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Title: The impact of the new GPS signals on positioning accuracy for urban bus location based services
Author: El Hajj, Mireille
ISNI:       0000 0004 6496 4335
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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Increased bus patronage has the potential to facilitate the achievement of transport sustainability in cities in the developed and developing countries by alleviating congestion and its consequences including delays and pollution. However, this requires bus-friendly policies and a significant improvement in the efficiency of urban bus operations. Such operations consist of a large number of location based services such ‘countdown’ which requires the computation of bus arrival times at bus stops. However, to date there is a lack of agreement globally on the location based services and their key performance indicators expressed in the form of the required navigation performance parameters of accuracy, integrity (quality of or confidence in the position accuracy), continuity of service, and service availability. As a result of this, there is currently no optimal positioning system specification for bus operations. This thesis addresses these two issues and contributes to the field by firstly creating a comprehensive list of location-based services together with the required navigation performance for some of the applications. This is through a comprehensive literature review, consultation with a subject matter expert, and augmentation with, for the first time, a global survey of the major bus operators. Secondly, by demonstrating that a significant improvement in positioning accuracy is achievable with multi-constellation differential positioning. This is achieved through a comparative analysis of GPS only and augmentation with GLONASS and local differential positioning. Thirdly, the benefits of the new signals are demonstrated in the measurement and position domains, using established and novel mathematical models. The thesis analyses in detail the measurement qualities of the legacy and new signals in the measurement and position domains. The results of the former demonstrate the superiority of the L5 signal both in terms of signal strength and measurement precision, over the legacy L1 coarse acquisition (C/A) code measurements, with the new L2C as the weakest. The results of the position domain analysis show a significant improvement in positioning accuracy over the use L1 C/A code measurements alone, as a result of the mitigation of the ionospheric error through the combined use of the L1 C/A and L2C code measurements. The improvements in 3D positioning accuracy at the 95th percentile range from 22% (6m) in the clean (unobstructed environment) to 48% (13.66m) in the urban environment. The corresponding 2D horizontal positioning accuracy at the 95th percentile are 3.33m and 9.03m respectively. These improvements would not only enable more of the location based services to be supported but also facilitate the achievement of higher accuracy performance when using carrier phase measurements through enhanced ambiguity resolution.
Supervisor: Ochieng, Washington Sponsor: Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral