Design And Implementation Of The Algorithm Of GPS Related Positioning Based On Precise Ephemeris

The traditional GPS point positioning uses the satellite orbit parameters and satellite clock corrected value provided by the broadcast ephemeris and pseudo range measured by C/A code. This method only needs a GPS receiver to obtain the receiver position coordinates in WGS-84 coordinate system. But satellite positions calculated by broadcast ephemeris solution have a deviation of a few meters to tens of meters from actual position and the error of satellite clock correction is ±20ns. Precise ephemeris is a file including the high accuracy location of the satellite provided by a global GPS service organization which has higher accuracy of satellite position than the broadcast ephemeris can provide. However access to the updating file has a certain delay.This paper is a pre-research project from the internship company. The project is mainly studied for real-time receiver positioning using precise ephemeris. The precise ephemeris file can provide satellite position precision, thus improving the precision of GPS positioning,but cannot meet the application environment that requires real-time precise positioning for the delay of the file. The combined positioning process includes absolute positioning using precise ephemeris and relative positioning, can use relative positioning calculating real-time results after the absolute positioning calculating the absolute positioning results. Therefore the real-time positioning results can be get as well as the precision of the results being high.In this paper, the absolute positioning including the precise satellite position and precise clock offset provided by precise ephemeris and C/A code pseudo range in traditional GPS single point positioning is used to calculate the position of the receiver coordinates. The advantage of this is that the operation flow is convenient and the calculation precision is small,and the accuracy of the final result is higher than that of the traditional GPS single point positioning. This paper uses Lagrange interpolation method to calculate satellite position at any time of the day from the original satellite location provided of every 15 min, thus ensuring that satellite position data can be obtained at the times that the receiver is receiving satellite data. This method is easy to implement and time-consuming small,and ensure the accuracy of the location. Besides precise ephemeris, Broadcast ephemeris and RINEX ephemeris are used to calculate the position of the satellites. The results of the three methods mentioned above are compared to verify that the accuracy of satellite position provided by3 precise ephemeris is higher.In the study of relative positioning, the receiver position is obtained by absolute positioning results, and the vector between the position of the known receiver and the unknown receiver is calculated. With the two known factor the position of the unknown receiver can be solved.This course is real-time positioning. Position of other mobile station receiver can be acquired quickly after knowing the position of base station receiver. In this process, the solution of the two receiver position vector is the key, which is called the baseline vector solution. In this paper, LAMBDA algorithm and integer least square method are used to compare the results of integer ambiguity in the baseline vector solution,which verifies that LAMBDA algorithm advances the calculation speed with the results precision unchanged.