Safran Skydel User Manual

This value controls the delay applied to RF transmission to align the RF with the PPS OUT signal. This preference is used only if both Sync Time Master and Sync Time Slave are unchecked. In this case, the SDR is using its own internal PPS reference. See section Synchronize Simulators for Sync Time settings details.

The value is calibrated for different sampling rates. The user may adjust this value if it is necessary to offset or align the PPS OUT signal of the SDR with the PPS signal of the GNSS receiver under test. In most cases, the value should be left to its default.

This value represents a delay between a reference PPS pulse (on the PPS IN port) and the beginning of the RF signal. The default value is 2000.000000ms. The resolution is 0.000001ms (1ns). The effectiveness of this value differs depending on the radio type you are using (examples follow).

To synchronize radios connected to different computers, each computer running Skydel must talk to each other. If the radios are connected to the same computer, but used by different Skydel instances, each instance must talk to each other as well. In any event, one of the Skydel instances must be defined as the server (master) while each of the other Skydel instances are clients (slaves). The client settings control which server the Skydel slaves will try to connect to. The server settings control which port the Skydel master will listen on. You can read more details about this in the Synchronize Simulators section.

You can synchronize radios to the output of a timing receiver. This can be used to synchronize Skydel to the live sky or some other signal source. The timing receiver can be an OctoClock-G from Ettus or another receiver that supports NMEA messages (required sentences are "$GPGGA" and "$GPRMC"). The accuracy of this type of synchronization is better than 50 ns.

In the Settings - Output, select the X300 SDR in the dropdown list and click Add.

When adding a USRP radio such as the X300, the IP address and clock source are preset with default values as defined in the Preferences. If the default values are incorrect for your setup, click Edit under the radio name to edit the radio settings.

Take a moment to look at the front of the USRP X300 radio. You will notice that it has an RF A TX port and an RF B TX port.

The markings on the radio correspond to the labels in the Output settings. For example, any signals assigned to RF A in the Output settings will be generated and output by the USRP X300 RF A TX port. To assign signals, click the “Edit” button for the corresponding output.

The Signal Selection dialog box will help you choose the signals that you want to be generated for each output. Start by selecting Upper L-Band (e.g. L1) or Lower L-Band (e.g. L2).

If you have the Advanced Jammer option enabled, the Output Type will also include the Interference option.

If Gaussian Noise is checked, Skydel will add noise to reproduce realistic C/No.

Next, select the signals that you would like this output to generate. As you make selections, you will notice that the dialog box will update the Ideal Sampling Rate as well as disable code types that are not compatible with your current selection. For example, when selecting Galileo E5 AltBOC in the lower L-band, the current sampling rate changes to 60 MSps (Mega Samples per second). Also, the GLONASS G2 and Galileo E6 HAS signals are disabled because they are too far away from the E5 signals to fit within the same RF band. To work around this, you can either choose a radio that can support higher sampling rate or use an additional output (or additional radio).

You may constrain this output to keep its sample rate low by changing the Max Sample Rate to a lower value. Alternatively, you may constrain the output to remain high by changing the Min Sample Rate to a higher value.

Due to a limitation in the hardware, some SDR models require that all outputs must have the same sampling rate. For example, if the signals selection on RF A requires 25 MSps and the signals selection on RF B requires 12.5 MSps, both outputs will be set to 25 MSps. For SDR models with this constraint, the selected sampling rate is always the highest sampling rate of any available output.

Only signals for which you have an active license will be available for choosing.

Galileo E5 AltBOC can be generated if you have an active Galileo E5 license by clicking E5 AltBOC or both E5a and E5b under Signal.

The default gain for the USRP X300 radio is 80 dB. You can change the gain by 1 dB step between 80 dB and 115 dB. See Reference Power Level section below for more details.

Once you have made your signal selection, click the “Ok” button to return to the Output settings. The simulation will not run if you try to assign the same signal to multiple outputs. Once you have completed your signal selection for all outputs, the Output settings should look something like this.

Once you have selected a radio, you can click the Reference Power button to get the nominal power at the TX connector.

For the X300, the reference power level is -50 dBm at the TX connector for a single GPS L1C/A signal.

The main concern when configuring the Output settings is staying within the performance limitations of both the CPU and the GPU. Skydel is a software-defined GNSS simulator, so the number of signals that can be simulated is limited by the performance of the software running on the computer (most simulators are limited by the number of hardware channels they have). The number of signals that can be simulated depends on a number of factors:

If you hit the performance limit of your computer, you have 2 options. Option 1 is to reduce any of the items listed above. Option 2 is to increase the performance of the hardware.

When you select signals with different carrier frequencies, Skydel must increase the sample rate to cover both signals and use a carrier frequency in-between the 2 signals. However, if you assign these signals to different RF outputs (RF A vs RF B), Skydel will reduce the sampling rate. This will greatly reduce the workload for the GPU.

Once you have completed the signal selection, you can test the performance of the GPU by clicking the Test GPU Speed button. The GPU Benchmark dialog box will display the signals that you have selected in the Output settings. Signal types that you have not selected will not be part of the test. The benchmark assumes 14 satellites for GPS and 10 satellites for each of the other constellations. If you only expect 10 GPS satellites to be in view, you can lower this value to more accurately reflect the conditions you will observe during your simulation.

Once you are satisfied with your selection, click the Start button to begin the test. Once the test has completed, you will see a score for the GPU. A score higher than 1.00 means the GPU performance is sufficient for this signal selection. However, you don’t want to cut it too close, we recommend a score of 1.10 or higher. A score of less than 1.00 means the GPU doesn’t have enough performance to generate the signals in real time. Try reconfiguring the Output settings to use smaller sample rates, reducing the number of satellites, or reducing the number of signals selected.

To save IQ data to a file, select “File” as the output type and click the “Add” button. (If you already have X300s configured, you will have to delete each of them before proceeding).

Skydel will prompt you to name the file that you would like to save the IQ data to. You should consider saving this data on a hard drive with plenty of space and fast writing speed because IQ data files can grow very large over time. You can add multiple IQ data files by clicking the “Add” button. This step is necessary if you want to save both L1 and L2 data. Add signals to each individual IQ file using the Signal Selection dialog box that is used for X300 SDRs. Once you have selected each of the desired signals, your output settings should look something like this:

When you are ready, start the simulation. Skydel will begin saving data into the specified files.

