# Patent

## Title
Method for PHICH resource allocation

## Abstract

A method is disclosed for PHICH resource allocation in a wireless communication system that supports flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration. The method comprising allocating a PHICH resource for both first UEs and second UEs according to LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a national stage application of International Application No. PCT/JP2014/056083 entitled “METHOD FOR PHICH RESOURCE ALLOCATION,” filed on Feb. 28, 2014, which claims the benefit of priority of Australian Patent Application No. AU2013900937, filed on Mar. 18, 2013, the disclosures of which are incorporated herein in their entirety by reference thereto.
TECHNICAL FIELD
The present invention relates to a method for PHICH resource allocation.
BACKGROUND ART
The following abbreviations may be found herein:













3GPP
THIRD GENERATION PARTNERSHIP



PROJECT


ACK
ACKNOWLEDGEMENT


BW
BANDWIDTH


CCE
CONTROL CHANNEL ELEMENT


CRS
CELL-SPECIFIC REFERENCE SIGNAL


DL
DOWNLINK


DM-RS
DEMODULATION REFERENCE SIGNAL


eNB (OR eNodeB)
LTE BASE STATION


HARQ (OR H-ARQ)
HYBRID AUTOMATIC REPEAT REQUEST


ICIC
INTER-CELL INTERFERENCE



COORDINATION


IE
INFORMATION ELEMENT


LTE
LONG TERM EVOLUTION


LTE-A
LONG TERM EVOLUTION ADVANCED


MIB
MASTER INFORMATION BLOCK


NACK
NEGATIVE ACKNOWLEDGEMENT


OFDM
ORTHOGONAL FREQUENCY DIVISION



MULTIPLEX


OFDMA
ORTHOGONAL FREQUENCY DIVISION



MULTIPLE ACCESS


PBCH
PHYSICAL BROADCAST CHANNEL


PCFICH
PHYSICAL CONTROL FORMAT



INDICATOR CHANNEL


PDCCH
PHYSICAL DOWNLINK CONTROL



CHANNEL


PDSCH
PHYSICAL DOWNLINK SHARED CHANNEL


PHICH
PHYSICAL HARQ INDICATOR CHANNEL


PRB
PHYSICAL RESOURCE BLOCK


PUSCH
PHYSICAL UPLINK SHARED CHANNEL


RE
RESOURCE ELEMENT


REG
RESOURCE ELEMENT GROUP


TDD
TIME DIVISION DUPLEX


UE
USER EQUIPMENT


UL
UPLINK









LTE wireless communication systems aim to provide enhanced services by means of higher data rates and lower latency with reduced cost. One benefit of deploying LTE TDD systems is to enable asymmetric UL-DL allocations in a radio frame. Typically if more data is to be sent in DL, there can be a higher number of DL subframes in a radio frame to accommodate that greater data volume. In LTE TDD systems, asymmetric resource allocation is realized by providing seven different semi-statically configured UL-DL subframe configurations for a given radio frame, as specified in Table 4.2-2 of 3GPP TS 36.211 v 10.5.0 (2012-06) which is extracted below.







TABLE 4.2-2







Uplink-downlink configurations










DOWNLINK-



UPLINK-
TO-UPLINK


DOWNLINK
SWITCH-POINT
SUBFRAME NUMBER


















CONFIGURATION
PERIODICITY
0
1
2
3
4
5
6
7
8
9





0
5 MS
D
S
U
U
U
D
S
U
U
U


1
5 MS
D
S
U
U
D
D
S
U
U
D


2
5 MS
D
S
U
D
D
D
S
U
D
D


3
10 MS 
D
S
U
U
U
D
D
D
D
D


4
10 MS 
D
S
U
U
D
D
D
D
D
D


5
10 MS 
D
S
U
D
D
D
D
D
D
D


6
5 MS
D
S
U
U
U
D
S
U
U
D









In the table above, “D” indicates a DL subframe, “U” indicates an UL subframe and “S” indicates a special subframe. The different UL-DL configurations in the table provide between 40% and 90% DL subframes, and in conventional practice the UL-DL configuration in use at an eNB is informed to the UE (and changed) only via system information on the broadcast channel. The UL-DL configuration is only configured semi-statically and so may not adapt to the instantaneous traffic situation. This is inefficient in terms of resource utilization, particularly in small cells or cells with a small number of users where the traffic situation can often change rapidly.
To address this inefficiency, a flexible TDD configuration study item for LTE-A Release 11 (Rel. 11) was completed. Evaluations in the study item revealed possibly significant performance benefits by allowing TDD UL-DL reconfiguration based on traffic adaptation in small cells. The studies also recommend interference mitigation scheme(s) for systems with TDD UL-DL reconfiguration.
As with asymmetric UL-DL configuration and flexible TDD allocation, there are several challenges to overcome before any implementation may be considered viable. One particular challenge is to allow reconfiguration of TDD UL-DL configuration on at most a radio frame basis without significant impact on the current 3GPP specification, and to allow coexistence with legacy (i.e. Rel. 8, 9, 10) UEs. It is thought that improving PHICH resource allocation and maintaining backward compatibility may help in this regard.
FIG. 1 shows UE ACK/NACK procedure 100 (PUSCH transmission and PHICH reception) in TDD system. As an example of the LTE timing rules specified in Rel. 11 and illustrated in FIG. 1, one DL subframe may have the responsibility to send HARQ-ACK bits for 0, 1 or 2 UL subframe(s), depending on the adopted TDD configuration and DL subframe index. For instance:

    
    
        If TDD configuration #0 is used, DL subframe #0 (101) in radio frame n is responsible for sending HARQ-ACK for two UL subframes (105), namely UL subframes #3 and #4 in radio frame ‘n−1’, and DL subframe #1 (102) in radio frame n is responsible for sending HARQ-ACK for one UL subframe, namely subframe #7 (106) in radio frame ‘n−1’.
        If TDD configuration #2 is used, then DL subframe #0 (103) has no responsibility for sending HARQ-ACK feedback for any UL transmission and, as a result, there is no PHICH resource allocation on this DL subframe (103).
        If TDD configuration #3 is used, then DL subframe #0 (104) is responsible for sending HARQ-ACK feedback for one UL subframe, namely subframe #4 (107).
        etc
    
    


The PHICH resource allocation on each DL/Special subframe for each TDD configuration is further illustrated in FIG. 2. The factor mi (as given by individual entries in the table) indicates how many copies of PHICH resource are assigned on a given DL subframe in the TDD system.
In Rel. 8, 9, 10 and 11, PDCCH is transmitted on CCE which is made up by REs (or REGs) not occupied by CRS, PCFICH and PHICH. The antenna port for CRS can be determined by blind decoding of PBCH and REs used for PCFICH are predefined. Although PHICH configuration can be determined from PHICH-Config via PBCH/MIB decoding, nevertheless for TDD systems it is still not sufficient to determine how many REs (or REGs) are used for PHICH. For example, for a configured DL system BW of 10 MHz, assuming Ng=1/6, then NPHICHGroup=2, it is still necessary to know the factor mi which depends on eNB configured UL-DL configuration in order to further determine the exact number of REs (or REGs) occupied by PHICH resource.
The value of mi is related to TDD configuration and DL subframe index. As a result, in order to figure out the REs used for PHICH and thus determine the REs (or REGs) that are carrying PDCCH(s), the TDD configuration should be determined first. However, TDD configuration is transmitted in SIB1 via PDCCH with an associated PDSCH and the problem becomes tricky because the index of TDD configuration is needed in order to decode PDCCH with an associated PDSCH which contains the index of TDD configuration. This is therefore a “chicken-egg” problem. One way to solve this problem, as was agreed in the standardization meeting, is that a UE should perform blind decoding by assuming on a particular subframe the possible value of mi in order to get the TDD configuration, and start to use the detected TDD configuration to decode other PDCCH.
FIG. 3 shows PDCCH blind decoding and PHICH resource assignment 300. As illustrated in FIG. 3, for different TDD configurations/DL subframes, the REG available for PDCCH transmission may be different, although PHICH configuration PHICH-Config stays the same

