Beamforming and non-orthogonal multiple access for rate and secrecy enhancement of fifth generation communication system

The fifth-generation (5G) communication systems have many anticipated functionalities and requirements such as high data rate, massive connectivity, wide coverage area, low latency and enhanced secrecy performance. In order to meet these criteria, communication schemes that combine 5G key enabling technologies need to be investigated. In this thesis, a novel communication system that merges non-orthogonal multiple access (NOMA), energy harvesting, beamforming, and full-duplex (FD) techniques in order to enhance both capacity and secrecy of 5G system is introduced. In the capacity improving scheme, NOMA is first combined with beamforming to serve more than one user in each beamforming vector. Next, simultaneous wireless information and power transfer (SWIPT) technique is exploited to encourage the strong user (user with better channel condition) to relay the information messages of the weak user (user with poor channel condition) in FD manner. The total sum rate maximisation problem is formulated and solved by means of convex-concave procedure. The system performance is also analysed by deriving the outage probability of both users. Additionally, the model is extended to a more general case wherein the users are moving, and the outage probability of this dynamic topology is provided by means of the stochastic geometry framework. Novel secure schemes are also introduced to safeguard legitimate users’ information from internal and external eavesdroppers. In the internal eavesdropper’s case, artificial signal concept is adopted to protect NOMA’s weak user’s information from being intercepted by the strong user. The secrecy outage probability of theweak user is derived and validated. In addition, game theory discipline is exploited to provide an efficient eavesdropping avoidance algorithm. Null-steering beamforming is adopted in the external eavesdropper’s case in two different schemes namely self and nonself-cooperative jamming. In self-cooperative strategy, the base station applies the null-steering jamming to impair the eavesdropper channel, while sending the information-bearing signals to the intended legitimate users. Whereas in the nonself-cooperative jamming scheme, the base station provides the helpers with the required information and power by means of SWIPT technique in the first phase. The helpers deploy null-steering beamforming to jam the eavesdropper during the information exchange between the base station and the intended users in the second phase. The secrecy outage probability of the legitimate users is derived in both jamming schemes. Game theory is also introduced to the nonself-cooperative jamming scheme for further improvements on the secrecy outage behaviour and the economic revenue of the system. The proposed capacity enhancing scheme demonstrates about 200% higher sum rate when compared with the non-cooperative and half-duplex cooperative NOMA systems. In addition, the novel secure scheme in the internal eavesdropper case is proven to enhance the information security of the weak user without compromising the functionalities of the strong user or NOMA superiority over orthogonal multiple access systems. Null-steering based jamming system also illustrates improved secrecy performance in the external eavesdropper case when compared to the conventional jamming schemes. Numerical simulations are carried out in order to validate the derived closed-form expressions and to illustrate the performance enhancement achieved by the proposed schemes where the rate is increased by 200% and the secrecy outage probability is decreased by 33% when compared to the baseline systems

A zero-sum game approach for non-orthogonal multiple access systems: legitimate eavesdropper case

In this paper, secure communication in non-orthogonal multiple access (NOMA) downlink system is considered wherein two NOMA users with channel gain difference are paired in each transmission slot. The user with poor channel condition (weak user) is entrusted, while the user with good channel condition (strong user) is a potential eavesdropper. The weak user data can be intercepted by the strong user since the strong user needs to decode the weak user's message for successive interference cancellation operation in NOMA. To impair strong user's eavesdropping capability, weak user's information-bearing signal is merged with an artificial signal (AS). Thus, the eavesdropping process requires extra decoding step at higher power level. The secrecy outage probability of the weak user is derived and provided in closed-form expression. The weak user faces a choice between transmitting the information-bearing signal with the total power and the deploying the AS technique, whereas the strong user can choose whether to eavesdrop the weak user's message or not. To investigate users' power-secrecy tradeoffs, their interactions are modeled as a non-cooperative zero-sum game. The existence of Nash equilibria (NEs) of the proposed game is first analyzed, and pure and mixed-strategy NE profiles are provided. In addition, numerical simulations are conducted to validate the analytical results and to prove that AS-Aided proposed scheme enhances the secrecy performance of NOMA systems while maintaining the NOMA superiority over OMA systems

