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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
IEEE 802.15.4 Relative Location Date Submitted
May 2004 Source Neiyer Correal, Frederick
Martin, Motorola, Inc. Contact F. Martin,
Motorola, Inc., 8000 W. Sunrise Blvd.
Plantation, FL 33322 Voice 1 954-723-6395, FAX
1 954-723-3712, E-Mail f.martin_at_motorola.com Re
Technical Contribution to TG4A Abstract Relati
ve location based on received signal strength
ranging can be used for 2 dimensional location
in personal area networks. Purpose To provide
information on potential location performance of
networks based on IEEE 802.15.4. Notice This
document has been prepared to assist the IEEE
P802.15. It is offered as a basis for discussion
and is not binding on the contributing
individual(s) or organization(s). The material in
this document is subject to change in form and
content after further study. The contributor(s)
reserve(s) the right to add, amend or withdraw
material contained herein. Release The
contributor acknowledges and accepts that this
contribution becomes the property of IEEE and may
be made publicly available by P802.15.
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Motivation for Relative Location Techniques

• Device data must be accompanied by its location
• Actuator must know where to act
• Alarm must be localized to be useful to a human
  operator
• Placing locating every device is
  labor-intensive
• Cost of device location must be considered
• GPS cost, power consumption can be prohibitive
• Only an outdoor solution
• Local Positioning Systems (LPS) need intensive
  installation
• High Cost of wiring
• Labor intensive

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Relative Location

• Goal Self-location with few known-location
  nodes
• Without wired infrastructure
• Applicable to any environment

• Difficulties
• Ad hoc connectivity
• Advantages
• Reference devices are the infrastructure
• Peer-to-peer range measurement possible
• Accuracy/range extension

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Relative Location

• Conventional Location
• Devices are located only with respect to fixed
  base stations

• Relative Location
• All devices calculate the distance to their
  neighbors

central computer
central computer
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Synch / data
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Architectural Blueprint
Architectural Blueprint
Characteristics Long path lengths Complex
installation
Benefits Higher rates Location Accuracy/Range
Extension
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Relative Location in 1 Dimension
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Relative Location Physical Analogy

• Relative location analogy
• Nails represent absolute location information
• Springs natural lengths are the estimated range
  between nodes
• Spools are nodes

Relative Range Data
Location Mapping Algorithm
Spools will move in the direction of force until
sum of forces equals zero
Reference and Blind NeuRFons
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Range Estimation Techniques

• Various media are possible
• RF Infrared Ultrasound Acoustic

Signal Strength Techniques
Time-Based Techniques

• Time Difference of Arrival (TDOA) relies on time
  synch
• (ns) time-synch unlikely
• Time-of-Arrival (TOA) can be measured via
  round-trip
• At 1 meter range resolution for 3 ns time
  resolution (RF signal), wide bandwidth signal is
  needed.

• Received Signal Strength (RSS) is considered
  coarse due to the multipath channel
• Range estimate variance increases with range
• WE WILL FOCUS ON RSS ON RF SIGNALS

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Relative Location Simulation
Path Loss Errors of s 6 dB Single room, 20 m by
10 m 3, 4, or 6 Reference devices 1 to 10
Blindfolded devices Reference devices located in
corners Other devices placed at random

• Simulation of Indoor Relative Location
• Signal Strength as a Ranging Technology
• Location Accuracy improves with either
• More Reference devices
• More Blindfolded devices.

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Relative Location Experiment Set-up

• Measurements
• Mot. Labs Plantation FL, office environment
• 13 by 15 m area
• 44 devices (0.2 /m2)
• 4 reference devices in corners of area
• Nodes at 1m height
• Multipoint to multipoint
• 44435 9460 measurements
• 2.4 GHz signal, 40 MHz BW

Figure Area Map, Device and Location
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Relative Location Experiment Set-up
T
True Location
Relative Location Estimate
Key
R

• RMS Location Error of 2.14 m
• Histogram of Errors

RMS is 15 of Ref. device separation
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Relative Location Radio Testbed

• Testbed Device
• 900 MHz, 50 kbit/s FM
• 8 channels
• Sensor Suite
• RSS Ranging

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Relative Location Measurement Results

• Environments
• Outdoor Parking Lot
• Residential Home
• 9m x 9m area, 4 by 4 grid
• Reference nodes at corners
• RMS location errors
• 1.0m in parking lot
• 2.1m in house

Above Map of the Perkins home and grid of 16
device locations. Side Parking lot
experiment. Devices are located on top of blue
upside-down recycling bins.
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Summary

• 802.15.4 can be used for location under some
  conditions
• RSSI appears to be a viable method for location
  resolution
• Cooperative location can enhance location
  estimation
• -- higher density of nodes results in improved
  location estimation
• For reference node separation on order of 10m, 2D
  location with RMS errors on order of 2m is
  possible
• For more information, see
• N. Patwari, A. O. Hero, III, M. Perkins, N.
  Correal, R. J. ODea, Relative location
  estimation in wireless sensor networks, IEEE
  Trans. On Signal Processing, vol. 51, no. 8,
  August, 2003, pp. 2137-2148.