    
    
        Case 1: No PHICH resource assignment, mi=0 4 REGs (301) are used for PCFICH transmission, all other REGs can be used for PDCCH transmission
        Case 2: PHICH resource assignment for one UL subframe, mi=1 Beside the 4 REGs used for PCFICH transmission, another 6 REGs (302) are used for PHICH transmission, and the remaining REGs can be used for PDCCH transmission
        Case 3: PHICH resource assignment for two UL subframes, mi=2 6 additional REGs are used for PHICH transmission, and the remaining REGs can be used for PDCCH transmission.
    
    


From the above example, it can be appreciated that if a UE has an incorrect understanding of the mi value (which is determined by TDD configuration and subframe index), or PHICH resource is not assigned according to factor mi known by the UE, then the UE will have an incorrect understanding of CCE to REG mapping and will fail to decode PDCCH.
SUMMARY OF INVENTION
Technical Problem
In flexible-TDD systems, it is highly likely that the TDD configuration of legacy UEs will not be the same as the TDD configuration used by flexible-TDD UEs. If PHICH resource is assigned to flexible-TDD UEs by following factor mi related to TDD configuration of flexible-TDD UEs, then legacy UEs will have problem in decoding PDCCH. It would be desirable to maintain backward compatibility in flexible-TDD systems while sending HARQ-ACK for UL transmission.
It is to be clearly understood that mere reference herein to previous or existing apparatus, systems, methods, practices, publications or other information, or to any associated problems or issues, does not constitute an acknowledgement or admission that any of those things individually or in any combination formed part of the common general knowledge of those skilled in the field, or that they are admissible prior art.
Solution to Problem
In one form, the present invention relates broadly to a method for PHICH resource allocation (or a method for resource allocation for the transmission of PUSCH HARQ-ACK feedback) in a wireless communication system that supports a flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, the method comprising allocating PHICH resources for both first UEs and second UEs according to LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs. Generally, the first UEs will be flexible-TDD UEs (e.g. Rel. 12 & beyond UEs) and the second UEs will be legacy UEs (e.g. Rel. 8, 9, 10 or 11 UEs), and the term ‘first UEs’ and ‘second UEs’ may be understood accordingly in the following description.
In the form of the invention described in the previous paragraph, the method may also include, determining that PHICH resource is allocated for second UEs with factor mi=2, determining that HARQ-ACK for only one UL subframe should be fed back for first UEs, and allocating PHICH resource with IPHICH=1 for first UEs. The method may further include determining that PHICH resource is assigned for second UEs with factor mi=1, determining that HARQ-ACK for two UL subframes should be fed back, and allocating the assigned PHICH resource with IPHICH=1 for first UEs to accommodate PUSCH HARQ feedback for the second subframe.
In another form, the present invention relates broadly to a method for PHICH resource allocation (or a method for resource allocation for the transmission of PUSCH HARQ-ACK feedback) in a wireless communication system that supports a flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, the method involving, for a given subframe of a radio frame:
determining that the subframe is not a DL subframe in both the TDD UL-DL configuration in use by first UEs and the TDD UL-DL configuration in use by second UEs,
determining that the subframe is a DL subframe in the TDD UL-DL configuration in use by first UEs but an UL subframe in the TDD UL-DL configuration in use second UEs, and
allocating PHICH resource according to LTE timing rules applicable to the TDD UL-DL configuration in use by first UEs.
In the form of the invention described in the previous paragraph, the method may also include, determining that said given subframe is a DL subframe in the TDD UL-DL configuration in use by first UEs and also in the TDD UL-DL configuration in use by second UEs, determining that a PHICH resource is not required (in the TDD UL-DL configuration in use) by second UEs for said subframe, and allocating no PHICH resource to the subframe. The method may further include, for said subframe, determining that a PHICH resource is required (in the TDD UL-DL configuration in use) by first UEs, calculating the PHICH resource required for sending PUSCH HARQ-ACK or remaining PUSCH HARQ-ACK, and allocating the PHICH resource for transmission thereof via ePHICH IE if available and enabled or via UL grant if ePHICH IE is not available or not enabled.
The method may further include determining that a PHICH resource is required (in the TDD UL-DL configuration in use) by second UEs for said given subframe, determining that PHICH resource is not required (in the TDD UL-DL configuration in use) by first UEs, and allocating the PHICH resource according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs.
The method may further include determining that a PHICH resource is required (in the TDD UL-DL configuration in use) by first UEs for said subframe, determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs is not less than that required (in the TDD UL-DL configuration in use) by first UEs, determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs is not more than that required (in the TDD UL-DL configuration in use) by first UEs, and allocating the PHICH resource according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs.
The method may further include determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs in said subframe is more than that required (in the TDD UL-DL configuration in use) by first UEs for said given subframe, allocating PHICH resource according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs, and allocating PHICH resource with IPHICH=1 for first UEs.
The method may further include determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs in said subframe is less than that required (in the TDD UL-DL configuration in use) by first UEs, allocating the PHICH resource according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs, and allocating the PHICH resource for first UEs to accommodate HARQ-ACK for associated UL subframe(s) that have PUSCH HARQ-ACK timing aligned with that of second UEs.
The method may further include, for said given subframe, calculating the PHICH resource required for sending PUSCH HARQ-ACK or remaining PUSCH HARQ-ACK of first UEs, and allocating PHICH resource for transmission thereof via ePHICH IE if this is available and enabled or via UL grant if ePHICH IE is not available or not enabled.
In another form, the present invention relates broadly to a wireless communication system including a base station, first UEs and second UEs, wherein the wireless communication system supports a flexible TDD UL-DL configuration, different TDD UL-DL configurations are available and the TDD UL-DL configuration used by the first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by the second UEs which operate according to a long term TDD UL-DL configuration, and wherein the base station is operable to perform the method for PHICH resource allocation as described in the various forms of the invention above.
In another form, the present invention relates broadly to a base station operable for use in a wireless communication system that supports a flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, and wherein the base station is operable to perform a method as described in the various method forms of the invention above.
In another form, the present invention relates broadly to a method for use by first UEs for PUSCH HARQ-ACK and PHICH signalling (or a method for reception of PUSCH HARQ-ACK for use by UEs) in a wireless communication system that supports flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by the first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, the method involving, for a given flexible DL subframe of a radio frame in the TDD UL-DL configuration in use by the first UEs:
determining that the corresponding subframe in the TDD UL-DL configuration in use by the second UEs is not a DL subframe,
determining that the given DL subframe in the TDD UL-DL configuration in use by the first UEs is to carry PUSCH HARQ-ACK, and
monitoring for PHICH allocation according to LTE timing rules applicable to the TDD UL-DL configuration in use by first UEs.
In the form of the invention described in the previous paragraph, the method may further include, determining that the corresponding subframe in the TDD UL-DL configuration in use by the second UEs is a DL subframe, determining that said corresponding subframe in the TDD UL-DL configuration in use by the second UEs is not allocated PHICH resource according to the LTE timing rules applicable to the TDD UL-DL configuration in use by the second UEs, determining that the given DL subframe in the TDD UL-DL configuration in use by the first UEs is to carry PUSCH HARQ-ACK, and performing the following on the subframe:
UL grant monitoring for HARQ-ACK corresponding to previously sent PUSCH, if ePHICH is not configured;
ePHICH monitoring for HARQ-ACK corresponding to previously sent PUSCH, if ePHICH is configured; and
PDCCH(s) monitoring taking into account the number of REs allocated for PHICH for second UEs.
The method may further include, for the given flexible DL subframe, determining that said corresponding subframe in the TDD UL-DL configuration in use by the second UEs is allocated PHICH resource according to the LTE timing rules applicable to the TDD UL-DL configuration in use by the second UEs, determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs is not less than that required (in the TDD UL-DL configuration in use) by first UEs, determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs is not more than that required (in the TDD UL-DL configuration in use) by first UEs, and performing PHICH monitoring according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs and performing PDCCH(s) monitoring taking into account the number of REs allocated for PHICH for second UEs.
The method may further include, for the given flexible DL subframe, determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs is more than that required (in the TDD UL-DL configuration in use) by first UEs, and performing PHICH monitoring with IPHICH=1 and performing PDCCH(s) monitoring taking into account the number of REs allocated for PHICH for second UEs.
The method may further include, for the given flexible DL subframe, determining that the PHICH resource required (in the TDD UL-DL configuration in use) by second UEs is less than that required (in the TDD UL-DL configuration in use) by first UEs, and performing on the subframe:
PHICH monitoring for HARQ-ACK of associated UL subframe(s) having PUSCH HARQ-ACK timing aligned with that of the TDD UL-DL configuration in use by second UEs,
UL grant monitoring for HARQ-ACK of associated UL subframe(s) that is/are not included in the PHICH of second UEs, if ePHICH is not configured,
ePHICH monitoring for HARQ-ACK of associated UL subframe(s) that is/are not included in the PHICH of second UEs, if ePHICH is configured,
PDCCH(s) monitoring taking into account the number of REs allocated for PHICH for second UEs.
In another form, the invention relates broadly to a mobile station operable for use as a first UE in a wireless communication system that supports a flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, and wherein the mobile station is operable to perform the method for PUSCH HARQ-ACK and PHICH signalling for use by first UEs as described above.
In another form, the invention relates broadly to a method for use in ePHICH mapping in a wireless communication system that supports a flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs which operate according to the flexible TDD configuration can be different to the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, the method comprising using a subset of spare bits out of a set of spare bits in a master information block (MIB) for ePHICH configuration. Preferably, the method comprises using three out of ten spare bits in a MIB for ePHICH configuration.
Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.
Advantageous Effects of Invention
According to the present invention, it is possible to provide a flexible TDD wireless communication systems.



