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GUS Type 1 Maintainers Refresher Training PowerPoint Presentation
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GUS Type 1 Maintainers Refresher Training

GUS Type 1 Maintainers Refresher Training

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GUS Type 1 Maintainers Refresher Training

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  1. GUS Type 1 Maintainers Refresher Training GUS Type 1 Operations

  2. Acronyms

  3. GUST Operation Consists of the following: • Two Hardware Configuration Items (HWCI): • SGS Type 1 • RFU • One Computer Software Configuration Item (CSCI) - GUS Processing Type 1 (GPT) GUS Type 1 performs the following: • Terrestrial Communications • Message processing, encoding, modulation (70 Mhz) • RF conversion (C-band), amplification, uplink of GEO signal-in-space (containing WAAS User Message (WUM)) • RF reception (L-band) of GEO signal-in-space

  4. GUS Type 1 Functional Block Diagram

  5. GUST Processor Provides the following: • Interface between the SGST and external items for status, configuration control, and data. • WUMs received via TCN and routed to Safety Computer (SC) • Receives commands from O&Ms and routes them to SC for control of Primary and Backup switching • Provides status, fault detection, fault isolation, and configuration control of the GUST • Provides status exchange between GUST pairs

  6. SGST Safety Computer Provides the following: • Hosts the algorithms that develop the control inputs to the frequency-control loop necessary for the generation of the WAAS Ranging Signal. • Identical to WMS Safety Computer only has more signals to interface. • Comprised of two WAAS Message Processors (WMPs) • Processes identical data and sends to Comparator

  7. SGST Safety Computer Functions are: • Formats WAAS message • Data encoding • CRC checking • Integrity Checking • Generate WAAS Ranging Signal to manipulate the Signal Generator • Code/carrier phase relationship is adjusted under control of SC to compensate for iono delay

  8. GUST Comparator • Receives two types of messages from WMPs, L1 and L5 • The WMP identifies when message is L5 by asserting a logic 1 and de-asserts (logic 0) when message is L1 • Both L1 and L5 supplied, compared, and transferred to Sig Gen within a single epoch • Sent serial, L1 first, then L5

  9. GUST Receiver • Capable of tracking L1, L2, and L5 SIS • Receives and processes signals from GPS and WAAS GEO satellites • Outputs the following: • Satellite ranging measurements • GPS timing information • WAAS GEO message monitoring data • Has three independent receiver sections: • Omni • Test • GEO

  10. GUST WAAS Signal Generator (SG) • Comprised to two independent L1 and L5 SGs which precisely control the frequencies and phases of L1 and L5 codes and carriers • Produces two independent L1 and L5 70 Mhz IF signals • Message, command, and status interfaces between the SC and SG for L1 and L5 are independent • Allows for independent L1 and L5 control and message data streams

  11. RFU HWCI • Responsible for upconverting the modulated IF signal to C-band, adjusting uplink radiated power, and transmitting a narrow beam RF signal to the GEO satellite • Receives L1 and L5 IF signal (70 Mhz) from SG • Converts signals to L1 and L5 C-band low power signals • These signals modulate two KPAs which provide high power output to transmit RF carries to GEO

  12. RFU HWCI - continued • Incorporates loop back test paths to allow for checking proper system operation • TLT loopback of RF signal to be transmitted (down convert to L-band) • Manual switch loopback thru L-band LNAs for local equipment check • Downlink L-band signal loopback thru L-band LNAs

  13. GPT CSCI • GUS Processing CSCI is resident in the GUST Processor and two WMPs • Provides the control and monitoring of the uplink equipment used to transmit data to the GEO and downlink equipment used to monitor the SIS • Provides capability for maintenance personnel to perform maintenance activites and configure the GUST system equipment.

  14. GPT Functional Flow Monitor and Control RFU - RFU equipment control and monitoring • Control GUST Operation and Maintenance • Display GUST Status • Provide maintainer capabilities • Receive GP Input Logs • Receiver initialization • Receiver log processing Control WAAS Signal Generator - Signal generator initialization - Control loop processing Determin GUST Operational Status - RF switching monitoring - GUST fault reporting Monitor Downlink Signal - Signal and message quality monitoring of downlink messages Control Clock Steering - Atomic clock initialization - Clock frequency adjustments Control GUST Mode - IF switch control/monitoring - Validation and coordination of GUST mode transistions • Process Received WAAS Message • WAAS message processing • Output FEC-encoded messages • C&V source selection GUSTP • M&C Input/Output • Status Data • Commands • C&V Input/Output • WAAS Message • GUST Data/Status • Receiver Input/Output • Receiver Logs • Initialization Cmds WAAS Message Processor (WMP) 1& 2 Encoded WAAS Messages Output to Comparator Signal Generator Input/Output Status/Data Atomic Clock Output/Input

