Half-Duplex or Full-Duplex Communications: A Capacity Analysis under Self-Interference

In-band full-duplex (FD) communication provides a promising alternative to half-duplex (HD) for wireless systems, due to increased spectral efficiency and capacity. In this paper, HD and FD radio implementations of two way, two hop and two way two hop communication are compared in terms of degrees of freedom (DoF) and achievable rate, under a realistic residual self-interference (SI) model. DoF analysis is carried out for each communication scenario, and achievable rates are computed at finite SNR levels for HD, antenna conserved (AC) and RF chain conserved (RC) FD radio implementations. The DoF analysis indicates that for the two way channel, AC FD performs strictly below HD with imperfect SI cancellation, and RC FD DoF trade-off is superior, when the SI can be sufficiently cancelled. For the two hop channel, FD is better when the relay has large number of antennas and enough SI cancellation. For the two way two hop channel, when both nodes require similar throughput, HD is generally better than FD; for asymmetric traffic, FD can achieve better rate pairs than HD, provided the relay has sufficient number of antennas and SI suppression. Computed achievable rates for each scenario indicate that DoF results also extend to finite SNR.