Technologies such as IEEE 802.11 wireless LANs (WLANs) have revolutionized the way people think about networks, by offering users freedom from the constraints of physical wires. Mobile users are interested in exploiting the full functionality of the technology at their fingertips, as wireless networks bring closer the “anything, anytime, anywhere” promise of mobile networking [1, 2].
Routing in wireless mobile ad hoc networks (MANETs) has been an active area of research for many years [3, 4]. A MANET is an autonomous network that can be formed without (necessarily) using a pre-existing infrastructure. The characteristics such as self-organizing make MANETs prevalent today and continue to grow in popularity. Without centralized administration, individual nodes in MANETs are responsible for dynamically discovering which other nodes they can directly communicate with. A key assumption is that not all nodes can directly communicate with each other, so mobile nodes forward packets to each other, that is, multi-hop, allowing communication among nodes outside the wireless transmission range. The node mobility, dynamic topology, and the fundamentally limited capacity of the wireless medium, together with wireless transmission effects such as attenuation, multipath propagation, and interference, combine to create significant challenges for routing protocols operating.
Firstly, recent research shows, that the single routing protocol reflects some limitations in the case of highly dynamic network topology and strictly limited resources. One observation of single routing AODV [5] is that, though the source discovers multiple paths during the route discovery process, it chooses only the shortest delay route and discards the rest. Also, frequent route breaks cause the intermediate nodes to drop packets because no alternate path to the destination is available. Therefore, multipath routing algorithms have drawn researchers’ attention. The multipath routing allows building multiple paths between a source-destination pair. It can provide benefits such as fault tolerance, load balancing, bandwidth aggregation, and improvement in QoS metrics such as delay [7– 25].
Another key issue is cross-layer optimization. For MANETs protocol design, the physical layer must adapt to rapid changes in link characteristics, the MAC layer needs to minimize collisions and allow fair access, and the network layer needs to make a routing decision for effective data delivery to the destination, and so on. The cross-layer design is desirable for improving performance in MANETs since the methodology of layered protocol design does not necessarily lead to an optimum solution for a dynamic environment. Under the layered protocol design, MANET routing protocols are unable to retrieve energy and location information from the underlying data link layer and physical layer and, thus, unable to calculate routes based on such information. In this work, we use cross-layer design to refer to protocol design and optimization, that is, make use of the node energy signal from the physical layer to optimize routing decisions. Finally, the IEEE 802.11e standard was developed to offer QoS capabilities to WLANs (e.g., MANETs), offering significant improvements to multimedia traffic MANETs will also benefit from this new technology since the most widely deployed and used wireless interfaces are IEEE 802.11-based. Currently, relatively little research work has focused on the interaction between IEEE 802.11e and multipath routing protocols. In this work, the performance of CMRP gain obtained from IEEE 802.11e is demonstrated, using a series of simulation experiments.
Based on the cross-layer design, we propose a multipath routing protocol (CMRP), in consideration of IEEE 802.11e technology, to improve dynamic multi-hop routing performance for MANETs. CMRP uses signal strength information to optimize routing decisions and path quality. The purpose of this work is to ensure wireless multi-hop network performance improvement. Our simulation results demonstrate that, in the combination of the IEEE 802.11e standard at the MAC layer, CMRP provides significant performance improvement in terms of average end-to-end delay, route overhead, route discovery frequency, and packet loss as well.
The remainder of this paper is organized as follows. Section 2 discusses related work on current MANETs routing protocols. Section 3 proposes the cross-layer optimized multipath routing protocol and presents the details of its implementation. Section 4 discusses the performance improvement of CMRP using the IEEE 802.11e standard. Section 5 involves thorough analyses and evaluation of the CMRP performance in simulation methodology. Finally, Section 6 concludes the paper.