1 / 34

Interfacing with the Simulator

Interfacing with the Simulator. 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

tausiq
Download Presentation

Interfacing with the Simulator

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related