WO2013113155A1

WO2013113155A1 - Configuration for detection of physical harq indicator channel

Info

Publication number: WO2013113155A1
Application number: PCT/CN2012/070803
Authority: WO
Inventors: Chunyan Gao; Erlin Zeng; Shuang TAN; Jing HAN; Wei Hong; Wei Bai; Haiming Wang
Original assignee: Renesas Mobile Corp
Current assignee: Renesas Electronics Corp
Priority date: 2012-01-31
Filing date: 2012-01-31
Publication date: 2013-08-08
Anticipated expiration: 2014-07-31

Abstract

The specification and drawings present a new method, apparatus and software related product (e.g., a computer readable memory) for configuring a detection of a E- PHICH (or PHICH in general) in DL for monitoring a PUSCH to reduce resource reservation for the PHICH and correspondingly reduce an impact on detection of (E-)PDCCH and (E-)PDSCH, e.g., in LTE-A systems. The UEs may be configured (e.g., by an eNB) to detect E-PHICH or not to detect: the configuration can be not to detect E-PHCIH at all, or always to detect it, or to detect only in some subframes. The configuration may be UE specific or common to a group of UEs. If a UE is configured not to detect E-PHICH in a DL subframe #n, and if according to the defined HARQ timing the UE needs to detect a HARQ-ACK information in the same subframe, then the UE will try to detect UL and/or DL grant in the subframe #n which will provide the desired HARQ (or ACK/NACK/DTX) information.

Description

CONFIGURATION FOR DETECTION OF PHYSICAL HARQ

INDICATOR CHANNEL Technical Field

The exemplary and non-limiting embodiments of this invention relate generally to wireless communications and more specifically to configuring a detection of a PHICH (or E-PHICH) for monitoring a PUSCH to reduce a resource reservation for the E-PHICH, e.g., in LTE-A systems.

Background Art

The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows: 3 GPP 3^r generation partnership project

AC acknowledgement

A/N acknowledge/non- acknowledge

ARQ automatic repeat request

CA carrier aggregation

CC component carrier

CRC cyclic redundancy check

DCI downlink control information

DL downlink

DMRS demodulation RS

eNB, eNodeB evolved node B /base station in an E-UTRAN system

E-PDCCH evolved physical downlink control channel

E-PDSCH evolved physical downlink shared channel

E-PHICH evolved physical hybrid ARQ indicator channel

DTX discontinuous reception

HARQ hybrid automatic repeat request

ICIC inter-cell interference coordination

LTE long term evolution

LTE-A long term evolution advanced MCS modulation and coding schemes

MTC machine type communication

MU-MIMO multi-use multiple-input multiple- output

NAC negative acknowledgement

OFDM orthogonal frequency division multiplexing

PDCCH physical downlink control channel

PDSCH physical downlink shared channel

PHICH physical hybrid ARQ indicator channel

PRB physical resource block

PUCCH physical uplink control channel

PUSCH physical uplink shared channel

RA resource allocation

RE resource element

RS reference signal

RM Reed-Mull er

RRC radio resource control

SNR signal-to-noise ratio

TBCC tail-biting convolutional coding

TDD time division duplex

S/P serial to parallel

UE user equipment

UL uplink

VRB virtual resource block In LTE Release 10 of 3GPP, a downlink control channel is spanned and interleaved with a system bandwidth in order to achieve frequency diversity. This wide band feature makes it difficult to handle inter- cell interference. This limitation and the general need for an increase in control channel capacity amongst other factors, led to a working assumption supporting the introduction of an enhanced PDCCH (E-PDCCH) in Release 11 of 3 GPP, see RANI, Draft Report of 3GPP TSG RAN WG1 #66bis v 0.1.0 (Zhuhai, P.R. China, 10^th-14^th October 2011). To support the low cost MTC with narrow bandwidth is another use case of E-PDCCH. In legacy systems DL HARQ-ACK signalling is transmitted on a PHICH. If in the Release 1 1 of 3GPP a UE is configured to receive UL grants on the evolved PDCCH, e.g., due to operating in an extension carrier, due to ICIC or due to being unable to access a wide band PDCCH, a new mechanism may be required for DL HARQ-ACK signalling and the new mechanism for DL HARQ-ACK is identified as E-PHICH, e.g., see Rl-11 682 "Views on Enhanced PHICH, Ericsson, 3 GPP TSG-RAN WG1 #67, San Francisco, 14^th-18^th November 201 1, and Rl-114067 "PHICH Enhancement)", Alcatel-Lucent, 3 GPP TSG-RAN WG1 #67, San Francisco, 14^th- 18^th November 2011.