When saving data to IQ Files, your GPU does not need to pass the performance test. Skydel will generate the file as fast as it is able, which, depending upon the performance of your GPU and your hard drive, may be slower or faster than real-time.

When you generate an IQ file with Skydel, you get 2 files per RF output:

Configuring Safran’s Skydel for an anechoic chamber is a 4-step process:

Step 1 is usually performed by an Safran engineer or qualified personnel. It requires a keen understanding of the computer motherboard and its PCIe bus routing in order to optimize the data transfer between the different peripherals (CPU, GPU, RAM, NIC, etc.). Typically, the result of this step is stored in a file named hardware.xml. The path to this file must be properly set in Skydel USRP preferences.

Steps 2 and 3 are done within the Anechoic Chamber Builder software. Once these steps are complete, the software will output the results into an ANEC file.

Step 4 is done in Skydel.

In the Settings - Output, select the Anechoic Chamber in the dropdown list and click Add. Locate your ANEC file and click Open.

The output settings page is divided in 2 parts:

The sky view in the Constellations subtab does not show any satellites in view simply because there are no GNSS signals selected in this scenario. Click Select Signals.

Choose the desired signals and click OK. The main window is updated.

The GNSS tab is updated with useful information such as the RF outputs' associations with each signals and satellites. Moving the mouse over a row in the table will highlight in green the corresponding antenna in the sky view on the right (see image below).

In this example, the row indicates that GPS SV ID 3 and 22 are mapped to the same physical output: 1B. The next row also indicates the same output 1B is being used to transmit Galileo SV ID 33.

Below the table you will find a text report listing the angular distance between the GNSS satellite and the physical antenna used for transmission. Skydel will do its best to minimize angular distance, but it is useful to look at this table and validate that the distances are acceptable for your scenario. Here’s a text report example:

Some SV ID are marked with an asterisk, such as number 22*. It means that the SV ID 22 is currently below the masking angle and should it be moving above the masking angle during the simulation, it will be transmitted using this physical output.

Wavefront output can only be used with the GSG Wavefront system. It leverages the multi-instance synchronization feature of the Skydel software to enable simulation scenarios including high-dynamics trajectories (GNSS and non-GNSS).

GSG Wavefront generates phase-synchronized signals in real-time, to realistically simulate the signals received by a CRPA.

You can find a more detailed description of GSG Wavefront in the product manual. Your GSG Wavefront also includes an XML file. This file describes your hardware architecture and its simulation capability.

Your system contains more than one computer:

It is only necessary to change settings on the Wavefront Controller; those settings also control the Nodes. The following instructions only concern the Wavefront Controller.

To view or change the GSG Wavefront settings, navigate to the Settings - Output menu. Select Wavefront Controller in the dropdown list and click Add. Locate the hardware file and click Open.

The output settings page will display three tabs.

Setting a Custom Time is the most common method of controlling the start time of the simulation. Every time you run the simulation, it will start at the same time. You can change the custom time by clicking on the time field itself.

You can specify the time with any of the fields provided. The other fields will update to reflect the changes that you have made. For example, you can set the date and time to 7/1/2016 and 07:00:00. The week and second will automatically be updated to 1903 and 457200.

If you select Current Computer Time, your simulation will be synchronized to the computer system time to within approximately 10 seconds. This is due to the time it takes to start the streaming process with the radios. Synchronizing in this way can be useful if you want your simulation to be close to true time. However, for tight synchronization with a time reference, it is necessary to use a timing receiver.

If you want to synchronize your simulation with more accuracy, you can select GPS Timing Receiver Time. Ensure that your timing receiver preference is set correctly. Once everything is configured correctly, you will be able to see a preview of the start time.

Skydel will communicate with the timing receiver during the initialization process and ensure that the simulation starts at the specified time. This process happens after the radio initialization, so a precise synchronization can be achieved.

If desirable, you can add an offset to the simulation start time computed by the GPS Timing Receiver. The value must be an integer between -3600 and +3600 seconds.

You can specify the current leap seconds (LS) value and the date of the next leap seconds future (LSF) event.

The LS value is used by the receiver to convert GPS system time to UTC time. NMEA data is marked with UTC timestamps. If the receiver and the simulator use different LS values to compute the UTC time, it will make the NMEA output difficult to compare, especially in the receiver deviation graph.

If you uncheck (disable) the LSF event, Skydel will set the LSF value in the navigation message to the current leap seconds value regardless of the LSF value that you entered.

If you enable the LSF event checkbox and the simulation start time is set for after the LSF event date, Skydel will use the LSF value as the current leap seconds value. You should keep in mind that the LSF event occurs at the end of the specified day, at exactly midnight UTC. You can see the effective leap seconds value (LS vs. LSF) in the dashboard.

Skydel allows any date for the leap seconds future event, but usually the date is set to either June 30th or December 31st.

By setting the duration you can choose how long you would like the simulation to run. By default, the duration is set to Unlimited.

Click the dropdown box to select the desired duration. If you would like to specify a duration other than what is listed, select the Other option. You can then specify the amount of days, hours, minutes, and/or seconds you would like the simulation to run.

The Atmosphere settings are located in the Settings - Global - Atmosphere menu.

The Atmosphere sub-menu contains the Nominal and Errors atmosphere settings.

The Earth Orientation Parameters settings are located in the Settings - Global - Earth Orientation Parameters menu.

Default Earth Orientation Parameters range from January 1st to December 31st of the year of the default simulation start time.

The Import button opens a dialog to import Earth Orientation Parameters from a CSV file.

Below are the column descriptions for each Earth Orientation Parameter.

The Logging settings are located in the Settings - Global - Logging menu.

Use the Logging settings to control how Skydel logs data during a simulation.

The Signal Level settings are located in the Settings - Global - Signal Level menu.

You can use the Signal Level settings to control the output power of the satellite signals being generated relative to the nominal value, which depends on your hardware setup. When you configure the output, you can click on the Reference Power button to see the nominal value of your hardware. To adjust the power level of the transmitted signal, you can either change the Global offset or the offset specific to the code type that you are adjusting. By default, Skydel uses a 0 dB global offset, and a realistic offset for all of the other code types. This will correctly model the fact that not all constellations and code types are generated at the same power level. For example, according to the specifications, P-Code should operate at 3 dB less than C/A code.

