# Detection of RINEX-2 Files With Mixed GPS L2P(Y)/L2C Carrier Phase Observations
## 6 Conclusions and Outlook  
The detection of mixed GPS L2P(Y)/L2C carrier phase observations in RINEX-2 files with non-aligned quarter cycle biases is performed best by analyzing fractional widelane ambiguities. Either of the MW linear combination or of the widelane carrier phase linear combination. The main advantage of an analysis in PPP mode lies in the simplicity of the processing setup since no baselines need to be formed. Its drawback comes from the dependence of the MW linear combination on code delays. Some receivers seem to possess MW code delays that do not fit to the satellite individual fractional bias corrections valid for the majority of the receivers.  
If mixed carrier phase observations are not aligned on the level of quarter cycles, the L2 bias can prevent ambiguity fixing. However, ambiguity fixing is often successful despite an L2 bias in long baselines or in PPP mode where fixing algorithms based on widelane and ionosphere-free linear combinations are used. Coordinate errors that reach the centimeter level occur with the GPS satellite constellation of early 2018, even in daily solutions, and mainly affect the height component. These coordinate errors depend on the geographical location of the station. There are regions where the coordinate errors average out and do not exceed 1 mm over a period of one day.  
The L2 quarter cycle problem can easily be resolved by carefully selected settings of GNSS receiver and RINEX conversion software. It would also disappear with the complete transition from data format RINEX-2 to RINEX-3. In a few years' time, all Block IIA and IIR satellites will have ceased operation. Furthermore, the US government restricted its commitment to support GPS P(Y) signals until at least two years after there are 24 operational satellites broadcasting L5, i.e., 24 satellites of Block IIF and III [16]. When P(Y) code signals are not available anymore, the L2 quarter cycle problem  
Figure 7: Epoch-by-epoch coordinate errors of station BIK0 (Bishkek, Kyrgyzstan) on DoY 150/18 due to L2 quarter cycle biases: ionosphere-free linear combination with ambiguities being fixed, estimation of tropospheric zenith delays enabled.  
vanishes. On the other hand, with the introduction of L1C on Block III satellites [1; 17], a new quarter cycle problem may occur in RINEX-2 files since L1C and the legacy L1C/A signal will be in quadrature.  
The data centers or station operators were informed about their stations with detected L2 quarter cycle problems. Receiver configuration or RINEX conversion software settings of several of the affected stations were adapted so that these stations do not produce any further defective RINEX-2 files.  
All observation data analyzed in this study were made available free of charge by one of the following institutions or data centers: International GNSS Service (IGS), Crustal Dynamics Data Information System (CDDIS), Geoscience Australia, EUREF Permanent Network (EPN), German Federal Agency for Cartography and Geodesy (BKG), and US National Geodetic Survey (NGS).  
The author declares no conflict of interest.