Wireless sensor networks have attracted great attention in research and industrial development due to its fast-growing application potentials. New techniques must be developed for sensor networks due to their lack of infrastructure support and the constraints on computation capability, memory space, communication bandwidth, and above all, energy supply. To prolong the life time of a battery-powered sensor network, an energy efficient routing algorithm for data collection is essential. We propose a new geographic routing algorithm that forwards packets from sensors to base stations along efficient routes. The algorithm eliminates the voids that cause non-optimal routing paths in geographic routing. It replaces the right-hand rule by distance upgrading. It is fully distributed and responds to topology changes instantly with localized operations. We formally prove the correctness of the algorithm and evaluate its performance by simulations.

In mobile ad hoc networks(MANET), the limited wireless spectrum, distributed multiple access control, low complexity, and high mobility together impose significant challenges for MAC protocol design to provide reliable wireless communications with high data rates. In contention based MAC protocols, such as 802.11 MAC, each multi-hop data flow encounters contentions not only from the transmissions of itself, but also from other flows that bypassing the neighborhood. This paper presents a Dynamic Token Ring based MAC protocol(DRP) for mobile ad hoc networks, which aims to solve the intra-flow and inter-flow contention problems in MAC layer. It is called dynamic, since the token ring in a cluster can be a low-priority ring or a high priority ring. The node can join high priority ring dynamically according to transmission status. The simulation results show that DRP has superior performance in improving data delivery efficiency and avoiding collisions. It is a good solution for inter-flow/intra-flow contention as well as hidden/exposed terminal problems.

Location-areas is a popular location management scheme in cellular networks In the location areas scheme, a service area is partitioned into location areas, each consisting of contiguous cells. A mobile terminal updates its location whenever it moves into a cell that belongs to a new location area. However, no matter how the location areas are designed, the ping-pong location update effect exists when a mobile terminal moves back and forth between two location areas. The paper defines a new kind of ping-pong effect referred to as the generalized ping-pong effect, and shows that it accounts for a nonnegligible portion of the total location update cost. Although several strategies have been proposed to reduce the ping-pong effect in the literature, they either eliminate no generalized ping-pong effect or introduce a larger paging cost. This paper proposes a triple-layer location management strategy to eliminate the generalized ping-pong effect, therefore greatly reducing the total location update cost. Simulation results show that the triple-layer strategy outperforms the existing schemes designed to reduce the ping-pong effect.

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Location tracking keeps track of the location of mobile users in a mobile network. It involves two basic operations: updating and paging. Accordingly the cost of location tracking consists of two parts: updating cost and paging cost. Efforts have been made to minimize the total tracking cost. One of the strategies is the reporting center scheme which selects some cells as reporting centers. Mobile users will only update their location when they move into a new reporting center, and when a call arrives, the vicinity of the reporting center will be paged to find the specific user. This scheme decreases updating cost while increasing paging cost. Hac and zhou proposed an algorithm to minimize the total cost of the reporting center scheme. This paper presents a variation of the reporting center scheme which clusters the reporting centers based on some specific criteria. Thus updating cost will be further decreased but the paging cost will increase. The paper compares the performance of the variation with the original reporting center scheme and shows that the variation scheme outperforms the original one when the call-to-mobility ratio is lower than some threshold.