WO2016074739A1

WO2016074739A1 - Method and apparatus for performing codebook subset restriction

Info

Publication number: WO2016074739A1
Application number: PCT/EP2014/074560
Authority: WO
Inventors: Mihai Enescu; Karol Schober; Mikko Kokkonen
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2014-11-14
Filing date: 2014-11-14
Publication date: 2016-05-19

Abstract

A method and apparatus can be configured to transmit an indicator to a network node. The method may also include receiving at least one set of codebook-subset-restriction. The at least one set of codebook-subset-restriction may be configured based on the indicator. The method may also include receiving a tag. The method may also include carrying out blind detection based on the received at least one set of codebook-subset- restriction and the received tag. The method may also include carrying out interference cancellation based on the received tag.

Description

DESCRIPTION TITLE

METHOD AND APPARATUS FOR PERFORMING CODEBOOK SUBSET RESTRICTION

BACKGROUND: Field:

[0001] Embodiments of the invention relate to performing codebook subset restriction for multi-user-multiple-input-and-multiple-output technologies.

Description of the Related Art:

[0002] Long-term Evolution (LTE) is a standard for wireless communication that seeks to provide improved speed and capacity for wireless communications by using new modulation/signal processing techniques. The standard was proposed by the 3^rd Generation Partnership Project (3GPP), and is based upon previous network technologies. Since its inception, LTE has seen extensive deployment in a wide variety of contexts involving the communication of data.

SUMMARY:

[0003] According to a first embodiment, a method may comprise transmitting, by a network element, an indicator to a network node. The method may also comprise receiving at least one set of codebook-subset-restriction. The at least one set of codebook-subset-restriction is configured based on the indicator. The method may also comprise receiving a tag. The method may also comprise carrying out blind detection based on the received at least one set of codebook-subset-restriction and the received tag. The method may also comprise carrying out interference cancellation based on the received tag.

[0004] In the method of the first embodiment, the network element may comprise a multiuser-interference-cancellation-capable user equipment.

[0005] In the method of the first embodiment, the transmitting the indicator may comprise transmitting at least one of a precoding matrix indicator and a channel quality indicator.

[0006] In the method of the first embodiment, the received at least one set of codebook- subset-restriction corresponds to potential multi-user multiple-input-and-multiple-output pairs/co-scheduled users. [0007] In the method of the first embodiment, the transmitted signal from the same point/cell is intended to multi-user multiple-input-and-multiple-output pairs/co-scheduled users are sharing the same time and frequency resource.

[0008] In the method of the first embodiment, the received at least one set of codebook- subset-restriction is signaled semi-statically over higher layers.

[0009] In the method of the first embodiment, the receiving the tag may comprise receiving the tag via downlink-control information.

[00010] In the method of the first embodiment, the tag may comprise a dynamic parameter, and the at least one set of codebook-subset-restriction may comprise a semi-static parameter.

[0010] In the method of the first embodiment, receiving the tag may comprise receiving a CBSRJJEtag.

[0011] According to a second embodiment, an apparatus may comprise at least one processor. The apparatus may also comprise at least one memory including computer program code. The at least one memory and the computer program code may be configured, with the at least one processor, to cause the apparatus at least tojransmit an indicator to a network node. The apparatus may also be caused to receive at least one set of codebook-subset-restriction. The at least one set of codebook-subset-restriction is configured based on the indicator. The apparatus may also be caused to receive a tag. The apparatus may also be caused to carry out blind detection based on the received at least one set of codebook-subset-restriction and the received tag. The apparatus may also be caused to carry out interference cancellation based on the received tag.

[0012] In the apparatus of the second embodiment, the apparatus may comprise a multiuser-interference-cancellation-capable user equipment.

[0013] In the apparatus of the second embodiment, the transmitting the indicator may comprise transmitting at least one of a precoding matrix indicator and a channel quality indicator.

[0014] In the apparatus of the second embodiment, the received at least one set of codebook-subset-restriction corresponds to potential multi-user multiple-input-and-multiple- output pairs/co-scheduled users.

[0015] In the apparatus of the second embodiment, the received at least one set of codebook-subset-restriction is signaled semi-statically over higher layers. [0016] In the apparatus of the second embodiment, the receiving the tag may comprise receiving the tag via downlink-control information.

[0017] In the apparatus of the second embodiment, the tag may comprise a dynamic parameter, and the at least one set of codebook-subset-restriction may comprise a semi- static parameter.

