Abstract
The broadcast nature of wireless communications along with the recent explosion on the number of wireless devices make of wireless security a major challenge. It is clear that in next generation high dense networks and Internet of Things (IoT) terminals will be more vulnerable to attacks. Traditional cryptography in high layers requires large complexity and resources which is unpractical in general and unfeasible in energy constraint devices. Hence, this thesis aims to enhance the secrecy performance of wireless systems by performing physical layer security (PLS). In PLS, the principle is that the channel quality of the legitimate user is better than that of the eavesdropper’s. However, it is difficult to guarantee this on a permanent basis. Thus, we exploit relay selection schemes and artificial noise methods in order to improve the security of the system.We are also aware that the booming number of wireless devices is bound to cause a large amount of carbon emission. Hence, realizing a sustainable wireless network is an urgent challenge that we need to meet. This motivates us to exploit radio frequency (RF) energy harvesting (EH) techniques to achieve green communication networks. This technique allows energy constraint nodes to harvest energy from existing wireless networks such as cellular, WiFi, TV or satellite, thus prolonging their lifetime and achieving a long-lived system.
The explosion on the number of wireless devices also lead wireless networks to be dense and heterogeneous. Traditional wired backhaul can ensure the connection between the macro-base station (BS) and the small cell (SC). However, deployment and maintenance are troublesome and expensive. This motivates us to consider wireless backhaul, which is a suitable alternative to wired backhaul. However, wireless backhaul is not as reliable as its wired counterpart due to channel fading and non-line-of-sight (11LOS) propagation. Thus, we analyze the influence of wireless backhaul reliability on wireless networks.
A large number of wireless devices also result in spectrum shortages. The cognitive radio network (CRN) is a promising solution to overcome the challenge. Underlay CRNs allow secondary users (SUs) to access the licensed spectrum of the primary user (PU) when the interference from the SU to the primary network is below a tolerance threshold, thus increasing the utilization of the spectrum.
In this thesis, PLS together with EH and CRN under unreliable backhaul (UB) connections are investigated to achieve a secure and sustainable wireless network. The contributions of each of the chapters are summarized below.
In Chapter 3, an EH relay network over Nakagami-i« fading is investigated to achieve a green and secure system. The source and relays can harvest energy from the power beacon. The eavesdropper wire taps the information from both the source and the relays. Two relay selection schemes are proposed, namely, partial relay selection (PRS) and optimal relay selection (ORS) to enhance system performance.
In Chapter 4, backhaul reliability is taken into account to study a secure and green communication system. A Bernoulli process is used to model wireless backhaul reliability. This is the first time that backhaul reliability is considered in an EH network.
In Chapter 5, in order to enhance secrecy performance of wireless networks, artificial noise is applied. A jammer sends artificial noise to degrade the performance of the eavesdropper while keeping the legitimate user unaffected.
In Chapter 6, an underlay CRN with multiple PUs and a single SU under UB is presented to overcome the spectrum shortage in wireless
networks.
| Date of Award | Dec 2019 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Emi Garcia-Palacios (Supervisor) & Trung Q. Duong (Supervisor) |