Wendong Yang

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.

A Stackelberg security game with cooperative jamming over a multiuser OFDMA network

In this paper we investigate a cooperative jamming (CJ) strategy based Stackelberg security game to improve physical layer security over multiuser OFDMA networks. Each source node tries to deliver messages to its intended destination node securely in the presence of a passive eavesdropper. Fortunately, these node pairs can resort to a friendly jammer to enhance their communication. But the jamming service is not free and the friendly jammer charges each pair for some cost. Obviously there is a tradeoff between the friendly jammer and the source-destination pairs. Consequently, a two-level Stackelberg game model is proposed, where the friendly jammer plays the seller and the source-destination pairs are the buyers. We analyze the Stackelberg Equilibrium from two sides respectively and prove the existence and uniqueness of the Stackelberg Equilibrium. Correspondingly, we also develop a distributed iterative power allocation algorithm to reach the Stackelberg Equilibrium point. Numerical Results demonstrate that the system sum secrecy rate is really improved and the physical layer security performance is effectively meliorated.

A Fully Distributed Algorithm for Dynamic Channel Adaptation in Canonical Communication Networks

In this letter, a low-complexity, fully distributed algorithm is designed for dynamic channel adaptation in a canonical communication network, where each player can independently update its action without any information exchange. Both the static and dynamic channel environments are studied. The proposed algorithm converges to a set of correlated equilibria with probability one. Moreover, the optimality property of the problem is analyzed. Simulation results demonstrate that the proposed algorithm achieves a near-optimal performance for interference mitigation.

Channel estimation for two-way relay OFDM networks

We consider the channel estimation for two-way relay OFDM networks. We proposed an LS-based channel estimation algorithm under block-based training schemes. Based on the mean square error (MSE) criterion, the condition and the design method for optimal training sequences are discussed. To reduce peak-to-average power ratio (PAPR), a special sequence called Zadoff-Chu sequence is employed to design the optimal training sequence, which can achieve both minimum MSE performance and excellent PAPR performance.

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.

Energy efficiency analysis and enhancement for secure transmission in SWIPT systems exploiting full duplex techniques

This paper investigates the secure transmission in simultaneous wireless information and power transfer (SWIPT) system, where a source node communicates with a wireless-powered full duplex destination node in the presence of a passive eavesdropping node. To take advantage of the benefits from SWIPT and full duplex techniques, we propose a two-phase time-sharing protocol: the destination node harvests energy form the source node in the first phase, while the information-bearing signal is transmitted under the protection of artificial noise sent from the destination node in the second phase. The transmit power of the artificial noise is converted from the harvested energy and self-interference exists at the destination. We derive the closed-form expressions for the connection outage probability (COP), the secrecy outage probability (SOP) and the transmission outage probability (TOP), based on which the secrecy energy efficiency (SEE) is formulated. Furthermore, we determine the optimal time allocation factor and transmission power that maximize the SEE while satisfying the COP and SOP constraints. Finally, numerical results verify our analytical results and show that there are tradeoffs among security, reliability and energy efficiency. When the residual loopback interference is mitigated under some certain level, our proposed optimization scheme can significantly boost the SEE.

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.

Distributed Relay Selection in OFDM-Based Cooperative Wireless Networks

In this paper, we investigate distributed relay selection in OFDM-based cooperative wireless networks. A selective Decode-and-Forward relaying strategy is adopted, in which one relay is selected to forward the entire OFDM symbol. Theoretical outage performance is analyzed and evaluated first. Then six relay selection schemes based on different selection criteria are given. The outage performance of one of the schemes coincides with the theoretical value and all the schemes need only local CSI and can thus be implemented in a distributed way. Monte Carlo simulations validate our analysis and show that significant performance gain can be obtained compared to that of direct transmission.

Security performance of multiple antennas multiple relaying networks with outdated relay selection

We investigate physical-layer security (PLS) for multi-antenna and multi-relay networks with transmit beamforming and relay selection under feedback delay. The connection outage probability (COP) and secrecy outage probability (SOP) are derived to evaluate the reliability and security. Besides, we introduce a novel definition of the reliable-and-secure probability (RSP) to combat the correlation between COP and SOP introduced by the corporate source-relay link. Based on this, to measure the overall efficiency of the system achieving reliable and secure transmission, we further investigate the modified secrecy throughput performance and develop the optimal design of secrecy codeword rate setting to maximize the secrecy throughput. Numerical results verify the analysis and suggest the importance of secrecy codeword rate setting on the security performance.