METHOD OF EFFECTING CHANNEL ESTIMATION FOR A FADING CHANNEL WHEN TRANSMITTING SYMBOL SEQUENCES

摘要

Symbols (y(n-L)) in a symbol sequence transmitted via afading channel are estimated (~(n-L)) in an equalizer havinga channel estimating filter (CEST). An error signal (e(n))influences an adaptation circuit (10) which controlsadjustable coefficients (7) so as to form a channel estimate(c1(n), c2(n) c3(n)), which is adapted during the whole ofthe symbol sequence. The adaptation circuit (10) performs anadaptation algorithm, which is influenced by mean energyvalues (U(n)) obtained from the channel estimate in amean-value-forming circuit (15). Subsequent to fading theadaptation algorithm is able to control the coefficients (7)so that one of the coefficients will erroneously dominate thechannel estimate, with erroneous estimation of symbols(~(n-L)) as a result. This is counteracted by selecting thelargest of the mean energy values U(n)), this largest valueinfluencing the adaptation algorithm (10). When the signalstrength of the transmitted symbols falls beneath a thresholdvalue, the coefficient which dominated the channel estimate,for instance the first coefficient (c1(n)), is sustained toalso dominate after fading and the remaining coefficients areset to zero: