OTuO4.pdf

OSA/OFC/NFOEC 2011

Cost-effective Fiber-Wireless Networks Thas A Nirmalathas Christina Lim, Yizhuo Zhang, Prasanna A Gamage, Dalma Novak, Rod Waterhouse The University of Melbourne

Outline

• Fiber-wireless networks – – integration of optical and wireless networks – optical as a viable backhaul technology

• Technologies – – – –

Signal transport options Analog photonic link poses performance issues Digital techniques Cost effective integration: Unified optical backhaul

• Focus on digital techniques: – Digitized RF-over-fiber – Digital IQ Transmission

• Summary

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

OSA/OFC/NFOEC 2011

Broadband Wireless: – opportunity for optical technologies in mobile backhaul

Growth in Backhaul Traffic

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Broadband Wireless Network

OSA/OFC/NFOEC 2011

Rural and Remote Communities

Mobile Switching Centers Metro/Core Network

Wireless Mesh Network Wireless Personal Area Networks (WPAN)

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Mobile or Fixed Network for City/Suburban areas

OTuO4.pdf OSA/OFC/NFOEC 2011

Frequency Spectrum Allocation

• Radio Frequency (RF) range

– 3 kHz – 30 GHz • Spectrum allocation • FM broadcast • TV broadcast • GPS

30 MHz

• TV broadcast • Mobile telephone • Cordless • Wireless networking 300 MHz

• Wireless networking • Satellite links • Satellite TV • Microwave links

3 GHz

• Radio astronomy • Satellite links • Remote sensing

30 GHz

Wireless Communications

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

300 GHz

OSA/OFC/NFOEC 2011

OTuO4.pdf

Bandwidth Allocation – Wireless Communications

GSM WiFi 1800 802.1 GSM / 1b/g WiFi 802.11a UMT 900 1900 S

0.3

1

2

3 WiMAX 802.16

MVDSMBS MVDDS LMDS WPAN

1 0

30

100 Frequency (GHz)

Wireless Communications concentrated in the lower microwave regions

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Wireless Trends

OSA/OFC/NFOEC 2011

• Convergence of cellular network and fixed wireless access • High bit-rate + mobility • Frequency spectrum congestion • Improve coding – more efficient spectral usage by increasing no. of bits per hertz • Reduce cell size – increase capacity by limiting number of users per cell • Moving up in frequency band

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OTuO4.pdf OSA/OFC/NFOEC 2011

Broadband Wireless Access Networks Wireless Access

Wireless Access

Fiber-Feed Networks

Microwave backbone

Base Station

• Radio links – Microwave /Millimeter-wave links

• Backbone Networks: Optical fiber feed networks – interconnection between Base-Stations and the Central Office (CO) – “Fiber-Wireless / Fiber-Radio”

• Base-Stations – functionally simple and compact – integrated/ hybrid subsystems with electronic, photonic and antenna components Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Central Office

OSA/OFC/NFOEC 2011

OTuO4.pdf

Opportunity to Reduce Carbon Footprint of Wireless?

Mobile Network Mobile handsets

Fixed Narrowband

2002

20X increase

Global Telecoms Footprint (devices & infrastructure) 1450+% growth

2020

0

100

Broadband Modems Department of Electrical and Electronic Engineering

200

300

400

Footprint (MtCO2 p.a.) Fixed Broadband Adapted from “SMART 2020: Enabling the low carbon economy in the information age,” GeSI, 2008 www.gesi.org Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Unified Optical Backhaul Network For Broadband Wireless and Wired Access

BS BS CO BS Metro and Core Network Connectivity

CO

BS

CO

BS Passive Optical and/or WDM Networks Department of Electrical and Electronic Engineering

Dedicated Optical Fiber Feeder Networks for Broadband Wireless Networks

Highly Integrate d with Optical Access Network s

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

OTuO4.pdf OSA/OFC/NFOEC 2011

Wireless Signal Transport over Fiber

Central Office (CO)

Optical Interface

RF Interface

Base-Station (BS)

fRF Baseband Over Fiber

RF Over Fiber

fIF Baseband Modulation (either as a fully decoded signal or I,Q pair ) Department of Electrical and Electronic Engineering

IF Over Fiber

Radio-Frequency (RF) Modulation

Intermediate Frequency (IF) Modulation Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

