The Cricket Indoor Location System - Nissanka Bodhi Priyantha and Michel Goraczko MIT Computer Science and Artificial Intelligence Lab ...
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
The Cricket Indoor Location
System
Nissanka Bodhi Priyantha
and
Michel Goraczko
MIT Computer Science and Artificial Intelligence
Lab
http://nms.lcs.mit.edu/cricket
Cricket • Location for mobile applications – Resource discovery – Human/Robot navigation/tracking – Games • Location-aware sensing – Routing – Data dissemination – Annotating data with location information
Resource Discovery
“Print map on a color printer,”
and system sends data to the
nearest available color printer
Virtual/Physical Games
Location-Aware Sensing
• Ubiquitously deployed
networked sensors can Temperature, light,
enable new forms of sound sensors, buzzer
monitoring and control
– Tracking assets (RF-ID
tags)
– Monitoring conditions
– Traffic, facilities, physical
plant, leaks, smoke, fire…
• Sensor streams usually need
to be annotated with location
and time for them to be
useful
• Goal: Cricket-enabled
sensors
Functionality:
Space, Position, Orientation
Corridor
(x y z)
● Space: Rooms, parts of rooms Room 7(N)
● Position: Coordinates
● Orientation: Direction vector
Room 7(S)
Cricket provides all three
Design Goals for Cricket • Must operate well indoors • Must scale to large numbers of devices • Should not violate user location privacy • Must be easy to deploy and administer • Should have low energy consumption
Cricket Architecture
info = “a2”
Beacon
info = “a1”
Estimate distances
Listener to infer location
Passive listeners + active beacons scales well,
helps preserve user privacy
Decentralized network of autonomous beaconsSPACE = NE43-510
COORD = (146 272 0)
Obtain linear distance estimates
Pick nearest to infer “space”
Solve for device’s (x, y, z)
Determine w.r.t. each beacon and deduce
orientation vectorDetermining Distance
Beacon RF data
(space name)
Ultrasound
(pulse)
Listener
• The
A beacon
listener
transmits
measures
an the
RF time
and an
gapultrasonic
between
signal
the receipt
simultaneously
of RF and ultrasonic signals
– RF
Velocity
carries
of location
ultrasound
data,Multiple Beacons Cause
Complications
Beacon A Beacon B
Incorrect distance
Listener t
RF B RF A US B US A
• Beacon transmissions are uncoordinated
• Ultrasonic pulses reflect off walls
These make the correlation problem hard and can lead
to incorrect distance estimates
Solution: Distributed scheduling algorithmsSolution
• Distributed beacon scheduling
– Carrier-sense + randomized transmission (reduces
chances of concurrent beaconing)
– Idle time between beacon chirps to allow ultrasound
to “die down”
– Another possibility is distributed TDMA
• Listener inference algorithm
– Processing distance samples to estimate location
– Key problem is outlier rejectionExample Estimation Algorithm:
Windowed MinMode
Frequenc A
y B
5
Distance
5 10 (feet)
A B
Actual distance (feet) 6 8
Mode (feet) 6 8
Mean (feet) 7.2 6.4
Majority 9 10Kalman Filter: For Mobile Listeners
● Min-mode based estimation is “slow”
– Needs multiple samples from a beacon
– Poor performance with mobile listeners
● Solution: Use a Kalman filter based estimator
– Kalman filter uses a “predict and correct” approach
to filter outliersBeacon Autoconfiguration
● For listeners to compute their position,
beacons need to transmit their locations
● Problem: How do beacons determine their
locations?
