Precision Analysis of CNAV Broadcast Ephemeris and Its Impact on the User Positioning

摘要

GPS broadcast ephemeris error is an important factor affecting the real-time positioning accuracy. Since April 2014, the IGS provided two new broadcast ephemeris products, namely LNAV (Legacy Navigation Message) and CNAV (Civil Navigation Message). Compared with LNAV, CNAV was broadcasted only on Block IIR-M and IIF satellites. This paper introduces the parameters of satellite orbit calculation in CNAV, and algorithm of satellite orbits calculation is introduced by using CNAV broadcast ephemeris. CNAV satellite orbits and clocks of one year are calculated and evaluated by using the IGS precise products as reference. Results show that mean and RMS of CNAV orbits error is less than 0.4 and 2 m for all three components, respectively; RMS of 3D orbits error is about 3 m. RMS of CNAV satellite clock error is about 1.5 ns. CNAV SISRE is around 0.6 m. User pseudo-range positioning using CNAV shows similar performance as the LNAV.