| 摘要 |
PURPOSE:To attain compensation of a frequency offset with a wide pull-in range without the use of AFC(automatic frequency control) by feeding back frequency offset information predicted from a pilot symbol phase fluctuation quantity of a base band signal to a local frequency oscillation section so as to avoid cut-off of part of a signal by an LPF in an on-land mobile communications QAM(quadruple amplitude modulation). CONSTITUTION:A phase fluctuation quantity from a past pilot symbol is observed from an output of a pilot symbol detection section 3 and average phase fluctuation quantity is obtained from the phase fluctuation quantity to predict an offset frequency by an offset frequency detection section 5, and an output of the offset frequency detection section 5 is given to a local frequency oscillator section 6 for quasi- synchronization detection to control the oscillating frequency thereby compensating the frequency offset. Moreover, the controlled input of the local frequency oscillator section 6 is switched to an initial value detection section 7 at the time of start and after the initial value detection section 7 detects an initial value to switch an offset frequency detection section 5 with changeover means S1, S2, S3 and the initial value detection section 7 has a wide frequency tracking range at first and thereafter, narrow down the range gradually. |
