An Efficient Self Interference Cancellation Structure For Full Duplex Radios

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.

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).

The objective of this monograph is to present a timely overview of self-interference cancellation techniques and discuss the challenges and possible solutions to implement effective self-interference cancellation in 6G networks.

"Full-duplex (FD) wireless communications can potentially double the spectral efficiency by transmitting and receiving simultaneously over the same frequency at a cost of a large power difference between the high-power self-interference (SI), and the low-power intended signal received from the remote transmitter. SI can be reduced gradually by a combination of radio-frequency (RF) and baseband SI-cancellation stages. Each stage requires the estimation of various distortions that the SI endures, such as SI-channel and transceiver nonlinearities. This thesis deals with the development of SI-cancellation techniques that are well adapted to FD operations.We address SI-cancellation for FD operations in the presence of imperfect RF components. In particular, we develop a new scheme to jointly estimate the IQ mixer imbalance, power amplifier (PA) nonlinearities, up-/down-conversion phase-noise and SI-channel. First, we study and develop a baseband model that captures the most significant transceiver RF imperfections, for both separate- and common-oscillator structures used in the up- and down-conversions. A basis expansion model (BEM) is then derived to approximate the time-varying phase-noise, and to transform the problem of estimating the time-varying phase-noise into the estimation of a set of static coefficients. Using the method of maximum likelihood (ML) criterion, the likelihood function is derived in the presence of the unknown intended signal, which leads to the joint estimation of the intended channel, the SI-channel, the nonlinear impairments and the phase-noise. When the intended signal is unknown, an iterative procedure is developed to find the ML estimate of the different parameters based on its own known transmitted data, the known pilot symbols, and the statistic of the unknown intended signal received from the intended transmitter. We consider the two pilot-insertion structures used in LTE for the frequency-multiplexed pilots and the time-multiplexed pilots. Compared to training-based techniques, the full use of the received signal significantly reduces the required number of pilot symbols. Simulation results indicate that the proposed algorithms can offer a superior SI-cancellation performance, with the resulting signal-to-SI-and-noise ratio (SINR) being very close to the signal-to-noise ratio (SNR).Moreover, we study the power of SI after each cancellation stage, taking into account the transceiver impairments. One SI-cancellation scheme, which combines antenna cancellation, RF cancellation and digital cancellation, provides results from real world experiments that show the feasibility of an FD design. In general, it is difficult to assess the exact level of the SI reduction that is obtainable due to the interactions among factors such as transceiver impairments, wireless propagation channel and estimation error. We hereby identify the main factors that affect the cancellation performance. This allows for a better understanding of the obtained performance, and leads to the development of new methods that improves the cancellation capability of FD systems. We address the impact of each transceiver impairment in FD systems, and specify the limiting factors of the RF and baseband SI-cancellation stages for a given architecture. In addition, we demonstrate that reducing the SI before the LNA/ADC, via the RF SI-cancellation stage is necessary to avoid high quantization noise from the ADC. The analysis further reveals that the transmitter nonlinearities need to be modeled and canceled in the baseband SI-cancellation stage. Finally, in light of our simulation results, we discuss the trade-off between the amount of SI-cancellation and the number of cancellation stages, and propose the potential case scenarios for operations with one digital cancellation." --

This book introduces the development of self-interference (SI)-cancellation techniques for full-duplex wireless communication systems. The authors rely on estimation theory and signal processing to develop SI-cancellation algorithms by generating an estimate of the received SI and subtracting it from the received signal. The authors also cover two new SI-cancellation methods using the new concept of active signal injection (ASI) for full-duplex MIMO-OFDM systems. The ASI approach adds an appropriate cancelling signal to each transmitted signal such that the combined signals from transmit antennas attenuate the SI at the receive antennas. The authors illustrate that the SI-pre-cancelling signal does not affect the data-bearing signal. This book is for researchers and professionals working in wireless communications and engineers willing to understand the challenges of deploying full-duplex and practical solutions to implement a full-duplex system. Advanced-level students in electrical engineering and computer science studying wireless communications will also find this book useful as a secondary textbook.