Method and arrangement for detecting the presence of a training signal in a modem receiver.

摘要

For rapidly detecting a periodic training signal in a modem receiver, delay line storage (21) is provided for a signal section which is equal to one training signal period (q • M samples) plus an addi- tipnal adjacent window (q • W samples). Thus, the stored signal section includes two windows (17', 19) which are offset by one training signal period and which are similar if a training signal is present. In evaluation means (41) connected to the two windows (17', 19), two auxiliary signals (z,, z2) are generated - (61, 65) which represent the signal energy and the correlation, respectively, of the samples in the two windows. From the auxiliary signals, a dissimilarity metric (z,) is derived (69) and is compared (73) to a given threshold for generating an indicator signal - (CYC) which becomes active when a training signal is present, i.e. when the two window contents are similar and the metric (z,) falls below the threshold. A carrier frequency offset estimate (Δ f) is also derived from the second auxiliary signal (z2).