doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January 2016

Nan Chi, Junwen Zhang, Fudan UniverisitySlide 1

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: High-speed VLC for Wireless backhaul communication

Date Submitted: January 2016

Source: Prof. Nan Chi, Dr. Junwen Zhang Company: Fudan Univerisity

Address: Fu Dan University, 220 Handan Rd., Yangpu District, Shanghai

Voice: Tel: 0086-21-65642983, E-Mail: nanchi@fudan.edu.cn hustzjw@gmail.com

Abstract: In response to «Call for Proposals for OWC Channel Models» issued by 802.15.7r1, this

contribution presents the PHY technologies proposal of outdoor free space VLC long distance transmission

for high rate PD communication in wireless backhaul (mobile back haul).

Purpose: Call for Proposal Response

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.

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 2

High-speed VLC for Wireless backhaul

communication

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 3

Outlines

Background and Introduction

Scenario Targets

Description of Proposed Solutions

Some Experiment Results

Occlusions

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 4

Response to the TCD Document4.5.1 Applications/Use cases

The following High Speed Photodiode Receiver applications/use cases were presented in response to

TG7r1 Call for Applications.

……

4. Wireless Backhaul (Small Cell Backhaul, Surveillance Backhaul, LAN Bridging)

B4: Wireless Backhaul

4.5.3 ……The standard must define a range of data rates with

minimum supported connectivity of at least 1 Mbps at the PHY SAP.

The standard must support at least one PHY mode that supports peak

data rates of 10 Gbps at the PHY SAP.

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 5

Application Scenarios: Mobile backhauling

Backhaul is a top priority for small cell

deployments •80% of small cells will have wireless backhaul

•Cost of fiber is ~4x greater than wireless (cumulative

CAPEX/OPEX)

•Small Cell mesh inter-connectivity over

~250m •Large indoor and outdoor public spaces

* According to InterDigital Whitepaper 2013

*A typical mmW backhaul link

VLC outdoor free-space

high speed PD

communication for mobile

backhaul

• It shares the same

CAPEX/OPEX advantages with

mmW

• More competitive with lower

device cost

Characters:

Large indoor/outdoor public

spaces

Distance: ~50 m~1 km

Speed: ~Gbps

Link: mainly Point-to-point

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

Wireless Backhaul• Requirements

Small Cells

Backhaul @VLC

Single Hop

Wireless

Backhauling

Multiple Hop

Wireless

Backhauling

# of hops 1 <5

Distance per

link

<1km <150m

Data Rate ~2-20Gbps ~2-20Gbps

Latency <35ms <35ms (total )

QoS/QoE Yes Yes

Availability 99.99% 99.99%

Backhaul @VLC

Wireless backhauling with single hop

Wireless backhauling with Multiple hops

Small Cells

Backhaul @VLC Backhaul @VLC

Source: from 802.11 TGay Use Cases

Requirements are open for discussion

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 7

Targets

• High-speed VLC Out-door long-distance communication

for mobile backhaul

• Data Rates Speed: ~Gbps

• Distance: 50m~1km, typical ~50-500 m

• Environment: Large indoor/outdoor public spaces

• Link: mainly Point-to-point

To provide a Out-door VLC free-space link for high-speed user

applications.

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 8

Proposal Research Route

Simulation for Outdoor Long Distance VLC Transmission System

System Structure and Simulation Parameters Simulation Results and Analysis

Key Technique for High Speed Outdoor VLC Transmission SystemModulation

formatsPre Equalization and post-

equalizationDiversity reception

technology

VLC Free Space Transmission Channel ModelLED/PD Modulation Property Optics System design Free-space channel

Outdoor Transmission Experiments

System Structure Results and Analysis

Multiplexing Technology

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 9

TX： electronics：LED driving circuit，signal processing (coding,modulation, equalization)

optics：transmitter antenna RX：

optics：receiver antenna，PD electronics： signal processing (decoding,demodulation, equalization),

