| Summary: | 碩士 === 國立臺灣大學 === 電機工程學研究所 === 93 === Abstract
GPS is an accurate navigating system and generally used in civilian or military applications. But GPS receiver performance is usually degraded by intentional or unintentional RF interference. The interference may cause the navigation error and even saturate the receiver.
In this thesis, we use overlapped fast Fourier transform (OFFT) to simulate the performance of narrowband interference suppression. First, fast Fourier transform (FFT) can translate time sequence after analog to digital converter (ADC) to frequency domain. Then excision processing suppresses interference power in the spectrum. Inverse fast Fourier transform (IFFT) reconstruct the time sequence after interference excision. Besides interference suppression processing, in order to match specifications of the GP2015 and GP2021 chips, we design the frequency translation to transfer the central frequency of the GPS signal from 1.16MHz to 1.405MHz. The utilization of the phase-shifted method completes single sideband modulation.
Finally, according to the fixed-point simulation, we choose Altera Stratix EP1S25F780C5 chip to design the hardware circuits. Altera Quartus Ⅱ software is utilized for logic synthesis, circuit place and route and timing simulation. The Matlab software is used to verify the design of the narrowband suppression circuit and the frequency translation circuit. The simulation and the verification can show that overlapped fast Fourier transform is a powerful approach to suppress the single tone and multi-tone narrowband interference. But it costs much latency and needs much hardware cost.
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