Narrow Results

A new algorithm involving flank array geometry calibration under strong multipath conditions is proposed to address the problem of installation errors and the shell deformation. The derived linear mapping relationship between geometric error of sensors and signal eigenvector reduces the calculating difficulty in near calibration mode. By regarding the reflection as coherent visual sources in known position, the compensation strategy of strong multipath matching is put forward. Cramer–Rao bound (CRB) analysis for the calibration mode is employed. Numerical simulations and lake trials verify the efficiency of the proposed algorithm and illustrate the performance improvement under strong multipath conditions.

In mobile ad hoc networks (MANETs), link failures are caused frequently because of node’s mobility and use of unreliable wireless channels for data transmission. Multipath routing strategy can cope with the problem of the traffic overloads while balancing the network resource consumption. In the paper, an optimized node-disjoint multipath routing (ONMR) protocol based on ad hoc on-demand vector (AODV) is proposed to establish effective multipath to enhance the network reliability and robustness. The scheme combines the characteristics of reverse AODV (R-AODV) strategy and on-demand node-disjoint multipath routing protocol to determine available node-disjoint routes with minimum routing control overhead. Meanwhile, it adds the backup routing strategy to make the process of data salvation more efficient in case of link failure. The results obtained through various simulations show the effectiveness of the proposed scheme in terms of route availability, control overhead and packet delivery ratio.

The lack of resources in routers will become a crucial issue with the deployment of state storing protocols. In particular, single or any source multicast protocols will most probably take over large amounts of resources for maintaining multicast tree information. The aim of this paper is to study the possibility and benefit of using multiple shortest paths in order for a new member to reach a multicast tree. Such a mechanism would not reduce the overall amount of state information in the network but it would distribute this amount more evenly among all routers. The idea is to use alternate shortest paths provided by the underlying unicast routing protocol to avoid saturated routers, that is, routers that can not or do not want to store any more multicast state information. As the simulation results are very sensitive to the topology, we have used subgraphs of an Internet map. We have then simulated our multipath join mechanism and have found that depending on the tree size, the use of our mechanism can increase successful join attempts by up to 55% when the network is half saturated.

Existing TDMA-based MAC protocols for wireless sensor networks are not specifically built to consider communication channels that are prone to fading. We describe the impact of periodically changing environment on small-scale fading effects in industrial indoor wireless networks. Using a site-specific ray tracer, we show that the position of nodes and the periodic movements of objects with constant velocities in the environment have significant impact on signal fading. Finding that fading is approximately periodic, we propose a TDMA-based MAC protocol for wireless sensor networks built for industrial applications that uses link state dependent scheduling. In our approach, nodes gather samples of the channel quality and generate prediction sets from the sample sets in independent slots. Using the prediction sets, nodes only wake up to transmit/receive during scheduled slots that are predicted to be clear and sleep during scheduled slots that may potentially cause a transmitted signal to fade. We simulate our proposed protocol and compare its performance with the well published Z-MAC protocol. We found that our protocol significantly improves packet throughput and energy consumption as compared to Z-MAC. We also found that in conditions which are not perfect under our assumptions, the performance of our protocol degrades gracefully.