Robust pre‐filtering based space division multiple access over multi‐path channels

Abstract

A novel concept of time reversal division multiple access (TRDMA) is proposed recently as a low complexity, energy efficient wireless multi‐user access method. In this paper, we first generalize TRDMA as a pre‐filtering based space division multiple access communication system, where each user's signature waveform is derived from the information of channel impulse responses (CIRs) between basestation and location specific multiple mobile stations. We develop two pre‐filtering schemes: one is referred to as time reversal matched filter. The benefit of the time reversal matched filter is to fully collect energy at the sampling instant of the intended mobile station (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 multi‐user interference is completely eliminated. However, because 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 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. 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 robust‐ZFPF has improved the performance in mismatched condition. Copyright © 2013 John Wiley & Sons, Ltd.

A robust and distributed design for coordinated downlink beamforming for secure MISO interference channels

“…Unfortunately, such an assumption generally does not hold in practice for various reasons, for example, quantization errors, the limited length of training sequence, time varying nature of wireless channels and unexpected noisy environment. Therefore, perfect channel estimation is impossible, and channel estimation errors should be considered . As channel estimation errors are always inevitable and drastically degrade system performance, they should be taken into account in the beamforming design process to mitigate the negative effects on the system performance.…”