| 摘要 |
<p>A method of, and a receiver for, detecting the presence of digitally modulated data signals in which the receiver is periodically energised to detect the presence of the signals. The received signals/noise are converted using a quadrature frequency translation stage (16, 17, 18) into a complex signal which after differential decoding (28) contain n samples for each transmitted bit. A running sum of successive groups of m samples, where m < n, is obtained and an absolute value (Xi) of each group is derived. A weighting value (Wi) is selected by comparing each absolute value with predetermined statistics of expected values and the weighting value selected is multiplied by the associated absolute value to produce a product (S). The product is compared in a comparator (56) with a further threshold level (58) to derive an indication of the presence of data in the received signals. If the indication is negative the receiver is powered down to save power.</p> |
