Phase detectors in carrier recovery for offset QAM and VSB
First Claim
1. In an Offset QAM receiver that recovers in-phase signals sampled at in-phase sampling times and quadrature-phase signals sampled at quadrature-phase sampling times, a phase detector comprising:
- means for separating the in-phase signals into a first data stream at the in-phase sampling times and a second data stream at the quadrature-phase sampling times;
means for separating the quadrature-phase signals into a third data stream at the quadrature-phase sampling times and a fourth data stream at the in-phase sampling times;
means for generating a fifth data steam representing tentative decisions from the first data stream;
means for generating a sixth data steam representing tentative decisions from the third data stream;
means for comparing the first and fifth data streams to generate a first error signal;
means for comparing the third and sixth data streams to generate a second error signal;
means for combining the first error signal and the fourth data stream to form a first phase error signal; and
means for combining the second error signal and the second data stream to form a second phase error signal.
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Abstract
Improved carrier recovery, symbol timing, and carrier phase tracking systems and methods suitable for use in connection with a dual-mode QAM/VSB receiver system are disclosed. Carrier and phase recovery systems operate on complex signals representing symbols having the same time stamp for each phase error term. in-phase signals are sampled twice a symbol at the in-phase symbol sampling time and at the quadrature-phase symbol sampling time. The signals are de-multiplexed to generate I and XI data streams, where I represents the in-phase sampling time signals and XI represents mid-symbol point sample times. A similar procedure is carrier out on quadrature-phase signals. When the in-phase signal is de-multiplexed to generate a symbol I, the quadrature-phase signal is de-multiplexed to generate its mid-symbol point XQ. Both I and Q are decoded in a decision device to define a symbol error term, which is combined with the opposite mid-symbol signal to define a phase error term PI and PQ for each rail. In both cases, the symbol (I) decision (Î), and mid-symbol (XQ) in each phase error term (PI) computation will have the same prime index.
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Citations
8 Claims
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1. In an Offset QAM receiver that recovers in-phase signals sampled at in-phase sampling times and quadrature-phase signals sampled at quadrature-phase sampling times, a phase detector comprising:
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means for separating the in-phase signals into a first data stream at the in-phase sampling times and a second data stream at the quadrature-phase sampling times;
means for separating the quadrature-phase signals into a third data stream at the quadrature-phase sampling times and a fourth data stream at the in-phase sampling times;
means for generating a fifth data steam representing tentative decisions from the first data stream;
means for generating a sixth data steam representing tentative decisions from the third data stream;
means for comparing the first and fifth data streams to generate a first error signal;
means for comparing the third and sixth data streams to generate a second error signal;
means for combining the first error signal and the fourth data stream to form a first phase error signal; and
means for combining the second error signal and the second data stream to form a second phase error signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
a voltage controlled oscillator (VCO) and means for coupling the combined phase error signals to the VCO to reduce the combined phase error.
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5. The phase detector of claim 4, additionally comprising a phase de-rotator controlled by the VCO.
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6. The phase detector of claim 1 designed alternatively for phase detection of a VSB signal additionally comprising:
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means for separating the VSB signal into in-phase and quadrature phase data streams;
means for generating a data stream representing tentative decisions from the in-phase data stream;
means for comparing the in-phase data stream and the data stream representing tentative decisions to generate an error signal; and
means for combining the error signal and the quadrature phase data stream.
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7. The phase detector of claim 6, in which the means for generating the data stream representing tentative decisions from the in-phase data stream comprises decision devices.
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8. The phase detector of claim 7, additionally comprising a voltage controlled oscillator (VCO) and means for coupling the combined phase error signals and quadrature phase data stream to the VCO to reduce any difference therebetween.
Specification