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Interfacing with the Simulator

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  1. Interfacing with the Simulator

  2. Agenda • Simulator Overview • Connecting a Receiver • RF Output • Mon/Cal Output • Common Issues with Receiver Testing • Simulator Configurations • Hardware Configuration Files • License Keys • Additional Interface Connections • Trigger Inputs, Timer Outputs, External References, etc.

  3. Agenda • Simulator Overview • Connecting a Receiver • RF Output • Mon/Cal Output • Common Issues with Receiver Testing • Simulator Configurations • Hardware Configuration Files • License Keys • Additional Interface Connections • Trigger Inputs, Timer Outputs, External References, etc.

  4. Simulator Overview • Spirent’s satellite constellation simulators are comprised of a controller and a signal generator • Controllers • The controllers provide the primary interface for the user to control the signal generators • Controllers provide all of the scenario control functions, it simulates the GPS satellite constellation and user/vehicle motion, and sends digital data to signal generator for simulating the correct pseudoranges • Signal Generator • Signal generators convert the digital data from the controllers into representative RF signals received at the user antenna • Supports single or multi-constellations (GPS, GLONASS, Galileo) and frequencies (L1,L2,L5,E5,E6) • Provides various interfaces for connecting receivers, interferers, clock references and various synchronization inputs and outputs Controller Signal Generator

  5. 7000 Specifications

  6. 8000 Specifications • The dynamic specifications of the GSS8000 are shown below Notes 2 Value is RSS, +20dB to -30dB, at 21oC ±5oC. ±1.5dB 3-sigma all conditions. Run-to-run repeatability ±0.1dB 3 Digitisation-induced error for signal acceleration < 450m/s2, jerk < 500m/s3. Excludes contribution of inter-channel bias. Instantaneous accuracy degrades during higher dynamics. 4 Per carrier with 16 channels operating. For GLONASS only, the value is ±5cm RMS. 5 Between RF carrier #1 and any other RF carrier 6 For relative velocities <50,000 m/s 7 In-Band Spurious Bandwidths (relative to centre frequency unless otherwise stated): GPS: L1 ± 20.5MHz , L2 ± 20.5MHz , L5 ± 20.5MHz Galileo: E1 ± 20MHz , E6 ± 20MHz , E5a ± 25.5MHz , E5b ± 25.5MHz GLONASS: (relative to channel frequency 0) L1 ± 20MHz , L2 ± 20MHz 8 Value is typical. Worst case < 0.02 rad RMS 9 After 24 hour warm-up.

  7. Agenda • Simulator Overview • Connecting a Receiver • RF Output • Mon/Cal Output • Common Issues with Receiver Testing • Simulator Configurations • Hardware Configuration Files • License Keys • Additional Interface Connections • Trigger Inputs, Timer Outputs, External References, etc.

  8. Connecting a Receiver • The simulator output is presented as an open-circuit 50 transmission line via an N-type (or SMA) connector • There are 2 ways of transferring the signal from the simulator to the receiver • Direct coaxial connection modeling the connection from an antenna • Radiation in a controlled environment to an antenna connected to the receiver • NOTE: Broadcasting GPS falls within the FCC restricted frequency bands listed in Section 15.205(a) of Title 47 of the Code of Federal Regulations (CFR)

  9. Front Panel RF Output • This is the calibrated port to which all power settings in SimGEN are referenced • When 0dB is set on the power sliders, -130dBm is the nominal reference signal level at this port for L1 C/A code • The dynamic range for the simulators are dependent upon the hardware with typical ranges of +20dB to -40dB (8000 series) and ±20dB (7700/4760 series) • These ranges are relative from the reference signal level (-130dBm for instance)

  10. Additional Considerations • Impedance mismatches between the receiver, couplers and simulator RF output can cause signal power degradation by generating a high Standing Wave Ratio (SWR), which can impact the receiver’s C/No • The Voltage Standing Wave Ratio (VSWR) of the RF outputs is specified as 1.2:1 (in band) • The return loss of this is 20dB • To ensure maximum power transfer, it is important that any load connected to the RF output (cable and receiver input stage) also have an input VSWR or match of 1.2:1 or better (in 50 ohms) • Very often the test environment is not including the receiver’s antenna • Some receivers expect to have a load connected to the antenna input because the receivers expects an LNA • Often, the antenna includes a Low Noise Amplifier (LNA) which could have a gain of 30dB or so • This gain may need to be compensated for in the test environment

