution are: (a) simultaneous PUCCH-PUCCH transmission on both PCell and SCell; or (b) time-multiplexed PUCCH transmission. For this solution, the UE transmits PUCCH on the FDD SCell only if the UL subframe on the SCell corresponds to a DL subframe on the TDD PCell. Otherwise, if the subframe is a UL subframe for both FDD and TDD serving cells, PUCCH will be transmitted on the PCell.

[0056] An alternative solution would be to schedule the HARQ-ACK feedback corresponding to a DL assignment on the FDD SCell to be transmitted in the first valid UL subframe of the TDD PCell. Specifically, for a PDSCH detected in subframe n on the FDD SCell, the UE would transmit the corresponding HARQ-ACK feedback in the first valid UL subframe n+k, where k > 4. In the example of FIG 3, the HARQ-ACK feedback is transmitted in subframe 7 on the PCell.

[0057] Aperiodic or periodic CSI reporting may be configured in a manner similar to the case of single duplex mode carrier aggregation. For periodic CSI reporting, the priority of CSI reports is based on PUCCH reporting types and serving cell index. When the PCell operates in TDD mode, some restrictions may be placed on the channel quality indicator (CQI)/ precoding matrix indicator (PMI) reporting period of an FDD SCell, depending on the TDD UL/DL Configuration of the PCell. For example, if the PCell uses UL/DL Configuration 5, reporting periodicity of two-milliseconds may imply frequent dropping of CSI reporting for the FDD SCell. Accordingly, if the periodic CSI reporting occasion or subframe coincides with a DL subframe on the TDD PCell, the UE will not transmit the CSI report.

[0058] Generally, full duplex capability is required for a UE that supports FDD-TDD carrier aggregation. However, it is possible to allow a half-duplex UE to enjoy some of the benefits of FDD-TDD CA. For example, an LTE Release 11 TDD UE that is radio resource control (R C)-connected on a TDD serving cell can be configured to receive PDSCH on a secondary serving cell that uses the same TDD UL/DL configuration as the primary serving cell. If the SCell is operating in FDD mode, the UE may be configured to apply the same UL/DL configuration of the TDD PCell.

[0059] FIG. 4 shows usage of an FDD secondary serving cell for half-duplex TDD UEs employing TDD UL/DL Configuration 1. As shown in FIG. 4, subframes {2, 3, 7, 8} and {0, 1, 4, 5, 6, 9} are not valid DL or UL subframes respectively for the half-duplex TDD UE on the FDD SCell. Although this subframe restriction may initially seem to be a waste of network resources, the base station can assign other UEs (such as FDD UEs or other TDD UEs with full-duplex capability) to the unused resources. Moreover, the performance of a UE with half-duplex capability is similar to TDD-only carrier aggregation where the same UL/DL configuration is configured on each serving cell.

[0060] In a similar manner, a UE that only supports FDD duplex mode may be configured to receive downlink shared channel (DL-SCH) data on the PDSCH of an SCell, where the SCell is actually deployed on a TDD carrier. This scenario is possible when an FDD band overlaps in frequency with a TDD band. For example, 3 GPP Band 7 is an FDD band that overlaps in frequency with 3GPP TDD Band 41. An operator with spectrum in this RF region may choose to operate either as a TDD or FDD carrier. When operated as a TDD carrier, an FDD-only UE can be configured to receive data on this carrier by configuring the UE with a restricted set of subframes that matches the DL subframes on the TDD carrier.

[0061] FIG. 5 shows usage of a TDD cell as a secondary serving cell for an FDD-only UE. The UE may be configured with a bit map that indicates which subframes it should monitor for DL-SCH data. Frame (a) in FIG. 5 shows an example in which a TDD carrier is configured to operate in UL/DL Configuration 1. An FDD-only UE may be configured with a secondary serving cell on this TDD component carrier. Traditionally, the FDD-only UE monitors all subframes in a radio frame for DCI transmitted on the PDCCH or EPDCCH. However, for this TDD carrier, the FDD-only UE does not need to waste energy monitoring for DCI on the PDCCH/EPDCCH that cannot be transmitted in subframes {2, 3, 7, 8}, because those subframes are designated for UL. Accordingly, the FDD UE is configured with a bit map specifying a restricted set of subframes to monitor for DCI.

[0062] As shown in frame (b) of FIG. 5, the FDD-only UE monitors for DL-SCH data from the SCell on a restricted set of subframes {0, 4, 5, 9} . The bit map designating this restricted set of subframes may be semi-statically configured by RRC signaling.

[0063] In a different embodiment, the UE can be configured with an extended bit map that indicates: (a) subframes where to monitor for DCI; and (b) subframes where a detected DL assignment on the PDSCH is limited to fewer OFDM symbols than the maximum number of OFDM symbols in the subframe. This allows the UE to receive PDSCH on Special subframes. For example, when a TDD cell applies normal cyclic prefix in the downlink, Special Subframe Configuration 11 contains 11 OFDM symbols. Accordingly, the FDD-only UE is configured to receive a DL assignment in this subframe up to the 11th OFDM symbol.

