Proposed LOS Fast TTFF Signal Design for IRNSS
Creators: name: Rao, Vyasaraj
Publisher: name: Graduate Studies
Year: 2013
Subjects: subject: Engineering--Electronics and Electrical
subject: IRNSS TTFF
subject: Single frequency
subject: Dual frequency
subject: Optimal TTFF
subject: Cross Correlation
subject: Third Frequency
subject: HOT and SNAP start

description: Amongst GNSS receiver design criteria such as accuracy, sensitivity, channels etc., Time To First Fix (TTFF) is an important criterion, which defines how fast a navigation solution is available to the user since receiver power on. TTFF is defined as the time that a receiver takes to acquire and track a minimum of four satellites and extract the necessary information (ephemeris - primary parameter) from the demodulated navigation data bits. In the past decade, there has been a constant demand from the user community to optimize TTFF specifications. For example, for E911 use, Global Navigation Satellite System (GNSS) receivers integrated as a part of mobile handsets obtain assistance from a base station (terrestrial link) to enhance the TTFF. However, this link may not be always guaranteed. In addition, for military handheld equipment, to depend on a terrestrial link may not be practical. Thus, it becomes critical to optimize the TTFF parameter of a GNSS receiver from the satellites directly. This research work focuses primarily on improving the TTFF parameter of a GNSS receiver. As highlighted earlier, the TTFF depends on both receiver algorithms (to acquire and track a minimum of four satellites) and navigation data structure (to collect ephemeris as fast as possible from the satellites tracked). The former is receiver specific whereas the latter depends on the satellites. Since the upcoming Indian Regional Navigation Satellite System (IRNSS) is in its preliminary design stage, there is a large potential for improvement of the TTFF parameter without having to compromise on any other mission objectives. Towards this goal, several new signal design strategies have been proposed and analyzed. Though the upcoming IRNSS is considered as the target platform herein, the results can be extended to any emerging GNSS constellation. The research activities performed are categorized based on the service (civilian or restricted) and frequencies supported (single or dual). As a first objective, a signal design for single frequency system and a reference Navigation (NAV) data structure is developed. Subsequently, three new methods are proposed with an emphasis on minimizing TTFF in single frequency mode of receiver operation. Subsequently, three new methods are proposed with an emphasis on minimizing the TTFF in the single frequency mode of receiver operation. As a second objective, three new signal designs are proposed based on diversities of code and carrier. Third, a signal design for civilian and restricted services optimized for TTFF is proposed based on new cross correlation techniques. Lastly, third frequency of operation for IRNSS and thus a hot start are proposed. The results from the proposed methods are best till date. Using the relevant theory, these proposed methods are experimentally established and verified through testing and associated results. The research experiments make use of a reference hardware simulator and new software is developed to generate the proposed signals. To demonstrate the achievable benefits under each scheme, algorithms and new receiver software is written. Post integrated test results of each scheme are encouraging and will assist Line of Sight (LOS) TTFF performance drastically. In addition, this research presents some propositions that have drastic cost reductions. Finally, these results lead to recommendations on further research in the area of LOS TTFF.