Currently the design of the E-PDCCH is not decided yet, and the E-PHICH design may depends on the E-PDCCH design, e.g., whether to use precoded or non-precoded RS for demodulation, how to multiplex with E-PDCCH and E-PDSCH. However, it is clear that in order to get diversity gain, the E-PHICH is still expected to be in multiple PRBs. In such a case, the resource used by the E-PHICH may cause puncturing of the E-PDCCH/E-PDSCH which will degrade the performance; therefore, keeping the resource for the E-PHICH at a minimum is desired.

As shown above, the E-PHICH is needed in case the access to normal PDCCH is not available, and reduction in the E-PHICH resource reservation is desired. In LTE Release 10 of 3GPP, the PHICH resource comprises some reserved REs in the first 3 OFDM symbols in the control region, and each PHICH resource is linked implicitly to the scheduled PUSCH resource and the cyclic shift used for UL DMRS (see 3 GPP TS 36.213 V10.2.0 (20101-06). However, there may be some reservations for the PHICH resource, considering that not all PRBs will be scheduled as the start PRB of a PUSCH, not all PUSCHs will use MU-MIMO, some transmission will use adaptive HARQ which relies on a UL grant for a new transmission and retransmission rather than PHICH. In the E-PHICH design, it is desirable that such

over-reservation can be reduced.

The need for E-PHICH was mentioned in some 3 GPP contributions (see Rl -1 13682 "Views on Enhanced PHICH, Ericsson, 3 GPP TSG-RAN WG1 #67, San Francisco, 14^th-18^th November 2011 , and Rl-114067 "PHICH Enhancement)", Alcatel-Lucent, 3 GPP TSG-RAN WG1 #67, San Francisco, 14^th-l 8^th November 2011). However, there was no detail provided about how the E-PHICH channel is designed or mapped to physical channels, and also there was no discussion about how to optimize the E-PHICH resource reservations. Summary

According to a first aspect of the invention, a method comprising: receiving by a user equipment a configuration instruction from a network element not to detect a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; detecting the at least one downlink subframe; and if an uplink grant or a downlink grant is detected in the at least one downlink subframe, determining if a retransmission of an uplink subframe is needed using feedback information regarding the uplink subframe, the feedback information being comprised in the received uplink or downlink grant.

According to a first aspect of the invention, a method, comprising: configuring by a network element one or more user equipments of a plurality of user equipments not to monitor a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; and sending to at least one of the one or more user equipments a downlink subframe comprising a downlink grant or an uplink grant indicating whether an uplink retransmission for a received uplink subframe is needed.

According to a third aspect of the invention, an apparatus comprises: at least one processor and a memory storing a set of computer instructions, in which the processor and the memory storing the computer instructions are configured to cause the apparatus to: receive a configuration instruction from a network element not to detect a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; detect the at least one downlink subframe; and if an uplink grant or a downlink grant is detected in the at least one downlink subframe, determine if a retransmission of an uplink subframe is needed using feedback information regarding the uplink subframe, the feedback information being comprised in the received uplink or downlink grant.

According to a fourth aspect of the invention, an apparatus comprising: at least one processor and a memory storing a set of computer instructions, in which the processor and the memory storing the computer instructions are configured to cause the apparatus to: configure one or more user equipments of a plurality of user equipments not to monitor a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; and sending to at least one of the one or more user equipments a downlink subframe comprising a downlink grant or an uplink grant indicating whether an uplink retransmission for a received uplink subframe is needed.

According to a fifth aspect of the invention, a computer readable medium comprising a set of instructions, which, when executed on a user equipment causes the user equipment to perform the steps of: receiving a configuration instruction from a network element not to detect a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; detecting the at least one downlink subframe; and if an uplink grant or a downlink grant is detected in the at least one downlink subframe, determining if a retransmission of an uplink subframe is needed using feedback information regarding the uplink subframe, the feedback information being comprised in the received uplink or downlink grant.

