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Title: Enhancing physical-layer security in wireless powered communication network : challenges and opportunities
Author: Xing, Hong
ISNI:       0000 0004 5921 3449
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2016
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Among various means of energy harvesting (EH) for green communications, radio-frequency (RF)-enabled wireless energy harvesting (WEH), inter alia, has recently drawn significant interest for its long operational distance and effective energy multicasting; it thus motivates the paradigm of wireless powered communication network (WPCN). Nevertheless, besides benefitting from the broadcast nature of wireless channels, WPCN is also vulnerable in terms of confidentiality and privacy of the data transmission, since legitimate information may be eavesdropped by unauthorized parties. To resolve this issue, physical-layer security (PLS) has been proposed as a promising solution to achieve information-theoretic security. This thesis is devoted to addressing some major challenges encountered in enhancing PLS for WPCN while exploiting opportunities gained from WPCN by pragmatic and prominent transmitting and/or cooperative strategies along with corresponding optimal (suboptimal) resource allocations. This thesis begins with considering a three node single-input-single-output (SISO) fading wiretap channel, where the confidential messages sent to the information receivers (IRs) may be eavesdropped by the energy receivers (ERs) that are usually deployed nearer to the transmitter because of their high power receiving sensitivity. In this case, an artificial noise (AN)-aided transmission scheme, where the transmit power is split into two parts, to send the confidential message to the IR and an AN to interfere with the ER respectively, is proposed to facilitate the secrecy information transmission and yet meet the EH requirement. The fundamental challenges in balancing the goals between achieving PLS and satisfying ER’s EH requirement are modeled by various secrecy performances versus harvested energy trade-offs, the regions of which are enlarged by both dual decomposition-based optimal solutions and alternating optimization-based suboptimal solutions. On the other hand, under circumstances where some ERs are trustful, their self-sustaining features can also be favourable to providing PLS by means of cooperative jamming (CJ). In the second part of the thesis, a novel harvest-and-jam (HJ) relaying protocol is proposed for multiple multi-antenna ERs to assist in the secrecy information transmission via one multi-antenna amplify-and-forward (AF) relay. Joint optimization of the CJ covariance and AF-relay beamforming is studied using semidefinite relaxation (SDR) under perfect and imperfect channel state information (CSI) respectively. In particular, for the imperfect CSI case, a novel approach that jointly models channel imperfections induced by an arbitrary number of CJ helpers is proposed to equivalently reformulate the worst-case robust optimization problem into the convex optimization framework. Following the trend of WEH-enabled cooperative secrecy transmission, a more general wiretap channel with multiple WEH-enabled AF relays in the presence of multiple eavesdroppers all equipped with single antenna is studied in the last part of the thesis. To the end of combing the benefit of CJ and cooperative beamforming (CB), a new hybrid power splitting (PS) relaying strategy is proposed. In the first transmission phase each AF relay employs a PS receiver that splits a fraction of the received power for EH and consumes the rest for information receiving. In the second transmission phase the relay further divides its harvested power to forward the confidential information and to generate the jamming signals. The formulated secrecy rate maximization problems turn out to be very challenging due to the multiplicative variables in the relay weights. Under the centralized scheme, the global optimum joint CB and CJ solution is obtained for the static power splitting (SPS) case, while for the generalized dynamic power splitting (DPS) case, the global optimum CB-only solution is provided by utilizing SDR, which is then developed into a suboptimal joint CB and CJ design based on alternating optimization.
Supervisor: Nallanathan, Arumugam ; Nakhai, Mohammad Reza Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available