[0018] In the apparatus of the second embodiment, the receiving the tag may comprise receiving a CBSRJJEtag.

[0019] According to a third embodiment, a computer program product may be embodied on a non-transitory computer readable medium. The computer program product may be configured to control a processor to perform a process comprising transmitting, by a network element, an indicator to a network node. The process may also comprise receiving at least one set of codebook-subset-restriction. The at least one set of codebook-subset-restriction is configured based on the indicator. The process may also comprise receiving a tag. The process may also comprise carrying out blind detection based on the received at least one set of codebook-subset-restriction and the received tag. The process may also comprise carrying out interference cancellation based on the received tag.

[0020] According to a fourth embodiment, a method may comprise receiving, by a network element, an indicator from a user equipment. The method may also comprise configuring a codebook-subset restriction based on the received indicator. The method may also comprise transmitting the codebook-subset-restriction to the user equipment. The method may also comprise transmitting a tag to the user equipment. The codebook-subset-restriction and the tag enable the user equipment to carry out interference cancellation.

[0021] In the method of the fourth embodiment, the network element may comprise an evolved Node B.

[0022] In the method of the fourth embodiment, the receiving the indicator may comprise receiving at least one of a precoding matrix indicator and a channel quality indicator.

[0023] In the method of the fourth embodiment, the transmitted codebook-subset-restriction corresponds to potential multi-user multiple-input-and-multiple-output pairs/co-scheduled users.

[0024] In the method of the fourth embodiment, the codebook-subset-restriction is transmitted semi-statically over higher layers. [0025] In the method of the fourth embodiment, the transmitting the tag may comprise transmitting the tag via downlink-control information.

[0026] In the method of the fourth embodiment, the tag may comprise a dynamic parameter, and the at least one codebook-subset-restriction may comprise a semi-static parameter.

[0027] In the method of the fourth embodiment, the transmitting the tag may comprise transmitting a CBSRJJEtag.

[0028] According to a fifth embodiment, an apparatus may comprise at least one processor. The apparatus may also comprise at least one memory including computer program code. The at least one memory and the computer program code may be configured, with the at least one processor, to cause the apparatus at least to receive an indicator from a user equipment. The apparatus may also be caused to configure a codebook-subset restriction based on the received indicator. The apparatus may also be caused to transmit the codebook-subset-restriction to the user equipment. The apparatus may also be caused to transmit a tag to the user equipment. The codebook-subset-restriction and the tag enable the user equipment to carry out interference cancellation.

[0029] In the apparatus of the fifth embodiment, the apparatus may comprise an evolved Node B.

[0030] In the apparatus of the fifth embodiment, the receiving the indicator may comprise receiving at least one of a precoding matrix indicator and a channel quality indicator.

[0031] In the apparatus of the fifth embodiment, the transmitted codebook-subset-restriction corresponds to potential multi-user multiple-input-and-multiple-output pairs/co-scheduled users.

[0032] In the apparatus of the fifth embodiment, the codebook-subset-restriction is transmitted semi-statically over higher layers.

[0033] In the apparatus of the fifth embodiment, the transmitting the tag may comprise transmitting the tag via downlink-control information.

[0034] In the apparatus of the fifth embodiment, the tag may comprise a dynamic parameter, and the at least one codebook-subset-restriction may comprise a semi-static parameter.

[0035] In the apparatus of the fifth embodiment, the transmitting the tag may comprise transmitting a CBSRJJEtag. [0036] According to a sixth embodiment, a computer program product may be embodied on a non-transitory computer readable medium. The computer program product may be configured to control a processor to perform a process comprising receiving, by a network element, an indicator from a user equipment. The process may also comprise configuring a codebook-subset restriction based on the received indicator. The process may also comprise transmitting the codebook-subset-restriction to the user equipment. The process may also comprise transmitting a tag to the user equipment. The codebook-subset- restriction and the tag enable the user equipment to carry out interference cancellation.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0037] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[0038] Fig. 1 illustrates a flowchart of a method in accordance with embodiments of the invention.

[0039] Fig. 2 illustrates a flowchart of another method in accordance with embodiments of the invention.

[0040] Fig. 3 illustrates an apparatus in accordance with embodiments of the invention.

[0041] Fig. 4 illustrates another apparatus in accordance with embodiments of the invention.

