This paper investigates user scheduling in multi-user MIMO broadcast channel. We propose a leakagebased user scheduling scheme, in which a user＇s leakage power to other users is an important factor to determine whether the user should be selected. The accuracy of closed-form solution of SLNR （signal to leakage plus noise ratio） makes the proposed scheme outperform the traditional scheduling method based on SlNR （signal to interference plus noise ratio）. The proposed algorithms can work in case of perfect or limited feedback of CSI （channel state information） at transmitter, and the advantage is verified with numerical results. A tradeoff relation among feedback bits number, active user number and transmit/receive antennas number is analyzed, which serves as a system design guideline.
OFDM-CDMA is an attractive technique for broadband wireless communication. However, the high peakto-average power ratio （PAPR） of the downlink signals, generated from multiple spread codes, remains a serious problem. In this paper, a low-complexity multiple signal representation （MSR） scheme is proposed to control the PAPR problem in downlink OFDM-CDMA systems. The proposed scheme generates multiple candidate signals by a novel user grouping scheme, which is without distortion and can provide more PAPR reduction than the conventional MSR schemes, such as partial transmit sequence （PTS） and selective mapping （SLM）. Furthermore, a low-complexity processing structure is developed using a novel joint spreading and inverse fast Fourier transform （S-IFFT） to simplify the generation of multiple candidate signals. Complexity analysis and numerical results show that the OFDM-CDMA systems employing the proposed scheme have better tradeoff between PAPR reduction and computational complexity, compared with the conventional MSR schemes.
