Presents by Roland Yuen

1
Coherent System in Remote Antenna Application

• Presents by Roland Yuen

2
Overview

• Coherent system architecture
• Remote antenna Radio over fiber link
• Design issues with coherent system
• Potential system
• Conclusion
• References

3
Coherent system architecture
RF
Direct Modulation
4
Spurious Free Dynamic Range (SFDR)
1 Cox et al.

• The SNR in which its power due to non-linearity
  equals to the noise power.

5
Remote antenna Radio over fiber link
Downlink
ROF
G
Air
4 Fernando et al.
n_optical
n_air
Uplink
ROF
G
G
Air
n_optical
n_air

• Fiber loss Converter loss, attenuationAir loss
  fading (multipath) and shadowing (surrounding
  object)
• SFDR requirement 115 dBHz2/3 3

6
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.
7
External modulation or direct modulation?

• 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

8
Amplitude modulation or angle modulation (PM, FM)

• Bandwidth and dynamic range (SFDR)
• Electronics difficult to implement at high
  intermediate frequency

3 Kalman et al.
9
Relative Intensity Noise (RIN)

• 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 5050 power split ratio from 3 dB
  directional coupler.

10
Phase noise (PM, FM)

• 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

11
Potential systems

• Phase Modulation (PM) using phase modulator
• NdYAG 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

12
Conclusion

• 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

13
References

• 1 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
• 2 Direct-detection analog optical linksCox,
  C., III. Ackerman, E. Helkey, R. Betts, G.E.
  Microwave Theory and Techniques, IEEE
  Transactions on , Volume 45 Issue 8 , Aug.
  1997Page(s) 1375 1383
• 3 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
• 4 On the design of optical fiber based wireless
  access systems..Fernando X. N. Anpalagan
  A.WINCORE laboratory, Ryerson University,
  Toronto
• 5 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
• 6 Technique for optical SSB generation to
  overcome dispersion penalties in fiber-radio
  systemsSmith, G. H. Novak D. Ahmed Z
• 7 Phase noise in coherent analog AM-WIRNA
  optical linkTayor R. Poor H. V. Forrest
  Stephen