Idle listening, which is the state of monitoring communication media to check potential traffic, is the dominant source of energy consumption in WSNs. Duty cycling, which makes nodes periodically turn off their RF communication module, can effectively reduce the energy consumptionduetoidlelistening.Butitintroducessleepdelay due to the sleep state of a receiver. High duty cycle reduces sleep delay but increases energy consumption due to more frequent wakeups while low duty cycle reduces energy consumptionbutincreasessleepdelayduetoalongsleepstate. Todealwiththistradeoffbetweentheenergyconsumptionand the sleep delay, the existing WSN studies focuses on MAC protocols to support energy efficient yet high performance communications. To mitigate the impact of sleep delay on packet latency, many MAC protocols exploit dynamic duty cycling[1,2,3]orwakeupscheduling[4,5,6]. However, these optimizations are not a fundamental solution for eliminating idle listening since they still require dutycycling.Afewstudies[7,8]haveinvestigatedthedesign of a radio wave sensor, which is a dedicated RF module to checkforpotentialcommunications.Sincearadiowavesensor doesn'tdecodeanincomingsignal,itrequiresonlyasubsetof components from the RF communication module. Therefore, mostoftheconventionalradiowavesensorsareimplemented withoutamplifiers that consume heavy energy. However, it is hard to detect a signal weaker than the minimum signal strengthrequiredforpassingthroughasilicondiode.Therefore, Therefore,RFsensingrangesoftheexistingschemesaremuch shorterthanRFcommunicationranges[7,8]. Toprovidearadiowavesensorwiththesamesensitivityas theunderlyingRFcommunicationmodule,wepropose anew design of radio wave sensor called RF wakeup sensor. To equalize RF sensing range to communication range, the RF wakeup sensor uses a dedicated amplifier for input signal. Since the RF wakeup sensor does not have to extract information from a received signal, the amplifier in the RF wakeupsensorisindifferenttophasedistortion.Therefore,we can simplify conventional amplifier that consist of complex circuitsforprovidinghighlinearity.Consequently,weareable to design an ultralow power amplifier with the minimum circuitelements. If the RF wakeup sensor has no frequency filtering technique, the number of falsepositive wakeups due to unrelated signals willbe increased. Forthis purpose we use a frequency filter that requires neither mixer nor oscillator to selectively sense signal on the predefined frequency band. Since the frequency used for a communication is higher than intermediate frequency, RF wakeup sensor requires a precise frequency...
In wireless sensor networks (WSNs) duty cycling has been an imperative choice to reduce idle listening but it introduces sleep delay. Thus, the conventional WSN medium access control protocols are bound by the energy-latency tradeoff. To break through the tradeoff, we propose a radio wave sensor called radio frequency (RF) wakeup sensor that is dedicated to sense the presence of a RF signal. The distinctive feature of our design is that the RF wakeup sensor can provide the same sensitivity but with two orders of magnitude less energy than the underlying RF module. With RF wakeup sensor a sensor node no longer requires duty cycling. Instead, it can maintain a sleep state until its RF wakeup sensor detects a communication signal. According to our analysis, the response time of the RF wakeup sensor is much shorter than the minimum transmission time of a typical communication module. Therefore, we apply duty cycling to the RF wakeup sensor to further reduce the energy consumption without performance degradation. We evaluate the circuital characteristics of our RF wakeup sensor design by using Advanced Design System 2009 simulator. The results show that RF wakeup sensor allows a sensor node to completely turn off their communication module by performing the around-the-clock carrier sensing while it consumes only 0.07% energy of an idle communication module.Index Terms: Idle listening, radio frequency (RF) wave sensor, sleep delay, wireless communication, wireless sensor networks (WSN).
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