Carrier reproducing circuit including region deciding circuitry

• US 5,872,812 A
• Filed: 09/05/1996
• Issued: 02/16/1999
• Est. Priority Date: 01/30/1996
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Iwamatsu, Takanori, Saito, Naoyuki
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US08/697,966
• Time in Patent Office: 894 Days
• Field of Search: 375/326, 375/344, 375/327, 375/340, 375/354, 375/371, 375/376, 375/261, 375/264, 375/328, 331/12, 331/11, 331/17, 329/308, 329/309, 329/304
• US Class Current: 375/261
• CPC Class Codes: H04L 27/3827 in which the carrier is recovered using only the demodulated baseband signals

Abstract

A carrier reproducing circuit for detecting a phase error when an inputted baseband signal is out of phase and bringing the baseband signal into phase even in QAM systems in which normal signal points are located in a non-square pattern in a phase-amplitude signal space. When the baseband signal is out of phase, a first region decision circuit detects a presence of the baseband signal in a first region and outputs a first signal, and a second region decision circuit detects a presence of the baseband signal in a second region and outputs a second signal. If the second signal is not outputted over a predetermined period of time around the time at which the first signal is outputted, then a selective outputting circuit outputs a phase error detected by a phase error decision circuit with respect to the baseband signal at the time the first signal is outputted, to a control signal generator. If the second signal is outputted in the predetermined period of time, then the selective outputting circuit outputs the phase error detected by the phase error decision circuit with respect to the baseband signal at the time the first signal is outputted in a preceding cycle to the control signal generator.

Claims

1. A carrier reproducing circuit for a multi-valued quadrature amplitude modulation system in which normal signal points are located in a non-square pattern in a phase-amplitude signal space, comprising:

carrier outputting means for outputting a carrier which has a frequency and phase depending on a control signal;

quadrature demodulating means for quadrature-demodulating an inputted signal with said carrier and outputting a baseband signal;

phase error detecting means for detecting a phase error between the position of the baseband signal in a phase-amplitude signal space and the position of a corresponding one of a plurality of predetermined normal signal points in the phase-amplitude signal space;

control signal generating means for generating the control signal in order to reduce the phase error based on said phase error;

first region deciding means for detecting a presence of the baseband signal, when out of phase, in a first region composed of eight small regions defined around eight signal points, farthest from the center of the phase-amplitude signal space, and outputting a first signal;

second region deciding means for detecting a presence of the baseband signal, when out of phase, in a second region composed of four small regions defined across the axes of the phase-amplitude signal space outside of the normal signal points, and outputting a second signal; and

selective outputting means for outputting a phase error detected by said phase error detecting means with respect to the baseband signal at the time said first signal is outputted, to said control signal generating means, if said second signal is not outputted over a predetermined period of time around the time at which said first signal is outputted, and outputting a phase error detected by said phase error detecting means with respect to the baseband signal at the time said first signal is outputted in a preceding cycle, to said control signal generating means, if said second signal is outputted in said predetermined period of time.

2. A carrier reproducing circuit according to claim 1, further comprising:

delaying means for delaying the baseband signal which has been quadrature-demodulated;

said first region deciding means comprising means for detecting a presence of the baseband signal in said first region and outputting said first signal based on the baseband signal delayed by said delaying means;

said second region deciding means comprising means for detecting a presence of the baseband signal in said second region and outputting said second signal based on the baseband signal delayed by said delaying means;

said selective outputting means comprising means for outputting the phase error detected by said phase error detecting means with respect to the baseband signal at the time said first signal is outputted, to said control signal generating means, if said second signal is not outputted due to a predetermined number of baseband signals with respect to said predetermined number of baseband signals inputted around the baseband signal for which said first signal is outputted, and outputting the phase error detected by said phase error detecting means with respect to the baseband signal at the time said first signal is outputted in the preceding cycle, to said control signal generating means, if said second signal is outputted due to said predetermined number of baseband signals.

3. A carrier reproducing circuit according to claim 1, further comprising:

a first shift register for shifting the second signal outputted from said second region deciding means each time a baseband signal is inputted and holding the shifted second signal at a predetermined number of stages thereof; and

ORing means for ORing signals held in the stages of said first shift register;

said selective outputting means comprising;

first selecting means for outputting the phase error detected by said phase error detecting means with respect to the baseband signal at the time said first signal is outputted, if said first signal is outputted, and outputting the phase error detected by said phase error detecting means with respect to the baseband signal at the time said first signal is outputted in the preceding cycle, if said first signal is not outputted;

a second shift register for shifting an output signal from said first selecting means each time a baseband signal is inputted and holding the shifted output signal at half as many as said predetermined number of stages; and

second selecting means for outputting an output signal from a final stage of said second shift register to said control signal generating means if a signal corresponding to said second signal is not outputted from said ORing means, and outputting the phase error detected by said phase error detecting means with respect to the baseband signal at the time said first signal is outputted in the preceding cycle, if a signal corresponding to said second signal is outputted from said ORing means.

4. A carrier reproducing circuit for a multi-valued quadrature amplitude modulation system in which normal signal points are located in a non-square pattern in a phase-amplitude signal space, comprising:

carrier outputting means for outputting a carrier which has a frequency and phase depending on a control signal;

quadrature demodulating means for quadrature-demodulating an inputted signal with said carrier and outputting a baseband signal;

phase error detecting means for detecting a phase error between the position of the baseband signal in a phase-amplitude signal space and the position of a corresponding one of a plurality of predetermined normal signal points in the phase-amplitude signal space, outputting a first signal if said baseband signal is leading the corresponding normal signal point in phase, and outputting a second signal if said baseband signal is lagging the corresponding normal signal point in phase;

control signal generating means for generating a control signal to delay said carrier in phase when said first input signal is inputted thereto, and generating a control signal to advance said carrier in phase when said second input signal is inputted thereto;

said non-square pattern being devoid of small square segments in respective quadrants thereof, each of said small square segments being divided into a leading phase region and a lagging phase region by a straight line passing through the origin of the phase-amplitude signal space;

region deciding means for detecting a presence of the baseband signal in said leading phase region and outputting said second signal when the baseband signal is out of phase, and detecting a presence of the baseband signal in said lagging phase region and outputting said first signal when the baseband signal is out of phase; and

selective outputting means for causing said control signal generating means to output an output signal from said phase error detecting means when the baseband signal is in phase, and causing said control signal generating means to output an output signal from said region deciding means when the baseband signal is out of phase.