[0042] Fig. 5 illustrates another apparatus in accordance with embodiments of the invention.

[0043] Fig. 6 illustrates another apparatus in accordance with embodiments of the invention. [0044] Fig. 7 illustrates another apparatus in accordance with embodiments of the invention.

[0045] Fig. 8 illustrates a system in accordance with embodiments of the invention.

DETAILED DESCRIPTION: [0046] 3GPP Release 13 discusses possible improvements to Multi-User Multiple-lnput- and-Multiple-Output (MU-MIMO) technologies in the context of non-linear receivers. Improving MU-MIMO may relate to improving the performing of MU MIMO interference cancellation (MU-MIMO IC). One obstacle to effective implementation of MU-MIMO results from the fact that Channel-State Information (CSI) at the transmitter may be imperfect. The imperfect CSI at the transmitter may cause unpredictable interference at the corresponding receiver. Although CSI at the transmitter may be improved, such improved CSI at the transmitter is generally provided at the expense of increasing an amount of feedback overhead (higher feedback overhead). Further, regardless of the improvements made in CSI, CSI quality may still be limited by channel estimation error.

[0047] In one possible method for improving MU-MIMO performance, the feedback overhead can be kept unchanged by using a non-linear receiver. By using the non-linear receiver, an amount of unpredictable interference from a co-scheduled UE can be suppressed.

[0048] Non-linear receivers, such as Symbol-Level-lnterference-Cancellation (SLIC) or Reduced-Complexity Maximum Likelihood (R-ML) receivers, may enable efficient MU-MIMO operation on common-reference symbols (CRS). With CRS-based MU-MIMO (from Release 8), which generally provides poor performance, Zero-Forcing (ZF) cannot be applied and the probability of finding an optimal/orthogonal MU MIMO pair is limited. These technical difficulties may be overcome by using non-orthogonal pairing and by using co-scheduled user-interference suppression at the receiver.

[0049] In order to support CRS-based MU-MIMO operation with interference cancellation, advanced non-linear receivers may need to know a precoding matrix Indicator (PMI), power offset (P_A), and/or modulation order (MOD) of co-scheduled UE(s). These parameters may be signaled as a part of downlink control information (DCI). However, in order to implement such DCI signalling, each MU co-scheduled UE, at each eNB employing 4Tx, would require, for example, 4bits of signalling (for PMI), 3bits of signalling (for P_A), and 2 bits of signalling (for MOD) to be signaled dynamically, where PMI and MOD may be frequency selective as well. Hence, implementing a full dynamic signaling of paired UEs is generally not feasible, because it creates high control overhead. In 3GPP LTE, a downlink transmitter may employ a different PMI per each Physical-Resource-Block-pair (PRB-pair), resulting in 50x4=200 control bits, in case of a 10MHz system bandwidth.

[0050] Furthermore, a RAN4 work item (directed to Network-Aided-lnterference- Cancellation-and-Suppression (NAICS)) has established that a UE may blindly estimate parameters (such as PMI, P_A and Modulation order) of up to 2 interfering layers. Therefore, signaling dynamic parameters in the context of MU-MIMO may be unnecessary. The process of parameter-blind detection by the UE may be understood as the estimation of a particular parameter based on a received signal and without any detailed information about the corresponding parameter. On the other hand, in order to ease the complexity burden of the UE, the blind detection process can be aided by state/semi-static parameter signaling. In NAICS, the blind detection is performed for dynamic parameters of interfering transmission on PRB-pair in frequency and in every sub-frame in time. On the other hand, the same study item determined that performing blind detection of 16 PMIs may be complex, and a majority of companies agreed that codebook subset restriction may be required. Subset restriction may involve signaling a bitmap over higher-layers by transmitter to the receiver, which restricts the receiver's PMI search-space to those PMIs marked within the bitmap.

[0051] In the context of inter-cell NAICS, a bitmap that contains a codebook subset of codewords (utilized in interfering cells) was proposed to be signaled over the higher-layers between eNBs and further to the NAICS UE in the serving eNBs. While such an operation may be suitable for inter-cell NAICS, a different approach may be required for MU-MIMO IC. Unlike in inter-cell NAICS operation, the PMIs of co-scheduled UEs are known at the serving eNB, and, therefore, performing a semi-static signalling of a subset may significantly limit scheduling flexibility. On the other hand, due to the dynamic nature of MU pairing, a signaling solution that operates in a dynamic way may need to be determined.

