Some improvements to the conventional algorithms for
data aided frequency synchronisation in cellular systems are introduced in a new method
executable by the user equipments of various standards, i.e. 3GPP CDMA-TDMA, FDD mode at 3.84 Mcps, TDD mode at 3.84 Mcps, TDD mode at 1.28 Mcps; CWTS TD-SCDMA;
GSM / DCS / GPRS. The method begins to obtain the suboptimal frequency errors Deltafi using a well known formula which calculates the argument of the autocorrelation over a subset of the
baseband samples of the detected training sequence. The errors Deltafi are stored into a
shift register L-position long and averaged to obtain an estimated frequency error Deltafi used for recursively correcting the reference frequency of the
local oscillator, as: fi=fi-1+KDeltafi where K (0<=K<=1) is
a weighting factor. Contrarily to the simple averaged error of the prior art, a sign criterion is used by which the average is performed on the only terms having the most recurrent algebraic sign among the stored terms Deltafi. The content of the
shift register is corrected after each non-null
frequency correction by subtracting K.Deltafi to all the stored terms Deltafi. Besides the frequency is corrected upon the following optional conditions, each other independents: The number of terms Deltafi having equal algebraic sign is greater than a constant alpha lower than L. The standard deviation sigma of the averaged terms Deltafi is lower than beta.sigmaold, being sigmaold the sigma of the last non-null
frequency correction, and beta a constant >=1. After a minimum number gamma of iterations between two non-null frequency corrections are spent, being gamma a constant comprised between 1 and L. According to another variant the iterations of the recursive update are subdivided into an initial group with a higher K value for achieving fast convergence and a subsequent group with a lower K for achieving the required accuracy (FIG. 13).