This document summarizes the work of a radio-over-fiber research group at the Technical University of Denmark. The group consists of 6 staff members and 12 PhD researchers from 15 different countries. Their work focuses on developing next generation access networks using radio-over-fiber technology. This involves using optical fiber to transmit radio frequency signals from a central office to remote antenna bases. Key challenges include improving receiver sensitivity, reach, and the number of supported users while increasing tolerance to fiber impairments. The group is exploring using phase modulation formats and digital signal processing techniques at the receiver to address these challenges. Their goal is to develop a converged optical network that can transport both wired and wireless signals on a common infrastructure.

1. Radio-over-fiber
Idelfonso Tafur Monroy
E-mail: idtm@fotonik.dtu.dk
Neil Guerrero Gonzalez
CPqD

2. 2
Metro-access and short range
communications group

3. 3
Team members
Staff (6)
Idelfonso Tafur Monroy, Prof.
Darko Zibar, Assoc. Prof.
Jesper B. Jensen, Asst. Prof.
J.J.Vegas Olmos, Asst. Prof.
Antonio Caballero, Postdoc
PhD Researchers (12 )
Cyd Delgado
Jose Estaran
Bomin Li
Valeria Arlunno
Xiaodan Pang
Alexander Lebedev
Maisara Othman
Roberto Rodes
Tien Thang Pham
Robert Borkowski
Supannee Learkthanakhachon
Gerson de Los Santos
A Copenhagen based, young and dynamic team, that combines
diversity in expertise and cultural backgrounds (15 nationalities)
Ongoing MSc students projects
(6)
David Montero, visit. Asst.
Prof.

4. 4
Next generation access networks services
Central Office
PSTN
Internet
Private Home with
Small Repeater
Mobile access
Wireless
Stuff
Wireless
Access in
the City
Requirements:
• Versatile – handle a variety of signals
• Efficient bandwidth utilization
• Bidirectional
• Dynamic and reconfigurable
• Long-reach (~100 km)

5. 5
Hybrid fiber wireless networks
CO
Service integration
Unified optical
network platform
Different
modulation
formats
BS
Different
bit rates
Radio over fiber (RoF) technology to increase
the capacity, coverage and mobility
Challenges:
• Integration with existing infrastructures
• Fulfill optical power budget
• Increase receiver sensitivity, reach and number of
users
• Improve the tolerance to fiber transmission
impairments
• Perform signal detection and demodulation of
different modulation formats and bit rates

6. 6
Where? Network scenario1
[1] Alcatel Radio-over-Fibre solution, 2007
Convergence between fixed and wireless networks the goal to bring the
bandwidth of fixed network to mobile user

7. 7
To take into account: Global data traffic
1 Exabyte = 1018 bytes
Drivers for traffic growth
Mobility
Cloud
Video
From CISCO analysis

8. 8
Connectivity any time, any where
Source: Transfer Jet Toshiba

9. 9
Challenges
Capacity
Scalability and sustainability
Connectivity anytime, anywhere
Manageability

10. 10
100 Gbit/s wireless links
Bring the capacity of baseband optical links to
wireless links
1988 1992 1996 2000 2004 2008 2012
10Mbps
100Mbps
1Gbps
10Gbps
100Gbps
W
ireless
links
(standard
W
LAN)
W
ireless links (research)
Optical serial interface (products)
Bitrate
Year
Optical serial interface (research)

11. 11
How to achieve multi gigabit wireless links
Higher RF carrier frequencies
• GHz of bandwidth available
• Higher Air attenuation
Courtesy of J. Mitchell, UCL1
Frequency (GHz)
10
GSM
900MHz
1800MHz
UMTS
~2GHz
WLAN
2.4GHz
5.1GHz
LMDS
28GHz
29GHz
31GHz
HiperAccess
18GHz
42GHz
MVDS
40GHz
WIMAX
2.5GHz
3.5GHz
802.20
~3.5GHz
UWB
3.1-10.6 GHz
Wireless HD
60GHz
6040 75 110
Future gigabit
links
Advanced modulation techniques
• High spectral efficiency
• Stringent requirements on
linearity and SNR

