Carrier and clock combined synchronization method for OQPSK modulation

Abstract

The invention provides a carrier and clock combined synchronization method for OQPSK modulation. The method comprises the following steps of: performing coarse estimation on carrier frequency by use of the cyclic spectrum characteristic of an OQPSK signal; performing series expansion on the error function of a COSTAS loop and simplifying the error function; and estimating the residual carrier frequency offset based on the maximum likelihood principle, and meanwhile, estimating the clock. According to the carrier and clock combined synchronization method for OQPSK modulation, the coarse frequency offset of the carrier is obtained by use of a square spectrum estimation method and quick locking of a large frequency offset signal is realized; the error function of a carrier synchronization loop is expanded in Taylor series and optimized so that the complexity of an algorithm is greatly reduced under the condition of guaranteeing the synchronization performance, and the accuracy of a signal synchronization result is ensured by use of the carrier synchronization loop so that the signal length needed by calculating the cyclic spectrum of the signal can be reduced; based on the maximum likelihood principle, sliding accumulation is performed on two paths of IQ signals after filtering time delay and an angle of amplitude is calculated, and meanwhile, the residual carrier frequency offset and the clock phase are estimated, so that mutual influence of clock estimation and carrier estimation is avoided.

Description

technical field [0001] The invention relates to the field of signal modulation, in particular to a combined carrier and clock synchronization method for OQPSK modulation. Background technique [0002] OQPSK is a constant-envelope digital modulation technique, and the quadrature branch symbol and the in-phase branch symbol are offset in time by a bit interval, that is, half a symbol period. The OQPSK signal eliminates the radian deflection phenomenon of adjacent symbols. In the actual communication system with limited bandwidth, the envelope fluctuation is small. After passing through the nonlinear power amplifier, there will be no obvious power spectrum sidelobe growth effect, and it has high spectrum utilization and High power utilization features. [0003] The expression of the OQPSK signal is: [0004] s ( t , θ ) = P [ I ...

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Problems solved by technology

[0024] The purpose of the present invention is to propose a carrier and clock joint synchronization method for OQPSK modulation, to solve the mutual interference problem of carrier phase synchronization and clock synchronization in OQPSK modulation, and to realize fast capture of carrier frequency at the same time, and after capture, there is a very small phase jitter

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