The aim of this paper is to describe a strategy to provide improved accuracy of primary navigation parameters to the Indian regional Navigational satellites. The broadcast parameters of the Navic satellites can be classified under two category, one is the validity period of 7200s called long period normal sets and second one is the validity period of 900s called short period contingency sets of primary navigation parameters. The Navic satellite constellation works with minimum number of synchronous satellites to provide the best user solution within India and boundaries. Thus the outage of any one or more satellites will increase the Dilution of Precision (DOP) and degrades the user solution for any sudden anomalous behaviour of the measurements. This anomalous behaviour (called events) arises due to on-board frequency variations, frequent planned Station Keeping (SK) operations because of synchronous orbits, IRNSS system time scale switch-over or the combination of events. In loop back the broadcast parameters accuracy was continuously monitored through Line of Sight (LOS) range error from the observed IRNSS ground reference stations range measurements. In begin conditions the Least square (Lsq) based solutions were accurate and the observed LOS error were as expected. But post the occurrence of any event, the accumulation of batch data starts freshly for least square solution. The obtained Lsq based solution was inaccurate due to lack of data under many circumstances. During the events occurrence to minimize the outage duration of the satellite contingency sets were generated using continuously running Kalman Filter based near real time estimation using one-way measurements. But the filter estimated state may not be optimum at the particular epoch. Hence a strategy of forward and backward approach (FBF) was adopted just before parameter uplink through sequential (KF) for adaptation of real behaviours of the measurements to providing an improved optimal solution.

러시아의 위성항법시스템인 GLONASS(GLObal NAvigation Satellite System)는 2011년 10월 이후 정상적으로 재가동되었으며 지속적으로 시스템 구성이 현대화되고 있다. 최근 2017년 10월 16일 발사된 GLONASS 752 위성(GLONASS-M)이 정상 작동됨에 따라서 2세 대 위성인 GLONASS-M 22기와 3세대 위성인 GLONASS-K 1기로 총 24기 위성이 구축되었다. 따라서 본 논문은 현재의 GLONASS 위성 항법시스템의 항법위성으로부터 실데이터를 수신하여 항법파라미터 특성 및 성능을 분석하고자 하였다. 수신된 데이터를 분석한 결과 항상 항법위성 5~11기가 동시에 가시선상에 있어서 항법신호를 수신할 수 있음을 확인하였으며, 실험에 이용된 위성들의 DOP(Dilution of Position)는 GDOP, PDOP, HDOP, VDOP, TDOP 각각 2.790, 2.424, 1.169, 2.123, 1.381을 얻었다. 또한 수신된 데이터의 위치 정밀도를 분석 한 결과 표준편차 1.4m로 매우 우수하였다. 결과적으로 GLONASS와 GPS(Global Positioning System)는 성능이 거의 동일하며 향후 GLONASS 시스템의 이용 확대가 기대된다.