According to a sixth aspect of the invention, a computer readable medium comprising a set of instructions, which, when executed on a network element causes the network element to perform the steps of: configuring one or more user equipments of a plurality of user equipments not to monitor a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; and sending to at least one of the one or more user equipments a downlink subframe comprising a downlink grant or an uplink grant indicating whether an uplink retransmission for a received uplink subframe is needed.

Brief Description of the Drawings:

For a better understanding of the nature and objects of the present invention, reference is made to the following detailed description taken in conjunction with the following drawings, in which:

Figure 1 is a time diagram illustrating different mode of operation of HARQ-ACK feedback using E-PHICH, and DL and UL grants for one UE, according to embodiments of the invention;

Figures 2-3 are flow charts demonstrating implementation of exemplary embodiments of the invention; and

Figure 4 is a block diagram of wireless devices for practicing exemplary embodiments of the invention.

Detailed Description

A new method, apparatus, and software related product (e.g., a computer readable memory) are presented for configuring a detection of a E- PHICH (or PHICH in general) in DL for monitoring a PUSCH to reduce resource reservation for the PHICH and correspondingly reduce an impact on detection of (E-)PDCCH and (E-)PDSCH, e.g., in LTE-A systems. According to an embodiment of the invention, UEs may be configured (e.g., by an eNB) to detect E-PHICH or not to detect: the configuration can be not to detect E-PHCIH at all, or always to detect it, or to detect only in some subframes. The configuration may be UE specific or common to a group of UEs.

For example, if a UE is configured not to detect E-PHICH in a DL subframe #n, and if according to the defined HARQ timing the UE needs to detect a HARQ-ACK information in the same subframe, then the UE will try to detect UL and/or DL grant in the subframe #n which will provide the desired HARQ (or AC /NACK/DTX) information.

When there is no UL grant but a DL grant is detected in the subframe #n, UE should obtain the HARQ (feedback) information via the DL grant. For example, DL grant' s DCI in the UE specific search space may be extended by N bits to convey the HARQ information, where N is a positive integer. In this case the retransmission may be performed according to non-adaptive mechanism using predefined UL resources and other transmission parameters. In another embodiment, some bit(s) of the DL grant's DCI may be reinterpreted/redefined to provide the desired HARQ (ACK/NACK) information for the corresponding UL transmission with no E-PHICH configured in this DL subframe #n. The reinterpreted bit(s) can be resource allocation type field, e.g., in DCI format 1 , the resource allocation type can be

redefined/reinterpreted as follows:

- Ί ' : ACK and resource allocation type 1 ;

- '0' NACK and resource allocation type 0.

In DCI format 1 A, the localized/distributed VRB assignment flag can be redefined as follows:

- ' 1 ' : ACK and distributed VRB ;

- '0' : NACK and localized VRB.

In another embodiment, if no DL grant and UL grant are detected, the UE can assume that an ACK is sent by eNB, i.e., no retransmission is needed.

Moreover, if the UL grant is detected, the UE will transmit PUSCH in the following UL subframe (e.g., subframe n+4) based on the UL grant message, which may contain resource assignment, modulation and coding scheme (MCS), new data indicator (NDI), etc. The decision about retransmission or sending a new transmission in this following UL subframe n+4 can be made based on NDI. The NDI bit can implicitly indicate ACK NACK, i.e. "new data" implies ACK and "non-new data" implies NACK. If the UL grant is provided by the eNB, no HARQ information is appended to the DL grant.

It is further noted that by detecting the UL grant, the UE will know when and how to transmit uplink data, except in the case of non-adaptive retransmission where the UE can retransmit data according to ACK/NACK information and a predefined schedule for the non-adaptive retransmission. But even for the non-adaptive retransmission, the UL grant can be used to schedule UL retransmission with a higlier priority than ACK/NACK and the cost of higher overhead.

