The differential code bias (DCB) is the differential
hardware (e.g., the satellite or receiver) delay that occurs between
two different observations obtained at the same or two different
frequencies. There are two approaches used to estimate DCBs for
receivers and satellites: the relative and absolute methods. The
relative method utilizes a GPS network, while the absolute method determines DCBs from a single station (zero difference).
Three receiver types based on the pseudo-range observables were
used here to collect the GPS data: Codeless Tracking, Cross
Correlation, and Non-Cross Correlation styles. According to its
types, GPS receivers have responded to restrictions on the GPS
signal structure in different ways. The main goal of the current
research is providing a method to determine the DCBs of GPS
satellites and dual frequency receivers. The developed mathematical model was based on spherical harmonic function and
geometry-free combination of pseudo-range observables (C/A
or/and P-code) according to receiver type. A new elevationdependent weighting function with respect to GPS satellites in
our algorithm was applied. The applied weighting function was
used to consider the quality variation of satellite DCBs, which is
caused by pseudo-range measurement errors. The code of the
proposed mathematical model was written using MATLAB
and is called Bzero difference differential code bias estimation
(ZDDCBE)^. This code was tested and evaluated using data
from IGS GNSS stations and different types of GPS stations
out of IGS network installed in Egypt and Saudi Arabia. The
estimated values from the ZDDCBE code show a good agreement with the IGS analysis centers with a mean error of estimation for the receiver DCB equal 5.94%. Therefore, the ZDDCBE
code can be used to estimate the DCB for any type of receiver
regardless if the receiver is from IGS network or not. |
