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Title: Secure simultaneous wireless information and power transfer in MIMO systems
Author: Alageli, Mahmoud Milad
ISNI:       0000 0004 8505 7216
Awarding Body: Newcastle University
Current Institution: University of Newcastle upon Tyne
Date of Award: 2019
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Simultaneous wireless information and power transfer (SWIPT) is a promising technology that is based on utilizing radio frequency (RF) transmission for both energy harvesting and data transfer. Due to the nature of the broadcast channel, the implementation of SWIPT faces a security challenge in cancelling the crosstalk between the information users (IUs) and the information-untrusted energy harvesters (EHs). This thesis focuses on the design of downlink transmission to jointly improve the power and data transfer in three SWIPT system scenarios: a multipleinput multiple-output (MIMO) system comprising multiple IUs and multiple passive EHs; a multi-cell massive MIMO system comprising multiple IUs and a single information-untrusted dual-antenna active EH; and a cell-free massive MIMO system comprising multiple IUs and a single information-untrusted dual-antenna active EH. Three novel design methods for each of these systems are proposed and analyzed thoroughly. For the MIMO system with passive EHs, a perfect knowledge of channel state information (CSI) at the base station (BS) is assumed. The SWIPT performance is assessed by the worst-case sum secrecy rate subject to a lower limit on the total/individual harvested energy by the EHs. Transmit beamforming is employed for the information and the artificial noise (AN) signals to maximize the worst-case sum secrecy rate for two cases: with cooperative EHs and non-cooperative EHs. The beamforming design is formulated as a convex rank-unconstrained semidefinite programming (SDP) problem. Using dual multipliers which satisfy Slater's and the Karush-Kuhn-Tucker (KKT) conditions, a rank-one optimal solution is derived. In addition, two different sub-optimal solutions for the low and high harvested energy constraint regions based on null space projection of the beamforming vectors with per beamforming vector power control are provided. As a by-product, total transmit power minimization with constraints on minimum total harvested energy and the minimum worst-case secrecy rate is considered. The massive MIMO system with dual-antenna active EH introduces new design challenges: downlink training is infeasible with the large number of transmit antennas; the active eavesdropping attack results in correlated uplink channel estimates for the attacked IU which increases the information leakage to the untrusted EH; corrupted CSI prevents the BS from accurately predicting the received signal powers at the users. Two design problems are considered: for the information-untrusted EH, the problem is to maximize the worst-case ergodic secrecy rate (ESR) under a constraint on the worst-case average harvested energy (AHE) by the EH; and when the EH eavesdrops one or multiple IUs for energy harvesting (information-trusted EH), the problem is to maximize the sum-rate of the IUs under a constraint on the AHE. Asymptotic expressions for a lower bound on ESR and AHE are derived in the large system limit. The obtained expressions are used to optimize the power allocation for downlink transmissions which include: information signals, AN and energy signal towards the IUs, legitimate and illegitimate antennas of the EH, respectively. The third system, cell-free massive MIMO, consists of a large number of randomly located access points (APs) that cooperate via a central processing unit and serve multiple IUs and a single information-untrusted dual-antenna active EH. Since the transmit power constraint is per AP, the secrecy rate is non-linear in terms of the transmit power elements and that imposes new challenges in formulating a convex power control problem. To deal with these non-linearities, a new method of balancing the transmit power among the APs via relaxed SDP programming which is proved to be rank-one globally optimal is derived. A fair performance comparison between the proposed cell-free and the previously proposed colocated massive MIMO system shows that the cell-free MIMO outperforms the colocated MIMO. In summary, some of the most important open issues in optimising the SWIPT transmission for wire-taped MIMO, multi-cell massive MIMO and cell-free massive MIMO systems are considered and novel methods to address these problems are proposed. Hence, this work will help to establish more secure and SWIPTefficient MIMO systems due to the development of optimal and generalized designs of downlink signal transmission. In addition, the proposed designs will give much insight to future researchers in how to tackle the secrecy issue in SWIPT systems, particularly under active attack, which has previously lacked in-depth study in the literature.
Supervisor: Not available Sponsor: Ministry of Higher Education and Scientific Research, Libya
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available