# Detection of RINEX-2 Files With Mixed GPS L2P(Y)/L2C Carrier Phase Observations
## 4 Observation Data Sets and Detection Results
L2 carrier phase observations of the other 71 station files exhibited no L2 quarter cycle problems (open symbols in Figure 4). Some of them showed large systematic biases between L2C and non-L2C satellites, which cannot be explained by phase biases. Systematic delays of the code signals are suspected to be the main cause. The validation by Algorithms 2 and 3 reveals that Algorithm 1 produces reliable detection results if the absolute value of the computed bias is larger 0.125 WL cy and its standard deviation is smaller than 0.03 WL cy. If the standard deviation is larger, correct and defective RINEX-2 files cannot always be reliably separated using Algorithm 1. Then, the other algorithms must also be applied, which considerably increases the necessary effort. The data centers of CDDIS, EPN/BKG, and NGS contain RINEX-2 files affected by the L2 quarter cycle problem, whereas the Australian data center, APREF, does not (Table 3). This is true for those files that are available at APREF only. As mentioned before, files present at CDDIS and other data centers were assigned to CDDIS and the affected files are listed for this data center. In fact, even APREF contains a few affected RINEX-2 files, which were copied from other data centers. Figure 4: Estimated L2 biases between non-L2C and L2C measurements according to algorithm 1, validations (filled symbols) or rejections (open symbols) by Algorithms 2 or 3. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Data Center**} & **Number of Station** & **Number of RINEX-2 Files with** \\  & **Files Processed** & **L2 Quarter Cycle Problem** \\ \hline CDDIS & 495 & 23 (4.6\%) \\ APREF & 186 & - \\ EPN/ BKG & 223 & 13 (5.8\%) \\ NGS & 1720 & 36 (2.1\%) \\ \hline Sum & 2624 & 72 (2.7\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Detection Results by Data Center. Within the networks of EPN/BKG and NGS, most affected stations are geographically clustered: Spain, Tennessee, Alabama, and Nevada (Figure 5). In both networks, station operators are in charge of certain regions, and there they tend to have the same receiver configuration and software setups. Most affected stations files from CDDIS belong to a single agency that operates receivers from one manufacturer and probably uses similar software setups. All affected stations are equipped with receivers from just a small number of manufacturers. The number of receiver manufacturers without any affected stations is much longer (Table 4). It should be emphasized that the L2 quarter cycle problem is not expected to be caused by faulty receivers but rather by inadequate receiver configuration or, probably more often, by using incorrect option settings of the RINEX-2 conversion software. Affected stations with TPS or Leica/NovAtel receivers exhibit a MW bias of around \(-0.25\) cycles, whereas most Javad receivers show quarter cycle biases of the opposite sign (Figure 4). This is in accordance with earlier findings by [PERSON] et al. (2012) [15] and indicates that the RINEX-2 L2 quarter cycle problem has probably existed for many years and is a persistent one. Independent of the L2 quarter cycle problem, the results illustrated by Figure 4 contain valuable information on the ability to fix MW ambiguities in PPP data processing. Small standard deviations indicate that the applied \(FCBMW\),\(CIP2\) corrections are valid for this observation data set, and MW ambiguity fixing is not affected by any biases. Of all the examined station files, 97.3% produced very small standard deviations of less than 0.04 WL cy. The remaining 2.7%, however, had larger standard deviations, some even exceeding 0.08 WL cy. Here, remaining code delays can prevent successful widel