BRIEF DESCRIPTION OF DRAWINGS
Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:
FIG. 1 illustrates UE ACK/NACK procedure (PUSCH transmission and PHICH reception) in a TDD system. In other words, FIG. 1 helps to illustrate the operation of the LTE timing rules for PUSCH HARQ-ACK feedback according to TDD UL-DL configuration and subframe number.
FIG. 2 contains a table with the factor mi for different subframes in different UL-DL configurations.
FIG. 3 contains three illustrations corresponding to the example given with reference to Case 1, Case 2 and Case 3 respectively in the Background section above.
FIG. 4 is a schematic illustration of a flexible-TDD wireless communication system.
FIG. 5 contains illustrations corresponding to different example situations which are used to explain the operation of the invention (or at least embodiments of the invention) in such situations.
FIG. 6 contains illustrations corresponding to different example situations which are used to explain the operation of the invention (or at least embodiments of the invention) in such situations.
FIG. 7 contains illustrations corresponding to different example situations which are used to explain the operation of the invention (or at least embodiments of the invention) in such situations.
FIG. 8 contains illustrations corresponding to different example situations which are used to explain the operation of the invention (or at least embodiments of the invention) in such situations.
FIG. 9 contains illustrations corresponding to different example situations which are used to explain the operation of the invention (or at least embodiments of the invention) in such situations.
FIG. 10 contains illustrations corresponding to different example situations which are used to explain the operation of the invention (or at least embodiments of the invention) in such situations.
FIG. 11 contains illustrations corresponding to different example situations which are used to explain the operation of the invention (or at least embodiments of the invention) in such situations.
FIG. 12A contains a flow chart illustrating a method for resource allocation for the transmission of PUSCH HARQ-ACK feedback according to an embodiment of the invention.
FIG. 12B contains the flow chart illustrating a method for resource allocation for the transmission of PUSCH HARQ-ACK feedback according to an embodiment of the invention.
The method represented by the flow chart in FIG. 12A and FIG. 12B may be performed by a base station/eNB.
FIG. 13A contains a flow chart illustrating a method for the reception of PUSCH HARQ-ACK which may be used by UEs that operate according to the flexible TDD configuration (i.e. by first UEs such as, e.g., Rel. 12 & beyond UEs) according to an embodiment of the invention.
FIG. 13B contains the flow chart illustrating a method for the reception of PUSCH HARQ-ACK which may be used by UEs that operate according to the flexible TDD configuration (i.e. by first UEs such as, e.g., Rel. 12 & beyond UEs) according to an embodiment of the invention.
FIG. 14 helps to illustrate/explain a method for use in ePHICH mapping.
FIG. 15 helps to illustrate/explain a method for use in ePHICH mapping.
FIG. 16 helps to illustrate/explain a method for use in ePHICH mapping.