[0052] Embodiments of the present invention propose a dynamic signaling method that may minimize control overhead, may maximize scheduler flexibility, and, at the same time, may limit UE complexity due to blind detection. The complexity of blind detection may grow linearly with the number of PMIs signaled in codebook subset restriction. In case the PMI and modulation order are blind-detected jointly, each additional PMI factorizes the complexity of modulation order detection, which is typically high.

[0053] Embodiments of the present invention configure a UE-specific codebook subset restriction, where codeboook (CB) subsets of all potential users in MU-MIMO are semi- statically signaled over the higher layers to the MU-IC UE. This semi-static signaling may be performed via Radio-Resource-Control (RRC). Afterwards, an eNB may dynamically indicate (via, for example, Downlink-Control Information (DCI)) which users have been co-scheduled to the target MU-IC UE. In certain embodiments, the eNB may provide this indication to only the target MU-IC UE. By this operation, the PMI search space may be limited to 4 or 6 PMIs per UE/spatial layer, which was determined to be feasible from the perspective of PMI blind detection. [0054] Embodiments of the present invention may include the following LTE UE and eNB procedures. With regard to UE procedures, the (MU-IC capable) UE may transmit/signal the PMI/CQI feedback to the eNB. The MU-IC UE receives, via higher layer signaling, one or more sets of Codebook-Subset-Restriction (CBSR). These CBRSs correspond to UEs that can be potentially co-scheduled in MU-MIMO with MU-IC UE. The MU-IC UE receives, by downlink-control information (DCI), a CBSRJJEtag. The CBSRJJEtag indicates to the MU- IC UE how many UEs have been co-scheduled and the corresponding CBRSs of the paired UEs. By knowing the subsets of all possible interfering PMIs, the MU-IC UE is able to perform PMI blind detection with lower complexity. After blind detection, the MU-IC UE may also perform Physical-Downlink-Shared-Channel (PDSCH) Interference Cancellation (IC) for the MU pairs, as indicated by the CBSRJJEtag.

[0055] With regard to eNB procedures, an eNB may receive UE CSI feedback (PMI/CQI) from a UE (such as from a MU-IC capable UE, for example). The eNB may configure a codebook-subset restriction (CBSR) for each MU-IC UE (based on the received UE feedback). In certain embodiments, the codebook subset size may have a small size, for example, a size of 4-6 PMIs. However, in other embodiments, the codebook subset size may be configured to any desired value. Each CBSR set may be tagged with an index. For example, if 4 UEs are potential MU pairs, then 2 bits can be used as CBSR tags. This tag can be referred to as a CBSR_UEtag. Alternatively, a bit map of 4 bits can be used to indicate which UE is co-scheduled within the UE-allocated Bandwidth (BW). The eNB may then inform the MU-IC UE, via semi-static communication (by RRC, for example), of one or more CBSR sets that correspond to potential MU-MIMO pairs. The eNB may inform the UE, via DCI, of the CBSRJJEtag.

[0056] In the future, the number of users to be multiplexed in MU-MIMO operation may be determined, and certain restrictions relating to the size of the configured subsets may be determined. In 3GPP LTE Release 13, a realistic enhancement may be implementing up to 4-layer MU-MIMOs.

[0057] Certain embodiments of the present invention may apply the above-described methods in order to provide dynamic information of scheduled PMI for primary users as well. The signaling performed by certain embodiments of the present invention may differ from the signaling performed by legacy technologies. In legacy technology, a wideband codeword may be explicitly signalled, and a sub-band feedback may include one confirmation bit in DCI. This one confirmation bit may indicate that the eNB has successfully received sub- band PMI feedback on a Physical-Uplink-Shared-Channel (PUSCH), and that the eNB has used those PMIs for downlink transmission. [0058] With respect to a preconfigured CBSR together with blind detection, according to certain embodiments of the present invention: (1 ) the eNB may not need to send information via DCI, (2) the eNB may freely choose transmitted PMIs from the sub-set, (3) UE decoding may be feasible, and/or (4) the complexity of a UE terminal may be within the parameters of 3GPP Release 12.

[0059] CBSRs may be configured based on PMI feedback, for example, when wide-band PMI feedback is present. A reported-PMI's neighboring PMIs may be configured as a subset. Such a configuration may guarantee that UE mobility will not make a subset outdated due to a slow pace of higher-layer signaling. If a sub-band PMI feedback is reported, an eNB may configure a subset that covers all reported PMIs.

