| Ad Hoc network is a multi-hop, non-centralized and self-organizing wireless network. Each node in the network is mobile and it can maintain linked with other nodes dynamically without the help of fixed infrastructual. The network is characterized by dynamic topology, high node mobility, low channel bandwidth and limited capacity. As a special wireless network, it has been widely used not only in military combat and disaster relief environment, but also in commercial activities. Its unique features make the traditional wired network routing protocol inapplicable directly for Ad Hoc networks. Therefore, the appropriate routing protocols for Ad Hoc networks have to be designed. As the key technology of network operation, routing protocol is a decisive factor of the practical application and the operation efficiency of the networks.Multipath routing has a lot of advantages in load balance, bandwidth utilization, fault tolerance and adaptation to the dynamic topology compared to single path routing. Generally speaking, multipath routing proposed for Ad Hoc networks can be classified as constructing node-disjoint, link-disjoint and non-disjoint paths. Node-disjoint multipath routing has advantages in almost every respect over other two multipath routing. However, due to the limitation of the network node density, node-disjoint multiple paths are also the most difficult to discover.In this paper, the multipath routing protocol for Ad Hoc networks is researched thoroughly. The main researches include the node-disjoint multipath routing protocol for large-scale network environments, the node-disjoint multipath routing protocol for high-speed mobile network environments and the radio-disjoint multipath routing for high demand of real-time transmission and large data streaming environments. The main achievements of this paper are as follows:(1) From the perspective of protocol scalability, a geographic routing algorithm called ZMG is proposed to construct maximally node-disjoint multiple paths. All nodes in the network are considered in the same plane area. By use of the location information, the plane area is divided into disjoint regions by elliptic curves. Each node discovers multiple paths and forwards data packets within a disjoint sub-zone. The algorithm discovers paths in disjoint sub-zones, which not only guarantees the path disjointness, but also avoids the control overhead of the route discovery required in topology-based protocols that improves the routing efficiency. In the process of forwarding, two forwarding mode are defined. Also, the corresponding forwarding strategies and conditions for mutual transformation are proposed. The strategies can successfully find node-disjoint multiple paths in networks with high node density and maximally node-disjoint multiple paths in networks with low node density. Experiments show that the protocol is a node-disjoint multipath routing protocol for large-scale network environments.(2) From the perspective of the adaptation to dynamic topology, a beacon-less geographic multipath routing protocol called BGM is proposed. Taking the inherent defect of beacon mechanism of geographic routing into account, the protocol makes further improvements in ZMG protocol in combination with the beacon-less location-based routing mechanism. BGM protocol uses the same zoning method with ZMG, but adds the beacon-less mechanism into the forwarding strategy. Two forwarding delay functions are introduced to ensure that the two forwarding modes with beacon-less mechanism are operated. In order to assist the process of contention, the division of the forwarding area is refined. Also, the contention-based forwarding algorithm is designed with the forwarding delay functions. The BGM protocol not only further reduces the control overhead, but also adapts the dynamic network topology changes further more. It is a multipath routing protocol for high-speed mobile network environments.(3) The most existing beacon-less geographic routing protocols do not take into account the actual result of the unreliability of the wireless channel, which leads to the unsatisfactory performances in the practical application. With the analysis of this situation, a link-quality aware beacon-less geographic routing protocol based on cross-layer technique is proposed. The protocol uses the SNR value obtained from the physical layer to determine the quality of the communication link between nodes and forwards data by use of the MAC layer with RTS/CTS mechanism. Without adding any control packets, the protocol fully considers the link quality factor in the contention-based mechanism. By selecting the link with better communication quality, the protocol reduces the retransmissions and improves the overall network performance, including the packet delivery ratio, end-to-end delay and the number of copies.(4) Taking into account the interference of using multiple paths simultaneously, a maximally radio-disjoint geographic multipath routing protocol called RD-GMR for high demand of real-time transmission and large streaming environments is proposed. This protocol divides the forwarding area between the source node and the destination node into three areas and adopts different forwarding strategies in each area. Moreover, the distance between two nodes is used to estimate the interference radius of nodes in the intermediate area and the interference marking algorithm is applied to mark the interference nodes which cannot take part in the selection of other paths. In addition, the local control mechanism is employed in the source area and destination area, which provides an effective solution for the inevitable interference regions. The protocol constructs the minimize-interference multiple paths with short average path length. It not only effectively improves the packet delivery ratio and the network throughput, but also reduces the end-to-end delay. It is a protocol for the network applications of high demand on real-time and reliability transmission. |
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