Xue Zhang

Social Contribution-Based Routing Protocol for Vehicular Network with Selfish Nodes

Routing in vehicular network is a challenging task due to the characteristic of intermittent connectivity, especially when nodes behave selfishly in the real world. Previous works usually assume that all nodes in the network are willing to forward packets for others, which is impractical in real world. Selfish behaviors of nodes would degrade network performance greatly. In this paper, we propose SCR, a social contribution-based routing protocol, for selfish vehicular network. When making forwarding decision, SCR considers both the delivery probability to the destination and the social contributions of the relay node. The delivery probability is determined by the social relations among nodes and social contribution is used as the incentive to stimulate selfish nodes to be more cooperative, which consists of reciprocal contribution and community contribution. The node with higher delivery probability and lower social contributions is the preferred candidate for the next hop. Simulation results show that SCR achieves better performance than other social routing protocols with the incentive scheme.

Principles for Energy-Efficient Topology Control in Wireless Sensor Networks

Topology control is one of the most important energy-saving techniques used in wireless sensor networks. It has evolved into two dominant research directions: power control and sleep scheduling. Although many topology control algorithms and protocols are claimed to be highly energy-efficient, this is not necessarily the case in real systems due to various isolated considerations. In this paper, based on a simple and comprehensive analysis of energy consumption, we propose three necessary principles for energy-efficient topology control for wireless sensor networks. Topology control should (1) consider power control and sleep scheduling jointly, (2) be aware of traffic load, and (3) be done in conjunction with routing. We wish this paper could contribute to the development of the research on topology control for wireless sensor networks.

Quantitative analysis of the effect of transmitting power on the capacity of wireless ad hoc networks

This paper presents a fundamental understanding regarding the effect that transmitting power has on the capacity of wireless ad hoc networks. Under the assumption that all interference is essentially regarded as noise, we carry out a quantitative analysis from the perspective of information theory. First, we answer the question, How much information can be carried per unit bandwidth over a wireless ad hoc network under a certain power assignment and nodal distribution? We then prove that the maximum network capacity, whether in bps (bits per second) or in bmps (bit-meters per second), strictly increases with respect to the total transmitting power under a fixed-proportion assignment, and that there is a limit as the total transmitting power goes to infinity. We further conclude that the maximum power efficiency, whether in bpJ (bits per Joule) or in bmpJ (bit-meters per Joule), strictly decreases with respect to the total transmitting power under a fixed-proportion assignment. We also show that the maximum network capacity, whether in bps or in bmps, follows an O(n) scaling law, where n is the number of nodes, which coincides with previous asymptotic conclusions. Finally, we highlight the practical implications of the results for power allocation, power assignment, and transmission scheduling. The contributions of this paper may be worthy of consideration by wireless network designers.

Mobile content distribution with vehicular cloud in urban VANETs

Plenty of multimedia contents such as traffic images, surveillance video, music and movie will flood into vehicular ad hoc networks. However, content distribution over VANETs is not a easy task, due to the high mobility of vehicles and intermittent connectivity. Infrastructure-based scheme can relieve the problem, but with a large amount of investment. In this paper, we propose a mobile content distribution scheme based on roadside parking cloud (RPC), which is formed by the parked car on the roadside, and mobile cloud (MC), which is formed by moving cars on the road. According to a trip history model, a mobile car can estimate its following trajectory. When it wants to download the content, gateway node of the RPC will work out a downloading schedule, which tells it how much chunks it can download from which RPCs. Moreover, the helper of the mobile car in mobile cloud would deliver specified chunks to it when there is lack of RPC in the following trip. Simulation results show that cloud-based scheme performs better than inter-vehicle communication approach and cluster-based scheme.

