Documentation

# phased.LOSChannel

Narrowband LOS propagation channel

## Description

The phased.LOSChannel models the propagation of narrowband electromagnetic signals through a line-of-sight (LOS) channel from a source to a destination. In an LOS channel, propagation paths are straight lines from point to point. The propagation model in the LOS channel includes free-space attenuation in addition to attenuation due to atmospheric gases, rain, fog, and clouds. You can use phased.LOSChannel to model the propagation of signals between multiple points simultaneously.

While the System object™ works for all frequencies, the attenuation models for atmospheric gases and rain are valid for electromagnetic signals in the frequency range 1–1000 GHz only. The attenuation model for fog and clouds is valid for 10–1000 GHz. Outside these frequency ranges, the System object uses the nearest valid value.

The phased.LOSChannel System object applies range-dependent time delays to the signals, as well as gains or losses. When either the source or destination is moving, the System object applies Doppler shifts.

Like the phased.FreeSpace System object, the phased.LOSChannel System object supports two-way propagation.

To compute the propagation delay for specified source and receiver points:

1. Define and set up your LOS channel using the Construction procedure. You can set the System object properties during construction or leave them at their default values. Some properties are tunable and can be changed at any time.

2. Call the step method to compute the propagated signal using the properties of the phased.LOSChannel System object.

### Note

Starting in R2016b, instead of using the step method to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

## Construction

sLOS = phased.LOSChannel creates an LOS attenuating propagation channel System object, sLOS.

sLOS = phased.LOSChannel(Name,Value) creates a System object, sLOS, with each specified property Name set to the specified Value. You can specify additional name and value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

## Properties

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Signal propagation speed, specified as a positive scalar. Units are in meters per second. The default propagation speed is the value returned by physconst('LightSpeed'). See physconst for more information.

Example: 3e8

Data Types: double

Operating frequency, specified as a positive scalar. Units are in Hz.

Example: 1e9

Data Types: double

Option to enable the atmospheric attenuation model, specified as a false or true. Set this property to true to add signal attenuation caused by atmospheric gases, rain, fog, or clouds. Set this property to false to ignore atmospheric effects in propagation.

Setting SpecifyAtmosphere to true, enables the Temperature, DryAirPressure, WaterVapourDensity, LiquidWaterDensity, and RainRate properties.

Data Types: logical

Ambient temperature, specified as a real-valued scalar. Units are in degrees Celsius.

Example: 20.0

#### Dependencies

To enable this property, set SpecifyAtmosphere to true.

Data Types: double

Atmospheric dry air pressure, specified as a positive real-valued scalar. Units are in pascals (Pa). The default value of this property corresponds to one standard atmosphere.

Example: 101.0e3

#### Dependencies

To enable this property, set SpecifyAtmosphere to true.

Data Types: double

Atmospheric water vapor density, specified as a positive real-valued scalar. Units are in g/m3.

Example: 7.4

#### Dependencies

To enable this property, set SpecifyAtmosphere to true.

Data Types: double

Liquid water density of fog or clouds, specified as a nonnegative real-valued scalar. Units are in g/m3. Typical values for liquid water density are 0.05 for medium fog and 0.5 for thick fog.

Example: 0.1

#### Dependencies

To enable this property, set SpecifyAtmosphere to true.

Data Types: double

Rainfall rate, specified as a nonnegative scalar. Units are in mm/hr.

Example: 10.0

#### Dependencies

To enable this property, set SpecifyAtmosphere to true.

Data Types: double

Enable two-way propagation, specified as a false or true. Set this property to true to perform round-trip propagation between the signal origin and destination specified in step. Set this property to false to perform only one-way propagation from the origin to the destination.

Example: true

Data Types: logical

Sample rate of signal, specified as a positive scalar. Units are in Hz. The System object uses this quantity to calculate the propagation delay in units of samples.

Example: 1e6

Data Types: double

Source of maximum one-way propagation distance, specified as 'Auto' or 'Property'. The maximum one-way propagation distance is used to allocate sufficient memory for signal delay computation. When you set this property to 'Auto', the System object automatically allocates memory. When you set this property to 'Property', you specify the maximum one-way propagation distance using the value of the MaximumDistance property.

