Unquantized and uncoded channel state information feedback on wireless channels [mobile radio applications]

We propose a channel state information (CSI) feedback scheme based on unquantized and uncoded (UQ-UC) transmission. We consider a system where a mobile terminal obtains the downlink CSI and feeds it back to the base station using an uplink feedback channel. If the downlink channel is an independent Rayleigh fading channel, then the CSI may be viewed as an output of a complex independent identically distributed Gaussian source. Further, if the uplink feedback channel is AWGN, it can be shown that that UQ-UC CSI transmission (that incurs zero delay) is optimal in that it achieves the same MMSE distortion as a scheme that optimally (in the Shannon sense) quantizes and encodes the CSI while theoretically incurring infinite delay. Since the UQ-UC transmission is suboptimal on correlated wireless channels, we propose a simple linear CSI feedback receiver that can be used to improve the performance while still retaining the attractive zero-delay feature. We provide bounds on the performance of the UQ-UC CSI feedback. Furthermore, we explore its application and performance in multiple antenna multiuser wireless systems.