Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA ECA) is a distributed MAC protocol that allows collision-free access to the medium in WLAN. The only difference between CSMA ECA and the well-known CSMA CA is that the former uses a deterministic backoff after successful transmissions. Collision-free operation is reached after a transient state during which some collisions may occur. This article shows that the duration of the transient state can be shortened by appropriately setting the contention parameters. Standard absorbing Markov Chain theory can be used to describe the behaviour of the system in the transient state and to predict the expected number of slots to reach the collision-free operation. The article also introduces CSMA E2CA, in which a deterministic backoff is used two consecutive times after a successful transmission. CSMA E2CA converges quicker to collision-free operation and delivers higher performance than CSMA CA in harsh wireless scenarios with high frame error rates. To achieve collision-free operations when the number of contenders is large, it may be necessary to dynamically adjust the contention parameter. The last part of the article suggests an approach for such parameter adjustment which is validated by simulation results.
An insightful comparison between CSMA ECA and ZeroCollision is presented in @cite_8 . ZeroCollision converges quicker to the collision-free operation and CSMA ECA presents a behaviour that is more similar to current CSMA CA. This similarity may ease the implementation of CSMA ECA. The results in this reference also show that ZeroCollision is superior to CSMA ECA in the presence of channel errors. Additionally, the cited article also extends both protocols to converge quicker to collision-free operation, to deliver higher performance in lossy channels, and to operate in a collision-free fashion in the presence of a large number of stations. The names of these extended protocols are L-ZC, L-MAC, A-L-ZC and A-L-MAC. Furthermore, the concept of is introduced. We will revisit this concept in Section as a means to substantially improve the performance of CSMA ECA.
@cite_8
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By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then design two schemes that are practically realisable, decentralised approximations of this optimal scheme and operate with different amounts of sensing information. We achieve this by (1) introducing learning algorithms that can substantially speed up convergence to collision free operation; (2) developing a decentralised schedule length adaptation scheme that provides long-run fair (uniform) access to the medium while maintaining collision-free access for arbitrary numbers of stations.