Digitally Assisted Rf Analog Self Interference Cancellation For Wideband Full Duplex Radios

The ever-increasing demand for more data from users is pushing the development of alternative wireless technologies to improve upon network capacity. Full-Duplex radios provide an exciting opportunity to theoretically double the available spectral efficiency of wireless networks by simultaneously transmitting and receiving signals in the same frequency band. The main challenge that is presented in the implementation of a full-duplex radio is the high power transmitter leaking to the sensitive receiver chain and masking the desired receive signal to be decoded. This transmitter leakage is referred to as self interference and it is required that this self interference signal be cancelled below the receiver noise floor to achieve the full benefits of a full-duplex radio. Cancellation of the self interference signal is realized through several techniques, categorized as passive suppression, digital cancellation, and analog cancellation. These methods all have their challenges in achieving the full amount of cancellation necessary and therefore all three techniques are typically employed in the system. In this thesis, a novel digitally assisted radio frequency (RF) analog self interference canceller is proposed to suppress the self interference signal before the receiver chain for wide modulation bandwidth signals. This canceller augments minimum complexity RF-analog interference cancellation hardware that uses an RF vector multiplier in combination with a flexible digital rational function finite impulse response filter. The simple topology reduces the number of impairments added to the system through the analog components and identifies the parameters of the proposed filter in a deterministic and single iteration algorithm. The hardware proof-of-concept prototype is built using off-the-shelf RF-analog components and demonstrates excellent cancellation performance. Using four TX test signals with modulation bandwidths of 20~MHz, 40~MHz, 80~MHz, and 120~MHz, the self interference canceller achieves a minimum of 50~dB, 47~dB, 42~dB, and 40~dB of cancellation respectively. This thesis reviews the previously proposed self interference cancellation topologies, system non-idealities that provide challenges for full-duplex implementation, and the realization of the proposed RF-analog self interference canceller.

Many wireless systems could benefit from the ability to transmit and receive on the same frequency at the same time, which is known as In-Band Full-Duplex (IBFD). This technology could lead to enhanced spectral efficiency for future wireless networks, such as fifth-generation New Radio (5G NR) and beyond, and could enable capabilities and applications that were previously considered impossible, such as IBFD with phased array systems. In this exciting new book, experts from industry, academic, and federal research institutions discuss the various approaches that can be taken to suppress the inherent self-interference that is generated in IBFD systems. Both static and adaptive techniques that span across the propagation, analog and digital domains are presented. Details and measured results that encompass high-isolation antenna designs, RF, and photonic cancellation as well as signal processing approaches, which include beamforming and linear/non-linear equalization are detailed. Throughout this book, state-of-the-art IBFD systems that utilize these technologies will be provided as practical examples for various applications. Expert IBFD perspectives from multiple research organizations and companies, which would provide readers with the most accurate state-of-the-art approaches. This is the first book that dives into both the techniques that make IBFD systems possible as well as several different applications that use IBFD technology.

With fast increasing demand of the wireless network, the current spectrum used for commercial wireless communication becomes very crowed. So it is critical to find an more efficient way to make the limited spectrum provide larger capacity and throughput. Full-duplex communication technology has caused much attention in the past ten years since it can double the spectrum efficiency theoretically. While the main challenge obstructing it promoting into the market is the self-interference problem in a full duplex system. This dissertation focus on the self-interference cancellation (SIC) theories. The RF impairments occurred in the practical full-duplex system will be discussed. Among them, the phase noise and I/Q imbalance are regarded as the bottleneck of the self-interference cancellation and a detailed analyzing will be included in this dissertation. The general self-interference cancellation methods can be divided into passive self-interference cancellation and active self-interference cancellation where the active cancellation can be further divided into digital cancellation, analog cancellation and hybrid cancellation. This dissertation will review the theories of the passive and active self-interference cancellation. For the analog cancellation, two models (quadratic model and affine model) will be explored to handle the I/Q imbalance and phase noise. Both of these two models are based on the blind tuning algorithm which has two procedures: training and optimizing. This dissertation will introduce the development of the algorithm. It contains the computer simulation results as well as the hardware experimental results to prove the validation of the proposed ideas.

In the third part of this dissertation, a novel all-analog RF interference canceler is proposed. Radio self-interference cancellation (SIC) is the fundamental enabler for full-duplex radios. While SIC methods based on baseband digital signal processing and/or beamforming are inadequate, an all-analog method is useful to drastically reduce the self-interference as the first stage of SIC. It is shown that a uniform architecture with uniformly distributed RF attenuators has a performance highly dependent on the carrier frequency. It is also shown that a new architecture with the attenuators distributed in a clustered fashion has important advantages over the uniform architecture. These advantages are shown numerically through random multipath interference channels, number of control bits in step attenuators, attenuation-dependent phases, single and multi-level structures, etc.

Currently deployed cellular networks use bands which have been licensed and approved by the FCC. With the developments in cellular standards Rel-10 LTE advanced which supports carrier aggregation has been established where a multiple carriers are aggregated to provide a larger bandwidth. As cellular operators explore the possibility of extending the carrier aggregation to the unlicensed spectrum in the 5GHz, current developments in creating a friendly ecosystem in unlicensed bands have been summarized which form the basis of Rel-13 LTE- Licensed Assisted Access.

This is one of the first books on the emerging research topic of digital compensation of RF imperfections. The book presents a new multidisciplinary vision on the design of wireless communication systems. In this approach the imperfections of the RF front-ends are accepted and digital signal processing algorithms are designed to suppress their impact on system performance. The book focuses on multiple-antenna orthogonal frequency division multiplexing (MIMO OFDM).