Real time implementation of Vector Delay Lock Loop on a GNSS receiver hardware with an open software interface

In standard GNSS receivers scalar tracking is used to track the satellite signals. In this approach each signal and satellite is tracked independently. The vector tracking (VT) algorithm uses information about the movement of the antenna to calculate a combined tracking solution for all signals. This makes the tracking more stable and robust against shadowing and multipath effects. It delivers an improved navigation solution, which is less noisy. Present developments in VT have already shown good results in post processing with software-defined radio (SDR). This paper presents the results of the real-time VT developed on a GNSS hardware platform. The theory and the implementation of the used Kalman filter (KF) is described. The hardware setup, using a GNSS receiver with an open software interface is presented. First results using vector delay locked loop (VDLL) in a signal generator scenario with short-shadowed satellites are shown. It is described how the VDLL with an extended Kalman filter (EKF) calculates a navigation solution. This output is then used to compute the code numerical correlation oscillator (NCO) values for multiple space vehicles simultaneously and to steer the hardware NCOs in the receiver to close the tracking loops. The code tracking loops have to be closed simultaneously and as fast as possible to avoid timing issues.