AFC circuit, carrier recovery circuit and receiver device capable of regenerating a carrier reliably even at the time of low C/N ratio

Year	Description
1999	Invention patented by Kazuhiko Shibuya, Junji Kumada, Yuichi Iwadate, Hiroyuki Hamazumi, Toshihiro Nomoto, Kouichi Takano, Tomohiro Saito, Shoji Tanaka, Fumiaki Minematsu, Akinori Hashimoto, Shigeyuki Itoh, Hajime Matsumura, Hisakazu Katoh, and Masaru Takechi on May 13th, 1999. Abstract: Stabilized carrier recovery is achieved even at the time of a low C/N ratio by measuring the phase of a signal and controlling VCO or NCO (Numerical Controlled Oscillator) using only a period having few constellation points. At this time, false lock phenomenon is avoided as follows. That is, relatively short SYNC modulated by an already-known pattern is entered into a modulation wave, VCO or NCO oscillation frequency is swept in a wide range and sweep is stopped at a frequency in which the SYNC can be received, thereby carrying out coarse control AFC. Further, a period having long to some extent, having few constellation points is provided in the modulation wave and then, a difference between the frequency of a received modulated signal and a local oscillation signal of VCO or NCO is obtained in this period. This frequency difference is analyzed according to the phase differential function method, self-correlation function method or count method, and the VCO or NCO is controlled based on this result of analysis.
Source: selected by the editor from original sources.

Invention: AFC circuit, carrier recovery circuit and receiver device capable of regenerating a carrier reliably even at the time of low C/N ratio