LOS Channel

The attenuation or path loss in a LOS broadband channel consists of four components.

,

where:

Each component is measured in units of magnitude, not in dB.

When the source and target are stationary relative to each other, the output of the block can be written as . Value represents a delay, and — distribution losses. The delay is calculated from , where is the propagation distance, and — the speed of propagation. The losses on the way in free space are determined by the expression

,

where — the wavelength of the signal.

This formula assumes that the target is in the far zone of the transmitting element or array. In the near-field, the formula for losses along the propagation path in free space is invalid and can lead to losses of less than one, which is equivalent to signal amplification. For this reason, losses are set to one for the range values. .

When there is relative movement between the source and the target, the processing also introduces a frequency shift. This shift corresponds to the Doppler shift between the starting and ending points. The frequency shift is for unilateral distribution and for two-way distribution. Parameter — this is the relative velocity of the target relative to the source.

This model calculates the attenuation of signals propagating through atmospheric gases.

Electromagnetic signals weaken as they propagate through the atmosphere. This effect is mainly due to the resonant absorption lines of oxygen and water vapor, with nitrogen contributing less. The model also includes a continuous absorption spectrum below 10 GHz. The model calculates the specific attenuation (attenuation per kilometer) as a function of temperature, pressure, water vapor density, and signal frequency. The atmospheric gas model is valid for frequencies of 1-1000 GHz and is applicable to polarized and unpolarized fields.

The formula for the specific attenuation at each frequency is:

.

Value It is an imaginary part of the complex refraction of the atmosphere and consists of spectral linear and continuous components.:

.

The spectral component consists of the sum of discrete spectral terms consisting of a localized function of the frequency band, multiplied by the strength of the spectral line, . For atmospheric oxygen, the strength of each spectral line is:

.

For atmospheric water vapor, the strength of each spectral line is:

.

where:

The units of pressure measurement are hectopascals (gPa), and temperatures are degrees Kelvin.

Specific pressure of water vapor, , is related to the density of water vapor, , as follows:

.

The total atmospheric pressure is:

.

For each oxygen line depends on two parameters, and . Similarly, each water vapor line depends on two parameters, and .

Localized bandwidth functions they are complex functions of frequency. These functions depend on the empirical parameters of the model.

To calculate the total attenuation for narrowband signals in a path, the function multiplies the specific attenuation by the length of the path., . Then the total attenuation is:

.

The attenuation model can be applied to broadband signals. First, divide the broadband signal into frequency sub-bands and apply signal attenuation to each sub-band. Then sum all the attenuated subband signals into a total attenuated signal.

This model calculates the attenuation of signals propagating through fog or clouds.

Fog or clouds are the same atmospheric phenomenon. The model calculates the specific attenuation (attenuation per kilometer) of a signal as a function of liquid water density, signal frequency, and temperature. The model is applicable to polarized and unpolarized fields. The formula for the specific attenuation at each frequency is:

,

where:

The attenuation model in clouds and fog is valid for frequencies of 10-1000 GHz. The units of measurement of the specific attenuation coefficient are (dB/km)/(g/m3).

To calculate the total attenuation of narrowband signals on a path, the function multiplies the specific attenuation by the path length. . The total attenuation is .

The attenuation model can be applied to broadband signals. First, divide the broadband signal into frequency sub-bands and apply narrowband attenuation to each sub-band. Then sum all the attenuated subband signals into a total attenuated signal.

This model calculates the attenuation of signals propagating through areas where precipitation occurs. Rain attenuation is the dominant attenuation mechanism and can vary from place to place and from year to year.

Electromagnetic signals are attenuated as they propagate through the precipitation area. The model calculates the specific attenuation (attenuation per kilometer) of a signal as a function of rain intensity, signal frequency, polarization, and elevation angle of the trajectory. Specific attenuation, , is modeled as a power law depending on the intensity of rain

,

where:

This attenuation model is valid for frequencies of 1-1000 GHz.

To calculate the total attenuation of a narrowband signal on the path, the function multiplies the specific attenuation by the effective propagation distance., . Then the total attenuation is .

The effective distance is the geometric distance multiplied by the scale factor:

,

where:

Precipitation rate , used in these calculations, represents the long-term statistical precipitation rate . This is the rate of precipitation, which is exceeded in 0.01% of cases.

The attenuation model can be applied to broadband signals. First, divide the broadband signal into frequency sub-bands and apply attenuation to each sub-band. Then sum all the attenuated subband signals into a total attenuated signal.