Transcript Coherent System in Remote Antenna Application

Coherent System in Remote
Antenna Application
Presents by Roland Yuen
Overview
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Coherent system architecture
Remote antenna: Radio over fiber link
Design issues with coherent system
Potential system
Conclusion
References
Coherent system
architecture
Laser source:
DFB, Nd:YAG
RF
SMF at
1330 nm or
1550 nm
3 dB directional coupler with
balance detector
Optical combiner with signal
detector
RF
or External
Direct
Modulation
Modulation
Polarization
Control
Local Oscillator
Laser
Receiver
Spurious Free Dynamic
Range (SFDR)
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[1] Cox et al.
The SNR in which its power due to non-linearity equals
to the noise power.
Remote antenna: Radio over
fiber link
ROF
[4] Fernando et al.
G
n_optical
n_optical
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n_air
ROF
G
Downlink
Air
G
Air
n_air
Fiber loss: Converter loss, attenuation
Air loss: fading (multipath) and shadowing
(surrounding object)
SFDR requirement: 115 dB·Hz2/3 [3]
Uplink
Design issues with coherent
system
External modulation or direct modulation?
 Power consideration – gain in external
modulation and loss in direct modulation
[1] Cox et al.
External modulation or
direct modulation?
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Bandwidth and intermediate frequency
External modulation and direct modulation
have 70 GHz and 20 GHz electrical
bandwidth respectively. [2]
Linearization: Optical or electrical
Increase SFDR
Optical: Dual polarization, Multiple cascaded
modulator [3]
Electrical: Predistortion circuit [3]
Amplitude modulation or
angle modulation (PM, FM)
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Bandwidth and dynamic range (SFDR)
Electronics – difficult to implement at
high intermediate frequency
[3] Kalman et al.
Relative Intensity Noise
(RIN)
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Dominate when power are high for it is
proportional to the square of the mean optical
power.
Balance receiver: Majority of the RIN noise
can be cancelled
Balance receiver need to have very close
matched photodiodes; 50:50 power split ratio
from 3 dB directional coupler.
Phase noise (PM, FM)
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Phase noise only affects angle
modulation system
Optical cancellation: Optical signal
sideband (SSB) [6]
Electronics cancellation: Phase noise
cancellation circuit, AM-WIRNA [5],[7]
Increase IF: IF limitation [3]
Potential systems
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Phase Modulation (PM) using phase
modulator
Nd:YAG for transmitter and DFB laser
local oscillator
Single receiver with optical combiner:
RIN does not affect the system
IF amplifier (5-10 GHz)
Phase noise cancellation circuit
Conclusion
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Coherent system enables angle modulation
that has more SFDR
In remote antenna,losses in air channel lead
to high SFDR requirement (uplink)
Phase noise cancellation circuit further
increase SFDR in angle modulation
Potential system is to employ angle
modulation with external phase modulator
References
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[5]
[6]
[7]
An analytic and experimental comparison of direct and external modulation in analog fiber-optic links
Cox, C.H., III; Betts, G.E.; Johnson, L.M.;
Microwave Theory and Techniques, IEEE Transactions on , Volume: 38 Issue: 5 , May 1990
Page(s): 501 –509
Direct-detection analog optical links
Cox, C., III.; Ackerman, E.; Helkey, R.; Betts, G.E.;
Microwave Theory and Techniques, IEEE Transactions on , Volume: 45 Issue: 8 , Aug. 1997
Page(s): 1375 –1383
Dynamic range of coherent analog fiber-optic links
Kalman, R.F.; Fan, J.C.; Kazovsky, L.G.;
Lightwave Technology, Journal of , Volume: 12 Issue: 7 , July 1994
Page(s): 1263 –1277
On the design of optical fiber based wireless access systems..
Fernando X. N.; Anpalagan A.;
WINCORE laboratory, Ryerson University, Toronto
Optically coherent direct modulated FM analog link with phase noise canceling circuit
Taylor, R.; Forrest, S.;
Lightwave Technology, Journal of , Volume: 17 Issue: 4 , April 1999
Page(s): 556 –563
Technique for optical SSB generation to overcome dispersion penalties in fiber-radio systems
Smith, G. H.; Novak D.; Ahmed Z;
Phase noise in coherent analog AM-WIRNA optical link
Tayor R.; Poor H. V.; Forrest Stephen;