Channel prediction and feedback in multiuser broadcast channels

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.