Comparison of Vector-Based Software Receiver Implementations with Application to Ultra-Tight GPS/INS Integration

This paper investigates three different Kalman filter implementation options to estimate signal tracking errors in a GPS receiver with particular emphasis given to the carrier phase. The three options are outlined in terms of the system and measurement models. Initial assessment of the different options is performed in scalar-tracking mode with strong signals to assess their relative carrier phase tracking performance. Each option is then evaluated in vector-tracking mode both with strong signals collected in the field and with attenuated signals collected with a hardware GPS simulator. Results indicate that only two of the three options are able to track incoming signals in vector-tracking mode. Furthermore, both options are shown to be able to track the carrier phase up to an attenuation of about 15 dB and still maintain a velocity solution accurate to a few centimeters per second.