  11. Monitor/Calibration Output • The Monitor/Calibration output provides the same channels/signals as output on the front RF port, but at a much higher signal power • This is also called the Mon/Cal (Monitor/Calibration) output • This port is used in calibration of the signal generator because of the increase in signal power • The higher signal power is +50dB greater than the front RF port • The Mon/Cal or Cal port is located on the back of the signal generators • There is one Mon/Cal output for each RF output

  12. Monitor/Calibration Output (cont.) • Use of the Calibration output is not without several precautions • The Calibration output provides an unrealistic C/No with the satellite signal levels 50dB greater than the front RF output (-80dBm for L1 C/A code for example) • This can cause problems for the receiver because of the high signal power level and unrealistic C/No • The Calibration output power is not the calibrated RF output, all calibrations are referenced to the primary front RF Output • Thus, setting -130dBm on the power sliders in SimGEN ≠ -80dBm, but maybe -79.52 dBm for example • For these reasons, making receiver C/No measurements should be avoided as they will be artificially high or not precise enough • For non sensitivity or power level critical tests however, the Calibration output port can be useful because of the higher power level

  13. Monitor/Calibration Output (cont.) • If using the calibration output, it is not uncommon to attenuated the signal to obtain the desired C/No at the receiver • When doing so, it is important to note that some GPS receivers supply DC power via its antenna input through the antenna cable • If this is the case, then the user should make sure a DC block is used to protect the attenuator from overheating and potentially damaging the attenuator and other equipment V Attenuator I

  14. Agenda • Simulator Overview • Connecting a Receiver • RF Output • Mon/Cal Output • Common Issues with Receiver Testing • Simulator Configurations • Hardware Configuration Files • License Keys • Additional Interface Connections • Trigger Inputs, Timer Outputs, External References, etc.

  15. Common Issues with Receiver Testing • Depending upon the test setup, there are some common issues that can arise when testing receivers that can be easily mitigated • If no satellites are seen by the receiver then… • The signal level may be too low • Increase the signal level in SimGEN by the power sliders or global offset • Include a Low Noise Amplifier (LNA) on the front RF output • Use the Calibration Output port and attenuate as required • Remember the previously mentioned precautions when using this port • Check requirements for active antenna use with the receiver • Some receivers require a load on the RF input to indicate that is connected to an active antenna, if so the user can include a DC block or LNA • Spirent’s signal generator RF output ports are internally DC isolated to ±50V

  16. Common Issues with Receiver Testing (cont.) • If the receiver is seeing some satellites, but not navigating then… • Do Nothing • Wait for the receivers’ “search the sky mode” to sequentially ‘learn’ where and when it is (this can take several minutes as the complete C/A code NAV data message takes 12.5 minutes to download the almanac) • Reset the Receiver • Reset the receiver by either sending a reset command or removing the battery and power cycling for forcing the receiver to perform a Cold Start • If the receiver was ‘moved’ to a very different location • If there was a big change in time, such as going from ‘live-sky’ to the simulator which may have a previous date causing the receiver to try to “go back in time” with it’s current information from the ‘live-sky’ • Assist the Receiver • Initialize the receiver with the simulation date, time and position • Initialize the receiver with the almanac used in the simulation

  17. Common Issues with Receiver Testing (cont.) • If your receiver is tracking non-simulated satellites then the receiver may be exhibiting a phenomenon unique to a simulator-receiver set-up called false locking which can sometimes occur if the simulator power is too high • The tell-tale signs of false locking are: • The receiver C/No display varies randomly on all channels • The receiver appears to be trying to track satellites that are not being simulated • The answer is simple – turn down the volume! • Reduce the output power by using the power sliders, global offset or by externally attenuating the signals • A False locking will prevent a receiver from navigating • The level at which false locking occurs will vary between different receivers

  18. Agenda • Simulator Overview • Connecting a Receiver • RF Output • Mon/Cal Output • Common Issues with Receiver Testing • Simulator Configurations • Hardware Configuration Files • License Keys • Additional Interface Connections • Trigger Inputs, Timer Outputs, External References, etc.

