Link Quality Aware Robust Routing for Mobile Multihop Ad Hoc Networks

Abstract

A mobile ad hoc network (MANET) (Perkins, 2001; Siva Ram Murthy & Manoj, 2004; IETF, 2009) is a collection of mobile nodes without any fixed infrastructure or any form of centralized administration. In other words, it is a temporary network of mobile nodes without existing communication infrastructure such as access points or base stations. In such a network, each node plays a router for multihop routing as well. MANETs can be effectively applied to military battlefields, emergency disaster relief, and other applicationspecific areas including wireless sensor networks and vehicular ad hoc networks. In mobile ad hoc networks, interference and noise are two major obstacles in realizing their full potential capability in delivering signals. In wireless links, the signal propagation is affected by path loss, shadowing and multi-path fading, and dynamic interferences generate additional noise from time to time degrading link quality. In this study, as an effective and practical metric of link quality, signal-to-interference plus noise ratio (SINR) is used because it takes interference and noise as well as signal strength into account. Note that SINR is measurable with no additional support at the receiver (Krco & Dupcinov, 2003; Zhao et al., 2005). Furthermore, as nodes are fast moving, poor links are unpredictably increased. Actually, it is shown that the communication quality of mobile ad hoc networks is low and users can experience strong fluctuation in link quality in practical operation environments (Gaertner & Cahill, 2004). In particular, sending real-time multimedia over mobile ad hoc networks is more challenging because it is very sensitive for packet loss and the networks are error prone due to node mobility and weak links (Karlsson et al., 2005). Accordingly, it is very important to include as many high-quality links as possible in a routing path. Also, the dynamic behavior of link quality should be taken into consideration in protocol design. In the IEEE 802.11 MAC (IEEE, 1999), broadcast packets are transmitted at the base data rate of 1 Mbps. It is mainly due to the potential demand that a broadcast packet should cover as large area as possible in the wireless LAN environment. Note here that, given radio hardware and transmit power, the transmission range is affected by the transmit rate. In mobile ad hoc networks, the route request (RREQ) packet in routing protocols is a broadcast packet. Therefore, if a distant node receiving an RREQ rebroadcasts the RREQ, a long weak link with low data rate can be included in the discovered route. Intuitively, this helps the routing protocols to find out the minimum hop-count route from source to destination. Note here that the minimum hopcount route is a routing path with the minimum number of hops from source to destination and sometimes called the shortest path in the viewpoint of graph algorithm. However, such