Low power downlink MAC protocols for infrastructure wireless sensor networks

This paper addresses low power medium access control ( MAC) protocols for the downlink channel of infrastructure wireless sensor networks. Access points are assumed to be energy unconstrained. The trade-off between the power consumption of the sensor nodes and the transmission delay is analyzed, focusing on low traffic. We describe WiseMAC ( Wireless Sensor MAC), a new protocol for the downlink of infrastructure wireless sensor networks. Another original contribution is the presentation and analysis of PTIP ( Periodic Terminal Initiated Polling). Here, polling is used in the reversed direction as compared to common polling protocols. WiseMAC and PTIP are compared with PSM ( Power Save Mode), the power save protocol used in both the IEEE 802.11 and IEEE 802.15.4 ZigBee standards. Analytical expressions are derived for the power consumption and the transmission delay for each protocol, as a function of the wake- up period. It is shown that WiseMAC provides, with lowbit rate radio transceivers, a significantly lower power consumption than PSM. Although less energy efficient than WiseMAC and PSM, it is shown that PTIP can, thanks to its implementation simplicity, become attractive for applications tolerating large transmission delays.