ntia / p528

U.S. reference implementation of Recommendation ITU-R P.528 providing propagation path loss predictions for aeronautical mobile and radionavigation services using the VHF, UHF, and SHF bands

Recommendation ITU-R P.528-5 - U.S. Reference Implementation

Persistent Identifier:

This code repository contains the U.S. Reference Software Implementation of Recommendation ITU-R P.528. This Recommendation contains a method for predicting basic transmission loss in the frequency range 100-30 000 MHz for aeronautical services. The software implements Annex 2 of Rec P.528, the Step-by-Step method to computing propagation loss for air-to-ground paths.

Companion software (p528-gui) provides a Graphical User Interface (GUI) that can be used with this software implementation.

Inputs

Variable	Type	Units	Limits	Description
d__km	double	km	0 <= d__km	Great circle path distance between terminals
h_1__meter	double	meter	1.5 <= h_1__meter <= 20 000	Height of the low terminal
h_2__meter	double	meter	1.5 <= h_2__meter <= 20 000	Height of the high terminal
f__mhz	double	MHz	100 <= f__mhz <= 30 000	Frequency
T_pol	int			Polarization 0 = Horizontal 1 = Vertical
time	double		1 <= time <= 99	Time percentage

Outputs

Outputs to P.528 are contained within a defined Results structure.

Variable	Type	Units	Description
d__km	double	km	Great circle path distance. Could be slightly different than specified in input variable if within LOS region
A__db	double	dB	Basic transmission loss
A_fs__db	double	dB	Free space basic transmission loss
A_a__db	double	dB	Median atmospheric absorption loss
theta_h1__rad	double	rad	Elevation angle of the ray at the low terminal
propagation_mode	int		Mode of propagation 1 = Line of Sight 2 = Diffraction 3 = Troposcatter
warnings	int		Warning flags

Error Codes and Warning Flags

P.528 supports a defined list of error codes and warning flags. A complete list can be found here.

Example Values

The below table includes a select set of example inputs and outputs for testing purposes. The P.528 CSV data files contain an extensive set of validation example values.

d__km	h_1__meter	h_2__meter	f__mhz	T_pol	time	A__db
15	10	1 000	500	0	50	110.0
100	100	15 000	3 600	0	90	151.6
1 500	15	10 000	5 700	0	10	293.4
30	8	20 000	22 000	1	50	151.1

Notes on Code Style

• In general, variables follow the naming convention in which a single underscore denotes a subscript (pseudo-LaTeX format), where a double underscore is followed by the units, i.e. h_1__meter.
• Variables are named to match their corresponding mathematical variables in the underlying Recommendation text.
• Wherever possible, equation numbers are provided. It is assumed that a user reviewing this source code would have a copy of the Recommendation's text available as a primary reference.

Configure and Build

C++ Software

The software is designed to be built into a DLL (or corresponding library for non-Windows systems). The source code can be built for any OS that supports the standard C++ libraries. A Visual Studio 2019 project file is provided for Windows users to support the build process and configuration.

C#/.NET Wrapper Software

The .NET support of P.528 consists of a simple pass-through wrapper around the native DLL. It is compiled to target .NET Framework 4.8. Distribution and updates are provided through the published NuGet package.

References

• Recommendation ITU-R P.528
• Rec ITU-R P.528 GUI

Contact

For questions, contact Billy Kozma, [email protected]

p528's Issues

Add license file, please

Relax upper height limit

The in-force version of Rec P.528 has an upper terminal height limit of 20km. The software implements this as a hard limit and will not execute outside of this bounds (it returns an error). However, various activities are performing work where it would be useful to allow P.528 to operate above 20km with appropriate disclaimers to the user.

Action: relax the upper terminal limit, such that the user gets a warning if they enter a value above 20km stating that they are operating outside the bounds of the Recommendation. However, still allow the software to compute and return a result.

dotnet core support

.NET support is currently provided via .NET Framework v4.8. Support for .NET Core, and in particular cross-platform .NET support, would be useful. With the completion of #16 such cross-platform .NET Core should be possible.

Add .NET wrapper code

Develop a fully supported .NET wrapper that can be built and offered via NuGet packages.

Add NuGet package manifest

Create a NuGet package manifest file for publishing to GitHub Packages

Add cmake support

Currently, although the software is written without any platform specific requirements, the repo doesn't contain any build/compile support for non-Windows platforms. Only a Visual Studio project file is included. The addition of a cmake file, with corresponding build instructions, would expand support to other platforms, such as Linux.

NakagamiRice.cpp

p528/src/NakagamiRice.cpp

Line 29 in 50d9c97

double VF_i = LinearInterpolation(data::NR_Data[i - 1][K_INDEX], data::NR_Data[i - i][j - 1 + 1], data::NR_Data[i][0], data::NR_Data[i][j - 1 + 1], K);

ReShaper C++ is showing a potential issue ("Both sides of operator are equivalent [misc-redundant-expression]") with this line:

data::NR_Data[i - i]

I think this is a typo and it should read i-1

But the more I look at this code the more I think there is a general issue (could be wrong)

Looking at a test input of

Result res{};
Main(1, 1.5, 1000, 1200, 0.01, &res);

and putting a breakpoint on the NakagamiRice function I think there are cases when the index goes negative (j == 0 so data::P[j - 1] is an issue)

You can better trap this by converting to use std::array or std::vector and running in debug and the debugger traps the issue