[0064] Frame (c) in FIG. 5 shows a restricted set of subframes that includes the Special subframes {1, 6} . An FDD-only UE may be configured to receive data on less than the total number of OFDM symbols in the Special subframes.

[0065] In either embodiment (using a restricted set of subframes that includes just DL subframes, or that includes DL and Special subframes), the HARQ-ACK timeline should follow the FDD procedure if the UL carrier is FDD. For example, when a DL assignment is received in subframe n, the UE transmits the HARQ-ACK feedback in subframe n + 4.

[0066] FIG. 6 is a block diagram of internal details of a mobile UE 601 and a base station 603, such as an eNB, operating in a network system, such as the system of FIG. 1. Mobile UE

601 may communicate with multiple base stations 603 in a carrier aggregation operation. Mobile UE 601 may represent any of a variety of devices, such as a server, a desktop computer, a laptop computer, a cellular phone, a Personal Digital Assistant (PDA), a smart phone or other electronic device. In some embodiments, the electronic mobile UE 601 communicates with eNB

602 based on an LTE or evolved universal terrestrial radio access (E-UTRA) protocol. Alternatively, another communication protocol now known or later developed can be used.

[0067] Mobile UE 601 includes a processor 603 coupled to a memory 604 and a transceiver 605. The memory 604 stores (software) applications 606 for execution by the processor 603. The applications could include any known or future application useful for individuals or organizations. These applications could be categorized as operating systems (OS), device drivers, databases, multimedia tools, presentation tools, Internet browsers, emailers, voice-Over-Internet protocol (VOIP) tools, file browsers, firewalls, instant messaging, finance tools, games, word processors or other categories. Regardless of the exact nature of the applications, at least some of the applications may direct the mobile UE 601 to transmit UL signals to eNB (base station) 602 periodically or continuously via the transceiver 605.

[0068] Transceiver 605 includes uplink logic which may be implemented by execution of instructions that control the operation of the transceiver. Some of these instructions may be stored in memory 604 and executed when needed by processor 603. The components of the uplink logic may involve the physical (PHY) layer and/or the media access control (MAC) layer of the transceiver 605. Transceiver 605 includes one or more receivers 607 and one or more transmitters 608.

[0069] Processor 603 may send or receive data to various input/output devices 609. A subscriber identity module (SIM) card stores and retrieves information used for making calls via the cellular system. A Bluetooth baseband unit may be provided for wireless connection to a microphone and headset for sending and receiving voice data. Processor 603 may send information to a display unit for interaction with a user of mobile UE 601 during a call process. The display may also display pictures received from the network, from a local camera, or from other sources such as a universal serial bus (USB) connector. Processor 603 may also send a video stream to the display that is received from various sources, such as the cellular network via RF transceiver 605 or the camera.

[0070] eNB 602 includes a processor 610 coupled to a memory 611, symbol processing circuitry 612, and a transceiver 613 via backplane bus 614. The memory stores applications 615 for execution by processor 610. The applications could include any known or future application useful for managing wireless communications. At least some of the applications 615 may direct eNB 602 to manage transmissions to or from mobile UE 601. eNB 602 may operate in an FDD or TDD mode and may communicate with other base stations (not shown) for carrier aggregation.

[0071] Transceiver 613 includes an uplink resource manager, which enables eNB 602 to selectively allocate uplink physical uplink shared channel (PUSCH) resources to mobile UE 601. The components of the uplink resource manager may involve the physical (PHY) layer and/or the media access control (MAC) layer of the transceiver 613. Transceiver 613 includes at least one receiver 615 for receiving transmissions from various UEs within range of eNB 602 and at least one transmitter 616 for transmitting data and control information to the various UEs within range of eNB 602. [0072] The uplink resource manager executes instructions that control the operation of transceiver 613. Some of these instructions may be located in memory 611 and executed when needed on processor 610. The resource manager controls the transmission resources allocated to each UE 601 served by eNB 602 and broadcasts control information via the PDCCH. UE 601 may receive TTD UL/DL configuration instructions from eNB 602.

[0073] Symbol processing circuitry 612 performs demodulation using known techniques. Random access signals are demodulated in symbol processing circuitry 612. During transmission and reception of voice data or other application data, receiver 617 may receive a random access signal from a UE 601. The random access signal is encoded to request a message size that is preferred by UE 601. UE 601 determines the preferred message size by using a message threshold provided by eNB 602.

[0074] When the mobile device 601 receives PDSCH from a TDD SCell 105 in a subframe n, it transmits a HARQ ACK to an FDD PCell 101 in subframe n+4. When the mobile device 601 receives PDSCH in a downlink subframe from an FDD SCell 105, it transmits a HARQ ACK corresponding to the PDSCH to a TDD PCell 101 in a selected uplink subframe. The selected uplink subframe may be the first valid uplink subframe following the downlink subframe. For example, where the downlink subframe carrying the PDSCH is subframe n, and the selected uplink subframe is subframe n+k, where k>4.

[0075] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.