Modeling And Analysis Of MAC Throughput In Ad Hoc Networks With Heterogeneous Transmit Power Levels

Ad hoc network as a new wireless communication network has gained wide attention. Due to its high reliability and survivability, ad hoc network has been widely applied in military area and civil area. The nodes in ad hoc networks are usually powered by limited capacity batteries. Therefore, how to reduce energy consumption and improve throughput becomes an urgent issue. Power control is one of the main measures. Now a lot of researches focus on design of power control mechanisms and great progress has been made in energy saving. In MAC layer, each data is transmitted with different power levels in ad hoc networks with power control mechanism. MAC layer is at the bottom of the protocol stack and provides a shared way of wireless channel for all nodes in the network. The transmission range, the physical carrier sense range and the collision range all depend on transmit power levels, which have an important impact on throughput. This paper foucuses on the MAC throughput modeling in ad hoc networks with heterogeneous transmit power levels. The main points of the work are summarized as follows.(1) This paper analysizes the capture effect in single-hop ad hoc networks with heterogeneous transmit power levels. With the capture model, the capture probability of the situation when two or three nodes transmit simultaneously is calculated. Furthermore, this paper analyzes the capture probability of the situation when large numbers of nodes transmit simultaneously according to Central Limit Theorem. Based on G. Bianchi’s model, a three-dimensional Markov chain model combined with transmit power is proposed. Then this paper analyzes the probability that node transmits successfully and saturation throughput. Comparions between the simulation results obtained by Qual Net simulator and the numerical results derived by the model validate the effectiveness of the model. With the capture rate, this paper analyzes the throughput of single-hop ad hoc networks with heterogeneous transmit power levels.(2) This paper analyzes the freezing progress and collision probability two difficulties of throughput modeling in multi-hop ad hoc networks with heterogeneous transmit power levels. Based on the protocol and channel condition, a four-dimensional Markov chain model is proposed, which consists of backoff progress, transmission progress and freezing progress. This paper differentiates the cases node selects transmit power with different probability in transmission progress. Each slot time in the model is fixed, which is equal to backoff slot time. Then this paper analyzes all cases collision occurs and calculates the collision probability. With the continuous time Markov chain, the freezing probability and freezing time are calculated. The throughput of each link can be calculated iteratively by establishing the relationship between the four-dimensional Markov chain and the continuous time Markov chain. Finally this paper analyzes the collision probability, transmission probability and throughput of each link with different transmit power levels according to the simulation results and the numerical results.