12. 12
How to achieve multi gigabit wireless links
75-110GHz
An untapped
frequency band
1 100 500
Wireless HD
60GHz
Saturated frequency bands (i.e
GSM, UMTS, WiFi, WiMAX, WLAN, U
WB, HiperAccess, LMDS, MVDS...)
Frequency
(GHz)
300-
500GHz
 Augmented reality
 HD Video Streaming
 Interactive Apps
3D Skype on ipads
 Mobile e-Health
 Machine-to-machine
 synch and go
Disaster recovery
Need for wireless bandwidth beyond current up to 10 GHz bands

13. 13
BTS Coverage vs Distributed Antenna Systems
DAS approach
•DAS attributes:
•Centralization of complex equipment and simple remote antennas
•Handover and load distribution/re-configurability
•Power consumption
BTS
BTS
BTS: base transceiver station

14. TU Dresden
Communications Laboratory
C.G. Schaeffer DTU Feb. 2009
Why Fibre Optics in Radio Systems ?
numerous lowcost base stations
without RF oscillators & modulators
with superior RF properties
higher RF carriers:
- reduced cell-size
- more subscribers per area
- frequency-reuse
- reduced RF power (EMI)
low fibre attenuation for
feeding the base stations
remote optical generation
of RF carriers
broadband data signals

15. 15
Radio over fibre: basics
Baseband
Intermedeiate
frequency (IF)
up-conversion
Frequency
up-
conversion
GHz
E/O
conversion
Light source
Optical spectrum
THz
Optical spectrum
fo fo
fr
fr
RF spectrum
Intensity modulaiton
THz
Optical fiber link
Radio transmitter
Radio-over-fibre

16. TU Dresden
Communications Laboratory
C.G. Schaeffer DTU Feb. 2009
Intensity Modulation & Direct Detection
Optical
Receiver
Optical to RF
Optical Fibre
RF
Output
RF Input
Optical
Transmitter
RF to Optical
Optical Power Spectrum
Optical
Frequency
RF-Components contributing
to fRF
fRF
f0
Phase sensitive
summation of all
optically generated
RF-Components at fRF

17. 17
Signal impairments
E/O
conversion
E/O
conversion Radio end
Fiber dispersion
Non-linearities
Phase noise
RF-powe fading
Crosstalk
Conversion efficiency
Link gain
Non-linearities
Intermodualtion products

18. 18
Dispersion induced RF-power fading

19. TU Dresden
Communications Laboratory
C.G. Schaeffer DTU Feb. 2009
Intensity Modulation & Fibre
Dispersion
Fibre length L (km)
Periodical RF power transfer:
Fibre Dispersion:
Wavelength:
Velocity of Light:
D
ps
km nm
17
1540nm
c
m
s
3 108
222
cos f
c
DL
0 2 4 6 8
60 GHz
40 GHz
1
0.5
Opt. power
Fundamental
3-dB frequency:
DL
c
f dB
2
1
3

20. 20
Radio-over-fiber Base Station
Dalma Novak

21. TU Dresden
Communications Laboratory
C.G. Schaeffer DTU Feb. 2009
Intensity Modulator for Sideband
Modulation
Principle: Mach-Zehnder Interferometer Bias
points
A
B
C
Electrical voltage V (a.u.)
Optical output power
0
0.
5
1
V0
A
B
C
DC bias
fMod-input
Optical
input
Optical
output
Optical Spectrum
f0 f1f-1
fRF = fMod
Optical Spectrum
f0 f1f-1
fRF = 2
fMod
Optical Spectrum
fop
t
f0 f1f-1
fRF = 4
fMod
f-2 f2

22. 22
Optical Single Sideband + carrier
Dalma Novak

23. 23
IF transport over fiber

24. 24
IF and remote LO transport over fiber

25. 25
Base-band-ovr fiber wireless transport

26. 26
A comparison of schemes

27. 27
Hybrid wireless-fibre systems
To metropolitan
network
Central
office
Antenna
base station:
: Optical fibre
Goal: Unified optical wireline and wireless signal transport systems
Coherent detection and DSP All-optical envelope detection
Approaches under study
Recovery &
protection Broadband
wireless bridge
Optical
fiber link
Optical
fiber link

