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IEEE Transactions on Signal and Information Processing over Networks

A Method Exploiting the Channel-Training Phase to Achieve Secrecy in a Fading Broadcast Channel

Gustavo Anjos, Daniel Castanheira, Adão Silva, Atílio Gameiro

Published Jan 1, 2022• 0 citations
Publisher

Abstract

This work considers a time-varying Rayleigh block fading broadcast channel formed by two users and an eavesdropper, external to the legitimate network. One of the users is the legitimate/trusted user and the other an untrusted user. The transmitter uses superposition coding to broadcast information to both users. The aim is to ensure the confidentiality of the legitimate user information against the untrusted user and eavesdropper. To satisfy these secrecy constraints, this work proposes an innovative secure channel-training method applied to a cooperative jamming scenario. The jammer uses interference alignment to achieve secrecy against the untrusted user; meanwhile, the developed channel-training method is designed exploiting the time-varying nature of the channel to extend the system secrecy also to the external eavesdropper. An information theoretical evaluation of the proposed scheme demonstrates that (1/4, 1/4) positive secure degrees of freedom are achievable in the presence of both untrusted users and external eavesdroppers.

DOI
10.1109/tsipn.2022.3161086

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This work considers a time-varying Rayleigh block fading broadcast channel formed by two users and an eavesdropper, external to the legitimate network. One of the users is the legitimate/trusted user and the other an untrusted user. The transmitter uses superposition coding to broadcast information to both users. The aim is to ensure the confidentiality of the legitimate user information against the untrusted user and eavesdropper. To satisfy these secrecy constraints, this work proposes an innovative secure channel-training method applied to a cooperative jamming scenario. The jammer uses interference alignment to achieve secrecy against the untrusted user; meanwhile, the developed channel-training method is designed exploiting the time-varying nature of the channel to extend the system secrecy also to the external eavesdropper. An information theoretical evaluation of the proposed scheme demonstrates that (1/4, 1/4) positive secure degrees of freedom are achievable in the presence of both untrusted users and external eavesdroppers.
The study of the physical layer has offered a new perspective to the problem of communication security. This led to the development of a vast set of ideas and techniques rooted in information theory which can be employed in practice to provide unbreakable security. The information-theoretic approach relies mainly on the physical nature of the communication medium. In a wireless medium, the unique features of the wireless communication channel, such as its fading and broadcast nature, can be exploited to achieve higher secure information rates. In this dissertation, we study the secure transmission problem in wireless channels from an information-theoretic perspective. We first consider the fading multiple access wiretap channel. We give two new achievable schemes that use the time-varying (fading) nature of the channel to align the interference from different users at the eavesdropper perfectly in a one-dimensional space while creating a higher-dimensional space for the interfering signals at the legitimate receiver hence allowing for better chance of recovery. While we achieve this alignment through signal scaling at the transmitters in our first scheme (scaling based alignment), we let nature provide this alignment through the ergodicity of the channel coefficients in the second scheme (ergodic secret alignment). For each scheme, we show that the achievable secrecy rates scale logarithmically with the signal-to-noise ratio (SNR). Next, we study the security gains that can be achieved in a wireless network by employing cooperation among the nodes which is possible due to the broadcast nature of the wireless channel. We investigate the role of passive (also known as deaf) cooperation in improving the achievable secrecy rates in a Gaussian multiple relay network with an external eavesdropper. We distinguish between two modes of deaf cooperation, namely, cooperative jamming (CJ) and noise forwarding (NF). We derive the conditions in which each mode of deaf cooperation achieves secrecy rates that are higher than the secrecy capacity of the original Gaussian wiretap channel. As a result, we show that a deaf helper cannot be a useful cooperative jammer and noise forwarder at the same time. We derive the optimal power control policy for each mode. We consider the deaf helper selection problem where a fixed-size set of deaf helpers (possibly operating in different modes) are to be selected from the set of available relays so that the achievable secrecy rate is maximized. We propose a simple and efficient suboptimal strategy for selection which is shown to be optimal when only one helper is selected. Furthermore, we study the role of a multi-antenna deaf helper. Unlike the single antenna case, we show that, in general, it is useful to split the helper's power between cooperative jamming and noise forwarding. Hence, we propose a deaf cooperation strategy for this model and derive its optimal power control policy. We also show, for specific class of relay-eavesdropper channels, that a simple cooperative jamming strategy yields a secrecy rate that approaches the secrecy capacity as the helper's power is increased. Finally, we consider the role of active cooperation for secrecy in the multiple relay networks. We propose several relaying strategies for secure communication and derive the achievable secrecy rate for each strategy. In our strategies the relays decode the source signal and then forward it to the destination either in a single-hop or a multi-hop fashion. Each relay scales its transmitted signal in a way that ensures that signal components from different relays are canceled out at the eavesdropper.
This work addresses the security of a two-user broadcast channel. The challenge of protecting a broadcast channel is associated with the necessity of securing the system, not only against eavesdropping attacks originating from external nodes, but also to ensure that the inside users do not eavesdrop on each other’s information. To address this issue, the present work proposes a cooperative jamming scheme that provides protection against eavesdropping attacks carried out simultaneously by inside users and external eavesdroppers. To achieve this goal, the developed scheme combines real interference alignment with a blind cooperative jamming technique defined in the literature. An information theoretical analysis shows that positive secure degrees of freedom are achievable using the proposed solution.
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.
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.
We consider a single-input multiple-output (SIMO) Rayleigh fading broadcast channel, where the transmitter sends some confidential information to one user which is a legitimate receiver in the presence of multiple eavesdroppers. The eavesdroppers are mutually independent and perfect secrecy is achieved when the transmitter and the legitimate receiver can communicate at some positive rate, while insuring that each eavesdropper gets zero bits of information. Here, we find the probability of non-zero secrecy mutual information and secure outage probability to investigate the outage behavior of proposed model. We also present a formulation of ergodic secrecy mutual information in the presence of multiple eavesdroppers.
We investigate the secure degrees of freedom (SDoF) of the wiretap and the K user Gaussian broadcast channels with multiple antennas at the transmitter, the legitimate receivers and an unknown number of eavesdroppers each with a number of antennas less than or equal to a known value NE. The channel matrices between the legitimate transmitter and the receivers are available everywhere, while the legitimate pair have no information about the eavesdroppers' channels. We provide the exact sum SDoF for the considered system. A new comprehensive upperbound is deduced and a new achievable scheme based on utilizing jamming is exploited. We prove that cooperative jamming is SDoF optimal even without the eavesdropper CSI available at the transmitters.