Novel Techniques and Algorithms to Provide Efficient Single Frequency Ionospheric Corrections for Future Satellite Based Navigation Systems

摘要

Signal delay due to ionosphere is the major source of error in any satellite based navigation system. There are two kinds of users of satellite based navigation namely dual frequency users and single frequency users. The dual frequency users make use of the frequency dependent nature of ionospheric delay to eliminate most of the ionospheric error in their line of sight. On the other hand, the single frequency users have to use the corrections broadcasted by the navigation satellites to eliminate the ionospheric error in their line of sight. GPS (Global Positioning System) uses the global ionospheric model developed by Klobuchar for ionospheric error removal using eight ionospheric coefficients which are broadcasted once in a day. Similar model has been adapted to IRNSS (Indian Regional Navigation Satellite System) /NAVIC (NAVigation with Indian Constellation) wherein these eight ionospheric coefficients are estimated by indigenously developed technique using the Indian regional ionospheric data. In this paper, four new techniques and their respective algorithms are designed and developed for providing these ionospheric corrections in an enhanced way (with extra parameters along with the existing eight coefficients) for future satellite based navigation systems and thereby achieving better single frequency position accuracies. This involves estimation and broadcast of existing eight ionospheric coefficients along with extra ionospheric parameters identified. The extra parameters identified for each of the four techniques are, 1) calm time ionospheric delay (A_1) as a single parameter and ionospheric phase (A_3) as a single parameter, 2) A_1 as a set of coefficients and A_3 as a single parameter, 3) A_1 as a single parameter and A3 as a set of coefficients, 4) A_1 as a set of coefficients and A_3 as a set of coefficients. All these newly developed techniques are analysed for several days using IRNSS ionospheric data available from IRNSS Stations located over Indian region. The measure of improvement of the novel techniques over the existing coefficients is about 15-16% (approx) and over the GPS coefficients is about 92-94% (approx).