Improvement of Explicit Channel Feedback for MIMO-OFDM WLAN and Its Implementation

In this paper, explicit channel feedback for MIMO- OFDM systems is investigated. We first show that by exploiting the finite signal space of the channel impulse response, sub-sampling smoothing filter can be designed to achieve both feedback reduction and noise suppression. Secondly, to improve the distribution of the signal to be quantized, it is better to extract the common scaling term from the spectral block to utilize frequency correlation rather than to extract from the spatial block. Simulation results show that the proposed channel feedback scheme with the good sub-sampling smoothing filter brings substantial performance gain and helps the reduction of feedback overhead compared to feedback of the noisy CSI with the grouping strategy. We also discuss the implementation of the feedback encoding block to evaluate the hardware requirements given the feedback throughput constraint. The feedback reduction ratio is also shown to be essential to hardware saving and processing cycles. The proposed scheme has been implemented in 90nm CMOS technology with a maximum operating clock frequency of 160 MHz. We demonstrate the feasibility of the proposed feedback encoding scheme with good performance and efficient hardware.