DESCRIPTION OF EMBODIMENTS
Explanations will hereafter be given with reference to, and in the context of, wireless communication systems that support Flexible-TDD UL-DL configuration, an example of which is shown schematically in FIG. 4. The wireless communication system (400) depicted in FIG. 4 consists of a Rel. 12 & beyond eNB (401) which is backward compatible with previous releases such as Rel. 8, Rel. 9, Rel. 10 and Rel. 11. The eNB (401) provides wireless connectivity, network access and coverage for second/legacy UE(s) (403) as well as Rel. 12 & and beyond (i.e. “first”) UE(s) (404). The eNB (401) further has a “TDD reconfiguration processing” function (402) which takes the UL-DL traffic ratio observed in unrestricted timeframe into consideration when it performs a TDD configuration switching algorithm for the selection of appropriate long term and short term TDD UL-DL configuration for legacy UE(s) (403) and Rel. 12 & beyond UE(s) (404) respectively, and a “PHICH resource mapping and HARQ feedback” function (402BIS) which takes into consideration the existence of legacy UE(s) operating within eNB (401) coverage and assigns PHICH resource that ensures no impact on legacy UE performance.
The eNB (401) will broadcast long term “TDD UL-DL configuration” to both legacy UE(s) (403) and Rel. 12 & beyond UE(s) using SIB1 (System Information Block type 1) (406). The TDD UL-DL configuration transmitted on SIB1 is considered “long term” configuration as the period for SIB1 update is the order of 640 ms. The eNB (401) will also communicate “short term” TDD UL-DL configuration but only to Rel. 12 & beyond UE(s) (404) using a fast signalling approach and the period for TDD UL-DL configuration update can be as little as 10 ms (i.e. radio frame basis). The eNB (401) will also transmit PHICHs on subframes that are determined by the “PHICH resource mapping and HARQ feedback” function (402BIS).
In addition to performing the reception and use of TDD UL-DL configuration broadcasted on SIB1, a Rel. 12 & beyond UE(s) (404) that operates within coverage of Rel. 12 & beyond eNB (401) will further comprise TDD reconfiguration processing function (405) which detects short term UL-DL configuration information (407). This function (405) will also perform PDSCH H-ARQ encoding and selection of the appropriate UL subframe(s) for sending PDSCH H-ARQ feedback to eNB (401). This function (405) will also perform the determination of DL subframe on which it will monitor for its UL grant for the transmission of UL-SCH. The function (405) further includes function (405BIS) which determines the required PHICH resource and DL subframe on which it will receive H-ARQ-ACK corresponding to UL-SCH that it sends in previously granted UL-subframe(s) using configured PHICH resource or/and UL grant or configured ePHICH resource.
For legacy UE(s) (403) operating within the Rel. 12 & beyond eNB (401) range, it/these shall use TDD UL-DL configuration broadcasted on SIB1 and operate according to the legacy specifications that it/they complies to. The eNB (401) may not schedule legacy UE(s) (403) to perform reception of PDSCH(s) or transmission of PUSCH(s) on the “flexible subframes”.
Embodiments of the invention may concern, inter alia, one or more of a method for PHICH/ePHICH resource allocation and in particular for determining appropriate physical resources including PHICH, UL Grant, and ePHICH for sending of PUSCH HARQ-ACK (408), a procedure that may be implemented as eNB's PHICH resource mapping and HARQ feedback function (402BIS) for the correct selection of physical resources for the transmission of PUSCH HARQ-ACK ensuring no impact on legacy UE operating within eNB (401) coverage, and a procedure that may be implemented as the Rel. 12 & beyond UE PHICH information processing function (405BIS) for the correct reception PUSCH HARQ-ACK and processing of PHICH. FIG. 4 also shows PUCCH/PUSCH carries HARQ-ACK feedback for PDSCH or PDCCH indication SPS release (409).
Reference Configuration Selection for UL-SCH HARQ Timing
As legacy UE(s) have no knowledge of the Flexible-TDD system in use, PHICH resource assignment in embodiments of the invention will generally follow the TDD configuration used by legacy UE(s), at least on fixed DL subframes. This may help to ensure that there is no performance impact on legacy UE(s) with regard to the reception of PHICH(s) and PDCCH(s) intended for it/them.
For example, in FIG. 5 (FIG. 5 shows resource assignment 500), configuration #3 is configured for legacy UE(s) and by following the LTE timing rules for configuration #3, the HARQ-ACK bits for UL subframe #4 (501) in radio frame #n is transmitted on DL subframe #0 (502) in radio frame #(n+1). Simultaneously, there exists a flexible-TDD UE with configuration #0. By following the Rel. 8 LTE timing rule for configuration #0, DL subframe #0 (502) in radio frame #(n+1) is configured to transmit HARQ-ACK for two UL subframes, namely subframes #3 (503) and #4 (504) in radio frame #n for flexible-TDD UE. If factor mi=2 is used for PHICH resource assignment to accommodate HARQ-ACK for the two UL subframes (subframes #3 and #4), then more REGs should be occupied by PHICH(s) and more importantly, this is unknown to the legacy UE which is configured with UL-DL configuration #3. As a result, the legacy UE will include REGs used for additional PHICH Group(s) in the PDCCH blind decoding process and will never succeed in PDCCH blind decoding intended for it.
Therefore, if the PHICH resource required for the legacy system (i.e. required by legacy UEs) is less than that for the concurrent flexible-TDD system (flexible TDD UEs), no more PHICH resource is assigned by the eNB, and the eNB should decide how the existing PHICH resource can be used by flexible-TDD UE in the manner discussed below.
Referring to FIG. 6 (FIG. 6 shows resource assignment 600), the legacy UE is configured with configuration #5 and the flexible-TDD UE is configured with configuration #0. According to the Rel. 8 LTE timing rule for UL-DL configuration #5, for legacy UE, DL subframe #0 (603) is not allocated for HARQ-ACK transmission for any UL transmission using PHICH resource. For flexible-TDD UE though, if the LTE timing rule of UL-DL configuration #0 is followed, then DL subframe #0 should be configured for sending HARQ-ACK for two UL subframes, namely subframe #3 (601) and subframe #4 (602). This would cause the legacy UE to miss its intended PDCCH(s) decoding because it understands that no PHICH RE(s) are allocated on the current subframe. Therefore, in order to achieve backward compatibility, no PHICH resource is assigned on PDCCH region for the flexible-TDD UE.
Thus, there is no PHICH resource assignment even when flexible TDD UEs require it. In this case, the eNB should send ACK/NACK in the manner discussed below and the flexible TDD UE should be aware of the method to be used.
Referring now to FIG. 7 (FIG. 7 shows resource assignment 700), as another example, the legacy UE is configured with TDD UL-DL configuration #0 and flexible-TDD UE is configured with TDD UL-DL configuration #4. It is possible that the transmission direction of subframe #4 (702) follows the direction of the flexible-TDD system and is used as DL subframe (704), however, PHICH resource for subframe #4 (702) is still assigned in subframe #0 (705) according to timing rule of UL-DL configuration #0 to guarantee no impact on legacy UE PDCCH decoding (Subframe #3 (701) is same as subframe #3 (601).). Furthermore, since the UL HARQ-ACK for UL transmission of the flexible-TDD UE in UL subframe #3 (703) is transmitted in DL subframe #9 by following the timing rule defined for UL-DL configuration #4, PHICH resource for UL subframe #3 in DL subframe #0 (705) is over allocated in order to maintain backward compatibility i.e. allowing the legacy UE to correctly performing PDCCH(s) intended for its use. Thus, the PHICH resource is reserved for the legacy system even when there is no UL transmission on the associated subframe.
