基于子带预编码的多点协作OFDM系统定时对齐

Timing alignment for subband precoding based coordinated multi-point OFDM systems

在正交频分复用(orthogonal frequency division multiplexing,OFDM)的多点协作(coordinated multi-point,CoMP)系统中,以子带为单位进行信道状态信息的反馈和预编码处理,可以有效降低反馈开销。但当参与协作的不同基站到达用户存在传输时延差时,会导致用户经历的等效信道多径时延扩大,增大子带内信道的起伏,进一步增大逐子带信道反馈的误差。该文分析了基站传输时延差对信道反馈误差的影响,提出了基于传输时延差长期统计值反馈的频域相位旋转法进行定时对齐,来改善传输时延差对逐子带处理OFDM-CoMP系统性能的影响。仿真结果表明:该方法只需增加较少的运算量及反馈信息即可获得明显的系统和速率增益,适用于实际OFDM-CoMP系统。

In orthogonal frequency division multiplexing （OFDM） based coordinated multi-point （CoMP） systems, per subband processing for channel state information （CSI） feedback and precoding is an efficient method to reduce feedback overhead. However, when the transmissions from cooperative base stations to certain users suffer different delays, the users will experience larger equivalent multi-path delays, which will further increase the error in the CSI feedback in a subband. This study analyzes the impact of different delays from cooperative base stations on the CSI feedback error. Long-term statistics on the differences in the transmission delays are used to develop a phase rotation approach in the frequency domain for timing alignment to reduce the impact of the different delays. Simulations show that this method achieves a significant system sum rate gain with only a few additional computations and a little feedback information, so it is suitable for practical OFDM based CoMP systems.