When using the default settings, the transmit power of a GPS C/A code signal has 80 dB of gain. Typically, for a vehicle on Earth, this will translate into a power level of -50 dBm (measured at the TX port of a X300 radio). When using 60 dB of attenuation, this -50 dBm signal will become -110 dBm. This is the correct power level to simulate a 20 dB LNA. You may refer to the power level section for more details.

There are three ways you can increase or decrease the power level of a signal:

By using any of these three options, you can obtain a +50 dB increase in the power level of a generated signal. However, it is not recommended to push the power levels this high on too many satellites. At some point, it will end up saturating the I/Q data samples. When this happens, Skydel will warn you that I/Q has been saturated.

If you need to increase the global power offset by more than 30 dB, you can remove some of the attenuation instead.

You can enable or disable the “Signal Strength Model” by checking or unchecking the box.

The Signal Strength Model adjusts the transmit power of each satellite by modeling the following effects:

The Synchronize Simulators settings are located in the Settings - Global - Synchronize Simulators menu.

You can use the Synchronize Simulators settings to specify how Skydel instances connect to each other to perform the synchronization. This setting will be used for both multiple Skydel instances running on the same computer as well as synchronization among multiple computers.

Determine which Skydel instance will be the master. Check the Sync Time (Master) check box on that instance of Skydel. Skydel will then begin listening for incoming connections.

Check the Sync Time (Slave) checkbox on each remaining instance of Skydel. These Skydel instances will then connect to the master instance.

At this point, all Skydel instances are connected and will synchronize their radios.

Once you start the simulation on the master instance, each Skydel instance should start running automatically. It does not matter whether each Skydel instance are running on the same computer, or separate ones.

Skydel is capable of pushing a master’s configuration to all of the slaves. To do so, in the master instance of Skydel, go to the Settings - Global - Synchronize Simulators section.

Pushing the configuration can be done either manually by clicking the Broadcast now button. It can also be automatically broadcast at every simulation start by checking the Broadcast configuration on simulation start checkbox.

Applying exclusions is used to control which parts of the Slaves' configuration will be retained. For example, if you check the Vehicle Motion filter, after a configuration broadcast all the Slaves will use the master’s configuration, except for the vehicle motion. This can be useful to simulate the same scenario with different vehicles.

When the Skydel Master broadcast a configuration, radios are associated by their names. For example, "Radio 1" on the Master instance will be matched to "Radio 1" on the Slave(s). When excluding Radios only, only the physical radio configuration (IP address and Clock) will be retained by the Slave(s). The output signals configuration will be pushed. To exclude both, check the Outputs and Radios option.

It is possible to use the GPS Time from a GPS Timing receiver as the start time of the simulation for all instances of Skydel. For example, this can be very handy when simulating RTK scenarios and you don’t want to reset the GNSS receivers at each simulation.

In this case, only the master instance of Skydel needs to be connected to the GPS Timing Receiver.

For the Master instance: in the "Start Time" settings screen, "GPS Time" must be set to "GPS Timing Receiver Time".

For the Slave instance(s): in the "Start Time" settings screen, "GPS Time" must be set to "Custom Time".

When starting the simulation, the master instance will read the "GPS Timing Receiver" time. This will become the GPS simulation’s start time. The master instance will push this value to each of the slave instances.

In order to have synchronized simulators, each radio must be connected with a common 10 MHz and PPS signal as indicated in the Hardware Setup section.

The Satellite Data Update settings are located in the Settings - Global - SV Data Update menu.

Use the settings in this page to control how Skydel updates satellite data during a simulation.

There are two different modes to choose from:

The selection of the mode is done either directly in the interface or using the API command SetSVDataUpdateMode.

The General settings are located in the Settings - GPS - General menu.

The General settings control the “Issue of Data” (IODC and IODE) of the downlink data. Disabling the checkbox "Override RINEX IODE" makes Skydel use the IODE values from the RINEX instead of the value indicated in the "Issue of Data" button.

The “almanac first upload” offset controls when the first almanac update will occur after the simulation starts. The update can occur in the middle of a message as illustrated in the image below.

By default, the first update will occur 12 hours (43200 seconds) after the start of the simulation. This setting can be changed independently of the update interval. For example, you could set the first update to occur at 300 seconds and then every 43200 seconds after that first update.

In the general settings, you can also import a RINEX, YUMA or SEM file to set the orbits of the GPS Satellites.

To import a RINEX file, click the Import button in the General settings screen. Skydel will prompt you to confirm your intent. You will then be asked to provide a RINEX-compatible file. Sample files are located in “Skydel-SDX/Templates”. Importing a RINEX file will override each of the current Orbits, Perturbations, Clock & Group Delay and Health settings. Note that ionospheric parameters of the RINEX files are not imported.

The “signal propagation delay” should always be checked. When unchecked, the propagation delay and the Doppler shift are removed from the simulation. This feature is useful for calibrating the simulator’s PPS with an oscilloscope before measuring or calibrating a timing receiver. If you want to use Skydel to calibrate or verify the calibration of a timing receiver, contact Safran Trusted 4D Canada’s technical support.

The data sets settings are located in the Settings - GPS - Data Sets menu. This menu manages the different data sets imported in the configuration.

A data set describes the state of the satellites in the constellation. This includes orbital, health, perturbation, and signal control information for all satellites. Different data sets can be used to simulate specific parameters for satellite orbits as well as the information transmitted in ephemeris and almanac parts of the navigation messages. Data sets are imported using RINEX, SEM or YUMA files.

In the Data Sets settings page, each column represents an imported data set. Each row represents a type of data set to which a data set is assigned. The data set types are:

To add a data set to the configuration, click the "Add Data Set…​" button and select the RINEX, SEM or YUMA parameter file to import. The name of the data set will by default be the name of the imported file. All data set names must be unique.

By default, there is only the default data set and it is not displayed in the page as shown in the image above.

The active data set is the working set of the user. It is the data set that is displayed in the other settings pages like Orbits, Perturbations, Clock & Group Delay and Health. The name of the current active data set is displayed at the top of these pages. Modifying fields in one of these pages will modify the active data set. Switching to another active data set will not revert the changes made on the previous active data set.

By default, the active data set is the default data set.