PHICH Resource Selection for Flexible-TDD UE with PHICH Resource Assigned According to Factor mi=2
In FIG. 8 (FIG. 8 shows resource assignment 800), the legacy UE is configured with TDD UL-DL configuration #0 and the flexible-TDD UE is configured with UL-DL configuration #6. By following the LTE timing rule defined for UL-DL configuration #0, the factor mi=2 is used for PHICH resource assignment and HARQ-ACK for UL subframe #3 (801) and UL subframe #4 (802) in radio frame #n are send on DL subframe #0 (803) in radio frame # (n+1). In this example, DL subframe #0 (803) in radio frame # (n+1) may also be responsible to send HARQ-ACK for one UL subframe, namely #4 (804) in radio frame #n by following timing rule defined for UL-DL configuration #6. As there are two copies of PHICH resource assigned by factor mi=2, which of the copies of PHICH resource is allocated and used by flexible-TDD UEs should be decided and understood by flexible TDD UEs.
The straight forward solution in this case is to use PHICH resource related to IPHICH=0. However, legacy UE on UL subframe #3 and flexible-TDD UE on UL subframe #4 both can have the same first PRB (Physical Resource Block) for UL transmission and the probability of PHICH collision may be increased. Instead of that, using PHICH resource related to IPHICH=1 for flexible TDD UE may be more promising since legacy UE and flexible-TDD UE on the same UL subframe cannot use the same first PRB for UL transmission and thus PHICH collision can be more controllable.
In reference to FIG. 9 (FIG. 9 shows resource assignment 900) as another example, the legacy UEs use the same configuration #0 and the same parameters for PHICH resource assignment as in FIG. 8. Flexible-TDD UEs are configured with TDD configuration #1 and follow a reference configuration #0 for HARQ-ACK timing. As a result, the HARQ-ACK for UL subframe #3 (904) in radio frame #n is sent on DL subframe #0 (903) in radio frame #(n+1) rather than on DL subframe #9 (905) in radio frame #n. Similar to the example depicted in FIG. 8, as there are two copies of PHICH resource assigned by factor mi=2, the copy of PHICH resource allocated to and used by flexible-TDD UEs should be decided and understood by the flexible TDD UEs.
The first option is that PHICH resource related to IPHICH=0 should be used by flexible-TDD UEs because the same first PRB index cannot be used by two UEs on the same UL subframe. However, it is worth mentioning that, for example, subframe #4 (902) in radio frame #n has higher chance than subframe #3 (901) in radio frame #n of being configured as a DL subframe by flexible-TDD system and thus the PHICH resources assigned for IPHICH=1 are never used by legacy UE. From the perspective of alleviating PHICH resource collision, it may therefore be beneficial to map HARQ-ACK of UL subframe #3 (904) of flexible-TDD UE to PHICH resource related to IPHICH=1 (the second copy of PHICH resource, as illustrated in (303) of FIG. 3). FIG. 9 also shows subframe #4 (906).
Therefore, feedback HARQ-ACK on PHICH resource associated with IPHICH=1 can be served as a unified solution for different cases. Otherwise, case specific solutions need to be applied.
HARQ-ACK Transmission for UL Transmission in DL Subframe with PHICH Resource Assigned According to Factor mi=1 and Flexible-TDD UE HARQ-ACK Feedback for Two UL Subframes
In reference to FIG. 10 (FIG. 10 shows resource assignment 1000), Flexible-TDD UE should feedback HARQ-ACK for two UL subframes: subframe #3 (1001) and subframe #4 (1002) in radio frame #n, and PHICH resource is assigned according to factor mi=1 to ensure backward compatibility. The HARQ-ACK of only one UL subframe is allowed for transmission on PHICH, but there is a need for HARQ-ACK of two UL subframes to be transmitted. It would be more promising to send HARQ-ACK for UL subframe #4 (1002) in radio frame #n rather than UL subframe #3 (1001) in radio frame #n for the sake of not increasing the probability of PHICH resource collision. The HARQ-ACK for the remaining UL subframe that cannot be transmitted using the reference configuration (e.g. subframe #3 (1001) in radio frame #n), can be transmitted via UL grant or ePHICH in the same subframe. The HARQ-ACK for UL subframe #4 (1004) in radio frame #n is sent on DL subframe #0 (1003) in radio frame #(n+1).
UL-HARQ Feedback in One DL Subframe without PHICH Resource for Flexible-TDD System
In reference to FIG. 11 (FIG. 11 shows resource assignment 1100), there is no PHICH resource assignment on DL subframe #0 (1103) in radio frame #(n+1) by following the timing rule defined for UL-DL configuration #1 configured for legacy UE, but flexible-TDD system with the configured UL-DL configuration #0 needs to feedback HARQ-ACK for one/two UL subframe(s). In this case, the HARQ-ACK can be sent via UL grant implicitly, or on ePHICH explicitly. DL subframe #0 should be configured for sending HARQ-ACK for two UL subframes, namely subframe #3 (1101) and subframe #4 (1102) in FIG. 11. FIG. 11 also shows subframe #2 (1104).
Thus, an illustration of the procedure which may be implemented within a base station such as eNB (401) in FIG. 4 as “eNB's PHICH resource mapping and HARQ feedback” function (402BIS) for the correct selection of physical resources for the transmission of PUSCH HARQ-ACK ensuring no impact on legacy UE operating within eNB (401) coverage is given in the flowchart in FIG. 12A and FIG. 12B.
Similarly, a corresponding procedure which may be implemented at/in a mobile station (UE) such as Rel. 12 & beyond UE (404) in FIG. 4 as “Rel. 12 & beyond (i.e. first) UE PHICH information processing function (405BIS) for the correct reception PUSCH HARQ-ACK and processing of PHICH is given in the flowchart shown in FIG. 13A and FIG. 13B.
Following on from the embodiments of the invention discussed above, a related issue concerns the design of ePHICH resource mapping. In particular, it may be possible for ePHICH to be implemented using a backward compatible carrier where PDCCH region/PHICH is still reserved for legacy UE. In this regard, 3-bits in MIB may be used to indicate the semi-static ePHICH configuration in Rel. 11. Hence, if ePHICH and PHICH can be configured at the same time, 3-bits out of 10 spare bits in MIB can be used to indicate the ePHICH configuration. The N(group, PHICH) calculation, modulation and coding method may be reused.
The mapping of ePHICH on PRB is unknown to the legacy UE, and therefore the legacy UE should not be scheduled on PRB used for ePHICH transmission, otherwise, the performance of PDSCH will degrade. Also, for the sake of reducing the scheduling limitation of legacy UE and frequency domain ICIC, ePHICH should be assigned on a limited number of PRBs. On the other hand, ePHICH should also be distributed across DL bandwidth in order to achieve frequency diversity gain. Therefore a mapping method similar to Rel. 11 can be adopted.
Described below are about 11 steps for ePHICH resource mapping. For the purposes of explanation, let

