Journal of Interconnection Networks

In this paper, we propose a multipath routing scheme for wireless mobile networks which extends the Ad Hoc On-demand Multipath Distance Vector (AOMDV) routing protocol, by introducing a novel load-balancing approach to concurrently distribute the traffic among the multiple paths. The traffic-path allocation scheme is based on cross-layer measurements of path statistics reflecting the size and congestion level of each path. In order to provide an efficient support to the proposed routing scheme at the MAC layer, we also study the composition effect of a IEEE 802.11-based enhanced MAC forwarding mechanism called Fast Forward (FF), used to reduce the effects of self-contention among frames at the MAC layer. The protocol framework has been modelled and extensively simulated for a large set of metrics and scenarios. Simulation results provide guidelines for multi-hop communication solutions under both static and mobile scenarios and different traffic loads.

Routing in multi-hop wireless networks is typically greedy, with every connection attempting to establish a path with the smallest number of hops. However, interference plays a major role in limiting the capacity of such networks. While recent protocols have attempted to account for interference, they do so reactively and without coordination. Approaches that coordinate routing to account for mutual interference achieve better performance than traditional approaches. Modeling routing with interference constraints is a complex non-linear optimization problem. We approach the problem using a Multi Commodity flow (MCF) formulation. We analyze the interaction of multiple routes and propose effective objective functions which attempt to maximize interference separation while limiting path inflation. We also show that the pattern of interference experienced by a link plays an important role in defining capacity. The model is directly useful in traffic engineering, provisioning and QoS admission control for mesh networks. In addition, it provides a tool for analyzing effective operation in MHWN providing insight into developing effective distributed protocols for them. We evaluate the formulation against routes obtained using a conventional routing algorithm under several scenarios and show that better performance is achieved in terms of throughput, goodput, and end-to-end delay.

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.

Wireless Sensor Networks (WSNs) have proven their success in a variety of applications for monitoring physical and critical environments. However, the streaming nature, limited resources, and the unreliability of wireless communication are among the factors that affect the Quality of Service (QoS) of WSNs. In this paper, we propose a data mining technique to extract behavioral patterns about the sensor nodes during their operation. The behavioral patterns, which we refer to as Chronological Patterns, can be thought of as tutorials that teach about the set of sensors that report on events within a defined time interval and the order in which the events were detected. Chronological Patterns can serve as a helpful tool for predicting behaviors in order to enhance the performance of the WSN and thus improve the overall QoS. The proposed technique consists of: a formal definition of the Chronological Patterns and a new representation structure, which we refer to as Chlorotical Tree (CT), that facilities the mining of these patterns. To report about the performance of the CT, several experiments have been conducted to evaluate the CT using different density factors.

Multi-hop ad hoc networks allow establishing local groups of communicating devices in a self-organizing way. However, when considering realistic mobility patterns, such networks most often get divided in a set of disjoint partitions. This presence of partitions is an obstacle to communication within these networks. Ad hoc networks are generally composed of devices capable of communicating in a geographical neighborhood for free (e.g. using Wi-Fi or Bluetooth). In most cases a communication infrastructure is available. It can be a set of access point as well as a GSM/UMTS network. The use of such an infrastructure is billed, but it permits to interconnect distant nodes, through what we call “bypass links”. The objective of our work is to optimize the placement of these long-range links. To this end we rely on small-world network properties, which consist in a high clustering coefficient and a low characteristic path length. In this article we investigate the use of three genetic algorithms (generational, steady-state, and cooperative coevolutionary) to optimize three instances of this topology control problem and present initial evidence of their capacity to solve it.

IEEE802.11 WLANs show increasing growth in popularity. Since these networks operate in the unlicensed ISM bands where the number of non-overlapping channels is limited, the growing number of wireless nodes leads to interference. It is well known that the interference leads to degraded performance of WLANs, especially in densely populated areas where the number of overlapping nodes is very large. Channel assignment algorithms have been proposed in recent years, in order to minimize or avoid interference between neighboring access points and hence alleviating the problem. In particular, weighted assignment algorithms have been frequently occurring in the literature. However, the effects of these algorithms are currently not well understood. In this paper, we present results, which show that weighted channel assignment algorithms that do not consider traffic categories can lead to heavy interference among WLANs with delay sensitive traffic, e.g. voice traffic. In order to overcome this, we instead propose a weighted access category channel assignment algorithm (WACCA). We present results from experiments, which show that WACCA achieves a small degree of Interference (DOI) as compared with a greedy algorithm. We also show that there is a tradeoff with convergence time. Furthermore, we propose an integration of WACCA with dynamic transmission power control and show how this combined method produces even more gain.