Saving Energy in Wi-Fi Hotspots through 802.11 PSM: an Analytical Model

Wi-Fi hotspots are becoming very popular. Due to limited costs, they are an optimal solution to provide wireless Internet access to nomadic users. A key point to exploit the potentialities of Wi-Fi hotspots is managing the scarce energetic resoureces of mobile devices. To this end, the IEEE 802.11 standard defines a Power-Saving Mode, aimed at reducing the energy consumption due to networking activities. In this paper we provide an analytical model of this algorithm. We derive closed formulas for the main factors that impact energy consumption, and investigate their dependence on key parameters, such as the number of users inside the hotspot, the (wired) Internet throughput and the MAC protocol parameters. The results reported show that, in a standard TCP/IP architecture, the 802.11 PSM scales quite well with respect to the number of users inside the hotspot. However, in some cases, it can even increase the energy consumption obtained without energy management. Thus, our analysis can be used as a bottom-line to enhance energy management beyond the current limitations of the 802.11 PSM.

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