Improving the IEEE 802.15.4 Slotted CSMA/CA MAC for time-critical events in wireless sensor networks

摘要

In beacon-enabled mode, IEEE 802.15.4 is ruled by the slottedCSMA/CA Medium Access Control (MAC) protocol. The standardslotted CSMA/CA mechanism does not provide any means ofdifferentiated services to improve the quality of service for timecriticalevents (such as alarms, time slot reservation, PANmanagement messages etc.). In this paper, we present and discusspractical service differentiation mechanisms to improve theperformance of slotted CSMA/CA for time-critical events, with onlyminor add-ons to the protocol. The contribution of our proposal ismore practical than theoretical since our initial requirement is toleave the original algorithm of the slotted CSMA/CA unchanged, butrather tuning its parameters adequately according to the criticality ofthe messages. We present a simulation study based on an accuratemodel of the IEEE 802.15.4 MAC protocol, to evaluate thedifferentiated service strategies. Four scenarios with different settingsof the slotted CSMA/CA parameters are defined. Each scenario isevaluated for FIFO and Priority Queuing. The impact of the hiddennodeproblem is also analyzed, and a solution to mitigate it isproposed.