This paper investigates the physical layer security of frequency-hopping (FH) transmission schemes when the hopping sequence is publicly known. We consider a single-antenna transmitter communicating with a legitimate receiver over a channel estimated with a known error distribution, in the presence of a passive eavesdropper whose channel statistics are available at the transmitter. We show that, when the number of hopping frequencies is sufficiently large, the instantaneous channel fluctuations induced by FH transmissions can be effectively averaged out, and the secrecy performance is accurately predicted by the ergodic secrecy rate (ESR). The ESR is maximized by selecting the optimal modulation order from a set of admissible finite constellations. We derive a closed-form condition on the optimal modulation order, which only depends on the tail probabilities of the legitimate and eavesdropper signal-to-noise ratio (SNR) distributions, and we propose an efficient algorithm for its computation. In particular, we demonstrate that a positive secrecy rate can be achieved even when the eavesdropper has a higher average SNR than the legitimate receiver, provided that the spread of the eavesdropper SNR distribution is sufficiently large. Numerical results validate the proposed framework under a variety of channel models.
This paper investigates the physical layer security of frequency-hopping (FH) transmission schemes when the hopping sequence is publicly known. We consider a single-antenna transmitter communicating with a legitimate receiver over a channel estimated with a known error distribution, in the presence of a passive eavesdropper whose channel statistics are available at the transmitter. We show that, when the number of hopping frequencies is sufficiently large, the instantaneous channel fluctuations induced by FH transmissions can be effectively averaged out, and the secrecy performance is accurately predicted by the ergodic secrecy rate (ESR). The ESR is maximized by selecting the optimal modulation order from a set of admissible finite constellations. We derive a closed-form condition on the optimal modulation order, which only depends on the tail probabilities of the legitimate and eavesdropper signal-to-noise ratio (SNR) distributions, and we propose an efficient algorithm for its computation. In particular, we demonstrate that a positive secrecy rate can be achieved even when the eavesdropper has a higher average SNR than the legitimate receiver, provided that the spread of the eavesdropper SNR distribution is sufficiently large. Numerical results validate the proposed framework under a variety of channel models.
In this paper, by taking into account the requirements of information secrecy and transmission resiliency, we present a comprehensive scheme enabling secure device-to-device (D2D) networks, where a single-antenna transmitter communicates with a half-duplex single-antenna receiver in the presence of a passive eavesdropper and an adversary jammer. Motivated by physical layer security techniques, artificial noise injection scheme is proposed to ensure communication secrecy. To improve the resiliency against jamming attack, the D2D nodes utilize the frequency hopping technique. Under this system model, we examine the achievable ergodic secrecy rate (ESR) by deriving a new closed-form expression. Furthermore, the optimal power allocation between the artificial noise and data signal is studied for maximizing the ESR. Numerical examples and discussions are provided to depict the efficiency of our proposed scheme compared with the state-of-the-arts.
Physical Layer Security of MRC in Fisher–Snedecor F Fading Channels
The physical layer security (PLS) is explored in quasi-static Fisher-Snedecor F Fading Channels with maximal ratio combining (MRC), which have been used to model the conventional and emerging realistic wireless communication channels. We consider the secure transmission of privileged information from a single antenna legitimate transmitter to L-antenna legitimate receiver are wiretapped by L-antenna eavesdropper. The receiver maximizes the probability of secure transmission by adopting MRC, whereas eavesdropper maximizes the probability of eavesdropping by adopting MRC. We derive PLS secrecy metrics for a system setup where the transmitter is having no channel state information (CSI) of both the receiver and eavesdropper. Specifically, we derive a novel closed-form expressions for secure outage probability (SOP) and strictly positive secrecy capacity (SPSC). Furthermore, to obtain important insight into the effect of channel parameters on the secrecy performance, an asymptotic analysis is conducted for SOP at high signal-to-noise ratio (SNR) regime.
