International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 11, November 2013
ISSN 2319 - 4847
Analysis of Q-Factor at Different Wavelength in
FSO Under Different Weather Conditions
Pinky Vishwakarma 1 and Jay Prakash Vijay 2
1
Rajasthan Technical University, Kota
Abstract
Free space optics (FSO) has the great potential for future communication. FSO link is a license free, secure and easily deployable
and offers low bit error rate link. Over the last two decades free space optical communication (FSO) has becomes more and more
interesting as an adjacent or alternative to radio frequency communication. However weather influenced reduced availability had
been the main cause for its restricted growth. The performance of the proposed model has been compared with well known model
for measured Q-Factor of continental clear and fog weather at different values of wavelength. The analysis is carried out that
which ranges of wavelength remains unaffected in different weather condition for free space optical communication.
Keywords: Free Space optics (FSO), Q-Factor; Wavelength, Weather
1. INTRODUCTION
FREE SPACE OPTICS (FSO) is a major hot topic in communication systems nowadays; it’s a technology that uses light
beam propagating from the transmitter through Free Space to transmit data received at the other side of the two point
communication system. FSO is often referred to as Fibreless Optics or Optical Wireless Communication [1]. The high
carrier frequency of FSO in the range of 20THz to 375THz, renders it to provide high data rates. It can be considered as
an Optical Fiber replacement especially when the physical connections are impractical due to several considerations.
The increased applications of wireless communication have many disadvantages such as Bandwidth regulations, power
limiting, high data rates etc. Where FSO may appears as its main advantages are: 1) no licensing requirements or tariffs
for link utilization; 2) absence of radiofrequency radiation hazards; 3) no need of road digging as in the case of optical
fiber; 4) large bandwidth which enables high data rates; 5) low power consumption [2] . FSO Links are suitable for few
Gb/s rates over distances in the range 1-5 km [3]. Different FSO implementation scenarios recently under research are
ground-to-ground, satellite uplink/downlink, inter-satellite or deep space probes to ground, ground-to-air e.g. UAV,HAP
/ air-to-ground terminal. The propagation channel for FSO is atmosphere and FSO links are mainly affected by the local
weather. The most detrimental attenuation factor is fog among all the attenuation factors of FSO. The performance of
FSO links can be analyzed by prediction of attenuation factor in terms of visibility.
In this paper we have used Kruse model that predict the specific attenuation in terms of visibility. It has been calculated
for the different conditions like fog, haze and clear at different wavelengths.
Major Challenges faced by FSO is that it use the air as a transmitting media between transmitters and receivers where
various weather conditions can affect the performance of FSO Link, most likely known weather phenomena are scattering
and Turbulence which causes attenuation in the transmitted Signal those results in high bit error rate or signal loss at the
receiver end [4]. In this paper we have focused on the atmospheric effects on FSO in different conditions.
FSO is just starting to be applied to solve the Internet “last-mile” interconnectivity problem. Some believe that it may be
the unlimited bandwidth solution for the metro urban core of downtown building to-building communication, as well as
the optimal technology for home-to-home and office-to-office connectivity. FSO systems have been shown to be reliable
(99.9% to 99.999%) communication channels with fast bandwidth. They are easy to set up and provide cost-effective
solutions. The industry, however, does not yet know how to properly deploy them in telecom networks. To address these
concerns, the FSO community recently launched the Free Space Optics Alliance to educate the communication industry
as a whole. It is believed that industry-wide education will enable standards to emerge and growth of FSO technology to
occur. Finally, it should be noted that to better quantify the technical and scientific aspects of FSO, there is still a need for
research in new laser sources, atmospheric spectroscopy, multi-beam and active alignment techniques and multi-detector
averaging.
The remainder of this paper has been organized as follows: Section 2 presents the FSO model link using Bit Error Rate.
Prediction of continental fog attenuation using visibility data is described in section 3. In section 4 performance of FSO is
analyzed in different weather conditions at different wavelengths. Based on the theory presented a numerical analysis is
carried out. Concluding remarks finalize this paper in section 5.