  15. GUSTP Software • Developed to Level D • Purpose is to interface with the C&V, GUST Receiver, WMPs, and M&C • Receives WAAS messages (1/sec) from C&Vs • Forwards WUM (from selected source) to WMPs • Sends selected C&V source to C&V • Receives GUST mode switch request from C&V for Primary/Backup determination

  16. WMP Software • Developed to Level B • Major processes: • Receive message process • Determine GUST mode process • Monitor downlink process • Control WAAS Signal Generator process • Control Clock Steering • Provides for monitoring of antenna load switch to insure that the switch position matches the mode of operation

  17. Receive Message Process • Each WMP receives data from all operational C&Vs. Only a the selected source used. • Both GUSTs will attempt to select the same C&V as primary data source • C&V selected automatically or by operator • If selected becomes unavailable a different will be selected • Messages validated for TOA and correct CRC • If no message received for broadcast in next 1 second epoch, will output “Loss Message” to GEO

  18. Receive Message Process - continued • Loss Message - Type 6 - all satellites, UDREI set to 15 (Don’t Use) and CRC set to invalid value. • User correctly interpret as missed message since CRC wrong • If misses CRC will not used due to “Don’t Use” • Either way, protects from HMI • Two consecutive Loss Messages, WMP will switch selected source. If no C&V available, will go to Backup • Valid WUM, creates preamble and CRC, copy saved for later comparison • Time stamped WUM sent to comparator, if passes bit-by-bit compare, sent to SG for modulation

  19. Determine GUST Mode Process • Primary/Backup determination is coordinated between two GUSTs • Switched either due to fault or operator action • Backup does everything Primary does, except: • Radiates into dummy load • Cannot perform RFU/GEO downlink L1 and C-band comparison checks. • Selected C&V monitoring SIS via WRE inputs, if stop seeing SIS, commands a switch of the GUST pair.

  20. Determine GUST Mode Process • Steps to completing switch: • C&V issues command for Primary GUST to go to Backup • Waits for response that Primary is now in Backup (confirmed by loss of SIS from WREs) • When confirmed, issues command for Backup to switch to Primary • If C&V does not receive response from former Primary GUST that it is in Backup, it will wait until is sees loss of SIS from WREs before commanding the Backup to Primary • When switch made, former Primary GUST assures that it does actually drop power and cease to radiate by: • WMP tells the GUST Processor to notify M&C to change antenna load switch to dummy load • WMP validates change by monitoring switch position

  21. Determine GUST Mode Process • To counter possibility of antenna switch not being moved, WMP issues a Transmit Inhibit to SG (either WMP can issue this) • Only the Primary GUST can make determination of no SIS (by monitoring its signal) and fault. Backup GUST cannot move to Primary, even when observing no SIS, on its own, must be commanded by C&V

  22. Mitigation for Simultaneous Radiation RFU RFU SGST SGS GUSTP GUSP M&C M&C Level D Level D Antenna/Dummy Antenna/Dummy Antenna/Dummy Level D, GFE Level D, GFE Load Switch Load Switch Load Switch Command Command Status Status ALS Reset Reset ANT DUMMY ANT DUMMY WMP WMP TSWM TSWM NO I/F Switch NO CMP CMP I/F Switch WSG SG (1 & 2) (1 & 2) COM COM Normally Open Normally Open Level B Level B NC NC COM COM TXINH TXINH RF m Switch RF m Switch MON 1 MON 1 MON 2 MON 2 2X – one for L1 and one for L5 2X – one for L1 and one for L5 NOTE: Having two contacts per switch eliminates single point of failures and possible HMI

  23. Monitor Downlink Process • Three loopback checks are in WMP safety design to monitor the accuracy and quality of the WUM • Local Loopback (Loop 1) - signal is looped back before the RF switch (L1 and L5 paths, and L2 directly from SG) • RFU Antenna Loopback (Loop 2) - the signal is looped back from the GEO via the RFU antenna (path for L1 and path for L5) • GUST Antenna Loopback (Loop 3) - the L1 signal is looped back from the GEO via the Omni antenna and L5 directly from SG) • Primary GUST WMPs monitor via the three methods above for bad/missing messages and performance • Backup GUST WMPs monitor their performance by Local Loopback only.