Thus, a network element such as eNB may configure one or more UEs of a plurality of UEs served by the eNB not to monitor or detect the E-PHICH (more generally PHICH) . Instead these one or more UEs would detect in a downlink subframe a downlink grant and/or an uplink grant to determine at least if an uplink retransmission needs to be performed. Then the eNB sends to each of the one or more user equipments a DL subframe comprising an

ACK/NACK DTX indication on a received UL subframe in the DL grant or in the uplink grant to determine if an uplink retransmission is needed. At the same time the eNB can further configure one or more other user equipments of the plurality of user equipments to monitor the PHICH and to process the ACK NACK/DTX information in a normal way.

Then, each UE served by the eNB may be configured (by receiving an appropriate instruction from the eNB) not to monitor/detect the E-PHICH in at least one downlink subframe. After detecting the at least one downlink subframe, and if one or more of an uplink grant and a downlink grant are detected in the at least one downlink subframe, the UE may determine if the uplink re- transmission is needed. The uplink grant comprises at least information for sending a next uplink subframe which may a retransmission or a new transmission subframe, e.g., based on the ACK/NACK/DTX comprised in the DL grant.

Furthermore, not all UEs need to detect E-PHICH for the PUSCH transmission, and the

E-PHICH resource can be reserved considering (but not being limited to) the following factors: a) how many UEs can bear with non-adaptive HARQ transmission; b) how many UEs have high DL and UL traffic. Based on this information, the network element such as eNB may assign a DL resource to the PHICH, such that the configuration of the PHICH for the UEs described herein may be based on the collected information and on the assigned resource for the PHICH as further described herein.

For the UEs with a lot of DL traffic, the E-PHICH can be embedded in a DL grant as it is likely that the UE will have the DL grant in a large portion of the DL sub frames. For UEs with less DL traffic, the UL grant can be sent in case no DL grant available in corresponding subframes or change of MCS/resource allocation is needed. It is assumed that no matter how the ACK/NACK for PUSCH is sent in E-PHICH or DL UL grant, the same HARQ timing may be used, for example it can be 4ms HARQ delay, but for the TDD system it can be longer than 4ms.

According to a further embodiment, the configuration for the E-PHICH detection may be subframe dependent, e.g., some UEs may be configured to detect the E-PHICH only in odd subframes, while other UEs may be configured to detect the E-PHICH only in even subframes, or some UEs can be configured not to detect the E-PHICH at all as discussed herein.

It is further noted that for the UEs configured not to detect E-PHICH, if it has PUSCH in a subframe n-4, it will detect the DL grant in a subframe n assuming that HARQ information is embedded there which will cause a larger DCI size or reinterpretation of some field.

Since not all PUSCH PRBs will need an E-PHICH, reserving E-PHICH for each UL PRB will be a waste. Then considering this, the mapping from the PUSCH PRB to an

E-PHICH resource can be a multiple- to-one mapping, i.e., multiple UL PRB index map to same E-PHICH resource. The collision can be avoided by sending HARQ information for some UEs in the DL or UL grant rather than an E-PHICH.

Figure 1 shows a time diagram illustrating different modes of operation of

HARQ-ACK feedback using E-PHICH, and DL and UL grants for one UE, according to embodiments of the invention. In a time period between t₀ and ti with a low communication traffic for PUSCH subframes 1 through M, the UE is configured to detect E-PHICH with subsequent retransmission (if needed) using existing mechanism.

In a time period between ti and t₂ with a high communication traffic for PUSCH subframes M+l through M+N, the UE is configured to not detect the E-PHICH and the eNB add HARQ-ACK feedback information in DL grant for detection by the UE with subsequent retransmission (if needed) using non-adaptive mechanism for retransmission.

In a time period between t₂ and t₃ with a less communication traffic (than in the time period between t_t and t₂₎ for PUSCH subframes M+N+l through M+P, the UE is configured to not detect the E-PHICH and the eNB add HARQ-ACK feedback information in UL grant for detection by the UE with subsequent retransmission (if needed) using adaptive mechanism for retransmission as explained herein. In a time period between t3 and with a high quality of transmission (low SNR) with a relatively low communication traffic for PUSCH subframes M+P+l through M+S, the UE is configured to not detect the E-PHICH and the eNB does not add acknowledgement feedback information in UL or DL grant (or UL and/or DL grants are not sent) no retransmission is assumed by the UE.

