Scalable Modulation for Loran

Loran Integrity Performance Panel

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


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


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


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


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


Fundamental Trades Depend on Legacy Receiver Support

Support All Legacy rcvrs

Intrapulse Frequency Modulation (IFM)

Support Timing Legacy rcvrs

PPM w/ Extra Pulses

Support No Legacy rcvrs

Pulse Position Modulation (PPM)

2001 Tests based on this assumption

Least Mature Concept

Similar to earlier, lower data rate schemes

Phased implementation possible Hedge against req’ts that we do not yet understand.

Best perf. for new users.

On-air rcvr testing using operational LORSTAs is possible.

Most complex signal format, modulator, & receiver (highest technical risk).

$30-40M (ROM) to modify SSX. (international accept.?)

May need new spectrum to recover perf. loss.

Will need TBD additional pulses increasing energy costs and CRI

Cost to legacy users.

Need for international coordination.

Phased implementation impossible.


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)


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?


Analysis Tools are Developed ex. IFM 16 Level Performance


Can Analyze Scalable LDC Ex. Detection of Change


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)?

Scalable Modulation for Loran

Documents

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