12.00 dang the ngoc free space optical communication systems

8/10/2019 12.00 Dang the Ngoc Free Space Optical Communication Systems

http://slidepdf.com/reader/full/1200-dang-the-ngoc-free-space-optical-communication-systems 1/19

Dang The Ngoc

Free-Space Optical Communications:Performance Evaluation and Improvement Methods

Department of Optical Communications

Posts and Telecommunications Institute of Technology, Vietnam

Researcher link workshop:Recent Advances and Developments in Communication Systems



1. Free-Space Optical Communications

IntroductionFSO

Free- S pace Optical Communications or Free-Space Optics Atmospheric Optical Communications A line-of-sight technology that enables data transmission based on the

propagation of light in free space. Advantages

High speedLicense-freeQuick deployment

Cost-effectiveness Applications

Metro network extensionsLast-mile accessWireless backhaulRedundant links to back up fiberTransmission in populated city areas3

Source: http://www.surajinformatics.com/fso-free-

space-optics.htm

http://www.surajinformatics.com/fso-free-space-optics.htm











1. Free-Space Optical Communications (2)

Model of FSO Systems

4



1. Free-Space Optical Communications (3)

ChallengesHigh channel loss depending on the weather conditions

Atmospheric turbulence caused by the variations in therefractive index

Pointing error (or misalignment fading) due to narrow opticalbeam and building sway

LimitationsLimited to short-haul communicationsRequired a light-of-sight connections

5



2. Atmospheric Channels (1)

Atmospheric AttenuationThe atmospheric channel attenuates the signal traversing it as aresult of absorption and scattering processes.The concentrations of matter in the atmosphere, which result inthe signal attenuation vary spatially and temporally, and willdepend on the weathe r cond i t ions .The attenuation of optical power through the atmospheric isdescribed by the exponential Beers-Lambert Law as [6]

al is the attenuation coefficient: at clear air is 0.43 dB/km; at haze is 4.3dB/km; and at fog is 43 dB/km

d is the transmission distance

6

d h l l exp (1)




Atmospheric TurbulenceCause

It is induced by the variations in the refractive index due to inhomogeneties intemperature and pressure changes

EffectIt causes rapid fluctuations in the intensity and phase of received signal(scintillation)

StrengthIs described by the refractive index structure constant,Weak turbulence: log-normal distributionModerate-to-strong turbulence: Gamma-Gamma distribution

7

2

nC




Strong Atmospheric TurbulenceThe intensity (Gamma-Gamma) distribution

ha : channel state for atmospheric turbulence (.): Gamma functionK - (.): modified Bessel function

R: Rytov variance

8

aaah h K hh f

a

22 1

2

2

(2)

1

67512

2

1

11.11

49.0exp

R

R

1

65512

2

169.01

51.0exp

R

R

6112

672 2

23.1 d C n R



Misalignment Fading (or pointing errors): themisalignment between transmitter and receiver

CauseWind loads; Thermal expansions; EarthquakesThe movement of building can vary

from 1/200 to 1/800 of the building height

EffectOptical intensity fluctuation (or fading) at the receiver

Model

h p : channel state for misalignment fading : the ratio between the equivalent beam radius and the pointing

error displacement standard deviation

A0: the fraction of the collected power at the center of the beam


9

01

0

2

0,2

2 Ahh Ah f p p ph p

(3)



Combined channel model

h: channel state

hl : path loss (deterministic) ha: atmospheric turbulence (random) h p: pointing error (random)


10

pal hhhh (4)

l h Ah

aaa

l

h dhh K hhh A

h f 0

22

2 22 121

0

22

(5)



FSO system using on-off keying modulation (OOK)Photo current at the output of the photo-detector

Signal-to-noise ratio

3. Performance Evaluation

11

(6)

(7)

Background noise Thermal noise

(8)



Spatial DiversityTakes advantage of multiple transmit/receive apertures

Increases the total average transmit power of the link andallows the system to cover longer distances.Significantly reduce the outage probability and improve theoutage capacity of a multiple-input multiple-output (MIMO) link[20], [21].

