Bernese GPS Software Version 5.0 - Bernese GNSS Software

13. Differential Code Biases
13.1 Introduction
For all precise GNSS applications which are supported by code observation data, existing
code (or pseudorange) biases represent a non-negligible error source. This includes “timeoriented”
applications such as high-precision GPS satellite clock estimation as well as time
transfer among GPS observing stations, but also code-based resolution of carrier phase
ambiguities. For ionosphere analysis, consideration of interfrequency code biases is an issue
for a long time.
13.1.1 Various Code Observable Types
Geodetic GNSS receivers provide C/A code, subsequently addressed as C1, plus a subset of
the following code observable types:
• P1,
• P2,
• X2, equivalent to C1+(P2−P1).
For completeness, it should be mentioned that GPS satellites of the Block IIR-M generation
transmit a civil code signal on the second frequency, which is commonly addressed as C2
(respective L2C in the RINEX 3 standard).
13.1.2 Different Receiver Classes
We have to distinguish between three receiver classes:
• P1/P2—receivers providing C1, P1, P2,
• C1/X2—so-called cross-correlation (CC) receivers providing C1 and a particular linear
combination of code observables (denoted here with X2),
• C1/P2—modern generations of receivers providing C1 and P2.
Note that it is common practice to disregard C1 code data coming from the first receiver
class.
Bernese GPS Software Version 5.0 Page 279