Abstract: The multi-constellation global navigation satellite system precise point positioning(GNSS PPP) technology has been extensively and deeply applied in the field of time transfer. In environments such as time comparison in time keeping laboratories and mobile time comparison tests at fixed sites, the precise coordinates of the receiver's antenna can be measured in advance. When performing GNSS PPP calculations under these conditions, the known high-precision coordinates can be used to accelerate the convergence time of the time transfer result. A method is proposed that uses the known 3D precise coordinates as the initial parameters of the Kalman filter. The corresponding system uncertainty, the elements of the Kalman filter covariance matrix, is set to small values. This reduces the impact of 3D coordinate calculation on the overall convergence process. The results show that, with known precise coordinates, the proposed method improved the convergence speed by approximately 30%～50% compared to traditional GNSS PPP time comparison methods. The accuracy and stability of the time comparison after convergence are comparable to traditional GNSS PPP. The RMS can reach the nanosecond level, and the stability can reach 1E-13 per hour.

Key words: multi-constellation global navigation satellite system precise point positioning, time and frequency, GNSS