[1] Low-cost, low-power wireless sensor networks (mote networks) have the potential to revolutionize data collection methods in hydrology. They promise the ability to monitor catchments at very high spatial and temporal resolution with flexible sampling schemes, real time data processing and high levels of quality control. We operated an experimental network of 41 motes monitoring seven different parameters each at 15 min intervals for 10 months in a small forested catchment in southwestern British Columbia, Canada, to determine if this emerging technology is suitable for use by hydrologists in its current form. Our particular interests were ease of setup, sampling reliability, power consumption, and hardware resilience. We found that while motes gave the ability to monitor a catchment at resolution levels that were previously impossible, they still need to evolve into an easier to use, more reliable platform before they can replace traditional data collection methods.
Mesh router (MR) placement is one of the fundamental issues that need to be addressed carefully to achieve a desired performance of a wireless mesh network (WMN). The objective of the MR placement schemes is to systematically determine the minimal number of MRs and their positions while satisfying various constraints, such as coverage, connectivity, traffic demand, etc. This paper explores the solution for placing the MRs with multiple transmission rates, which influence both transmission range and wireless link capacity. In the paper, we first formulate the problem with a mixed integer programming model. We then present a heuristic placement algorithm called ILSearch which takes into account both multiple transmission rates and co-channel interference. The ILSearch consists of two components: (1) Coverage MR determination which greedily exploits the capability of each selected MR to cover mesh clients (MCs); and (2) Relay MR determination that incrementally chooses the additional MRs for traffic relaying through the local search. Our simulation has not only shown that ILSearch can effectively obtain the MR placement that meets all the constraints, but also demonstrated that a MR placement which considers the variable transmission rates outperforms those don't.
It is well known that 802.11 suffers from both inefficiency and unfairness in the face of competition and interference. This paper provides a detailed analysis of the impact of topology and traffic type on network performance when two flows compete with each other for airspace. We consider both TCP and UDP flows and a comprehensive set of node topologies. We vary these topologies to consider all combinations of the following four node-to-node interactions: (1) nodes unable to read or sense each other, (2) nodes able to sense each other but not able to read each other's packets and nodes able to communicate with (3) weak and with (4) strong signal. We evaluate all possible cases through simulation and show that the cases can be reduced to 9 UDP and 10 TCP 802.11g models with similar efficiency/fairness characteristics. We also validate our simulation results with extensive experiments conducted in a laboratory testbed. These more detailed models improve on previous work such as hidden-/exposed-terminal categorization and are thus better suited as a basis for adaptive techniques to improve performance in 802.11 multi-hop WLAN or Mesh Networks.
The network performance such as node capacity in a Wireless Mesh Network (WMN) could be limited due to inappropriate interface configuration. Mesh routers (MRs) with heavy load may suffer from interface shortage. On the other hand, a MR with less load experiences a low utilization of interfaces. In this paper, we advocate heterogeneous interface configuration to appropriately configure the MRs' interfaces. It achieves the purpose of minimizing the total number of interfaces in a WMN while guaranteeing the various constraints such as traffic demand. We first formulate the problem when the traffic demand is non-uniformly distributed. On the basis of theoretical analysis, we propose a heuristic algorithm to find a "close-tooptimal" solution for interface configuration. Our simulation shows the effectiveness of our proposed heuristic algorithm.
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