z(p)(i)={tilde over (y)}(p)(4i),{tilde over (y)}(p)(4i+1),{tilde over (y)}(p)(4i+2),{tilde over (y)}(p)(4i+3)(i=0,1,2)  (1):

denote symbol quadruplet i for antenna port p. Mapping to resource elements may be defined in terms of symbol quadruplets according to the following steps:

1. Mapping of REG
Four consecutive REs in PRBs used for ePHICH but not used for DM-RS, CSI-RS or CRS form one REG.
In reference to FIG. 14 (FIG. 14 shows mapping 1400), CRS is configured, and accordingly there are two REGs (1401) and (1402) in OFDM symbol #4, two REGs (1403) and (1404) in OFDM symbol #7 and two REGs (1405) and (1406) in OFDM symbol #11. There are therefore a total of 6 REGs in one PRB for ePHICH (i.e. NRBeREG=6) with the presence of CRS.
In reference to FIG. 15 (FIG. 15 shows mapping 1500), CRS is not configured, and accordingly there are 3 REGs (1501), (1502) and (1503) in OFDM symbol #4, 3 REGs (1504), (1505) and (1506) in OFDM symbol #7 and 3 REGs (1507), (1508) and (1509) in OFDM symbol #11. There are therefore a total of 9 REGs in one PRB for ePHICH (i.e. NRBeREG=9) without the presence of CRS.
For special subframe, because of the limited number of DL symbols on DL subframe, ePHICH is mapped to OFDMA symbol #4, #7, #8 rather than #4, #7, #11 in normal DL subframe. The mapping pattern is similar to OFDMA #4 and #7 (with only two REGs on one OFDMA symbol of one PRB when CRS is configured), although CRS is not configured on OFDMA symbol #8.
2. Determine the PRBs used for ePHICH
Based on PHICH configuration (and additional parameter mi in TDD system) and the value of NRBeREG, the UE can determine the number of PRB used for PHICH, and the calculation of PRB number for ePHICH can be expressed as follows:

NePHICHRB=3┌NePHICHgroup/NRBeREG┐  (2):

For example, assuming, Ng=2, NRBDL=6, based on




  
    
      
        
          N
          PHICH
          group
        
        =
        
          {
          
            
              
                
                  ⌈
                  
                    
                      N
                      g
                    
                    ⁡
                    
                      (
                      
                        
                          N
                          RB
                          DL
                        
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                        8
                      
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                  2
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                        N
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                    ⌉
                  
                
              
            
          
        
      
    
    
      
        (
        3
        )
      
    
  
  
    
      
        
          N
          ePHICH
          group
        
        =
        
          
            ⌈
            
              
                N
                g
              
              ⁡
              
                (
                
                  
                    N
                    RB
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          =
          
            
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              ·
              
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                  (
                  
                    6
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            =
            2
          
        
      
    
    
      
        (
        4
        )
      
    
  




(In the equation (3), the upper is for normal cyclic prefix, and the lower is for extended cyclic prefix.)

One ePHICH group takes 12 RE=3 REGs.
If CRS is configured, one PRB can provide 6 eREG for ePHICH and eREG belongs to the same PRB cannot be assigned to the same ePHICH group in order to achieve diversity gain. As a result, at least 3 PRBs are needed.
3. Determine the location of PRBs for ePHICH
As mentioned above, PRBs used for ePHICH should be distributed on DL bandwidth in order to achieve frequency diversity gain. The location of PRB for ePHICH also depends on a cell-specific value offsetcell-xPRB in order to achieve frequency domain ICIC. The index of PRB used by cell-x for ePHICH can be determined by




  
    
      
        
          {
          
            
              
                offset
                
                  cell
                  -
                  x
                
                PRB
              
              +
              j
            
            ,
            
              
                offset
                
                  cell
                  -
                  x
                
                PRB
              
              +
              j
              +
              
                
                  N
                  RB
                  DL
                
                3
              
            
            ,
            
              
                offset
                
                  cell
                  -
                  x
                
                PRB
              
              +
              j
              +
              
                
                  2
                  ·
                  
                    N
                    RB
                    DL
                  
                
                3
              
            
          
          }
        
        ,
        
          

        
        ⁢
        
          
        
        ⁢
        
          j
          =
          
            0
            ⁢
            
              
            
            ⁢
            ...
            ⁢
            
              
            
            ⁢
            
              
                N
                ePHICH
                RB
              
              3
            
          
        
      
    
    
      
        (
        5
        )
      
    
  




In reference to FIG. 16 (FIG. 16 shows mapping 1600), assuming NePHICHRB=3, NRBDL=6 and offsetcell-xPRB=0, then the PRB indexes for these 3 PRBs are {0 (1601), 2 (1602), 4 (1603)} respectively.
4. Indexing REG for ePHICH
Let n1′ denote the number of resource element groups for ePHICH in OFDM symbol 1′.
Number the resource-element groups not assigned to PCFICH in OFDM symbol 1′ from 0 to n1′−1, starting from the resource-element group with the lowest frequency-domain index.
5. Initialize m′=0 (PHICH mapping unit number)
6. For each value of i=0, 1, 2
7. Symbol-quadruplet z(p)(i) from ePHICH mapping unit m′ is mapped to the resource-element group represented by (k′,l′)i where the indices ki′ and li′ are given by steps 8 and 9 below:
8. The time-domain index li′ is given by




  
    
      
        
          l
          i
          ′
        
        =
        
          {
          
            
              
                
                  4
                  ⁢
                  
                    (
                    
                      
                        
                          l
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                        i
                      
                      =
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                    )
                  
                
              
            
            
              
                
                  7
                  ⁢
                  
                    (
                    
                      
                        
                          l
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                        i
                      
                      =
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                    )
                  
                
              
            
            
              
                
                  8
                  ⁢
                  
                    
                  
                  ⁢
                  or
                  ⁢
                  
                    
                  
                  ⁢
                  11
                  ⁢
                  
                    (
                    
                      
                        
                          l
                          _
                        
                        i
                      
                      =
                      2
                    
                    )
                  
                
              
            
          
        
      
    
    
      
        (
        6
        )
      
    
  
  
    
      
        
          
            l
            _
          
          i
        
        =
        
          {
          
            
              
                
                  
                    (
                    
                      
                        offset
                        
                          cell
                          -
                          x
                        
                        sym
                      
                      +
                      
                        m
                        ′
                      
                    
                    )
                  
                  ⁢
                  mod
                  ⁢
                  
                    
                  
                  ⁢
                  3
                
              
            
            
              
                
                  
                    (
                    
                      
                        
                          (
                          
                            
                              offset
                              
                                cell
                                -
                                x
                              
                              sym
                            
                            +
                            
                              m
                              ′
                            
                          
                          )
                        
                        ⁢
                        mod
                        ⁢
                        
                          
                        
                        ⁢
                        3
                      
                      +
                      i
                    
                    )
                  
                  ⁢
                  mod
                  ⁢
                  
                    
                  
                  ⁢
                  3
                
              
            
          
        
      
    
    
      
        (
        7
        )
      
    
  




(In the equation (6), when li′ equals 8 or 11, for special subframe li′ equals 8, and for normal subframe li′ equals 11. In the equation (7), the upper is for normal PHICH duration, all subframes, and the lower is for otherwise (Extended duration).

and offsetcell-xsym is the time domain offset of ePHICH resource for cell-x.
9. Set the frequency-domain index ki′ to the resource-element group assigned the number

ni  (8):

in step 4 above, where the number (8) is given by




  
    
      
        
          
            n
            _
          
          i
        
        =
        
          {
          
            
              
                
                  
                    (
                    
                      
                        offset
                        
                          cell
                          -
                          x
                        
                        freq
                      
                      +
                      
                        ⌊
                        
                          
                            m
                            ′
                          
                          /
                          3
                        
                        ⌋
                      
                    
                    )
                  
