rf rangingfor indoor tracking and positioning · wpi technology workshop: precision indoor location...

RF Ranging for Indoor Tracking and Positioning

WPI Technology Workshop: Precision Indoor Personnel

Location and Tracking for Emergency Responders

Dennis McCrady

Robert Goldberg

Tim Pfister

August 7, 2006

WPI Technology Workshop: Precision Indoor Location and Tracking for Emergency Responders l August 7, 2006 l 2


Agenda

• Background

• RF Ranging System Description

• Keys to Accurate RF Ranging

• RF Ranging Performance

– Laboratory

– Field (Over the Air)

• ITT Software Defined Radios (SDR)

• Conclusions



Background

• GPS provides excellent accuracy in areas where it can be received

• Satellite navigation improvements are on the horizon

– GPS III and Galileo

– When?

– What improvements will finally be implemented?

• In the meantime, GPS restricted environments require multiple technologies in a blended solution

– Use GPS when available

– Inertial sensors (MEMS are feasible)

– RF ranging systems (TOA, DTOA, AOA)

• Focus on RF ranging (TOA) technology developed at ITT

– Implemented within a direct sequence spread spectrum communication system

– Utilizes waveforms, modem, and networking protocol to facilitate the RF ranging application



RF Ranging System Description

• System is comprised of mobile (M) and reference (R) wireless units (WU)

– RWUs can be mobile

• MWU uses a minimum of 3 RWUs for 3D location

– Range based on two way TOA

– Can vary update rate

– Additional RWUs improve solution

• Carrier Sense Multiple Access –Collision Avoidance protocol controls media access for ranging as it does for communications

• Solution can be relative to local coordinate system or absolute if RWUs have GPS

MOBILE

FIXEDREFERENCE

MOBILE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

BUILDING

MOBILE

FIXEDREFERENCE

FIXEDREFERENCE

MOBILEMOBILE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

FIXEDREFERENCE

BUILDING

Good RF Ranging Accuracy is Achieved in All Environments

by Establishing an Error Budget and Attention to Key Details



• No permanent infrastructure

– Two-way ranging eliminates need for synchronized clocks

– 1 ppm clocks are sufficient

– Internal delay calibration

• Use optimum carrier frequency for propagation in buildings and urban areas: 300-450 MHz

• Use the highest achievable bandwidthsupported by the frequency allocation (Crammer Rao Bound):

CRB = 1/(BW x SNR1/2)

• Use a two part TOA ranging waveform: acquisition then TOA synchronization symbols

• Leading edge curve fitting to minimize multipath (MP) effects

• Quadrature Multi-Frequency Ranging (QMFR) for multipath mitigation – ITT patented technique

Keys to Accurate RF Ranging

NIJ-005

Note: 1) 1 <= N1 <= 128

2) 384 <= N2 <= 511

Mod Turn-On & AGC

Setting Times (N1

Symbols, 128 Chips per

Symbol)

TOASynchronization

2 Symbols

(1023 Chips per

Symbol)

Acquisition Sequence (16


Symbol)

MultipathWindow

(N2 Chi ps)

Mod Turn-Off Time

(10 Symbols, 128 Chips

per Symbol)

TOA Ranging Waveform

NIJ-005

Note: 1) 1 <= N1 <= 128

2) 384 <= N2 <= 511

Mod Turn-On & AGC

Setting Times (N1


Symbol)

TOASynchronization

2 Symbols

(1023 Chips per

Symbol)

Acquisition Sequence (16


Symbol)

MultipathWindow

(N2 Chi ps)

Mod Turn-Off Time

(10 Symbols, 128 Chips

per Symbol)

TOA Ranging Waveform

Two Part Ranging Waveform Reduces Required Processing

Main PathCorrelationFunction

MultipathCorrelationFunction

Distorted Leading Edge of Correlation

Function(Main Path + Multipath)

NIJ_003

Main PathCorrelationFunction

MultipathCorrelationFunction

Distorted Leading Edge of Correlation

Function(Main Path + Multipath)

