  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) under a realistic residual self-interference (SI) model. DoF analysis is
carried out for each communication scenario for HD, antenna conserved (AC) and
RF chain conserved (RC) FD radio implementations. The DoF analysis indicates
that for the two way channel, the achievable AC FD with imperfect SI
cancellation performs strictly below HD, 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,
the achievable DoF pairs for FD do not outperform HD. FD still can achieve
better DoF pairs than HD, provided the relay has sufficient number of antennas
and SI suppression.