28. 28
All-optical envelope detection for wireless
signals
Modulation
(envelope)
DC Bias
EAM
Radio-frequency carrier
Outputopticalpower
- Vbias
Half-wave
rectified signal
Lightwave carrier
Base station
Envelope
detector
Baseband
data out
•No High frequency mixers and
oscillators
•No frequency and bandwidth fixed
operation
For high carrier frequencies and
large bandwidth reduced
complexity is desirable
Envelope detection with
straightforward connectivity to
fiber links is an interesting
approach

29. 29
All-optical envelope detection
Example: upstream channel EPON
Desirable to use same technology for both wireline and wireless
Key enabling techniques based on all-optical wireless-to-optical
conversion

30. 30
Challenges/potential
Why optical phase-modulation?
0
0.5
1
Transmission
MZ phase (rad)
100%
0
2
4
6
0 0.5 1 1.5 2
Outputphase(rad)
Drive signal (V)
600%
(equivalent)
Linearity:
• Optical intensity modulators nonlinear
 Mach-Zehnder – sinusoidal
 EAM – exponential
• Optical phase linear
 If dominated by linear electro-optic effect
Phase-modulation has no fundamental limit on the dynamic range.
Large dynamic range enabling wide range of power levels

31. 31
Nonlinear and linear optical phase demodulation
0
0.5
1
Transmission
MZ phase (rad)
Photocurrent
Signal – LO phase difference
Large-signal
Modulation
•Open loop
•Closed loop
signal
LO
i~sin( signal - LO)
• Sinusoidal response of the receiver
Benefits of linear phase-modulation lost
90o
optical hybrid
LO
Signal in I(t)
Q(t)
Y(t)= I(t)+jQ(t)=exp( (t))exp( (t))
Linear phase demodulation

32. 32
Converged fixed and wireless network
Central office
Metropolitan network
CWlaser
Analog-to-digital
conversion
RFcarrierrecovery
Lineardemodulation
Digitalcarrierrecovery
Digital coherent receiver
LO laserc
Transmitter
Phase
modulator
b
Photonic wireless-wireline
converged network
a
Carrier recovery and demodulation performed using DSP
larger tolerances to phase noise and impairment compensation using DSP
Same receiver structure for fixed and wireless signal detection
OPSCODER project

33. 33 33
Radio over fiber (RoF) systems
Phase-modulated (PM) RoF systems

34. 34
The basis:
E1
OpticalHybrid
Photodetectors
Analog-to-Digital
Converter
0
90
ELO
E2
E3
E4
II(t)
IQ(t)
DigitalSignal
Processing
LO laser
Optical
Modulator
( )data t
ES
PC
ES
Transmitter
Coherent detector
Digital
receiver
Modulation index
( )s s
pi
j t data t
V
s sE P e
Optical signal
Electrical signal

35. 35 35
The basis:
ELO
ES
PC
LO
laser
E1
OpticalHybrid
Photodetectors
0
90
E2
E3
E4
Optical signal
Electrical signal
( ) cos( ( ))I out LO
pi
I t P P t data t
V
( ) sin( ( ))Q out LO
pi
I t P P t data t
V
( ( ))
( ) ( )pi
j t data t
V
I Qe I t jI t
Coherent receiver

36. 36 36
The basis:
E1
OpticalHybrid
Photodetectors
0
90
E2
E3
E4
Analog-to-Digital
Converter
DigitalReceiver
( ( ))
( ) ( )pi
j t data t
V
I Qe I t jI tOptical frequency/
phase offset
( ( ))
pi
j t data t
V
e
1. DPLL
2. Linear demodulator
3. RF signal demodulation
( ( ))
ln( )pi
j data t
V
e

37. 37 37
Signal parameters estimation:
Data clustering

38. 38 38
The basis:Analog-to-Digital
Converter
DigitalSignal
Processing
1. DPLL
2. Linear demodulator
3. RF signal demodulation
0
( ) 2 Re ( ) j t
Basebanddata t S t e
Complex baseband representation
0
( ) 2 Re ( ) j t
Basebanddata t S t e
Frequency downconversion
Quadrature demodulator
Synchronizer

39. 39 39
The basis:Analog-to-Digital
Converter
DPLLand
Lineardemodulator
Quadrature
demodulator
Synchronizer
( ) ( ) ( )Baseband I QS t s t js t
Symbol 1
Symbol 2
Symbol 3
Symbol 4
I
Q