[0060] Similarly, subsets of P_A and MOD may be preconfigured, to ease the complexity of blind detection at the UE, by limiting the number of P_A/MOD hypothesis. Unlike legacy LTE releases, PDSCH power offset P_A may be dynamically selected per subband, as a consequence of frequency-selective pairing with different users.

[0061] In view of the above, embodiments of the present invention may enable efficient blind detection of PMI at the UE, while also enabling a flexible scheduling operation in MU pairing.

[0062] Fig. 1 illustrates a flowchart of a method in accordance with embodiments of the invention. The method illustrated in Fig. 1 includes, at 1 10, transmitting, by a network element, an indicator to a network node. The method may also include, at 120, receiving at least one set of codebook-subset-restriction. The at least one set of codebook-subset- restriction may be configured based on the indicator. The method may also include, at 130, receiving a tag. The method may also include, at 140, carrying out blind detection based on the received at least one set of codebook-subset-restriction and the received tag. The method may also include, at 150, carrying out interference cancellation based on the received tag.

[0063] Fig. 2 illustrates a flowchart of a method in accordance with embodiments of the invention. The method illustrated in Fig. 2 includes, at 210, receiving, by a network element, an indicator from a user equipment. The method also includes, at 220, configuring a codebook-subset restriction based on the received indicator. The method also includes, at

230, transmitting the codebook-subset-restriction to the user equipment. The method may also include, at 240, transmitting a tag to the user equipment. The codebook-subset- restriction and the tag enable the user equipment to carry out interference cancellation.

[0064] Fig. 3 illustrates an apparatus in accordance with embodiments of the invention. In one embodiment, the apparatus can be a base station and/or an evolved Node B. The apparatus may also be a user equipment. Apparatus 10 can include a processor 22 for processing information and executing instructions or operations. Processor 22 can be any type of general or specific purpose processor. While a single processor 22 is shown in Fig. 3, multiple processors can be utilized according to other embodiments. Processor 22 can also include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples.

[0065] Apparatus 10 can further include a memory 14, coupled to processor 22, for storing information and instructions that can be executed by processor 22. Memory 14 can be one or more memories and of any type suitable to the local application environment, and can be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. For example, memory 14 include any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, or any other type of non-transitory machine or computer readable media. The instructions stored in memory 14 can include program instructions or computer program code that, when executed by processor 22, enable the apparatus 10 to perform tasks as described herein.

[0066] Apparatus 10 can also include one or more antennas (not shown) for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 can further include a transceiver 28 that modulates information on to a carrier waveform for transmission by the antenna(s) and demodulates information received via the antenna(s) for further processing by other elements of apparatus 10. In other embodiments, transceiver 28 can be capable of transmitting and receiving signals or data directly.

[0067] Processor 22 can perform functions associated with the operation of apparatus 10 including, without limitation, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 10, including processes related to management of communication resources.

[0068] In an embodiment, memory 14 can store software modules that provide functionality when executed by processor 22. The modules can include an operating system 15 that provides operating system functionality for apparatus 10. The memory can also store one or more functional modules 18, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 can be implemented in hardware, or as any suitable combination of hardware and software.

[0069] Fig. 4 illustrates an apparatus in accordance with embodiments of the invention. Apparatus 400 can be a network element/entity such as a user equipment, for example. Apparatus 400 can include a transmitting unit 410 that transmits an indicator to a network node. Apparatus 400 may also include a first receiving unit 420 that receives at least one set of codebook-subset-restriction. The at least one set of codebook-subset-restriction may be configured based on the indicator. Apparatus 400 may also include a second receiving unit 430 that receives a tag. Apparatus 400 may also include a detection unit 440 that carries out blind detection based on the received at least one set of codebook-subset-restriction and the received tag. Apparatus 400 may also include an interference-cancellation unit 450 that carries out interference cancellation based on the received tag.

[0070] Fig. 5 illustrates another apparatus in accordance with embodiments of the present invention. Apparatus 500 may include transmitting means 510 that transmits an indicator to a network node. Apparatus 500 may also include first receiving means 520 that receives at least one set of codebook-subset-restriction. The at least one set of codebook-subset- restriction may be configured based on the indicator. Apparatus 500 may also include second receiving means 530 that receives a tag. Apparatus 500 may also include detection means 540 that carries out blind detection based on the received at least one set of codebook-subset-restriction and the received tag. Apparatus 500 may also include interference-cancellation means 550 that carries out interference cancellation based on the received tag.

