All Or None? The Dilemma Of Handling Wifi Broadcast Traffic In Smartphone Suspend Mode

Smartphones save energy by entering a low power suspend mode (<20mW) when they are idle. We find that on some smartphones, WiFi broadcast frames interrupt suspend mode and force the phone to switch to active mode (>120mW). As a result, power consumption increases dramatically. To improve energy efficiency, some phones employ a hardware broadcast filter in the WiFi driver. All UDP broadcast frames other than Multicast DNS frames are blocked, thus none is received by upper layer applications. So, we have a dilemma of handling WiFi broadcast traffic during smartphone suspend mode: either receive all of them suffering high power consumption, or receive none of them sacrificing functionalities. In this paper, we propose Software Broadcast Filter (SBF) to address the dilemma. SBF is smarter than the hardware broadcast filter as it only filters out useless broadcast frames and does not impair functionalities of applications. SBF is also more energy efficient than the "receive all" method. Our trace driven evaluation shows that SBF can save up to 52% energy consumption than the "receive all" method.