Data Types: char

Maximum one-way propagation distance, specified as a positive real-valued scalar. Units are in meters. Any signal that propagates more than the maximum one-way distance is ignored. The maximum distance must be greater than or equal to the largest position-to-position distance.

Example: 5000

#### Dependencies

To enable this property, set the MaximumDistanceSource property to 'Property'.

Data Types: double

## Methods

 reset Reset states of System object step Propagate signal in LOS channel
Common to All System Objects
release

Allow System object property value changes

## Examples

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Propagate a polarized electromagnetic wave radiating from a short-dipole antenna element. The dipole is rotated 30° around the y-axis. Set the orientation of the local axis to coincide with the dipole. Assume the dipole radiates at 30.0 GHz. Propagate the signal toward a target approximately 10 km away.

Create the short-dipole antenna element and radiator System objects. Set the Polarization property to 'Combined' to generate polarized waves.

freq = 30.0e9; c = physconst('LightSpeed'); antenna = phased.ShortDipoleAntennaElement('FrequencyRange',[100e6 40e9], ... 'AxisDirection','Z'); radiator = phased.Radiator('Sensor',antenna, ... 'PropagationSpeed',c, ... 'OperatingFrequency',freq, ... 'Polarization','Combined', ... 'WeightsInputPort',false);

Create a signal to radiate. The signal envelope consists of several cycles of a 4 kHz sinusoid with amplitude set to unity. Set the sampling frequency to 1 MHz.

fsig = 4.0e3; fs = 1.0e6; t = [1:1000]/fs; signal = sin(2*pi*fsig*t'); laxes = roty(30)*eye(3,3);

Use a phased.FreeSpace System object to propagate the field from the origin to the destination in free space.

fschannel = phased.FreeSpace('PropagationSpeed',c,... 'OperatingFrequency',freq,... 'TwoWayPropagation',false,... 'SampleRate',fs);

Use a phased.LOSChannel System object to propagate the field from the origin to the destination in the LOS channel. Attenuation is due to atmospheric gases and fog.

loschannel = phased.LOSChannel('PropagationSpeed',c,... 'OperatingFrequency',freq,... 'TwoWayPropagation',false,... 'SampleRate',fs,'SpecifyAtmosphere',true,'LiquidWaterDensity',0.5);

Set the signal origin, signal origin velocity, signal destination, and signal destination velocity.

source_pos = [0;0;0]; target_pos = [10000;200;0]; source_vel = [0;0;0]; target_vel = [0;0;0]; [~,radiatingAngles] = rangeangle(target_pos,source_pos,laxes);

Radiate the signal towards the target. The radiated signal is a struct containing the polarized field.

rad_sig = radiator(signal,radiatingAngles,laxes);

Propagate the signals to the target in free space.

prop_sig = fschannel(rad_sig,source_pos,target_pos,... source_vel,target_vel);

Propagate the signals to the target in the LOS channel.

prop_att_sig = loschannel(rad_sig,source_pos,target_pos,... source_vel,target_vel);

Plot the z-components of both the free-space and LOS-channel-propagated signals.

plot(1e6*t,real(prop_sig.Z),1e6*t,real(prop_att_sig.Z)) grid xlabel('Time (\mu sec)') legend('z_{fsp}','z_{los}')

The LOS channel signal is attenuated as compared to the free-space signal.

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## References

[1] Radiocommunication Sector of the International Telecommunication Union. Recommendation ITU-R P.676-10: Attenuation by atmospheric gases. 2013.

[2] Radiocommunication Sector of the International Telecommunication Union. Recommendation ITU-R P.840-6: Attenuation due to clouds and fog. 2013.

[3] Radiocommunication Sector of the International Telecommunication Union. Recommendation ITU-R P.838-3: Specific attenuation model for rain for use in prediction methods. 2005.

[4] Seybold, J. Introduction to RF Propagation. New York: Wiley & Sons, 2005.

[5] Skolnik, M. Introduction to Radar Systems, 3rd Ed. New York: McGraw-Hill, 2001.