The Loran Integrity Performance Panel (LORIPP)

The Loran Integrity Performance Panel (LORIPP) The LORIPP Team Loran Team Meeting McLean, VA July 30, 2002

LORIPP Background • What is LORIPP and why does it exist? • Determine Requirements (System Engineering) • Identify Threats to Loran and Determine Threat Allocations (Fault Tree) • Bound/Mitigate Effects of these Threats • Develop Threat Models • Provide Substantiated Information on Loran Capabilities • What will we accomplish? • Prove Stand Alone Loran Can Act as a Redundant Navigation System (RNP 0.3 or 0.5)

Threats to Loran Integrity • Transmitter • Propagation Effects • Interference (Atmospheric Noise, P Static, Sky Wave) • Ground Wave Propagation Phenomena (ASF, ECD, SNR) • Receiver

LORIPP Work Plan • Transmitter Performance (LSU, PIG, Tom G., NAVCEN) • Receiver Algorithms & Performance (PIG, Stanford, USCGA) • Fault Tree (Stanford, Kevin B., NAVCEN) • System Engineering (PIG, Bob W.) • P-Static Evaluation (Bob E., Bob T., Bob L., Bob W., Frank G., Kevin B.) • Atmospheric Noise (Stanford, PIG, Kevin B., Bob W.) • Ground Wave Propagation: ASF, ECD and Signal Strength (Bob W., USCGA, NAVCEN, LSU, PIG, Tom G., OU, FAATC) • Loran Communications (Stanford, PIG, Frank G.) • Sky Wave (Bob W., USCGA) • Documentation & Meeting Logistics (Tom G., Stanford, NAVCEN)

System Engineering • Development of Coverage Analysis Tools • Calculation of Continuity & 95% Accuracy • Reliability, i.e., Mean Time between Failures, etc. • Avionics • New Transmitter Equipment (validate assumptions)

Fault Tree • Integrity Fault Tree • Continuity Fault Tree • Determine Allocations in Error Budget • ECD (propagation, receiver calibration, receiver noise) • TOA (receiver noise) • Tails of the distributions

Preliminary Integrity Fault Tree Probability (HPE > HPL) > 10-7/hour Probability Transmitter Caused HMI Probability Propagation Caused HMI Probability Receiver Caused HMI Transmitter Timing Evil Waveform CW RFI Sky Wave ASF Effects ECD Cross Rate

Transmitter Performance • Determine ABS Threshold, Time to Blink from Onset of Fault, Probability of Out of Tolerance w/o blink • Determine Transmitted ECD Tolerance, Blink on transmitted ECD? *** • Determine Threat Monitor Requirements at transmitter, Certification Requirements for Monitors • Calibration re UTC • Chain Operations • TOE verus SAM • Analysis of coverage under each situation • Control of TOE to UTC vs measurement of TOE to UTC and transmission of measured offset

Receiver Algorithms & Performance (1/2) • Determine the probability of false alarm & missed detection of blink/off air at given SNR (given time to alarm requirement) • Establish SNR Threshold (for reliably identifying the correct station & cycle) with 7 9s of confidence • Master independent, multi-chain navigation • Resolution of 200 usec cross chain lane ambiguities • Identification of secondary w/o master • Loran Cycle Integrity Calculations • Weighted Sum Squared Error vs Sum Squared Error • Analysis of probability of cycle slips after verifying cycle integrity

Receiver Algorithms & Performance (2/2) • Input from Potential Manufacturers – Validate Assumptions of HMI Analysis • Determine ECD Requirement • Determine Loop Time Constants • Develop Simulator • Averaging time • HPL calculation

Cycle Resolution Verifies that the correct cycle is being tracked Determine Pwc (probability of being on the wrong cycle) HPL Calculation Determines the 99.99999% confidence bound on horizontal error Determine HPL HPL < 0.3 NM HPL < 0.5 NM Pwc < 1x10-7 Cannot meet RNP 0.3 or 0.5 Requirements HPL > 0.3 NM (RNP 0.3) HPL > 0.5 NM (RNP 0.5) Pwc > 1x10-7 Basic Receiver HMI Algorithm

P Static • Educate LORIPP via tutorial paper and briefing. • Determine how P static fits into Fault Tree • Different faults caused by P static and Allocations • What would the continuity allocation be? • What is max level of P static • Developing H-field Antenna Test Plan and, at a minimum, determine a figure for SNR drop outdoors

Atmospheric Noise • Determine the necessary analysis level, i.e., 95%, 99%, or 99.9%, worst time period or averaged over time? • Determine and Develop Applicable Databases • Time Domain Model for Simulation • Determine the credit that can be claimed for non-linear processing • Implement Results in Simulator and Receiver

Ground Wave Propagation: ASF, ECD and Signal Strength • Data Collection • Guidance/requirements definition for data collection effort (also collecting ECD & SNR data) • Coordinate with Atmospheric Noise Threat Model • Data Analysis • 99.99999% bounds on remaining errors • Correlated vs. Uncorrelated terms • Mathematical modeling & prediction including terrain of SS, ECD, & ASF?

Sky Wave • Quantify effects on TOA bias • Quantify effects on ECD bias • Receiver technology for mitigation • Integrity Allocation & Threat Model

Loran Communications • Effects on Navigation if Signals are Modulated • Impact on Availability, Integrity, Accuracy, & Continuity if Loran Data is Transmitted • What data? • And at what rates? • Quantify the benefits provided by the data channel in improving Loran Nav. performance (Availability, Integrity, Accuracy, & Continuity)

Documentation & Meeting Logistics • Collect White Papers from Briefings • Loran/LORIPP Web resource? • Meeting Minutes • Organize Project and Arrange Priorities • Determine Documentation Methodology

Summary • The LORIPP just had its first meeting this past week • The major (critical) issues for Loran RNP 0.3 were discussed • A work plan was developed to gather the data and perform the analysis necessary to prove Loran performance • Future meetings are planned to further develop the integrity analysis – late September

The Loran Integrity Performance Panel (LORIPP)