Research On Multi-rate For Wireless Ad Hoc Network

A wireless ad hoc network is a set of nodes that can communicate with others in a multi-hop fashion without any assistance of fixed infrastructures. Its main advantage is that it can be rapidly deployed without base station. A wireless ad hoc network can be applied where pre-deployment of network infrastructure is difficult or impossible, for example, mobile meeting, disaster areas, armies on the march.IEEE 802.11 protocol has been accepted as a standard protocol of Medium Access Control (MAC) layer and Physical layer (PHY). The original IEEE 802.11 protocol provides only a single rate. By employing different modulation and channel coding schemes, the IEEE 802.11 PHY provides multiple transmission rates. However it does not specify any schemes to efficiently utilize the multiple transmission rates. Moreover multi-rate is conducive to increase throughput and energy efficiency, thus the research of multi-rate has great significance. The paper focusing on the MAC layer, studies two aspects about multi-rate of ad hoc network, which contain enhancing the throughput and saving energy.Aiming at enhancing the throughput, the paper compares and analyzes several rate adaptation protocols, and improves the Receiver-Based Auto Rate(RBAR)protocol, for one thing, modifies the frame format, which avoids the modification of PHY layer and keeps the compatibility and inter-operation with the standard protocol; for another thing, increases the rate adaptation of fragment, which improves the ability to adapt the channel variation and enhances the throughput. The simulation shows that the protocol has higher throughput than RBAR.Aiming at saving energy, the thesis studies the energy-efficient rate adaptation protocol on the basis of the Distributed Power Control(DPC)algorithm, which selects the most energy-efficient rate under the current channel condition by estimating the channel state online and combinating the energy efficiency level with local queue utilization in order to save energy. Additionally, the protocol alters the backoff interval according to the buffer occupancy, then the transmitting node delay the transmissions using this information, thus reducing packet drops and retransmissions. The simulation shows that the protocol can decrease the loss rate of packet, increase the transmission rate and consume less energy.