LOS Channel
Narrowband line-of-sight propagation channel
Libraries:
Phased Array System Toolbox /
Environment and Target
Description
The LOS Channel block propagates signals from a point in space to another point in space by line-of-sight (LOS) channels. The block can also propagate signals from one point to multiple points or from multiple points back to one point. The block models propagation time, free-space propagation loss, Doppler shift, and atmospheric as well as weather loss. The block assumes that the propagation speed is much greater than the object speed in which case the stop-and-hop model is valid.
When propagating a signal in an LOS channel to an object and back, you can use a single block to compute two-way LOS channel propagation delays or two blocks to perform two one-way propagation delays in each direction. Because the LOS channel propagation delay is not necessarily an integer multiple of the sampling interval, it can turn out that the total round trip delay in samples when you use a two-way propagation block differs from the delay in samples when you use two one-way propagation blocks. For this reason, it is recommended that, when possible, you use a single two-way propagation block.
Ports
Input
X — Narrowband signal
M-element complex-valued column vector,
M-by-N complex-valued
matrix.
Narrowband signal, specified as an M-element complex-valued column vector or M-by-N complex-valued matrix. The quantity M is the number of sample values of the signal and N is the number of signals to propagate. When you specify N signals, you need to specify N signal origins or N signal destinations.
The size of the first dimension of the input matrix can vary to simulate a changing signal length. A size change can occur, for example, in the case of a pulse waveform with variable pulse repetition frequency.
Pos1 — Signal origin
3-by-1 real-valued column vector | 3-by-N real-valued matrix
Signal origin, specified as a 3-by-1 real-valued column vector or
3-by-N real-valued matrix. The quantity
N is the number of propagated signals and equals
the dimension specified in the signal input port X
.
If Pos1
is a column vector, it takes the form
[x; y; z]
. If Pos1
is a
matrix, each column specifies a different signal origin and has the form
[x; y; z]
. Pos1
and
Pos2
cannot both be specified as matrices
— at least one must be a 3-by-1 column vector. Position units are
meters.
Data Types: double
Pos2 — Signal destination
3-by-1 real-valued column vector | 3-by-N real-valued matrix
Signal destination, specified as a 3-by-1 real-valued column vector or
3-by-N real-valued matrix. The quantity
N is the number of propagated signals and equals
the dimension specified in the signal in the input port
X
. If Pos2
is a column
vector, it takes the form [x; y; z]
. If
Pos2
is a matrix, each column specifies a
different signal origin and has the form [x; y; z]
.
Pos2
and Pos1
cannot both
be specified as matrices — at least one must be a 3-by-1 column
vector. Position units are meters.
Data Types: double
Vel1 — Signal origin velocity
3-by-1 real-valued column vector | 3-by-N real-valued matrix
Signal origin velocity, specified as a 3-by-1 real-valued column vector or
3-by-N real-valued matrix. The quantity
N is the number of propagated signals and equals
the dimension specified in the signal into the port
X
. If Vel1
is a column
vector, it takes the form [Vx; Vy; zV]
. If
Vel1
is a matrix, each column specifies a
different signal origin and has the form [Vx; Vy;
Vz]
. The dimensions of Vel1
must agree
with the dimensions of Pos1
.
Vel1
and Vel2
cannot both
be specified as matrices — at least one must be a 3-by-1 column
vector. Position units are meters.
Data Types: double
Vel2 — Signal destination velocity
3-by-1 real-valued column vector | 3-by-N real-valued matrix
Signal destination velocity, specified as a 3-by-1 real-valued column vector or
3-by-N real-valued matrix. The quantity
N is the number of propagated signals and equals
the dimension specified in the signal into the port
X
. If Vel2
is a column
vector, it takes the form [Vx; Vy; zV]
. If
Vel2
is a matrix, each column specifies a
different signal origin and has the form [Vx; Vy;
Vz]
. The dimensions of Vel2
must agree
with the dimensions of Pos2
.
