CSMA/CCA: A modified CSMA/CA protocol mitigating the fairness problem for IEEE 802.11 DCF

Abstract

Carrier sense multiple access with collision avoidance (CSMA/CA)has been adopted by the IEEE 802.11 standards for wireless localarea networks (WLANs). Using a distributed coordination function(DCF), the CSMA/CA protocol reduces collisions and improves theoverall throughput. To mitigate fairness issues arising withCSMA/CA, we develop a modified version that we term CSMA withcopying collision avoidance (CSMA/CCA). A station in CSMA/CCAcontends for the shared wireless medium by employing a binaryexponential backoff similar to CSMA/CA. Different from CSMA/CA,CSMA/CCA copies the contention window (CW) size piggybacked in theMAC header of an overheard data frame within its basic service set(BSS) and updates its backoff counter according to the new CWsize. Simulations carried out in several WLAN configurationsillustrate that CSMA/CCA improves fairness relative to CSMA/CA andoffers considerable advantages for deployment in the802.11-standard-based WLANs.