Two-path successive relaying with threshold-based opportunistic zero-forcing beamforming

Two-path successive relaying scheme is designed to restore the spectral inefficiency due to a half-duplex constraint. When not operating in orthogonal channels, the relay pair used in successive relaying scheme interferes each other. This inter-relay interference degrades the outage performance of the successive relaying scheme significantly. So, the zero forcing beamforming (ZFB) has been proposed to remove the inter-relay interference. But using ZFB (U-ZFB) does not always guarantee better performance than not using ZFB (N-ZFB) due to a loss of diversity gain. In this paper, we propose the two-path successive relaying with threshold-based opportunistic ZFB where only inter-relay interference channel information is available and switching-decision is made by comparing the inter-relay interference with a threshold to be determined. We provide optimal thresholds at each relay. Numerical results show that the outage probability of the proposed two-path successive relaying with threshold-based opportunistic ZFB is better than the outage probabilities of U-ZFB only and N-ZFB only and give insights.