Ntia special Publication 94-30 a technical Report to the Secretary of Transportation on a National Approach to Augmented gps services
Security. Loran-C does not use encryption or any methods for controlling user access. Infrastructure Cost
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- Data Link Characteristics
- Time Frame of Availability
- 4.1 System Technical Capabilities
- 4.2 Capabilities Versus Requirements
Security. Loran-C does not use encryption or any methods for controlling user access. Infrastructure Cost. Infrastructure costs to modify existing Loran-C sites to transmit differential corrections are estimated to be $100K per station. The cost of building a new Loran-C site is estimated at $8M to $10M. Loran-C sites will need upgrades within the next few years to replace aging equipment. The cost of upgrading an existing Loran site to include solid-state equipment is estimated at $5M. User Cost. While there is an existing stock of Loran-C receivers, new receivers would be required to meet combined GPS/Loran-C capabilities. While FAA-certified equipment for air navigation could cost less than $1,000 per unit, the cost of installing and inspecting a unit in an aircraft would bring the cost to several thousand dollars per unit. However, the cost of portable GPS/Loran-C units for non-navigation uses, such as for ground vehicles, is expected to be less than $1,000. Data Link Characteristics. The Loran-C system is centered at 100 kHz and could transmit differential GPS data by time-shifting the Loran-C bursts. This technique results in a data rate of up to 30 bps. Data Format. To overcome the low data rates inherent in a Loran-C differential GPS system, a fully asynchronous message format is proposed. Every satellite correction would be transmitted in a single compressed message. Time Frame of Availability. The basic Loran-C infrastructure is in place. Modifications and implementation schedules could not meet a date prior to 1998. 4 EVALUATION OF AUGMENTED GPS SYSTEMS This section compares the technical capabilities of the 11 systems described in Section 3 with the user requirements identified in Section 2. An analytical decision matrix was developed to assist in determining the final recommendations of this study. The matrix served as a guide in evaluating the augmented GPS systems and architectures that were considered but did not provide an absolute solution to determine the most capable augmented GPS architecture. The decision matrix consisted of two stages. The first stage, the use of which is illustrated in Tables 4-1 through 4-22, is the Technical Capabilities Evaluation. During this stage, user requirements and augmented GPS system performance specifications were tabulated. The 11 systems evaluated were: 1) U.S. Coast Guard (USCG) — This system employs LF/MF beacons and is currently being deployed by USCG and the U.S. Army Corps of Engineers to provide coverage of U.S. coasts, harbors, harbor approaches, and inland waterways. 2) U.S. Coast Guard, Expanded (USCG(E)) — This system expands the USCG LF/MF beacon system to provide nationwide coverage. 3) FM Subcarrier (FM) — The FM subcarrier system provides differential corrections using the subcarriers of FM broadcast stations. 4) Wide Area System 1 (WAS 1) — This system is composed of the FAA GEO satellite-based Wide Area Augmentation System (WAAS) to meet the integrity, availability, and accuracy requirements of aviation users for the en route through Category I precision approach phases of flight and approximately 150 local area differential GPS (LADGPS) systems for Category II/III precision approach requirements. 5) Wide Area System 2 (WAS 2) — This system is composed of the FAA WAAS to meet the requirements of aviation users for the en route through non-precision approach phases of flight. In addition to the WAAS, approximately 770 LADGPS systems are needed for Category I/II/III approach requirements. In this system, the WAAS provides integrity and availability only; it does not provide accuracy corrections. 6) Wide Area System 3 (WAS 3) — This system is the same as WAS 1 except that a frequency other than L1 is used to provide differential corrections. 7) Wide Area System 4 (WAS 4) — This system is the same as WAS 1 except that all communication links are encrypted to provide signal security. 8) Wide Area System 5 (WAS 5) — This is a GEO satellite-based system provided by private industry. 9) Wide Area System 6 (WAS 6) — This is a LEO satellite-based system provided by private industry. 10) Continuously Operating Reference Stations (CORS) — This system is designed and will be deployed throughout the country to meet the post-processing requirements of GPS users. 11) Loran-C — This system uses Loran-C as a communications link to provide differential corrections. 4.1 System Technical Capabilities The technical capabilities of the 11 systems described in Section 3 are summarized in Table 4-1. Some of the parameters used in Section 3 to describe the systems are not included in the table. Parameters were excluded if system suppliers did not provide a specification for that parameter, system performance could not be evaluated, or the parameter did not provide discrimination between systems. A detailed justification for Table 4-1 entries is provided in Appendix I. 4.2 Capabilities Versus Requirements Tables 4-2 through 4-17 display the degree to which each of the 11 systems satisfy user requirements. Each mode and phase of operation identified in Section 2 is compared in a separate table. Each block in these tables indicates a "YES" if the system specification meets or exceeds the required value and a "NO" if the specification does not meet the requirement. These tables provide an evaluation of the technical capabilities of each system for each mode and phase of operation. Table 4-1. Augmented GPS System Capabilities
* CORS is not a real-time system. ** Not specified for this system.
Table 4-2. Augmented GPS System Evaluation, Aviation, Oceanic En Route
Table 4-3. Augmented GPS System Evaluation, Aviation, Domestic En Route
Table 4-4. Augmented GPS System Evaluation, Aviation, Terminal
Table 4-5. Augmented GPS System Evaluation, Aviation, Non-precision Approach and Landing
Table 4-6. Augmented GPS System Evaluation, Aviation, Category I Precision Approach and Landing
Table 4-7. Augmented GPS System Evaluation, Marine, Harbor/Harbor Approach
Table 4-8. Augmented GPS System Evaluation, Marine, Coastal
Table 4-9. Augmented GPS System Evaluation, Marine, Ocean
* Met by SPS.
Table 4-10. Augmented GPS System Evaluation, Land, Highway
Table 4-11. Augmented GPS System Evaluation, Land, Highway (Collision Avoidance)
Table 4-12. Augmented GPS System Evaluation, Land, Railroad
Table 4-13. Augmented GPS System Evaluation, Land, Railroad (Control)
Table 4-14. Augmented GPS System Evaluation, Survey, Land
Table 4-15. Augmented GPS System Evaluation, Survey, Hydro
Table 4-16. Augmented GPS System Evaluation, Survey, Deformation Analysis
Table 4-17. Augmented GPS System Evaluation, Survey, Mapping
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