Broadcasting over the fading wiretap channel is investigated for the situation without the channel state information (CSI) at the transmitter and subject to a delay constraint. A new broadcast approach is developed, which integrates secure superposition coding studied in the authors' previous work and embedded coding in a hybrid fashion. This scheme outperforms the previous approaches for the cases when the eavesdropper's channel is fading. The secrecy rate achievable via the new broadcast approach is derived, and the structure of the optimal power allocation function across the secure coding layers is characterized via techniques for solving the problem of constrained calculus of variations. A notion of probabilistic secrecy is introduced and studied, which characterizes the probability that a certain secrecy rate is achieved for any given fading block. Numerical examples are provided to demonstrate the impact of CSI at the transmitter if not available and the channel fluctuation of the eavesdropper on the average secrecy rate.
Broadcasting over the fading wiretap channel is investigated for the situation without the channel state information (CSI) at the transmitter and subject to a delay constraint. A new broadcast approach is developed, which integrates secure superposition coding studied in the authors' previous work and embedded coding in a hybrid fashion. This scheme outperforms the previous approaches for the cases when the eavesdropper's channel is fading. The secrecy rate achievable via the new broadcast approach is derived, and the structure of the optimal power allocation function across the secure coding layers is characterized via techniques for solving the problem of constrained calculus of variations. A notion of probabilistic secrecy is introduced and studied, which characterizes the probability that a certain secrecy rate is achieved for any given fading block. Numerical examples are provided to demonstrate the impact of CSI at the transmitter if not available and the channel fluctuation of the eavesdropper on the average secrecy rate.
A (layered) broadcast approach is studied for the fading wiretap channel without the channel state information (CSI) at the transmitter. Two broadcast schemes, based on superposition coding and embedded coding, respectively, are developed to encode information into a number of layers and use stochastic encoding to keep the corresponding information secret from an eavesdropper. The layers that can be successfully and securely transmitted are determined by the channel states to the legitimate receiver and the eavesdropper. The advantage of these broadcast approaches is that the transmitter does not need to know the CSI to the legitimate receiver and the eavesdropper, but the scheme still adapts to the channel states of the legitimate receiver and the eavesdropper. Three scenarios of block fading wiretap channels with stringent delay constraints are studied, in which either the legitimate receiver's channel, the eavesdropper's channel, or both channels are fading. For each scenario, the secrecy rate that can be achieved via the broadcast approach developed in this paper is derived, and the optimal power allocation over the layers (or the conditions on the optimal power allocation) is also characterized. A notion of probabilistic secrecy, which characterizes the probability that a certain secrecy rate of decoded messages is achieved during one block, is also introduced and studied for scenarios when the eavesdropper's channel is fading. Numerical examples are provided to demonstrate the impact of the CSI at the transmitter and the channel fluctuations of the eavesdropper on the average secrecy rate. These examples also demonstrate the advantage of the proposed broadcast approach over the compound channel approach.
A (layered) broadcast approach is studied for fading wiretap channels. The basic idea is to employ superposition coding to encode information into a number of layers and use stochastic encoding for each layer to keep the corresponding information secret from an eavesdropper. The legitimate receiver successively decodes information one layer after another by canceling the interference caused by the layers that the receiver has already decoded. The advantage of this approach is that the transmitter does not need to know the channel states to the legitimate receiver and the eavesdropper, but can still securely transmit certain layers of information to the legitimate receiver. The layers that can be securely transmitted are determined by the channel states to the legitimate receiver and the eavesdropper. The Gaussian wiretap channel with fixed channel gains is first studied to illustrate the idea of the broadcast approach. Three cases of block fading wiretap channels with a stringent delay constraint are then studied, in which either the legitimate receiver's channel, the eavesdropper's channel, or both channels are fading. For each case, the secrecy rate that can be achieved by using the broadcast approach is obtained, and the optimal power allocation over the layers (or the conditions on the optimal power allocation) is also derived.
