CAT: High- PreCision Acoustic Motion Tracking PowerPoint Presentation

CAT: High-PreCision Acoustic Motion Tracking

Wenguang Mao, Jian He, Lili Qiu

UT Austin

MobiCom

2016

Why motion tracking?

Motion-based Games

Virtual Reality

Why motion tracking?Support motion-based interaction

Smart Appliance

Possible solutions

Vision

based approach

Needs extra hardwareDepends on lighting conditionComputationally heavy

Possible solutions

RF

based approach

WiFi : limited accuracy (e.g., 10 cm [Chronos16])RFID: limited accuracy (e.g., 4 cm [RF-Idraw])60 GHz waves: extra hardware not widely available 60GHz Antenna

Acoustic Signal

Slow propagation – helpful to achieve

high accuracy

Easily available speakers and mics –

widely available

Low sampling rate – feasible for

SW processing

CAT

 

 

CAT

Key Components

Distributed FMCW

Doppler Shift

Optimization Framework

Audio Samples

Movement Trajectory

Distance

Velocity

CAT

FMCWFMCW for propagation delay estimation

Less bandwidth usage than using a sharp pulse

Send a chirp whose freq. changes linearly over time

Estimate the frequency difference

, and

~ distance travelled by the chirp

 

 

 

Distributed FMCWSpeaker (sender) and microphone (receiver):Not known when the chirp is sent Two-step distance estimation

Sampling rate offset

Drift compensation

Time

Frequency

Transmitted

Received

Two-Step Distance EstimationDecompose distance

into two parts

 

 

Pseudo-transmission time

Reference point

Two-Step Distance EstimationDecompose distance

into two parts

 

 

Pseudo-transmission time

Reference point

Pseudo-Transmission Time

Time

Frequency

Transmitted

Received

 

Pseudo-Transmitted

 

 

 

 

Two-Step Distance EstimationDecompose distance

into two parts

 

 

Pseudo-transmission time

Reference point

Reference Point

 

 

Doppler +

Doppler -

Drift Compensation

Estimated distance drift over time

Drift CompensationDue to imperfect clocks, the sender and the receiver have different the sampling ratesE.g., 44100.1 Hz (sender), 44099.9 Hz (receiver)

1764 samples at the receiver

1764 samples at the sender

Prop. delay

Chirp 1

Prop. Delay

Chirp 2

Chirp diff.

Drift Compensation

Drift Compensation

 

Doppler Shift Measurement

Measure frequency shift

between transmitted and received signals

Velocity is given by

 

 

Optimization frameworkFusing distance and velocity measurementsFind position

that fits the measurements best

Efficient algorithm for solving it

Incorporate IMU measurements

 

 

Dist. measurement fitting error

Vel. measurement fitting error

Multiple tracking periods

Smooth the estimated results

No error accumulation

Experiments2D tracking with 2 speakers2D tracking with 3 speakers

3D tracking with 4 speakers

2D Tracking Accuracy

CAT is accurate and fusing distance/velocity significantly improves the performance

 

6mm

8 cm

2 cm

 

3D Tracking

8-9 mm 3D tracking error

User Study

(a) CAT

(b)

AAMouse

(Doppler only)

4mm trace error

 easy to use

Red: reference

Blue: traced by users

ConclusionDistributed FMCW to support a separate sender and receiverOptimization framework and algorithm to fuse distance and velocity over time

CAT tracking system

Achieves mm-level accuracy on commodity devices

Future work: develop new applications