Each row (Ephemeris, Almanac, Orbit) represents the assignations of data sets to these data set types. Only one data set can be assigned to a specific data set type - each row is mutually exclusive.

By default, all data set types are assigned to the default data set.

By clicking on any of the data set’s name, a menu containing the following actions will appear:

The Message Modification settings are located in the Settings - GPS - Message Modification menu.

Up to four sub-menus can be present:

Message Modification settings let you override the downlink data being transmitted by the GPS satellites.

All Message Modifications globally work the same way. The modifications will be applied only if all their specified conditions are met. Some conditions are common to all navigation message types like start time, stop time, sender SV ID and signals. And some are specials to the navigation message type (subframe, page, message type, word, etc…​).

Messages modifications can be added either in idle mode or during a simulation. During a simulation, the message modification events are applied at the start of the next navigation message respecting the event’s conditions.

The Message Sequence settings appear in the menu only if GPS L2C, L5, M-Code and/or L1C features are enabled on your license.

If more than one of these features are enabled, the Message Sequence settings are located in the Settings - GPS - Message Sequence menu.

If only one of these features is enabled, the Message Sequence menu is replaced with the appropriate settings screen (L2C Message Sequence, L5 Message Sequence, MNAV Message Sequence or CNAV-2 Message Sequence).

Use the Message Sequence settings to modify the transmission order of L2C or L5 messages. Once all messages have been transmitted, the satellites will loop back to the beginning of the sequence.

Use the Message Sequence settings to modify the different pages of L1C messages. The messages will loop on the enabled pages.

The Orbits settings are located in the Settings - GPS - Orbits menu.

You can use the Orbits settings to control the locations of the satellites within the constellation. To make a change to a satellite’s orbit, you must first select the appropriate SV ID.

Click the value of an orbital parameter to modify it. When modifying a parameter, you have the option to replicate this value for all remaining satellites.

If you want to remove Doppler shift on the satellite, you can uncheck the “Update sat. position during simulation” checkbox. This will violate the laws of physics and suspend the satellite in a fixed location relative to the Earth. This can be useful for certain types of testing.

The Orbits settings will display the parameters of the active data set (see Data Sets).

The Perturbations settings are located in the Settings - GPS - Perturbations menu.

The Perturbations settings can be used to modify the harmonic corrections of the satellite’s orbit. To make a change to a satellite’s perturbations, you must first select the appropriate SV ID.

You can easily clear the perturbations for a satellite by clicking the Clear Sat button. You can clear the perturbations for all satellites by clicking the Clear All Sat button.

The Perturbations settings will display the parameters of the active data set (see Data Sets).

The Clock & Group Delay settings are located in the Settings - GPS - Signal Control menu.

You can use the Clock & Group Delay settings to modify the satellite clock errors and inter-signal biases. To make a change to a satellite’s clock and group delay, you must first select the appropriate SV ID.

The Clock & Group Delay settings will display the parameters of the active data set (see Data Sets).

The Health settings are located in the Settings - GPS - Health menu.

Use the Health settings to modify the health bits being broadcast by the satellites. These values will be broadcast in the ephemeris, the almanac, and in the page 25 health message. To make a change to a satellite’s health you first have to select the appropriate SV ID.

Use the Apply-to-all button to apply the health bits to all satellites.

L1/L2 Signal Health and Data Health are applied to the NAV message for both L1 C/A and P-Code signals. L1, L2 and L5 Health Bits are applied to the CNAV message for L2C signals. L1C Health Bit is applied to the CNAV-2 message for L1C signals. If the health value indicates that the signal is not being transmitted and you want the satellite to stop transmitting the signal, you must manually turn off the RF in the Signal Enable/Disable screen.

The Health settings will display the parameters of the active data set (see Data Sets).

The Multipath settings are located in the Settings - GPS - Multipath menu.

To simulate multipath propagation, each path (or echo) must be entered manually. To replicate a NLOS (Non-Line-of-Sight) scenario, it’s also possible to disable the direct line of sight so that only echoes will reach the receiver antenna. To do so, uncheck the Line of Sight (LoS) Enabled box.

For each echo, you can control 4 fundamental attributes: pseudorange offset, power loss, Doppler shift and carrier phase offset.

For each satellite, you can add up to 3 echoes per signal. Adding an echo for GPS L1C/A will not automatically add an echo for the other signals on the same satellite: L1P, L2P, L2C, etc. Each of them has to be added individually.

To disable echoes, click on Disable Echoes button. A window will open, letting you specify the echoes that you want to disable.

Check the Reset echo attributes box if you also want to reset the echo attributes (pseudorange offset, power loss, etc.). Otherwise, the echo will be disabled. However, the attributes will be preserved so that you can enable them in the future with the same values.

Click the Summary button to view all multipath echoes in a table format.

The Signals settings are located in the Settings - GPS - Signal Enable/Disable menu.

Use the Signals settings to modify which signals are being broadcast by the satellites. The RF column controls if any signal will be transmitted at all from that satellite. The other columns can turn individual signal types on and off.

If you uncheck the Present flag, it will not transmit any RF and all the other satellites will indicate this satellite as unhealthy.

Assigned data sets (see Data Sets) will have an impact on the presence, RF and signals flags. A satellite that is not present in the "Almanac" data set will not be present in the simulation and its row will be disabled.

Furthermore, a satellite that is not present in either of the "Ephemeris" or "Orbit" data sets cannot be simulated and will therefore have its RF and signals flags disabled.

The PRN selection settings are located in the Settings - GPS - Transmitted PRN menu.

Use these settings to modify which PRN should be transmitted by each satellite for each signal.

You simply have to select a SV ID and click the "Edit PRNs…​" button.

You can choose the PRN you want to use for each signal.

In most settings page where information is shown for one satellite at the time, such as the orbital settings page, the PRN value is displayed along with the SV ID. If the satellite uses more than one PRN, Skydel will display a more detailed list.

The Errors settings are located in the Settings - GPS - Errors menu.

The Errors menu contains three submenus:

The Antenna settings are located in the Settings - GPS - Antenna menu.

You can use the Antenna settings to change how the satellite’s antenna is modeled. Changing the antenna model will affect the power and phase offset of the transmitted signals. Phase offsets are expressed in angles.

The General settings are located in the Settings - GLONASS - General menu.

To import a RINEX file, click the Select button in the General settings screen.

