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GALORE update: time and location services in a tiered sensor architecture

Naim Busek {ndbusek@lecs.cs.ucla.edu}

Vladimir Bychkovskiy {vladimir@lecs.cs.ucla.edu}

Jeremy Elson {jelson@lecs.cs.ucla.edu}

Lewis Girod {girod@lecs.cs.ucla.edu}

Advisor: Deborah Estrin {destrin@cs.ucla.edu}

NEST PI Meeting

July 2002

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System Design Motes:

Periodically emit coded acoustic “chirps” (511 bits)

IPAQs: Listen for chirps (buffer time series -

mote can’t do this) run matched filter Share ranges with each other via

802.11; trilaterate IPAQs currently configured with their

position; future: range to each other; self-configure

Time sync Allows computation of acoustic time-

of-flight One IPAQ has a “MoteNIC” to sync

mote and IPAQ domains

Compaq IPAQModel 3760

Modified moteshave audioamplifiers anda speaker

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Inter and Intra Node Sync 4 timesync modalities:

2 RBS (mote to mote, IPAQ to IPAQ) 2 intra-node (IPAQ to motenic, IPAQ to codec)

CPU 1

802.11

IPAQ 802.11Broadcaster

CPU 2

802.11

CODEC 1 CODEC 2

Convertto CPU1

(RMS 0uS)

Convertto CPU1

(RMS 1uS)

Convertto Mote1

(RMS 10uS)Convertto CPU2

(RMS 0uS)

1These results from “Rene” Mote using slower radio (53uS bit time) and approximate bit timing.Reported results from the “Mica” stack (20uS bits time) indicate 0.25uS packet timing.

Acoustic Pulse Acoustic Pulse

Acoustic Mote

Mote 1

IPAQ 1 IPAQ 2

MoteBroadcaster Convert

to CPU1(RMS 0uS)

Convertto CPU1

(RMS 2uS)

4Time

Mote to Mote Timesync: 10 usec RMS

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Positioning Algorithms

Positioning algorithm Converts range data into consistent coordinate system So far, positioning algorithm developed in simulation

IPAQ specific domain knowledge Speaker and microphone not co-located Therefore ranges are not always equal to “reverse range”

Acoustics-specific domain knowledge Acoustic error model Major component of error is excess path length caused by

non-line-of-sight ranges Current implementation uses customized mass-spring

model to compensate for NLOS

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Results of Positioning Algorithm on Simulated Data

RMS Position error = 2.8cmRMS Range error = 2.5cmInput noise:• 2cm variance• quantized to 0.71cm• 10% NLOS, uniform 0-40cm excess path, uncorrelated

cm

cm

cm