Research On The Capacity Of Wireless Ad Hoc Networks

Recently, wireless ad hoc networks become a kind of the novel technology in the field of the wireless communication. Without the need for centralized infrastructure support, wireless ad hoc networks having many salient features such as ease of deployment, low cost and low maintenance, has attracted many researchers'considerable attention. The problem on the capacity of wireless ad hoc networks has been put forwarded naturally. The capacity of wireless ad hoc networks is measured by the data transmitted successfully per second on average, about which the discussions are complicated. Firstly, the definition of the capacity of wireless ad hoc networks must be given reasonably. Subsequently, the network model needs to be abstracted and constructed, including the functional models of a variety of nodes, the network topology models, the transmission link models and so on. It is very difficult to determine the above models. One hand, the simple models have no idea to account for the essence of the network. On the other hand, there is no way to deal with the too complex models in math. Moreover, many factors will influence on the network capacity, for example, the choice of the communication method, the traffic pattern, the routing algorithm, the media access control, even the adoption of the new technology. Until now, the research about the capacity of wireless ad hoc networks has been still at the initial stage, where many problems can be studied further. In this dissertation, the capacity of wireless ad hoc networks will be analyzed in the wireless mobile communication circumstances, based on the network mathematical models. The purpose of this dissertation is to improve the performance of the network capacity and provide the theory for establishing the high quality network.Firstly, a wireless ad hoc relay network model is presented, and its capacity problem is discussed. Different traffic patterns will lead to different results on the capacity of wireless ad hoc networks. In the previous literatures, there is only one source node and one destination node in the network, and other nodes act as relay for the communication. As one enlargement, there is at most ns source nodes transmitting signal simultaneously in the network, and some multiple access and broadcasting methods are allowed in our model. The limitations on the capacity of wireless ad hoc relay networks are derived by max-flow min-cut theorem in the graph theory. The results are very important since the Gaussian source and Gaussian channel model are adopted during the analysis process.The technology of ultra wide band (UWB) is applied to the research about the capacity of wireless ad hoc networks. Compared with the existing results on the capacity of wireless ad hoc networks, wireless ad hoc network models under ultra wide band (UWB) are established on the three dimension sphere surface and in the two dimension plane in this dissertation. The restriction of the maximum transmission power of network nodes is assumed. The transmission band is arbitrary large, and the transmission link can be adjusted adaptively. The capacity of wireless ad hoc networks on the three dimension sphere surface is analyzed by the properties of voronoi cell in the graph theory, and the capacity of wireless ad hoc networks in the two dimension plane is discussed by the percolation theory. Our conclusion is that the capacity of wireless ad hoc networks under ultra wide band increases as the number of nodes in the network. One hand, it shows UWB technology is an effective way to improve the network capacity. On the other hand, it provides the theoretical foundation for the integration of UWB technology and wireless ad hoc networks.From the novel point of view, the wireless ad hoc network model is established by the graph theory, and the corresponding network capacity is discussed. The aim is how to obtain the maximum network capacity in wireless ad hoc networks. The main idea is that the network capacity can achieve the maximum when network resources that are limited during nodes communicate with each other are used up minimally on the same condition. In the model, resources consumed by the transmission of nodes in the network can be considered to be a set, where every kind of the resources as one subset will not be intersected each other. According to the above idea, the linear equation of network resources consumed is set up. Multi-node short path algorithm is applied to solve the capacity of wireless ad hoc networks. The fast algorithm to solve the linear equation is presented by our analysis that the capacity of wireless ad hoc networks associating with the routing problem.Subsequently, the problem on the capacity of hybrid wireless networks is studied, based on the criterion of the transmission delay. A hybrid wireless network is the novel network model, where a few base stations are placed within an ad hoc network. In hybrid wireless networks, data can be transmitted in multi-hop fashion or in infrastructure mode. The research about the capacity of hybrid wireless networks is more complicated. In this dissertation, a hybrid wireless network model including both static nodes and mobile nodes is established, and the new routing strategy under the delay constraint is proposed. According to the graphic computation method, the analytical expressions of mathematical expected value on the capacity in hybrid wireless networks are derived. Furthermore, the system and traffic dependent adaptive routing algorithm (STARA) is adopted to analyze the network capacity, which makes the capacity change adaptively as the network topology and the traffic distribution.The capacity of hybrid wireless networks under ultra-wide band is discussed. The scheme that the technology of ultra-wide band is used in hybrid wireless networks is presented and the corresponding network model is established. The bandwidth allocated in multi-hop fashion is obtained by analysis. The method of code division multiple access is introduced to be an optimal medium access control method. The capabilities of data carried in multi-hop fashion and in infrastructure mode are evaluated by the unit of cell. According to the limit theory, the analytical expressions of bound on the capacity in hybrid wireless networks under ultra-wide band are derived. Comparing with the results without the technology of ultra-wide band, the network capacity can be improved at least 12dB.Finally, a general framework to analyze the capacity of hybrid wireless networks in code division multiple access scheme by the markov chain approach is proposed. The mathematical analytical expressions of the finite-population system under some routing policy are derived. By our analysis, the capacity will be increased as the number of base stations and will keep steady at last. For the given condition, we consider the capability of the hybrid wireless network offering loads would be determined, which could exist the theoretic limit depending upon the number of base stations.