DIMINISHING MAC OVERHEAD BY USE OF PERIODIC AND COOPERATIVE ACK SCHEMES IN 802.11 WIRELESS NETWORKS

摘要

This paper presents schemes that reduces ACK (acknowledgement) overhead in IEEE 802.11 wireless networks and further improve network performance in high error rate cases. While the ACK takes only 20us in 802.11a at 54Mbps, a combination of SIFS period and preamble makes ACK the second largest overhead next to channel access overhead. To reduce ACK overhead, we proposed periodic and cooperative ACK schemes. In periodic ACK scheme, a single ACK is used to periodically acknowledge multiple packets received independently at different transmission occasions on each channel separately. However, the periodic ACK scheme suffers throughput degradation in high error rates. To overcome this issue, a cooperative ACK scheme was applied. In cooperative ACK, a single ACK is sent on one of the active channels to acknowledge multiple packets received on different channels collectively, rather than acknowledging multiple packets received on each channel separately. This reduces ACK timeouts that would result in excessive retransmissions since an ACK timeout on one channel would be recovered on another channel thus improving network performance. Extensive simulation in ns3 shows that the proposed schemes improve network throughput by considerable amount in various environments.