– Manual configuration (e.g., counting ceiling tiles) is
possible but tedious
● Goal: Scalable autoconfigurationBeacon Autoconfiguration:
For a Small Number of Beacons
B
A dAB
dA dB
● Place the listener under each beacon and
collect distances to each beacons
● Calculate inter-beacon distances
● Calculate beacon coordinates
– Selecet three initial beacons and assign coordiantes
– Trangulate the others using these threeBeacon Autoconfiguration:
Anchor Free Localization (AFL)
● For large number of beacons
● AFL is a two phase distributed algorithm for
node localization
– Phase 1: Fold-free initialization'
– Phase 2: Optimization
● AFL needs local inter-beacon distances
– Cricket beacons cannot measure interbeacon
distances
● Listener-assisted AFL
– Use a mobile listener to patch-together disconncted
beaconsCricket Hardware Platforms
• Two platforms
– CF interface
– Rs232 interface
• Both platforms can be software configured as
a Beacon or a Listener
– Unused submodules can be powered down to save
energy
• Can be programmed using a standard Mica
programming board (MIB-510CA)Cricket Hardware
Cricket Block Diagram
Host Interface Serial ID RF interface
CF or RS 232 CC1000
Temperature
Ultrasonic Tx u-controller
Sensor
Atmega 128L
51-pin mote
Ultrasonic Rx interface
• Ultrasonic transmitter
– 40kHz piezo transmitter
– Driven by a 12V square wave
• Ultrasonic receiver
– 40kHz piezo sensor
– Two amplifier stages followed by an envelope
detector
– Second amp stage has software adjustable gainCricket Block Diagram
• RF interface
– CC1000 based – similar to Mica2
– Additionally, there is a carrier threshold detector
• Mote connector
– Can interface with a Mica sensor board or a Mica
– Communication with Mica through RS232 or I2C
interface
• Temperature sensor
– On-board temperature sensor
– Used to offset ultrasonic velocity change with
temperatureUltrasonic Ranging
Characteristics
• Radiation pattern
– Easy to block the signal at the transmitter, but
not at the receiverCricket Precision
● Distance estimation performance
● Area coverage
– Error vs distance
● Beacon densityDistance Estimation Performance
Coverage Area
● Ultrasound range is 10.5 meters
● Radio range must be larger then ultrasound
True Distance vs mesured distance
500
450
400
Mesured distance
350
300
250
200
150
100
50
0
0 50 100 150 200 250 300 350 400 450
True distanceTinyOS architecture and
implementation
● Application (CricketBeacon and
CricketListener)
● Modification to the radio stack
● Ultrasound activation
Idle state
● Compensation (800-1200ms)
● Scheduling
Receive
(30ms + 1-3ms)
*
If failed
Send
* The receive while is reset each time a beacon is heardCricket API
● Serial/CF port API
ASCII
Binary (not implemented yet)
● TinyOS API
example:
module Cricket {
command getDistance( int Beaconid)
command BeaconRecord getClosestBeacon
(int order)
event beaconUpdate(BeaconRecord rec)
event beaconChanged()
}Cricket Serial API
Serial
Beacon Listener Command Direction Parameters Type
Parameter Description Read Write Read Write ASCII BIN Get Output Put Input ASCII BIN
ASCII/BIN Mode Communication protocol
to use • • • • MD 0x01 String[1] Char
Node ID Unique node id • • ID 0x02 N/A String[16] Long
Space Name User specified space id • • • • SN 0x03 String[12] String[12]
Distance Distance between the lis-
tener and the beacon • • DB 0x04 string[5],string[2] ushort,char
Duration Ultrasound time of flight
(uncorrected) • DR 0x05 string[5],string[2] ushort,char
Coordinates Coordinates of the node
(x y z) • • • • PC 0x06 String[1],3*string[6],string[2] Char,3*short,char
Sleep Sleep range between
beacon chirp • • SL 0x07 2*string[5],string[2] 2*ushort,char
Ultrasound lifetime The ultrasound life be-
fore the wave attenuate • • • • UL 0x08 string[5],string[2] ushort,char
Temperature Temperature on the node • • TP 0x09 string[5],string[2] ushort,char
Battery Level Reading of the voltage
level from the battery • • BL 0x0A String[5] Short
Uptime Time since powered up • • UP 0x0B string[5],string[2] ushort,char
Version Software version • • VR 0x0C None String[5] String[5]
Filter Event filter • • FL 0x0D String[128] String[128]
User defined User defined • • DG 0xFF String[128] VariableCricket Demo ● Ranging ● 2D localisation demo ● ASCII serial API demo
You can also read
