The aim of this paper is to investigate a security solution in the physical layer of a wireless channel. By considering secrecy outage probability, a method of maximizing the average secrecy throughput through adaptive power and transmissions rate with Artificial Noise (AN) will be presented. This system performance secrecy throughput is evaluated by the different impacts of system parameters. The results show that transmissions with AN and with adaptive optimal power control will significantly increase the secrecy throughput.
The aim of this paper is to investigate a security solution in the physical layer of a wireless channel. By considering secrecy outage probability, a method of maximizing the average secrecy throughput through adaptive power and transmissions rate with Artificial Noise (AN) will be presented. This system performance secrecy throughput is evaluated by the different impacts of system parameters. The results show that transmissions with AN and with adaptive optimal power control will significantly increase the secrecy throughput.
We investigate the optimal physical-layer secure transmission with artificial noise in the wiretap channel with N antennas at the transmitter, a single antenna at the receiver, and M antennas at the eavesdropper. We analyze the performance and determine the optimal transmission parameters for two distinct schemes: 1) an on-off transmission scheme and 2) an adaptive transmission scheme. For the on-off transmission scheme, where a channel-realization-independent secrecy rate is used for all transmission periods, we derive closed-form expressions for the secure transmission probability, the hybrid outage probability, and the effective secrecy throughput. For the adaptive transmission scheme, where a channel-realization-dependent secrecy rate is used for each transmission period, we derive closed-form expressions for the secure transmission probability, the secrecy outage probability, and the effective secrecy throughput. Using these closed-form expressions, we determine the optimal power allocation between information signals and artificial noise signals for both schemes to maximize the secure transmission probability. We also determine the optimal secrecy rate for both schemes to maximize the effective secrecy throughput. We explicitly examine the impact of N and M on the optimal power allocation and the optimal secrecy rate. Finally, we demonstrate the performance gain of the adaptive transmission scheme over the on-off transmission scheme.
Exploiting the randomness embedded in wireless channels, the physical-layer security techniques can provide additional security robustness against malicious eavesdropping at the physical layer of communication systems. To further this line of study, this thesis focuses on developing advanced multi-antenna transmission strategies for enhancing the secrecy performance of wireless communication systems. Assuming perfect channel feedback from the desired receiver and none from the eavesdropper, we consider beamforming with smartly injected artificial noise, aiming to confuse the eavesdropper whilst leaving the desired receiver unaffected. The system parameters are either chosen to be fixed for all transmissions, or adaptively adjusted based on the channel feedback from the desired receiver. For both cases, we provide novel and explicit design solutions for achieving the maximum throughput subject to a secrecy outage constraint. We then derive accurate approximations for the maximum throughput, and give new insights into the additional power cost for achieving a higher security level and the throughput gain of adaptive transmission over non-adaptive transmission. Having investigated the perfect feedback scenario, we then relax the feedback assumption and consider practical effects imposed by limited feedback constraints on the channel from the desired receiver to the transmitter. To deal with quantization error due to limited feedback whilst also accounting for unknown channel of the eavesdropper, we specify a connection outage constraint to guarantee the reliability of desired communication and a secrecy outage constraint to guard against malicious eavesdropping. Under dual outage constraints, we derive a novel optimized rate-adaptive transmission design to maximize the average secrecy throughput. New insights regarding the optimal power/feedback allocation and the number of feedback bits required for efficient quantization are obtained through our analysis. Our preceding study focused on isolated point-to-point transmission without any interference. However, the performance of contemporary wireless networks is often limited by interference from concurrent transmissions. To characterize the impact of interference on secure communication, we consider an interference-limited large-scale network. To confuse the malicious eavesdroppers, in addition to information-bearing signals, the transmitters are designed to generate artificial noise through either beamforming or antenna sectoring in a distributed manner. For both cases, using tools from stochastic geometry, we provide a statistical characterization of the reliability performance of desired communication and the secrecy performance against eavesdropping. We then investigate the networkwide secrecy throughput performance and optimize the transmit power allocation. Our analysis reveals interesting differences between the beamforming and sectoring approaches in terms of the optimal power allocation and the maximum networkwide secrecy throughput.
