| 摘要 |
An apparatus for, and method of detecting a carrier signal of a QAM signal. The method comprises the steps of: (a) sampling the digital-in-phase binary components I and Q of an incoming QAM modulated signal, (b) down-converting the components I and Q to a baseband frequency, (c) scaling the components I and Q so that the I and Q magnitudes are within a range of those expected for the constellation, (d) deriving the average times-n phase for the constellation, (e) determining the phase of the carrier signal, and (f) determining the frequency of the carrier signal by calculating the maximum amplitude component in the complex Fourier transform F of data from the samples. The average times-n phase is derived by calculating the complex vector PHI where PHI is given by formula (I) where is an index running over symbols in the constellation; is the √-1; rp is the radius to the constellation point; &phgr;d is the phase of the constellation point; is the constellation symmetry (For example 4 for four-fold symmetry, e.g., for 16QAM); and, is a smoothing function. The frequency of the carrier signal is calculated according to the following equation F(&ohgr;)= SIGMA dWdΦ*(rd)exp(in&phis;d-i&ohgr;d) is the amplitude of a data sample; Φp is the phase of a data sample; Wd is a (real positive) windowing function (e.g. Hanning); &ohgr; is angular frequency = 2&Pgr;f, where f is the real frequency. |
