Channel prediction and feedback in multiuser broadcast channels

Abstract

Multiuser linear precoding requires channel state information (CSI) at the transmitter. In the absence of channel reciprocity between the uplink and downlink, a feedback mechanism must be designed to communicate CSI estimates from the mobile receivers to the transmitter. Limiting the total feedback rate is an important design goal for multiuser multiple-input, multiple-output systems, as the feedback overhead can potentially consume a large percentage of system resources, especially when the total number of antennas is large. In this paper, we focus on the challenges of feedback delay and reducing feedback rate; we predict N-frames-ahead, based on the one-step Kalman predictor, and derive a theoretical expression for the prediction mean squared error (MSE). We present simulation results that illustrate a tradeoff between prediction MSE and computational complexity, and also demonstrate situations where adaptive delta modulation (ADM) can be used to exploit temporal redundancy and reduce the required feedback rate.