Skydel will ask you to provide a RINEX-compatible file. Sample files are located in “Skydel-SDX/Templates”. Importing a RINEX file will override each of the current Orbits, Perturbations, and Clock settings.

When importing the RINEX file, Skydel will compare the leap second from the RINEX and the leap second defined in the Start Time settings. If the values mismatch, Skydel will display this warning:

GLONASS is particularly sensitive to leap second errors because its reference time is attached to the UTC time.

The GLONASS RINEX file does not define orbits using Keplerian elements. Instead it provides absolute positions which must be interpolated. These positions are only valid for the given RINEX observation time and can’t be easily extrapolated in the past or future. Therefore, when you import a RINEX file, you must set the simulation Start Time to the same day as the imported RINEX file.

Unlike other constellations, GLONASS system time is relative to UTC time. Whenever a leap second is added (or subtracted), it directly affects the GLONASS system time. When a second is added, it always occurs at the end of a quarter at midnight UTC. The following image illustrates how Skydel realigns the next subframe with the new UTC time after the leap second event.

When a second is subtracted, the behaviour is similar, but the first transmitted string after the event is String #2.

Leap seconds future event is configured in the Settings - Start Time menu.

The F/NAV Source Diversity settings are located in the Settings - GALILEO - F/NAV Source Diversity menu.

You can use the F/NAV Source Diversity settings to control which almanacs will be broadcast first for each satellite. In the F/NAV navigation message plan, each Galileo satellite can start broadcasting the almanac with an offset for the PRN value. This offset is known as the k parameter in the Galileo ICD. It is set for each of the active satellites, and enables improvements to almanac transport time by exploiting source diversity.

Keplerian parameters found in RINEX files cannot be extrapolated for BEIDOU geostationary satellites as they are for other constellations and for other types of satellites. For that reason, BEIDOU geostationary satellites require multiple RINEX blocks to be simulated properly. The simulator will use these blocks and interpolate the position of the satellite correctly.

The default template BEIDOU ephemeris RINEX file found in “Skydel-SDX/Templates” contains two weeks worth of RINEX blocks for GEO satellites. If a longer simulation is required, the users should import their own RINEX files. Note that when the end of the GEO blocks is reached, the simulation will continue, but the position of GEO satellites will become incorrect (a warning will be shown at that point). Also note that an old configuration will not have Beidou GEO satellites: the importation of a new RINEX file will be required in order to activate them.

To ensure the quality of the simulation of BEIDOU GEO satellites, the edition of orbit parameters has been disabled for this type of satellite. This means pages "Orbits" and "Perturbations" have been disabled for GEO satellites.

The L1S augmentations settings are located in the Settings - QZSS - L1S augmentations menu.

The L1S augmentations page allows to set augmentations which will be used to fill the QZSS L1S navigation message.

The Add button will add the L1S augmentation to the list. The dialog box will stay open so that you may easily add a similar L1S augmentation. When you are done creating augmentations, close the dialog box.

To edit an augmentation, simply select the desired line in the list and click on the Edit button.

The General settings are located in the Settings - SBAS - General menu.

The current Skydel version supports fast corrections for GPS and SBAS and long term corrections for GPS only.

The Message Sequence settings are located in the Settings - SBAS - Message Sequence menu.

Each message type has the same 1-second duration. The message sequence changes according to the maximum update interval for each message type.

By default, fast corrections (message types 2, 3, 4 and 5) have a maximum update interval of 6 seconds and the other message types have longer intervals such as 120 seconds or 300 seconds.

When all maximum update interval conditions can not be respected, the default configuration will be used for the generation of the message sequence.

The generated message sequence starts at 12:00:00, is unique and of length defined by the the lowest common denominator of all different maximum update intervals. An offset is applied to the sequence starting index depending on the simulation start time.

Concerning fast corrections, message type 2 will transmit data sets for the first 13 satellites designated in the PRN mask. Message type 3 contains data sets for the following 13 satellites, and so on. If, for example, there are data sets for only 37 satellites to transmit, message types 2, 3 and 4 will be transmitted, but not message type 5 (it’s not needed since data sets are all empty). In this case, the fast corrections message sequence will be 2, 3, 4, 2, 3, 4, 2, 3, 4. This means we can insert 3 other message types before rolling back to fast correction messages.

The delays given in the message 26 consist of the addition of the delays from the current ionospheric model in Settings - Global - Atmosphere - Nominal and the offsets provided in Settings - Global - Atmosphere - Errors (if enabled).

The Health settings are located in the Settings - SBAS - Health menu.

When a check box is checked, it means On. For example, if the Ranging is checked, the Ranging is On which means the corresponding bit in the navigation message is set to zero.

The service provider indicates if the SBAS satellite is assigned to WAAS (0), EGNOS (1), MSAS (2), etc. In the Signal Level settings, you can control the power offset for each service provider.

The default service provider might not be adequate if you import a RINEX file.

Use the Apply-to-all button to apply a health parameter to all the satellites.

The Ionospheric Masks settings are located in the Settings - SBAS - Ionospheric masks menu.

This panel describes the content of the SBAS message 18 as an ionospheric grid, where each IGP tells if the position is monitored by the SBAS satellite of the selected service provider. You can switch service providers with the combo box located below the map.

Information about the highlighted IGP (latitude, longitude, flag(s)) is shown below the map. As some IGP from different bands are located at the same coordinates, it is sometimes normal to have different flags for the same position on the map. The points are either blue (band 0 to 8) or orange (bands 9 and 10). Points present on two bands at once are illustrated with two colored triangles.

You can edit the map by selecting first a service provider and then clicking the Edit button. This will open a dialog containing an editable map.

Each IGP can be selected and set to true or false by lighting them up or off with a click of the mouse, or by dragging an area with the mouse to change the value of many points at once.

Rolling over the map with the mouse will highlight the different bands and display their number. You can select or deselect bands using the controls at the top in order to help with setting the different points' values, for example by including or excluding bands. When you deselect a band, its IGPs can’t be edited, thus preventing unwanted changes.

You can import or export the grid for the current service provider in CSV format, where each line describes a grid band (0 to 11), an IGP index (1 to 201, depending on the band) and the flag applied (0 or 1). A button is provided to revert to the default mask. These are the only actions that change all the bands, whether selected or not.

Click OK to save your changes or click Cancel to revert them.

