Interclass Collision Protection for IEEE 802.11e Wireless LANs

Abstract

Distributed Coordination Function (DCF) in IEEE 802.11 and Enhanced Distributed Channel Access (EDCA) in IEEE 802.11e are contention-based access mechanism in wireless LAN. Both DCF and EDCA reduce collisions based on Inter-Frame Space (IFS) and backoff mechanisms. However, collisions are unavoidable even with the two mechanisms. Especially, in the EDCA, collisions can be classified into interclass and intra-class collision. To eliminate interclass collision in wireless LAN, we propose an Interclass Collision Protection (ICP) scheme by employing Collision Protection Period (CPP) after backoff. Different number of backoff time-slots is inserted to each class. Higher class stations are allowed to transmit before lower class stations end backoff period. Analysis is performed with one dimensional discrete-time markov chain for the EDCA and proposed ICP-based EDCA. Collision probability and throughput of each channel access is examined. Throughput increase is more than doubled with reduced collision probability when the system is saturated.