Abstract
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.
Highlights
It is often desirable to track carrier phase information for Global Positioning System (GPS)-based applications that require a high level of measurement accuracy even if carrier phase tracking is more difficult than tracking the frequency
If the GPS receiver is expected to perform at high levels of dynamics, the Phase Lock Loop (PLL) can be aided by a Frequency Lock Loop (FLL) as a FLL-assisted PLL structure [1]
A new approach for Fuzzy Logic-based GPS signal tracking using Inertial Navigation System (INS)-based Doppler aiding is presented as a modification of the original fuzzy tracking system
Summary
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. Another mathematical tool that suits coupling of INS and GPS signals is Fuzzy Logic It has already been used in some research for enhancing the performance of an integrated GPS/INS systems but, to the authors’ knowledge, existing research has not focused on improving the tracking loop in the context of interference mitigation [11, 12]. The ultratightly coupled integration technique [15,16,17], used combines the INS/GPS solution and the GPS signal tracking functions into a single estimation algorithm in which the INS measurements are fed back to the receiver to decrease GPS signal tracking errors and enhance GPS positioning performance This scheme helps the receiver tracking loop for retrieving signal lock if it is lost due to interference or jamming. It is shown that the main enhancements of the INS-assisted Fuzzy based tracking loop consist in a reduction of processing time, better tracking continuity, and faster reacquisition time, characteristics that are of fundamental importance for the most high dynamics applications
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