Local Topology Information Based MAC And Routing Algorithms For Ad Hoc Networks

The future wireless communications environment will comprise not only the infrastructure networks, such as cellular and satellite networks, but also the infrastruc-tureless networks, ad hoc networks, which are only composed of many nodes. In this dissertation, we do some research on the multihop single channel ad hoc networks. For an ad hoc network, "hidden terminal" and "exposed terminal" problems are well-known issues, which are caused by the inequable awareness of the wireless channel for different nodes. In addition, due to the frequently changed wireless capacity, network topology, etc., the time-varying characteristic becomes another important problem. The two basic problems make it very difficult to obtain all the nodes' states for any node of the network.However, the local network topology and connectivity are easily obtained and updated. In this dissertation, we fully utilize this information and investigate the MAC and routing protocols in depth. The main contributions can be summarized as follows:1. We analyze the throughput performance for multihop ad hoc networks with and without capture when MAC layer adopts slotted ALOHA. Based on the analysis results, we propose a node-degree-based slotted ALOHA protocol, which consists of two parts: 1) a modified Pseudo-Bayesian algorithm, used to estimate the degrees of nodes for multihop ad hoc networks; 2) the adjusting process for packet transmission probabilities, each node dynamically adjusting its packet transmission probability according to the destination's degree. The theoretical and simulation results have shown that the proposed protocol can improve the network throughput greatly compared with the traditional slotted ALOHA protocol, in which the nodes' packet transmission probabilities are fixed. In addition, for the traditional or the new proposed ALOHA with capture, the less the capture ratio the more prominent the capture effect and the greater the network throughput.2. A node-degree-based CSMA/CA protocol is proposed, in which a state parameter q is introduced to the CSMA/CA mechanism of IEEE 802.11 standard. Considering the packet loss phenomenon, we put forward a new two-dimensional Markov model for CSMA/CA protocol. Based on the proposed model, the packet transmission performance is analyzed when CSMA/CA is adopted in multihop ad hoc networks.According to the number of competing nodes obtained from our analysis, each node can dynamically adjust q, thus equivalently changing the initial contention window. Through changing the contention window, the network performance can be improved.3. Aiming to combat the frequently changes of network topology, a neighbor-table-based hybrid multipath routing (NTB-HMPR) is brought forward for ad hoc networks. In NTB-HMPR, the multiple paths are not necessary to be disjoint. Furthermore, we utilize the reliability theory to analyze the route reliabilities of disjoint and non-disjoint multipath routings. The analysis results have shown that the non-disjoint multipath routings can provide more route redundance under unreliable wireless links, thus being more reliable. In addition, the unreliable the wireless links, the more distinct the advantage of non-disjoint multipath routings. In NTB-HMPR, we not only make use of neighbor tables to refresh the local routes in route caches, but also utilize them to estimate the statistical characteristics of wireless links, which can be used to aid route selection. During route discovery process, we bring forward a combined route selection criterion to select the best route based on the attributes of multiple routes. The simulation results have shown that NTB-HMPR are superior to DSR and V-SMR on the packet delivery ratio, packet end to end delay and total transmitted route requests. But this is achieved at the cost of more overhead, which is mainly caused by the periodic transmissions of beacon signals. In practice, we can reduce the overhead by increasing the transmission periodic period.4. We propose an active-node-degree-based routing (ANDBR) formultihop ad hoc networ...