Carrier sense multiple access with enhanced collision avoidance (CSMA/ECA) is a distributed MAC protocol that allows collisionfree/naccess to the medium in WLANs. The only difference between CSMA/ECA and the well-known CSMA/CA is that the former/nuses a deterministic backoff after successful transmissions. Collision-free operation is reached after a transient state during which/nsome collisions may occur. This paper shows that the duration of the transient state can be shortened by appropriately setting the/ncontention parameters. Standard absorbing Markov chain theory is used to describe the behaviour of the system in the transient/nstate and to predict the expected number of slots to reach the collision-free operation. The paper also introduces CSMA/E2CA,/nin which a deterministic backoff is used two consecutive times after a successful transmission. CSMA/E2CA converges quicker to/ncollision-free operation and delivers higher performance than CSMA/ECA, specially in harsh wireless scenarios with high frameerror/nrates. The last part of the paper addresses scenarios with a large number of contenders. We suggest dynamic parameter/nadjustment techniques to accommodate a varying (and potentially high) number of contenders. The effectiveness of these/nadjustments in preventing collisions is validated by means of simulation

The present paper is the extended version of a MACOM/nworkshop paper. The authors benefited from the feedback/nand discussion in the workshop. The authors are specially/nindebted with N. Abramson for his clarifications regarding/nAloha and with D. Malone for providing recent and/nvaluable references. This work has been partially supported/nby the Spanish Government under Projects nos. TEC2008-/n0655/TEC (GEPETO, Plan Nacional I+D) and CSD2008-/n00010 (COMONSENS, Consolider-Ingenio Program).