Sum-Rate Distortion in MIMO Broadcast Channels with Irregular Limited Feedback

Recent research in multiuser MIMO systems has focused on providing partial channel state information (CSI) at the transmitter as an alternative to full CSI in order to reduce overhead. However, there is an implicit loss in data throughput even due to partial CSI feedback which is not included in conventional sum-rate computations. We introduce a sum-rate distortion model including the implicit loss for a multiuser MIMO downlink with block diagonalization. A distortion function is subsequently presented which accounts for quantization error at the receiver, feedback latency due to non-homogenous receiver channel coherence times and the loss in net capacity due to feedback overhead. This system model is used to derive bounds on the amount of feedback that can be supported under various antenna, channel and signal-to-noise ratio scenarios. Simulation results are presented to show the impact of feedback on the sum- rate for multi-antenna wireless systems with multiple users.