Where to Predict the Channel in Cooperative Cellular Networks with Backhaul Delays?

Abstract:
This work focusses on the joint downlink transmission from multiple base stations (BSs) to multiple users using centralized or distributed linear precoding. This setup suffers from imperfect BS side channel state information (CSI), caused, e.g., by noisy pilot reception, feedback quantization or delays. Forwarding CSI feedback between BSs over a latency constraint backhaul adds additional delays. Distributed precoding causes CSI to be differently outdated at different BSs. These multiple delays raise the fundamental question, where to implement the channel prediction. At the user side only one specific delay can be compensated. In contrast, prediction at the BS side may account for multiple delays at the cost of less accurate CSI due to feedback quantization. This work shows that both, prediction before and after quantization, result in the same channel uncertainty motivating that prediction at the base station is preferable for distributed precoding.