                  ⁢
                  mod
                  ⁢
                  
                    
                  
                  ⁢
                  
                    
                      n
                      
                        l
                        i
                        ′
                      
                    
                    ⁡
                    
                      (
                      
                        i
                        =
                        0
                      
                      )
                    
                  
                
              
            
            
              
                
                  
                    (
                    
                      
                        offset
                        
                          cell
                          -
                          x
                        
                        freq
                      
                      +
                      
                        ⌊
                        
                          
                            m
                            ′
                          
                          /
                          3
                        
                        ⌋
                      
                      +
                      
                        ⌊
                        
                          
                            n
                            
                              l
                              i
                              ′
                            
                          
                          /
                          3
                        
                        ⌋
                      
                    
                    )
                  
                  ⁢
                  mod
                  ⁢
                  
                    
                  
                  ⁢
                  
                    
                      n
                      
                        l
                        i
                        ′
                      
                    
                    ⁡
                    
                      (
                      
                        i
                        =
                        1
                      
                      )
                    
                  
                
              
            
            
              
                
                  
                    (
                    
                      
                        offset
                        
                          cell
                          -
                          x
                        
                        freq
                      
                      +
                      
                        ⌊
                        
                          
                            m
                            ′
                          
                          /
                          3
                        
                        ⌋
                      
                      +
                      
                        ⌊
                        
                          2
                          ⁢
                          
                            
                          
                          ⁢
                          
                            
                              n
                              
                                l
                                i
                                ′
                              
                            
                            /
                            3
                          
                        
                        ⌋
                      
                    
                    )
                  
                  ⁢
                  mod
                  ⁢
                  
                    
                  
                  ⁢
                  
                    
                      n
                      
                        l
                        i
                        ′
                      
                    
                    ⁡
                    
                      (
                      
                        i
                        =
                        2
                      
                      )
                    
                  
                
              
            
          
        
      
    
    
      
        (
        9
        )
      
    
  




and, offsetcell-xsym is the frequency domain offset of ePHICH resource for cell-x.
In reference to FIG. 16, assuming offsetcell-xsym=0 and offsetcell-xfreq=0
If normal duration is configured
REG #0 (1604), REG #2 (1610) and REG #4 (1616) in OFDMA symbol #4 are used for ePHICH group #0.
REG #0 (1605), REG #2 (1611) and REG #4 (1617) in OFDMA symbol #7 are used for ePHICH group #1.
Cell with

offsetcell-ysym≠0  (10):

or

offsetcell-yfreq≠0  (11):

can use other REGs, for instance.
If offsetcell-ysym=0 and offsetcell-yfreq=1 is configured for cell-y
REG #1 (1609), REG #3 (1615) and REG #5 (1621) in OFDMA symbol #4 are used for ePHICH group #0.
REG #1 (1608), REG #3 (1614) and REG #5 (1620) in OFDMA symbol #7 are used for ePHICH group #1.
If extended duration is configured
REG #0 (1604) in OFDMA symbol #4, REG #2 (1611) in OFDMA symbol #7 and REG #4 (1618) in OFDMA symbol #11 are used for ePHICH group #0.
REG #0 (1605) in OFDMA symbol #7, REG #2 (1612) in OFDMA symbol #11 and REG #4 (1616) in OFDMA symbol #4 are used for ePHICH group #0.
Similarly, for Cell with

offsetcell-xsym≠0  (12):

or

offsetcell-xfreq≠0  (13):

can used other REGs for ePHICH.
FIG. 16 also shows REG #0 (1606), REG #1 (1607), REG #3 (1613) and REG #5 (1619).
10. Increase m′ by 1.
11. Repeat from step 5 until all PHICH mapping units have been assigned.
In the present specification and claims (if any), the word ‘comprising’ and its derivatives including ‘comprises’ and ‘comprise’ include each of the stated integers but does not exclude the inclusion of one or more further integers.
Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ (or ‘one aspect’ or ‘an aspect’) means that a particular feature, function, structure, or characteristic described in connection with the embodiment (or aspect) is included in at least one embodiment (or aspects) of the present invention. Thus, for example, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, functions, structures, or characteristics may be combined in any suitable manner in one or more combinations.
In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.
The above-mentioned processing may be executed by a computer. Also, it is possible to provide a computer program which causes a programmable computer device to execute the above-mentioned processing. The program can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g. magneto-optical disks), CD-ROM, CD-R, CD-R/W, and semiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory), etc.). The software modules may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the software modules to a computer via a wired communication line (e.g. electric wires, and optical fibers) or a wireless communication line.
This application is based upon and claims the benefit of priority from Australian provisional patent application No. 2013900937, filed on Mar. 18, 2013, the disclosure of which is incorporated herein in its entirely by reference.
REFERENCE SIGNS LIST


    100 UE ACK/NACK PROCEDURE
    101 DL SUBFRAME #0
    102 DL SUBFRAME #1
    103 DL SUBFRAME #0
    104 DL SUBFRAME #0
    105 TWO UL SUBFRAMES
    106 SUBFRAME #7
    107 SUBFRAME #4
    300 PHICH RESOURCE ASSIGNMENT
    301 4 REGs
    302 6 REGs
    303 SECOND COPY OF PHICH RESOURCE
    400 WIRELESS COMMUNICATION SYSTEM
    401 eNB
    402 “TDD RECONFIGURATION PROCESSING” FUNCTION
    402BIS “PHICH RESOURCE MAPPING AND HARQ FEEDBACK” FUNCTION
    403 LEGACY UE(S)
    404 REL. 12 & BEYOND UE(S)
    405 TDD RECONFIGURATION PROCESSING FUNCTION
    405BIS PHICH INFORMATION PROCESSING FUNCTION
    406 SIB1
    407 UL-DL CONFIGURATION INFORMATION
    408 PUSCH HARQ-ACK
    409 HARQ-ACK FEEDBACK FOR PDSCH OR PDCCH INDICATION SPS RELEASE
    500 RESOURCE ASSIGNMENT
    501 UL SUBFRAME #4
    502 DL SUBFRAME #0
    503 SUBFRAME #3
    504 SUBFRAME #4
    600 RESOURCE ASSIGNMENT
    601 SUBFRAME #3
    602 SUBFRAME #4
    603 DL SUBFRAME #0
    700 RESOURCE ASSIGNMENT
    701 SUBFRAME #3
    702 SUBFRAME #4
    703 UL SUBFRAME #3
    704 DL SUBFRAME
    705 SUBFRAME #0
    800 RESOURCE ASSIGNMENT
    801 UL SUBFRAME #3
    802 UL SUBFRAME #4
    803 DL SUBFRAME #0
    804 UL SUBFRAME #4
    900 RESOURCE ASSIGNMENT
    901 SUBFRAME #3
    902 SUBFRAME #4
    903 DL SUBFRAME #0
    904 UL SUBFRAME #3
    905 DL SUBFRAME #9
    906 SUBFRAME #4
    1000 RESOURCE ASSIGNMENT
    1001 SUBFRAME #3
    1002 SUBFRAME #4
    1003 DL SUBFRAME #0
    1004 UL SUBFRAME #4
    1100 RESOURCE ASSIGNMENT
    1101 SUBFRAME #3
    1102 SUBFRAME #4
    1103 DL SUBFRAME #0
    1104 SUBFRAME #2
    1400 MAPPING
    1401 to 1406 TWO REGS
    1500 MAPPING
    1501 to 1509 3 REGS
    1600 MAPPING
    1601 to 1603 PRB INDEX
    1604 to 1606 REG #0
    1607 to 1609 REG #1
    1610 to 1612 REG #2
    1613 to 1615 REG #3
    1616 to 1618 REG #4
    1619 to 1621 REG #5

