This Enhanced Loran (eLoran) Definition Document has been published by the International Loran Association to provide a high-level definition of eLoran for policy makers, service providers, and users. It was developed in November 2006 at the United States Coast Guard Navigation Center by an international team of authors.
Enhanced Loran is an internationally-standardized positioning, navigation, and timing (PNT) service for use by many modes of transport and in other applications. It is the latest in the long-standing and proven series of low-frequency, LOng-RAnge Navigation (LORAN) systems, one that takes full advantage of 21st century technology.
eLoran meets the accuracy, availability, integrity, and continuity performance requirements for aviation non-precision instrument approaches, maritime harbor entrance and approach maneuvers, land-mobile vehicle navigation, and location-based services, and is a precise source of time and frequency for applications such as telecommunications1.
eLoran is an independent, dissimilar, complement to Global Navigation Satellite Systems (GNSS). It allows GNSS users to retain the safety, security, and economic benefits of GNSS, even when their satellite services are disrupted.
The eLoran System
eLoran meets a set of worldwide standards and operates wholly independently of GPS, GLONASS, Galileo, or any future GNSS. Each user’s eLoran receiver will be operable in all regions where an eLoran service is provided. eLoran receivers shall work automatically, with minimal user input.
The core eLoran system comprises modernized control centers, transmitting stations and monitoring sites. eLoran transmissions are synchronized to an identifiable, publicly-certified, source of Coordinated Universal Time (UTC) by a method wholly independent of GNSS. This allows the eLoran Service Provider to operate on a time scale that is synchronized with but operates independently of GNSS time scales. Synchronizing to a common time source will also allow receivers to employ a mixture of eLoran and satellite signals.
The principal difference between eLoran and traditional Loran-C is the addition of a data channel on the transmitted signal. This conveys application-specific corrections, warnings, and signal integrity information to the user’s receiver. It is this data channel that allows eLoran to meet the very demanding requirements of landing aircraft using non-precision instrument approaches and bringing ships safely into harbor in low-visibility conditions. eLoran is also capable of providing the exceedingly precise time and frequency references needed by the telecommunications systems that carry voice and internet communications.
eLoran Service Provision
eLoran services are provided by a Core eLoran Service Provider and various Application Service Providers:
- Core eLoran Service Provider – delivering a highly precise version of the core signal originally described in the US Coast Guard Specification of the Transmitted Loran-C Signal; and
- Application Service Providers – (e.g. aviation, maritime, etc …) delivering application-specific data (e.g. differential Loran messages or early skywave warnings) that may be communicated using the eLoran data channel.
eLoran’s enhanced accuracy, availability, integrity and continuity meets the requirements for aviation non-precision instrument approaches, maritime harbor entrance and approach maneuvers, land-mobile vehicle navigation, and location-based services. It also allows absolute UTC time to be recovered with an accuracy of 50 nanoseconds as well as meeting the Stratum 1 frequency standard needed by telecommunications users.
|0.004 – 0.01 nautical mile (8 – 20 meters)||0.999 – 0.9999||0.999999 (1 x 10-7)||0.999 – 0.9999 over 150 seconds|
1. Accuracy to meet maritime harbor entrance and approach.
2. Availability, integrity and continuity to meet aviation non-precision approach in the U.S.
eLoran System Performance Requirements
eLoran services will deliver safety, security and economic benefits to a wide range of stakeholders (e.g. governments, service providers) and users (e.g. aviation, maritime):
- allowing aviation communications, navigation and surveillance functions to migrate to digital communications;
- enabling maritime e-Navigation including permanent or temporary virtual AtoNs to be used to mark dangerous waters;
- supporting road user charging providing authentication; and
- maintaining synchronization of wired and wireless telecommunications without the need for expensive external oscillators.
The Way Ahead
eLoran is an independent, dissimilar complement to GNSS. As such, it will allow PNT users with demanding safety-critical or mission-critical applications to secure their safety, security and economic benefits even when their satellite services are disrupted.
eLoran is capable of meeting the accuracy, availability, integrity, and continuity performance requirements for:
- aviation non-precision instrument approaches;
- maritime harbor entrance and approach maneuvers;
- land-mobile vehicle navigation;
- location-based services; and
- precise time and frequency users.
This document, the first of several needed to fully define the system, marks the beginning of an international effort to secure accurate and reliable sources of PNT for 21st century users with demanding safety-critical or mission-critical applications.
1 Loran’s Capability to Mitigate the Impact of a GPS Outage on GPS Position, Navigation, and Time Applications; Prepared for the Federal Aviation Administration, Vice President for Technical Operations, Navigation Services Directorate; dated March 2004.