Equalized Time Reversal Beamforming for Indoor Wireless Communications

The purpose of this paper is twofold. First, we provide a novel analysis of a baseband timereversal (TR) beamforming system using two propagation models commonly used in indoor wireless communications. This analysis applies to pico and femtocells in conventional wideband systems such as WiFi networks. We derive a new closed-form approximation for the inter-symbol interference (ISI) power in such scenarios without using rate back-off, 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. Second, we propose an Equalized TR (ETR) technique that mitigates the ISI of conventional TR. ETR uses a ZF 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 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, even though the total received power is greater for conventional TR. Index Terms Time-reversal, beamforming, bit error probability, space-time focusing. This work has been supported in part by the Ohio Supercomputer Center (OSC) under grants PAS-0061 and PAS-0110, and by a Fulbright Colombia Fellowship. The authors are with the ElectroScience Laboratory, Department of Electrical and Computer Engineering, The Ohio State University, 1330 Kinnear Rd., Columbus, OH 43212 USA, (614) 292-6993 (e-mail: {viteri.5,teixeira.5}@osu.edu). C. Viteri-Mera is also with the Department of Electronics Engineering, Univeridad de Nariño, Pasto, Colombia. DRAFT 2