Performance of a Multiuser Downlink System Applying Thresholding Feedback with Imperfect Channel Information

We consider a multiuser downlink system where the base station (BS) only has imperfect channel quality information (CQI) due to both feedback delay and estimation error at the receiver. Using coherent detection, the signal portion due to delay is accommodated while the estimation error is random and can be considered as noise. A thresholding feedback scheme is used to reduce the overall amount of feedback which is typically set by the system. Then, a fixed rate and a variable rate transmission scheme are analyzed which are then optimized to obtain the highest average system goodput. By using variable rate with optimized parameters, system goodput increases significantly in comparison with the fixed rate strategy. The feedback delay is shown to affect system performance with the severity increasing over time. Finally, the match between analysis and simulation are verified by the experiments.