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Considering a nonregenerative untrusted relay network, we investigate three different secure transmission strategies, for example, noncooperative strategy, conventional amplify-and-forward (AF) strategy, and cooperative jamming (CJ) strategy. To thoroughly assess the secrecy performance achieved by the three strategies, we derive the closed-form expressions for the connection outage probability and secrecy outage probability regarding each strategy. Based on these expressions, the reliability and security tradeoff (RST) is examined to facilitate the design of the transmitting parameters. We then present the closed-form expression for the effective secrecy throughput (EST) and characterize the overall efficiency of these transmission strategies. Furthermore, we conduct the asymptotic analysis for the secrecy throughput, which enables us to determine the optimal transmission strategy under different scenarios. Our analytical and numerical results demonstrate that compared with the noncooperative and AF strategies, the CJ strategy possesses the best performance in terms of RST. Additionally, we also find that the EST performance of the AF strategy is nearly invariable when the quality of the second hop changes. [ABSTRACT FROM AUTHOR]

Decode-and-forward relaying is a promising enhancement to existing radio access networks and is currently being standardized in 3GPP to be part of the LTE-Advanced release 10. Two inband operation modes of relay nodes are to be supported, namely Type 1 and Type 1b. Relay nodes promise to offer considerable gain for system capacity or coverage depending on the deployment prioritization. However, the performance of relays, as any other radio access point, significantly depends on the propagation characteristics of the deployment environment. Hence, in this paper, we investigate the performance of Type 1 and Type 1b inband relaying within the LTE-Advanced framework in different propagation scenarios in terms of both coverage extension capabilities and capacity enhancements. A comparison between Type 1 and Type 1b relay nodes is as well presented to study the effect of the relaying overhead on the system performance in inband relay node deployments. System level simulations show that Type 1 and Type 1b inband relay deployments offer low to very high gains depending on the deployment environment. As well, it is shown that the effect of the relaying overhead is minimal on coverage extension whereas it is more evident on system throughput. [ABSTRACT FROM AUTHOR]

Road-based directional broadcast protocols are proposed in the literatures to offset efficiency of message dissemination of traditional broadcast protocol in urban vehicular ad hoc networks. However, these protocols cannot provide enough reliability and efficiency for vehicles’ misclassification at intersection or on straight road. Therefore, we present regular-hexagon-equilateral-triangle area grouping–based broadcast protocol for urban vehicular ad hoc networks. The area covered by relay node is averagely divided using regular-hexagon-equilateral-triangle, and vehicles are grouped according to the area that they reside. The algorithm for constructing regular-hexagon-equilateral-triangle is proposed. We adopt same vehicles’ grouping method at intersection and on straight road, and no neighbor list is maintained to identify road intersection. We design waiting time formula to calculate time for node forwarding message. It is ruled that node with waiting time dropping to zero first is defined as the relay node, and this relay node transmits message. So there is only one relay node which forwards message in each group. It also rules in regular-hexagon-equilateral-triangle area grouping–based broadcast protocol that each relay node forwards the same message only once, therefore, it limits redundant message retransmission. Using the vehicles’ grouping method and selection strategy of relay node as mentioned above, the proposed protocol enables message to be transmitted in different directions along different roads at the same time. Simulation indicates that our protocol has a better performance [ABSTRACT FROM AUTHOR]

In wireless sensor networks, node placement plays a significant role in terms of meeting design goals, such as cost effectiveness, connectivity, lifetime, and data latency. In tunnel environments, the energy consumption of sensor nodes and relay nodes is imbalanced because of the long and narrow shape of tunnels. In this article, to reduce the use of extra batteries and the number of forwarding times for a message, we propose a new approach to assist in the placement of relay nodes for two-tier wireless sensor networks in a tunnel environment. The approach proposed is based on the principle that working relay nodes can change approximately at the same time during network operation. It seems the relay nodes move to a new place when they are instead by dormant relay nodes. The approach provides a novel method that has been proved to find optimal places to deploy relay nodes in tunnel environment. Moreover, the approach balances the energy consumption of entire sensor nodes and prolongs the lifetime of entire networks significantly, which is shown in simulations. [ABSTRACT FROM AUTHOR]

Mobile roaming authentication scheme achieves the mutual authentication and session key establishment between the mobile user and the foreign agent. In 2013, Xie et al. pointed out that Chen et al.'s scheme is vulnerable to offline password attack, and does not achieve fair session key generation, user untraceability, user friendliness, and perfect forward secrecy, and then they proposed an improved scheme. In this paper, we propose an improvement of Xie et al.'s scheme, since the foreign agent may confuse the mobile users when multiple mobile users simultaneously access the foreign agent in Xie et al.'s scheme. Further, we prove the formal security of the proposed scheme, and present the performance comparison between our scheme and some related schemes. The proposed scheme is more efficient and secure than other related schemes and is suitable for using in the global mobility network. [ABSTRACT FROM AUTHOR]