Hybrid beamforming techniques for massive MIMO full duplex radio systems

Full Duplex (FD) radio has emerged as a promising solution to increase the data rates by up to a factor of two via simultaneous transmission and reception in the same frequency band. Self-interference (SI) is a significant challenge to deal with to achieve an ideal FD operation, which could be $90-100$~dB higher than the received signal of interest. SI cancellation techniques can mitigate the SI signal in the propagation domain or perform active cancellation by subtracting a copy of the transmitted signal on the receive side. Beamforming is also a potent tool for FD systems, which can mitigate the SI signal while meeting the data traffic requirements. It can be distinguished into two main categories: emph{fully digital beamforming} or emph{hybrid beamforming (HYBF)}. The former is helpful for the traditional multiple-input-multiple-output (MIMO) FD systems with a limited number of antennas, typically deployed in sub-$6$ GHz. The latter can be used for the massive MIMO (mMIMO) systems in millimeter wave (mmWave) band, such that they can be built cost-efficiently with a fewer number of radio-frequency (RF) chains. This thesis aims to present several digital and HYBF designs for FD systems, starting from very simple and then covering the most challenging scenarios for FD systems. Moreover, a novel and scalable SI architecture is also presented, promising for the mMIMO FD systems. One of the major drawbacks of the literature on multi-user FD communication systems is that it does not contain any distributed solution. As the FD paradigm shifts towards the mmWave band, several new challenges arise, which can make the implementation of the centralized HYBF designs infeasible, especially in a large or/and dense multi-cell network, for which a mathematical analysis is also presented. To make FD feasible in large or/and dense networks, we present the concept of per-link parallel and distributed (P$&$D) HYBF by introducing the first-ever P$&$D algorithm for mmWave, which enables parallel optimization of the beamformers at the multi-processor FD base stations and has very low complexity. Intelligent reflecting surfaces (IRSs) are prominent for the next generation of wireless communication systems. In the final part of this thesis, the concept of near-field IRSs for the mmWave FD systems is introduced to leverage the full potential of FD operation while drastically reducing the hardware cost and minimizing power consumption.