1. Joonil Choi, Gil Kim, Junghoon Suh, Junmo Kim, Sungjin Kim Samsung Electronics +82-31-280-9638 joon.il.choi@samsung.com ABSTRACT: Under the limited feedback for ZF-BF MU-MIMO system, the user sum-rate performance gets saturated even as SINR increases. We introduced ZF-BF with user cooperation systems to compensate performance loss caused by limited feedback. In this contribution, we show user clustering algorithm in detail. TITLE: Zeroforcing Beamforming with User Cooperation - Clustering TSG-C RECOMMENDATION: FYI Samsung Electronics grants a free, irrevocable license to 3GPP2 and its Organizational Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner's name any Organizational Partner's standards publication even though it may include all or portions of this contribution; and at the Organizational Partner's sole discretion to permit others to reproduce in whole or in part such contribution or the resulting Organizational Partner's standards publication. Samsung Electronics is also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution. This document has been prepared by Samsung Electronics to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on Samsung Electronics. Samsung Electronics specifically reserves the right to amend or modify the material contained herein and to any intellectual property of Samsung Electronics other than provided in the copyright statement above. DATE: Dec. 03, 2007 SOURCE: C00-20071203-008

2. Action Items from previous meeting  User clustering problem Short distance between users in the cluster High probability of large channel correlations among users Performance loss in ZF-BF systems How to consider the channel correlations among users while clustering?  Simulation results

3. User Clustering Algorithm  Deploy infrastructure relays in the cell [1] Relays become cluster header Relay schedules users in the cluster according to the CDIs –SUS (Semi-orthogonal User Selection), etc.. Relay feedbacks CDIs of selected users to BS Fig. 1. Two stage feedback scheme (a) RS scheduling(b) RS feedback

4. User Clustering Algorithm  Criterion of clustering Explicit clustering Distance based clustering CQI based clustering Implicit clustering Threshold based clustering –No exact matching between cluster header and users –Cluster header schedules the users only if the strength of user’s feedback signal exceeds certain threshold

5. User Clustering Algorithm  Signaling chart BS broadcasts pilot signals to MSs MSs estimate their channel states and feedback to RS RS schedules users according to CDIs RS feedbacks CDIs of selected users to BS BS generates ZF precoding matrix BS broadcasts precoded signals Users cooperate with each other

6. User Clustering Algorithm  Main effects of algorithm User clustering Only users closed to relay will become cluster Channel correlation Only users which have low channel correlation will be selected by relay Good cooperation channel Good performance in ZF-BF

7. Simulation Results  Simulation setup i.i.d Rayleigh fading channel between BS-MS AWGN channel with noise variance No among MSs [2,3] # of tx and rx antenna : Nt=4, Nr=1 # of users in a cluster : 4 (no scheduling is needed)

8. Simulation Results

9. References  [1] P. Kuo, Junghoon Suh, and Sungjin Kim, “A Feedback Scheme for ZFBF-Based MIMO Broadcast Systems with Infrastructure Relay Stations,” submitted for WCNC 2008.  [2] N. Jindal, U. Mitra, and A. Goldsmith, “Capacity of ad-hoc networks with node cooperation,” in Proc. IEEE ISIT, Chicago, IL, USA, June 2004, p. 271.  [3] C. T. K. Ng, N. Jindal, A. J. Goldsmith, and U. Mitra, “Capacity gain from two-transmitter and two-receiver cooperation,” accepted for publication in IEEE Trans. Info. Theory.