Impact of Limited Feedback on the Performance of MIMO Macrodiversity Transmission

In this paper, we study the performance of the multiple-input multiple-output macrodiversity transmission with limited feedback. The downlink scenario, where multiple transmitters serve the user simultaneously, is considered. We find it necessary to modify the model of the quantized channel by Jinal (2006) such that the phase ambiguity in the vector quantization procedure can be characterized. Using the modified model, we show that the conventional limited feedback methods cannot obtain the macrodiversity gain even when the size of the codebook is asymptotically large, and that the macrodiversity gain can be attained by adding only one bit of phase feedback. Our analysis can apply to both random vector quantization and any fixed codebook setup, and is verified by the simulation results.