The secrecy outage of a two-user slow fading broadcast channel is studied in this paper. We consider the scenario where independent and confidential messages are transmitted to each user using superposition coding in the presence of an external eavesdropper. We assume the instantaneous channel state information (CSI) of the eavesdropper's channel is not available and the secrecy outage can be claimed for each user. The secrecy outage probability of each user conditioned on the instantaneous CSI of the legitimate channel is studied and used to derive the achievable secrecy rate region under the conditional secrecy outage probability constraints. The average achievable secrecy rate, i.e. the secrecy throughput, is studied as the measure of performance under the slow fading. The optimal secrecy rate allocation strategy that achieves the boundary of the achievable secrecy throughput region is characterized for the general case and for the maximum sum secrecy throughput. Numerical results of the secrecy throughput regions are shown, and the parameters that influence the secrecy throughput are discussed.
In this work, we investigate the problem of secure broadcasting over block-fading wiretap channels with limited channel knowledge at the transmitter. More particularly, we analyze the effect of having a finite rate feedback on the throughput of multi-user broadcast wiretap channels. We consider that the transmitter is only provided by a b -bits feedback of the main channel state information (CSI) sent by each legitimate receiver, at the beginning of each fading block, over error-free public links with limited capacity. Also, we assume that the transmitter is aware of the statistics of the eavesdropper's CSI but not of its channel's realizations. Under these assumptions of CSI uncertainty, we characterize the ergodic secrecy capacity of the system when a common message is broadcasted to all legitimate receivers, the ergodic secrecy sum-capacity when multiple independent messages are transmitted, and the ergodic secrecy capacity region for the broadcast channel with confidential messages (BCCM). In all three scenarios, we show that as long as the transmitter has some knowledge of the main CSI, obtained even through a 1-bit CSI feedback, a non-zero secrecy rate can still be achieved. The impact of having the feedback sent over a binary erasure channel (BEC) is also investigated for the BCCM case. Here again, and even with the possibility of having the feedback bits erased, a positive secrecy rate can still be achieved as long as the erasure event is not a probability-one event. An asymptotic analysis of the obtained results is provided for the high SNR regime, and the scaling law of the system, when the number of legitimate receivers is large, is also presented.
In this paper we study the block fading binary erasure wiretap channel, where the transmitter sends secret messages to a legitimate receiver over a block fading erasure channel in the presence of an eavesdropper. The eavesdropper receives the transmitted secret message over a separate block fading binary erasure channel. It is assumed that the transmitter knows the instantaneous channel state information (CSI) of the main channel and knows only the probability distribution of the capacity of the wiretap channel. We mainly consider the case where the transmitter adapts the code based on the CSI of the main channel in order to achieve either a certain secrecy rate or a certain level of secrecy. We compare the two proposed scenarios for the adaptive coding method based on the probability of secrecy outage and the average throughput.
The issue of physical layer security for the wireless communication with slow fading is addressed in this paper, and the secrecy outage performance is concerned. The system is modeled as a wiretap channel, and each of the transmitter and receivers is equipped with a single antenna. The channel state information (CSI) about the channel from the transmitter to the legitimate receiver (the main channel) is assumed to be perfectly known by the transmitter and the receivers, while the transmitter does not know the CSI about the channel from the transmitter to the eavesdropper (the eavesdropper's channel) but its probability density function (PDF). Differing from the fixed secrecy rate scheme and the on/off scheme in the literature, this paper adaptively chooses the secrecy rate. The secrecy rate for each value of the main channel gain is determined by the required secrecy outage probability and the PDF of the eavesdropper's channel, and the secrecy throughput is maximized under the constraint of the transmit power for the required secrecy outage probability. The quasi-static Rayleigh fading channel is used to compare our scheme with the two existing schemes, and simulation results show that our scheme outperforms them when small secrecy outage probabilities are required.