GDI Sensor Net

RIP07-13-2002 11-18-2002

GDI Data Analysis

Robert Szewczyk

December 20, 2002

Global statistics

• 43 distinct nodes reporting data at various times

• 1132548 packets logged in the DB

• 3 maintenance events, roughly every month

• Heavy mote losses – 4% daily

• Best nodes – nearly 90000 packets on a pair of AA batteries, over 2.5 months unattended operation

Sample data collected

• Collected light levels, temperature, relative humidity, thermopile IR and ambient temperature

Sample data – sensor discussion

• Thermopile sensor -- difficult to gain the confidence in the readings– Good correlation between the ambient temperature readout from the

thermopile and the measured temperature» But difficult to scale it

– Difficult to determine appropriate signal processing for the IR signal» Low confidence even as a occupancy detector

• Pressure sensor– Not used in the application, produced even less reliable nodes

• Humidity sensor– packaging problems – bulky, battery drain when wet– addressed in the next revision of the weather board

• Temperature sensor– resolution significantly lower than advertised;– reported in a plausible temperatures in a wide range (-10 +60 deg C)– Very good correspondence with Coast Guard data

• Light sensor – Known limitations, good baseline indication of mote health

Power Management

• Expected 6+ months @ 3% duty cycle– Real world performance

MUCH worse – best node lasted only 2.5 months

• Correlation between packet success rate and battery voltage – Boost converter provides

less consistency than expected

– Batteries can be drained down to 0.8 V per cell, poor reliability below 1.1 V per cell

Battery voltage at node 57, the most reliable mote from the initial deployment. Last packet from that node on that set of batteries was received on 9/24; the node reliability declined drastically after 9/22.

Network analysis

• Several underlying causes for packet loss– Laptop / database crash – connection to the laptop was only

available 47% of the time

– Low battery levels

– Collisions

– Environmental conditions – wind blowing antennas out of alignment, rain affecting humidity sensor and short-circuiting the battery

• Packet loss distribution– Packet loss does not behave like an independent distribution

– Work in progress to bin the potential causes of packet loss

Loss distribution

Phase stability

Conclusions

• First application that stressed low power and unattended long-term operation

• What we learned – Need a lot of diagnostic information to support long running

apps

» Gain confidence in the sensor readings

» Diagnose and remotely repair faults (if possible); provide bounded downtime

» Components addressing many concerns either exist or will soon exists – link layer acks, channel monitoring component, watchdog timer, etc.

– Boost converter falls short of expectations

» Poor efficiency

» Reduced performance on weaker batteries

Conclusions (cont.)

• Future work– Application redeployment in a more controlled environment

– Further root cause analysis

– Incorporating the lessons learned into Generic Sensor Kit and second generation weather board

• Accessing GDI data– http://www.greatduckisland.net

– PostgreSQL database

» Server: dbsvr.berkeley.intel-research.net

» Username: reader

» Password: readonly

» Database: gdi

» Most interesting table: weather

Mote 18: Outside

Mote 26: Burrow 115a

Mote 53: Burrow 115b

Mote 47: Burrow 88a

Mote 40: Burrow 88b

Mote 39: Burrow 84