SUMMARYSeveral multiple-input multiple-output (MIMO) techniques have been proposed for 3GPP WCDMA/HSDPA systems and several performance evaluation for the comparison purpose are in progress. Most MIMO candidates in HSDPA have been generally designed for pointto-point communication, which means that a single-user throughput is of their major concern. However, multiple users and user scheduling need to be considered in wireless packet transmission, so as to maximize system throughput. In this paper we propose an effective user scheduling technique in both space and time domains that offers three main benefits, which are the spatial-beamforming, uplink feedback signaling, and advanced receivers. Furthermore, user scheduling is combined with modified successive interference cancellation (SIC) reception, which allocates all transmit antennas to the best user with SIC or each transmit antenna to different users with minimum mean squared-error (MMSE). Simulation results show that the proposed scheme has higher user diversity gain than other MIMO candidates in terms of achievable throughput.

SUMMARYRecently, a number of techniques have been introduced to exploit multiuser diversity of a wireless multiple-input multiple-output (MIMO) broadcast channel (BC) that consists of a base station with t transmit antennas and K users with multiple antennas. However, prior works have ignored the rate overhead associated with feedback of MIMO BC channel state information at transmitter (CSIT), which is roughly K times larger than single-user MIMO CSIT (i.e., it is O(tr) where r = K k=1 r k and r k is the number of antennas at the kth user). Considering the amount of feedback signaling, quantization is a necessity for effective feedback transmission as a form of partial CSIT. In this paper, we propose the greedy multi-channel selection diversity (greedy MCSD) scheme based on block MMSE QR decomposition with dirty paper coding (block MMSE-DP), where partial CSIT is almost sufficient. The sum-rate performance of our novel scheme approaches extremely close to the sum capacity of MIMO BC as the number of users increases, whereas the feedback overhead is reduced by a factor of 2t 3 /L(t 2 −t), in which L is the number of active channel vectors. Simulation results validate the expectation from the analysis. In addition, the proposed scheme is shown to be appropriate for reconfigurable implementation. key words: MIMO, broadcast channel (BC), adaptive precoding, SDR implementation

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