This paper proposes a wideband self-interference cancellation scheme for beyond 5G full-duplex communications. Especially, optical components are explored to achieve efficient wideband RF cancellation. We use a fiber array to form multiple independent tunable delay lines for a low-complexity and low-cost design. The processing and implementation details are given, and its performance is evaluated with practical concerns (e.g., inaccurate hardware measurements and tuning speed). Then, a nonlinear digital canceller is utilised to generate a replicate of the received baseband digitised self-interference signal along with the nonlinear effects induced by the power amplifier. The relationship between RF and digital cancellation is explored, and an appropriate RF cancellation amount is given based on this. Simulation results illustrate that more than 30 dB of RF cancellation can be achieved within 400 MHz bandwidth centred at 2.5 GHz, and the residual self-interference is brought to close the noise floor by the nonlinear digital canceller with practical transceiver nonlinearity and distortions.

This paper develops a 3GPP-inspired design for the in- band-full-duplex (IBFD) integrated access and backhaul (IAB) networks in the frequency range 2 (FR2) band, which can enhance the spectral efficiency (SE) and coverage while reducing the latency. However, the self-interference (SI), which is usually more than 100 dB higher than the signal-of-interest, becomes the major bottleneck in developing these IBFD networks. We design and analyze a subarray-based hybrid beamforming IBFD-IAB system with the RF beamformers obtained via RF codebooks given by a modified Linde-Buzo-Gray (LBG) algorithm. The SI is canceled in three stages, where the first stage of antenna isolation is assumed to be successfully deployed. The second stage consists of the optical domain (OD)-based RF cancellation, where cancelers are connected with the RF chain pairs. The third stage is comprised of the digital cancellation via successive interference cancellation followed by minimum mean-squared error baseband receiver. Multiuser interference in the access link is canceled by zero-forcing at the IAB-node transmitter. Simulations show that under 400 MHz bandwidth, our proposed OD-based RF cancellation can achieve around 25 dB of cancellation with 100 taps. Moreover, the higher the hardware impairment and channel estimation error, the worse digital cancellation ability we can obtain.

The full-duplex (FD) integrated access and backhaul (IAB) technique is considered in the 3rd Generation Partnership Project (3GPP) release 16 to address the demand for high capacity, large coverage and low latency millimeter wave (mmWave) beyond 5G networks. However, the self-interference (SI) appears on the FD-IAB-node, becoming the major bottleneck in the development of these novel networks. With the assumption of successful antenna isolation, this paper proposes an SI cancellation (SIC) technique for the wideband mmWave-FD-IAB multiuser networks with the cost-efficient subarray hybrid precoding structure. The fiber Bragg grating-based analog canceler is established between the RF chain pairs of the FD-IAB-node, and the minimum mean square error baseband combiner is used at the FD-IAB-node receiver to cancel the residual SI digitally. Further, hardware impairment (HWI) is considered to capture the transceiver distortion. Simulation results show that the proposed FD-IAB network capacity is almost doubled compared to the half-duplex-IAB system when the effect of HWI is low.

Integrated Access and Backhaul (IAB) systems, millimeter-wave (mmWave), and full-duplex (FD) are the critical technologies for the 5G and beyond cellular networks. The capacity and efficiency are significantly enhanced, thanks to the large available bandwidth and simultaneous transmission. However, self-interference (SI) becomes significant, which needs to be canceled in different stages. In this paper, under the mmWave-FD-IAB systems, we propose a fast hybrid precoding algorithm using the Nyström method for the wideband single-user scenario. SI and residual SI (RSI) is canceled by RF precoder and minimum mean squared error combiner at the IAB-node transmitter and receiver, respectively. RF insertion loss with different kinds of phase shifters (PSs) and channel estimation error are considered for accounting the impact of the RF components impairment and channel uncertainty. Simulations show that the proposed design can enhance the backhaul link spectral efficiency and cancel the SI efficiently at the IAB-node. Moreover, passive PSs can tolerate more RSI than active PSs.