Modeling And Analyzing Throughput For Wireless Ad Hoc Networks With Directional Antenna

Wireless ad hoc network does not rely on fixed infrastructures. It is easy-organized, flexible, and robust. So it is widely used in military and civilian communications. Using directional antennas in ad hoc networks can expand transmission distance, improve the ability of anti-interfere and increase spatial reuse and network throughput. In recent years, the advantages of directional antennas have widely attracted interest of many researchers. However, there are still some unsolved questions, such as “How to quantitatively analyze the relationship between beam-width and network throughput?” “What is the upper limit in different network topologies?” “How to develop an analytical model to analyze the network throughput in specific directional MAC protocol?”. As is known to my best knowledge, few works are able to give the satisfactory answers about the above questions. In the paper, we research analytical approach and develop an analytical model to analyze the saturation throughput in single-hop ad hoc networks, which provides the theory basis for improving performance of MAC protocol. The main contributions of the paper are as follows:(1) Approach of analyzing the upper limit of MAC throughput is studied. We propose the concept of directional-link-concurrency graph to describe the constraint conditions for concurrent transmissions. We also define the maximize throughput problem as the multi-commodity flow problem, which is known to be NP-hard. In the paper, four different algorithms are proposed in unfair and completely fair conditions. Then the complexities of algorithms are analyzed. Through those algorithms, the relationship between beam-width and network throughput are quantitatively studied.(2) Analytical model to analyze the saturation throughput in typical directional random access protocol(D-MAC protocol) is studied. Simulation results show that different links have different saturation throughput due to the hidden and exposed terminals. Therefore, the analytical models for omni-directional networks are not suitable for directional networks. In the paper, we develop a three-dimensional markov chain model to research the nodes' backoff behavior. Through the analysis of three different types of conflicts, we calculate the transmission probability and the collision probability of per-link in single-hop networks. In addition, we further calculate the saturation throughput of every link. Simulation results in different network topologies prove the effectiveness of the proposed model. Finally, we compare the theoretical results and the simulation results of D-MAC protocol with the ideal upper limit in network throughput, which points out that the protocol overhead has a significant influence on the throughput performance.