  19. Simulator Configurations • Depending upon the system (L1, L1/L2, L1/L2+Interferers, 4-output L1/L2, multi-chassis systems, GPS L1 and Galileo L1/E5, etc.) there are many different possible configurations for some systems • For instance maybe an L1/L2 system can also be configured as a combined L1+L1, or a 4-output dual chassis L1/L2 system can be split into two separate 2-output L1/L2 chassis’s • How does SimGEN know which configuration is being used and which simulators to use during the simulation? • Fortunately Spirent automatically defines the configurations available via a sig_gen.txt file located on the SimGEN PC and allows the user to easily select the desired configuration in SimGEN • In addition to the configuration file, license keys for each purchased signal generator are also required and automatically provided on the SimGEN PC when delivered

  20. sig_gen.txt File • For each simulator it is necessary to have a sig_gen.txt file • The sig_gen.txt file specifies the available hardware configurations to the user given the equipment they have • Every sig_gen.txt file is user specific; none are the same • It defines not only the simulators but also any additional equipment such as interferers and combiner units for example • Each delivered new system is provided with the sig_gen.txt file already configured • For updates or changes, please contact Spirent Technical Support

  21. License Keys • With each system, Spirent provides a unique License Key that identifies each piece of hardware in the system • This allows the SimGEN PC to ‘use’ the designated hardware for testing • The keys are shown and entered in the Hardware Keys Utility shown to the right • Contact Spirent if keys get lost of if assistance is needed in entering keys Simulator Keys

  22. Agenda • Simulator Overview • Connecting a Receiver • RF Output • Mon/Cal Output • Common Issues with Receiver Testing • Simulator Configurations • Hardware Configuration Files • License Keys • Additional Interface Connections • Trigger Inputs, Timer Outputs, External References, etc.

  23. Additional Interconnection Options • In addition to the RF outputs, the signal generators also provide other connections that can be used to support various unique test requirements • Such requirements may be: • Triggering the start of the simulation with a hardware trigger pulse • To synchronize with additional test equipment or remote systems • Add an additional interference or jamming signal on the RF output

  24. External Reference Input • All of the signal generators support the capability to ‘lock’ onto an external reference • This is useful for: • Improving the clock accuracy used in the simulation to mitigate clock drift by using a rubidium reference clock for example • Synchronizing the simulator with other equipment using the same reference clock so actions and events are performed at the same time • Typically the simulator supports synchronizing with external reference frequency rates of 1, 5, 10, and 10.23 MHz and the Power: -5 to +10dBm, Accuracy ±1ppm • The external reference is labeled as Ext Ref In and is located on the back of the signal generator with a BNC, 50 connector as shown below

  25. External Reference Input (cont.) • The external reference for the signal generator is specified in SimGEN under the Hardware Configuration menu shown to the right • The user must select and highlight the desired Current Mappings > RF Output in order to modify the Output (O/P) details • The external frequency used must be defined correctly for the signal generator • For instance if a 10MHz frequency from an external Rubidium clock is used, then 10MHz must be defined here

  26. Sync Input • Some signal generators also provide the ability to sync to an external TTL level 1PPS (pulse-per-second) timing source if available to bring the Signal Generator timers into synchronization with the remote system • The Sync input (Sync In) connects with a BNC, 50 input connectors located on the back of the signal generator as shown below • The sync signal is applied to the Sync In input of the signal generator when external Trigger is Disabled or when Delayed mode is in use • If using the Sync In to keep the signal generator in synchronization with the remote system, Spirent recommends that the user should also supply a 10 MHz external reference signal • This avoids the Simulator drifting in time with respect to the remote system over the duration of a run

  27. Additional Reference Outputs • Besides synchronizing to an external reference, the signal generators can also provide one or more reference signal outputs so that other equipment can synchronize to the signal generator • For the GSS7700 and GSS8000, this is the 10.23MHz Reference output (Int Ref Out) shown below • For the GSS6560, this is the 10MHz and 1PPS Output signals shown below