[0071] Fig. 6 illustrates another apparatus in accordance with embodiments of the invention. Apparatus 600 can be a network element/entity such as a base station / evolved Node B, for example. Apparatus 600 can include a receiving unit 610 that receives an indicator from a user equipment. Apparatus 600 may also include a configuring unit 620 that configures a codebook-subset restriction based on the received indicator. Apparatus 600 may also include a first transmitting unit 630 that transmits the codebook-subset-restriction to the user equipment. Apparatus 600 may also include a second transmitting unit 640 that transmits a tag to the user equipment. The codebook-subset-restriction and the tag enable the user equipment to carry out interference cancellation.

[0072] Fig. 7 illustrates another apparatus in accordance with embodiments of the invention. Apparatus 700 may include a receiving means 710 that receives an indicator from a user equipment. Apparatus 700 may also include a configuring means 720 that configures a codebook-subset restriction based on the received indicator. Apparatus 700 may also include a first transmitting means 730 that transmits the codebook-subset-restriction to a user equipment. Apparatus 700 may also include a second transmitting means 740 that transmits a tag to the user equipment. The codebook-subset-restriction and the tag may enable the user equipment to carry out interference cancellation.

[0073] Fig. 8 illustrates a system in accordance with embodiments of the invention. System 800 may include a first apparatus 810. First apparatus 810 may include first transmitting means 81 1 that transmits an indicator to a second apparatus 820. First apparatus 810 may also include first receiving means 812 that receives at least one set of codebook-subset- restriction. The at least one set of codebook-subset-restriction may be configured based on the indicator. First apparatus 810 may also include second receiving means 813 that receives a tag. First apparatus 810 may also include detection means 814 that carries out blind detection based on the received at least one set of codebook-subset-restriction and the received tag. First apparatus 810 may also include interference-cancellation means 815 that carries out interference cancellation based on the received tag. System 800 may also include a second apparatus 820. Second apparatus 820 may include third receiving means 821 that receives the indicator from first apparatus 810. Second apparatus 820 may also include a configuring means 822 that configures the codebook-subset restriction based on the received indicator. Second apparatus 820 may also include second transmitting means 823 that transmits the codebook-subset-restriction to the first apparatus 810. Second apparatus 820 may also include third transmitting means 824 that transmits the tag to first apparatus 810. The codebook-subset-restriction and the tag may enable the first apparatus 810 to carry out interference cancellation.

[0074] The described features, advantages, and characteristics of the invention can be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages can be recognized in certain embodiments that may not be present in all embodiments of the invention. One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed.

Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.

Claims

WE CLAIM:

1 . A method, comprising: transmitting, by a network element, an indicator to a network node; receiving at least one set of codebook-subset-restriction, wherein the at least one set of codebook-subset-restriction is configured based on the indicator; receiving a tag; carrying out blind detection based on the received at least one set of codebook- subset-restriction and the received tag; and carrying out interference cancellation based on the received tag.

2. The method according to claim 1 , wherein the network element comprises a multiuser-interference-cancellation-capable user equipment.

3. The method according to claim 1 or 2, wherein the transmitting the indicator comprises transmitting at least one of a precoding matrix indicator and a channel quality indicator.

4. The method according to any of claims 1 -3, wherein the received at least one set of codebook-subset-restriction corresponds to potential multi-user multiple-input-and- multiple-output pairs/co-scheduled users.

5. The method according to any of claims 1 -4, wherein the received at least one set of codebook-subset-restriction is signaled semi-statically over higher layers.

6. The method according to any of claims 1 -5, wherein the receiving the tag comprises receiving the tag via downlink-control information.

7. The method according to any of claims 1 -6, wherein the tag comprises a dynamic parameter, and the at least one set of codebook-subset-restriction comprises a semi-static parameter.

8. The method according to any of claims 1 -7, wherein the receiving the tag comprises receiving a CBSRJJEtag.

9. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus at least to transmit an indicator to a network node; receive at least one set of codebook-subset-restriction, wherein the at least one set of codebook-subset-restriction is configured based on the indicator; receive a tag; carry out blind detection based on the received at least one set of codebook-subset- restriction and the received tag; and carry out interference cancellation based on the received tag.

