A Fair Randomized Contention Resolution Protocol for Wireless Nodes without Collision Detection Capabilities

Contention-based protocols are commonly used for providing channel access to the nodes wishing to communicate. The Binary Exponential Back off (BEB) is a well-known contention protocol implemented by the IEEE 802.11 standard. Despite its widespread use, Medium Access Control (MAC) protocols employing BEB struggle to concede channel access when the number of contending nodes increases. The main contribution of this work is to propose a randomized contention protocol to the case where the contending stations have no-collision detection (NCD) capabilities. The proposed protocol, termed RNCD, explores the use of tone signaling to provide fair selection of a transmitter. We show that the task of selecting a single transmitter, among n ≥ 2 NCD-stations, can be accomplished in 48n time slots with probability of at least 1 - 2^-1.5n. Furthermore, RNCD works without previous knowledge on the number of contending nodes. For comparison purpose, RNCD and BEB were implemented in OMNeT++ Simulator. For n = 256, the simulation results show that RNCD can deliver twice as much transmissions per second while channel access resolution takes less than 1% of the time needed by the BEB protocol. Different from the exponential growth tendency observed in the channel access time of the BEB implementation, the RNCD has a logarithmic tendency allowing it to better comply with QoS demands of real-time applications.