FPGA Implementation of an FFT-Based Carrier Frequency Estimation Algorithm

Abstract

Carrier synchronization is an essential part of digital communication systems. In essence, carrier synchronization is the process of estimating and correcting any carrier phase and frequency differences between the transmitted and received signals. Typically, carrier synchronization is achieved using a phase lock loop (PLL) system; however, this method is unreliable when experiencing frequency offsets larger than 30 kHz. This thesis evaluates the FPGA implementation of a combined FFT and PLL-based carrier phase synchronization system. The algorithm includes non-data-aided, FFT-based, frequency estimator used to initialize a data-aided, PLL-based phase estimator. The frequency estimator algorithm employs a resource-efficient strategy of averaging several small FFTs instead of using one large FFT, which results in a rough estimate of the frequency offset. Since it is initialized with a rough frequency estimate, this hybrid design allows the PLL to start in a state close to frequency lock and focus mainly on phase synchronization. The results show that the algorithm demonstrates comparable performance, based on performance metrics such as bit-error rate (BER) and estimator error variance, to alternative frequency estimation strategies and simulation models. Moreover, the FFT-initialized PLL approach improves the frequency acquisition range of the PLL while achieving similar BER performance as the PLL-only system.