Resource allocation between feedback and forward links: Impact on system performance and CSI

The performance of multiple-input multiple-output (MIMO) communication systems is greatly increased by exploiting channel state information (CSI) for the transmitter design. In systems where channel reciprocity does not hold, a limited feedback link can be used to send the CSI from the receiver to the transmitter. However, the resources for the feedback link come at the expense of resources for the forward link. This paper studies the trade-off between the accuracy of the feedback information and system performance. The optimum resource allocation is presented as the solution to an analytic equation for different beamforming transmission schemes to maximize the worst-case performance, in a framework including both time-division duplexing (TDD) and frequency-division duplexing (FDD).