Transcript Document
Loran-C Applicability for Mitigating the Vulnerability of GPS in Navigation Applications and as a Secondary Method of Transmitting WAAS Corrections. This document is confidential and is intended solely for the use and information of the client to whom it is addressed. Scope–Loran System Performance Loran is a terrestrial-based low-frequency hyperbolic navigation system operating at a carrier frequency of 100 Khz The Loran receiver computes lines of position (LOPs) based on the time of arrival difference between two or more time-synchronized transmitting stations of a Loran chain. Current Loran-C System Performance Characteristics (Signal-in-Space) ACCURACY (2drms) PREDICTABLE 0.25nm (460m) REPEATABLE AVAILABILITY 60-300 ft. (18-90m) 99.7% COVERAGE Continental US, Alaska Selected overseas Areas FIX RELIABILITY FIX RATE 99.7%* 10-20 fix/sec. DIMENSION 2D + Time SYSTEM CAPACITY AMBIGUITY POTENTIAL Unlimited Yes, easily Resolved *Triad reliability Potential Loran System Performance characteristics-- Depends on your Terms of Reference Filename/RPS Number 1 Scope- The currently defined Loran coverage (per 2001 FRP) Filename/RPS Number 3 Requirements Summary (RNP.3 and RNP.5) Accuracy (minimum) 802 meters Accuracy (target) 307 meters Monitor Limit (minimum) 926 meters Monitor Limit (target) 556 meters Integrity 10-7/hour Time-to-alert 10 seconds Availability (minimum) 99.9 Availability (target) 99.99 Continuity (minimum) 99.9 Continuity (target) 99.99 Filename/RPS Number 4 Factors Linking Major Elements Accuracy Availability Continuity Integrity Time Filename/RPS Number 5 Major Program Elements (with a few examples) Policy - Radionavigation System Mix - Define Requirements Operations Doctrine - TOT vs SAM - Blink Transmitting Equipment -New TFE -New SSX User Equipment - All-in-View Receiver - H-field antenna Filename/RPS Number 6 Considerations Influencing all Major Elements (with a few examples) New and Legacy Users - Do we support navigation legacy users? - Do we support timing legacy users? Data Channel - Do we do this at all? - What type of modulation? Propagation - How do we collect data for ASF? - How do we implement ASF corrections? Cost/Benefit Alternatives Politics Filename/RPS Number 7 Factors Linking Major Elements– Integrity (derived from RTCA SC-181) A measure of confidence in the estimated position , expressed as the probability that he system will detect and annunciate the condition where the total system error is greater that the cross track containment limit. [derived from ICAO Doc. 9613, RTCA/DO-208] The ability of a system to provide timely warnings to users when the system should not be used for navigation. FAA requirement– 99.99999 within .3nm? -- 10 seconds for an integrity alert Filename/RPS Number 8 Factors Linking Major Elements-- Accuracy (derived from ICAO Doc. 9613, RTCA/DO-208) The degree of conformance between the estimated, measured, or desired position and/or the velocity of a platform at a given time and its true position or velocity. Radionavigation performance accuracy is usually presented as a statistical measure of system error and is specified as: a) Predictable – The accuracy of a position in relation to the geographic or geodetic coordinates of the earth. b) Repeatable – The accuracy with which a user can return to a position whose coordinates have been measured at a previous time with the same navigation system. c) Relative – The accuracy with which a user can determine one position relative to another position regardless of any error in their true positions. (derived from RTCA DO236) Required Navigation Performance (RNP) Accuracy statements are needed for a defined application in a defined area. There are additional requirements BEYOND accuracy applied to a particular RNP (e.g., continuity, integrity, availability) FAA requirement– RNAV .3nmRNP is desired goal (.16 nm 95%) .43 nm 95% is needed to provide performance better than VOR Filename/RPS Number 9 Factors Linking Major Elements-- Availability (derived from ICAO Doc. 9613, RTCA/DO-208) The ability of the system to provide the required function and performance at the initiation of the intended operation. Availability is also an indication of the ability of the system to provide usable service within the specified coverage area. Signal availability is the percentage of time that navigational signals transmitted from external sources are available for use. Availability is a function of both the physical characteristics of the environment and the technical capabilities of the transmitter facilities. FAA Requirement– 99.9- 99.99 Filename/RPS Number 10 Factors Linking Major Elements-- Continuity (derived from ICAO Doc. 9650) The capability of the total system (comprising all elements necessary to maintain aircraft position within the defined airspace) to perform its function without nonscheduled interruptions during the intended operation. The continuity risk is the probability that the system will be unintentionally interrupted and not provide guidance information for the intended operation. More specifically, continuity is the probability that the system will be available for the duration of a phase of operation, presuming that the system was available at the beginning of that phase of operation.[1] [1] Note – for operations in "Required Navigation Performance (RNP) airspace: Containment continuity is the term that applies to RNP RNAV airspace. Containment continuity is the capability of the total system to satisfy the containment integrity requirement without nonscheduled interruptions during the intended operation. Nonscheduled operation is defined to be either1) total loss of navigation capability; 2) a failure of the system which is annunciated as loss of RNP RNAV capability; or, 3) a false annunciation of loss of RNP RNAV capability while the system is working properly. Containment continuity is specified by the maximum allowable probability for interruption. FAA Requirement– 99.99 or 99.9 Filename/RPS Number 11 Factors Linking Major Elements-- Time (TrueTime) A stratum level is a hierarchical structure categorized by the clock source accuracy. A Primary Reference Source (PRS) has a stratum level 1. Stratum 1 is classified as the highest level with an accuracy of 110-11 or better. This level requires a Cesium or a GPS or Loran-C disciplined oscillator. Stratum 2 has an accuracy of 1.610-8, and requires a Rubidium or double oven oscillator for holdover stability. Stratum 3 has an accuracy of 4.610-6 which can be met with an oven controlled quartz oscillator. Stratum 4 has an accuracy of 3.210-5. Loran is a Stratum 1 time source Loran Master Stations are synchronized to UTC within 100nsec or better FAA requirement– none specified Filename/RPS Number 12 What has been happening Some people have changed views on Loran-- more positive FAA Transition Report-- Concurrent Clearance DOT Report-- Delivered ASF Discussions-- ongoing with OU, USCGA, LSU, NAVCEN, PIG others? Funding Discussions-- Identify what you need. National and International Outreach– Tell our story to other users groups. Filename/RPS Number 13