Chunxiao Cai

When Does Relay Transmission Give a More Secure Connection in Wireless Ad Hoc Networks

Relay transmission can enhance coverage and throughput, whereas it can be vulnerable to eavesdropping attacks due to the additional transmission of the source message at the relay. Thus, whether or not one should use relay transmission for secure communication is an interesting and important problem. In this paper, we consider the transmission of a confidential message from a source to a destination in a decentralized wireless network in the presence of randomly distributed eavesdroppers. The source-destination pair can be potentially assisted by randomly distributed relays. For an arbitrary relay, we derive exact expressions of secure connection probability for both colluding and noncolluding eavesdroppers. We further obtain lower bound expressions on the secure connection probability, which are accurate when the eavesdropper density is small. Using these lower bound expressions, we propose a relay selection strategy to improve the secure connection probability. By analytically comparing the secure connection probability for direct transmission and relay transmission, we address the important problem of whether or not to relay and discuss the condition for relay transmission in terms of the relay density and source-destination distance. These analytical results are accurate in the small eavesdropper density regime.

Outage probability of two-way amplify-and-forward relaying system with interference-limited relay

In the paper, we investigate the overall outage probability (OOP) of the two-way amplify-and-forward (AF) relaying systems in an interference-limited Rayleigh fading environment. More specifically, assuming the presence of Rayleigh faded multiple interferers at the AF relay and noisy sources, an approximate closed-form expression for the OOP are derived. In addition, it is shown that, in terms of the outage probability performance, the worst scenario appears to be the case with equal received-power interferers, for a given total received interference power in this system model. The analysis results are verified through comparison with the simulation results.

Joint subcarrier and power allocation for physical layer security in cooperative OFDMA networks

In this paper, a joint subcarrier and power allocation algorithm is proposed to improve the physical layer security in cooperative orthogonal frequency division multiple access (OFDMA) networks, where several source-destination pairs and one untrusted relay are involved. The relay is friendly and intends to help these pairs to enhance their communications. However, it may be overheard by a malicious eavesdropper at the same time. To optimize the joint subcarrier and power allocation with low complexity, we divide the optimization problem into two simpler subproblems. Firstly, the subcarriers are assigned to the source-destination pairs by employing the dual approach under the assumption that the relay power is equally allocated to all the subcarriers. Then, the relay power is allocated to the subcarriers based on the alternative ascending clock auction mechanism. In addition, we prove that the two subproblems can converge after a finite number of iterations. We also find that the proposed auction is cheat-proof and, thus, can avoid the cheating behaviors in the auction process. Numerical results demonstrate that our proposed algorithm can effectively improve the system sum secrecy rate, and the convergence performance is also desirable.

Overall outage probability of two-way amplify-and-forward relaying in Nakagami-m fading channels

Analytically studying the overall outage performance of two-way amplify-and-forward (AF) relaying systems has always been a difficult task. In this paper we study the overall outage probability (OOP) for the two-way amplify-and-forward (AF) relaying system. The channels are independent but not identically Nakagami-m fading distributed. We obtain the tight closed-form OOP approximated expression for the system. Our results indicate that the tight closed-form approximation can march the simulation perfectly in large signal-to-noise ratios (SNRs). The theoretical analysis can be further applied to study the two-way multiple-relay systems in Nakagami-m fading channels.

Secure Connectivity Using Randomize-and-Forward Strategy in Cooperative Wireless Networks

In this letter, we study the problem of secure connectivity for colluding eavesdropper using randomize-and-forward (RF) strategy in cooperative wireless networks, where the distribution of the eavesdroppers is a homogenous Poisson point process (PPP). Considering the case of fixed relay, the exact expression for the secure connectivity probability is obtained. Then we obtain the lower bound and find that the lower bound gives accurate approximation of the exact secure connectivity probability when the eavesdropper density is small. Based on the lower bound expression, we obtain the optimal area of relay location and the approximate farthest secure distance between the source and destination for a given secure connectivity probability in the small eavesdropper density regime. Furthermore, we extend the model of fixed relay to random relay, and get the lower bound expression for the secure connectivity probability.

Performance Analysis with Partial Relay Selection in Amplify-and-Forward Cooperative Networks

This paper studies the performance with partial relay selection in amplify-and-forward (AF) cooperative networks, where the relay node is selected depending on the instantaneous channel information of source-relay hop. The channels are independent but not identically distributed Rayleigh fading distributed. We obtain the exact outage probability expression and symbol error rate (SER) expression in this system. Our results are verified through comparison with Monte Carlo simulations.

Average secrecy rate analysis with relay selection using decode-and-forward strategy in cooperative networks

In this paper, we study average secrecy rate with relay selection with decode-and-forward (DF) strategy in cooperative networks. The channels are modeled as independent identically Rayleigh distributed coefficients. Exact closed-form expression for average secrecy rate with relay selection is derived. Our results are verified through comparison with Monte Carlo simulations.

Performance analysis of selection decode-and-forward relay networks over Nakagami-m fading channels

In this paper, we analyze the performance of single relay selection cooperative wireless networks using decode-and-forward relaying. Under optimum relay selection, the expressions for asymptotic outage probability, average symbol error probability are derived over Nakagami-m fading channels. Then we improve the performance of the system through optimum power allocation based on asymptotic outage probability and asymptotic average symbol error probability. Our results are verified through comparison with Monte Carlo simulations.

Resource allocation for physical layer security in cooperative OFDM networks

In this paper, we consider the problem of resource allocation scheme for physical layer security in cooperative orthogonal frequency division multiple (OFDM) networks using amplify-and-forward (AF) strategy. To maximize the secrecy rate, the joint optimization of power allocation, subcarrier allocation and subcarrier pairing is proposed. The optimization problem can be solved efficiently by dual method. To reduce the complexity, two suboptimal algorithms are proposed. Monte Carlo simulations are carried out to validate our analysis.

Secrecy Rates for Relay Selection in OFDMA Networks

In this paper, we study the secrecy communication using physical layer security in OFDMA networks. The expressions of secrecy rates and outage probability are derived in OFDMA networks using Decode-and-Forward (DF) strategy. Monte Carlo simulations are carried out to validate our analysis.