A Novel Approach to Mobile Outdoor QoS Map Generation

International audienceRay Tracing is an electromagnetic wave propagation modeling approach used for accurate generation of Quality of Service (QoS) maps in mobile networks. Due to its complexity, current implementation of Ray Tracing fails to generate such maps in wide areas. In this paper, we propose an optimization to Ray Tracing able to accurately generate QoS maps in a reasonable time. Using a site-specific ray launching technique and an alternative to the reception test process, we divide by almost 1200 the execution time of Ray Tracing with less than 2% of memory usage as compared to baseline solutions

Site-specific ray generation for accurate estimation of signal power

International audienceRay Tracing is a propagation modelling approach that accurately estimates the signal power received by end users while taking into account the details of the environment in their vicinity. This accuracy is at the cost of high computational load and high memory consumption due to the heavy computation performed by processes such as Ray Generation. In this paper, we introduce a site-specific ray generation technique able to generate up to 1 million rays within 5 seconds and a root mean square error for bandwidth estimation within 2 Mbps. Depending on the location of the antenna and the coverage area, our technique gives the minimum possible number of rays required in order to estimate end-users' signal power received and their download bitrate

Beamforming in Wireless Energy Harvesting Communications Systems: A Survey

Wireless energy harvesting (EH) is a promising solution to prolong lifetime of power-constrained networks such as military and sensor networks. The high sensitivity of energy transfer to signal decay due to path loss and fading, promotes multi-antenna techniques like beamforming as the candidate transmission scheme for EH networks. Exploiting beamforming in EH networks has gained overwhelming interest, and lot of literature has appeared recently regarding this topic. The objective of this paper is to point out the state-of-the-art research activity on beamforming implementation in EH wireless networks. We first review the basic concepts and architecture of EH wireless networks. In addition, we also discuss the effects of beamforming transmission scheme on system performance in EH wireless communication. Furthermore, we present a comprehensive survey of multi-antenna EH communications. We cover the supporting network architectures like broadcasting, relay, and cognitive radio networks with the various beamforming deployment within the network architecture. We classify the different beamforming approaches in each network topology according to its design objective such as increasing the throughput, enhancing the energy transfer efficiency, and minimizing the total transmit power, with paying special attention to exploiting the physical layer security. We also survey major advances as well as open issues, challenges, and future research directions in multi-antenna EH communications

A game-theoretical modelling approach for enhancing the physical layer security of non-orthogonal multiple access system

This paper investigates the physical layer security of a downlink non-orthogonal multiple access (NOMA) communication system, wherein a base station is communicating with two paired active users in the presence of an eavesdropper and multiple idle nodes (helpers). In order to enhance the secrecy performance, a two-phase harvest-and-jam null-steering jamming technique is deployed. In the first phase, the base station provides the helper with power in addition to active users and eavesdropper's information via simultaneous wireless information and power transfer technique. The helpers exploit the harvested energy and the information received in the first phase to build a null-steering beamformer and jam the eavesdropper, during the information exchange between the base station and the legitimate users in the second phase. A game theory is introduced to the proposed scheme, and the base station-helpers interactions are modeled as a Stackelberg game, where the helpers play the leader role and the base station is the follower. The utility functions of both the leader and follower are formed, and the Stackelberg equilibrium is reached by means of the backward induction technique. The proposed scheme demonstrates better secrecy performance when compared with the artificial noise-aided secure NOMA system

A novel approach for ray tracing optimization in wireless communication

International audienceRay Tracing is a propagation modeling approach that accurately estimates the signal power received by end users while considering the details of the environment in their vicinity. The accuracy of this estimation is at the cost of high computational load and high memory consumption due to the heavy computation performed by processes such as the Ray Generation. In this paper, we introduce a site-specific ray generation technique able to generate up to 1 million rays within 5 seconds and a root mean square error for bandwidth estimation within 2 Mbps. Depending on the location of the antenna, the coverage area, the type of the terrain and the computational resources available, our technique gives the minimum possible number of rays required to accurately estimate end-users' signal power received and their download bitrate

On the outage probability of large scale decode-and-forward relay wireless networks

This paper considers a wireless network consisting of large number of clusters, wherein each cluster represents a decode-and-forward (DF) relay network. Two main scenarios according to the distances among the nodes in the network are investigated. In the case of deterministic distances, the outage probability is obtained in a closed-form expression. Whereas for the case when these distances are independent random variables, the framework of Stochastic Geometry (SG) is exploited for deriving the closed-form of the outage probability in case of Rayleigh fading channel. Furthermore, a lower and upper bound for the outage probability in case of general fading channel have been also provided. Numerical simulations are carried out to validate the derived analytical expressions, and to illustrate how the obtained results can be utilized in interference management of such networks