Channel Extrapolation in FDD Massive MIMO: Theoretical Analysis and Numerical Validation
Channel Extrapolation in FDD Massive MIMO: Theoretical Analysis and Numerical Validation
复制标题
DOI：
10.1109/globecom38437.2019.9013411
复制
发表时间：
2019-02
期刊：
影响因子：
--
通讯作者：
François Rottenberg;Rui Wang;Jianzhong Zhang;A. Molisch
中科院分区：
文献类型：
--
作者：
François Rottenberg;Rui Wang;Jianzhong Zhang;A. Molisch
大规模MIMO系统的下行信道估计在频分双工（FDD）模式下会产生很大的开销，因为训练量通常随发射天线数量的增加而增加。相反，使用从测量的上行链路估计到下行链路频带的信道外推完全消除了这种开销。本文研究了信道外推在频率上的理论极限。我们强调了基于高分辨率信道估计的外推的优势。推导了外推信道均方误差（MSE）的下界。还提出了一个简化的LB，给出了在实践中可以预期的信噪比增益和外推范围的物理直觉。简化LB的有效性依赖于路径分离良好的假设。信噪比增益随接收天线数线性增加，外推性能损失随频率与训练带宽之比二次增长。使用3GPP信道模型对理论LB进行了数值评估，并表明可以通过实际的高分辨率参数提取算法达到LB。我们的研究结果表明，在SISO系统中，外推范围有很强的局限性，而在多天线设置中，由于路径在延迟角域更容易分离，可以获得更有希望的结果。
Downlink channel estimation in massive MIMO systems is well known to generate a large overhead in frequency division duplex (FDD) mode as the amount of training generally scales with the number of transmit antennas. Using instead an extrapolation of the channel from the measured uplink estimates to the downlink frequency band completely removes this overhead. In this paper, we investigate the theoretical limits of channel extrapolation in frequency. We highlight the advantage of basing the extrapolation on high-resolution channel estimation. A lower bound (LB) on the mean squared error (MSE) of the extrapolated channel is derived. A simplified LB is also proposed, giving physical intuition on the SNR gain and extrapolation range that can be expected in practice. The validity of the simplified LB relies on the assumption that the paths are well separated. The SNR gain then linearly improves with the number of receive antennas while the extrapolation performance penalty quadratically scales with the ratio of the frequency and the training bandwidth. The theoretical LB is numerically evaluated using a 3GPP channel model and we show that the LB can be reached by practical high-resolution parameter extraction algorithms. Our results show that there are strong limitations on the extrapolation range than can be expected in SISO systems while much more promising results can be obtained in the multiple-antenna setting as the paths can be more easily separated in the delay-angle domain.