In this paper, we investigate the secure transmission design with practical assumptions on the channel state information (CSI). Specifically, the CSI of the legitimate link is imperfectly estimated and the CSI of the eavesdropper is unknown to the legitimate users. We derive both a fixed-rate and an adaptive-rate transmission schemes by explicitly considering the rate parameters of the wiretap code in the secure transmission design. The derived schemes achieve the maximum throughput subject to constraints on the secrecy performance against eavesdropping and the reliability performance against channel estimation error. For a given target throughput requirement, our numerical results illustrate how the security performance needs to be compromised when the accuracy of channel estimation reduces. One interesting finding is that the security cost of having a small amount of channel estimation error is low, while the security cost increases fast when the channel estimation error becomes considerable.
In this paper, we investigate the secure transmission design with practical assumptions on the channel state information (CSI). Specifically, the CSI of the legitimate link is imperfectly estimated and the CSI of the eavesdropper is unknown to the legitimate users. We derive both a fixed-rate and an adaptive-rate transmission schemes by explicitly considering the rate parameters of the wiretap code in the secure transmission design. The derived schemes achieve the maximum throughput subject to constraints on the secrecy performance against eavesdropping and the reliability performance against channel estimation error. For a given target throughput requirement, our numerical results illustrate how the security performance needs to be compromised when the accuracy of channel estimation reduces. One interesting finding is that the security cost of having a small amount of channel estimation error is low, while the security cost increases fast when the channel estimation error becomes considerable.
Physical layer security has recently been regarded as an emerging technique to complement and improve the communication security in future wireless networks. The current research and development in physical layer security are often based on the ideal assumption of perfect channel knowledge or the capability of variable-rate transmissions. In this paper, we study the secure transmission design in more practical scenarios by considering channel estimation errors at the receiver and investigating both fixed-rate and variable-rate transmissions. Assuming quasi-static fading channels, we design secure on-off transmission schemes to maximize the throughput subject to a constraint on secrecy outage probability. For systems with given and fixed encoding rates, we show how the optimal on-off transmission thresholds and the achievable throughput vary with the amount of knowledge on the eavesdropper's channel. In particular, our design covers the interesting case where the eavesdropper also uses the pilots sent from the transmitter to obtain imperfect channel estimation. An interesting observation is that using too much pilot power can harm the throughput of secure transmission if both the legitimate receiver and the eavesdropper have channel estimation errors, while the secure transmission always benefits from increasing pilot power when only the legitimate receiver has channel estimation errors but not the eavesdropper. When the encoding rates are controllable parameters to design, we further derive both a non-adaptive and an adaptive rate transmission schemes by jointly optimizing the encoding rates and the on-off transmission thresholds to maximize the throughput of secure transmissions.
In this paper, we investigate the physical-layer security of slow fading wiretap channel with channel estimation errors. We aim to maximize the reliable secrecy rate under constraints of secrecy outage probability and reliability outage probability. To this end, we propose an adaptive (ADP) transmission scheme in which the communication rate and secrecy rate are adaptively adjusted based on the estimated imperfect channel state information (CSI) of the legitimate channel. The optimal solution is obtained by solving a single-variable maximization problem, where the objective function is log-concave. Numerical results are provided to verify our approach as well as to show the impact of imperfect CSI on the secrecy throughput.
We design new secure on-off transmission schemes in wiretap channels with outdated channel state information (CSI). In our design, we consider not only the outdated CSI from the legitimate receiver but two distinct scenarios as well, depending on whether the outdated CSI from the eavesdropper is known at the transmitter. Under this consideration, our schemes exploit useful knowledge contained in the available outdated CSI, and based on this, the transmitter decides on whether to transmit or not. We derive new closed-form expressions for the transmission probability, the connection outage probability, the secrecy outage probability, and the reliable and secure transmission probability to characterize the achievable performance. Based on these results, we present the optimal solutions that maximize the secrecy throughput under dual connection and secrecy outage constraints. Our analytical and numerical results offer detailed insights into the design of the wiretap coding parameters and the imposed outage constraints. We further show that allowing more freedom on the codeword transmission rate enables a larger feasible region of the dual outage constraints by exploiting the tradeoff between reliability and security.
We study secure transmission considering the practical scenario in which only outdated knowledge of the legitimate receiver's channel and statistical knowledge of the eavesdropper's channel are available at the transmitter. Conditioned on the limited channel knowledge, we adopt an on-off secure transmission scheme and propose a versatile strategy to determine the codeword transmission rate. We first analyze the outage performance of the system and then provide the design of optimal wiretap code parameters maximizing the secrecy throughput. Compared with the existing solution in the literature, the proposed secure transmission design enlarges the achievable reliability-security region and increases the maximum secrecy throughput.
We investigate the problem of secure broadcasting over fast fading channels with imperfect main channel state information (CSI) at the transmitter. In particular, we analyze the effect of the noisy estimation of the main CSI on the throughput of a broadcast channel where the transmission is intended for multiple legitimate receivers in the presence of an eavesdropper. Besides, we consider the realistic case where the transmitter is only aware of the statistics of the eavesdropper's CSI and not of its channel's realizations. First, we discuss the common message transmission case where the source broadcasts the same information to all the receivers, and we provide an upper and a lower bound on the ergodic secrecy capacity. For this case, we show that the secrecy rate is limited by the legitimate receiver having, on average, the worst main channel link and we prove that a nonzero secrecy rate can still be achieved even when the CSI at the transmitter is noisy. Then, we look at the independent messages case where the transmitter broadcasts multiple messages to the receivers, and each intended user is interested in an independent message. For this case, we present an expression for the achievable secrecy sum-rate and an upper bound on the secrecy sum-capacity and we show that, in the limit of large number of legitimate receivers K, our achievable secrecy sum-rate follows the scaling law log ((1-α)log(K)), where α is the estimation error variance of the main CSI. The special cases of high SNR, perfect and no-main CSI are also analyzed. Analytical derivations and numerical results are presented to illustrate the obtained expressions for the case of independent and identically distributed Rayleigh fading channels.
We investigate the problem of secure broadcasting over fast fading channels with imperfect main channel state information (CSI) at the transmitter. In particular, we analyze the effect of the noisy estimation of the main CSI on the throughput of a broadcast channel where the transmission is intended for multiple legitimate receivers in the presence of an eavesdropper. Besides, we consider the realistic case where the transmitter is only aware of the statistics of the eavesdropper's CSI and not of its channel's realizations. First, we discuss the common message transmission case where the source broadcasts the same information to all the receivers, and we provide an upper and a lower bounds on the ergodic secrecy capacity. For this case, we show that the secrecy rate is limited by the legitimate receiver having, on average, the worst main channel link and we prove that a non-zero secrecy rate can still be achieved even when the CSI at the transmitter is noisy. Then, we look at the independent messages case where the transmitter broadcasts multiple messages to the receivers, and each intended user is interested in an independent message. For this case, we present an expression for the achievable secrecy sum-rate and an upper bound on the secrecy sum-capacity and we show that, in the limit of large number of legitimate receivers K, our achievable secrecy sum-rate follows the scaling law log((1-a ) log(K)), where is the estimation error variance of the main CSI. The special cases of high SNR, perfect and no-main CSI are also analyzed. Analytical derivations and numerical results are presented to illustrate the obtained expressions for the case of independent and identically distributed Rayleigh fading channels.