40. 40 40
The basis: problem statement
Phase offset
( ) kj
k Baseband ky s k e
Noise

41. 41
41
Classical solution: Viterbi and Viterbi
( ) kj
k Baseband ky s k e
2
( )
( ) ( ) ( )
l
j
M
Baseband I Qs k s t js t e
2
( )
( ) ( ) ( )
l
j
M
Baseband I Qs k s t js t e
4MQPSK
2
( )
(2 )
( ) 1
l
j M
M j lM
Basebands k e e
2
( )
(2 )
( ) 1
l
j M
M j lM
Basebands k e e
No data
(Non-data-aided)

42. 42
Classical solution: Viterbi and Viterbi
2
( )
(2 )
( ) 1
l
j M
M j lM
Basebands k e e
No data
(Non-data-aided)
( ) kjMM M M
k Baseband ky s k e
Objective function( ) Re kjMM
k k
k
L y eexp[ ]kjM M
k
k
e j y It is maximized
for one phasor
ky ( )kF y
arg( )ky
(.)
k
1
arg(.)
M
M
ky
• How to recover the phase of multi-amplitude
signals?
• How to estimate other data signal parameters such
as modulation format?
• How to track time-varying data transmission
conditions?

43. 43
A novel point of view: data clustering
Phase offset
K-means
clustering
Cluster
Centroid
• Phase offset estimation and compensation
• Reconfigurable phase offset estimation
• Modulation format recognition
• Frequency offset compensation

44. 44
The principle:
Centroid
Cluster 1
Centroid
Cluster 2
Centroid
Cluster 3
Centroid
Cluster 4
1u
2u
3u
4u
(a)
Shortest
distance
2u
3u
4u
1u
ix
1ix
(b)
1d
2d
3d 4d
Updated Centroid
Cluster 1
1u
ix
,1newu
1ix
(c)(d)

45. 45
RF phase recovery:
Flexible configuration and simple upgrade for
supporting different modulation formats
Cluster
Prototype
Phase
compensation
Symbol 3
Symbol 4
Symbol 5
Symbol 6
Symbol 7
Symbol 8
Symbol 1
Symbol 2
Demodulation

46. 46
12 14 16 18 20 22
4
3
2
B2B, Viterbi & Viterbi
B2B, k-means
40 Km, Viterbi & Viterbi
40 Km, k-means
-log(BER)
OSNR [dB]
1 dB
312.5 Mbaud 8PSK single carrier at 5 GHz
Viterbi and Viterbi vs. K-means:
K-means performs equally well as
Viterbi and Viterbi

47. 47
Reconfigurable phase offset estimation:
PSK QAM
16 QAM with
phase offset Level threshold
Level 1
Level 2
Level 3
Low complex QAM
phase recovery

48. 48
Automatic modulation format detection:
Level threshold
Level 1
Level 2
Level 3
Multilevel detection
Centroid k
Cluster
dmin(k,j+1)
dmin(k,j)
Centroid
k+2
dmin(k+2,j)
dmin(k+2,j+1)
Centroid
minvar( ( , ) )s d k j
Condition of symmetry
Signal
Histogram/
K-means clustering
Number of
levels/
Number of
clusters
Multilevel?/
Symmetry?
Right
16QAM/8PSK/
QPSK Signal
Format
Recognition
K-means
Re-initialization
AMFD process
Reconfigurable
CarrierRecovery
Wrong

49. 49
Automatic modulation format detection:
Centroid k
Cluster
dmin(k,j+1)
dmin(k,j)
Centroid
k+2
dmin(k+2,j)
dmin(k+2,j+1)
Centroid
minvar( ( , ) )s d k j
Condition of symmetry
100 1000
0,000
0,001
0,002
0,003
0,004
0,005
0,006
0,007
Symmetry
Data samples
OSNR 20 dB
OSNR 24 dB
Threshold
QPSK 8PSK
0,000
0,005
0,010
0,015
0,020
Threshold
Hypothesis
Wrong QPSK id.
Symmetry
True QPSK id.
Truedetection
Wrongdetection
200 data-samples are required for
automatic modulation format detection
Modulation format = 8PSK