OSA/OFC/NFOEC 2011

Antenna Base-Station Configurations

 Centralized channel frequency management  Air-interface independent  Multi-band operation possible  High-speed optoelectronic interfaces

BS fLO

BS

O/E

 Air-interface independent  Lower cost optoelectronic interfaces  Low cost upstream transport possible

Department of Electrical and Electronic Engineering

fIFm

fLO

•••

 Centralized channel frequency management still possible

 LO required

fIF1 •••

Y

Y

O/E

Standard Telco Approach: Digital Baseband-over-Fiber

O/E

O/E

O/E BS

Fiber-Radio Approach 2: IF-over-Fiber

Y

Fiber-Radio Approach 1: RF-over-Fiber

O/E

fIFn

 Mature digital hardware  Low speed opto-electronic interfaces  Digital fiber transmission and improved intermodulation characteristics  Air-interface dependent  Complex design

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

OSA/OFC/NFOEC 2011

Digitized RF/IF Transport – Best of Both Worlds

Direct digitization of RF

Digitization of IF

O/E BS BS

O/E

Y

DAC

Y

O/E

DAC

ADC

fLO

O/E ADC

 Maintains advantages of RF-over-fiber

 Maintains advantages of IF over fiber

 Band-pass sampling method

 Multi-band systems possible

 Digital optical link

 Feasible with available technologies

 No sampling chipsets are available for broadband applications today

Department of Electrical and Electronic Engineering

 Digital optical link

 LO required

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

OTuO4.pdf

Cost-effective Optical and Wireless Integration

OSA/OFC/NFOEC 2011

• Capacity to be integrated with mainstream digital optical network – Compatible network topology, interfaces and architectures

• Construct low-cost, high-performance optical link for transporting wireless signals – Higher dynamic range – Better link gain – Lower inter-modulation distortion – Longer reach

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15

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

PON based Feeder Network Options

OSA/OFC/NFOEC 2011

(a) Sharing spare fiber for point-to-point connection suitable RoF or DRoF links Metro Network P2P

BS

CO (OLT) Edge Node e.g. 1G EPON, 2.5 GPON, 10GPON

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Optica l RFI

ONU

BS

BS

(b) RoF as an RF overlay over PON

(c) DRoF over PON, EPON, GPON or 10G EPON as required

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Dense WDM based Feeder Network

OSA/OFC/NFOEC 2011

BS

CO (OLT) Edge Node

D W D M D W D M

BS

A dedicated wavelength is assigned for each BS and ONU in the network

ONU

M. Bakaul et al, IEEE Photon. Technol. Lett., vol. 18, no. 21, pp. 2311-2313, 2006..

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OTuO4.pdf

WDM PON based Feeder Networks

BS

CO (OL T) Edge Node

C W D M

BS

ONU

ONU ONU

BS 1.T.Jeyasinghe et al , OECC2006, OFC07.

BS

(a) Course WDM is used to separate BSs from other conventional ONUs ONU

(b) Course WDM channels overlaid over conventional PON is used to separate BSs from other conventional ONUs

M. Bakaul et al, Proc. of the IEEE Internat. Top. Meet. on Microwave Photonics (MWP’07), pp. 41-44, Victoria, Canada, Oct. 2007. Department of Electrical and Electronic Engineering

OSA/OFC/NFOEC 2011

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

OTuO4.pdf

Cost-effective Optical and Wireless Integration

• Capacity to be integrated with mainstream digital optical network. • Construct low-cost, high-performance optical link for transporting wireless signals – Higher dynamic range – Better link gain – Lower inter-modulation distortion – Longer reach

Department of Electrical and Electronic Engineering

19

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

OTuO4.pdf

Digitized RF/IF Transport – Best of Both Worlds

Direct digitization of RF

Digitization of IF

O/E BS BS

O/E

Y

DAC

Y

O/E

DAC

ADC

fLO

O/E ADC

 Maintains advantages of RF-over-fiber

 Maintains advantages of IF over fiber

 Band-pass sampling method

 Multi-band systems possible

 Digital optical link

 Feasible with available technologies

 No sampling chipsets are available for broadband applications today

Department of Electrical and Electronic Engineering

 Digital optical link

 LO required

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Digitized RF over Fiber and RF over Fiber

