Site selection plan and installation guidelines for a nationwide differential GPS service

Ketchum, Ronald L.; Lemmon, John J.; Hoffman, J. Randy · 1997 · ROSA P / United States. National Telecommunications and Information Administration

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Summary

This 1997 report by the Institute for Telecommunication Sciences provides site selection plans and installation guidelines for establishing a nationwide Differential GPS (DGPS) service in the United States. The research addresses the limitation of the Standard Positioning Service (SPS), which offers only ~100 meters of accuracy due to Selective Availability, failing to meet the sub-10-meter requirements of civil navigation, public safety, and infrastructure management. The document aims to facilitate the expansion of the existing U.S. Coast Guard (USCG) and Army Corps of Engineers (COE) coastal DGPS network to cover the entire continental U.S., Alaska, and Hawaii, thereby supporting surface transportation, emergency services, and industrial applications. The methodology involves analyzing existing DGPS broadcast site coverage and determining the minimum number of additional sites required to achieve nationwide signal redundancy. The authors utilize the USCG’s medium-frequency radiobeacon system (285–325 kHz) as the broadcast model, which transmits differential corrections via Minimum Shift Keying modulation. The study evaluates signal propagation characteristics, noting that medium-frequency waves offer extensive coverage with low power and minimal terrain interference. The analysis incorporates existing USCG/COE sites, 15 existing GWEN radio transmitter sites, and identifies specific locations for new broadcast sites to fill coverage gaps. The report also details technical specifications for site configuration, including reference antenna masts, equipment racks, shelter requirements, and power needs, ensuring compatibility with existing control stations in Alexandria, VA, and Petaluma, CA. Key findings indicate that the existing USCG and COE network already covers over two-thirds of the continental United States. To achieve complete nationwide coverage with redundant signal reception (allowing users to receive corrections from at least two beacons), the study recommends adding a minimum of seven additional DGPS broadcast sites in the contiguous U.S., along with specific additions for Alaska and Hawaii. The proposed system is designed to provide position accuracy within 8 meters (2drms) 95% of the time, with broadcast availability exceeding 99.7%. Integrity monitoring ensures that alarms are transmitted to users within 4 seconds of fault detection. The report provides detailed predicted signal coverage maps for each proposed site, demonstrating how the expanded network eliminates coverage voids in inland regions. The significance of this work lies in providing the technical blueprint for a national infrastructure that enhances GPS utility for civilian and commercial sectors. By standardizing site selection and installation, the guidelines enable the deployment of a reliable, high-accuracy positioning service that supports Intelligent Transportation Systems, precise agriculture, surveying, and emergency response. The report establishes that a nationwide DGPS service is technically feasible using existing technology and infrastructure, offering substantial improvements in safety, efficiency, and operational capability across diverse industries.

Key finding

The nationwide DGPS service design achieves position accuracy within 8 meters and availability exceeding 99.7 percent by utilizing a network of radiobeacon broadcast sites with overlapping coverage.

Methodology

theoretical

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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