A study on event-driven TDMA protocol for wireless sensor networks

MAC protocol controls the activity of wireless radio of sensor nodes directly so that it is the major consumer of sensor energy and the energy efficiency of MAC protocol makes a strong impact on the network performance. TDMA-based MAC protocol is inherently collision-free and can rule out idle listening since nodes know when to transmit. However, conventional TDMA protocol is not suitable for event-driven applications. In this paper, we present ED-TDMA, an event-driven TDMA protocol for wireless sensor networks. Then we conduct extensive simulations to compare it with other MAC protocols such as BMA, S-MAC, and LMAC. Simulation results show that ED-TDMA performs better for event-driven application in wireless sensor networks with high-density deployment and under low traffic.

Proportion-Integral Power Control for Wireless Ad Hoc Networks

Power control plays an important role in wireless communications. However, most existing power control protocols are not efficient enough to be applied in real ad hoc network systems. In this paper, we propose PIPC (Proportion-Integral Power Control), a novel closed-loop power control algorithm that can be used in conjunction with any routing protocol as long as the routing table of a node provides enough knowledge of local network topology. PIPC adaptively adjusts the transmission power for each node through an improved version of the classical PID (Proportion-Integral-Differential) control. The topology derived under PIPC is also fed back to the routing table that is used as its input. Both theoretical analysis and simulation study show that PIPC has a good performance.

PREG: a practical power control algorithm based on a novel proximity graph for heterogeneous wireless sensor networks

Power control is one of the most important techniques used in wireless sensor networks. However, most power control algorithms proposed so far are impractical, because previous work usually makes such perfect assumptions as uniform transmission ranges, location-awareness, and so on. In this paper, we propose REG (Relative Energy-cost Graph), an algorithm to derive a novel proximity graph, which is optimal in the sense of sparseness while preserving the least energy consumption path between any two nodes. And based on REG, we further put forward a new practical power control algorithm PREG (Practicalized REG) for heterogeneous networks. Our theoretical analyses and simulation results show that PREG has a better performance than other power control algorithms thanks to its high practicality and energy efficiency.

PCAR: A power controlled routing protocol for wireless ad hoc networks

Power control and routing are two fundamental supporting techniques for wireless communications in ad hoc networks. However, most existing power control and routing proposals are not really efficient enough, due to separate considerations on them. In this paper, motivated by the observation on the necessity and feasibility of the combination of power control and routing, we propose a power controlled routing protocol PCAR (Power Controlled Ad hoc Routing). The basic idea is to develop power control on top of the distance-vector routing mechanism that is based on the classical distributed Bellman-Ford algorithm. Each node adjusts the transmission power automatically through the PIPC (Proportion-Integral Power Control) algorithm that we previously proposed. Both theoretical analysis and simulation results show that PCAR has a good performance.

Automatic control on transmission power in wireless networking

The automatic control theory plays an important role in modern industries. With the rapid development of the Internet and a variety of wireless networks, its application field has been becoming wider and wider. However, in the design of networking protocols, instead of utilizing the classical control theory, most software engineers favor open-loop control. In reality, closed-loop control may well serve as a simple and efficient part in some cases. In this paper, we try to apply the classical control theory to the adjustment on the transmission power in wireless networking. As a result, we propose APC (Automatic Power Control), a distributed power control algorithm that can be used in conjunction with any routing protocols as long as the routing table of each node provides enough knowledge of local network topology. The basic idea of APC is to adjust the transmission power for each wireless node through an improved version of the classical PID (Proportion-Integral-Differential) control. The network topology derived under APC is also fed back to the routing table that is used as its input. Both theoretical analysis and simulation study show that APC is an effective application of the classical control theory in wireless networking.

A Study on MAC Protocols for Wireless Sensor Networks

Medium Access Control (MAC) is an important technique that ensures the successful operation of WSN because it controls the radios activity of sensor nodes, which consumes nodes major energy. MAC protocols must be energy efficient in wireless sensor networks. In this paper, we study MAC protocols for WSNs, including schedule-based protocols such as TDMA and contention-based protocols such as S-MAC. Then we make comparisons with some typical MAC protocols to show the impaction on network performance under different scenarios.