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1 Project Ttle Date Submtted IEEE Broadband Wreless Access Workng Group < Double-Stage DL MU-MIMO Scheme Source(s) Yang Tang, Young Hoon Kwon, Yajun Kou, Shahab Sanaye, Bo We, Zhgang Rong, Janmn Lu E-mal: Huawe Re: IEEE m-08/016r1: Call for Contrbutons on Project m System Descrpton Document (SDD). Target topc: Downlnk MIMO Schemes and Uplnk control Structures. Abstract Purpose Notce Release Patent Polcy Ths contrbuton proposes mult user MIMO scheme for downlnk transmsson For dscusson and approval by TGm Ths document does not represent the agreed vews of the IEEE Workng Group or any of ts subgroups. It represents only the vews of the partcpants lsted n the Source(s) feld above. It s offered as a bass for dscusson. It s not bndng on the contrbutor(s), who reserve(s) the rght to add, amend or wthdraw materal contaned heren. The contrbutor grants a free, rrevocable lcense to the IEEE to ncorporate materal contaned n ths contrbuton, and any modfcatons thereof, n the creaton of an IEEE Standards publcaton; to copyrght n the IEEE s name any IEEE Standards publcaton even though t may nclude portons of ths contrbuton; and at the IEEE s sole dscreton to permt others to reproduce n whole or n part the resultng IEEE Standards publcaton. The contrbutor also acknowledges and accepts that ths contrbuton may be made publc by IEEE The contrbutor s famlar wth the IEEE-SA Patent Polcy and Procedures: < and < Further nformaton s located at < and < HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 1

2 Outlne Motvaton and observatons Proposed double stage MU-MIMO Selected smulatons Remarks and conclusons HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 2

3 Motvaton & Observatons Motvaton and Observatons: - MU-MIMO potentally provde hgher throughput compared to SU- MIMO. - More precse channel quantzaton s requred for MU-MIMO compared to SU-MIMO. (Ths ndcates the necessty of a large codebook and large feedback overhead per MS) - Due to feedback channel capacty s lmted, hgh feedback overhead may prevent MU-MIMO from beng useful n real applcatons. - Only a few actve MSs are scheduled. It s wasteful to make every MS feed back channel state nformaton. - If only small porton of actve MSs feed back CSI to BS, large feedback overhead per MS does not mean large overall feedback overhead. HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 3

4 Double-stage MU-MIMO (2S-MU-MIMO) - Objectves: 1. Increase channel quantzaton accuracy by applyng large codebook( >10 bts). 2. Lmt the overall feedback overhead wthout sacrfcng system performance. 3. Mantan the attractve propertes of MU-MIMO technques. {Common Plot, feedback crtera for Stage I} {PF,PMI} f feedback crtera for Stage I s satsfed; Stage I {PMI correspondng to the largest PF, feedback crtera for Stage II} BS {PF,PMI} f feedback crtera for Stage II s satsfed {schedulng and precodng nformaton} MS Stage II HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 4

5 2S-MU-MIMO: Stage I (2-1) - Feedback crtera for Stage I: PF I Prorty factor of MS s no less than the predetermned threshold. PF I log 2(1 + SNR R = β α ) T where parameters α and β tune the farness of scheduler, s average throughput of MS and T s broadcasted threshold nformaton for Stage I. SNR s MU-MIMO precodng technque specfc. For example, for non-untary and untary precodng, are respectvely defned as follow: R Non-untary precodng Untary precodng SNR hw ' max σ = 2 2 w CB SINR = max q p hw hw ' 2 p 2 q ' 2 + σ I wp W W CB HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 5

6 2S-MU-MIMO: Stage I (2-2) MS If feedback crtera for Stage I s satsfed, MS pcks up a codeword n predefned codebook for Stage I, whch has mnmum chordal dstance from ts own channel state nformaton. The correspondng PF and PMI are fed back to BS; Otherwse, MS keeps dle; BS Compare all feedbacks. Broadcast PMI assocated wth the largest prorty factor and correspondng codeword s denoted by. w max I Broadcast feedback crtera for Stage II. HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 6

7 2S-MU-MIMO: Stage II (2-1) SINR - Feedback crtera for Stage II: 1. Refned prorty factor of MS s no less than the predetermned threshold; PF where s broadcasted threshold nformaton for Stage II. PF II II T II log 2(1 + SINR II = β R PF II α ) T 2. related CSI has not been feedback n Stage I. II s MU-MIMO precodng technque specfc. For example, when non-untary II precodng and untary precodng technques are used, can be obtan as follow SINR II Non-untary precodng h w SNR II = N h w w = h w H 2 max I max I ( w ( w max I max I h h H H ) ) Untary precodng SNR II h w = I + N H 2 w and w max I belong to same untary matrx codeword U I represent the nterference assocated wth U HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 7

