Abstract
Carrier sense multiple access with collision avoidance (CSMA/CA) has been adopted by the IEEE 802.11 standards for wireless local area networks (WLANs). Using a distributed coordination function (DCF), the CSMA/CA protocol reduces collisions and improves the overall throughput. To mitigate fairness issues arising with CSMA/CA, we develop a modified version that we term CSMA with copying collision avoidance (CSMA/CCA). A station in CSMA/CCA contends for the shared wireless medium by employing a binary exponential backoff similar to CSMA/CA. Different from CSMA/CA, CSMA/CCA copies the contention window (CW) size piggybacked in the MAC header of an overheard data frame within its basic service set (BSS) and updates its backoff counter according to the new CW size. Simulations carried out in several WLAN configurations illustrate that CSMA/CCA improves fairness relative to CSMA/CA and offers considerable advantages for deployment in the 802.11-standard-based WLANs.
Highlights
The medium access control (MAC) protocol is the main element determining how efficiently the limited communication bandwidth of the underlying wireless channel is shared in a wireless local area network (WLAN)
The main contribution of this paper is a practical MAC protocol, which is different from the prior work in the following: (1) it is tailored for IEEE 802.11 distributed coordination function (DCF); (2) unlike the continuous-value backoff copying, contention window (CW) size copying incurs only 3 bits overhead which can be absorbed by the current standards; (3) while GDCF [13] implements the gentle CW decrease based on the individual station’s contention history, our gentle CW size decrease algorithm takes into account the overall channel traffic; and (4) by the CW size reset function, we mitigate the shadowed-receiver problem which remains unresolved in MACAW [4]
In our novel CCA scheme, we define CW size copying routines and propose a gentle binary exponential backoff (BEB) equipped with reset (GBEBwR) algorithm modified from the BEB algorithm to control the CW size of each initial station
Summary
The medium access control (MAC) protocol is the main element determining how efficiently the limited communication bandwidth of the underlying wireless channel is shared in a wireless local area network (WLAN). The main contribution of this paper is a practical MAC protocol, which is different from the prior work in the following: (1) it is tailored for IEEE 802.11 DCF; (2) unlike the continuous-value backoff copying, CW size copying incurs only 3 bits overhead which can be absorbed by the current standards; (3) while GDCF [13] implements the gentle CW decrease based on the individual station’s contention history, our gentle CW size decrease algorithm takes into account the overall channel traffic; and (4) by the CW size reset function, we mitigate the shadowed-receiver problem which remains unresolved in MACAW [4]. The purpose of RTS and CTS frames is to carry the duration of the following DATA/ACK exchange Based on this information, all other stations in the WLAN are able to update their network allocation vectors (NAVs), which indicate how long the channel will remain busy. The detailed design of the CW size copying routines and the GBEBwR algorithm are presented
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