Improvements of transmission reliability in wireless multihop and interworking networks

Abstract

A wireless ad hoc network is a new-type of network where wireless devices communicate with each other without the support of an infrastructure. Because there is no infrastructure that manages communication among stations, each node functions as a router. Thus, communication within a wireless ad hoc network occurs across multiple stations. Though this multihop communication characteristic has some advantages, it also has some challenging problems, such as, routing, wireless channel contention, hidden/exposed node problems, and etc. As a result, performance over this multihop communication path is seriously limited. In addition, the transport control protocol (TCP) which is widely used in the Internet yields poor performance in wireless ad hoc networks. This poor performance of TCP in wireless ad hoc networks is due to not only the limited performance of multihop path, but also the fundamental assumption of TCP operation. TCP interprets a packet loss as a sign of network congestion, and consequently invokes congestion control and avoidance procedures. Due to the problems of multihop communication path in wireless ad hoc networks, packet losses occur frequently, which makes TCP invoke unnecessary congestion control procedure and, as a result, makes TCP provide poor performance. To investigate the performance of TCP in wireless multihop networks, we analyze the performance of wireless multihop networks using IEEE 802.11 DCF mode and the performance of TCP over this multihop path. Based on the analysis of IEEE 802.11 DCF mode with considering hidden node problem, we extend the analysis to the multihop case. Then, based on the TCP analysis model by Gupta, we calculate the maximum performance of TCP in wireless multihop networks. The analysis results show that the normalized throughput performance over wireless multihop networks is severely limited about 0.1 due to hidden/exposed node problems. Moreover, increased packet drop probabil...