| 摘要 |
<p>A method and device for measuring the slope of the envelope delay characteristic in a transmission channel. The slope is determined from a received measurement signal having a frequency spectrum that includes three rays at frequencies fo, f1 and f2, which are approximately located in the center and at the edges of the useful passband of the channel. At the output of the channel, the three components at frequencies fo, f1 and f2 are extracted from the received measurement signal, and the instantaneous phases psi 0, psi 1 and psi 2 of these three components are measured. The value of the slope S of the envelope delay characteristic is obtained from the relation <IMAGE> where phi o', phi 1' and phi 2' are the phases of the three rays at frequencies fo, f1 and f2 of the measurement signal sent over the channel. When the data transmission system employs double sideband-quadrature carrier (DSB-QC) modulation, the measurement signal is generated by causing the carrier to undergo successive phase changes of + pi /2 and - pi /2 radians at the signaling rate. The receiver includes a set of fixed equalizers and the appropriate fixed equalizer is selected as a function of the measured slope.</p> |
