A dynamic adaptive acknowledgment strategy for TCP over multihop wireless networks

Multihop wireless networks based on the IEEE 802.11 MAC protocol are promising for ad hoc networks in small scale today. The 802.11 protocol minimizes the well-known hidden node problem but does not eliminate it completely. Consequently, the end-to-end bandwidth utilization may be quite poor if the involved protocols do not interact smoothly. In particular, the TCP protocol does not manage to obtain efficient bandwidth utilization because its congestion control mechanism is not tailored to such a complex environment. The main problems with TCP in such networks are the excessive amount of both spurious retransmissions and contention between data and acknowledgment (ACK) packets for the transmission medium. In this paper, we propose a dynamic adaptive strategy for minimizing the number of ACK packets in transit and mitigating spurious retransmissions. Using this strategy, the receiver adjusts itself to the wireless channel condition by delaying more ACK packets when the channel is in good condition and less otherwise. Our technique not only improves bandwidth utilization but also reduces power consumption by retransmitting much less than a regular TCP does. Extensive simulation evaluations show that our scheme provides very good enhancements in a variety of scenarios.