New GNSS Navigation Messages for Inherent Fast TTFF and High Sensitivity - Underlying Theory Study and System Analysis

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In the navigation applications on mobile devices, the extreme demands for fast Time To First position Fix (TTFF) and high sensitivity have been driving the technology innovations in these areas in recent years. Assisted GNSS (AGNSS) and Ephemeris Extension (EE) technologies constitute the efforts to improve the TTFF and sensitivity. However, it is challenging for both AGNSS and EE. For AGNSS, while it attempts to improve TTFF on sensitivity on mobile devices, it is subject to frequent ephemeris expiration and therefore it requires the mobile devices to be always or frequently connected to the assisting networks. For EE - a technology complementary to the AGNSS to improve TTFF, although it requires little connectivity to assisting networks by directly using some extended ephemerides (valid for days) in the first position fix, such extended ephemerides can be hardly used as the aiding data for tracking weak signals. In the analysis of the challenges, this thesis points out that, such challenges are originated from the weakness in the fundamental design of the existing GNSSs – the life expectancy of ephemeris is too short. Then this thesis proposes an alternative solution for future GNSSs, to fundamentally resolve the above issues by broadcasting some new navigation (NAV) messages with validity for up to 24 hours instead of those used by current GNSSs. Through the study of the TTFF and sensitivity fundamentals, this thesis fully explains how the ephemeris life expectancy relates to TTFF and sensitivity; and through fundamental study on orbital determination theories and ephemeris extension practices, this thesis confirms the feasibility to obtain long-validity ephemerides; and through some simulated uses of the long-validity ephemerides in some typical scenarios, this thesis further confirms the navigation availability and accuracy using the proposed new NAV messages are comparable to those using the current NAV messages. Therefore, for a GNSS that deploys the proposed NAV messages, the capability to achieve fast TTFF and high sensitivity on a mobile device is inherently enhanced, with minimum or even no reliance on assisting infrastructures.
GNSS, Navigation messages, Time To First Fix, TTFF, Sensitivity, Ephemeris Extension
Zhang, W.. (2018). New GNSS Navigation Messages for Inherent Fast TTFF and High Sensitivity - Underlying Theory Study and System Analysis (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/31910