Estimation of the carrier frequency error of a π/4 DQPSKtransmitter signal using the intersymbol correlation method

摘要

This papers discusses an algorithm to estimate the modulationaccuracy of transmitters using π/4 DQPSK modulation, one of thedigital modulation methods in use. In the past, modulation accuracy hasbeen measured using a estimation method based on linear approximation.However, the need to repeat calculations with this method made itdifficult to achieve high speed. Another problem involved with theestimation method using linear approximation was the large estimationerror that occurred if the offset between the transmitted carrierfrequency and the nominal frequency is large, or if the S/N ratio issmall. A new algorithm was developed to estimate the carrier frequencyerror by calculating the intersymbol correlation. Because it does notrequire iteration, this intersymbol correlation achieves a two-foldimprovement in speed over the linear approximation method, and exhibitsonly a small error, even when the carrier frequency error is large orthe S/N ratio is small