A GNSS Software-Defined Receiver with Vector Tracking Techniques for Land Vehicle Navigation

This paper presents a vector tracking (VT) architecture based on global navigation satellite system (GNSS) software-defined receiver (SDR). The incoming signal is firstly acquired with the partially matched filter algorithm. Then, the frequency lock loop (FLL) which can tolerate higher dynamics in tracking is exploited to initialize the tracking process of the GNSS SDR. After the incoming signal is stably being locked, the FLL will be replaced by the phase lock loop (PLL) to output the more accurate estimation of the carrier phase error. The measurements, i.e., pseudo-range, carrier phase, Doppler, carrier-to-noise density ratio (C//N-0), etc., will subsequently be obtained after the bit and frame synchronization procedures. Furthermore, the weighted non-linear least square (WNLS) method is adopted in this work to compute the navigation solutions on the condition that the number of the space vehicle (SV) is adequate, i.e., more than four SVs for a separate navigation system, global positioning system (GPS), to offer reliable solutions in terms of three-dimension (3-D) positions and clock bias, and 3-D velocities and clock drift. The weighted matrix would be formed with two approaches, and the elevation angle and the C/N-0 will be taken into consideration to construct it, respectively. After that, the user velocity estimations and the receiver clock drift with the satellite positions and velocities from the ephemeris in the current channels will be fed back to the carrier numerically controlled oscillator (NCO). Moreover, the code NCO would also be assisted by the formed local frequency replica with the carrier NCO. Therefore, a vector tracking architecture can be finally given in this way. Both delay lock loop (DLL) and PLL are controlled by positioning, velocity, and time (PVT) feedbacks. Field tests demonstrate the performances of the proposed VT-based GNSS SDR for the land vehicle navigation.