Sum-Rate Reduction due to Limited Feedback in MIMO Broadcast Channels with Block-Diagonalization

There is an implicit loss in data throughput due to channel state information (CSI) feedback for a multiple- input multiple-output (MIMO) system. This loss has usually not been considered in conventional sum-rate studies. Recently, a duplex model was introduced for a single-user point-to-point MIMO system to calculate the rate loss due to the feedback. This paper extends the duplex system model for a multi-user MIMO downlink with block diagonalization. In other words, this paper will determine the sum-rate loss and show what is the trade-off between user data and CSI overhead rate. In addition, effects of quantization error at the receiver and noisy feedback upon the loss in net system capacity are presented. Finally, simulation results verify the impact of feedback on the sum-rate for multiple user multi-antenna wireless systems.