Connecting Things to the Web using Programmable Low-power WiFi Modules

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Presentation at the Second International Workshop on the Web of Things (WoT 2011), San Francisco, CA, USA.
http://www.webofthings.org/wot/2011/

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Connecting Things to the Web using Programmable Low-power WiFi Modules

  1. 1. Connecting Things to the Web usingProgrammable Low-power WiFi ModulesBenedikt Ostermaier, Matthias Kovatsch, Silvia Santini{ostermaier | kovatsch | santinis}@inf.ethz.chSunday, 12 June 2011 Institute for Pervasive Computing / Distributed Systems Group
  2. 2. Internet of Things Now Optimized LoWPANs WiFi infrastructureMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 2
  3. 3. Platform: Roving RN-131G Programmable low-power WiFi module  44 MHz 32-bit RISC CPU  128 kB RAM, 2 kB non-volatile RAM  2 MB ROM, 8 MBit flash Built-in IEEE 802.11b/g transceiver with on-board antenna  Rates of up to 54 Mbit/s  WEP, WPA-PSK and WPA2-PSK RN-131 Interfaces  UART, SPI, SDIO, RFID  10 GPIOs, 8 analog sensor I/Fs Runs eCos with lwIP TCP/IP stack 37 mm / 1.46 inMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 3
  4. 4. Platform: Low-power Current consumption  212 mA when active (max. TX)  4 µA when sleeping Hardware support  Power Management Unit  Wake-up on sensor or timer events Sleep mode  2 kB battery-backed RAM  Short wake-up time (~35 ms until connected)Matthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 4
  5. 5. Connecting to Things Physical connection electronic attached Batteries Power supply Light switch Chair sensor sleeping vs. always on Grid Power outlet Room sign prototype vs. ad-hocMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 5
  6. 6. Connecting Things to the Web REST: maps nicely to physical resources Single-threaded Web serverHTTP callbacks (Webhooks) RESTful API for sensors, , actuators, configurationMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 6
  7. 7. Putting Things Together http://lightswitch / /position /callback http://poweroutlet / /power /consumptionMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 7
  8. 8. HTTP Callbacks on Sensor Events POST /power HTTP/1.1 Host: poweroutlet Content-Length: 4 Content-Type: text/plain Connection: close Referer: http://lightswitch/position User-Agent: WiFiNode 0.4 Date: Sat, 01 Feb 2011 12:45:26 GMT Last-Modified: Sat, 01 Feb 2011 12:45:26 GMT X-SensorEvent-Count: 12 X-Last-Uptime: 88 true http://lightswitch/ http://poweroutlet/powerMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 8
  9. 9. ZEnergy Efficiency Z Z Up to 212 mA when active  Maximize sleep time Z  Only report events  Optimize wake-up and uptime Z Problem: Availability  Sleeping for sensors only  Heartbeats  Poll configuration updates  Setup with /sleep resource or “double-click” Button “sensor“ prototypeMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 9
  10. 10. 450Evaluation 400Wake-up Cycle 3501. Enable CPU and RAM Average uptime [ms] 3002. Boot application Other 250 Callback3. Find AP and connect* DNS4. Run DHCP* 200 DHCP5. Run DNS* 150 WiFi6. Open TCP socket 1007. Perform HTTP callback 508. Close TCP socket 09. Go to sleep Office Home1 Home2 * can be optimizedMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 10
  11. 11. Results Reed and PIR sensor Battery-powered sensors  >99% data reception rate without retries  ~300‘000 Callbacks with two AAA batteries  ~8 years with 100 callbacks per day Grid-powered actuators  ~24 ms round trip time (~19 ms for Apache)  Real-time support WiFi Plogg prototypeMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 11
  12. 12. Conclusions and Outlook Sufficient battery life for event-based sensing WiFi infrastructure greatly reduces deployment costs However, may also introduce some hard-to-trace problems Hardware support for real energy savings Future Work  RFID bootstrapping  JavaScript programming Subtle notification device prototypeMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 12

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