Abstract
Carrier sense multiple access with enhanced collision avoidance (CSMA/ECA) is a distributed MAC protocol that allows collision-free access to the medium in WLANs. 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 paper shows that the duration of the transient state can be shortened by appropriately setting the contention parameters. Standard absorbing Markov chain theory is 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 paper 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/ECA, specially in harsh wireless scenarios with high frame-error rates. The last part of the paper addresses scenarios with a large number of contenders. We suggest dynamic parameter adjustment techniques to accommodate a varying (and potentially high) number of contenders. The effectiveness of these adjustments in preventing collisions is validated by means of simulation.
Highlights
Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA/ECA) is a distributed medium access control (MAC) protocol that allows collision-free access to the medium in WLANs
Standard absorbing Markov Chain theory is 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
A downside of carrier sense multiple access with collision avoidance (CSMA/CA) is that only a fraction of the channel time is devoted to successful transmissions while the remainder is wasted in the form of collisions and empty channel
Summary
IRELESS Local Area Networks (WLANs) are a popular choice as a last-hop connection to the Internet. A downside of CSMA/CA is that only a fraction of the channel time is devoted to successful transmissions while the remainder is wasted in the form of collisions and empty channel. CSMA/ECA reaches collision-free operation after a transient state. Standard Markov Chain theorems can be used to estimate the expected number of slots required to reach the collision-free operation. These analytical results are validated by means of simulation. A limitation of CSMA/E2CA is that the number of contenders that can operate in a collision-free fashion is limited.
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