Evaluation of ambiguity resolution performance using LAMBDA method and real data
by
Leandro Baroni
National Institute for Space Research, Sao Jose dos Campos, SP, Brazil
Coauthors: Hélio Koiti Kuga Kyle O'Keefe

The Global Positioning System (GPS) is a satellite-based navigation system that allows the user to determine position and time with high precision. Using the carrier phase measurements, it is possible to reduce positioning error up to 100 times, if compared with standard positioning. Although very accurate, this type of measurement contains an inherent difficulty that is the determination of the ambiguity in the number of wavelengths of the corresponding signal.

The objective of this work is to estimate the position coordinates of a GPS receiver ("user") using its data and also data from another receiver placed in a known landmark ("base"). Such data are double differenced, and performance of ambiguity resolution with LAMBDA method using real static and kinematic data is evaluated.

However, in long baselines situations (above 20km), the ambiguity resolution performance decreases. Therefore, it would be necessary to take into account some problems which affect differential positioning, such as ionosphere influence. During the processing of GPS measurements, the float solution and the ambiguity resolution process were reset once every 5 minutes. Results are shown in terms of correct ambiguity fix percentage and processing time in both situations, and are expected to show that when ionospheric modeling is added in the kinematic test, the correct fix is attained faster and its percentage increases.

Date received: April 28, 2008