Simple algorithms have been developed in the area of node localization in a wireless sensor network. For these simple algorithms to work, several assumptions were made. However, the accuracy of such assumptions affects the effectiveness and performance of such algorithms. For example, the irregular propagation pattern of transmission range is often neglected in both simulation and analysis. This paper investigates the accuracy of these assumptions and proposes some modifications to improve the hop count localization algorithm in an actual physical implementation.

Localization schemes using hop-counts to reference nodes of known positions have been proposed to localize nodes in a sensor network. However, these schemes usually work well only when the networks have uniform and dense node distribution. A novel density-aware hop-count localization (DHL) algorithm is described to improve the accuracy of location estimation when the node distribution is non-uniform. When the density is low, each hop traversed is not necessarily equivalent to the maximum range distance. A range ratio is used to adjust the accumulated hop-count and this effectively reduces distance overestimation. Simulations show that our algorithm improves the localization accuracy compared to the algorithms without density considerations. The overhead incurred by DHL is found to be lower than that incurred by conventional schemes.

A mobile ad hoc network is an autonomous system of infrastructure-less, multihop, wireless mobile nodes. Reactive routing protocols perform well in this environment due to their ability to cope quickly against topological changes. This paper proposes a new routing protocol named CHAMP (caching and multiple path) routing protocol. CHAMP uses cooperative packet caching and shortest multipath routing to reduce packet loss due to frequent route failures. We show through extensive simulation results that these two techniques yield significant improvement in terms of packet delivery, end-to-end delay and routing overhead. We also show that existing protocol optimizations employed to reduce packet loss due to frequent route failures, namely local repair in AODV and packet salvaging in DSR, are not effective at high mobility rates and high network traffic.

In an ad hoc sensor network clock synchronization is a serious issue as nodes in the sensor network have different clock drifts. One of the common solutions for the time synchronization among these nodes is the active transmission of time stamp messages. However this method consumes some resources and channel bandwidth, and is not suitable for resource constrained nodes in the sensor network. This work presents a novel method with minimum overhead that reduces clock drift effects in the synchronization of nodes in sensor networks using relative time-slot referencing TDMA based MAC protocol.

A mobile ad hoc network is an autonomous system of infrastructureless, multihop wireless mobile nodes. Reactive routing protocols perform well in such an environment due to their ability to cope quickly against topological changes. In this paper, we propose a new routing protocol called Caching and Multipath (CHAMP) Routing Protocol. CHAMP uses cooperative packet caching and shortest multipath routing to reduce packet loss due to frequent route breakdowns. Simulation results reveal that by using a five-packet data cache, CHAMP exhibits excellent improvement in packet delivery, outperforming AODV and DSR by at most 30% in stressful scenarios. Furthermore, end-to-end delay is significantly reduced while routing overhead is lower at high mobility rates.

This paper discusses and investigates the effects of mobility on positioning of wireless ad hoc networks. We present a mobility-enhanced ad hoc positioning (MAP) scheme, where we leverage on the mobility of nodes within network. The scheme uses the hop counts information from fixed reference nodes to perform positioning and improves accuracy by using mobile nodes to "bridge" gaps within neighborhoods where accurate information was not available. Simulation shows that using mobility does improve the performance of such "hop count"-based positioning schemes.