A.2.4 Avionics Code User’s Guide1
A.2.4 User’s Guide to Running the Avionics Code
Compiled by Justin Rhodes
The avionics code collection consists primarily of small scripts designed to analyze and visualize different aspects of the telecommunications systems onboard the launch vehicle. Due to the nature of the topic, much of our analysis was performed at a high level, leaving fewer direct calculations than other areas of the project. Below you will find our efforts to quantify and support our chosen design.
Index
fnc_link_budget.m / J. Rhodes / page2margin_vs_distance.m / J. Rhodes / page 4
bps_eval.m / J. Rhodes / page 6
doppler_shift.m / J. Rhodes / page 8
AAE450_Ground_Tracking.m / T. Lorenzana / page 9
User’s Guide forfnc_link_budget.m
Written by Justin M. Rhodes
Revision 1.0 – 30January 2008
Description:
The function fnc_link_budget.m accepts a series of input parameters that describe the basic design of a telecommunications system. These inputs are then processed through the link budget calculations to determine the link budget margin and several other system design parameters.
Assumptions:
The following variables were assumed to have certain values. An explanation of these assumed values can be found Section A.2.2.3.
Variable Name / Description / Assumed Valuetransmit_line_loss / Signal line loss on the transmitted [dB] / -1
propagation_polarization_loss / Signal loss caused by propagation and polarization effects [dB] / -0.3
receive_pointing_offset / Pointing error on the receiving antenna [degrees] / 0.2
system_noise_temp / Noise temperature level of the path through which the signal travels [Kelvin] / 135
required_signal_to_noise / Required level of signal to noise ratio for the system [dB] / 9.6
implementation_loss / Signal loss due to issues resulting from putting the whole system together [dB] / -1
Call line:
The function can be called with the following line of code:
[margin, transmit_diameter, eirp, receive_beamwidth] = fnc_link_budget(frequency, transmit_power, transmit_beamwidth, transmit_pointing_offset, path_length, receive_diameter, data_rate)
Inputs:
All of the variables that are passed into the function are described below:
Variable Name / Descriptionfrequency / Signal frequency [GHz]
transmit_power / Power supplied to the transmitter [Watts]
transmit_beamwidth / Beamwidth angle of the transmitting antenna’s main lobe. This is a property of the antenna design. [degrees]
transmit_pointing_offset / Pointing error in the transmitting antenna [degrees]
path_length / Maximum path length the signal is required to travel [km]
receive_diameter / Diameter of the receiving antenna, assuming a dipole antenna [m]
data_rate / Required data rate across the telecom link [bps]
Outputs:
All of the variables that returned by the function are described below:
Variable Name / Descriptionmargin / Final signal link margin [dB]
transmit_diameter / Diameter of the transmitting antenna to support the design, for a dipole antenna [m]
eirp / Equivalent isotropically radiated power – the amount of power an isotropic antenna would have to emit for this design. Design comparison tool. [dB-Watts]
receive_beamwidth / Pointing error in the transmitting antenna [degrees]
User’s Guide formargin_vs_distance.m
Written by Justin M. Rhodes
Revision 1.0 – 30 January 2008
Description:
The scriptmargin_vs_distance.m calculates the final signal margin for a range of maximum path lengths. Multiple signal frequencies can be evaluated at once. The resulting data is then plotted for visual analysis.
Uses:
This script calls the following function:
fnc_link_budget.m
User Inputs:
All of the variables that are initially set in the script are described below:
Variable Name / Descriptiontransmit_power / Power supplied to the transmitter [Watts]
transmit_beamwidth / Beamwidth angle of the transmitting antenna’s main lobe. This is a property of the antenna design. [degrees]
transmit_pointing_offset / Pointing error in the transmitting antenna [degrees]
receive_diameter / Diameter of the receiving antenna, assuming a dipole antenna [m]
data_rate / Required data rate across the telecom link [bps]
max_path / Maximum path length the signal is required to travel. Path lengths from 0 to max_path are evaluated. [km]
Sample Output:
This script produces a figure in the following format:
User’s Guide forbps_eval.m
Written by Justin M. Rhodes
Revision 1.0 – 30 January 2008
Description:
The scriptbps_eval.m calculates the final signal margin for a range of required data rates. Multiple signal frequencies can be evaluated at once. The resulting data is then plotted for visual analysis.
Uses:
This script calls the following function:
fnc_link_budget.m
User Inputs:
All of the variables that are initially set in the script are described below:
Variable Name / Descriptiontransmit_power / Power supplied to the transmitter [Watts]
transmit_beamwidth / Beamwidth angle of the transmitting antenna’s main lobe. This is a property of the antenna design. [degrees]
transmit_pointing_offset / Pointing error in the transmitting antenna [degrees]
receive_diameter / Diameter of the receiving antenna, assuming a dipole antenna [m]
path_length / Maximum path length the signal is required to travel [km]
max_datarate / Required data rate across the telecom link. Values from 0 to max_datarate are evaluated. [bps]
Sample Output:
This script produces a figure in the following format:
User’s Guide fordoppler_shift.m
Written by Justin M. Rhodes
Revision 1.0 – 30 January 2008
Description:
This scriptdoppler_shift.m calculates Doppler shift in kHz at a given vehicle velocity. Multiple signal frequencies can be evaluated at once. The resulting data is then plotted for visual analysis.
User Inputs:
All of the variables that are initially set in the script are described below:
Variable Name / Descriptiondelta_v / Row array of velocity values to evaluate in the form of [startvalue:increment:endvalue]. [m/s]
frequency / Row array of signal frequencies to evaluate. [MHz]
Sample Output:
This script produces a figure in the following format:
User’s Guide forAAE450_Ground_Tracking.m
Written by Timothy Lorenzana
Revision 9 - 27 March 2008
Description:
The purpose of this code is to have a graphical representation of the signal projection from the launch vehicle to the ground. The computational computer language used was MATLAB. The code works by using nominal trajectory data and simplified signal theory, as discussed in section A.2.2.10 of this report, in order to calculate a ground signal path and coverage area.
Assumptions:
The code assumes the balloon drifts in only one direction, to the East, of its initial launch point. The code also assumes the Earth only rotates about its North Celestial Pole.
Input Section:
The code has two input sections. The first input section is titled “User Defined Inputs”. The only input here is the maximum path length for the telecommunications system being used. The second input is a load file titled “ephemeris.text”. This file is an output of the trajectory code, and its contents can be found in trajectory portion of the appendix.
The inputs used in this code are listed below.
Variable Name / Descriptionpath_l / Maximum antenna path length [km]
t = ephemeris(:,1) / Time vector [seconds]
x = ephemeris(:,2) / Position vector in the Cartesian coordinate system [meters]
y = ephemeris(:,3) / Position vector in the Cartesian coordinate system [meters]
z = ephemeris(:,4) / Position vector in the Cartesian coordinate system [meters]
Output Section:
The code outputs a figure with the Earth plotted in blue, the ground track plotted in red, and the signal coverage area plotted in green. The code also outputs the total distance covered by the ground track, and an approximate signal coverage area.
The variables given as outputs of this code are given in the table below.
Variable Name / Descriptionground_track / Total ground distance covered during ascent [km]
signal_area / Approximate signal coverage area [km2]
Sample Output:
This code produces a figure in the following format:
Compiled by: Justin Rhodes