Physical Layer of VLC system

Visible light

transmission

LED

coding

modulation

Pre-equalizationO to E

TxModule

LED ModulationRx Module

AD

AD

Demodulator

Decoder

Data

BasebandQ

I

Phase

Signal processing

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 10

To achieve the high speed VLC

The pre-equalization and post-equalization technology for the high-

speed VLC systems

Modulation formats:

• Single-carrier based CAP-QAM

• Multi-carrier based OFDM or DMT with bit-loading

Multiplexing Technology

• Multiplexing Technology using different color LED

• MIMO for multiplexing gain

• Receiver-diversity reception technology

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 11

Phosphor LED 10dB bandwidth<15MHz

RGB LED 10dB bandwidth<25MHz

1. LED bandwidth limitations

Higher order modulation and pre-equaliztion

• Software/ hardware pre-equalization

• OFDM/DMT

• Single Carrier、CAP and so on

Advanced post-equalization techniques

• ZF、DFE、RLS、DD-LMS

• CMMA、M-CMMA

• Volterra

2. VLC system Nonlinear

Inter-symbol interference

LED nonlinearity

Solutions

10dB Bandwidth LED Nonlinearity

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

Pre-equalization

Visible light

transmission

LED

coding

modulation O to E

TxModule

LED ModulationRx Module

AD

AD

Demodulator

Decoder

Data

BasebandQ

I

Phase

Signal processing

Pre-equalization schemes:

Hardware Equalization：hardware circuit design

Software Equalization：digital signal processing

VLC Channel Pre-equalization

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

Software Pre-equalization—FIR response—Channel response Pre-equalization

Obtain the channel knowledge(H) at

the RF domain

Make pre-equalization Tx*1/H at the

baseband

w/o pre-equlizationwith pre-equlization

Y. Wang, et al, IEEE Communication Letters, Vol. 18, No. 10

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

Hardware bridged-T amplitude equalizer

R2 R3

Z11

Z22

RLC Network2

RLC Network1

Data In

LED

Driving

Circuit

2

11 22 0=Z Z R 211

4 2

1 1

1/ (1 )

1

LRS

j LR

C L

Z11 : RLC network1 (R1, C1 and L1)

Z22 : RLC network2 (R4, C2 and L2)

R2 =R3 =R0

X. Huang, et al, OFC 2015, Tu2G.1

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

Hardware bridged-T amplitude equalizer

Performances

<month year>

Slide 15 Junwen Zhang, Nan Chi, Fudan Univerisity

Spectrum of a 250-MHz CAP signal after pre-EQ

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

16

Carrier-less Amplitude Phase (CAP) modulation format

-8 -5 0 5 8-0.3

-0.2

-0.1

0

0.1

0.2

0.3

-8 -5 0 5 8-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 0.1 0.2 0.3 0.4 0.5-100

-90

-80

-70

-60

-50

-40

-30

-20

Normalized Frequency ( rad/sample)

Pow

er/

frequency (

dB

/rad/s

am

ple

)

Carrierless Amplitude and Phase (CAP) is a multi-level modulation scheme proposed

by Bell Lad in 1970

At transmitter a pair of orthogonal filters is used as Hilbert pair for modulation

At receiver a pair of matched filter is used for demodulation

I Qs t I t f t Q t f t

Orthogonal Shaping Filters

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

DMT with Bit-loading Background

<month year>

Slide 17 Junwen Zhang, Nan Chi, Fudan Univerisity

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 18

Pre-qualizer Bias Tee

EA1

LE

D

Lens

TIA

LED

TX RX

PIN

Arbitrary

Waveform

Generator

Blue Filter

Oscilloscope

EA2

EA3

Output+

Output-

Channel1

Channel2

TIA+

-

DC supply

GND

AMP

DC supply

AMP

AMP

AWG710 54855A

Bit-loading based OFDM-DMT modulation for

Gbps VLC

X. Huang, et al, IEEE Photonics Journal, 2015

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 19

0 50 100 150 200 250

0

10

20

30(a) SNR estimation (dB)

