Choosing the coherent integration time for Kalman filter-based carrier-phase tracking of GNSS signals

Carrier phase-based positioning using Global Navigation Satellite System (GNSS) signals can provide centimeter-level accuracy; however, to do so requires robust, continuous tracking of the phase of the received signal. The phase-locked loop is typically the weakest link in GNSS signal processing, with frequent cycle slips and loss of lock occurring at lower signal-to-noise ratios. One way to improve the signal-to-noise ratio is to increase the coherent integration time; however doing so reduces the loop update rate, thereby degrading performance. This paper investigates this trade-off between sensitivity and loop update rate by investigation of the Kalman filter-based tracking loop. It is shown that it is possible to choose an optimal integration time for a given application. A relatively straightforward procedure is given to determine this optimal value. The results are confirmed through real-time kinematic processing of live satellite signals.