10. The apparatus according to claim 9, wherein the apparatus comprises a multiuser-interference-cancellation-capable user equipment.

1 1 . The apparatus according to claim 9 or 10, wherein the transmitting the indicator comprises transmitting at least one of a precoding matrix indicator and a channel quality indicator.

12. The apparatus according to any of claims 9-1 1 , wherein the received at least one set of codebook-subset-restriction corresponds to potential multi-user multiple-input-and- multiple-output pairs/co-scheduled users.

13. The apparatus according to any of claims 9-12, wherein the received at least one set of codebook-subset-restriction is signaled semi-statically over higher layers.

14. The apparatus according to any of claims 9-13, wherein the receiving the tag comprises receiving the tag via downlink-control information.

15. The apparatus according to any of claims 9-14, wherein the tag comprises a dynamic parameter, and the at least one set of codebook-subset-restriction comprises a semi-static parameter.

16. The apparatus according to any of claims 9-15, wherein the receiving the tag comprises receiving a CBSRJJEtag.

17. A computer program product, embodied on a non-transitory computer readable medium, the computer program product configured to control a processor to perform a process comprising: transmitting, by a network element, an indicator to a network node; receiving at least one set of codebook-subset-restriction, wherein the at least one set of codebook-subset-restriction is configured based on the indicator; receiving a tag; carrying out blind detection based on the received at least one set of codebook- subset-restriction and the received tag; and carrying out interference cancellation based on the received tag.

18. A method, comprising: receiving, by a network element, an indicator from a user equipment; configuring a codebook-subset restriction based on the received indicator; transmitting the codebook-subset-restriction to the user equipment; and transmitting a tag to the user equipment, wherein the codebook-subset-restriction and the tag enable the user equipment to carry out interference cancellation.

19. The method according to claim 18, wherein the network element comprises an evolved Node B.

20. The method according to claim 18 or 19, wherein the receiving the indicator comprises receiving at least one of a precoding matrix indicator and a channel quality indicator.

21. The method according to any of claims 18-20, wherein the transmitted codebook- subset-restriction corresponds to potential multi-user multiple-input-and-multiple-output pairs/co-scheduled users.

22. The method according to any of claims 18-21 , wherein the codebook-subset- restriction is transmitted semi-statically over higher layers.

23. The method according to any of claims 18-22, wherein the transmitting the tag comprises transmitting the tag via downlink-control information.

24. The method according to any of claims 18-23, wherein the tag comprises a dynamic parameter, and the at least one codebook-subset-restriction comprises a semi- static parameter.

25. The method according to any of claims 18-24, wherein the transmitting the tag comprises transmitting a CBSR_UEtag.

26. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus at least to receive an indicator from a user equipment; configure a codebook-subset restriction based on the received indicator; transmit the codebook-subset-restriction to the user equipment; and transmit a tag to the user equipment, wherein the codebook-subset-restriction and the tag enable the user equipment to carry out interference cancellation.

27. The apparatus according to claim 26, wherein the apparatus comprises an evolved Node B.

28. The apparatus according to claim 26 or 27, wherein the receiving the indicator comprises receiving at least one of a precoding matrix indicator and a channel quality indicator.

29. The apparatus according to any of claims 26-28, wherein the transmitted codebook-subset-restriction corresponds to potential multi-user multiple-input-and-multiple- output pairs/co-scheduled users.

30. The apparatus according to any of claims 26-29, wherein the codebook-subset- restriction is transmitted semi-statically over higher layers.

31 . The apparatus according to any of claims 26-30, wherein the transmitting the tag comprises transmitting the tag via downlink-control information.

32. The apparatus according to any of claims 26-31 , wherein the tag comprises a dynamic parameter, and the at least one codebook-subset-restriction comprises a semi- static parameter.

33. The apparatus according to any of claims 26-32, wherein the transmitting the tag comprises transmitting a CBSR_UEtag.

34. A computer program product, embodied on a non-transitory computer readable medium, the computer program product configured to control a processor to perform a process comprising: receiving, by a network element, an indicator from a user equipment; configuring a codebook-subset restriction based on the received indicator; transmitting the codebook-subset-restriction to the user equipment; and transmitting a tag to the user equipment, wherein the codebook-subset-restriction and the tag enable the user equipment to carry out interference cancellation.