**7. Summary**

**Figure 35.** SNR with and without turbulence, SNRref and SNR, respectively, versus transmission range.

a beam size of ωeff (

source.

l

206 Contemporary Issues in Wireless Communications

atmospheric turbulence on the intensity.

Figure 35 indicates SNR versus expansion of the beam size resulting from air turbulence. For

SNR = 4.7 dB and SNReff = 3.4 dB. From these results, we conclude that when the beam expands, the loss in terms of the beam intensity increases. This leads to the decrease in the SNR value, and therefore the BER increases as indicated in Fig. 36. For a spot size of 0.015 m, the BER = 10–115, and when the spot size of the beam is 0.33 m, the BER increases up to 10–5 approximately. From the results above, we conclude that the narrow beam shows a limited effect of the

Figure 37 shows the BER versus link range between transmitter and receiver. This figure graphically represents the BER as a function of the irradiance variance. For 3500 m, BER is 10–6 for the SNR and 10–5 for the SNReff. For an irradiance variance 0.05 the BER 10–6 for the SNR and 10–5 for the SNReff. From the results obtained, we conclude that to improve the performance of the FSO transmission systems, it is recommended to shorten the link range between transmitter and receiver. Another improvement of the signal quality offered by the FSO systems includes using the 1550 nm wavelength. The SNR of FSO systems with 1550 nm wavelength is higher than that corresponding to 1000 and 850 nm wavelengths. To reduce the atmospheric turbulence effects on FSO systems, we suggest using the 1550 nm wavelength. Moreover, for the 1550 nm wavelength, the allowable power is largely higher compared to smaller wavelengths (about 50 times compared to 850 nm). This shows that the system operates well during heavier attenuation of the atmosphere since we can safely increase power at the

) = 0.015 m, the SNR = 64 dB and SNReff = 62 dB, but for ωeff (

l

) = 0.33 m, the

Recently, telecommunication and computer networking are moving toward optics communi‐ cation. Because the light is the hasten medium to transmit, the huge information, it's cost effective, flexibility, quick deployment, and the promise of optical bandwidth.

FSO is considered as alternative choice that can be employed as a reliable solution to broadband short distance applications. However, mobile operators are planning to use this technology to short distance links. In this chapter, we briefly introduced the concepts of FSO technology, mathematical approach of this technique. Practical part, we take the climate effects for deployment of FSO in Yemeni territorial as a case study. We have studied in detail the total attenuation influencing FSO systems. The total attenuation in this case study depends on two parameters: scattering and geometric losses. This work was concentrated on two different designs as demonstrated in Table 6. These results showed that when the link range, divergence angle, and transmitter aperture were increasing, the geometric loss increased too. But, we found that geometric loss decreased with the increasing of the receiver aperture diameter. Total attenuation also increased with increasing of the distance link, low visibility, and with decreasing of the wavelength. It was also shown that the effect of rainfall on the FSO system performance was so small that we can neglect it. In general, FSO performance was bad in Taiz at the low visibility compared to Sana'a and Aden. However, in the average visibility, the FSO performance was effective in three cities.

We concentrate on the scintillation effects on the performance of FSO links. The analysis was carried out for the variance, SNR, and BER in the environment of Yemen. Scintillation for the Yemeni environment is wavelength and distance dependent. The wavelength of 1550 nm turned out to be interesting since it is less sensitive to atmospheric turbulence and harmless to the human eye. The results indicate that the performance of the FSO system is good during the worst conditions in Yemen. To improve the transmission efficiency of FSO systems, the wavelength of 1550 nm must be used and the distance between transmitter and receiver must be reduced. To achieve a BER of 10–9 during air turbulence, the distance between transmitter and receiver should be 2600 m. Thus, the FSO system may be applied in Yemeni territorial efficiently even in case of the presence of air turbulence.