Digital Signal ADC Processor

BPF

IF

E-O

BPF

RF fc fc IF

Fiberoptic Networ k

BPF

O-E RF Central Office (CO) (a) RoF Transport Digitized RF(Serial) Digital E-O Signal Processor Fiber-optic Network Digital Signal O-E Processor

CO

Digitized RF(Serial) (b) DRoF Transport

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Amp Y

O-E E-O Amp BPF Base-Station (BS)

BPF Amp O-E

DAC

E-O

ADC

Y

Digital DAC Signal Processor

OSA/OFC/NFOEC 2011

BS

Amp BPF

BPF – Bandpass filter Amp – Amplifier DAC – Digital to Analog Converter ADC – Anaglog to Digital Converter

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

OSA/OFC/NFOEC 2011

Analog optical link nonlinearity

Down link

BPF Data Source

O-E

E-O

× RF

BS

CO fc



Amp

SMF

fc

Data Source

BPF

×

RF

Up link

BPF

BPF Amp E-O

O-E SMF

Intermodulation distortion – Nonlinearity of both microwave and optical components.  

E-O Modulator nonlinearity [1] Interface – Increased complexity and high cost

[1] T. Kurniawan, et. al., "Performance analysis of optimized millimeter-wave fiber radio links,“ IEEE Trans. Microw. Theory Tech., vol. 54, no. 2, pp. 921-928, 2006.

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22

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf OSA/OFC/NFOEC 2011

Digitized RF transport over fiber

Digital Signal DAC Processor

Digital Signal ADC Processor

BPF Digitized RF IF × RF fc fc BPF Digitized RF IF × RF

Down link E-O E-O

Amp O-E

DAC

SMF

BPF

Up link O-E O-E

Amp E-O

ADC

SMF CO

BS

Analog optical link link Digitized RF optical 

Cost related Issues Advantages    

Jitter noise Allows partial OR complete obsolete of analog components Quantization noise Flexible and reconfigurable hardware such as FPGA Optical linkdynamic bit rate range Enhanced Sampling optical frequency Improved power budget

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23

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

BPF

OTuO4.pdf

OSA/OFC/NFOEC 2011

Digitized RF transport over fiber

Digital Signal DAC Processor

Digital Signal ADC Processor

BPF Digitized RF IF × RF fc fc BPF Digitized RF IF × RF

Down link E-O

Amp O-E

DAC

SMF

BPF

Up link O-E

Amp E-O

SMF CO

BS

ADC BPF

Digitized RF optical link 

Cost related Issues    

Jitter noise Quantization noise Optical link bit rate Sampling frequency



Advantages 



  Department of Electrical and Electronic Engineering

Allows partial OR complete obsolete of analog components Flexible and reconfigurable hardware such as FPGA Enhanced dynamic range Improved optical power budget

24

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf OSA/OFC/NFOEC 2011

Bandpass sampling fL

-5fs

-4fs

-3fs

-2fs

-fs

0

fs

Down converted Spectrum 

Bandpass sampling   

2fs

fU

3fs

fU-fL = fs/2

4fs

Original Spectrum 

fU  1 ≤ n z ≤ Ig   f f − L   U

2f

2f

U L Sampling frequency – fraction of the highest frequency of the ≤ fsamp ≤ signal nz − 1 nz Frequency conversion without mixers Limitation - Out-of-band noise aliasing

Department of Electrical and Electronic Engineering

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5fs

6fs

(1)

(2)

OTuO4.pdf

OSA/OFC/NFOEC 2011

Analytical model for digitized RF optical link Direct digitization

Data recovery Signal reconstruction

Optical link SMF

VSG

E-O

n bit ADC

O-E

Matched Filter Correlator

n bit DAC

Out-of-band noise aliasing  Jitter noise  Quantization noise 

Noise due to optical link errors  Dispersion power penalty 



Department of Electrical and Electronic Engineering

Jitter noise

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

VSA

OTuO4.pdf OSA/OFC/NFOEC 2011

Signal Considered

fc = 2.475GHz

GB

20 MHz

GB

fL

fU

50 MHz Roll off factor, α

= 0.25

Symbol rate

= 6 MSym/s

Modulation Format

= 16 QAM

Guard band (GB) fsamp

= 15 MHz = 125 MS/s

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

OTuO4.pdf

Analytical results of SNR of a digitized RF over fiber linl 90 80

SNR (dB)

