Equalized Time Reversal Beamforming for Indoor Wireless Communications

Abstract

One of the technologies with potential to provide advanced beamforming capabilities for future indoor wireless communications is time-reversal (TR). By using the channel impulse response as a pre-filter at the transmitter, TR provides automatic spatial focusing of the signal at the receiver. In this paper we present two contributions on single-user indoor wideband TR systems. First, we provide a novel analysis of a baseband time-reversal (TR) beamforming system using two propagation models commonly used in indoor wireless communications. We derive a new closed-form approximation for the inter-symbol interference (ISI) power in such scenarios, which leads to a more accurate estimation of the probability of bit error compared to previous works. We define performance parameters for the spatial focusing and time compression properties of TR beamforming and find closed-form approximations for them. We use this parameters to compare TR performance under different propagation conditions and channel models. Second, we propose an Equalized TR (ETR) technique that mitigates the ISI of conventional TR. ETR uses a zero-forcing pre-equalizer at the transmitter in cascade configuration with the TR pre-filter. We derive theoretical performance bounds for ETR and show that it greatly enhances the BER performance of conventional TR with minimal impact to its beamforming capability. By means of numerical simulations, we verify our closed-form approximations and show that the proposed ETR technique outperforms conventional TR with respect to the BER under any SNR.