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GPS C1, P1 and P2 Codes and Receiver Types
|Title||GPS C1, P1 and P2 Codes and Receiver Types|
|Author(s)||J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.|
|Year of Publication||2011|
As explained in GPS Services, under Anti-Spoofing (A/S) conditions, P-codes (P1, P2) are encrypted to (Y1, Y2) for non-authorised users. Nevertheless, many commercial receivers are able to provide P1, P2 measurements among the C1. The generation of such P1, P2 codes under A/S conditions depends of the code tracking technology, which must be taken into account for a correct DCBs handling.
For instance, Cross Correlated receivers (e.g. Rogue and Trimble 4000 models) provide a synthetic P2 code generated from C1 code and the cross correlation of encrypted Y2-Y1 codes (roughly speaking: P2:=C1+[Y2-Y1]). This leads to a P2 code measurement associated to C1, not P1, and thence, it must be corrected by the Differential Code Bias to have a consistent P2 measurement.
On the other hand, these receivers do not provide the P1 code, but the C1 code. Thence, the must be added to this C1 code to emulate a consistent P1 code measurement. In this way, the interfrequency bias will cancel when computing the Code ionosphere-free combination (PC) of such P1 and P2 codes.
Three different kind of receivers are usually considered (see more details in [Schaer, S. and Steingenberger, P., 2006] ).
- Type 1: Cross correlated receiver:
- The C1 and P2 measurements must be corrected by the :
- Type 2: Receivers reporting C1 in place of P1:
- The C1 must be corrected by the :
- Type 3: Receivers reporting L1,L2,P1,P2 as consistent set
- No bias removal is needed.
A RINEX conversion utility cc2noncc.f is provided by IGS to easily make code measurements consistent with P1/P2 data by applying satellite-dependent P1-C1 bias corrections. This tool is available at https://goby.nrl.navy.mil/IGStime/cc2noncc/cc2noncc.f
These DCBs corrections are only required for geodetic (high accuracy) surveying, as its impact on the coordinates accuracy is at the level of few millimetres.
- ^ [Schaer, S. and Steingenberger, P., 2006] Schaer, S. and Steingenberger, P., 2006. Determination and Use of GPS Differential Code Bias Values.