  24. Three Loopback Paths

  25. Local Loop Back - Loop 1 • L5 routed directly while L1 and L2 are combined and routed. L1 and L5 originate as C-band and are down converted by the TLT • The WUM in this loop is sent to the GUST receiver test section. The Local Loop WUM is then sent to the WMP for validation to ensure that the message data at that point compares with the message data generated for FEC encoding. • WMP monitors for “missing” from L1, L2, and L5 paths and monitors for “correct” messages.

  26. RFU Loop Back - Loop 2 • This loop has two paths - L1 and L5 • Loops back L1 and L5 messages received from GEO via RFU antenna. • Loop 2 is feed to the GUST receiver GEO section • Measurements performed by receiver aid the WMP control loop algorithm in: • Maintaining synchronism of the Ground Station SIS with the GPS epochs • Maintaining coherence of the L1 carrier and PRN code signals • Measurement of the L1 and L5 signals quality propagation characteristics of the uplink and downlink paths (iono)

  27. RFU Loop Back - Loop 2 - cont • WMPs compared L1 and L5 navigation data received with the saved navigation data which was stored in WMPs during broadcast • If messages do not match, Primary will transition to faulted mode. • WMPs monitor messages received to determine the health of the GUST and L1 and L5 signals for “missing messages”

  28. GUST Antenna Loop Back - Loop 3 • The GUST receiver OMNI section receives L1 signal from the GUST Omni antenna and L5 directly from the SG • Receiver output is used by WMPs for validation of correct message reception via GPS antenna and GUST receiver • This loopback test is performed reguardless of the other loopback tests when GUST is in Primary. If test fails, non critical error condition is reported (Sig Event 48)

  29. Control WAAS Generator Process freq reference error GPS GEO iono delay uplink tropo delay uplink Doppler uplink Hardware (inter-freq bias) Common Error Multipath iono downlink tropo downlink Doppler User Ground Station • Closed-loop control algorithm compensates for: • Uplink iono error • Uplink Doppler • Transponder freq error • Inter-freq delay

  30. Message Timing • WAAS messages must be provided to the SIGGEN with enough lead time so that they are received by users according to TOA

  31. Control WAAS Generator Process • The GPT CSCI initializes the WAAS Signal Generator and GUST receiver • System is synchronized to GPS time by obtaining GPS time from the GPS satellites via inputs from Omni antenna • 1 PPS reference signal from receiver is established • This 1 PPS signal is used as a time reference by the WMPs and SG to control transmission time of the WAAS uplink message

  32. Control WAAS Generator Process • Selected C&V provide WNT information to WMPs to cause the control loop to reduce the time bias between GST apparent clock and WNT • The operation of the SG is controlled by WMP SG control parameters. • These control parameters adjust the timing of the message out of the SG to ensure a coherent signal is transmitted from the GEO satellite at the correct frequency and on the correct 1-second epoch.

  33. Control WAAS Generator Process • Selected C&V provide WNT information to WMPs to cause the control loop to reduce the time bias between GST apparent clock and WNT • The operation of the SG is controlled by WMP SG control parameters. • These control parameters adjust the timing of the message out of the SG to ensure a coherent signal is transmitted from the GEO satellite at the correct frequency and on the correct 1-second epoch.

  34. The GUS clock is steered to the GPS time epoch. The GUS receiver clock error is the deviation of its one-second pulse from the GPS epoch. The clock steering algorithm is initialized with the Type 9 message. This design keeps the GUS receiver clock 1 pulse per second synchronized with the GPS time epoch. Since the 10-MHz frequency standard is the frequency reference for the receiver, its frequency output needs to be controlled so that the 1 PPS is adjusted. A proportional, integral and differential (PID) controller has been designed to synchronize to the GPS time at GUS locations. Clock Steering Algorithm

  35. Clock Steering Diagram Primary GUST Clock Steering

  36. Control WAAS Generator Process • Selected C&V provide WNT information to WMPs to cause the control loop to reduce the time bias between GST apparent clock and WNT • The operation of the SG is controlled by WMP SG control parameters. • These control parameters adjust the timing of the message out of the SG to ensure a coherent signal is transmitted from the GEO satellite at the correct frequency and on the correct 1-second epoch.

  37. Summary of Briefing • GUST HWCI • SGST • RFU • GUST CSCI • GUSTP software - Level D • WMP software - Level B • Receive Message Process • Determine GUST Mode Process • Monitor Downlink Signal Process • Control WAAS Generator Process • Clock Steering Process