Evaluation of low rate channel feedback schemes for MIMO systems

Based on measured MIMO channel impulse responses, this paper investigates and compares low rate channel feedback techniques and their influence on the throughput. The main focus is on codebook based precoding techniques which only require a few bits in the feedback to achieve near optimal performance. Three types of precoding schemes are compared. The first technique uses a combination of both long term and low rate short term CSI at the transmitter, whereas the second technique uses only the low rate short term CSI at the transmitter. These first two techniques have been proposed by Tung et al. The third technique is the closed loop spatial multiplexing mode proposed in LTE Release 8. All these techniques are here evaluated for measured 4×2 MIMO channels. The results indicate the benefits of the proposed techniques (i.e. technique one and two) over the LTE codebook.