One of the key technologies for the future cellular networks is full-duplex (FD) enabled Integrated Access and Backhaul (IAB) networks operating in the millimeter-wave (mmWave) frequencies. The main challenge in realizing the FD-IAB networks is mitigating the impact of self-interference (SI) in the wideband mmWave frequencies. In this article, we first introduce the 3GPP IAB network architectures and wideband mmWave channel models. By utilizing the subarray-based hybrid precoding scheme, at the FD-IAB-node, multiuser interference is mitigated using zero-forcing (ZF) at the transmitter, whereas the residual SI after successfully deploying antenna and analog cancellation is canceled by minimum mean square error (MMSE) baseband combiner at the receiver. The spectral efficiency (SE) is evaluated for the RF insertion loss (RFIL) with different kinds of phase shifters and the channel uncertainty. Simulation results show that, in the presence of the RFIL, the almost double SE, which is close to that obtained from fully connected hybrid precoding, can be achieved as compared with half-duplex systems, when the uncertainties are of low strength.

This paper develops a 3GPP-inspired design for the 1 in-band-full-duplex (IBFD) integrated access and backhaul (IAB) 2 networks in the frequency range 2 (FR2) band, which can 3 enhance the spectral efficiency (SE) and coverage while reducing 4 the latency. However, the self-interference (SI), which is usually 5 more than 100 dB higher than the signal-of-interest, becomes the 6 major bottleneck in developing these IBFD networks. We design 7 and analyze a subarray-based hybrid beamforming IBFD-IAB 8 system with the RF beamformers obtained via RF codebooks 9 given by a modified Linde-Buzo-Gray (LBG) algorithm. The 10 SI is canceled in three stages, where the first stage of antenna 11 isolation is assumed to be successfully deployed. The second stage 12 consists of the optical domain (OD)-based RF cancellation, where 13 cancelers are connected with the RF chain pairs. The third stage 14 is comprised of the digital cancellation via successive interference 15 cancellation followed by minimum mean-squared error baseband 16 receiver. Multiuser interference in the access link is canceled by 17 zero-forcing at the IAB-node transmitter. Simulations show that 18 under 400 MHz bandwidth, our proposed OD-based RF cancel-19 lation can achieve around 25 dB of cancellation with 100 taps. 20 Moreover, the higher the hardware impairment and channel 21 estimation error, the worse digital cancellation ability we can 22 obtain. 23 Index Terms-Wideband in-band-full-duplex millimeter wave 24 (FR2 band), subarray hybrid beamforming, integrated access and 25 backhaul, codebook design, self-interference cancellation. 26 I. INTRODUCTION 27 F REQUENCY range 2 (FR2) band (i.e., millimeter wave) 28 communications have been identified as the key technol-29 ogy for the beyond fifth-generation (5G) wireless communi-30 cations to provide much larger bandwidth, narrower beam, 31

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