In Figure 1 M, N, P and S are integers and S>P>N>M>1.

Figure 2 shows an exemplary flow chart demonstrating implementation of some embodiments of the invention by a UE. It is noted that the order of steps shown in Figure 2 is not required, so in principle the various steps may be performed out of the illustrated order. Also certain steps may be skipped, different steps may be added or substituted, or selected step/steps or groups of steps may be performed separately.

In a method according to this exemplary embodiment, as shown in Figure 2, in a first step 40, the UE receives a configuration instruction from a serving eNB regarding detecting or not detecting (E)-PHICH in DL subframe(s). In a next step 42, the UE sends a PUSCH in UL subframe n-4 to the eNB. In a next step 44, the UE receives a DL subframe n from the eNB.

In a next logical step 46, it is determined whether the UE is configured to detect the (E)-PHICH. If that is not the case, in a next step 48, the UE detects DL grant or UL grant (comprising ACK/NACK feedback information) in the DL subframe n and the process goes to step 52. However, if it is determined that the UE is configured to detect the (E)-PHICH, in a next step 50, the UE detects (E)-PHICH on a configured resource. In a next step 52, the UE determines whether retransmission or new transmission needs to be sent in UL subframe n+4 using the UL grant if detected based on feedback information comprised in the DL or UL grant, as described herein.

Figure 3 shows an exemplary flow chart demonstrating implementation of some embodiments of the invention performed by the eNB. It is noted that the order of steps shown in Figure 3 is not required, so in principle the various steps may be performed out of the illustrated order. Also certain steps maybe skipped, different steps maybe added or substituted, or selected step/steps or groups of steps may be performed separately.

In a method according to this exemplary embodiment, as shown in Figure 3, in a first step 60, the eNB configures one or more UEs of a plurality of UEs not to detect (E)-PHICH in DL subframe(s). In a next step 62, the eNB configures one or more other UEs of the plurality of UEs to monitor/detect (E)-PHICH in DL subframe(s). In a next step 64, the eNB sends to at least one of the one or more user equipments a downlink subframe comprising a DL grant or an UL grant comprising feedback information on the received UL subframe, for providing an indication whether an UL retransmission for the received uplink subframe is needed based on the feedback information. In a next step 66, the eNB sends to at least one of the one or more other UEs a DL subframe comprising (E)-PHICH for providing an indication whether an UL retransmission for the received UL subframe is needed. In a next step 68, steps 60 and 62 under different traffic conditions and/or different UEs added are performed again, and the process goes to step 64.

Figure 4 shows an example of a block diagram demonstrating LTE devices comprised in a network 10 including an eNB 80, and UEs 82 and 84, according to an embodiment of the invention. Figure 4 is a simplified block diagram of various electronic devices that are suitable for practicing the exemplary embodiments of this invention, e.g., in reference to Figures 1-3, and a specific manner in which components of an electronic device are configured to cause that electronic device to operate. Each of the UEs 82 and 84 may be implemented as a mobile phone, a wireless communication device, a camera phone, a portable wireless device and the like.

The eNB 80 comprises at least one transmitter 80a at least one receiver 80b_; at least one processor 80c at least one memory 80d and a DRX control application module 80e. The transmitter 80a and the receiver 80b and corresponding antennas (not shown in Figure 4) may be configured to provide wireless communications with the UEs 82 and 84 according to the embodiment of the invention. The transmitter 80a and the receiver 80b may be generally means for transmitting/receiving and may be implemented as a transceiver, or a structural equivalence thereof. It is further noted that the same requirements and considerations are applied to transmitters and receivers of the devices 82 and 84.

Furthermore, the eNB 80 may further comprise communicating means such as a modem 80f, e.g., built on an RF front end chip of the eNB 80, which also carries the TX 80a and RX 80b for bidirectional wireless communications wireless links 81a and 81b (for implementing/facilitating steps 40-50 in Figure 2 and steps 60-66 in Figure 3) with the devices 82 and 84 respectively. A similar concept is applicable to the devices 82and 84 shown in Figure 4. Various embodiments of the at least one memory 80d (e.g., computer readable memory) may include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the processor 80c include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors. Similar embodiments are applicable to memories and processors in other devices

82 and 84 shown in Figure 4.

