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: [email protected] [email protected]
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