Where to predict the channel for cooperative multi-cell transmission over correlated subcarriers?

In this work we discuss the aspect of channel prediction for cooperative multi-cell downlink transmission, where channel state information (CSI) of all users need to be available at all cooperating base stations (BSs). We assume that users feed CSI back to its local BS which forwards it to the other cooperating BSs using backhaul connections. In case of feedback and backhaul latency, CSI of a single user equipment (UE) is affected by multiple delays. Compensating for the delay via channel prediction raises the question of where to place the predictor. Prediction at the UE before the channel observations are quantized allows to compensate only for a single delay. Prediction at the BS side keeps the flexibility to compensate for the actual delay at each base station, at the drawback that less accurate information is available due to feedback quantization. This paper extends previous work from a transmission over uncorrelated subcarriers to the more realistic transmission over correlated subcarriers. Previously, we have shown that prediction before and after quantization results in the same channel uncertainty. As a consequence, prediction at the BS is always preferable if multiple delays need to be compensated. This paper shows that this result remains valid also for correlated subcarriers.