Analysis of the digital null-seeker architecture's steady-state error for GNSS receivers
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Abstract
In this paper, the architecture of closed-loop synchronizers is studied. For a GNSS (Global Navigation Satellite System) receiver, the fine estimation of the code delay and Doppler frequency is generally performed by two concatenated null-seekers, the PLL (Phase Lock Loop), and the DLL (Delay Lock Loop). The null-seeker is implemented, tested and analyzed in a software receiver. The noise equivalent bandwidth, integration time and different incoming signal structures are considered for testing and performance evaluation. Different tests have been performed by changing the input signal from a step unit function to a ramp signal and finally to a parabolic shaped signal. The noise-free steady state value of estimation error is evaluated. The type of loop filter defines the tracking capability of the loop. The estimation error must quickly reach zero for a certain input model and any initial error, in the absence of noise.
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