0 50 100 150 200 2500

5

(b) Bit allocation

0 50 100 150 200 2500

5

(c) Power allocation

Subcarrier index

Bit-loading based OFDM-DMT modulation for

Gbps VLC

X. Huang, et al, IEEE Photonics Journal, 2015

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 20

1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.70

20

40

60

80

100

120

140

Cu

rre

nt

Voltage

V-I curve of the Red Chip

Bias Voltage (V)

Cu

rren

t (m

A)

Linear

Curve

Measured Curve

TOV

Signal Vpp

Bias Voltage

LED nonlinearity

LED nonlinearity seriously degrades the system performance;

The LED forward current exhibits strong nonlinearity with the bias voltage;

Two factors dominate the nonlinear effects: DC bias voltage and the input

signal peak-to-peak value (Vpp);

Volterra nonlinear equalizer

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 21

1Z 1Z( )x n

We

igh

ts

Up

da

te

( )ly n

( )e n

0 ( )w n1( )w n 2 ( )w n ( )iw n

( )klw n

( )nly n00( )w n 01( )w n

11( )w n 12( )w n 22( )w n 02( )w n

( )y n

Ref.

Linear

Equalizer

Nonlinear

Equalizer

1

0

( )

1 1

0

( )

( ) ( ) ( )

( ) ( )

( ) ( ) ( )

l

nl

l nl

N

i

i

y n

NL NL

kl

k l k

y n

y n y n y n

w n x n i

w n x n k x n l

The Volterra series based equalizer is considered as a promising

solution to mitigate the LED nonlinearity;

The Volterra series expansion contains a linear term and nonlinear

series.

M-CMMA is utilized to update the weights of the nonlinear

equalizer without using training symbols

Principle

Volterra nonlinear equalizer

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 22

RGB LED

PIN

lens&

filter

Free Space

Red

Green

BlueEq.

EA

DC

Bias

AW

G OSC

EACh1

Ch2

Ch2

BG

R

Data in

QA

M M

ap

pin

g

Up

-Sa

mp

le

I/Q

Se

pa

rati

on

CAP Modulation

( )Qf t

Data out

QA

M

De

ma

pp

ing

LE

&

Vo

lte

rra

NL

E

Do

wn

-Sa

mp

le

( )Im t

( )Qm t

CAP Demodulation

( )If t

Color-division Multiplexing

Same idea of Wavelength-division multiplexing (WDM) used in fiber-optics

To triple the capacity or speed of VLC system

RGB bandwidth is larger than the p-LED

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 23

Data in

QAM Mapping

Up-Sample

I/Q Separation

Data out

QAM Demapping

DD-LMS

M-CMMA

Down-Sample

Bias

RGB LED

APD 1

APD 2

LPF

w1

LPF

w2

Σ

MRC

lens&

filter

50m

VLC outdoor transmissionCAP Modulation

Red

Green

Blue

LPF

EA

DC

Bias( )If t ( )Qf t

( )Im t ( )Qm t

CAP Demodulation

Eq.

LPF

EA

DC

Bias

Eq.

LPF

DC

Eq.

EA

RGB LED (LED Engine) Multiplexing for high-speed VLC (WDM

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 24

Out-door Long distance testing results

0 50 100 150 200-80

-60

-40

-20

0

20

0 50 100 150 200 250-80

-60

-40

-20

0

20

0 50 100 150 200 250-80

-60

-40

-20

0

20

10 20 30 40 50

1E-6

1E-5

1E-4

1E-3

BE

R

Distance

Red Chip

Green Chip

Blue Chip

@3.8e-3

BE

R

Distance (m)

Frequency (MHz)

Pow

er (

dB

)

Frequency (MHz)

Pow

er (

dB

)

Frequency (MHz)

Po

wer (

dB

)

Red Chip

Green Chip

Blue Chip

(a)

10 20 30 40 50

20

40

60

80

100

Red Chip

Green Chip

Blue Chip

Illu

min

atio

n

DistanceDistance (m)

Illu

min

ati

on

(lx

)

10 lx

15 lx

19 lx

54 lx

85 lx

66 lx

90 lx

71 lx

97 lx

(b)

BER vs distance Illumination vs distance

At the distance of 50m, the total data rate of 1.8Gb/s can be achieved with the BER

less than the 7 % FEC limit of 3.8x10-3.