NIJ_003

MP Distorts the Correlation Function Used for TOA



Performance - Laboratory

• QMFR was not running in WU hardware for lab measurements

• QMFR TOA data captured by Logic Analyzer and processed off line

• Different length cables to emulate direct path and multipath

• QMFR versus single frequency non-QMFR compared using 10 trials

• QMFR TOA (Mean + σ) approximately twice as accurate as non-QMFR TOA

PC

1

WU

1

2

dB

Logic

Analyzer

ATT

0-20

AT

0-20 dB

2

dBWU

2PC

2

Combiner

Time Delay 1

Or TD1+TD2

Or TD1+TD3

Or TD4

ADC

OUT

Splitter

ADC

OUT

Floppy Disc

Transfer Floppy Disc

Transfer

Logic

Analyzer

PC

1

WU

1

2

dB

Logic

Analyzer

ATT

0-20

AT

0-20 dB

2

dBWU

2PC

2

Combiner

Time Delay 1

Or TD1+TD2

Or TD1+TD3

Or TD4

ADC

OUT

Splitter

ADC

OUT

Floppy Disc

Transfer Floppy Disc

Transfer

Logic

Analyzer

5.511.515ns 8dB

4.2512.060ns 0dB

2.04.030ns 0dB

2.57.015ns 0dB

0.51.0Direct path only

QMFR

(ns)

NON-

QMFR

(ns)

MULTIPATH

CONDITION



Performance – Field (Over the Air)

• Testing conducted at McKenna MOUT area of Fort Benning, Georgia

• 1 MWU and 5-8 RWUs that included GPS coordinates – QMFR not used

• RWUs were 1-750m from the MWU and the TOA update rate was 1/second

• TOA integrated with IMU and baro – results were driven by TOA accuracy

• Phase 3 waveform improvements resulted in establishing a .5m CEP accuracy limit and greatly improved accuracy in the harsh environments

Metric Phase 2 Measured Performance (m)

Circular Error Probable

Phase 3 Measured Performance (m)

Circular Error Probable

Phase 3 Measured Performance (m)

95 %

Goal (m) 95%

Horizontal Position Accuracy – Open Terrain

Not Measured 0.45 0.70 10

Horizontal PositionAccuracy – Urban Terrain

8.2 3.1 7.9 3

Horizontal Position Accuracy – In Building Terrain

13.8 4.8 7.0 1

Horizontal Position Accuracy – Forest Terrain

66.5 3.9 8.6 10

Vertical Position Accuracy – In Building Terrain

19.9 0.35 1.0 1



ITT Software Defined Radios



ITT Sensor Radio

ITT Actively Working on Design for Low Cost Sensor Radio with Production Goal of $500

SDR for Unattended Sensors

3.3” x 3” x 1”

Prototypes

Available



ITT Wearable Soldier Radio

Technical Description� 1 Mbps and 2.6 Mbps at 1.2 MHz BW

� SCA 2.2 Compliant

� Supports Voice, Data, Video traffic

� UHF 225-450 MHz; Up to 5 W Xmit power

� Range: 2 Km open field, 1 km Urban

� Type III COMSEC, Type 1 Upgradeable

� Internal Commercial GPS Receiver

� Interfaces: Ethernet, USB, RS-232, Headset

� SWAP: 24 Cu In, 1.2 lbs, < 5W avg power

� Includes adaptive power management

� Prototype Available Now

� EDM Available Fall 2006

� Radio (Wearable and Handheld) for Dismounted Soldiers

� Provides CNR voice for dismounted units

� Radio automatically generates position report without the need for attached PDA

� Demonstrated integration with FBCB2 for SA data collection and display

� Demonstrated Tactical Internet interoperation

� Simple HMI minimizes training and operator interaction during mission

Operational Description



Conclusions• Two-way RF ranging with real time delay calibration (loop back)

– Synchronization of mobile and reference WU clocks not required

– Infrastructure not required

• Two part waveform reduces real time processing requirements and

improves mobility and multipath performance

• QMFR provides orthogonal multipath and direct path

– Enables more accurate leading edge curve fit of the correlation function

resulting in a more accurate TOA estimate

• Over the air past performance at Fort Benning, Georgia without QMFR

– .5m horizontal CEP in open terrain

– 3-5m horizontal CEP in harsh environments

• Future performance estimate with QMFR

– 1.5-2.5m horizontal CEP in harsh environments

Future: Integrate RF ranging into ITT SDR and Field Test

rf rangingfor indoor tracking and positioning · wpi technology workshop: precision indoor location...

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