Achieving Massive MIMO Gains in FDD Downlink Systems Without CSI Feedback

The need for channel state information (CSIT) is crucial for the improved spectral efficiency of massive multiple-input multiple-output (MIMO) systems. In FDD massive MIMO systems, CSIT is obtained through downlink channel estimation and user feedback, but this process becomes challenging as the number of antennas increases, resulting in reduced spectral efficiency. In this paper, we show that even in FDD systems, the TDD massive MIMO gain is attainable without explicit CSIT training and feedback, by using UL pilots. We present a novel DL channel reconstruction method from uplink pilots and a robust downlink precoding technique, proving that the FDD massive MIMO gains are achievable without CSI training and feedback. Our results are verified through system-level simulations.