Secure Communication Based On Physical Layer Security In Wireless Channel

Due to an inherent broadcast and openness nature of the wireless medium, which imposes stronger challenges on the security of wireless communications since it is easy for adversary users to gain an un-inhibited access to the information signal transmitted over the medium, hence there is a strong need to protect the information conveying from one point to another in wireless medium.Securing information over the wireless system was initially tackled with the use of data encryption algorithm, which requires the sharing of secret key among two or more legitimate communicating partners. However, the use of data encryption techniques was found to be cumbersome, complex and prone to attack by eavesdropper if it's has capacity to decode the transmitted signal. In order to tackle these challenges, information-theoretic security addresses these problems at the physical layer of open system interconnect (OSI) model by using different tools from wireless communication theory, signal processing approach, stochastic processing, game theory and information theory. In any of these approaches, physical layer in OSI model is intelligently designed to exploit the characteristics of the wireless medium, such as fading of the channel, signal interference within the network node or any other associated nodes, nodes cooperation, and use of external relays and multi-dimensional signaling, to provide system security or improving the existing security level. In this dissertation, several studies were provided that can be employed in the improvement of security of several fundamental wireless network configurations from an information-theoretic point of view.The main contributions of this thesis are listed as following:1. We analyze the secrecy performance of a full-duplex system in a broadcast wireless channel that undergoes Rayleigh fading. In this work, closed form expressions for probability of non-zero secrecy capacity and secrecy outage probability were derived. The performance analysis and the simulation results show that there is an improvement in secrecy level in wireless channel if the full-duplex receiver can transmits an additional artificial noise as it is also receiving information signal from the transmitter, compared to direct application of AN in a broadcast wireless system. It is also concluded that secure transmission is possible even if the eavesdropper has a close proximity to the information source more than the legitimate receiver.2. We propose the use of guard node to improve the securing level in a cellular system. In this work, a novel technique was introduced where we consider the deployment of independent guard nodes to prevent eavesdropper from intercepting the transmitted messages between the transmitter and the receiver. The guard nodes are used to assist the information source to protect the secure message by transmitting additional noise to degrade the eavesdropper channel. In the analysis, we take both the uplink and downlink communications into consideration. The performance analyses show that a secure and robust system can be achieved by applying this novel technique.3. In order to improve the secure transmission in relay system, a new transmission scheme was proposed by improving on sub-optimal jamming scheme (SSJ) techniques. In this scheme, the relay with best signal-to-noise ratio will be chosen and made to applied its power to transmit the confidential message to the receiver when its has a condition that favor secure transmission is available while the another relay node with worst SNR will be transmitting noise to degrade the illegitimate receiver terminal at all the time. The simulation results show that the eavesdropper is at disadvantage to have access to the transmitted signal because the forwarding relay will only transmit the confidential message whenever the condition that favors secure transmission is available otherwise a common message will be transmitted over the wireless channel.4. Secrecy improvement in wireless channel can also be achieved by using the end-user noise contributed technique. In this contribution, I propose the use of relay node that bridges the transmission between the information source and the receivers. In this technique, we considers a dual-hop transmission in which during the first hop, destination node contribute the noise which can be received by both the relays and eavesdropper while during the second-hop, the transmitter is transmitting the signal while the relay is equally transmit an amplified signal from transmitter. The performance evaluation shows the effect of noise contributed from the destination node on the general secrecy performance.5. To reduce the intercept probability of two-way point-to-point transmission, we propose a random linear code based secure transmission scheme where the data symbols of the transmitter are encoded with the generators determined by the receiver. The code is constructed in such a way that the eavesdropper cannot decode any one data symbol unless it can intercept all the two way transmissions between the transmitter and the legitimate receiver. Hence very low crack probability can be achieved with long code length or low transmit power.