8 2S-MU-MIMO: Stage II (2-2) MS - If feedback crtera for Stage II s satsfed, MS pcks up a codeword n predefned codebook for Stage II, whch has mnmum chordal dstance from ts own channel state nformaton. The correspondng PF and PMI are feed back to BS; - Otherwse, MS keeps dle; BS - Broadcast the scheduled MS nformaton - Determne precodng matrx based on all feedback (Stage I&II) HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 8

9 Smulatons 2-1 Sze of Feedback Overhead (bts) NO. of MS 12bts 2S-ZFBF Wth threshold 12 bts ZFBF wth threshold 2 12 bts ZFBF wth threshold 1 6 bts ZFBF wthout threshold Smulaton Setup: No. Tx Ant. = 4; No Rx Ant. = 1; No. Stream=2 Channel Model:..d. Raylegh fadng No. of ndependent channel realzatons: 3000 Code book type: Grassmannan Lne Packng (6 bts/12 bts) SNR = 10 db; α=1; β=0; HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 9

10 Smulatons 2-2 HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 10

11 Flowchart of 2S-MU-MIMO Tme slot N-1 Stage 2 Tme slot N Tme slot N+1 Tme slot N+2 Stage 1 Stage 2 BS broadcasts: FB crtera (Stage1&2) for slot N (optonal) PMI of max.pf n slot N-1. BS MS Stage 1 Stage 2 BS broadcasts: FB crtera (Stage1&2) for tme slot N+1(optonal) PMI of max.pf n slot N. BS broadcasts: Schedulng & precodng nformaton for tme slot N+1 based on all CSI feedback n Stage 1 of tme (N-1) and Stage 1&2 of tme N MS feedback {PF,PMI} f crtera for stage 1 and/or stage 2 are satsfed. Stage 1 Stage 2 BS broadcasts: Schedulng & precodng Informaton for tme slot N+2 based on all CSI feedback n Stage 1 of slot N and Stage 1&2 of slot N+1 MS feed back {PF,PMI} f crtera for stage 1and/or stage 2 are satsfed. HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 11

12 Compatblty of 2S-MU-MIMO 2S-MU-MIMO can be easly converted nto conventonal MU-MIMO by adjustng the threshold. (e.g. T=0 and TII=nf.) Tme slot N-1 Tme slot N Tme slot N+1 Tme slot N+2 Stage 2: No Feedback Stage 1: Full Feedback Stage 2: No Feedback Stage 1: Full Feedback Stage 2: No Feedback Stage 1: Full Feedback Stage 2: No Feedback Stage 1: Full Feedback HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 12

13 Conclusons: 1. Threshold based algorthm s smple and can sgnfcantly reduce feedback overhead, especally when number of MS s large. However, t s hard, f not mpossble, to be drectly mplemented when both prorty factor and PMI (for example: ZFBF) are nvolvedn schedulng. 2. Hghly accurate channel quantzaton s a must requrement for MU-MIMO. Smulatons suggest that large codebook (10+ bts) should be adopted for MU-MIMO, especally for uncorrelated MIMO. 3. When only a few MS feed back CSI to BS, large feedback overhead per MS would not mean large overall feedback overhead any more. Advantages of 2S-MU-MIMO 1. 2S-MU-MIMO makes threshold based algorthm work more effcently than t does n conventonal sngle stage MU-MIMO. 2. 2S-MU-MIMO adopts large codebook for each selected MS and, at the same tme, mantans low overall feedback overhead by mplementng threshold based algorthms. 3. 2S-MU-MIMO can be easly converted to conventonal MU-MIMO wth specal threshold settng. HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 13

14 Text proposal Insert the followng text n Chapter 11 (Physcal Layer): 11.Z1 Codebook desgn for DL MIMO 11.Z1.X1 Codebook for MU-MIMO To fulfll the potental of MU-MIMO over SU-MIMO, codebook of MU-MIMO shall be specfcally defned Z2 DL Control Channel 11.Z3.X3 Broadcastng Channel 11.Z3.X31 Broadcastng Channel for double-stage MU-MIMO Feedback crtera for both stage I and II should be broadcasted n perodcal and/or event drven manner.. In stage 1, BS shall broadcast schedulng nformaton made n stage 1 and correspondng PMI. In stage 2, BS shall broadcast updated schedulng nformaton made n stage 2 and precodng matrx nformaton 11.Z3.X4 Feedback Channel The CSI feedback channel should support CDM based multple access MS shall feed back CSI based on feedback crtera (stage 1 and 2) broadcasted by BS HUAWEI TECHNOLOGIES CO., LTD. Huawe Propretary Page 14