RELADO: RELiable and ADaptive Opportunistic Routing Protocol for Wireless Mesh Networks

RELADO: RELiable and ADaptive Opportunistic Routing Protocol for Wireless Mesh Networks

Raffaele Bruno (Institute of Informatics and Telematics of Consiglio Nazionale delle Ricerche, Italy), Marco Conti (Institute of Informatics and Telematics of Consiglio Nazionale delle Ricerche, Italy) and Maddalena Nurchis (Institute of Informatics and Telematics of Consiglio Nazionale delle Ricerche, Italy)
DOI: 10.4018/jaras.2012070104
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Opportunistic routing is considered as one of the most promising techniques to effectively limit performance degradation in wireless mesh networks caused by unpredictable channel variations and high loss rates. This paradigm defers the selection of the next hop after the packet reception to take advantage of any opportunity provided by broadcast transmissions. Most of the existing opportunistic approaches base the forwarder selection on end-to-end principles. However, in multi-hop wireless environments the cost of a path is not uniformly distributed over space, nor constant over time, hence even two equal-cost paths might present significantly different link quality distributions one from the other. This encourages the use of localized context to implement a more accurate selection of the possible forwarders after each packet transmission. Hence, in this paper the authors propose RELADO, an adaptive opportunistic routing protocol able to efficiently combine end-to-end with local information to ensure transmission resilience across the network. With this flexibility, RELADO is able to reduce packet loss by ensuring the best trade-off between throughput maximization and packet progress. An extensive set of ns2 simulations confirms the potentiality of RELADO to improve network performance when compared to both legacy unicast and opportunistic routing protocols.
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Wireless multi-hop networks are comprised of devices that cooperatively relay packets for other devices, ensuring communication between any non-adjacent source-destination pair (Conti et al., 2007). This paradigm has been applied to many different domains, leading to the deployment of various types of networks (e.g., sensor networks, vehicular networks, etc.). Nowadays, Wireless Mesh Networks (WMNs) are one of the most attracting applications of this networking paradigm, due to their inherent capability to reduce the cost and complexity of network deployment, configuration and maintenance. Indeed, a set of static Mesh Routers automatically forms and maintains a wireless backbone, which constitutes the infrastructure responsible for guaranteeing multi-hop communications within the network. Any static or mobile user (also called Mesh Client) can easily connect to the backbone by establishing a communication link with a nearby mesh router through any technology available at both nodes (e.g., Ethernet, 802.11, etc.). Then, each mesh client uses the multi-hop wireless backbone to connect with other mesh clients. In addition, a few mesh routers, called Mesh Gateways, are also connected to the Internet, enabling the mesh backbone to easily extend the coverage provided by the gateways to all the mesh clients (Akyildiz et al., 2005). In fact, wireless mesh networks have been originally conceived as a low-cost wireless extension of existing infrastructure-based wired networks. However, nowadays the foresee application scenarios for WMNs include several different cases, such as public safety communications, community-based networks, and on-demand communication systems for first responders (Bruno et al., 2005).

The attractive features of wireless mesh networks, such as self-organization, low up-front cost and ease of incremental deployment (Karrer et al., 2004), have stimulated a large body of work in the research community and in the standardization groups of different wireless technologies (e.g., 802.11s, 802.11e, etc.). Routing protocols design is one of the fundamental aspects to be considered in order to guarantee robust and low-overhead communications through the mesh backbone. The most intuitive approach to develop solutions for such networks is the application of the routing paradigm originally designed for the wired domain, that is, the selection of the minimum-cost path between a source and a destination (Clausen et al., 2003; Perkins et al., 2003). This choice implies a point-to-point link abstraction and relies on the assumption that link-layer retransmissions can effectively deal with packet losses. Although this approach has been the first attempt to make wireless mesh networks a reality, it has recently revealed its limitations when dealing with unreliability and unpredictability of wireless transmissions. Indeed, wireless medium is intrinsically broadcast, thus concurrent packet transmissions may potentially interfere with each other, leading to severe performance degradation due to the high channel contention. In addition, channel conditions may significantly change both in time and space, making a pre-determined path ineffective in providing a resilient communication (Biswas et al., 2005; Camp et al., 2006; Chachulski et al., 2007; Ramachandran et al., 2007). Indeed, despite the static nature of mesh routers, the high variability of link quality may cause topology and routes instability similarly as mobility in Mobile Ad hoc Networks (aka MANETs). In addition, particular network conditions may exacerbate this instability. For instance, very challenged environments are typical in applications such as disaster recovery and emergency situations, where WMNs are foreseen to be a key technology to substitute legacy infrastructure-based communication systems (e.g., cellular networks). However, also unplanned deployments of community-based networks make very difficult to guarantee high quality and stable wireless links between mesh nodes. Hence, a great deal of effort has been made in the development of more robust and resilient routing paradigms for WMNs.

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