70

SNROptical Link @ BER = 10-9 SNRDAC jitter Noise SNROut-of-Band Noise Aliasing

60 50 SNRADC jitter Noise 40 SNRLink

30 20 10 3

Quantized Noise Limited 4

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5

Jitter Noise Limited 6

7 8 9 Resolution (n)

10

11

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

12

OTuO4.pdf OSA/OFC/NFOEC 2011

Experimental setup - digitization

Direct digitization

Data recovery Signal reconstruction

Optical link 20 km SMF

VSG

DSO Quantizer Preamble Coder PPG ADC

VCSEL

DSO Matched Filter Correlator

PIN

DC Bias 8 mA

Decoder AWG DAC

125 MHz

125 MHz

RF carrier frequency

VSA

Quantized Signal

1.5

= 2.475 GHz

8 bit resolution

Symbol rate

= 6 MSym/s

Modulation Format

= 16 QAM

Roll off factor, α

= 0.25

Guard band (GB)

= 15 MHz

Amplitude (V)

1.0 0.5 0

-0.5

-1.0 -1.5 0

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5

10 15 Time (ms)

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

20

25

OTuO4.pdf OSA/OFC/NFOEC 2011

Experimental setup – digitized RF transmission

Direct digitization

Data recovery Signal reconstruction

Optical link 20 km SMF

VSG

DSO Quantizer Preamble Coder PPG ADC

DSO Matched Filter Correlator

PIN

VCSEL

DC Bias 8 mA

Decoder AWG DAC

125 MHz

125 MHz

2.0

Detected Signal @ BER = 10-9

Coded Output with Preamble 8 bit resolution

1.5

40 30 20 10 0 -10 -20 -30 -40

8 bit resolution

Voltage (mV)

Voltage (V)

1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 0

VSA

20

40 60 Time (ns)

Department of Electrical and Electronic Engineering

80

100

0

5 10 15 20 25 30 35 40 45 50 Time (ns)

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf OSA/OFC/NFOEC 2011

RF Spectra – original RF component

Direct digitization

Data recovery Signal reconstruction

Optical link 20 km SMF

DSO Quantizer Preamble Coder PPG ADC

VSG

VCSEL

PIN

DC Bias 8 mA

VSA

Original signal at 2.475 GHz – n = 8

DAC output – n = 8 bit resolution -40 -50

-10

RF Power (dB)

Decoder AWG DAC

125 MHz

125 MHz

0

DSO Matched Filter Correlator

-60

-20

-70

-30

-80

-40

-90

-50

-100

-60

-110

-70

-120

-80 0

-130

100

200 300 400 Frequency (MHz)

Department of Electrical and Electronic Engineering

500

-140

Centre 2.475GHz

5 MHz/

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Span 50 MHz

OTuO4.pdf

OSA/OFC/NFOEC 2011

RF Spectra – downconverted image

Direct digitization

Data recovery Signal reconstruction

Optical link 20 km SMF

DSO Quantizer Preamble Coder PPG ADC

VSG

VCSEL

PIN

DC Bias 8 mA

RF Power (dB)

Decoder AWG DAC

VSA

125 MHz

125 MHz

0

DSO Matched Filter Correlator

Image at 25 MHz – n = 8

DAC output – n = 8 bit resolution 2

-10

-10

-20

-20

-30

-30 -40

-40

-50

-50

-60

-60

-70

-70

-80

-80 0

-90

100

200 300 400 Frequency (MHz)

Department of Electrical and Electronic Engineering

500

-98

Centre 25 MHz

5 MHz/

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Span 50 MHz

OTuO4.pdf

OSA/OFC/NFOEC 2011

Link BER

Direct digitization

Data recovery Signal reconstruction

Optical link 20 km SMF

VSG

DSO Quantizer Preamble Coder PPG ADC

VCSEL

PIN

DSO Matched Filter Correlator

Decoder AWG DAC

DC Bias 8 mA

125 MHz

125 MHz

8 bit resolution

Back to back 20 Km

-5

log10BER

VSA

-6 -7 -8 BER @ 10-9

-9 -10 -27

Department of Electrical and Electronic Engineering

-26

-25 -24 -23 -22 -21 Received Optical Power (dBm)

