Anchor

positions

Ground-truth

Tag Positions

Estimated Tag

Positions

Decimeter Accurate, Long Range Non-Line-of-Sight RF

Localization Solution for Public Safety Applications

PI: Hun-Seok Kim, Co-PI: David Blaauw, Dennis Sylvester

EECS, University of Michigan, Ann Arbor, MI

Introduction

System Overview

Key Techniques

A new RF solution for location based services

• Decimeter accuracy localization with > 100m localization range

• Low cost, small size form-factor, and ultra-low power for wearable tags

• Operable in NLOS and rich multipath environments

• Rapidly deployable, low complexity infrastructure anchors

Expected Results

Overall	system	block	diagram

1.	Active	Reflection:	Frequency	Converting	RF	Echo

• Increased the maximum operation range

• Distinction from passive reflections

• Flexibility of anchor waveform scheme

• Simple tag design

• No need for tag-anchor synchronization

2.	ToF Resolution	Enhancement	via	

Neural	Network:

• Interpolated time-domain channel impulse response

• Fully connected feedforward neural network

• Training data synthesized in Matlab (simulation)

• No need to use real-world training data

• Good improvement in multipath-rich environment

3.	ULP	Tag	IC	Design	with	Wakeup	Receiver:

4.	Emergency	Beacon	TX:

System Target Specification

Tag	

Spec.

• Power: <100μW in average, <200mW peak power.

• Full-duplex frequency-conversion active reflector with

5.8GHz / 2.4GHz dual-band

• Built-in wakeup receiver (<100μW) to initiate localization

• Built-in narrowband (1kHz) transmitter (10km link distance)

for emergency beacon TX

Anchor	

Spec.

• USRP X310 software defined radio

• MIMO, 80MHz bandwidth, -100dBm sensitivity with OFDM

symbol combining

Algorithm

• OFDM based time-of-flight estimation

• MIMO processing and OFDM symbol coherent combining

• Neural network based localization accuracy enhancement

• Neural network based semantic localization

• Real-time 3D localization with <1ms update rate via

coordination among anchors

System	

Spec.

• Localization range: >100m per dimension in NLOS

• Localization accuracy: standard deviation error estd <30cm

per dimension in NLOS

• Performance: real-time, 1ms refresh rate per localization fix

• To lower the average power to < 100μW

• Reflection is activated by wakeup command

• Q-enhancement receiver for better energy efficiency

• Fully integrated with antenna in centimeter-scale form factor

• Narrowband transmitter for longer range (>5km)

• Antenna and circuit co-designed

• Non-coherent modulation for TRX

• No need for off-chip crystal or PLL

5.	Semantic	Localization:

• Distinguish different environments base on channel

impulse response machine learning

• Identify the tag either inside or outside a specific domain

2 4 6 8 10

13.2

14.4

15.6

16.8

3.5

7.0

10.5

14.0

Measured Distance (m)

Trial Index

(10 symbols 

combined)

Neural Network

Baseline Algorithm

Office

Office

Ground 

Truth

Ground 

Truth

Wakeup 1 Pilot OFDM Wakeup 2 Pilot OFDM

Wakeup RX Pilot OFDM reflection

Wakeup RX Pilot OFDM reflection

Anchor:

Tag1:

Tag2:

time

Time of Flight Time of Flight

Wakeup RX

Wakeup RX

Matlab simulation	results

Tag CMOS IC Prototype 5.8 GHz

2.4 GHz

Anchor USRP X310 FPGA + RF card

fA2T = 5.8 GHz

fT2A = 2.4 GHz

...

...

DSP

0 Time (ns) 50 100

Time-Domain 

Channel Impulse 

Response h(t)

Active	Reflection

fshift

IFFT

FFT

Channel	

Impulse	

Response	

Estimation

0 10 20 30 40 50 60

Time (μs)

Time-Domain TX Signal

Pilot Tone OFDM Symbol

0 10 20 30 40 50 60

Time (μs)

Time-Domain RX Signal

To TRX 

Control

From TRX 

Control

Pilot Tone OFDM Symbol

5.8	GHz

5.8	GHz

5.8	GHz

5.8	GHz

Passive	reflection

(Interference)

2.4	GHz

Active	reflection

TAG Anchor

Anchor

Anchor

Triangulation	Localization	:

TDMA	between	each	anchor

Long	range,	wearable	tag

GPS RSSI UWB This	work

Range Global <20m <5m* >80m

Power High Low Medium Low

Accuracy 10s m <10	m mm <	m

Indoor	/	Outdoor Outdoor Both Both Both

Need	

Synchronization? Yes No Yes No

*Typically	for	accurate	locationing