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Residual Self-Interference Mitigation in Full-Duplex Two-Way MIMO Relaying NetworkAuthor: Nachiket Ayir Date: 2018-05-04 Report no: IIIT/TH/2018/18 Advisor:Ubaidulla P AbstractIn-band full-duplex (FD) communication that enables concurrent transmission and reception in a single frequency-time channel holds the promise of nearly doubling the spectral efficiency compared to the current half-duplex and out-of-band FD communication systems. The main hurdle in the practical implementation of such a full-duplex system is the loopback self-interference (LSI), which arises due to the FD operation of the communicating nodes. In such an FD transceiver, the transmit signal generally overpowers the intended receive signal making its detection extremely difficult. However, with the recent advancements in the LSI cancellation techniques, FD systems have finally become viable. Hence, it is no wonder that FD has been envisaged as one of the promising technologies for the next generation wireless networks, viz., 5G and beyond. In practice, the LSI cancellation process cannot eliminate the LSI completely due to various reasons, chief among them the difficulty in obtaining the perfect channel state information of the loopback channel. As a result, we are still left with a residual LSI, which would degrade the performance of an FD system. In this work, we consider the design of optimal transceiver and relay processing algorithms for FD multiple-input multiple-output (MIMO) cooperative networks. Specifically, we propose the algorithms for FD communication in three different scenarios: (i) a cognitive radio network, (ii) secure communication using physical layer security techniques, and (iii) a cellular network. In the cognitive radio setup, we consider the FD transceivers and the FD relay to be a part of the secondary network. The transceiver and the relay precoders are designed so as to ensure that the interference caused to the primary user is always below a specified threshold. We have considered the maximization of the receive signal-to-noise ratio (SNR) as the criterion for the design of the transceiver precoders. We have further extended this problem to the case where multiple relays are available for selection. A central control unit selects the relay that provides the highest receive SNR. In the next scenario, a passive eavesdropper tries to decode the data of the two legitimate FD transceivers. In this case, we consider secure communication between the legitimate transceivers using physical layer security techniques. The precoder and receive filter matrices are designed to ensure secure communication between the legitimate users. The secrecy performance of this system in the presence of a passive eavesdropper is analyzed by considering the relay signal as artificial noise for the eavesdropper. The effectiveness of the proposed design is evaluated in terms of the sum-secrecy-rate of the system. Finally, we consider a futuristic FD cellular network scenario where an FD base station communicates with two FD transceiver nodes, where one of the transceivers is assisted by an FD amplify-and-forward relay. In each of the scenarios, our prime focus is on mitigating the residual LSI and its detrimental effect on the performance of the system. The precoders at the transceiver nodes are designed to mitigate the LSI based on the requirements of their operating environment. The LSI at the relay is mitigated by incorporating it into the sum of meansquareerror (SMSE) minimization problem. The relay precoder and the transceiver receive filters are designed based on the minimization of the SMSE of the end-to-end communication. The resulting optimization problem is non-convex and hence a globally optimal solution is not guaranteed. We apply the coordinate descent method and the Karush-Kuhn-Tucker (KKT) conditions to obtain sub-optimal solutions. The complexities of the proposed algorithms are lower than that of the state-of-the-art algorithms, in terms of both number of computations and memory requirements. The various simulation results demonstrate the efficacy of our proposed designs in terms of LSI mitigation, power efficiency, number of iterations, and sum-rate performance. Full thesis: pdf Centre for Communications |
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