Students: Lior Betzalel Michael Schwarcz Academic Advisor: Prof. Nathan Blaunstein

 Over the last years the demand for fast, accessible wireless communication has greatly increased.  The use of wireless communication in schools, coffee shops, buses and trains became very common.  Furthermore the need for reliable wireless communication aboard airplanes became very important.

 There isn’t a full design of link budget for wireless communication in aircrafts accounting for the effects of atmospheric structures.  There isn’t a full prediction of fading phenomena in land-atmosphere communication links.  In order to reach a full link budget we have to take into account the environmental effects that have influence on the propagation of the radio signal and therefore on the quality of the channel.  We will focus on the tropospheric effects...

 Tropospheric effects involve interactions between the radio waves and the lower layer of Earth’s atmosphere.  These Include effects of the gases composing the air and hydrometeors such as rain, clouds, fog, pollutions and turbulent structures.  The tropospheric effects influence on the signal are: Absorption, Scattering, Diffraction.

 Absorption/Attenuation - occurs as the result of conversion from radio wave energy to thermal energy within an attenuating particle, such as a gas molecule and different hydrometeors. The absorption effects also rise with frequency of radio waves  Scattering - occurs from redirection of the radio waves into various directions. This process is frequency-dependent - wavelengths which are long when compared to the particles’ size will be only weakly scattered  Refraction - occurs as the result of propagation effects of layered quasi-homogeneous structure of the troposphere – it is simply the atmospheric bending of the radio path away from a straight line.

 Analysis of effects of gaseous quasi-regular atmosphere on attenuation of radio signals passing the Land-Atmospheric Communication Channel (LACC).  Analysis of effects of hydrometeors (clouds and rain) on fading of radio signals passing the LACC.  Prediction of total path loss in the LACC.  Link budget design for the LACC.

In order to find the total path loss we used MATHEMATICA to simulate the channel. We can easily predict the free space loss from the well known equation:  Path loss = Free space loss + Gas loss + Additional path loss

 Total attenuation in [dB]: where d is the link distance in [km] and r is a distance factor.  The ITU model was chosen to compute the attenuation due to rain, it depends only on frequency and rain rate at the region.  Specific attenution in [dB/km]: where a,b are regression coefficients which depends on frequency and R is the rainfall rate in [mm/hour].

ITU rain regions for Europe & Africa Specific attenuation versus frequency Due to rain at 1/5/10/20/50 [mm/hour] rainfall rate

The ITU provides a recommended model for fog or cloud attenuation that is valid up to 200GHz. The total cloud attenuation is: where: L is the total water density in kg/m² K1 is the specific attenuation coefficient in (dB/km)/(gr/m³) Θ is the elevation angle of the path

 This graph represent the total cloud attenuation versus frequency for several elevation angles, using worst-case cloud density ( 1.6kg/m² ) f [GHz] Total cloud attenuation [dB] Θ = 5˚ Θ = 45˚ Θ = 15˚ Θ = 90˚  The effects are, of course, frequency-dependent.  It can be seen that cloud attenuation starts to become a consideration above about 10GHz Total cloud attenuation versus frequency at 5/15/45/90 deg elevation angle

Gaseous molecules in atmosphere may absorb energy from radio waves passing through them, thereby causing attenuation.  The Attenuation in the atmosphere over a path length d is given by: while : (Attenuation due to oxygen dB/Km)(Attenuation due to water vapor dB/Km)

for oxygen: for water vapor: f - is the frequency in GHz.  - is the water vapor density expressed in g/m3 (7.5 g/m ³ ). Oxygen Water vapor

 For the simulation we used different height of transmitter and receiver antenna, and various frequencies.  for better results temperatures are taken into account by correction factors of –1.0% per  C   = 7.5 [g/m³]  p0= 1013 mb Total attenuation at 10/100/200 GHz 200 GHz 100 GHz 10 GHz

 Up to 20GHz attenuation is mostly due to free space loss. 10 [Km] 30 [Km] 50 [Km]

 According to our results, upper bound for frequencies is for f< GHz.  Up to f<20 [GHz] the main contributor to attenuation is free space loss.  At lower frequencies gaseous structures has the most influence on the total attenuation from all the atmospheric phenomena.  Because of the oxygen molecules, we can not use the frequency range of GHz.  Investigating the affects of turbulent structures on fading phenomena and total link budget design in land-aircraft wireless communication channels.