# An Enhanced Non-Coherent Pre-Filter Design for Tracking Error Estimation in GNSS Receivers  
[PERSON]  
1 College of Automation, Harbin Engineering University, Harbin 150001, China; [EMAIL_ADDRESS]. navigation accuracy of GNSS receivers in harsh environments such as weak signal condition and highly dynamic scenario. A classical GNSS signal is composed of a carrier, pseudo-random noise code (PRN code), and binary navigation message [9]. The GNSS receiver first estimates the PRN code phase, the phase of the carrier, and the carrier Doppler of the received GNSS signal. These parameters are referred to as GNSS signal parameters in the following. The estimation for GNSS signal parameters is done by the signal acquisition and tracking function of the GNSS receiver. The signal acquisition estimates GNSS signal parameters roughly in an opened-loop manner, while the signal tracking estimates these parameters accurately through closed-loop control [10]. A GNSS receiver must accomplish the signal acquisition before it switches to the signal tracking. After that, the GNSS receiver performs the measurement for pseudo-range, pseudo-range rate, and carrier phase according to the signal parameters estimated by signal tracking function. The physical meaning of pseudo-range and carrier phase is the relative distance between the GNSS receiver and navigation satellite, while the physical meaning of pseudo-range rate is the relative velocity between the receiver and the navigation satellite. The carrier phase, pseudo-range, and pseudo-range rate are referred to as GNSS measurement in the following. Meanwhile, the navigation message can also be extracted and demodulated to get the satellite ephemeris which can be used to calculate the position and velocity of navigation satellites. The above-mentioned signal processing--performed by GNSS receiver--can be referred to as the GNSS baseband signal processing. Finally, the GNSS receiver accomplishes the navigation computation to get the PVT parameters of the GNSS receiver itself through the GNSS measurements and GNSS satellite ephemeris. From the signal processing flow of GNSS receivers, it can be found that GNSS signal parameters estimation is the first step before the PVT solution can be obtained. Accurate signal parameters estimation is accomplished by tracking loops in the GNSS receiver. The tracking loops of the GNSS receiver include the carrier tracking loop and code tracking loop. Even though the tracking loops are able to accurately estimate the GNSS signal parameters, there still exits tracking error. The tracking error includes the carrier phase tracking error, carrier frequency tracking error, and code phase tracking error, which are referred to as carrier phase error, carrier frequency error, and code phase error for short in the following discussion. On the one hand, tracking error is the error signal of GNSS tracking loops that can be regarded as a kind of feedback control system. If the tracking error cannot be estimated accurately, it cannot be eliminated efficiently by the tracking loops. On the other hand, tracking error should be corrected in the GNSS measurement formulation phase. If the tracking error cannot be estimated precisely, the accuracy of GNSS measurements will decrease and the accuracy of PVT solution will subsequently decline. The tracking error estimation is especially crucial for low-cost GNSS receivers, because tracking error estimation of high accuracy will effectively improve the signal tracking ability and the accuracy of PVT determination. However, tracking error estimation is often corrupted by noise. That is because the tracking error is extracted from the noisy coherent integration and non-coherent integration, which are parts of GNSS baseband signal processing [11]. Generally, tracking error can be estimated by traditional discriminator or Kalman filter (KF)-based pre-filter.