Extending Body Sensor Nodes' Lifetime Using a Wearable Wake-up Radio Andres Gomez 1, Xin Wen 1, Michele Magno 1,2, Luca Benini 1,2 1 ETH Zurich 2 University of Bologna 22.05.2017 1
Introduction Headphone for auditory feedback Sink Node (SINK): Large Energy Supply Data Request via Bluetooth [1] Central Unit Gait Detection: Sink Node requests data from different sensor nodes at different times Both sensor nodes need to be on Sink node processes data to detect gait disturbances Sensor Node(S.N.): Limited Energy Supply Inertial Sensors [1] Casamassima, F.; Ferrari, A.; Milosevic, B.; Ginis, P.; Farella, E.; Rocchi, L. A Wearable System for Gait Training in Subjects with Parkinson s Disease. Sensors 2014, 14, 6229-6246. 22.05.2017 2
Power consumption of wearable nodes Synchronization schemes: Synchronous (duty-cycling) Asynchronous Wake-up radio shown to reduce idle power [2] Our Wake Up Radio (WUR): High sensitivity (up to -42dBm) Low power consumption (400 nw) fast reactivity (8us) Addressing capability Wireless Sensor Network (WSN) Body Area Networks (BAN)? [2] Hyocheol Jeong, Jeonghyun Kim, and Younghwan Yoo Adaptive Broadcasting Method Using Neighbor Type Information in Wireless Sensor Networks. Sensors 2011, 11(6), 5952-5967 22.05.2017 3
Contributions Evaluation of WUR for BAN applications How much energy can be saved? Are there any performance trade-offs? Range/sensitivity Addressing or not addressing 22.05.2017 4
System Architecture Bluetooth(BLU): BLU+Wake-up Radio Sensor MCU BLE Sensor MCU BLE interrupt WUR Sensor Sink P BLU Idle Listening t1 request t0 Tx Rx E IDLE,BLU E IDLE,WUR P WUR wake up Trade-off: small additional Main Radiocost, t higher latency WUR Idle listening t Sink request interrupt Tx Rx go to sleep t t t 22.05.2017 5
Wake-up Radio Architecture WUR has two outputs: -TRIGGER: Non-addressing mode: Sensor Node 1 Sink Node -DATA: Addressing mode: Sensor Node 2 Sensor Node 3 Sensor Node 1 Sink Node address? Sensor Node 2 Magno, M.; Benini, L., "An ultra low power high sensitivity wake-up radio receiver with addressing capability," Proc. IEEE WiMob Conf. 2014 Sensor Node 3 22.05.2017 6
Integrated Systems Laboratory What parameters are we interested in? Range/sensitivity Packet loss: number of lost packets during transmission TRIGGER OUTPUT: Success rate for trigger (SRT): SRT = number of received triggers total number of packets 100% DATA OUTPUT: Success rate for data transmission (SR): Data error rate (DER): DER = SR = number of wrong bits total number of bits 100% number of correct packets total number of packets 100% 22.05.2017 7
What parameters are we interested in? False positives (FP): Waking up when you don t need to Energy LOSS! Ex: Sink [Addr. A] SN1 Addr. A SN2 Addr. B False negatives (FN): Not waking up when you need to No energy loss, SINK sends new request Greater Latency Sensor Node 1 (Addr. A): if [DataReceived]==[Addr A]: True Positive Else < False Negative> Sensor Node 2 (Addr. B): if [DataReceived]==[Addr A]: True Negative if [DataReceived]==[Addr B]: < False Positive> 22.05.2017 8
Experimental Set-Up: Sink Nodes Sink Node with low gain antenna (MSP430FR5969+CC110L) 868 MHz 1.2 Kbits/s +10 dbm OOK modulation On chip antenna (0dBi) Sink Node with low gain antenna (EM430F6137RF900) 868 MHz 1.2 Kbits/s +10 dbm OOK modulation Off chip antenna (2dBi) 22.05.2017 9
Antenna Experimental set-up: Wearable Antennas (Sensor Node) Fxp280 Fxp14 Molex Frequency (MHz) 863 to 870 850 824 to 896 Return Loss (db) -20-7 -7.7 Efficiency (%) 40 52 67 Gain (dbi) 1.5 2 2.2 22.05.2017 10
Initial Characterization Sink 10cm 315cm SN 0xD5 (10000000)... 0xFF (11111111) 3 seconds interval 4 * 128 packets Compared TX/RX...... [Sink Node] Vs [Sensor Node] 22.05.2017 11
10 30 60 90 120 145 160 200 210 220 230 240 250 260 265 270 280 290 300 310 315 320 success rate [%] Experimental Result for Trigger Output 145cm 310cm 100 80 60 40 20 0 As expected, the sink node with high gain antenna reaches a larger range. Low SN with gain low sink gain nodeantenna High SN with gain high sink node gain antenna distance [cm] 22.05.2017 12
Success Rate [%] Experimental Result for Data Output 100 80 60 40 20 Success Rate for data transmission SN with low gain antenna SN with high gain antenna Data Error Rate [%] 100 80 60 Low gain SN: success rate decreases dramatically after 40cm. 40 High gain SN: works well up to 3.1 m 0 0 40 80 120 160 200 240 280 320 350 Distance [cm] 20 Data Error Rate 0 0 40 80 120 160 200 240 280 320 350 Distance [cm] SN with low gain antenna SN with high gain antenna 22.05.2017 13
Application scenario with CC430F6137 Payload A: 10101010 ---address 1 Payload B: 11010101 ---address 2 Distinguish between two feet Sink 100 packets, Molex, +10dBm, 868MHz, 1.2Kbits/s, OOK Two scenario: standing, walking 83cm Without addressing FP FN SN Left foot 50% ~0% Right foot 50% ~0% 22.05.2017 14
Experimental Result in addressing mode Percentage(%) 100 80 Standing FP FN LOSS Percentage(%) 100 FP FN LOSS 80 Walking 60 60 40 40 20 20 0 Left foot Right foot 0 Left foot Right foot PERFECT 22.05.2017 15
Lifetime Extension Bluetooth Bluetooth +WUR Idle power 92.4mW 400nW Tx Power 135.3mW 135.3mW Wake-up Time 3 seconds Walking Period 30 minutes Sitting Period 0-30 minutes Battery 150 mah E cycle = P idle t idle + P active t active Lifetime = C batt V cc E cycle t idle + t active 22.05.2017 16
Summary The WUR is suitable for BAN It decreases the total energy consumption, therefore extend the lifetime of BAN But it has some trade-offs with performance/cost : Sink node s antenna / transmit power Reduced range, FNs,packet loss 22.05.2017 17
Thank you for your attention! 22.05.201718
System Architecture Bluetooth(BLU): BLU+Wake-up Radio Sensor MCU BLE Sensor MCU BLE interrupt WUR Main Radio (SEN) P BLU Idle Listening t1 Sink Node request t0 Tx Rx t t Main Radio (SEN) WUR (SEN) Sink Node P WUR wake up interrupt Idle listening request Tx Rx sleep t t t 22.05.2017 19
Wake-up Radio Architecture Radio Frequency Wake-up radio Fully passive circuits Semi-active circuits Fully active circuits 0 power consumption x limited range/sensitivity: -25 dbm High sensitivity: -90dBm x Non-negligible power consumption: > 10 s μw Trade-off between power consumption and sensitivity Our WURxHigh sensitivity (up to -42dBm), low power consumption (400 nw), fast reactivity (8us), with addressing capability. 22.05.2017 20