-20

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Analytical Vs. Experimental Results

Theoretical Vs Experimental

50 45

SNRLink (dB)

40 35 30 25

SNRTheoretical

20

SNRExperimental @ 25 MHz

15 10 2

SNRExperimental @ 2.475 GHz 3

Department of Electrical and Electronic Engineering

4

5

6 7 8 9 10 11 12 13 Resolution (n)

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

OTuO4.pdf

Analog vs. Digitized – Optical power budget

60

SNR(dB)

50 40 30

OSA/OFC/NFOEC 2011

Launched Optical Power = 3 dBm Io = Digitized Digitized RF RF 16 dBm Io = 3d Bm

17.3 dB

Ana

log

20 10

RF

65 km

0 0 10 20 30 40 50 60 70 80 90 100110 Fiber Length (km)

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Key features

OTuO4.pdf

OSA/OFC/NFOEC 2011



Presented a digitized RF over fiber based on bandpass sampling.



Proposed transport technology is transparent to any modulation format.



Proposed an analytical model to assess the key design trade off.  

ADC determines the link performance. Link SNR is jitter noise limited  

 



SNR converges to 39 dB for the spectrum at 25 MHz SNR converges to 33 dB for the spectrum at 2.475 GHz

Optimal ADC bit resolution is 8. Digital optical link bandwidth < Analog optical link bandwidth

Experimentally demonstrated digitized RF over fiber.

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Transmission of Multiple Wireless Signals

Data Source 1

OSA/OFC/NFOEC 2011

× fc1

Data Source 2

×

BPF fc2

-------Data Source n

+

SMF

fcn × CO



O-E

E-O

BS

Research Issue   

Intermodulation distortion – CSO, CTO. RF crosstalk emanating from square-law-detection. Wideband modulators and photoreceivers are required.

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Bandpass Sampling of Multiple Wireless Signals

OSA/OFC/NFOEC 2011

fc,GSM

GB fL1

fc,WiMAX

200 KHz GB 10 MHz

GB fU1

fL2

20 MHz 30 MHz

WiMAX

GSM

RF carrier frequency

2.475 GHz

1.95 GHz

Modulation format

16 QAM

GMSK

Symbol/Data rate

6 MSym/s

270.833 kbps

a = 0.25

BT = 0.3

Filter parameter Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

GB fU2

Bandpass Sampling of Multiple Wireless Signals

-fU2 -fL2

nz

OSA/OFC/NFOEC 2011

-

-

2fU

OTuO4.pdf

≤ fsamp ≤

0

-fU1 -fL1

2fL nz − 1

 f U 1≤ n ≤ I  z gf − f L  U

GSM

(1)    

+

+

fL1 fU1

fL2 fU2 WiMAX

+

+

(2)

fsamp = 1250 MS/s BW1 + BW2 f IF − f IF ≥ (3) 2 2i-1 2i Optical link bit rate = 1250x8 = 125 10 Gbps fsamp = MS/s

BW2

BW1 fL1

fU1

Optical link bit rate = 125x8 = 1 Gbps Department of Electrical and Electronic Engineering

f

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

fL2

fU2

OTuO4.pdf OSA/OFC/NFOEC 2011

Bandpass Sampling of Multiple wireless signals

1

-+

-+

-+

-+

-+

- +

2

3

- +

4

Nyquist Zone ….. 31 32 ….. 5 6

-+

-+

-+

37 38 39 40

-+

-+

f 0

WiMAX

Department of Electrical and Electronic Engineering

GSM

fs

2fs

GSM

WiMAX

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Multi-channel Digitized RF over FIber

WiMAX VSG +

VSG GSM

Data recovery Signal reconstruction

Optical link

Direct digitization

20 km SMF DSO Quantizer Preamble Coder PPG ADC

VCSEL

PIN

DSO Matched Filter Correlator

DC Bias 8 mA

Modulation format Symbol/Data rate Filter parameter

GSM

VSA

0 -10

2.475 GHz 16 QAM 6 MSym/s α = 0.25

Department of Electrical and Electronic Engineering

1.95 GHz GMSK 270.833 kbps BT = 0.3

RF Power (dBm)

