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Abstract

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 .DELTA.{tilde over (f)}.sub.i 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 .DELTA.{tilde over (f)}.sub.i are stored into a shift register L-position long and averaged to obtain an estimated frequency error .DELTA.{circumflex over (f)}.sub.i used for recursively correcting the reference frequency of the local oscillator, as: {circumflex over (f)}.sub.i={circumflex over (f)}.sub.i-1+K.DELTA.{circumflex over (f)}.sub.i where K (0.ltoreq.K.ltoreq.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 .DELTA.{tilde over (f)}.sub.i. The content of the shift register is corrected after each non-null frequency correction by subtracting K.multidot..DELTA.{circumflex over (f)}.sub.i to all the stored terms .DELTA.{tilde over (f)}.sub.i. Besides the frequency is corrected upon the following optional conditions, each other independents: The number of terms .DELTA.{tilde over (f)}.sub.i having equal algebraic sign is greater than a constant .alpha. lower than L. The standard deviation .sigma. of the averaged terms .DELTA.{tilde over (f)}.sub.i is lower than .beta..multidot..sigma..sub.old, being .sigma..sub.old the .sigma. of the last non-null frequency correction, and .beta. a constant .gtoreq.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).

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First Claim