*4.1.1. Geometric loss*

This part illustrates the effects of geometric loss on the performance of FSO system. We calculated the value of geometric loss using Eq. (33) assuming that the link range is 1 km and beam divergence is 1 mrad at two different designs, which are considered as particular design specifications shown in Table 6, due to particular implementation especially based on the existing product available in the industry [38,39].


**Table 6.** Diameters of transmitter and receiver aperture of an FSO system.

There are a number of parameters that control geometric loss: transmission range, the diameter of transmitter and receiver apertures and laser beam divergence. These parameters also contribute to the design of FSO system, so that it is suitable during bad weather conditions.

**Figure 11.** Geometric loss (dB) versus link range (km).

SNR eff=

effect of geometric loss and atmospheric attenuation is small.

part of FSO system by series of simulations obtained results.

existing product available in the industry [38,39].

**Table 6.** Diameters of transmitter and receiver aperture of an FSO system.

longer wavelengths.

188 Contemporary Issues in Wireless Communications

*4.1.1. Geometric loss*

**4. Practical part: Case study**

SNR

The performance and reliability of FSO communication systems are affected and limited by atmospheric attenuation. It has a harmful effect by haze, rainfall, fog, and scintillation has a harmful effect of FSO system. The majority of the scattering occurred to the laser beam is due to the Mie scattering. This scattering is due to the fog and haze aerosols existed at the atmos‐ phere. This scattering is calculated through visibility. FSO attenuation at thick fog can reach values of hundreds dB. Thick fog reduces the visibility range to less than 50 m, and it can affect on the performance of FSO link for distances as small. The rain scattering (non-selective scattering) is wavelength independent and it does not introduce a significant attenuation in wireless IR links, it affect mainly on microwave and radio systems that transmit energy at

There are three effects on turbulence: scintillation, laser beam spreading and laser beam wander. Scintillation is due to variation in the refractive index structure of air, so if the light traveling through scintillation, it will experience intensity fluctuations. The Geometric loss depends on FSO components design such as beam divergence, aperture diameter of both transmitter and receiver. The total attenuation depends on atmospheric attenuation and Geometric loss. In order to reduce total attenuation, FSO system must be designed so that the

In this chapter, we will take Yemeni climate as a case study to study and analyze the practical

This part illustrates the effects of geometric loss on the performance of FSO system. We calculated the value of geometric loss using Eq. (33) assuming that the link range is 1 km and beam divergence is 1 mrad at two different designs, which are considered as particular design specifications shown in Table 6, due to particular implementation especially based on the

**design diameter of transmitter aperture diameter of receiver aperture**

design 1 8 cm 10 cm design 2 3.5 cm 7 cm

**4.1. Simulation results and discussion of geometric loss and total attenuation**

<sup>2</sup> <sup>2</sup>l

kω(l)2 5 6 (40)

1 + 1.33σi

**Figure 12.** Geometric loss (dB) versus divergence angle (mrad).

Figure 11 shows the geometric loss versus link range using the values presented in Table 6 and divergence angle is about 0.025 mrad. The link range is in the range of 0.5 to 5.0 km. Geometric loss is proportional to link range, which shows that the link range increases with the increases of geometric loss. As demonstrated in Fig. 11 the geometric loss is 1.3 dB at 0.5 km for design 1 and -3.4 dB for design 2. While at the distance of 5km the geometric loss for design 1 reaches 8.2 dB and 7.2 dB for design 2. Figure 12 illustrates the geometric loss versus the divergence angle. The divergence angle is in the range of 0.025 to 0.07 mrad. Geometric loss is proportional to divergence angle, which suggest that when the divergence angle increases, geometric loss enhances. For a 0.025 mrad divergence angle, the geometric loss is about 1.93 dB for design 1 and -10.5 dB for design 2. For a 0.07 mrad divergence angle, the geometric loss is about 4.6 dB for design 1 and -5.6 dB for design 2. That means by using a small divergence angle of laser beam in FSO systems, geometric loss effect is minimized.

