Time-Reversal Space Division Multiple Access over Multi-path Channels

A novel concept of time-reversal division multiple access (TRDMA) is proposed in [1] as a low-complexity, energy-efficient wireless multi-user access method. In this paper, we first generalize the work in [1] as a pre-filtering based space division multiple access (SDMA) communication system, where each user’s signature waveform is derived from the information of CIRs between basestation (BS) and location-specific multiple mobile stations (MS). We develop two pre-filtering schemes: one is based on the scheme as proposed in [1], we refer it as time-reversal matched filter (TRMF). The benefit of the TRMF is to fully collect energy at the sampling instant of the intended MS (spatial and temporal focusing). The second pre-filter, which is referred to as zero-forcing pre-filter (ZFPF), is derived to meet the zero-forcing criterion such that multiuser interference (MUI) is completely eliminated. However, since the uplink CIR is generally different from the downlink CIR, we present extensive analysis on the performance degradation of the ZFPF caused by this mismatched effect. Furthermore, to improve the robustness to mismatch, we propose a simple yet effective robust zero-forcing pre-filter (R-ZFPF). We investigate and compare the performances of both schemes under various scenarios in terms of power consumption and averaged signal-to-interference-plus-noise power ratio (SINR). It is shown in both analytical and simulation results that satisfying performance can be achieved by the proposed pre-filtering system. Moreover, we demonstrate that the proposed R-ZFPF comprehensively improves the performance in mismatch condition.