Two pilot frequency control for communication systems
US4479256A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Oct 4, 1982 |
| Grant date | Oct 23, 1984 |
| Priority date | — |
| Expiry date | Oct 4, 2002 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B7/208
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
Apparatus for synchronizing the frequency of locally generated pilot signals with those of remotely generated pilot signals where frequency errors are introduced during transmission. A pair of demodulated pilot signals F1' and F2' are filtered and mixed to derive a third signal having a frequency equal to F2'-F1'. The difference frequency has no frequency error component so the third signal is used in a phase locked loop to regenerate a reference frequency (fr) signal. Two methods are disclosed to extract a control signal which is proportional to the error frequency. In one embodiment one of the received pilots (F1') is divided in frequency by 1/k1 and then subtracted from fr to yield 1/k1 times the error frequency df. By integrating this signal it becomes usable as an AFC signal to control a local oscillator. In a second embodiment a signal having a frequency equal to the sum of the received pilot signals (F1'+F2') is mixed with a second signal having a frequency equal to (F1+F2+fr), and the difference signal is extracted. The difference signal contains the error frequency component and the reference frequency component. The reference frequency is cancelled out leaving the error f…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.