Cognitive Multihop Wireless Sensor Networks over Nakagami-m Fading Channels

This work is supported by the National Science Foundation of China (NSFC) under Grant 61372114, by the National 973 Program of China under Grant 2012CB316005, by the Joint Funds of NSFC-Guangdong under Grant U1035001, and by Beijing Higher Education Young Elite Teacher Project (no. YETP0434)

Secrecy performance of TAS/SC-based multi-hop harvest-to-transmit cognitive WSNs under joint constraint of interference and hardware imperfection

In this paper, we evaluate the secrecy performance of multi-hop cognitive wireless sensor networks (WSNs). In the secondary network, a source transmits its data to a destination via the multi-hop relaying model using the transmit antenna selection (TAS)/selection combining (SC) technique at each hop, in the presence of an eavesdropper who wants to receive the data illegally. The secondary transmitters, including the source and intermediate relays, have to harvest energy from radio-frequency signals of a power beacon for transmitting the source data. Moreover, their transmit power must be adjusted to satisfy the quality of service (QoS) of the primary network. Under the joint impact of hardware imperfection and interference constraint, expressions for the transmit power for the secondary transmitters are derived. We also derive exact and asymptotic expressions of secrecy outage probability (SOP) and probability of non-zero secrecy capacity (PNSC) for the proposed protocol over Rayleigh fading channel. The derivations are then verified by Monte Carlo simulations.Web of Science195art. no. 116

Physical layer security in 5G and beyond wireless networks enabling technologies

Information security has always been a critical concern for wireless communications due to the broadcast nature of the open wireless medium. Commonly, security relies on cryptographic encryption techniques at higher layers to ensure information security. However, traditional cryptographic methods may be inadequate or inappropriate due to novel improvements in the computational power of devices and optimization approaches. Therefore, supplementary techniques are required to secure the transmission data. Physical layer security (PLS) can improve the security of wireless communications by exploiting the characteristics of wireless channels. Therefore, we study the PLS performance in the fifth generation (5G) and beyond wireless networks enabling technologies in this thesis. The thesis consists of three main parts. In the first part, the PLS design and analysis for Device-to-Device (D2D) communication is carried out for several scenarios. More specifically, in this part, we study the underlay relay-aided D2D communications to improve the PLS of the cellular network. We propose a cooperative scheme, whereby the D2D pair, in return for being allowed to share the spectrum band of the cellular network, serves as a friendly jammer using full-duplex (FD) and half-duplex (HD) transmissions and relay selection to degrade the wiretapped signal at an eavesdropper. This part aims to show that spectrum sharing is advantageous for both D2D communications and cellular networks concerning reliability and robustness for the former and PLS enhancement for the latter. Closed-form expressions for the D2D outage probability, the secrecy outage probability (SOP), and the probability of non-zero secrecy capacity (PNSC) are derived to assess the proposed cooperative system model. The results show enhancing the robustness and reliability of D2D communication while simultaneously improving the cellular network’s PLS by generating jamming signals towards the eavesdropper. Furthermore, intensive Monte-Carlo simulations and numerical results are provided to verify the efficiency of the proposed schemes and validate the derived expressions’ accuracy. In the second part, we consider a secure underlay cognitive radio (CR) network in the presence of a primary passive eavesdropper. Herein, a secondary multi-antenna full-duplex destination node acts as a jammer to the primary eavesdropper to improve the PLS of the primary network. In return for this favor, the energy-constrained secondary source gets access to the primary network to transmit its information so long as the interference to the latter is below a certain level. As revealed in our analysis and simulation, the reliability and robustness of the CR network are improved, while the security level of the primary network is enhanced concurrently. Finally, we investigate the PLS design and analysis of reconfigurable intelligent surface (RIS)-aided wireless communication systems in an inband underlay D2D communication and the CR network. An RIS is used to adjust its reflecting elements to enhance the data transmission while improving the PLS concurrently. Furthermore, we investigate the design of active elements in RIS to overcome the double-fading problem introduced in the RISaided link in a wireless communications system. Towards this end, each active RIS element amplifies the reflected incident signal rather than only reflecting it as done in passive RIS modules. As revealed in our analysis and simulation, the use of active elements leads to a drastic reduction in the size of RIS to achieve a given performance level. Furthermore, a practical design for active RIS is proposed

Relay Selection Strategies for Multi-hop Cooperative Networks

In this dissertation we consider several relay selection strategies for multi-hop cooperative networks. The relay selection strategies we propose do not require a central controller (CC). Instead, the relay selection is on a hop-by-hop basis. As such, these strategies can be implemented in a distributed manner. Therefore, increasing the number of hops in the network would not increase the complexity or time consumed for the relay selection procedure of each hop. We first investigate the performance of a hop-by-hop relay selection strategy for multi-hop decode-and-forward (DF) cooperative networks. In each relay cluster, relays that successfully receive and decode the message from the previous hop form a decoding set for relaying, and the relay which has the highest signal-to-noise ratio (SNR) link to the next hop is then selected for retransmission. We analyze the performance of this method in terms of end-to-end outage probability, and we derive approximations for the ergodic capacity and the effective ergodic capacity of this strategy. Next we propose a novel hop-by-hop relay selection strategy where the relay in the decoding set with the largest number of ``good\u27\u27 channels to the next stage is selected for retransmission. We analyze the performance of this method in terms of end-to-end outage probability in the case of perfect and imperfect channel state information (CSI). We also investigate relay selection strategies in underlay spectrum sharing cognitive relay networks. We consider a two-hop DF cognitive relay network with a constraint on the interference to the primary user. The outage probability of the secondary user and the interference probability at the primary user are analyzed under imperfect CSI scenario. Finally we introduce a hop-by-hop relay selection strategy for underlay spectrum sharing multi-hop relay networks. Relay selection in each stage is only based on the CSI in that hop. It is shown that in terms of outage probability, the performance of this method is nearly optimal