50. 50
Frequency offset compensation:
The reconfigurable k-means clustering
algorithm allows multifunctional tasks
Frequency offset
effect
N samples
First N/2
samples
Second N/2
samples
Cluster
Centroid
Blue
constellation
rotation by
(1: )cleary N
( 1: 2 )darky N N

51. 51
Frequency offset compensation:
The reconfigurable k-means clustering
algorithm allows multifunctional tasks
12 13 14 15 16 17 18 19 20 21 22
4
3
2
Without frequency offset compensation
With frequency offset compensation
-log(BER)
OSNR [dB]
2.7 dB
1200 1100 1000 900 800 700 600
4
3
OSNR 22 dB
OSNR 20 dB
-log(BER) Data-symbols / time-blocks
Frequency offset 10 kHz
a) b)
312.5 Mbaud 8PSK single carrier at 5 GHz

52. 52 52
Heterogeneous optical network:
Reconfigurable digital coherent
receiver for Metro Access Networs

53. 53
State of the art: converged WDM access link
Tx. 1
Tx. 2
Tx. 3
Tx. 4
K. Prince et.al, PTL 2009
• 4 х 21.4 Gbit/s NRZ-DQPSK
• 2 х 250 Mbit/s @ 5 GHz coherent Rof with phase modulation
• 1 х 3.125 Gbit/s photonically generated IR-UWB
• 1 х 256 QAM WiMAX @ 5.8 GHz (12 Mbaud, 70 Mbit/s)
200 GHz spacing between WDM channels
NRZ-DQPSK
PM RoF
IR-UWB
QAM-WiMAX
Dedicated
NRZ-DQPSK
Receiver
Dedicated
PM RoF
receiver
Dedicated
IR-UWB
reciever
Dedicated
QAM-WiMAX
receiver
4 dedicated receivers…
Less atractive to
network operators…
- Maintenance & cost
issues associated with
Mixed receiver hardware
Single
reconfigurable
digital photonic
Receiver
To support
converged service delivery
over a single infrastructure

54. 54 54
Experimental Details

55. 55 55
PM-OFDM
Baseband
VCSEL
AWG
AWG
78 km
Deployed Fiber
EDFA
20mW
PPG
DATA DATA /
MZM
/2
CW
PPG
DATA DATA /
VOA
10 dB
1
2
4
IR-UWB
AWG
TLS
M
3
Single Coherent Receiver
10 dBVOA
90°Optical
Hybrid
PwrMn
LO
1 2 3 4
VCSEL
DigitalPhotonic
Receiver
DSO
Serial-Parallel
Mapper
IFFT
CP
DATAIN
AWG
VSG
CW
M
1 m wireless
transmission
Converged service delivery:
• 5 Gbps directly modulated VCSEL
• 20 Gbps QPSK baseband
• 2 Gbps phase-modulated IR-UWB
• 500 Mbps phase-modulated OFDM at
5 GHz carrier frequency
Experimental setup

56. 56
56
PM-OFDM
Baseband
VCSEL
AWG
AWG
78 km
Deployed Fiber
EDFA
20mW
PPG
DATA DATA /
MZM
/2
CW
PPG
DATA DATA /
VOA
10 dB
1
2
4
IR-UWB
AWG
TLS
M
3
Single Coherent Receiver
10 dBVOA
90°Optical
Hybrid
PwrMn
LO
1 2 3 4
VCSEL
DigitalPhotonic
Receiver
DSO
Serial-Parallel
Mapper
IFFT
CP
DATAIN
AWG
VSG
CW
M
1 m wireless
transmission
Linear demodulator
IR-UWB
Digital filtering (HPF)
Matched filtering
Symbol
synchronization
Signal demodulation
PM-OFDM
Symbol
synchronization
Delete Cyclic Prefix
FFT
Channel estimation
Demapper
Parallel-Serial
Signal demodulation
Optical frequency off-set
compensation (DPLL)
QPSK Baseband
Equalization
Clock recovery
Binary decision &
Differential decoding
Carrier recovery
IM VCSEL
Timing recovery
Digital filtering (HPF)
Signal demodulation
Thresholding
Digital chromatic dispersion compensation
Reconfigurable digital photonic receiver