RF carrier frequency

Decoder AWG DAC

125 MHz DAC output – 8 bit resolution

125 MHz

WiMAX

OSA/OFC/NFOEC 2011

-20 -30 -40 -50 GSM

-60

-70 QAM -80

0

0.1

0.2 0.3 0.4 RF Frequency (GHz)

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

0.5

OTuO4.pdf OSA/OFC/NFOEC 2011

Experimental Results

Direct digitization WiMAX VSG +

VSG GSM

Optical link

Data recoverySignal reconstruction

20 km SMF DSO Quantizer Preamble Coder PPG ADC

VCSEL

PIN

DSO Matched Filter Correlator

DC Bias 8 mA

Decoder AWG DAC

VSA

125 MHz

125 MHz

Image at 25 MHz – n = 8 -2 -10

-20

-20 -30

% EVM GSM 50 MHz 1.17 GSM 1.95 GHz 1.42 WiMAX 25 MHz 1.81 WiMAX 2.475 GHz 3.44

Image at 50 MHz – n = 8 -4 -10

33.3 dB

-30

-40

-40

-50

-50

-60

-60

-70

-70

-80

-80

40.8 dB

-90

-90

-100

Original signal at 1.95 GHz – n = 8

Original signal at 2.475 GHz – n = 8 -38

-43 -50

-50

-60 -70

27.8 dB

-60

40.0 dB

-70

-80 -80

-90 -90

-100 -100

-110 -110

-120 -120

-130 -130

-140

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Key features in our solution

OSA/OFC/NFOEC 2011



Presented multiple wireless signals transmission based on bandpass sampling.



Experimental demonstration showed that wireless signals can be recovered with good EVMs.



EVM for both wireless signals revealed that digitized RF optical link could be used to transport multiple wireless signals cost effectively in both down/up link. N-bits of resolution at fs sampling rate would produce data rate > Nfs



N~4-8 bits, fs ~100-500MHz => data rate < 5Gb/s

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Digitization of high frequency RF channels

RF signal

Data (50Mbps)

Bandpass sampling

Quantization

bias

P/S Digital signal

DSO+Software

OSA/OFC/NFOEC 2011

VCSEL

(ADC+DSP, Fs=500MHz) LO (18.125G Hz) 0

0 Original RF signal at 18.125 GHz

Power (dBm)

-20 -30 -40

Signal analyser

IF signal

IF generation

-10 -20

S/P

Digital signal

PD

-40 (DSP+DAC, Fs=500MHz) -50

-50 -60

Central office-60

-70

-70

17.625 17.825 18.025 18.225 18.425 18.625 Frequency (GHz)

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IF bands at 0.125, 0.375, 0.625, 0.875 GHz

Software+AWG+BPF -30 Power (dBm)

-10

26.4km SMF

Base station

0 100 200 300 400 500 600 700 800 900 100 Frequency (MHz) 0

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf OSA/OFC/NFOEC 2011

Measured EVM Vs. RF frequency

40

EVM (%)

30

BER=10-8 Error free

20

10

0 10

11

12

13 14 15 RF Frequency (GHz)

Fs=250MHz, BR=50Mb/s Fs=500MHz, BR=100Mb/s

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16

17

Fs=500MHz, BR=50Mb/s

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

18

OTuO4.pdf OSA/OFC/NFOEC 2011

Measured EVM Vs. Bit rate

30

RF=18GHz,Resolution=8bits RF=15GHz,Resolution=8bits RF=15GHz,Resolution=6bits RF=15GHz,Resolution=4bits

EVM (%)

25

Error Error free free

20

15

10 10

20

30

Department of Electrical and Electronic Engineering

40

50 60 Bit Rate (Mb/s)

70

80

90

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

100

OSA/OFC/NFOEC 2011

OTuO4.pdf

EVM Vs. Sampling rate Vs. Optical data rate

25 EVM (8 bits) EVM (6 bits) EVM (4 bits) data rate in optical link (8 bits) data rate in optical link (6 bits) data rate in optical link (4 bits)

EVM (%)

25

20

Error free

20

15

15

10

10

5

5

0 250

500

750

1000

1250

1500

1750

2000

2250

2500

Sampling rate (MHz)

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Data Rate in optical link (Gb/s)

