多入多出(MIMO)系统中的可变速率多用户分集技术

提出一种在MIMO系统中采用自适应调制实现可变速率多用户分集的方案。这种方案在仅需反馈子信道信噪比的条件下，最大化系统的总比特率。在发射端利用随机波束成形矩阵对发射信号进行波束成形，并根据‘灌水原理’对不同天线的发射信号进行功率分配；接受端对接收信号进行相应的线性处理后，估计出子信道的有效信噪比并将其反馈回发射端。发射端根据反馈的信噪比，采用比例调度算法选出期望用户。最后，在满足一定误码率的条件下，对期望用户的子信道进行自适应调制。仿真结果表明，当小区内的用户数足够多时，所提出的方案获得的系统吞吐量将收敛于在发射端使用特征波束成形矩阵的吞吐量。

Variable-rate Multiuser Diversity in MIMO Systems

An adaptive modulation technique for multiuser MIMO systems with multiuser diversity is proposed. This technique maximizes the sum of the instantaneous bit rate under a target BER constraint by feeding back sub-channel SNRs only. By generating a random transmit beamforming matrix with water-filling configuration, each user estimates and feeds back the effective SNRs for its sub-channels. With each user's sub-channel SNRs, the transmitter then schedules the transmission to one particular selected with proportional fair scheduling algorithm. Finally, adaptive modulation is applied to each sub-channel of the selected user based on the BER constraint. The simulation results show that the throughput of proposed method converges to that of eigen-beamforming when the number of users in a cell is large.