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

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

  • 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
  • Internet of Things Now Optimized LoWPANs WiFi infrastructureMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 2
  • 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
  • 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
  • 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
  • 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
  • Putting Things Together http://lightswitch / /position /callback http://poweroutlet / /power /consumptionMatthias Kovatsch Connecting Things to the Web using Programmable Low-power WiFi Modules 7
  • 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
  • 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
  • 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
  • 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
  • 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