Limitation:It may not be always possible to place the receivers sufficiently far apart.Implementing multiple transmit/receive aperture scheme and designingencoding/ decoding protocols increase the complexity and implementationcosts of the system

4. Performance Improvement Methods (2)

13



Relay TransmissionThe data signal from the source node (transmitter) is relayedto the destination node (receiver) through intermediateterminals called relays.Relay transmission help to increasing free-space linkcoverage [22]-[25]Light-of-Sight connectivity is not necessary

Limitation:

To increase the total communicating distance of the link, a huge number ofrelays must be placed between the communicating nodes, that in practice,may not be possible.


14




Numerical results

15



5. Conclusion and Future Research

Performance evaluation and improvement methodsare mainly applied to point-to-point communications

To support multiple users, it is necessary deploy FSO-based multiple-access communication systems.

Future researchStudying performance evaluation and improvement methodsfor FSO-based multiple-access communicationsCross layer design and performance analysis of FSO systems

16



Thank you for your attention!

Department of Optical Communications

Posts and Telecommunications Institute of Technology



References (1)

1. D.J. Heatley, D.R. W isely, I. Neild, and P. Cochrane, “Optical wireless: The story so far,” IEEE Commun. Mag., vol. 36, no. 1 2,pp. 72 – 82, Dec. 1998.

2. Q. Liu, C. Qiao, G. Mitchell, and S. Stanton, “Optical wireless communication networks for first - and last-mile broadband access[Invited],” J. Opt. Netw., vol. 4, no. 12, 807– 828, Dec. 2005.

3. fSONA Optical Wireless. [Online]. Available: http://www.fsona.com .

4. MRV Optical Communication Systems. [Online]. Available: http://www.mrv.com .

5. D. Kedar and S. Arnon, “Urban optical wireless communications networks: The main challenges and possible solutions,” IEEECommun. Mag., vol. 42, no. 5, pp. S2 –S7, Feb. 2004.

6.M.A. Naboulsi, H. Sizum,, and F. de Fornel, “Fog attenuation prediction for optical and infrared waves”, Opt. Eng., vol. 43, no. 2,pp. 319 –329, 2004.

7. X. Zhu and J. M. Khan, “Free -space optical communication through atmospheric turbulence channels,” IEEE Trans. Commun.,vol. 50, pp. 1293-1300, Aug. 2002.

8. I.I. Kim , B. McArthur and E.J. Korevaar, “Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze foroptical wireless communications,” Proc. SPIE, vol. 4214, pp.26– 37, Feb. 2001.

9. M. Ijaz , Z. Ghassemlooy , J. Pesek , O. Fiser , H. L. Minh, and E. Bentley, “Modeling of fog and smoke attenuation in free s paceoptical communications link under controlled laboratory conditions,” J. Lightw. Technol., vol. 31, no. 11, pp. 1720– 1726, Nov.2013.

10. M. Akiba, K. Ogawa, K. Walkamori, K. Kodate, S. Ito, “Measurement and simulation of the effect of snow fall on f ree space opt icalpropagation,” Applied Optics, vol. 47, no. 31, pp. 5736– 5743, 2008.

11. M.A. Al-Habash, L.C. Andrews, and R.L. Phillips, “Mathematical model for the irradiance probability density function of a laserbeam propagating through turbulent media,” Opt. Eng., vol. 40, no. 8, pp. 1554– 1562, Aug. 2001.

12. C.C. Davis and I. Smolyaninov, “The effect of atmospheric turbulence on bit -error-rate in an on-off keyed optical wireless syste m,”Proc. SPIE Free-Space Laser Commun. Laser Imaging, vol. 4489, pp. 126-137, Mar. 1997

13. A.A. Farid and S. Hranilovic, “Outage capacity optimization for freespace optical links with pointing errors,” IEEE J. Lightw .Technol., vol. 25, no. 7, July 2007.