Vel2
and Vel1
cannot both
be specified as matrices — at least one must be a 3-by-1 column
vector. Position units are meters.
Data Types: double
Output
Port_1 — Propagated narrowband signal
M-element complex-valued column vector,
M-by-N complex-valued
matrix.
Propagated signal, returned as a M-element complex-valued column
vector, M-by-N complex-valued
matrix. Y
will have the same dimensions as
X
.
The output Y
contains signal samples arriving at
the signal destination within the current time frame. The current time
frame is defined as the time spanned by the current input. Whenever it
takes longer than the current time frame for the signal to propagate
from the origin to the destination, the output contains no contribution
from the input of the current time frame.
Parameters
Propagation speed (m/s) — Signal propagation speed
physconst('LightSpeed')
(default) | positive scalar
Signal propagation speed, specified as a real-valued positive scalar. The default
value of the speed of light is the value returned by
physconst('LightSpeed')
.
Data Types: double
Signal carrier frequency (Hz) — Signal carrier frequency
3e8
(default) | positive scalar
Signal carrier frequency, specified as a positive scalar. Units are in Hz.
Data Types: double
Specify atmospheric parameters — Enable atmospheric attenuation model
off (default) | on
Select this parameter to enable to add signal attenuation caused by atmospheric gases, rain, fog, or clouds. When you select this parameter, the Temperature (degrees Celsius), Dry air pressure (Pa), Water vapour density (g/m^3), Liquid water density (g/m^3), and Rain rate (mm/hr) parameters appear in the dialog box.
Data Types: Boolean
Temperature (degrees Celsius) — Ambient temperature
15
(default) | real-valued scalar
Ambient temperature, specified as a real-valued scalar. Units are in degrees Celsius.
Dependencies
To enable this parameter, select the Specify atmospheric parameters checkbox.
Data Types: double
Dry air pressure (Pa) — Atmospheric dry air pressure
101.325e3
(default) | positive real-valued scalar
Atmospheric dry air pressure, specified as a positive real-valued scalar. Units are in pascals (Pa). The default value of this parameter corresponds to one standard atmosphere.
Dependencies
To enable this parameter, select the Specify atmospheric parameters checkbox.
Data Types: double
Water vapour density (g/m^3) — Atmospheric water vapor density
7.5
(default) | positive real-valued scalar
Atmospheric water vapor density, specified as a positive real-valued scalar. Units are in g/m3.
Dependencies
To enable this parameter, select the Specify atmospheric parameters checkbox.
Data Types: datetime
Liquid water density (g/m^3) — Liquid water density
0.0
(default) | nonnegative real-valued scalar
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.
Dependencies
To enable this parameter, select the Specify atmospheric parameters checkbox.
Data Types: double
Rain rate (mm/hr) — Rainfall rate
0.0
(default) | non-negative real-valued scalar
Rainfall rate, specified as a nonnegative real-valued scalar. Units are in mm/hr.
Dependencies
To enable this parameter, select the Specify atmospheric parameters checkbox.
Data Types: double
Perform two-way propagation — Enable two-way propagation
off
(default) | on
Select this check box to perform round-trip propagation between the origin and destination. Otherwise the block performs one-way propagation from the origin to the destination.
Inherit sample rate — Inherit sample rate from upstream blocks
on (default) | off
Select this parameter to inherit the sample rate from upstream blocks. Otherwise, specify the sample rate using the Sample rate (Hz) parameter.
Data Types: Boolean
Sample rate (Hz) — Sampling rate of signal
1e6
(default) | positive real-valued scalar
Specify the signal sampling rate as a positive scalar. Units are in Hz.
Dependencies
To enable this parameter, clear the Inherit sample rate check box.