We analyze and optimize the secrecy performance of artificial noise (AN) in multi-input single-output wiretap channels with multiple antennas at the transmitter and a single antenna at the receiver and the eavesdropper. We consider two transmission schemes: 1) an on-off transmission scheme with a constant secrecy rate for all transmission periods, and 2) an adaptive transmission scheme with a varying secrecy rate during each transmission period. For the on-off transmission scheme, an easy-to-compute expression is derived for the hybrid outage probability, which allows us to evaluate the transmission outage probability and the secrecy outage probability. For the adaptive transmission scheme where transmission outage does not occur, we derive a closed-form expression for the secrecy outage probability. Using these expressions, we determine the optimal power allocation between the information signal and the AN signal and also determine the optimal secrecy rate such that the effective secrecy throughput is maximized for both transmission schemes. We show that the maximum effective secrecy throughput requires more power to be allocated to the AN signal when the quality of the transmitter-receiver channel or the transmitter-eavesdropper channel improves. We also show that both transmission schemes achieve a higher maximum effective secrecy throughput while incurring a lower secrecy outage probability than existing schemes.
The motivation of this thesis is to contribute to the improvement of the physical-layer secrecy and privacy of wireless communication. Firstly, the rate and power adaptation technique is investigated to improve the energy efficiency of the physical-layer secrecy. We present the optimum rate and power adaptation rule that maximizes the average secrecy energy efficiency(SEE) subject to an average transmission power constraint. The SEE is defined as the outage secrecy capacity, the largest secrecy rate, such that the outage probability is less than a certain value, divided by the total power consumption (bits per joule). We also characterize the SEE gain provided by varying the rate and/or the power, and discuss the impact of the number of antennas on the optimum adaptation rule. Secondly, the joint impact of imperfect knowledge of the channel gain (channel uncertainty) and noise power (noise uncertainty) at the adversary is investigated to improve the physical-layer privacy. We characterize the covert throughput gain provided by the channel uncertainty as well as the covert throughput loss caused by the channel fading as a function of the noise uncertainty. We also show the impact the channel uncertainty on the total detection error probability and the covert throughput. Our result shows that the channel fading is crucial to hiding the signal transmission, particularly when the noise uncertainty is low and/or the receive SNR is high. The impact of the channel uncertainty on the total detection error probability and the covert throughput is more significant when the noise uncertainty is larger. Finally, hiding a covert (private) message in non-orthogonal multiple access (NOMA) systems by superimposing (embedding) it under other messages is proposed.We determine the total detection error probability (sum of false alarm and missed detection probability), the adversary's optimum detection strategy that minimizes the total detection error probability, and the communicator's optimum message hiding strategy that maximizes the total detection error probability. Additionally, we explore exploiting the channel variations to further increase the total detection error probability. We show that the total detection error probability increases and converges to 1 as the number of users increases and that the total detection error probability, hence the covert rate, can be increased by increasing the transmission power when the channel variation is exploited.
In this paper, we investigate the design of artificial-noise-aided secure multi-antenna transmission in slow fading channels. The primary design concerns include the transmit power allocation and the rate parameters of the wiretap code. We consider two scenarios with different complexity levels: 1) the design parameters are chosen to be fixed for all transmissions; and 2) they are adaptively adjusted based on the instantaneous channel feedback from the intended receiver. In both scenarios, we provide explicit design solutions for achieving the maximal throughput subject to a secrecy constraint, given by a maximum allowable secrecy outage probability. We then derive accurate approximations for the maximal throughput in both scenarios in the high signal-to-noise ratio region, and give new insights into the additional power cost for achieving a higher security level while maintaining a specified target throughput. In the end, the throughput gain of adaptive transmission over non-adaptive transmission is also quantified and analyzed.
Recently, the use of artificial noise has attracted considerable attention in enhancing the physical-layer security of wireless systems. However, the interaction between artificially generated noise and the inherent network interference can significantly affect the level of secrecy. In this paper, we consider the additional secrecy enhancement with artificial noise and secrecy protected zone in the presence of eavesdroppers and interferers with unknown locations. Specifically, we derive the secrecy transmission rate and investigate the relationship between artificial noise and various system parameters like secrecy protected zone radius and intensity of interferers and eavesdroppers on the secrecy transmission rate. In interference-limited networks, we derive the optimal power allocation between the information-bearing signal and artificial noise to maximize the achievable secrecy transmission rate subject to connection and secrecy outage probabilities. Numerical results show that artificial noise is still beneficial in the presence of inherent network interference to improve secrecy transmission rate and provide rules of thumb to quantify when optimal power allocation is useful.