Study On Wireless Network Rate Adaptation Algorithms

With the development of Internet, people have become more and more dependent on mobile information services. This trend is driving the technology of wireless network, which requires low cost and little dependency on infrastructure, to work up. The architectures and the systems of wireless networks just cater to this trend exactly.Wireless network means a LAN(Local area network) or Internet which uses wireless channel as a access media for data transmission. Because wireless ad hoc network doesn't need infrastructural communication instrument, it could be built up easily and quickly. With the primary purpose of designing the network, it could self-organize, self-repair, and has a good character of extension and flexibility.Compared with the former mature wired network, wireless ad hoc network may run without a central administration node, its topology structure also may change frequently. The communication between any two nodes is mainly based on sight of line or relayed by a middle node (that is multi-hop routing). So the capacity of the network is not used efficiently.In the serials of the IEEE802.11 protocols, many codec modulation technologies were used to provide multi-rate for a certain frame transmission. For example, 802.11a Physical layer (PHY) supports eight transmission rates (6~54 Mbps), 802.11b PHY supports four transmission rates (1-11 Mbps), and 802.11g PHY twelve rates (1-54 Mbps). The sender selects the best transmission rate based on dynamically adapting its decision to the time-varying wireless channels or its decision to mutative topology of the networks , this technology is called rate adaptation. Presently, the IEEE802.11 protocol MAC(Media access control) layer only defines data type on particular speed, but it does not specify any schemes to efficiently utilize multiple transmission rates so rate adaptation is in the spotlight.The thesis is organized as follows: Firstly, the configurations and the characteristics of ad hoc network based on IEEE802.11 are summarized. Secondly, according to the inherent limitation of wireless ad hoc network, some factors which can bring the negative performance to the network are construed. The transmission rate is one of the main reasons that can cause the network throughput up-and-down is also explained and a brief introduction to a widely used simulation software named Network Simulator Tool(NS2) was shown. Thirdly, a number of algorithms about rate adaptation which can affect the network throughput in recent years have been reviewed and compared respectively. Fourthly, an Anti-Fluctuating Robust Rate Adaptation Algorithm is proposed after RRAA (Robust Rate Adaptation Algorithm) had tested and summarized. Finally, the Anti-Fluctuating Robust Rate Adaptation Algorithm is proved to outperform the RRAA according to the experimental results.