14. W. Gappmair, S. Hranilovic, and E. Leitgeb, “Performance of PPM on terrestrial FSO links with turbulence and pointing errors,”IEEE Commun. Lett., vol. 14, no. 5, pp. 468 – 470, May. 2010.18

http://www.fsona.com/

http://www.mrv.com/

http://www.mrv.com/

http://www.fsona.com/



References (2)15. K. Kiasaleh, “Performance of APD -Based, PPM Free- Space Optical Communication Systems in Atmospheric Turbulence,” IEEE

Trans. Commun., vol. 53, no. 9, pp. 1455 –1461, Sept. 2005.16. B.T. Vu, N.T. Dang, T.C. Thang and A.T. Pham, “Bit -error rate analysis of rectangular QAM/FSO systems using APD receiver over

atmospheric turbulence channels,” IEEE/OSA J. Optical Commun. and Netw., vol. 5. iss. 5, pp. 437 –446, May 2013.

17. A.T. Pham, T.A. Luu, and N.T. Dang, “Performance Bounds for Turbo -coded 2-D FSO/CDMA Systems over AtmosphericTurbulence Channels,” IEICE Trans. on Fundamentals, vol. E93-A, no. 12, pp. 2696 –2699, Dec. 2010.

18. X. Zhu and J. Kahn, “Performance bounds for coded free -space optical communications through atmospheric turbulencechannels,” IEEE Trans. Commun., vol. 51, pp. 1233 –1239, Aug. 2003.

19. I. Djordjevic, B. Vasic, and M. Neifeld, “Power efficient LDPC -coded modulation for free-space optical communication over theatmospheric turbulence channel,” Proc. of Conference on Optical Fiber Communication and the National Fiber Optic Engineers

Conference (OFC/NFOEC), pp. 1 –3, March 2007.20. S.G. Wilson, M. Brandt- Pearce, Q. Cao, and J.H. Leveque, “Free -Space Optical MIMO Transmission With Q- ary PPM,” IEEE

Trans. Commun., vol. 53, no. 8, pp. 1402 –1412, Aug. 2005.

21. S.M. Navidpour, M. Uysal, and M. Kavehrad, “BER Performance of Free -Space Optical Transmission with Spatial Diversity,” IEEETrans. Wireless Comm., vol. 6, no. 8, pp. 2813 –2819, Aug. 2007.

22. J. Akella, M. Yuksel, and S. Kalyanaraman “Error Analysis of Multi -Hop Free- Space Optical Communication,” Proc. of IEEEInternational Conference on Commun., pp. 1777-1781, 2005.

23. M. Safari and M. Uysal, “Relay -assisted free- space optical communication,” IEEE Trans. Wireless Comm., vol. 7, no. 12, Dec.2008.

24. C.K. Datsikas, K.P. Peppas, N.C. Sagias, and G.S. Tombras, “Serial free -space optical relaying communications over Gamma-Gamma atmospheric turbulence channels,” J. Opt. Commun. Netw., vol. 2, no. 8, Agust 2010.

25. M. Feng, J. B.Wang, M. Sheng, L. L. Cao, X. X. Xie, M. Chen, “Outage performance for parallel relay -assisred free-space opticalcommunications in strong turbulence with pointing errors,” Proc. of International Conference on Wireless Commun. and SignalProcessing (WCSP), pp. 1 – 5, 2011.

26. I. Djordjevic, W. Ryan, B. Vasic, Coding for Optical Channels, Springer, 2010.

27. Ricklin, J.C. and Davidson, F.M.: “Atmospheric turbulence effects on a partially coherent Gaussian beam: Implications for fre espace laser communication,” J. Opt. Soc. Amer. A, Opt. Image Sci., vol. 19, no. 9, pp. 1794 –1802, 2002.

28. N.T. Dang and A.T. Pham, “Performance Improvement of FSO/CDMA Systems over Dispersive Turbulence Channel using Multi -wavelength PPM Signaling” OSA Optics Express vol 20 issue 24 pp 26786- 26797 Nov 2012

19

12.00 dang the ngoc free space optical communication systems

Documents