30

OTuO4.pdf

OSA/OFC/NFOEC 2011

Summary

• Demonstration of 18 GHz DRoF link with 4 Gbit/s optical data rate • Performance depends on carrier frequency, bit rate, ADC resolution, and sampling rate • Trade-off between the link performance and optical hardware requirement Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OTuO4.pdf

Alternative Approaches

• Direct digitization of RF • I,Q transmission over fiber

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

Direct Digitization

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

OSA/OFC/NFOEC 2011

OTuO4.pdf

A Comparison of Remote Radio Head Optical Transmission Technologies for Next Generation Wireless Systems David Wake1, Silvia Pato2, João Pedro2, Esther López3, Nathan Gomes1, Paulo Monteiro2 (1) University of Kent, Canterbury, UK (2) Nokia Siemens Networks Portugal S.A., Amadora, Portugal (3) ACORDE Technologies, S.A., Santander, Spain

OSA/OFC/NFOEC 2011

OTuO4.pdf

Transmission Link Designs Requirements

• 4 x 100MHz radio channels per link direction (downlink only shown here) • Single wavelength to allow low cost CWDM to be used to support multiple remote heads

DAC

IF to RF Optical Tx (Analogue )

Optical Fibre

1:4 splitter

DAC

IQmo d IQmo d IQmo d IQmo d

4:1 combiner

DAC

Optical Rx (Analogue )

IF to RF IF to RF IF to RF

ANALOGUE

Optical Fibre

DIGITAL

Optical Rx (Digital)

DAC

IQmod

IF to RF

DAC

IQmod

IF to RF

DAC

IQmo d IQmo d

IF to RF

DAC

IF to RF

RF signals

4:1 TDM mux

Optical Tx (Digital)

1:4 TDM demux

Remote Radio Head

Digital Base Station IQ signals

IQ signals

DAC

RF signals

Remote Radio Head

Digital Base Station

OTuO4.pdf

OSA/OFC/NFOEC 2011

Dynamic Range Comparison • Digital – For 16-bit ADC with 200MHz sampling rate – Blocking dynamic range typically 75dB – SFDR typically 85dB

• Analogue – For 100MHz bandwidth and 10dB optical power budget – Blocking dynamic range typically 65dB – SFDR typically 52dB

• Digital optical links have better performance for wideband systems – Performance limitations of analogue optical links can be largely mitigated using uplink power control or automatic gain control

OSA/OFC/NFOEC 2011

OTuO4.pdf

DBWS Wireless Range Calculations (uplink) Assumptions:

Wireless Range, m

No. of channels = 4 Channel BW = 100 MHz Frequency = 3.5 GHz L.O.S. (ple = 2) MS Tx power max. = 33 dBm MS Tx power min. = -10 dBm RAU antenna gain = 10 dBi Rx NF = 5 dB Rx sensitivity = -67 dBm (16-QAM) -59 dBm (64-QAM) -51 dBm (256-QAM) Analogue link gain = 12 dB Analogue link NF = 5.7 dB Optical power budget = 10 dB

10000

1000

digital analogue

100 16 QAM

64 QAM

256 QAM

OSA/OFC/NFOEC 2011

OTuO4.pdf

Cost Comparison Digital Type

Analogue Example

Cost (€)

Type

Example

13600

2GHz

Optical 2000 Zonu OZ510

2GHz power splitter + filters

Minicircuits ZA4PD-2+

Optical Tx/Rx

40Gb/s 40GbELR *

Mux / demux

40Gb/s Centellax 28000 MS4S1V 4:1 TDM 1M

Total cost

41600

Only optical transceiver and mux/demux costs compared; everything else is common Costs are for bidirectional link (two optical transceivers and four mux/demux units) * 40GbE-LR transceiver cost estimated from Cisco 10GbaseX2-LR and cost ratio of 3.4

Cost (€)

800

2800

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Department of Electrical and Electronic Engineering

Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

Summary

OTuO4.pdf

OSA/OFC/NFOEC 2011

• Cost-effective Integration of Optical and Wireless Networks – Low cost & high performance RF-over-Fiber links compatible with digital optical networks

• Provided an overview of: – Digitized RF over fibre. – Digital I-Q over Fiber Trasmission

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Thas Nirmalathas, OFC/NFOEC 2011 Tutorial

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