The illuminations for each color chip are 15lx, 19lx and 10lx at 50m.

It should be noted that the experiment is conducted at about 9:00 PM. The ambient

light noise mainly comes from the artificial light sources such as the street lights.

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 25

LED Equ. Modulation Data rate receiver distance institutionData

source

White light Pre OOK-NRZ 40Mbit/s PIN 2mUniversity of

OxfordPTL2008

Blue light - DMT-QAM 200Mbit/s PIN 2m Fraunhofer HHI PTL2009

RGB LED - DMT-WDM 803Mb/s APD 12cm Fraunhofer HHI OFC2011

White light Post CAP 1.1Gb/s PIN 23cmNational Chiao

Tung UniversityPTL2012

RGB LED Post SC-FDE 3.75Gb/s APD 1cmFudan

UniversityCOL2013

Micro-LED Pre/Post HW OFDM 3 Gb/s APD 5cmEdinbourgh

UniversityPTL2014

RGB LED Pre/Post SC-FDE 4.22Gb/s APD 10cm Fudan Univ. OPEX2014

RGBY LED Pre/Post DMT 5.6Gb/s PIN 1.5mScuola Superiore

Sant’AnnaECOC2014

RGB LED Pre/Post CAP 4.5Gb/s PIN 2m Fudan Univ. PJ2015

RGB LED Pre/Post CAP 1.8Gbb/s APD 50m Fudan Univ. OFC 2015

RGBY LED Pre/Post CAP 8Gb/s PIN 1m Fudan Univ. PTL 2015

RGBY LED Pre/Post DMT-BPL 9.5Gb/s PIN 1m Fudan Univ.Newly

Achieved

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 26

Conclusion

The out-door high-speed VLC modeling including three parts

LED/PD Modulation Property

Optical system design

Free-space channel

The pre-equalization and post-equalization technology for the high-speed VLC

systems

Modulation formats:

• Single-carrier based CAP-QAM

• Multi-carrier based OFDM or DMT with bit-loading

Multiplexing Technology

• Multiplexing Technology using different color LED

• MIMO for multiplexing gain

• Receiver-diversity reception technology

In this contribution, we propose several general technique considerations for high rate

PD VLC out-door communications.

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

January, 2016

Junwen Zhang, Nan Chi, Fudan UniverisitySlide 27

Appendix

doc.: IEEE 802.15-15-16-0019-01-007a

Submission

Post-equalization

Visible light

transmission

LED

coding

modulation O to E

TxModule

LED ModulationRx Module

AD

AD

Demodulator

Decoder

Data

BasebandQ

I

Phase

Signal processing

Post-equalization solutions:

ISI Equalization：Classical DFEModified Eqs

Nonlinear Compensations：Volterra series

VLC Channel Post-equalization

doc.: IEEE 802.15-15-16-0019-01-007a

Submission 29

Receiver diversity technology

Σ

1r 2r 3r Mr

ith branch SNR:2 /i i ir N

Combiner output

SNR:

1 2 3 M

In receiver diversity, the outputs of

multiple receivers are combined

which is a weighted sum of the

different branches

2

21

2

1

M

i ii

M

tot i ii

rr

N N

the output SNR:

The goal of MRC is to find the weight to maximize the output SNR

According to the Schwarz inequality, it is found that:

the maximum SNR of the combiner output is the sum of SNRs in each

branch:2

1 1/

M M

i i ii ir N

January, 2016