Improving TCP/IP performance over IEEE 802.11 wireless networks

Wireless telecommunication is characterized by high error rates and low bandwidth compared to wired networks. Errors in wireless telecommunications usually occur in bursts followed by periods of low BER. TCP and IP are not designed to work efficiently in high BER networks. Because TCP was designed for a low BER wireline network, it assumes that any lost packet is due to congestion rather then error. IEEE 802.11 is a MAC protocol for shared wireless medium. It is designed for creating wireless LANs with ad hoc or cellular topology. This thesis examines the performance of TCP/IP over ad hoc and cellular wireless networks using IEEE 802.11. IEEE 802.11 in a cellular network fails to support good quality voice and web traffic because of wireless errors. To avoid reduction in TCP transmission rate and to sufficiently reduce losses for good quality voice and web traffic, we show that a combination of retransmissions (ARQ) with forward error correction (FEC) can be used to mask wireless errors and provide a channel with a smaller error rate to TCP/IP. This allows IEEE 802.11 to support quality voice traffic with a loss rate less than 1% and web traffic at up to 75% lower response time, together with bulk TCP traffic in a cellular network. In ad hoc networks, bulk TCP transfers fail after 5 hops, whereas FEC and ARQ allow bulk TCP transfers to span up to at least 10 hops.