2. FREE SPACE OPTICAL LINK MODEL
FSO Link Parameters:Parameter
Symbol
Value
Transmission Rate
Bit Rate
1 Gbps
Volume 2, Issue 11, November 2013
Page 379
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 11, November 2013
ISSN 2319 - 4847
Link Distance
Z
1 Km
Optical Transmitted power
PT
320 mw
Transmitter wave length
Transmitter’s & Receiver's
optics efficiencies
Transmitter’s & Receiver's
Apertures
λ
1550 nm
0.8,0.75
10 cm
Figure 1 FSO Link Structure
In this section, we introduce in Table 1 important FSO parameters that formulate the designed link and kept constant by
various FSO vendors [5-6]. Other various specs and parameters mentioned in Section II are chosen from FSO vendors to
support following performance analysis [7,8]. during all the following analysis. These values are chosen to meet the latest
practical FSO links and are provided
3 .PREDICTION OF CONTINENTAL FOG ATTENUATION USING VISIBILITY DATA VISIBILITY:
According to the fog models visibility is defined as the distance to an object where the image distinction drops to 2% of
what it would be if the object were nearby instead.
As the fog produces huge signal attenuation
For considerable amount of time, therefore it was analyzed as the most destructive factor. The visibility is measured at
550nm wavelength which corresponds to the maximum intensity of solar spectrum. Visibility is the only one at most
parameter which describe fog and according to its definition given above. It is measured at meteorological stations or
airports. The specific attenuation in dB/km for Kim and Kruse model is given by[4].
att spec-Kim & kruse=
………(1)
Where,
V(km)= visibility
λ(nm)= wavelength
λ0 = visibility reference wavelength
For Kruse Model
……………….(2)
Equation no. (2) indicates that for any meteorological condition there will be less attenuation for higher wavelengths.
4. NUMERICAL RESULTS AND DISCUSSIONS
According to the model presented and using Matlab we regenerate the Q-Factor at different weather conditions by varying
wavelengths and also represented the corresponding output i.e. Q-factor vs wavelength graph and thus analyzing the
result.
Table 2 :Factor for clear condition at different wavelength
Volume 2, Issue 11, November 2013
Page 380
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 11, November 2013
ISSN 2319 - 4847
At λ=1551nm to 1560nm
Wavelength(nm
Q-Factor
)
1551
2113.64
1552
2113.48
1553
2113.32
1554
2113.16
1555
2113.00
1556
2112.84
1557
2112.68
1558
2112.52
1559
2112.36
1560
2112.20
At λ=781nm to 790nm
Wavelength(nm
Q-Factor
)
781
2211.04
782
2210.95
783
2210.86
784
2210.78
785
2210.69
786
2210.60
787
2210.52
788
2210.43
789
2210.34
790
2210.26
Table 3: Q-Factor for fog condition at different wavelengths
At λ=1551nm to 1560nm
Wavelength(nm
Q-Factor
)
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
Volume 2, Issue 11, November 2013
2237.29
2237.28
2237.28
2237.27
2237.27
2237.26
2237.26
2237.25
2237.24
2237.24
At λ=781nm to 790nm
Wavelength(nm
Q)
Factor
781
782
783
784
785
786
787
788
789
790
2239.22
2239.22
2239.22
2239.22
2239.22
2239.22
2239.22
2239.22
2239.22
2239.22
Page 381
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 11, November 2013
ISSN 2319 - 4847
In case of fog condition from the above result which is obtained it is clear that Q-factor for the range of 781nm-790nm
wavelength is absolutely constant than that of 1551nm-1560nm. Therefore, wave of range 781m-790m is suitable for free
space optical communication(FSO) in fog weather condition.
5. CONCLUSION
In this paper we have analyzed the Q-factor at different weather conditions in Free Space optical Communication. From
this find that the wavelength of range 781nm to 790nm is suitable in both clear as well as fog condition. The resultant QFactor is determined by using Kruse model and also find that there is minimum attenuation and power in the above
range of wavelength.
References
[1] S. Bloom, E. Korevaar, J. Schuster and H. Willebrand “Understanding the performance of free-space optics
[Invited],” Journal of optical networking, vol. 2. no.6, June.2003.
[2] S. Arnon “Optical Wireless Communications,” Encyclopedia of Optical Engineering, 2003.
[3] A. A. Farid and S. Hranilovic, “Outage capacity optimization for freespace optical links with pointing errors,” J.
Lightwave Technol., vol. 25, pp. 1702–1710, July 2007
[4] X. Zhu and J. Kahn, “Free space optical communication through atmospheric turbulence channels,” IEEE Trans.
Commun.,vol. 50, no. 8,pp. 1293–1300, Aug. 2002.
[5] fSONA Optical Wireless. [Online]. Available: http://www.fsona.com
[6] LIGHTPOINTE Wireless . [Online]. Available: www.lightpointe.com
[7] Applied Optoelectronics. [Online]. Available: http://www.aoinc.com.
[8] HAMAMATSU. [Online]. Available: http://www.hamamatsu.com
Volume 2, Issue 11, November 2013
Page 382