Hao Niu

Performance Study of Two-Hop Amplify-and-Forward Systems With Untrustworthy Relay Nodes

This paper investigates the problem of secure communication for amplify-and-forward (AF) systems with untrustworthy relay nodes. To achieve positive secrecy rate, the destination-based jamming (DBJ) technique is applied. We first focus on the single-relay scenario, for which the closed-form expression for the lower bound of the ergodic secrecy capacity (ESC) is derived. Afterward, we extend the DBJ method to the multi-relay scenario and propose a secure relay selection scheme that can maximize the achievable secrecy rate. Based on the extreme-value theory, the approximate ESC is characterized. Our work reveals an interesting result that, when the relay nodes are untrustworthy, the system performance worsens as the number of relays increases.

On the Combination of Cooperative Diversity and Multiuser Diversity in Multi-Source Multi-Relay Wireless Networks

This letter presents an analysis of the combined use of cooperative diversity and multiuser diversity (MUD) in multi-source multi-relay networks. A joint selection scheme, which selects the best source-relay pair to access the channel, is proposed. The main contribution of our work is the derivation of the exact and asymptotic expressions for the outage probability of the system with amplify-and-forward (AF) protocol. From these expressions it is indicated that the total diversity order of M +N can be achieved, where M and N are the number of source nodes and relay nodes, respectively. Based on the outage probability in high signal-to-noise-ratio (SNR) region, the optimum power allocation scheme is also given to improve the system performance.

Cooperative communications with relay selection in wireless sensor networks

Cooperative communications is a promising technology to improve the performance of wireless sensor networks. In this paper, we propose a novel relay selection scheme combined with feedback and adaptive forwarding in cooperative communication systems. A closed form expression for the tight lower bound of its outage probability is derived and a detailed analysis of its diversity-multiplexing-tradeoff (DMT) performance is presented. Simulation results demonstrate that our method outperforms a variety of existing relay selection schemes in terms of outage performance.

Inter-Relay Interference in Two-Path Digital Relaying Systems: Detrimental or Beneficial?

This Letter studies the two-path digital relaying systems, where two relay nodes alternately forward messages from the source to the destination. By applying the signal space diversity (SSD) technique, a novel adaptive scheme is proposed to deal with the inter-relay interference (IRI). Our work reveals that, with careful protocol design, the IRI becomes a beneficial resource that can be utilized rather than a detrimental factor that has to be suppressed. Simulation results demonstrate that, in high average SNR regions, the proposed method outperforms the existing alternatives in terms of symbol error probability.

Effect of Multiple Antennas at the Destination on the Diversity Performance of Amplify-and-Forward Systems With Partial Relay Selection

This letter considers the amplify-and-forward (AF) system consisting of a destination node with M antennas, and a source node and N relay nodes with a single antenna each. The “best” relay, which is selected depending on the instantaneous and partial channel knowledge, is assigned to assist the source transmission. By deriving the lower and upper bounds for the outage probability of the system, we show that the diversity order of min(M,N) can be achieved. This analysis gives a promising solution to improve the diversity performance of partial relay selection scheme.

Exploiting Fountain Codes for Secure Wireless Delivery

In this letter, a secure delivery scheme that exploits fountain codes is analyzed. For fountain-coded transmission, the receivers have to obtain a sufficient number of fountain packets to recover the original data. Secure delivery can be achieved if the legitimate user receives enough fountain packets first. For this purpose, we utilize the independent channel fading of different users to ensure a higher packet reception rate at the destination. The channel fading is competent if the destination is known to have a better average channel condition than that of the eavesdropper; otherwise, transmit power control relative to the destination channel is employed. Numerical results show that the intercept probability is reduced to zero exponentially as the number of source packets increases. Moreover, due to the ordinary fountain-coded transmission, the achievable data rate of the delivery depends only on the source-destination channel capacity rather than the system secrecy capacity.

Performance Analysis of a Threshold-Based Relay Selection Algorithm in Wireless Networks

Relay selection is an effective method to realize the cooperative diversity gain in wireless networks. In this paper, we study a threshold-based single relay selection algorithm. A reasonable threshold value is set at each relay node, and the first relay with the instantaneous channel gain larger than the threshold will be se-lected to cooperate with the source. The exact and closed form expression for its outage probability is de-rived over independent, non-identically distributed (i. n. i. d) Rayleigh channels. The complexity of the algo-rithm is also analyzed in detail. Simulation results are presented to verify our theoretical analysis.

Exploiting Multiuser Diversity in Wireless Cooperative Networks

In this paper, we present a framework to analyze the outage performance of the cooperative systems exploiting multiuser diversity (MUD). A two-hop wireless network consisting of a destination node, a relay node and multiple source nodes is considered. The asymptotic expressions of the system outage probability are derived for amplify-and-forward (AF) and decode-and-forward (DF) protocols. From these expressions it is shown that the diversity orders of K+1 and K can be achieved for AF and DF, respectively, where K is the number of source nodes in the network.

User cooperation analysis under eavesdropping attack: A game theory perspective

In this paper, the user cooperation behaviors under eavesdropping attack are analyzed through game theory. Considering the physical layer security, we prove that the conventional cooperation scheme actually deteriorates the secrecy performance compared to the direct transmission, given that the eavesdropper has a better channel condition to the users than the destination. In this case, the necessary condition of the cooperation that the users should obtain additional utilities from the cooperation is not satisfied, which makes the users have no incentive to participate in the cooperation game. In order to motivate users, an adaptive cooperation scheme is designed to improve the secrecy performance even if the eavesdropping channel is superior to the destinations channel, and it is also observed that the mutual cooperation is one of the Nash equilibriums. We further exploit the Stackelberg game with a punishment mechanism to make the mutual cooperation as the unique Nash equilibrium.

Secure transmission through multihop relaying in wireless body area networks

This paper analyzes the application of multihop relaying to improve the physical layer security of a wireless body area network (WBAN). Based on the channel characteristics of WBAN, the secrecy outage performance for single-hop and multihop transmission is studied. Results illustrate that multihop relaying performs much better than the single-hop due to the severe path loss caused by the human body.