Full-duplex wireless communication duplexing scheme: methodology and self-interference characteristics

Full-duplex scheme – or in-band full-duplex scheme – changes the duplexing paradigm in wireless communication networks. A communication-duplexing scheme utilizes a single frequency band to communicate bidirectionally and simultaneously over two parallel communication links. Indeed, reusing the same frequency band to occupy two information streams – e.g., uplink and downlink – doubles the utilizing the electromagnetic spectrum utilization efficiency, offering a twice more sum channel capacity. Moreover, a simultaneous presence of two data streams mitigates any inherent duplexing latency in exchanging data over the bidirectional link. However, self-interference-cancellation techniques must enhance wireless transceivers to enable a full-duplex scheme. The self-interference signal is severe, contaminated with wireless transceivers' hardware impairments, and dispersed by a self-interference radio channel. Thus, the characteristics of the self-interference signal make its cancellation a challenging task. Consequently, a successful self-interference cancellation, which can enable the full-duplex scheme, must be aware of sources of distortions to allow canceling the self-interference sufficiently. The author has systematically studied the self-interference cancellation in wireless full-duplex transceivers and self-interference radio channels. Firstly, the author presents a comprehensive self-interference signal-and-system models in a full-duplex wireless transceiver, where these models accommodate multiple antenna configurations – SISO, MISO, SIMO, and MIMO – and hardware impairments representation. Then, the author employs analytical tools to dissect the self-interference radio channel into the antenna's mutual coupling and wireless propagation backscattering segments. Next, a fundamental physical and mathematical description of the self-interference radio channel is provided by means of spherical vector wave expansion and antenna scattering matrix representation. Furthermore, experimental tools were used to investigate both channel segments by conducting radio-frequency measurements. In addition to measuring the antennas' mutual coupling for various antenna setups, the wireless propagation backscattering channel segment was measured over several frequency bands (from 2.0 GHz to 7.1 GHz) and in various indoor and outdoor environments. For the sake of a fully polarimetric backscattering self-interference radio channel modeling and characterization, dually polarized antennas' setups were used to measure co-polar and cross-polar self-interference channel components. Moreover, the author has developed and implemented a novel self-interference channel estimation technique that has vastly expanded the self-interference channel measurement dynamics to reach -135 dB. The power-delay profiles were presented and exploited to extract self-interference-channel-relevant parameters. These channel parameters are extensively analyzed by means of statistical tools utilizing quantitative techniques that include graphical techniques and classical confirmatory methods. Following the self-interference channel modeling, the dissertation addresses self-interference cancellation methodologies. Firstly, the author reveals the self-interference cancellation bounding limits and defines self-interference cancellation requirements based on conducted and radiated (over-the-air) metrics. Next, the author studies two self-interference cancellation techniques applied in the radio-frequency domain. Theoretical analysis, simulation, and experiments are used to study the self-interference cancellation techniques. The first technique is a novel technique based on antenna decoupling utilizing a lossless reactive network that interconnects the antenna ports and transceiver front-ends. The author analyzes the technique empirically, relying on the antennas' mutual coupling measurement results. The second technique is based on a self-interference signal injection utilizing an auxiliary transmitter with improved digital processing capabilities to cope with in-phase-and-quadrature imbalances in direct-conversion wireless transceivers.