Doppler-aided single-frequency real-time kinematic satellite
positioning in the urban environment.
Doctoral thesis, UCL (University College London).
Real-Time Kinematic (RTK) is one of the most precise Global Navigation Satellite Systems (GNSS) positioning technologies, with which users can obtain centimetre-level relative positioning accuracy in real-time. Routinely, expensive and dedicated dual-frequency,geodetic-quality receivers are used to provide RTK positioning. However a myriad of industrial and engineering applications (e.g., utility services, automated continuous monitoring of ground subsidence and deformation of man-made structures, robotics, intelligent transportation systems, agriculture, etc.) demand small-size, cost-effective and highly accurate GNSS positioning. This encourages the use of easily available low-cost single-frequency receivers with carrier-phase tracking and output capabilities and hence, the potential of those receivers to provide RTK positioning is examined in this thesis. A novel and effective Doppler-aided epoch-by-epoch processing technique is devised and developed to increase the single-frequency RTK positioning availability in GPS/GNSS challenged environments. The technique utilises raw Doppler frequency shift measurements to smooth code pseudoranges and also uses a new integer ambiguity estimation and validation technique. Doppler-smoothing of pseudoranges is motivated both by the continual availability and the centimetre-level precision, even in difficult urban canyons, of receiver generated raw Doppler frequency shift measurements. The influence of Doppler-smoothed pseudoranges on both the positioning and the carrier-phase integer ambiguity resolution is investigated. It is shown that in urban areas the proposed Doppler-smoothing technique is more robust and effective than that of the traditional carrier-smoothing of pseudoranges (e.g., the Hatch filter). Static and kinematic trials confirm this technique improves the precision of the code-based absolute and also relative positioning in urban areas characteristically of the order of 40%-50%. In the experimental trials carried out, Doppler-smoothing of pseudoranges also demonstrated improvements (close to 15%) in the ambiguity resolution success rate in instantaneous RTK for short baselines ( /approx 7 km), where the probability of fixing ambiguities to correct integer values is dominated by the relatively imprecise code pseudoranges. Furthermore, to increase the success rate of the integer ambiguity resolution (and hence the RTK availability) a single-frequency, epoch-by-epoch ambiguity resolution technique is introduced. Experimental results suggests that the new technique combined with Doppler-smoothing offers a large improvement (> 30%) in fixing the ‘correct’ integer ambiguities in a single-epoch for single-frequency users compared to conventional ambiguity resolution methods.
|Title:||Doppler-aided single-frequency real-time kinematic satellite positioning in the urban environment|
|Additional information:||Permission for digitisation not received|
|UCL classification:||UCL > School of BEAMS > Faculty of Engineering Science > Computer Science|
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