Downlink Channel Tracking for FDD Large-Scale Antenna Systems

This paper tackles the problem of channel state information acquisition in mobile frequency-division-duplex largescale antenna systems and proposes a novel low-complexity low-overhead method to track time-varying channels. Given the spatial reciprocity between uplink and downlink, the frequency-independent parameters are tracked from the uplink, greatly reducing the training and feedback overhead in the downlink. The uplink tracking method consists of two major modules. The first detection module works at the initial time instance to accurately estimate parameters by a detailed algorithm. Then, the second tracking module works at the subsequent instances to track the changes by utilizing a low-overhead algorithm, as well as, the parameters obtained at the previous instance. A simplified dictionary is further designed to decrease the computational complexity of the tracking module. Numerical results demonstrate that the proposed tracking method can successfully detect the newly occurred and disappeared paths, and accurately trace the changes of the time-varying channel.