57. 57
PM-OFDM
Baseband
VCSEL
AWG
AWG
78 km
Deployed Fiber
EDFA
20mW
PPG
DATA DATA /
MZM
/2
CW
PPG
DATA DATA /
VOA
10 dB
1
2
4
IR-UWB
AWG
TLS
M
3
Single Coherent Receiver
10 dBVOA
90°Optical
Hybrid
PwrMn
LO
1 2 3 4
VCSEL
DigitalPhotonic
Receiver
DSO
Serial-Parallel
Mapper
IFFT
CP
DATAIN
AWG
VSG
CW
M
1 m wireless
transmission
Optical transmission over
78 km of deployed fiber

58. 58
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59. 59
Results

60. 60
-26 -25 -24 -23 -22 -21 -20
5
4
3
2
B2B single channel
78km single channel
-log(BER)
Received Power [dBm]
Coherent VCSEL(a)
-26 -25 -24 -23 -22 -21 -20
5
4
3
2
B2B single channel
78km single channel
78km all wavelengths
-log(BER)
Received Power [dBm]
Coherent VCSEL(a)
No penalty for
multichannel
case

61. 61
-30 -29 -28 -27 -26
4
3
2
B2B single channel
78km single channel-log(BER)
Received Power [dBm]
(b) QPSK
-30 -29 -28 -27 -26
4
3
2
B2B single channel
B2B all wavelengths
78km single channel
78km all wavelengths
-log(BER)
Received Power [dBm]
(b) QPSK
0.5 dB penalty
for multichannel
case

62. 62
-26 -24 -22 -20 -18
5
4
3
2
1
B2B single channel
B2B all wavelengths
78km single channel
78km all wavelengths
-log(BER)
Received Power [dBm]
(c) IR-UWB
-26 -24 -22 -20 -18
5
4
3
2
1
B2B single channel
78km single channel
-log(BER)
Received Power [dBm]
(c) IR-UWB
No penalty for
multichannel
case

63. 63
-32 -31 -30 -29 -28 -27
5
4
3
2
B2B single channel
78 km single channel
-log(BER)
Received Power [dBm]
(d) OFDM RoF
-32 -31 -30 -29 -28 -27
5
4
3
2
B2B single channel
B2B all wavelengths
78 km single channel
78 km all wavelengths
-log(BER)
Received Power [dBm]
(d) OFDM RoF
No penalty for
multichannel
case

64. 64
Receiver sensitivity:
• -24 dBm for directly modulated VCSEL
• -27 dBm for QPSK baseband
• -23 dBm for phase-modulated IR-UWB
• -27.5 dBm for phase-modulated OFDM

65. 65
PM-OFDM
Baseband
VCSEL
AWG
AWG
78 km
Deployed Fiber
EDFA
20mW
PPG
DATA DATA /
MZM
/2
CW
PPG
DATA DATA /
VOA
10 dB
1
2
4
IR-UWB
AWG
TLS
M
3
Single Coherent Receiver
10 dBVOA
90°Optical
Hybrid
PwrMn
LO
1 2 3 4
VCSEL
DigitalPhotonic
Receiver
DSO
Serial-Parallel
Mapper
IFFT
CP
DATAIN
AWG
VSG
CW
M
1 m wireless
transmission
Summary:
• Successful WDM signal demodulation for all
four subsystems was demonstrated
• 78 km of optical fiber transmission was
achieved
• A BER value below FEC threshold was
achieved for all four subsystems

66. 100 Gbps Wireless Link in 75-110 GHz
Band Using Photonic Technologies

67. 67 DTU Fotonik, Danmarks Tekniske Universitet
Applications to gigabit wireless links
• Sync and go
• All wireless connectivity at business and home
• HD video streaming (uncompressed)
• Cloud computing
• Video-calls
http://wirelessgigabitalliance.org/
• Beyond LTE Cellular networks
• Disaster recovery links
• Fast deployment wireless networks
• Extension of optical fiber links
Optical fiber
Optical fiber
Optical fiber

68. 68 DTU Fotonik, Danmarks Tekniske Universitet
Principle of RF generation by optical heterodyning
•High capacity optical baseband generation
•Incoherent beating of the lasers at the PD
•Stringent requirement on laser linewidth
•Scalable to high RF frequencies
[1] U. Gliese et al., MTT 1998
[2] I. Insua et al., OFC 2009
[3] R. Sambaraju et al., PTL 2010
[4] D. Zibar et al., PTL 2011

