-WLAN Power management for 802.11 mesh networks using 802.15.4 Nilesh Mishra, Bhaskaran Raman, Abhinav Pathak Department of Computer Science and Engineering, Kameswari Chebrolu Department of Electrical Engineering,
802.11 Mesh Network 802.11 designed for indoor usage Usage of 802.11 for long distance connectivity Power as a constraint Lack of support in current hardware -WLAN Summary: Current 802.11 hardware is not power efficient but is being used to provide long distance connectivity
Power Consumption Measurements A typical mesh node Single board computer based 802.11 bridge/router Directional Antenna RF cable for connections * *http://www.hyperlinktech.com/web/hg2424g.php
Power Consumption Measurements (continued) Observations on power consumption: Increases with insertion of card Higher for Tx than Rx Considerable variation over different card makes Summary: Even idle power consumption is significant
Trivial solution Node 1 Node 3 Wired Gateway Node 2 Node 4
Requirements Node 1 Node 3 Wired Gateway Node 2 Node 4
WOW! Node 1 Node 3 Wired Gateway Node 2 Node 4
IEEE 802.15.4 Energy optimized Low cost radio (< $5) Works in the same 2.4GHz as 802.11 Sensor motes Sensing Subsystem Sensing Subsystem Sensor Battery Power Supply Power Supply Subsystem Subsystem Application Layer Application Layer Subsystem Subsystem ADC/DAC CPU Memory Microcontroller Microcontroller Software Radio Communication Communication Subsystem Subsystem
Architecture Node 1 Node 3 Wired Gateway Node 2 Node 4 Nodes turned off Remote turn on Multi-hop setting Delay due to boot up
Architecture Node 1 Antenna Node 2 RF switch or splitter Power switching circuit Battery
Implementation Details Use of Chipcon s CC2420 CCA mode Configurable frequency and energy threshold parameters Relay based switching circuit Does not store the state CCA modes of 802.15.4 Clear if energy below threshold Clear if valid 802.15.4 packet Clear if valid 802.15.4 packet and energy below threshold Summary: 802.15.4 compliant radio is able to detect 802.11 traffic
-WLAN Features On-demand, course-grained power on/off of networking equipments at a remote site. Use of off the shelf 802.15.4 compliant sensor motes working in 2.4 GHz. Setting ideal for rural deployment. Usage of data channel itself for remote wake-up No separate antenna (shared with 802.11 equipment).
Detection of 802.11 Transmission A laptop with D-Link DWL650 802.11b card running trafficgen application as data traffic source Packets of size 1462 bytes at 1Mbps with inter packet intervals of 10, 20 and 100ms Polling of CCA pin on sensor node every 3ms Summary: Traffic pattern of 802.11 successfully replicated on motes
Outdoor Evaluations Validation on 3.5Km IITK-Mohanpur link on DGP testbed External antenna connected Calibrated 802.11 card for determining RxPower Summary: Low sensitivity of 802.15.4 essential for working of -WLAN in long distance settings
Example Scenario Power consumption of Soekris acting as a router/switch with two wireless 802.11b cards = 7.7W (typical) Boot-up time for Soekris 50s VoIP service in Sarauhan in the DGP testbed Usage pattern: 15 calls/day of 71s avg duration Sensor mote typical values: V cc = 2.8V and I = 23mA with CPU and Radio receiving.
Example Scenario E no_wow = P up x T up E wow = E mote + E bootup + E usage where E mote = V mote x I mote x T idle E bootup = P bootup x T bootup E usage = P up x T active Using above values E no_wow = 120 Whrs E mote = 1.54Whrs E bootup = 1.04Whrs E usage = 7.73Whrs Thus power saving is: (E no_wow E wow )/ E no_wow Greater than 91%
Discussion Does not work on 802.11a Hibernation facility desired: faster boot-up Suffers from noise generated triggers Advanced usage: morphing topology More detailed study of usage pattern for better power savings.
Related Work Narrow band RF detector Wake-On-Wireless [Shieh, et al] Concept of smart brick and mini brick Separate frequency channel for wake-up Turducken: Hierarchical power management for mobile devices [Sorber, et al] Hierarchy of devices Decomposition of task Use of WiFi detectors Separate antenna for detection Separate data and trigger channels Suitable for low cost long distance links - Wireless Turducken Yes Yes No Yes No No No No Yes Wakeon-LAN Summary: Usage scenario for Rural Networking and use of 802.15.4 is unique
Application Scenarios VOIP usage in a typical setup 10-30 calls of 1-2 minutes duration Solar Power WiFi (http://www.green-wifi.org/) Low cost solar powered WiFi grid. On-demand data retrieval for bridge monitoring. Summary: -WLAN is useful in energy constrained use of 802.11 equipments
Applications BriMon Project IEEE 802.11 External Antenna Base node Node 4 IEEE 802.15.4 Node 3 Node 2 Node 1 With: Hemanth Haridas CSE,
Application BriMon Project With: Hemanth Haridas CSE,
Application BriMon Project With: Hemanth Haridas CSE,
New Developments Signature pattern based -WLAN Checks for a pattern in a code window Overcomes the problem of noise triggered false wake-up Works in existence of periodic or non periodic noise. Improvements in switching circuit Latching circuit Transistor based switch
Conclusions Lack of power save mode in current WiFi Mesh networking hardware Novel -WLAN mechanism for multi hop remote on-demand wake-up of mesh nodes. Substantial power savings using - WLAN (> 91%). tested and verified for rural deployment Newer applications emerging. Summary: Power management tools are required for current 802.11 based networks deployed in energy constrained scenarios