Joint Nullspace Projection-Based Interference Mitigation for Full-Duplex Relay-Assisted Multicell Networks

Full-duplex (FD) relaying is more spectrally efficient compared to its counterpart, conventional half-duplex (HD) relaying, since it allows simultaneous transmission and reception in the same frequency channel. Working in FD relaying scheme results in relay self-interference (SI) signal that degrades the system performance. Furthermore, in a multicell scenario, the FD relay is also subject to interrelay interference (IRI) and relay-to-destination interference (RDI) coming from co-channel relays in adjacent cells. Conventionally, zero-forcing (ZF) beamforming (BF) is adopted to mitigate either the SI, IRI, or RDI but not all of them simultaneously. In this article, beamforming (BF) matrices at the multiple-input-multiple-output (MIMO) relays are designed jointly to mitigate the SI, IRI, and RDI signals based on channel alignment and nullspace projection. In addition, joint power allocation for the source and relay is performed for maximizing the system performance in terms of ergodic capacity. Numerical results demonstrate and verify that the proposed scheme can achieve better outage probability and ergodic capacity compared to baseline schemes. Our findings reveal that MIMO FD relaying significantly improves the system performance compared to its counterpart conventional MIMO HD relaying.