Research On Self-Interference Suppressions For Co-Time Co-Frequency Full-Duplex EM Communications

Suffering from the explosion of data exchanging and the ever-increasing demand of high data rate,it is of great significance to improve the spectrum efficiency to satisfy the surging traffic of wireless communications.A potential and valuable solution is the utilization of the co-time co-frequency full-duplex(CCFD)architecture,where bidirectional communications are operated simultaneously under the same single carrier.Thus,the spectrum efficiency can be doubled theoretically compared with half-duplex schemes.To realize CCFD communications,the primary challenge is the suppression of the strong self-interference due to the limited isolation between transmitter(Tx)and local receiver(Rx).Although published literatures have presented some schemes of self-interference suppressions for single antenna or simple array systems,these studies cannot be applicable to the antenna arrays.The self-interference suppression resulting from the complicated mutual couplings remains a challenge.This dissertation will focus on the self-interference suppression for the antenna-array-based CCFD systems at antenna-and passive-analog-levels;the main contents are as follows.Chapter 1 gives a brief introduction of CCFD applications,and provides a summary review of self-interference suppressions at antenna-,analog-,and digitallevels,respectively.Besides,the issues and challenges of self-interference suppression for future communications are also summerized.Chapter 2 presents three dual-polarized antenna arrays with improved interport isolations by using differential feedings.The first one utilizes a symmetrical configuration with differential feeding to further cancel the mutual coupling among the array.Besides,the influence of magnitude and phase imbalances on the cancellation level is discussed,and a compact slotline-based balun featuring wide impedance bandwidth as well as small magnitude and phase imbalances is proposed.The second one is a simple and compact dual-polarized linear antenna array,where a high interport isolation is realized by using a symmetrically shared-intereface configuration.To achieve the high isolation in practice,a slotline-based 180° hybrid is proposed and studied as the feeding network of the linear array.The third one is a traveling-wave antenna array with a simple series-feeding network.By properly loading some resistors,special antenna elements served as loads are avoided compared to those typical traveling-wave arrays.Chapter 3 introduces three antenna arrays where the Tx and Rx are operated in the same polarizations for further improving the spectrum efficiency.The first one is a circularly polarized array integrated with a full-duplex network.The Tx and Rx share the same interface of the array,leading to a compact configuration.The proposed scheme characterizes good passive cancellations for the self-interference resulting from antenna level,including the mutual coupling and the leakage within the antenna array together with its feeding networks.The other two are OAM-based arrays using non-sequentially and sequentially rotated configurations,respectively.The two arrays feature high Tx-Rx isolation by using the proposed OAM-mode-selection methods.Especially for the sequentially rotated scheme,the physical and numerical relations between the excitations and generated OAM modes are studied.Chapter 4 provides a transmission-line-based decoupling technique for dual-polarized multiple-input and multiple-output(MIMO)antenna arrays in CCFD applications to maintain the capacity and improve the active impedance matching performance.The proposed scheme enables well-canceled mutual coupling for the adjacent elements under co-polarizations but without degrading the isolation of the cross-polarized ports.The realized decoupling network characterizes low profile and low insertion loss,and can be easily integrated and widely utilized for massive MIMO array systems.Chapter 5 presents the systematic experimental study on the self-interference suppression at the antenna-level of CCFD.Specifically,based on the related antenna array developed in this thesis,a CCFD experimental platform is constructed and the experimental studies are further performed in principle.The achieved performance in terms of the self-interference suppression in the CCFD EM communications is examined at the antenna level.Chapter 6 makes a systematic summary of this dissertation,and provides some relevant research fields and hot topics that are worthy of further in-depth study.