The Ionospheric GIVEI settings are located in the Settings - SBAS - Ionospheric GIVEI menu.

They describe the GIVE Indicators (GIVEI) used in the SBAS message 26 on an ionospheric grid, where each IGP describes a GIVEI value between 0 and 15. Each SBAS service provider has a different GIVEI map. You can switch service providers with the combo box located below the map.

Information about the highlighted IGP (latitude, longitude, GIVEI value) is shown below the map.

The Edit button opens a dialog with an editable version of the map of the selected service provider.

The controls provided for the edition of the GIVEI values operate in similar fashion as the ones for Atmospheric Errors.

You can import or export the grid in a CSV file following this format: [band index],[IGP index],[GIVEI value]

Click OK to save your changes or click Cancel to revert them.

The Body settings are located in the Settings - Vehicle - Body menu.

The Body settings can be used to control the trajectory of the simulated vehicle. To define the vehicle trajectory, select the desired trajectory type and click the Edit button.

The map and location search features of the trajectory editors will not work if you are not connected to the internet. Check the Proxy section for more information.

The Antenna settings are located in the Settings - Vehicle - Antenna menu.

You can use the Antenna settings to change how the receiver antenna is modeled. Changing the antenna model will affect the power and phase offset of received signals. Phase offsets are expressed in angles.

You can define one or more antenna models in Models and use the Sequencer to specify antenna model changes to occur during the simulation. By default, Skydel uses the default antenna defined in the Models menu.

The Elevation Mask settings are located in the Settings - Vehicle - Elevation Mask menu.

You can use the Elevation Mask settings to control which satellites will generate signals during the simulation. By default, “Mask Below Elevation Angle” is enabled and set to 10 degrees. This will disable satellites that have an elevation angle below 10 degrees. You can disable this mask completely (uncheck the box) or modify the angle itself by clicking on the value.

Disabling the “Mask Below Elevation Angle” is not the same as setting it to 0°. When “Mask Below Elevation Angle” is disabled, Skydel will generate signals with any elevation angle, including those below 0°. However, Skydel will still calculate the location of the Earth’s horizon to determine if a satellite’s signals would reach the receiver. In other words, Skydel will never generate a signal that has to pass through the Earth to be received.

You can enable the “Mask Above Elevation Angle” option. This will disable any satellite that is higher than the specified angle. This setting is not used very often and should be avoided unless you are absolutely sure that you know what you are doing.

To illustrate how a dynamic jammer works with Skydel, we’ll use a simple scenario where we will create an interference to jam GPS L1 C/A.

The first step is to assign GPS L1 C/A to RF A and then click Edit on RF B.

In the Signal Selection dialog box, choose the Interference output type. By default, the interference group is Group 1 and the central frequency is set to 1575.42 MHz. These values are good for this example; however, we will change the gain to 60 dB and the minimum sampling rate to 12.5 MSps.

Click Ok to close the Signal Selection dialog box. The output configuration should look like this:

As you can see, the gain for RF A is 80 dB and the gain for RF B is 60 dB. Before combining the outputs, RF A must be attenuated by 20 dB. While the difference in gain makes the hardware setup a little more complex, it has the great advantage of offering a much greater jammer-to-signal ratio for testing receivers under extreme conditions.

Now that we have Interference Group 1 mapped to RF B, we must add a transmitter. First, click on the interference submenu.

You can add Dynamic or Simplified transmitters in the Interference sub-menu.

Click on "Add Dynamic…​" and the “Add Transmitter” dialog box will appear.

Here you can change the transmitter name, reference power, etc. Each of these attributes can be changed later, so simply accept the default values for now. You can see the same options (Group 1 to 16) in the Group dropdown list as found in the Signal Selection dialog box. The difference is that it will tell you if the group is assigned to a physical output. In this case, it informs you that Group 1 is assigned to Radio 1 RF B. Click OK to add the dynamic transmitter.

Each time you add a transmitter, a new sub-menu with the transmitter’s name appears in the Interference sub-menu. In this case, the transmitter’s name is "Transmitter 1".

To configure the transmitter, click on the "Transmitter 1" sub-menu. The dynamic transmitter sub-menu contains four screens (General, Signal, Trajectory and Antenna) and a Remove button. In the General screen, you will see a message highlighted in yellow about an undefined trajectory.

Click on the trajectory button to bring the trajectory page screen of the transmitter. Set the circular trajectory with the following attributes:

To create an interesting scenario, we will create a receiver trajectory that will cross the transmitter at close range. Set a receiver circular trajectory with the following attributes:

Now the transmitter has a trajectory, but it is not transmitting anything. Lets add a Chirp signal.

Change the chirp bandwidth to 10 MHz and the sweep time to 10us. It is possible to add a signal with a different group than the transmitter, this allows a transmitter to jam different groups. To do so, you would have to uncheck "Use Default Group" and then change the signal group. For this example, let "Use Default Group" checked. To add the chirp signal, click Add. You will see the signal added to the list in the main windows. We will not add another chirp signal in this example, so you may click on the Close button.

The power for the chirp is measured in dB. This is relative to the transmitter reference power defined in the General page. Let’s go back in the General screen and reduce the power to -15 dBm. Also, uncheck the Enabled flag. We prefer not to have the jammer enabled when we start the simulation. This will allow some time for the receiver to track and lock on to the GPS signal. We will enable the jammer only after we have a lock on the receiver.

Let’s start the simulator now and connect a receiver in order to view the simulator, the receiver, and the transmitter in the map tab. Depending on the performance of your receiver, it may take more or less time to get the receiver’s solution. However, once you have it, the view in the map should look something like this:

If you expand the transmitter information panel at the right of the map, you will see that the transmitter is not enabled. This means that the transmitter is not broadcasting RF; however, as you can see in the map, the transmitter is moving on a circular path.

In the information panel, you will also find 2 values for the Reference Power: Tx and Rx. The Reference Power Tx is the power level that you set in the General screen of the transmitter. The Reference Power Rx is the perceived reference power at the receiver including the transmitter and receiver antenna patterns and the propagation loss. If you click on the "plus" button at the right of Reference Power (Rx), you will see more details.

The transmitter can be Visible or not by the receiver. If both receiver and transmitter altitude are inferiors to 100km, Skydel uses radio horizon to determine the transmitter visibility. Else Skydel looks if the transmitter is earth-masked.

