A comparison of linear and non-linear transmitter and receiver antenna array processing for interference nulling and diversity with non-zero CSI feedback delay

The performance of receiver, transmitter, and joint transmitter/receiver antenna array processing for interference nulling and diversity over fading radio links are compared and contrasted in this paper. Specific examples of linear and non-linear algorithms are considered in this context. To perform transmitter processing, a priori knowledge of the radio propagation channel is required at the transmitter. This is typically achieved by the provision of a feedback loop that supplies the transmitter with the channel state information (CSI). The impact on transmitter processing of non-zero delays in the CSI feedback loop is quantified in this paper. It is assumed that channel estimation is performed with perfect accuracy at the receiver, and that the feedback loop is error-free. It is shown that while transmitter processing out performs receiver processing at low relative Doppler frequencies, its performance degrades rapidly when the CSI feedback delay is greater than 2% of the channel coherence time. The results presented can be readily interpreted in the context of multi-user uplink and downlink in cellular systems, or collaborative signal processing among base stations.