Introduction

All GNSS signals transmitted by a satellite are referenced to a clock within that satellite. Each broadcast signal potentially also has a different electrical path that it follows within the satellite. The methods for accounting for these biases are referred to as Inter-Signal Corrections (ISCs). Applying an ISC to any signal other than the reference signal removes the electrical path group delay bias, relative to the reference signal, restoring that signal's time stamp tie to the SV clock.

Getting ISC Data

ISC data can be obtained from broadcast navigation messages, or from product files such as the daily DCB/DSB solutions generated by the German Space Operations Center.

ISC data must be requested using a combination of the following information:

Originating signal identifier
Time of interest

The above may be used in a call to NavLibrary::getISC() to obtain the desired data. These biases are always identified by a pair of signals, however, in the NavLibrary::getISC() implementation, a single ObsID representing the originating signal identifier may be used. In this case, the system's (constellation's) reference signal will be understood to be used as the target signal identifier.

Sign Convention

The following sign convention is used by InterSigCorr:

$\begin{eqnarray*} {bias} &=& {pseudorange} - {true\ range} \\ {pseudorange} &=& {true\ range} + {bias} \\ {true\ range} &=& {pseudorange} - {bias} \end{eqnarray*}$

This convention is the same as used in the SINEX_BIAS file format, and is also in common with corrections broadcast by most (if not all) GNSSes.