On the Downlink Transmission Strategies for MIMO-OFDM Systems

Chengkang PAN
Yueming CAI
Youyun XU

Publication
IEICE TRANSACTIONS on Communications   Vol.E89-B    No.3    pp.837-844
Publication Date: 2006/03/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.3.837
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
Keyword: 
MIMO-OFDM,  dirty paper coding,  downlink channel,  beamforming,  

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Summary: 
This paper addresses the downlink transmission strategies with dynamic resource allocation for multiuser MIMO-OFDM systems. The ultimate objective is to maximize the sum rate capacity subject to average power constraints. Considering that the performance of conventional Orthogonal Frequency Division Multiple Access (OFDMA) is limited by users' exclusive use to subcarrier, while Dirty Paper Coding (DPC) is capable of supporting multiple users, we propose joint subcarrier and power allocation and precoding schemes based on OFDMA combined with DPC, which is called DPC-OFDMA. The analysis is considered in two stages with channel state information (CSI) at transmitter. The first stage applies water-filling method to address subcarriers allocation, in which users are allowable to share subcarriers. The second stage employs DPC combined with precoding to deal with simultaneous transmissions of the users sharing the same subcarriers. An efficient algorithm to choose the best possible ordering of users for DPC and the optimal precoding design of each user are also involved. To reduce the complexity for practice, two simplified strategies are proposed. One is called suboptimal DPC-OFDMA, where the number of users using the same subcarrier is restricted. Another employs beamforming (BF) at every subcarrier referred as BF-DPC-OFDMA. Simulation results show that the proposed simplified strategies can approach the optimal performance for most cases, and have higher spectral efficiency than conventional time-sharing OFDMA.