The PHICH configuring application module 80e may provide various instructions for performing steps 60-68 shown in Figure 3. The module 80e may be implemented as an application computer program stored in the memory 80d, but in general it may be implemented as software, firmware and/or hardware module or a combination thereof. In particular, in the case of software or firmware, one embodiment may be implemented using a software related product such as a computer readable memory (e.g., non-transitory computer readable memory), computer readable medium or a computer readable storage structure comprising computer readable instructions (e.g., program instructions) using a computer program code (i.e., the software or firmware) thereon to be executed by a computer processor.

Furthermore, the module 80e may be implemented as a separate block or may be combined with any other module/block of the eNB 80, or it may be split into several blocks according to their functionality.

The devices 82 and 84 may have similar components as the eNB 80, as shown in Figure 4, so that the above discussion about components of the LPN 80 is fully applicable to the components of the devices 82, 84 and 86.

Moreover, the retransmission scheduling application module 83 in the UEs 82 and 84 may provide/facilitate various instructions for performing steps 40-52 in Figure 2. The module

83 may be implemented as an application computer program stored in the memory 85, but in general it may be implemented as software, firmware and/or hardware module or a

combination thereof. In particular, in the case of software or firmware, one embodiment may be implemented using a software related product such as a computer readable memory (e.g., non-transitory computer readable memory), computer readable medium or a computer readable storage structure comprising computer readable instructions (e.g., program instructions) using a computer program code (i.e., the software or firmware) thereon to be executed by a computer processor. The module 83 may be implemented as a separate block or may be combined with any other module/block of the UEs 82 or 84, or it may be split into several blocks according to their functionality.

It is noted that various non- limiting embodiments described herein may be used separately, combined or selectively combined for specific applications.

Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope of the invention, and the appended claims are intended to cover such modifications and

arrangements.

Claims

WHAT IS CLAIMED IS:

1. A method, comprising:

receiving by a user equipment a configuration instruction from a network element not to detect a physical hybrid automatic repeat request indicator channel in at least one downlink subframe;

detecting the at least one downlink subframe; and

if an uplink grant or a downlink grant is detected in the at least one downlink subframe, determining if a retransmission of an uplink subframe is needed using feedback information regarding the uplink subframe, the feedback information being comprised in the received uplink or downlink grant.

2. The method of claim 1, wherein the feedback information comprised in the downlink grant is a hybrid automatic repeat request for the uplink subframe added in the downlink grant.

3. The method of claim 1 , wherein the feedback information comprised in the downlink grant is provided by reinterpreting or redefining existing bits in the downlink grant without adding new bits in the downlink grant.

4. The method of claim 1 , wherein if no uplink grant nor downlink grant is detected, then the retransmission is not needed.

5. The method of claim 1, wherein the network element is an eNB.

6. A method, comprising:

configuring by a network element one or more user equipments of a plurality of user equipments not to monitor a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; and

sending to at least one of the one or more user equipments a downlink subframe comprising a downlink grant or an uplink grant indicating whether an uplink retransmission for a received uplink subframe is needed.

7. The method of claim 6, the downlink grant comprises a hybrid automatic repeat request for the received uplink subframe added in the downlink grant.

8. The method of claim 6, wherein the downlink grant indicates whether an uplink retransmission for the received uplink subframe is needed using reinterpreting or redefining existing bits without adding new bits in the downlink grant.

9. The method of claim 6, wherein the network element is an eNB.

10. The method of claim 6, further comprises:

further configuring one or more other user equipments of the plurality of user equipments to monitor the physical hybrid automatic repeat request indicator channel in the at least one downlink subframe.

1 1. The method of claim 10, wherein selected user equipments of the plurality of user equipments are configured to monitor the physical hybrid automatic repeat request indicator channel only in even subframes and further user equipments of the plurality of user equipments are configured to monitor the physical hybrid automatic repeat request indicator channel only in odd subframes.

12. The method of claim 10, wherein prior to the configuring and further configuring, the method comprises:

collecting by a network element information about the plurality of user equipments, the information comprises one or more of :

how many user equipments of the plurality of user equipments are configured to operate with a non-adaptive hybrid automatic repeat request transmission, and

how many user equipments of the plurality of user equipments have downlink traffic together with uplink transmissions above a predefined level; and

assigning a downlink resource to the physical hybrid automatic repeat request indicator channel based on said information, wherein the configuring and farther configuring are based on the collected information and on the assigned resource.

