Uplink-Aided Downlink Channel Estimation for a High-Mobility Massive MIMO-OTFS System

Abstract

The massive multi-input-multi-output (MIMO) system will greatly enhance the performance of the next-generation wireless communications for many applications e.g., high-mobility users. The orthogonal time frequency space (OTFS) is a promising technique for high-mobility massive MIMO use cases. However, the MIMO-OTFS system requires accurate downlink channel information for optimal performance. This paper studies an uplink-aided downlink channel estimation scheme targeting high-mobility user scenario based on a frequency division duplex massive MIMO-OTFS system. Most of the existing work over-looks the change in the delay, Doppler, and angle domain during a channel estimation process due to high mobility. In this work, we analyze the reciprocity between an uplink and a downlink channel and derive the estimation error due to the latency in processing the uplink channel estimates. Simulation results demonstrate that an uplink channel may change significantly in a high-mobility massive MIMO-OTFS system, given a reasonably small amount of processing latency. Such a change will lead to high error in downlink channel estimation. With the proof of concept, our future work will focus on refining the channel estimation framework with a reduction of the processing latency.