Access Delay and Throughput Evaluation of Block ACK under 802.11 WLAN

Y.-F. Wen, F.Y.-S. Lin, and K.-W. Lai (Taiwan)


Wireless LANs, Wireless Networks, DCF, Block ACK,Access delay, and Throughput.


The transmission bit rate on wireless media has increased, and will continue to increase, rapidly. However, the high overhead of 802.11 MAC (Media Access Control) protocol degrades the theoretical bandwidth. We therefore propose a block ACK approach to reduce the overhead and increase system capacity. Using block ACK to increase packet size overcomes the constraint of co-existing with Ethernet's maximum packet size. Our approach includes block ACK for the basic mode, the Request-to-Send/Clear-to- Send (RTS/CTS) mode, and IABA (Initial ACK then Block ACK). To understand delay and throughput effects, we propose an extended analytical model. The numerical results show the total throughput of the basic mode degrades as the number of MHs (Mobile Host) increases, but the IABA approach degrades smoothly. The RTS/CTS mechanism not only avoids hidden terminal problems, but also improves the total throughput so that it is higher than the maximum throughput of the original mechanism. Considering the delay issues, the numerical results show that the number of packets per block can not be increased infinitely.

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