In the spectrum subtab, you will see that the GPS signal is being transmitted on RF A; however, the spectrum for RF B should remain empty until you enable the transmitter.

Now, go to the transmitter’s General screen and enable the transmitter. You should now see the chirp appearing in the RF B spectrum.

The simulator and the transmitter are both on a circular path and they will soon cross each others path within 1m range. When that occurs, you will see the spectrum power increase rapidly.

At this point, the receiver should experience some heavy jamming and you should have difficulty tracking the signal, as you can see in the Deviation subtab.

As the simulation proceeds and the transmitter fades away, the deviation quickly improves.

This simple dynamic transmitter tutorial was for a -15 dBm jammer. This is a very weak jammer. We leave it to the user to experiment with stronger jammers to see how the jamming radius increases the effect on the receiver being tested.

The "IQ-File" jammer signal type enables the users to inject their own specific jammer waveform.

The waveform is stored in a binary file, containing a baseband IQ-Complex waveform. The format of the file is the same as the one described in section IQ Data Files.

For Skydel to correctly use the binary IQ-Samples file (ex: my-waveform.iq), a metadata file respecting the GNSS SDR Metadata Standard (http://sdr.ion.org/) must be found in the same folder (ex: my-waveform.xml). When using this standard, only metadata files with one Lane, System, Block, Chunk, Lump, Stream, Band and File are supported by Skydel.

Furthermore, the metadata must have the following values:

Skydel also supports the use of a text file as a metadata file (ex: my-waveform.iq.desc). This metadata file simply contains "Key-Value" pairs to describe the waveform. Here are the supported keys:

The text file must contain 1 Key/value pair per line. For example:

Power Level

The reference power level of the IQ-File signal is -130dBm, when the IQs of the file have a RMS value of 463.

For example, lets say that the IQ-File contains a CW waveform like this: I=463; Q=0; I=463; Q=0; I=463; Q=0; …​

When this file is used as a "IQ-File interference", and the transmitter is set to -130dBm, the output power will be -130dBm. However, it is important to understand that by default, RF outputs of interferences have a gain +40dB. So the actual RF signal power at the radio’s connector will be -90dBm.

It is possible for a single transmitter to jam several bands. By default, all the signals added to a transmitter will jam the signal group defined in the transmitter general menu. To enable multi-band jamming, you have to uncheck "Use Default Group" in a signal "Add" or "Edit" dialog, then you can select the group you want the signal to jam.

In the following example, the transmitter is set to jam the group 1, so all its signals will, by default, jam the group 1, but this Chirp signal is set to jam the group 2.

To start a spoofing instance, search for the shortcut Skydel Spoofer on your operating system or start the application in a command line shell with the --spoofing argument.

This instance is almost the same as a regular instance, with the following exceptions:

When the Advanced Spoofing feature is activated, you will see a new tab called Spoofers.

To add a spoofing transmitter, go into this tab and click on Add Spoofer…​ A spoofing transmitter is very close to a dynamic advanced jammer in its composition. We find the same General, Trajectory and Antenna sections.

In the Signal section, we have a summary of the spoofer’s status. Here we can see and edit the spoofing instance address. The default address can be changed in Skydel’s Preferences. Once connected, a table will show the spoofing signals detail.

In the Spoofers menu, next to the spoofer’s name, a LED is showing its status:

In the Settings menu, the LED next to the Spoofer submenu shows a global status:

Here are some additional resources that can help you when working with Jammers and Spoofers:

A description of the interfaces, or roles, that are implemented with plug-ins.

SkydelCoreInterface

The implementation of this role is mandatory, and provides access to multiple features:

Use simple_plugin as a basic plug-in example.

SkydelRadioTimeObserverInterface

When implemented, this role enables the reception of information regarding the radio time at a rate of 1000 Hz. It’s also possible for the plug-in to update its user interface during the simulation.

SkydelPositionObserverInterface

When implemented, this role enables the reception of real-time Skydel vehicle position data at a rate of 1000 Hz. It’s also possible for the plug-in to update its user interface during the simulation. Use position_observer_plugin as an example.

SkydelRawDataInterface

When implemented, this role enables the reception of real-time Skydel raw data at a rate of 1 Hz. It’s also possible for the plug-in to update its user interface during the simulation.

SkydelHilObserverInterface

When implemented, this role enables the reception of position data received through the HIL interface by Skydel in real-time. The plug-in can also update its user interface during the simulation. Use hil_observer_plugin as an example.

SkydelLicensingInterface

When implemented, this role allows a plug-in to decide whether it can be instantiated or not. To identify itself, Skydel will send a serial number associated with the active license via an encrypted communication channel.

SkydelInstrumentationInterface

When implemented, this role provides useful instrumenting information about Skydel. The plugin will receive a graph illustrating the relationship between each module of Skydel’s engine. Also, during a simulation it will receive statistics to help identify which module is throttling the simulation. Use skydel_default_instrumentation_plugin as an example.

SkydelRapiInterface

When implemented, this role gives direct access to Skydel’s remote API. This allows the plug-in to send commands to Skydel without establishing a server/client connection with the traditional remote API in python/C++/C#. Use rapi_plugin as an example.

When you install Skydel on a Linux system, the skydelsdx library is automatically installed. Python scripts can be run from anywhere.

For Windows users, the library can be found in the Skydel-SDX/API/Python/skydelsdx folder. You may run setup.py to make the library accessible from anywhere. If you choose not to do so, you should save your scripts in the parent folder and execute them from there. The Python interpreter will find the library in the skydelsdx sub-folder.

The Skydel Python API is open source and can be modified, copied, or reused any way that you want. However, Safran recommends using the API “as is” (as much as possible) so that migration to future releases of Skydel will be easier. Skydel is constantly evolving; Safran sometimes adds new functions or capabilities that require modifying existing features and the corresponding API. To mitigate impacts to your scripts, each Skydel version comes with release notes that include a list of modified, removed, and added API methods.

You will find several Python script examples in the Skydel-SDX/API/Python folder.

The “Export to Python” feature is, by far, the easiest way to learn how to automate Skydel.

When you click the Export to Python button, Skydel will generate a Python script that will replicate the content of the Automate list.

