  The full-duplex (FD) communication can achieve higher spectrum efficiency
than conventional half-duplex (HD) communication; however, self-interference
(SI) is the key hurdle. This paper is the first work to propose the intelligent
Omni surface (IOS)-assisted FD multi-input single-output (MISO) FD
communication systems to mitigate SI, which solves the frequency-selectivity
issue. In particular, two types of IOS are proposed, energy splitting (ES)-IOS
and mode switching (MS)-IOS. We aim to maximize data rate and minimize SI power
by optimizing the beamforming vectors, amplitudes and phase shifts for the
ES-IOS and the mode selection and phase shifts for the MS-IOS. However, the
formulated problems are non-convex and challenging to tackle directly. Thus, we
design alternative optimization algorithms to solve the problems iteratively.
Specifically, the quadratic constraint quadratic programming (QCQP) is employed
for the beamforming optimizations, amplitudes and phase shifts optimizations
for the ES-IOS and phase shifts optimizations for the MS-IOS. Nevertheless, the
binary variables of the MS-IOS render the mode selection optimization
intractable, and then we resort to semidefinite relaxation (SDR) and Gaussian
randomization procedure to solve it. Simulation results validate the proposed
algorithms' efficacy and show the effectiveness of both the IOSs in mitigating
SI compared to the case without an IOS.
