A Systems Approach to Sizing of Co-operative High-Accuracy Location (C-HALO) Services Validated by Experiments in San Francisco

This paper presents a methodology for assessing the accuracy gap between the current level-of-service provided by the US GPS constellation and DGPS, and the level-of-service envisaged by new Cooperative High-Accuracy LOcation (C-HALO) services that achieve decimeter accuracy. We present a novel GIS-based Hidden-Markov Model (HMM) predictive framework to estimate the fraction of roads with low satellite visibility counts that we call as the “dark area”, where C-HALO cannot be realized. Out of the total area of San Francisco (121 sq.km), 0.3 to 4% of the San Francisco streets are predicted to fall in the “dark” area with 95% confidence. Today, the DoD provides guarantees of 7m accuracies 97% of the time using the GPS constellation. Our dark area falls within this 3%. If it were covered by systematic new C-HALO investment, the nation might realize a similar performance guarantee at the decimeter level that would be meaningful for safe and efficient travel on the national roadway system.