Self-interference cancellation for channel-unaware differential space-time two-way relay networks

Abstract

This paper considers a channel-unaware communication scenario in which two single-antenna nodes exchange information via multiple two-way relays, each with multiple-antennas. The nodes use differential signalling and the relays use a novel non-regenerative relaying scheme that enables self-interference to be completely eliminated. This scheme maximizes the asymptotic signal-to-interference-plus-noise-ratio of the nodes. A necessary and sufficient condition for proper operation of this scheme is derived for relays with even number of antennas; such a scheme does not exist for odd number of antennas. The effect of this relaying scheme on the pairwise error probability (PEP) and the diversity order is investigated. More precisely, when self-interference is not cancelled perfectly, we show that a lower bound on the PEP approaches a non-zero constant at asymptotically high signal-to-noise ratios (SNRs), indicating a zero diversity order and an asymptotic error floor. Next, we show that, when self-interference is cancelled perfectly, the error floor vanishes and an upper bound on the PEP approaches zero at high SNRs. The diversity order in this case is shown to depend only on the number of relays, but not on the number of antennas. It is also shown that the diversity order converges to a constant value monotonically with the number of relay antennas. This suggests that increasing the number of relays is more beneficial than increasing the number of antennas of each relay.