Data Types: double
Maximum one-way propagation distance (m) — Maximum one-way propagation distance
10e3
(default) | positive real-valued scalar
Specify the maximum distance between the signal origin and the destination as a positive scalar. Units are in meters. Amplitudes of any signals that propagate beyond this distance will be set to zero.
Simulate using — Block simulation method
Interpreted Execution
(default) | Code Generation
Block simulation, specified as Interpreted Execution
or
Code Generation
. If you want your block to use the
MATLAB® interpreter, choose Interpreted Execution
. If
you want your block to run as compiled code, choose Code
Generation
. Compiled code requires time to compile but usually runs
faster.
Interpreted execution is useful when you are developing and tuning a model. The block
runs the underlying System object™ in MATLAB. You can change and execute your model quickly. When you are satisfied
with your results, you can then run the block using Code
Generation
. Long simulations run faster with generated code than in
interpreted execution. You can run repeated executions without recompiling, but if you
change any block parameters, then the block automatically recompiles before
execution.
This table shows how the Simulate using parameter affects the overall simulation behavior.
When the Simulink® model is in Accelerator
mode, the block mode specified
using Simulate using overrides the simulation mode.
Acceleration Modes
Block Simulation | Simulation Behavior | ||
Normal | Accelerator | Rapid Accelerator | |
Interpreted Execution | The block executes using the MATLAB interpreter. | The block executes using the MATLAB interpreter. | Creates a standalone executable from the model. |
Code Generation | The block is compiled. | All blocks in the model are compiled. |
For more information, see Choosing a Simulation Mode (Simulink).
Programmatic Use
Block
Parameter:SimulateUsing |
Type:enum |
Values:Interpreted
Execution , Code Generation |
Default:Interpreted
Execution |
More About
Attenuation and Loss Factors
Attenuation or path loss in the Wideband LOS channel consists of four components. L = LfspLgLcLr, where
Lfsp is the free-space path attenuation
Lg is the atmospheric path attenuation
Lc is the fog and cloud path attenuation
Lr is the rain path attenuation
Each component is in magnitude units, not in dB.
Propagation Delay, Doppler, and Free-Space Path Loss
When the origin and destination are stationary relative to each other, you can write the output signal of a free-space channel as Y(t) = x(t-τ)/Lfsp. The quantity τ is the signal delay and Lfsp is the free-space path loss. The delay τ is given by R/c, where R is the propagation distance and c is the propagation speed. The free-space path loss is given by
where λ is the signal wavelength.
This formula assumes that the target is in the far field of the transmitting element or array. In the near field, the free-space path loss formula is not valid and can result in a loss smaller than one, equivalent to a signal gain. Therefore, the loss is set to unity for range values, R ≤ λ/4π.
When the origin and destination have relative motion, the processing also introduces a Doppler frequency shift. The frequency shift is v/λ for one-way propagation and 2v/λ for two-way propagation. The quantity v is the relative speed of the destination with respect to the origin.
Atmospheric Gas Attenuation Model
This model calculates the attenuation of signals that propagate through atmospheric gases.
Electromagnetic signals attenuate when they propagate through the atmosphere. This effect is due primarily to the absorption resonance lines of oxygen and water vapor, with smaller contributions coming from nitrogen gas. The model also includes a continuous absorption spectrum below 10 GHz. The ITU model Recommendation ITU-R P.676-10: Attenuation by atmospheric gases is used. The model computes 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 from 1–1000 GHz and applies to polarized and nonpolarized fields.
The formula for specific attenuation at each frequency is
The quantity N"() is the imaginary part of the complex atmospheric refractivity and consists of a spectral line component and a continuous component:
The spectral component consists of a sum of discrete spectrum terms composed of a localized frequency bandwidth function, F(f)i, multiplied by a spectral line strength, Si. For atmospheric oxygen, each spectral line strength is
For atmospheric water vapor, each spectral line strength is
P is the dry air pressure, W is the water vapor partial pressure, and T is the ambient temperature. Pressure units are in hectoPascals (hPa) and temperature is in degrees Kelvin. The water vapor partial pressure, W, is related to the water vapor density, ρ, by
The total atmospheric pressure is P + W.
