Adaptive CSMA for Scalable Network Capacity in High-Density WLAN: A Hardware Prototyping Approach
Jianping Zhu, Bernard Metzler, X. Guo, Y. Liu · 2006
Abstract — Fast proliferation of 802.11 devices has led to the emergence of High-Density WLAN where 100s-1000s clients being serviced by 10s-100s of APs in a multi-cell environment. Scalable network capacity becomes a primary design challenge. In this paper, we investigate the impact of hidden/exposed terminal and the lack of capture effect on today’s 802.11 devices on network throughput. We argue that the CSMA/CA parameters in 802.11 MAC protocol need to be adaptive to the changing network topology, traffic and interference. We propose a combination of Receiving-Sensitivity adaptation to reduce stronger-last collision and a Clear-Channel-Assessment adaptation to balance the hidden/exposed terminal problems. We take a hardwarecentric approach to modify the 802.11 MAC protocol and prototype adaptation algorithms on Intel Centrino TM laptops. We demonstrate through testbed measurement that Receiving-Signal-Strength-Indicator and Packet-Error-Rate are effective are readily available metric on today’s 802.11 hardware for the two adaptation algorithms. Our results show that the adaptation algorithms are able to react to the changing network environment and quickly converge to the new value setting. Up to 300 % throughput increase has been observed with the adaptation algorithms.