| Ad hoc network is a wireless system without a fixed (wired or wireless) infrastructure. It is a self-organizing network composed of mobile nodes or users. Recently, Ad hoc network becomes the hot spot of wireless communications and Internet due to its flexible mobility support, and continuous and seamless multimedia communication. Ad hoc network is a complicated system. It involves a lot of technical aspects, of which MAC layer and routing layer are of the most importance. There are still quite a number of open problems in these areas.In our research, we focus on some important technologies about MAC and routing layers. The effect of interaction and combination of those technologies on the performance of ad hoc network are studied. The main research results of this dissertation are as follows:1. The analytical model of 802.11 DCF in multi-hop networks is proposed in this paper, which takes both MAC layer and network layer factors into account. Thus, It supports multi-hop network research better than its existing counterparts. The performance of 802.11 DCF Ad Hoc networks is studied with the model in this paper. In multi-hop Ad Hoc networks with randomly distributed nodes, we try to find the optimal transmission radii to maximize the expected progress of packets sent by a node for four routing schemes. It is shown that, with a given node distribution density, the expected progress of packets sent by a node decreases monotonously as the transmission radii increases. This implies that the optimal transmission radii does not exist in such a network, and a shorter transmission has an tendency to improve the network capacity, given that the connectivity of network is guaranteed.2. The effect of topology control technology on the performance of AD HOC is then studied in this paper. In the course of analysis and simulation model development, we take the impact of topology control on network layer, MAC layer and physical layer into consideration. This diverges from other relative works that only take the MAC layer perspective. Simulation results shows that topology control technology can reduce energy consumption and improve spatial reuse capability of the whole network, but the end-to-end throughput measure fails to be improved, which reflects the capability of network to support traffic. There seems to be a tendency~the higher spatial reuse capability a topology has, the weaker end-to-end throughput it results in. The main reason is that the number of packet forwarding events and transmission failure events increases, when topology control methods are applied.3. An enhanced RIEMS rate-adaptive MAC protocol (RIEMS+) is proposed, and its performance is studied. The RIEMS+ protocol overcomes the shortcoming in NAV update mechanism of the original RIEMS protocol, i.e., the channel reserve time information in different frames may have different values and ranges of impact, which results nodes have different cognition on channel status. Thus the probability of transmission failure decreases and the channel utility factor increases. Simulation results prove that the proposed method can improve the ETE throughput and average packet transmission delay obviously.4. A dynamic rate aware routing scheme is presented which helps to increase network throughput and to reduce the ETE transmission time needed to forward packets from source to destination in mobile Ad Hoc networks (MANET). This scheme divides routing function into two parts, wide area routing function and local area routing function . Local area routing function, as an independent sub layer, selects additional redirector properly between transmitter-receiver pairs to reduce average link transmission range, in order to achieve higher total transmission rate. A protocol implementing local area routing function , LDSR is presented. Simulation result shows that this new routing scheme outperforms traditional AD HOC routing protocols due to its better utilization of multi-rate support.
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