For each oxygen line, Si depends on two parameters, a1 and a2. Similarly, each water vapor line depends on two parameters, b1 and b2. The ITU documentation cited at the end of this section contains tabulations of these parameters as functions of frequency.
The localized frequency bandwidth functions Fi(f) are complicated functions of frequency described in the ITU references cited below. The functions depend on empirical model parameters that are also tabulated in the reference.
This model applies to both narrowband and wideband atmospheric attenuation. To compute the total attenuation for narrowband signals along a path, the function multiplies the specific attenuation by the path length, R. Then, the total attenuation is Lg= R(γo + γw). To apply the attenuation model to wideband signals, first, divide the wideband signal into frequency subbands, and apply attenuation to each subband. Then, sum all attenuated subband signals into the total attenuated signal.
Fog and Cloud Attenuation Model
This model calculates the attenuation of signals that propagate through fog or clouds.
Fog and cloud attenuation are due to the same atmospheric phenomenon. The ITU model, Recommendation ITU-R P.840-6: Attenuation due to clouds and fog is used. The model computes the specific attenuation (attenuation per kilometer), of a signal as a function of liquid water density, signal frequency, and temperature. The model applies to polarized and nonpolarized fields. The formula for specific attenuation at each frequency is
where M is the liquid water density in gm/m3. The quantity Kl(f) is the specific attenuation coefficient and depends on frequency. The cloud and fog attenuation model is valid for frequencies 10–1000 GHz. Units for the specific attenuation coefficient are (dB/km)/(g/m3).
To compute the total attenuation for narrowband signals along a path, the function multiplies the specific attenuation by the path length R. Total attenuation is Lc = Rγc. You can also apply the attenuation model to wideband signals. First, divide the wideband signal into frequency subbands, and apply narrowband attenuation to each subband. Then, sum all attenuated subband signals into the total attenuated signal.
Rainfall Attenuation Model
This model calculates the attenuation of signals that propagate through regions of rainfall. Rain attenuation is a dominant fading mechanism and can vary from location-to-location and from year-to-year.
Electromagnetic signals are attenuated when propagating through a region of rainfall. Rainfall attenuation is computed according to the ITU rainfall model Recommendation ITU-R P.838-3: Specific attenuation model for rain for use in prediction methods. The model computes the specific attenuation (attenuation per kilometer) of a signal as a function of rainfall rate, signal frequency, polarization, and path elevation angle. The specific attenuation, ɣR, is modeled as a power law with respect to rain rate
where R is rain rate. Units are in mm/hr. The parameter k and exponent α depend on the frequency, the polarization state, and the elevation angle of the signal path. The specific attenuation model is valid for frequencies from 1–1000 GHz.
To compute the total attenuation for narrowband signals along a path, the function multiplies the specific attenuation by the an effective propagation distance, deff. Then, the total attenuation is L = deffγR.
The effective distance is the geometric distance, d, multiplied by a scale factor
where f is the frequency. The article Recommendation ITU-R P.530-17 (12/2017): Propagation data and prediction methods required for the design of terrestrial line-of-sight systems presents a complete discussion for computing attenuation.
The rain rate, R, used in these computations is the long-term statistical rain rate, R0.01. This is the rain rate that is exceeded 0.01% of the time. The calculation of the statistical rain rate is discussed in Recommendation ITU-R P.837-7 (06/2017): Characteristics of precipitation for propagation modelling. This article also explains how to compute the attenuation for other percentages from the 0.01% value.
You can also apply the attenuation model to wideband signals. First, divide the wideband signal into frequency subbands and apply attenuation to each subband. Then, sum all attenuated subband signals into the total attenuated signal.
Version History
Introduced in R2016a
See Also
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