69. 69 DTU Fotonik, Danmarks Tekniske Universitet
Ƭ
16-QAM Optical Baseband
Transmitter
PolMux
Emulator
Heterodyne
Upconversion
PC X
Y XX
Y Y
W-band
LNA
EDFA
x2
LO
37 GHz
75–110 GHz
1551.6nm
1550.9
nm
LO
PD212.5 Gb/s
PPG
Ƭ
80GS/sADC
Downconversion
I/QSeparation
TimingOffsetRecovery
DecisionandBERTest
Equalizer
Receiver
π/2
87.5 GHz
1550.9 1551.6
PD1
d
X
Y
36cm
6dB
Ƭ
6dB
Ƭ
Experimental Setup
•Optical baseband 16-QAM generation using binary signal generator
•Free running ECL (100 kHz linewidth) as LO for photonic up-conversion
•Double-stage down-conversion:
1. Electrically W-band to 1-26GHz;
2. Digitally from 1-26 GHz to baseband
16-QAM Optical Baseband
Transmitter
PC
1550.9
nm
12.5 Gb/s
PPG
Ƭ
π/2
6dB
Ƭ
6dB
Ƭ
16-QAM Optical Baseband
Transmitter
PC
1550.9
nm
12.5 Gb/s
PPG
Ƭ
π/2
6dB
Ƭ
6dB
Ƭ
Ƭ
PolMux
Emulator
X
Y
Ƭ
PolMux
Emulator
X
Y
Heterodyne
Upconversion
XX
Y Y
1551.6nm
LO
PD2
PD1
X
Y
Heterodyne
Upconversion
XX
Y Y
1551.6nm
LO
PD2
PD1
X
Y
EDFA
W-band
LNA
x2
LO
37 GHz
80GS/sADC
Downconversion
I/QSeparation
TimingOffsetRecovery
DecisionandBERTest
Equalizer
Receiver
W-band
LNA
x2
LO
37 GHz
80GS/sADC
Downconversion
I/QSeparation
TimingOffsetRecovery
DecisionandBERTest
Equalizer
Receiver
87.5 GHz
1550.9 1551.6

70. 70 DTU Fotonik, Danmarks Tekniske Universitet
Experiment Setup
• For information:
– Both signal laser and LO laser has ~100 kHz linewidth, but drifting
fast within the range of 300 MHz;
– Signal and LO power are set to be equal;
– W-band LNA has 25 dB gain, max input power = -20 dBm;
– W-band Mixer is driven by LO at 74 GHz. With input RF with
frequency between 75-100 GHz, the output IF lies in the frequency
range 1-26 GHz;

71. 71 DTU Fotonik, Danmarks Tekniske Universitet
Experiment Setup
W-band
Antenna
100 GHz
PD
W1-WR10
Adaptor
W-band
Antenna
W-band
LNA
W-band
Mixer
LO
IF

72. 72 DTU Fotonik, Danmarks Tekniske Universitet
Experiment results
-1 0 1 2 3 4 5 6 7 8 9 10
5
4
3
2
1
Wireless d = 50cm
Wireless d = 150cm
Wireless d = 200cm
-log(BER)
Optical power into PD (dBm)
FEC
50 Gbit/s
•BER curves for 50 Gbit/s single
polarization 16-QAM with different
wireless distances
-1 0 1 2 3 4 5 6 7 8 9
5
4
3
2
1
Wireless d = 50 cm
Wireless d = 75 cm
Wireless d = 120 cm
-log(BER)
Optical power into PD (dBm)
FEC
100 Gbit/s
•BER curves for 100 Gbit/s PolMux
16-QAM with different wireless
distances
-1 0 1 2 3 4 5 6 7 8 9 10
5
4
3
2
1
Wireless d = 50cm
-log(BER)
Optical power into PD (dBm)
FEC
50 Gbit/s
-1 0 1 2 3 4 5 6 7 8 9 10
5
4
3
2
1
Wireless d = 50cm
Wireless d = 150cm
-log(BER)
Optical power into PD (dBm)
FEC
50 Gbit/s
-1 0 1 2 3 4 5 6 7 8 9
5
4
3
2
1
Wireless d = 50 cm
-log(BER)
Optical power into PD (dBm)
FEC
100 Gbit/s
-1 0 1 2 3 4 5 6 7 8 9
5
4
3
2
1
Wireless d = 50 cm
Wireless d = 75 cm
-log(BER)
Optical power into PD (dBm)
FEC
100 Gbit/s

