Multi-GNSS real-time clock estimation using the dual-thread parallel method

The development of Global Navigation Satellite System (GNSS) promotes multi-GNSS real-time precise point positioning (PPP) which raises a strong demand for real-time precise clock products. The increase of navigation systems and satellites leads to an extremely large number of observations, ambiguities and other unknowns, which makes the traditional undifferenced (UD) clock estimation method much time-consuming. We need processing of high computation efficiency for multi-GNSS real-time clock estimation. To satisfy the demand of multi-GNSS real-time clock estimation, we introduce a dual-thread parallel algorithm that consists of two threads with difference computation efficiency. The slow thread runs the traditional UD method and updates all the parameters of satellite and receiver clock, ZTD and ambiguity at a rather low rate. The fast thread runs a reduced UD method to update satellite clocks in real-time, in which the ZTDs and ambiguities are corrected with the latest estimates from the slow thread. Multi-GNSS observations of 75 stations are collected from DOY 200 to 230, 2015 to test the proposed algorithm. The dual-thread parallel method requires an average time of 2 s at each processing epoch, which is much faster than the traditional UD method. The multi-GNSS clock solutions of the introduced method exhibit good agreement with the WUM final products, with the RMS better than 0.2 ns, which is comparable to that of the UD method. Multi-GNSS kinematic PPP tests based on the clock solutions verify the introduced method further. The clock solution of the parallel method is precise enough to support real-time multi-GNSS PPP, which is comparable to the UD method and better than the ED method.