Estimable phase and code biases in the frame of global multi-GNSS processing

Signal biases are hardware delays that occur during the transmission and reception of GNSS signals. On the satellite side, there is a delay between the generation of a signal and its transmission at the antenna. The same is the case on the receiver side, where a delay occurs between signal reception at the antenna and the actual measurement of a specific signal in the receiver. As the name suggests, code biases refer to the delays affecting code observations. Similarly, phase observations are affected by phase biases. In general, signal biases differ per constellation, satellite, frequency, signal attribute, as well as receiver hardware and settings.

The main issue with signal biases is that they are usually not known. Therefore, they have to be estimated during GNSS processing. However, the relative nature of GNSS observations prevents the estimation of absolute signal biases. This results in several rank deficiencies in the normal equation system when signal biases are estimated together with other geodetic parameters in a global multi-GNSS processing.

We present a general approach based on eigenvalue analysis to solve these rank deficiencies. Therefore, the co-estimation of pseudo-absolute transmitter and receiver signal biases in our multi-GNSS processing becomes possible. This approach also enables ambiguity resolution of GLONASS phase obervations.