  28. Timer Outputs • For certain test environments, the user may want to slave off of the signal generator using a 1PPS output, or begin receiving timing signals once the scenario has started • The Timer Outputs are BNC and 50 and are located on the back of the signal generator (shown below) • They provide the user with a wide array of synchronization and timing capabilities for interfacing with external equipment • For instance the Timer Outputs are used by Spirent’s SimINERTIAL product for synchronization and for providing the interrupts used by the inertial simulator, SimINERTIAL • The default settings for each Timer Output are: • Output 1: 1PPS Ungated (continuously output) • Output 2: 1PPS Gated (output when the simulation starts) • Output 3: 1PPS Ungated (continuously output)

  29. Timer Outputs (cont.) • Defining the Timer Outputs are performed under the Hardware Configuration menu shown to the right • The options available for each Timer Output are: • 1PPS – 1Hz Output Pulses • UPDATE – High time 195.5ns (2 P-code chips), Period: 1, 2, or 4ms. All velocity changes occur at the mid-point of this pulse • 10PPS – 10Hz Output Pulses • 100PPS – 100Hz Output Pulses • HIGH / PHIGH – Permanently High • PLOW / DISABLED – Permanently Low • TPOP - A user definable update pulse for use in certain SimINERTIAL implementations • Enable Gated to have the Timer Output at the Start of the simulation

  30. Trigger Input • The signal generators also provide the ability to receiver external hardware trigger pulses for initiating the simulation • This can be used for having the simulation start immediately upon reception of the Trigger or begin on the next 1PPS • Using the Triggers is useful for remote testing when the remote system needs to be in control of exactly when the simulation starts • The Trigger input (Trig In) is a BNC, 50 input connector located on the back of the signal generator as shown below • The three Trigger modes supported by SimGEN and the Signal Generator are: • Disabled (Default) • Immediate • Delayed

  31. Trigger Input (cont.) • Configuring the Trigger modes can be performed remotely using the remote TR command or through SimGEN as shown to the right • If the Immediate trigger mode is selected, then the simulation will start immediately on reception of the external trigger pulse • If configured in the Delayed trigger mode, then upon reception of the external trigger, the simulation will start on the next internal 1PPS event • Note: If using the Trigger Input, there is a delay during the arming sequence of the hardware. This can be mitigated if the signal generator is armed prior to SimGEN receiving the Trigger In. • SimGEN will then start 200-400 nanoseconds after the Trigger In • Reference the SimREMOTE Manual for more information and timing diagrams

  32. Auxiliary Inputs • Typically used with Spirent’s GSS7765 Interference simulator or multi-chassis systems, the Aux RF In (or Jammer In on the GSS7700) is a useful combiner input port • Depending upon the number of RF outputs on the signal generator, there is typically one Aux RF In for each RF output • This is shown below GSS8000 and the GSS6560 L1-only • Signals fed through the Aux RF In port are combined with the satellite RF signals as described below • The Aux RF In has an insertion loss of approx 14.5dB • Supports input signals from 0.5-2 GHz

  33. Additional Outputs • For unique systems like the GSS7790 or multi-chassis signal generators, there are additional interconnections used on the back of the signal generators • For instance the GSS7790 also uses the following signals for Upconverting each RF channel as shown below • 137F (x1) Local Oscillator (LO) feed for Upconverter • 15v (x1) Power for Upconverter • 17F (x24) Individual output Intermediate Frequency (IF) signals

  34. Additional Outputs (cont.) • Another example are multi-chassis systems as shown below which uses the following additional interconnections so that the Auxiliary chassis slaves off of the Master to produce a coherent RF output • IF Aux I/P and IF Aux O/P – used for interchannel alignment between the Auxiliary and Master signal generators • FECL 2 and FECL IN – used to maintain coherent code and carrier between the signal generators (FECL = Frequency Emitter Coupled Logic) • INT REF OUT and REF IN – used to share the Reference frequency from the Master so both are using the same ‘heartbeat’ • 137f 2 and 137f IN – used to share the LO output from the Master