Figure 13 demonstrates the geometric loss versus the transmitter aperture diameter using the values presented in Table 1, divergence angle is about 0.025 mrad and the link range is 1 km. The transmitter aperture diameter is in the range of 2 to 22 cm. This figure shows that the transmitter aperture diameter rises with increases of the geometric loss. For transmitter aperture diameter of 2 cm, the geometric loss is about -7 dB for design 1 and -3.87 dB for design 2. For the transmitter aperture diameter of 20 cm, the geometric loss is about 7.7 dB for design 1 and 10.2 dB for design 2. That means the small transmitter aperture diameter is suggested to minimize in the geometric loss effect on FSO systems.

**Figure 13.** Geometric loss (dB) versus transmitter aperture diameter (m).

Figure 14 indicates the geometric loss versus the receiver aperture diameter using the values presented in Table 7, divergence angle is about 0.025 mrad and the link range is 1 km. When the receiver aperture diameter increases, the geometric loss decreases. For receiver aperture diameter of 2 cm, the geometric loss is about 14.4 dB for design 1 and 9.5 dB for design 2. For the receiver aperture diameter of 20 cm, the geometric loss is about -5.6 dB for design 1 and -10.5 dB for design 2.

**Figure 14.** Geometric loss (dB) versus receiver aperture diameter (m).

Figure 11 shows the geometric loss versus link range using the values presented in Table 6 and divergence angle is about 0.025 mrad. The link range is in the range of 0.5 to 5.0 km. Geometric loss is proportional to link range, which shows that the link range increases with the increases of geometric loss. As demonstrated in Fig. 11 the geometric loss is 1.3 dB at 0.5 km for design 1 and -3.4 dB for design 2. While at the distance of 5km the geometric loss for design 1 reaches 8.2 dB and 7.2 dB for design 2. Figure 12 illustrates the geometric loss versus the divergence angle. The divergence angle is in the range of 0.025 to 0.07 mrad. Geometric loss is proportional to divergence angle, which suggest that when the divergence angle increases, geometric loss enhances. For a 0.025 mrad divergence angle, the geometric loss is about 1.93 dB for design 1 and -10.5 dB for design 2. For a 0.07 mrad divergence angle, the geometric loss is about 4.6 dB for design 1 and -5.6 dB for design 2. That means by using a small divergence angle of laser

Figure 13 demonstrates the geometric loss versus the transmitter aperture diameter using the values presented in Table 1, divergence angle is about 0.025 mrad and the link range is 1 km. The transmitter aperture diameter is in the range of 2 to 22 cm. This figure shows that the transmitter aperture diameter rises with increases of the geometric loss. For transmitter aperture diameter of 2 cm, the geometric loss is about -7 dB for design 1 and -3.87 dB for design 2. For the transmitter aperture diameter of 20 cm, the geometric loss is about 7.7 dB for design 1 and 10.2 dB for design 2. That means the small transmitter aperture diameter is suggested

Figure 14 indicates the geometric loss versus the receiver aperture diameter using the values presented in Table 7, divergence angle is about 0.025 mrad and the link range is 1 km. When

beam in FSO systems, geometric loss effect is minimized.

190 Contemporary Issues in Wireless Communications

to minimize in the geometric loss effect on FSO systems.

**Figure 13.** Geometric loss (dB) versus transmitter aperture diameter (m).

That is to say that the large receiver aperture diameter will be used to reduce the geometric loss effect on the FSO systems. The results of geometric losses with design parameters are presented in Table 7. We note that the geometric loss at low values for receiver aperture diameter is high compared to the upper values. Because the aperture diameter of receiver is smaller than aperture diameter of transmitter. At a result, the aperture diameter of transmitter must be smaller than at the receiver side.


**Table 7.** Results of geometric loss with design parameters.