The following is an example of a Python script generated by Skydel:

In the above example, sim is an instance of the RemoteSimulator class. This class offers a high-level API that converts simple function calls into JSON objects. The class handles the transmission of those JSON objects to Skydel and interprets the results for you.

Before you can transmit requests to Skydel, you must first connect. The connect() method accepts 2 parameters: Skydel IP address and instance id. If no values are provided to the method, the defaults are “localhost” and “0”. Skydel is listening on port 4820 + id. If Skydel was started with instance id 2, it would be listening on port 4822. When connected, Skydel will display a robot emoji at the left end of the dashboard.

The connection is followed by a list of calls that you can easily recognize in the Automate list. The first call is to create a new configuration in Skydel.

The call method is generic. It can send any command: New, SetModulationTarget, etc. The parameter is a command object. This line can be replaced by 2 lines. First you create the command, and then you execute the call.

It is sometimes useful to proceed this way so that you can interrogate the command object after the call returns. Some commands will be updated as a result of the call method. For example, if you add a message modification without providing a unique identifier, the result will contain a unique identifier assigned by Skydel that you can re-use to update the message modification in the future.

The call method is blocking. This means that it will stop the script execution until Skydel returns a result (pass or fail). This blocking mechanism is referred to as a synchronous call. There is another method called post which is not blocking and this calling mechanism is referred as asynchronous. When using the asynchronous strategy, it is important to synchronize from time to time with the wait method.

Regardless of how the command was sent to Skydel (call or post), it will appear in the Automate tab.

If you become a heavy API user, you may notice that it takes some time to process hundreds or thousands of commands to change the settings. The reason is that Skydel updates the user interface after every command and redraws the sky view and power bars above the sliders. To avoid this, you can instruct Skydel to hold off GUI updates while it updates the settings.

Skydel will display a message in the title bar to signal when the GUI is locked.

You are encouraged to look into the skydelsdx library to better understand how it works. Also, the examples provided with Skydel will demonstrate how you can define custom vehicle trajectories, send real-time trajectories (hardware-in-the-loop), control interferences, etc.

The Skydel C++ API is located in Skydel-SDX/API/Cpp/sdx_api.

The C++ examples are located in the sdx_examples folder. To build the examples, use the CMakeLists.txt file in the parent folder.

The principles of the C++ library are the same as with the Python library. The syntax differences are minor and looking at the various examples should get you started quickly.

The Skydel C# API is located in Skydel-SDX/API/CSharp/SdxApi.

The C# examples are located in the SdxExamples folder. To build the examples, use the SdxExamples.sln file in the parent folder.

The principles of the C# library are the same as with the Python library. The syntax differences are minor and looking at the examples should get you started quickly.

Trajectories can be created through the API. You can create tracks as well as routes. They differ in that tracks are defined with time and position pairs, while routes are defined with speed and position pairs.

For detailed explanations about the geographic coordinate system used in Skydel, please consult the Six Degrees of Freedom section.

It is possible to retrieve information about the vehicle using the remote API. The available information are:

Please refer to the example_vehicle_info.py python script, the runExampleVehicleInfo C++ function or the RunExampleVehicleInfo C# function for a complete example.

Observations:

Observations:

The following image focuses on the last second to show more details.

Observations:

Observations:

There are multiple possible reasons that can explain this pattern:

Although everything is green or blue (no yellow, no red), this jitter might cause problems, especially if the timestamps are inaccurate. It is recommended to analyze the resulting receiver trajectory log for discontinuities or anomalies. Computing the first or second derivatives might also reveal insufficient precision in the HIL trajectory samples provided to Skydel.

The timestamp offset relative to the radio time of each HIL trajectory sample is also displayed in the performance subtab as shown in the image below.

HIL is a time-sensitive application and for that reason Skydel uses the User Datagram Protocol (UDP) to transmit the trajectory samples. UDP does not recover lost packets. A lost packet can be visible in the HIL graph when the T_join value is not too large.

If you zoom in, you can see a packet seems to be missing because the interval between the samples is stable except for 1 gap which resulted in non-deterministic extrapolation (yellow) of an older trajectory sample.

Skydel will extrapolate a sample until the moment when the constellation worker reaches the time defined by the sample reference time plus the T_join time. At that moment, the worker will use the next queued sample; if there are no queued samples, Skydel has no other choice than to extrapolate the sample beyond the limit defined by T_join. This situation is illustrated in yellow in the HIL graph. If this situation lasts long enough and the next sample arrives when its reference time plus T_join is already in the past, Skydel will not try to smooth the transition and it will snap the trajectory on the newly received sample. This condition is shown in red.

When the constellation worker is falling behind, you can see the effect in the performance graph as well as in the HIL graph as shown in the image below.

Using the previous example:

The HIL simulator sends the samples with a timestamp 16 ms in the future. You can observe the following optimal pattern:

Observations:

When the time offset is too large, the HIL simulator extrapolates too far in the future. Using the same conditions found in the optimal example above, but with a time offset of 25 ms instead of 16 ms, you can observe the following pattern:

Observations:

When the time offset is too small, the HIL simulator does not extrapolate far enough in the future. Using the same conditions found in the optimal example above, but with a time offset of only 13 ms instead of 16 ms, you can observe the following pattern:

Observations:

Observations:

There are multiple possible reasons that can explain this pattern. Refer to this section for explanations.

Observation:

For additional information on lost samples, read this section here.

When ordering SDR from National Instruments, you will receive a device with integrated daughterboards. You only need to order a 10 GbE cable, which is recommended and can be ordered from the National Instruments’ website.

IQ streaming option: "DTC-371-IQ" option is required.

If your planned setup includes more than one SDR (MIMO operation), you will need an external reference clock with multiple ports, such as this model.

Safran provides a zip package to prepare a N310 device to be used with Skydel. The instructions are written in a ReadMe file, contained in the install zip package. The package can be found in the users "drivers and firmwares" page under "N310 Setup" using the following link: users.skydelsolutions.com/drivers-and-firmwares↗.

If you accidentally burn the wrong FPGA image to your device, or if the programming of the FPGA image was interrupted, the device will probably be “bricked”. At this point, it will probably be impossible to reprogram the FPGA image via the 1 GbE or 10 GbE connection.

Don’t panic! You can unbrick your device by reprogramming the FPGA image with the JTAG port. Here’s a simple procedure to unbrick your device under Windows.