Achieving secure transmission in wireless network is a significantly important research topic. Classic cryptography encrypts a confidential message to an unreadable cipher message. Thus only the authentic receiver with correct secrecy key is able to decrypt the message. However, with the growing computational capability of adversaries, the requirement of secrecy key generation and distribution is getting stringent. Another method to achieve wireless security, which has attracted much attention in recent years, is through physical layer processing, named physical layer security. In a typical wiretap channel model consisting of a transmitter, a legal receiver and an adversary (illegal receiver), early works have proven that it is possible to achieve positive secrecy rate using multiple antenna techniques, such as beamforming, at the transmitter. In this thesis, we focus on two types of malicious behaviors of the adversary: passive eavesdropping and active attack. For the passive eavesdropping, we first consider the multi-input-single-output (MISO) wiretap channel, in which the legitimate transmitter utilizes the artificial noise aided precoding strategy to maximize the achievable secrecy rate of the channel. Both scenarios of known and unknown channel state information (CSI) for the eavesdropper channels are considered. By deriving the closed-form expression of ergodic secrecy rate, we prove that there exists an optimal power ratio between the information signal and the artificial noise. We then extend our study to a four-node fading channel model in a wireless relay network, which includes two single-antenna users, one single-antenna eavesdropper and one relay node equipped with multiple antennas. By studying the decode-and-forward (DF) scheme, cooperative jamming (CJ) scheme and one proposed hybrid relay scheme, relay-and-jamming (RJ), we aims to find the optimal relay scheme with the condition that the transmitter and the relay node are under individual power constraints and the CSI of the illegitimate channel is only statistically known. Our analysis shows that the hybrid RJ scheme is optimal when the transmitter has a relatively small power budget and/or the transmitter is far away from the intended receiver. Besides the passive eavesdropping, the adversary could also choose the active attack. The pilot spoofing attack is one active attack conducted by the adversary during the channel estimation phase of the legitimate transmission. In practical systems, the pilot signals are usually known \textit{a priori} and repeatedly used information. In this attack, an intelligent adversary spoofs the transmitter on the estimation of CSI by sending the identical pilot signal as the legitimate receiver. By doing so, the adversary could obtain a larger channel rate in the data transmission phase, and also drastically weaken the strength of the received signal at the legitimate receiver if the adversary utilizes large enough power. Due to the serious consequences caused by such an attack, we first propose an energy ratio detector (ERD) that explores the asymmetry of received signal power levels at the transmitter and the legitimate receiver when the attack occurs. Our analysis shows that the ERD could provide very high probability of detection with certain requirement on the false alarming probability. Furthermore, we design a two-way training based scheme to provide not only attack detection but also secure transmission. The two-way training based detector (TWTD) exploits the intrusive component created by the adversary, followed by a secure beamforming-assisted data transmission. In addition to the good detection performance, our scheme could estimate both legitimate and illegitimate channels, with which the beamforming could be designed for data transmission.
This paper investigates the secure precoding design and proposes a closed-form expression for the approximate achievable secrecy rate. It is assumed that the transmitter knows the full channel information at the legitimate receiver, and knows only the statistics of the channel information at the eavesdropper. We design a time-varying precoder so that it can produce time-varying interference to the eavesdropper, which is capable to resist the wiretap from unknown eavesdropper. Furthermore, we address the power-allocation between information and interference transmission to achieve the optimal secrecy performance. The analysis and numerical results show that the secure precoding design provide significant gains over recent precoding designs especially in high signal-to-noise-ratio (SNR) region. Additionally, the derived results can benefit the maximization of secrecy performance.
This paper studies physical-layer secure transmissions from a transmitter to a legitimate receiver against an eavesdropper over slow fading channels, taking into account the impact of finite blocklength secrecy coding. A comprehensive analysis and optimization framework is established to investigate secrecy throughput for both single- and multi-antenna transmitter scenarios. Both adaptive and non-adaptive design schemes are devised, in which the secrecy throughput is maximized by exploiting the instantaneous and statistical channel state information of the legitimate receiver, respectively. Specifically, optimal transmission policy, blocklength, and code rates are jointly designed to maximize the secrecy throughput. Additionally, null-space artificial noise is employed to improve the secrecy throughput for the multi-antenna setup with the optimal power allocation derived. Various important insights are developed. In particular, 1) increasing blocklength benefits both reliability and secrecy under the proposed transmission policy; 2) secrecy throughput monotonically increases with blocklength; 3) secrecy throughput initially increases but then decreases as secrecy rate increases, and the optimal secrecy rate maximizing the secrecy throughput should be carefully chosen in order to strike a good balance between rate and decoding correctness. Numerical results are eventually presented to verify theoretical findings.
This paper proposes a framework for the artificial noise assisted secure transmission in multiple-input, multiple-output, multiple antenna eavesdropper (MIMOME) wiretap channels in frequency-division duplexed (FDD) systems. We focus on a practical scenario that only the eavesdroppers' channel distribution information (CDI) is available and the imperfect channel state information (CSI) of the legitimate receiver is acquired through training and analog feedback. By taking explicitly into account the signaling overhead and training power overhead incurred by channel estimation and feedback, we define the achievable effective ergodic secrecy rate (ESR), and investigate a joint power allocation and training overhead optimization problem for the maximization of effective ESR. We first derive a deterministic approximation for the achievable effective ESR which facilitates the joint optimization. Then, efficient iterative algorithms are proposed to solve the considered nonconvex optimization problem. In particular, in the high-SNR regime, a block coordinate descent method (BCDM) is proposed to handle the joint optimization. In the low-SNR regime, we transform the problem into a sequence of geometric programmings (GPs) and locate its Karush-Kuhn-Tucker (KKT) solution using the successive convex approximation (SCA) method. For the general case of SNR, we maximize the lower bound of the achievable effective ESR. Simulation results corroborate the theoretical analysis and illustrate the secrecy performance of the proposed secure transmission scheme.