## Claims

1. A method for PHICH (Physical H-ARQ Indicator Channel) resource allocation in a wireless communication system that supports a flexible TDD UL-DL (Time Division Duplex Uplink-Downlink) configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs (User Equipments) which operate according to the flexible TDD configuration can be different from the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, the method involving, for a given subframe of a radio frame,
determining whether a first condition is fulfilled, wherein the first condition specifies that the said subframe is not a DL subframe in both the TDD UL-DL configuration in use by first UEs and in the TDD UL-DL configuration in use by second UEs,
determining whether a second condition is fulfilled, wherein the second condition specifies that the said subframe is a DL subframe in the TDD UL-DL configuration in use by first UEs and an UL subframe in the TDD UL-DL configuration in use by second UEs, and
allocating a PHICH resource based on determining that both of the first condition and the second condition are fulfilled, according to LTE timing rules applicable to the TDD UL-DL configuration in use by first UEs.

2. The method for PHICH resource allocation as claimed in claim 1 further including,
determining whether a third condition is fulfilled, wherein the third condition specifies that said given subframe is a DL subframe in the TDD UL-DL configuration in use by first UEs and also in the TDD UL-DL configuration in use by second UEs,
determining whether a fourth condition is fulfilled, wherein the fourth condition specifies that a PHICH resource is not required by second UEs for said given subframe, and
allocating no PHICH resource to the subframe when both of the third condition and the fourth condition are fulfilled.

3. The method for PHICH resource allocation as claimed in claim 2 further including, for said given subframe,
determining whether a fifth condition is fulfilled, wherein the fifth condition specifies that a PHICH resource is required by first UEs,
calculating the PHICH resource, when all of the third condition, the fourth condition and the fifth condition are fulfilled, required for sending PUSCH HARQ-ACK or remaining PUSCH HARQ-ACK, and
allocating the PHICH resource for transmission thereof via ePHICH IE if available and enabled or via UL grant if ePHICH IE is not available or not enabled.

4. The method for PHICH resource allocation as claimed in claim 2 further including,
determining whether a sixth condition is fulfilled, wherein the sixth condition specifies that a PHICH resource is required by second UEs for said given subframe,
determining whether a seventh condition is fulfilled, wherein the seventh condition specifies that the PHICH resource is not required by first UEs, and
allocating the PHICH resource, when all of the third condition, the sixth condition and the seventh condition are fulfilled, according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs.

5. The method for PHICH resource allocation as claimed in claim 4 further including,
determining whether an eighth condition is fulfilled, wherein the eighth condition specifies that a PHICH resource is required by first UEs for said given subframe,
determining whether a ninth condition is fulfilled, wherein the ninth condition specifies that the PHICH resource required by second UEs is not less than that required by first UEs,
determining whether a tenth condition is fulfilled, wherein the tenth condition specifies that the PHICH resource required by second UEs is not more than that required by first UEs, and
allocating the PHICH resource, when all of the third condition, the sixth condition, the eighth condition, the ninth condition and the tenth condition are fulfilled, according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs.

6. The method for PHICH resource allocation as claimed in claim 5 further including,
determining whether an eleventh condition is fulfilled, wherein the eleventh condition specifies that the PHICH resource required by second UEs is more than that required by first UEs for said given subframe,
allocating the PHICH resource, when all of the third condition, the sixth condition, the eighth condition, the ninth condition and the eleventh condition are fulfilled, according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs, and
allocating the PHICH resource with a PHICH group number (IPHICH) equal to one for first UEs.

7. The method for PHICH resource allocation as claimed in claim 5 further including,
determining whether a twelfth condition is fulfilled, wherein the twelfth condition specifies that the PHICH resource required by second UEs is less than that required by first UEs for said given subframe,
allocating the PHICH resource, when all of the third condition, the sixth condition, the eighth condition, and the twelfth condition are fulfilled, according to the LTE timing rules applicable to the TDD UL-DL configuration in use by second UEs, and
allocating the PHICH resource for first UEs to accommodate HARQ-ACK for (an) associated UL subframe(s) that have PUSCH HARQ-ACK timing aligned with that of second UEs.

8. The method for PHICH resource allocation as claimed in claim 7 further including, for said given subframe
calculating the PHICH resource, when all of the third condition, the sixth condition, the eighth condition, and the twelfth condition are fulfilled, required for sending PUSCH HARQ-ACK or remaining PUSCH HARQ-ACK of first UEs, and
allocating the PHICH resource for transmission thereof via ePHICH IE if this is available and enabled or via UL grant if ePHICH IE is not available or not enabled.

9. A base station configured for use in a wireless communication system that supports a flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by first UEs which are configured to operate according to the flexible TDD configuration can be different from the TDD UL-DL configuration used by second UEs which are configured to operate according to a long term TDD UL-DL configuration, wherein the base station comprises a processor and a memory storing instructions that, when executed by the processor, causes the processor to, for a given subframe of a radio frame,
determine whether a first condition is fulfilled, wherein the first condition specifies that the said subframe is not a DL subframe in both the TDD UL-DL configuration in use by first UEs and the TDD UL-DL configuration in use by second UEs;
determine whether a second condition is fulfilled, wherein the second condition specifies that the said subframe is a DL subframe in the TDD UL-DL configuration in use by first UEs and an UL subframe in the TDD UL-DL configuration in use by second UEs, and
allocate a PHICH resource based on determining that both of the first condition and the second condition are fulfilled, according to LTE timing rules applicable to the TDD UL-DL configuration in use by first UEs.

10. A mobile station configured for use by first UEs for PUSCH HARQ-ACK and PHICH signalling in a wireless communication system that supports a flexible TDD UL-DL configuration and in which different TDD UL-DL configurations are available and the TDD UL-DL configuration used by the first UEs which operate according to the flexible TDD configuration can be different from the TDD UL-DL configuration used by second UEs which operate according to a long term TDD UL-DL configuration, wherein the mobile station comprises a processor and a memory storing instructions that, when executed by the processor, causes the processor to, for a given flexible DL subframe of a radio frame in the TDD UL-DL configuration in use by the first UEs:
determine whether a first condition is fulfilled, wherein the first condition specifies that a corresponding subframe in the TDD UL-DL configuration in use by the second UEs is not a DL subframe,
determine whether a second condition is fulfilled, wherein the second condition specifies that the given DL subframe in the TDD UL-DL configuration in use by the first UEs is to carry PUSCH HARQ-ACK for first UEs, and
monitor for PHICH allocation based on determining that both of the first condition and the second condition are fulfilled, according to LTE timing rules applicable to the TDD UL-DL configuration in use by first UEs.