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Scalable Modulation for Loran

This paper discusses the purpose and implementation of scalable modulation methods for Loran Data Channels (LDC). It covers recent advancements in legacy-compatible modulation schemes that enhance Loran navigation. Key topics include the history of LDC, technical and program considerations, and the potential for high data rate communications. The analysis explores the trade-offs of different modulation schemes like PPM and IFM, while also addressing the importance of timing and integrity in Loran's performance. The paper aims to foster discussions about LDC's utility and navigate the challenges within this technology.

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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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