Autonomous Navigation Systems used in missiles and other high dynamic platforms are mostly dependent on the Global Positioning System (GPS). GPS users face limitations in terms of missile high dynamics and signal interference. Receiver’s tracking loops bandwidth requirements to avoid these problems are conflicting. The paper presents a novel signal frequency and phase tracking algorithm for very high dynamic conditions, which mitigates the conflicting choice of bandwidths and reduces tracking loop measurement noise. It exploits the flexibility of fuzzy control systems for directly generating the required Numerically Controlled Oscillator (NCO) tuning frequency using phase and frequency discriminators information and is labeled Fuzzy Frequency Phase Lock Loop (FFPLL). Because Fuzzy Systems can be computationally demanding and an Inertial Navigation System (INS) is often onboard the vehicle, an assisted INS Doppler version has been designed and is also proposed. Assessment of the new GPS tracking method is performed with both simulated and experimental data under jamming conditions. The main enhancements of the proposed system consist in reduced processing time, improved tracking continuity and faster reacquisition time. 1. Introduction It is often desirable to track carrier phase information for GPS-based applications that require a high level of measurement accuracy even if carrier phase tracking is more difficult than tracking the frequency. A Phase Lock Loop (PLL) can be used to track the incoming GPS carrier phase and hence extract the modulated navigation data. If the GPS receiver is expected to perform at high levels of dynamics, the PLL can be aided by a Frequency Lock Loop (FLL) as a FLL-assisted PLL structure [1]. Figure 1 [2] shows the basic block diagram of a standard FLL assisted PLL. The two first multiplication stages are required to wipe off the input signal carrier and Pseudo-Random Noise (PRN) code required for any Code Division Multiple Access (CDMA) communication system. A local replica of the PRN code is provided by the Delay Lock Loop (DLL) and is used to remove the PRN sequence from the incoming signal. The frequency and phase loop discriminators are used to estimate the frequency and phase error, respectively, between local and incoming carriers. The discriminator’s outputs, which represent the frequency and phase errors, are then filtered and used to tune the Numerically Controlled Oscillator (NCO), which adjusts the frequency of the local carrier wave. In this way, the local carrier wave tends to be a precise replica of the input
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