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Scalable Modulation for Loran

Scalable Modulation for Loran. Sherman Lo, Ben Peterson Second LORIPP Meeting Portland, OR September 23-24, 2002. Outline. Purpose of Scalable Modulation Recent History of LDC Means of Implementation Technical and Program Considerations Analysis Tools Final Thoughts.

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Scalable Modulation for Loran

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  1. Scalable Modulation for Loran Sherman Lo, Ben Peterson Second LORIPP Meeting Portland, OR September 23-24, 2002

  2. Outline • Purpose of Scalable Modulation • Recent History of LDC • Means of Implementation • Technical and Program Considerations • Analysis Tools • Final Thoughts

  3. Scalable Loran Data Channel (LDC) • Easier to Implement Legacy Compatible Low Data Rate Loran • Demonstrate and Publicize Utility of LDC • Could be used to aid Loran Navigation • High Data Rate Loran Provides More Utility • WAAS Broadcast, Aid to Loran Navigation • May not be Legacy Compatible • Can we create a modulation scheme that can be tuned from a low data rate, legacy compatible format to higher data rates? • Designed into User Receivers – No Need for New Equipment

  4. Recent LDC History • Dec. 2000: Discussed Lower Data Rate (170 bps) WAAS as Fallback, Do Full WAAS if possible. • 2001: Proof of concept of Full WAAS message @ 1Hz using Intrapulse Frequency Modulation (IFM) • Single fast rate (dual rated would be much more complex) • Legacy compatible format with some degradation in legacy navigation performance • Nov. 2001: Meeting at Megapulse • Agreement on how to implement IFM in SSX • Tentative commitment to do project • Mar. 2002: Presented options at Loran Murder Board, Legacy Support vs Optimized w/o Support • PPM vs. IFM

  5. Outcome of Loran Murder Board • Mar. 2002: Main Issue was Loran’s Ability to meet RNP 0.3. • Concern that LDC Complicated WAAS GEO Procurement & Confused Manufacturers • No Guidance on LDC, Virtually No Real Development since Murder Board

  6. Scalable Modulation Methods • Scalable PPM • PPM does not incur significant costs and technical risk associated with IFM • High data rate legacy (timing) receiver compatible may be possible (Not tested) • Scalable IFM • Better performance than PPM • Can be legacy compatible (with degradation) even at high data rates • PPM, IFM Combination

  7. Fundamental Trades Depend on Legacy Receiver Support

  8. Technical Considerations • For low data rate, legacy compatible LDC, 4 state IFM is technically better than 3 state PPM • 6 dB greater symbol separation, lower raw error rate • Higher (12/7) data rate enables 1 sec message, data wipeoff prior to CR canceling & navigation • No leading edge modulation/degradation of legacy performance • However, for full bandwidth WAAS, we recommended 8 state PPM w/ no legacy support • In earlier efforts, transmitter & receiver code produced by same people and changes in format easily accomplished • Desire to get receiver manufacturers building receivers means this no longer true • We need a signal spec, (at least a draft)

  9. Program Considerations • What value does LDC & Scalable LDC have? • Timing & Loran Integrity • WAAS/SBAS/GPS • Will Scalable Version Help with Acceptance? • Is a Decision Necessary in Near Future? • What is Necessary to Make a Decision? • Technical Issues • Program Issues • How does this Affect Loran Navigation Analysis?

  10. Analysis Tools are Developed ex. IFM 16 Level Performance

  11. Can Analyze Scalable LDC Ex. Detection of Change

  12. Final Thoughts • Do we need to confront the issues that were put on the table at the murder board but left on the table? • What analysis can we do (do we need to do) on LDC in terms of Loran Nav? • Do we need to decide anything beyond that (for now)? • LDC Utility, etc. • Do we need to do any more beyond that (for now)?

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