Investigation of ambiguity resolution performance of short-, Medium- and long-distance baselines based on four galileo frequencies

Rapid and high-precision positioning with a Global Navigation Satellite System (GNSS) is feasible only when carrier-phase observations can serve as very precise pseudo-range measurements after integer ambiguity parameters are resolved. With current GPS, for short-distance baseline, the reliability of ambiguity resolution with single-epoch data is not high. This makes it impossible to realize real-time precise navigation for safety-related applications. For medium- and long-distance baselines, it generally takes as long as more than twenty minutes to get ambiguity resolution and the reliability is not high. Fewer available carrier-phase data is an important reason for the above low reliability and low efficiency problems. With only two frequency carrier-phase data available, it is impossible to form frequency combinations with long equivalent wavelength, which is very important for ambiguity resolution when the noise of code pseudorange measurements is large. European Galileo system will provide signals in more frequency bands. Therefore it may be possible to resolve for the integer ambiguity faster and more reliable. Based on simulated data under different code and carrier-phase noise levels, this paper tries to investigate ambiguity resolution performance with four Galileo frequencies for short-, medium- and long-distance baselines. For short-distance baseline, geometry-based CAR method and LAMBDA method are used to test if it is possible to resolve for ambiguity within single epoch. For the CAR method, optimal combinations are carefully selected in terms of ADOP-based success-rates. For medium- and long -distance baselines, ionospheredelay parameters are eliminated from every epoch observation equations using the so-called equivalently eliminated observation equation system. As a result, integer property of ambiguities is kept. LAMBDA method is used to investigate the performance. For short baseline, the test results show that: When carrier-phase observation noise is less than 6mm and code observation noise is not higher than 2m, single epoch ambiguity resolution can be achieved with high success rate (>99%). When carrier phase observation noise is around 12mm, the success rate is very low, especially with CAR method. For medium- and long-distance baselines, the test results show that the average time required to fix ambiguity is generally about one minute. Even with 800 km baseline, the average time will not exceed two minutes.