73. 73 DTU Fotonik, Danmarks Tekniske Universitet
Experiment results
Ƭ
16-QAM Optical Baseband
Transmitter
PolMux
Emulator
Heterodyne
Upconversion
PC X
Y XX
Y Y
W-band
LNA
EDFA
x2
LO
37 GHz
75–110 GHz
1551.6nm
1550.9
nm
LO
PD212.5 Gb/s
PPG
Ƭ
80GS/sADC
Downconversion
I/QSeparation
TimingOffsetRecovery
DecisionandBERTest
Equalizer
Receiver
π/2
87.5 GHz
1550.9 1551.6
PD1
d
X
Y
36cm
6dB
Ƭ
6dB
Ƭ
X branch Y branch
X branch
Y branch
Constellations for 100 Gbit/s PolMux 16-QAM signal
•120 cm wireless distance
•8 dBm optical power into the photodiode

74. 74
Introduction to MIMO technique
1. If all Tx antennas transmits the same
data:
• Increase SNR
• Robust against physical disaster
2. If each Tx antenna transmits different
data simultaneously:
• Increase link capacity
• Diversity

75. 75
Training-based MIMO channel estimation
1t ,0
T
XT
2 Yt 0,
T
T
Time
X
Y
Training period Training period
DATATX
TY
TX
TY
t1 t2
DATA
DATA
DATA
x1 2 1
1 2 2
0
0
xx yX X
Y Y xy yy
RT RT T
RT RT T
h h
h h
x 1 1 2 2
1 1 2 2
xx y X X
Y Yxy yy
RT T RT T
RT T RT T
h h
h h
Channel transfer
matrix derived
Pros
 Simple expression
Cons
Required synchronization
Reduced the spectral efficiency due to the overhead

76. 76
Experimental Setup of MIMO-OFDM WDM
PON with DM-VCSEL

77. 77
MIMO-OFDM WDM PON with DM-VCSEL
Various separationVarious distance
 Successfully demodulated below the FEC limit over 7%
overhead
 198.5 Mb/s net data rate with 5.65 GHz
 Training symbols compensate for impairments in wireless link

78. 78
Experimental Setup of 2x2 MIMO-OFDM
Fiber-Wireless transmission system based
on PDM technique

79. 79
2x2 MIMO-OFDM Fiber-Wireless
Transmission System Based on PDM
Technique
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4
5
4
3
2
1
Pol-x 22.8km SMF d=1m
Pol-y 22.8km SMF d=1m
Pol-x 22.8km SMF d=2m
Pol-y 22.8km SMF d=2m
Pol-x 22.8km SMF d=3m
Pol-y 22.8km SMF d=3m
-log(BER)
Received optical power at PD [dBm]
FEC
-1
1
-1 1
-1
1
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4
5
4
3
2
1
Pol-x QPSK 22.8km SMF d=1m
Pol-y QPSK 22.8km SMF d=1m
Pol-x 16QAM 22.8km SMF d=1m
Pol-y 16QAM 22.8km SMF d=1m
-log(BER)
Received optical power at PD [dBm]
FEC
-3 -1 1 3
-3
-1
1
3
-3
-1
1
3
 4-QAM-OFDM  797 Mb/s
 16-QAM-OFDM  1.5 Gb/s
 Training symbols compensate the optical polarization rotation
and crosstalk in the wireless link

80. Find out more, videos of experiments,…
metroaccessgroup
idtm@fotonik.dtu.dk
We look for:
Researchers exchange & collaboration
EU Marie Curie postdoc grant applicants, August 2013
MSc & PhD studies and research stays

81. Metro-access and short range
communications group

82. 82
Conclusions of MIMO RoF
• Increase link capacity
• Channel estimation algorithm effectively
compensate for impairments in the wireless link
• VCSELs are an alternative optical source for
next generation access networks
• PDM alternative solution to double the capacity
• High potential for future in-door networks
system supporting gigabit/s wireless service