13. The method of claim 10, wherein the configuring and the further configuring are subframe specific.

14. An apparatus comprising:

at least one processor and a memory storing a set of computer instructions, in which the processor and the memory storing the computer instructions are configured to cause the apparatus to :

receive a configuration instruction from a network element not to detect a physical hybrid automatic repeat request indicator channel in at least one downlink subframe;

detect the at least one downlink subframe; and

if an uplink grant or a downlink grant is detected in the at least one downlink subframe, determine if a retransmission of an uplink subframe is needed using feedback information regarding the uplink subframe, the feedback information being comprised in the received uplink or downlink grant.

15. The apparatus of claim 14, wherein the feedback information comprised in the downlink grant is a hybrid automatic repeat request for the uplink subframe added in the downlink grant, or the feedback information is provided by reinterpreting or redefining existing bits in the downlink grant without adding new bits in the downlink grant.

16. The apparatus of claim 14, wherein if no uplink grant nor downlink grant is not detected, then the retransmission is not needed.

17. The apparatus of claim 14, wherein the network element is an eNB.

18. An apparatus comprising:

at least one processor and a memory storing a set of computer instructions, in which the processor and the memory storing the computer instructions are configured to cause the apparatus to:

configure one or more user equipments of a plurality of user equipments not to monitor a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; and

19. The apparatus of claim 18, the downlink grant comprises a hybrid automatic repeat request for the received uplink subframe added in the downlink grant, or the downlink grant indicates whether an uplink retransmission for the received uplink subframe is needed using reinterpreting or redefining existing bits without adding new bits in the downlink grant.

20. The apparatus of claim 18, wherein the network element is an eNB.

21. The apparatus of claim 18, wherein the computer instructions are configured to cause the apparatus to:

further configure one or more other user equipments of the plurality of user equipments to monitor the physical hybrid automatic repeat request indicator channel in the at least one downlink subframe.

22. The apparatus of claim 21 , wherein selected user equipments of the plurality of user equipments are configured to monitor the physical hybrid automatic repeat request indicator channel only in even subframes and further user equipments of the plurality of user equipments are configured to monitor the physical hybrid automatic repeat request indicator channel only in odd subframes.

23. The apparatus of claim 21 , wherein prior to the configuring and further configuring, the computer instructions are configured to cause the apparatus to:

collect information about the plurality of user equipments, the information comprises one or more of :

how many user equipments of the plurality of user equipments have downlink traffic together with uplink transmissions above a predefined level; and assign a downlink resource to the physical hybrid automatic repeat request indicator channel based on said information, wherein the configuring and further configuring are based on the collected information and on the assigned resource.

24. The apparatus of claim 21, wherein the configuring and the further configuring are subframe specific.

25. A computer readable medium comprising a set of instructions, which, when executed on a user equipment causes the user equipment to perform the steps of:

receiving a configuration instruction from a network element not to detect a physical hybrid automatic repeat request indicator channel in at least one downlink subframe;

detecting the at least one downlink subframe; and

26. The computer readable medium of claim 25, wherein the feedback information comprised in the downlink grant is a hybrid automatic repeat request for the uplink subframe added in the downlink grant, or the feedback information is provided by reinterpreting or redefining existing bits in the downlink grant without adding new bits in the downlink grant.

27. The computer readable medium of claim 25, wherein if no uplink grant nor downlink grant is detected, then the retransmission is not needed.

28. A computer readable medium comprising a set of instructions, which, when executed on a network element causes the network element to perform the steps of:

configuring one or more user equipments of a plurality of user equipments not to monitor a physical hybrid automatic repeat request indicator channel in at least one downlink subframe; and

29. The computer readable medium of claim 26, the downlink grant comprises a hybrid automatic repeat request for the received uplink subframe added in the downlink grant, or the downlink grant indicates whether an uplink retransmission for the received uplink subframe is needed using reinterpreting or redefining existing bits grant without adding new bits in the downlink grant.