OFDMA系统中多波束机会波束成形的门限反馈

多用户MIMO-OFDMA是未来无线通信的重要技术体制. 当MIMO-OFDMA系统利用全部用户获取多用户分集时，系统反馈量很大. 为了解决这一问题，提出一种基于门限反馈实现部分多用户分集的多波束机会波束成形算法. 用户计算每个子载波上各波束的接收信干比(signal to interference-plus-noise ratio, SINR)，把SINR 超过某一门限的信息反馈给基站. 以预设的平均资源利用率为目标，给出确定最佳门限值的方案，定量分析门限反馈算法的反馈量，证明其反馈总量随用户数目的增大而趋于一个较小的恒定值. 仿真结果表明，通过预设目标平均资源利用率可有效确定门限值，能在吞吐量性能损失很小的情况下显著降低系统的反馈开销.

Threshold-Based Feedback Scheme for Multi-beam Opportunistic Beamforming in OFDMA System

Multi-user MIMO-OFDMA is an important technology in the future wireless communications. In MIMO-OFDMA system, a large amount of feedback information has to be used to achieve multiuser diversity when all users are exploited. To deal with the problem, a multi-beam opportunistic beamforming scheme is proposed, in which partial multiuser diversity is achieved by setting a feedback threshold. Each user calculates the received signal to interference-plus-noise ratio (SINR) of each beam at individual subcarriers. The SINR value is transmitted to the base station only when it is larger than the threshold. The threshold is optimized to guarantee a target average resource utilization rate. The amount of feedback in the proposed scheme is quantified, and it is proved that feedback is limited to a fixed level. Simulation results indicate that optimal threshold can be determined effectively from a predefined resource utilization rate. Also, the feedback load can be reduced significantly with little capacity loss.