Study On Theory And Technology Of Network Forming In Mobile Ad Hoc Networks

Wireless networks provide users with the capability of ubiquitous communicating and access to information at anytime and anywhere, keep connections valid in continuous movement. Users are generally connected to network via base stations in traditional mobile communication systems and a wired backbone is commonly utilized to carry the information transferred among base stations. A mobile ad hoc network (MANET) is a special network that is self-organized by mobile nodes communicating with distributed protocol. Such a network can function in absence of fixed infrastructures, e.g. base stations. Compared with traditional cellular communication networks and wireless networks, mobile ad hoc networks have many advantages, such as infrastructureless, flexibility and low cost. Mobile ad hoc networks have wide applications, where the communication infrastructure is difficult or expensive to be set up, e.g. in military battlefields and emergence search-and-rescue environment.In this dissertation, key theory and technology of network forming in mobile ad hoc networks are studied. At first, the connectivity of mobile ad hoc sensor networks is investigated. Connectivity is a foundational problem in mobile ad hoc networks and involves in many aspects, which are relevant to energy efficiency and communication capacity. Connectivity commonly implies on fully connectivity, so any two nodes can be connected and communicate through at least one single hop or multihop path. In percolation theory, connectivity implies a unique cluster.Wireless sensor networks are special mobile ad hoc networks, which consist of a lot of nodes that are equipped with special sensor, radio transceiver and simple processor. In designing these works, connectivity is a fundamental problem. With the standard assumption of nodes uniformly distributed, theconnectivity is analyzed in the two and three dimensions ad hoc sensor networks according to bit error rate in communication rounting. And then, under the condition that there is no interference and certain interference environment, exact formulas of end-to-end average bit error rate and average connected number of hops in communication routing are derived. These formulas could determine some important parameters in designing these networks, e.g. node transmitting power, data rate, network covering area and node density. At the same time, node density affects end-to-end average bit error rate and network connectivity. In addition, it is shown that there exists threshold value in terms of node spatial density. Below this threshold, communication between nodes can't be achieved.Thereafter, this doctoral dissertation focuses on the connectivity of ad hoc sensor networks under the realistic and shadow fading environments. With the standard assumption of nodes uniformly distributed, the connectivity is theoretically computed in wireless ad hoc sensor networks. Under the realistic and shadow fading environments, formula is acquired according to networks covered methods. By using this formula, minimum node number with which network is connected is determined according to nodes covered radius, or opposed each other. All are helpful for network design and simulation in real engineering application.Next in this doctoral dissertation, adaptive modulation based connectivity enhancement mechanism for ad hoc networks is deeply investigated on the basis of three typical modulation modes, namely QPSK, 16—QAM and 64 —QAM, which are recommended by IEEE 802.16. By theory and numerical value analysis, and compared with single modulation mode, adaptive modulation can satisfy QoS requirement, improve network connectivity and increase throughput consequently.And then, this doctoral dissertation moves its attention to the address dynamical configuration in mobile ad hoc networks. Mobile ad hoc networks are infrastructure-less, highly dynamic, self-organized wireless networks, where central administration or configuration for IP address is impractical. In this doctoral dissertation, it is proposed that a leader selection algorithm is able to take into account the node's ability. The selected leader by this algorithm isresponsible for allocating IP address in mobile ad hoc networks. Then, an adaptively dynamic address allocation protocol is put forward, where network partition and merge are considered. On the condition that duplicate address detection algorithm (DAD) is applied, this protocol can allocate unique IP address to each node in mobile ad hoc networks. This protocol is simulated in NS2 simulation platform. The simulation results indicate that, with the finite control message exchange and bounded latency, this protocol assigns unique IP address to each node. It satisfies the practical network requirements.In the end, this doctoral dissertation discusses the adaptive routing protocol based on multimedia traffic in mobile ad hoc networks. In order to apply multimedia traffic, this doctoral dissertation studied the performance of AODV and DSR routing protocols for mobile ad hoc networks, which is based on 144Kbps transmission rate. Furthermore, the performances of the two protocols are compared and analyzed. The research results indicate that, packet delivery fraction is high and varies slowly in pace with mobility in AODV. As for average end-to-end delay, AODV behaves lower with the higher mobility. But DSR behaves lower compared with AODV with the lower mobility. At the same time, the algorithm of adaptive selection of routing protocols is proposed.