Under the constraints of quality of service and average transmission power, this paper studies the power control to maximize the energy efficiency of secure transmission. Assuming that the transmitter has imperfect channel state information, the derivation of the optimum power control rule and comparison of its resulting energy efficiency with various power control strategies are presented. Then, the impact of estimation error and number of antennas on the average secrecy energy efficiency (SEE) as well as the trade-off between the average SEE and quality of service will be characterized. The results show that the average SEE with the optimum power control increases significantly for small number of antennas or low transmit power. The results also show that the loss of average SEE is remarkably at high estimation error or extremely-high quality of service.
Under the constraints of quality of service and average transmission power, this paper studies the power control to maximize the energy efficiency of secure transmission. Assuming that the transmitter has imperfect channel state information, the derivation of the optimum power control rule and comparison of its resulting energy efficiency with various power control strategies are presented. Then, the impact of estimation error and number of antennas on the average secrecy energy efficiency (SEE) as well as the trade-off between the average SEE and quality of service will be characterized. The results show that the average SEE with the optimum power control increases significantly for small number of antennas or low transmit power. The results also show that the loss of average SEE is remarkably at high estimation error or extremely-high quality of service.
In this paper, secure transmission of information over an ergodic fading channel is studied in the presence of statistical quality of service (QoS) constraints.We employ effective capacity to measure the secure throughput of the system, i.e., effective secure throughput. We assume that the channel side information (CSI) of the main and the eavesdropper channels is available at the transmitter side. Under this assumption, we investigate the optimal power control policies that maximize the effective secure throughput. In particular, it is noted that opportunistic transmission is no longer optimal and the transmitter should not wait to send the data at a high rate until the main channel is much better than the eavesdropper channel. Moreover, it is shown that the benefits of adapting the power with respect to the CSI of both the eavesdropper and main channels rather than the CSI of only the main channel diminish as QoS constraints become more stringent.
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.
This paper considers an energy-efficient transmit design in a general multiple-input single-output multiple-eavesdropper (MISOME) wiretap channel. Specifically, a transmitter sends one confidential message to a legitimate receiver, which must be kept perfectly secure from several external multi-antenna eavesdroppers. Assuming imperfect channel state information (CSI) at the transmitter, our goal is to design the input transmit covariance, such that the worst-case secrecy energy efficiency (WC-SEE) is maximized, subject to the quality of service (QoS) and total transmit power constraints. Due to the nonconvexity of this problem, an equivalent parametric reformulation, based on the fractional programming theory, is proposed to recast this problem as a sequence of semidefinite programs. By this means, the maximum WC-SEE can be found via a root search algorithm. Moreover, we also give an approach to constructing a rank-one optimal covariance matrix of the confidential message from our proposed algorithm, which implies the optimality of transmit beamforming to achieve the maximum WC-SEE. Numerical results are presented to verify the efficacy of our proposed method.
In this letter, a multiple antennas-based truncated channel inversion power control (CIPC) secure transmission scheme with artificial noise (AN) is proposed. Specifically, the transmitter with multiple antennas varies the transmit power as per channel to ensure the received signal power equals a certain constant valueQ, and uses the residual power to transmit AN for interfering the eavesdropper. We first derive the expression for the probability of secure transmission. Relying on this, we then study the optimization problem in terms of the achieved effective secrecy throughput (EST), which quantifies the amount of information that the transmitter can securely send to the receiver, subject to the constraints that the probability of secure transmission is no less than a predetermined value. The numerical results show that increasing the transmission power will not continuously decrease the probability of secure transmission. Furthermore, we find that there exists an optimalQto maximize the EST performance, and the optimal value ofQincreases with the number of antennas.
With the rapid development of wireless communications, security becomes extremely important. In many applications, each transmitter desires to send independent and confidential message to its intended receiver while ensuring mutual information-theoretic secrecy. In this dissertation, I study strategies for enhanced secrecy in wireless communication systems with limited rate feedback and transmitter cooperation. The two-user Gaussian channel model is considered under different scenarios. The transmitters both require channel state information (CSI), which is quantized at the receiver and fed back through the sum-rate-limited feedback channels. The quantization errors reduce the beamforming gain from the direct transmitter, and cause interference leakage from the cross transmitter. In the first scenario, I introduce the wiretap channel model where one receiver is a known eavesdropper, and a second transmitter is used to send a cooperative jamming signal to degrade the eavesdropper's channel. I consider two cases, one where no information about the eavesdroppers is available, and one where statistical CSI is available. With no information about the eavesdroppers, I show how to choose the allocation of feedback bits to the transmitters in order to maximize the amount of jamming power available to interfere with the eavesdroppers, subject to maintaining the lower bound on the rate at a minimum quality-of-service level. For the case of statistical CSI, I derive an approximate lower bound on the average secrecy rate, and optimize the bound to find a suitable bit allocation and the transmit power allocated to the transmitters. In the second scenario, I consider the interference channel model where the two transmitters are amenable to cooperation for improving the overall secrecy performance of the system. I derive an approximation for the average secrecy rate of each link, and optimize the sum secrecy rate over the transmit power and feedback bits allocated to the transmitters. Interestingly, increasing the transmit power beyond a certain point decreases the secrecy performance. When the transmitters have the same number of antennas, I derive the results in closed form. Simulations validate the theoretical analysis and demonstrate the significant performance gains that result from the use of optimal transmit power control and intelligent feedback bit allocation.
In this paper, we study the problem of physical layer security in large-scale multiple input multiple output (LS-MIMO) systems. The large number of antenna elements in LS-MIMO system is exploited to enhance transmission security and improve system performance, especially when the eavesdropper is closer to the information source and has more antennas than the legitimate user. However, in practical systems, the problem becomes challenging because the eavesdropper channel state information (CSI) is usually unavailable without cooperation and the legitimate CSI may be imperfect due to channel estimation error. In this paper, we first analyze the performance of physical layer security without eavesdropper CSI and with imperfect legitimate CSI, and then propose an energy-efficient power allocation scheme to meet the demand for wireless security and quality of service (QoS) simultaneously. Finally, numerical results validate the effectiveness of the proposed scheme.