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US 5,001,727 AGranted
Carrier and data recovery and demodulation system
AssigneeTerra Marine Engineering, Inc.
InventorWilliam T. McDavid
Life of this patent
Estimating the term…
Abstract
A modulated carrier is received on a node (10) and then the I- and the Q-channels extracted with a local carrier clock (16) that is free-running relative to the modulated carrier. The I- and the Q-channels are then input to a digital signal processor (26) wherein a composite phase signal is generated representing the phase difference between the modulated carrier and the local carrier clock (16). The composite phase is output from a look-up table in an EPROM (30) and then the free-running phase the local carrier clock (16) and the modulated carrier is discriminated from the composite phase. The free-running phase is then subtracted from the composite phase to yield the phase modulation on the carrier.
Claims17
A method for demodulating a phase modulated carrier, comprising:
- receiving the phase modulated carrier with the phase modulated carrier operating at a first frequency;
- generating a local carrier clock at a second frequency, the second frequency proximate in frequency to the first frequency, the frequency of the local carrier clock independent of the received carrier;
- determining the phase difference as a function of time between the phase modulated carrier and the local carrier clock to provide a composite phase signal comprising the phase modulation on the phase modulated carrier and the free running phase difference between the modulated carrier and the local carrier clock;
- discriminating the free-running phase from the composite phase signal to provide a phase error signal, which phase error signal is a function of time;
- subtracting the phase error signal from the composite phase signal to provide the phase modulation on the phase modulated carrier;
- generating a bit clock;
- determining when the zero crossings in the phase modulation occur, the zero crossings corresponding to data transitions;
- and
- synchronizing the clock edges of the bit clocks to the zero crossings of the phase modulation.
6 more elements
A method for demodulating a phase modulated carrier, comprising:
- receiving the phase modulated carrier with the phase modulated carrier operating at a first frequency;
- generating a local carrier clock at a second frequency, the second frequency proximate in frequency to the first frequency, the frequency of the local carrier clock independent of the received carrier;
- determining the phase difference as a function of time between the phase modulated carrier and the local carrier clock to provide a composite phase signal comprising the phase modulation on the phase modulated carrier and the free running phase difference between the modulated carrier and the local carrier clock by the steps of:
- computing the quadrature component of the signal by a Hilbert transform filter to provide the quadrature channel as the Q-channel that is 90.degree. shifted in phase relative to the input signal which comprises the I-channel, and
- calculating the arctangent of the quotient of the magnitude of the I-channel and the magnitude of the Q-channel to provide the composite phase signal;
- discriminating the free-running phase from the composite phase signal to provide a phase error signal, which phase error signal is a function of time;
- and
- subtracting the phase error signal from the composite phase signal to provide the phase modulation on the phase modulated carrier.
5 more elements
A system for demodulating a phase quadrature modulated carrier, comprising:
- receive circuitry for receiving the phase modulated carrier with the phase modulated carrier operating at a first frequency;
- a local clock for generating a local carrier clock operating at a second frequency, said second frequency proximate in frequency to said first frequency and independent of said first frequency;
- means for determining the phase difference as a function of time between the phase modulated carrier and said local carrier clock to provide a composite phase signal, said composite phase signal comprised of the phase due to phase modulation on the phase modulated carrier and the free-running phase difference between the modulated carrier and said local carrier clock, said means for determining including:
- a first phase detector for determining the difference between the phase modulated carrier and said local carrier clock to provide an I-channel phase value,
- a first down converter for mixing the local carrier clock and phase modulated carrier to downconvert the phase modulated carrier to an intermediate frequency to provide an I-channel,
- a Hilbert transform filter for receiving the I-channel and computing the quadrature phase value thereof as a Q-channel, said Q-channel shifted in phase 90.degree. relative to said I-channel, and p2 means for calculating the actangent of the quotient of the magnitude of said I-channel and the magnitude of said Q-channel to provide said composite phase signal;
- means for discriminating the free-running phase from the composite phase signal to provide a phase error, which phase error signal is a function of time;
- and
- a subtraction circuit for subtracting the phase error signal from said composite phase signal to provide the phase modulation on the phase modulated carrier.
6 more elements
A system for demodulating a phase modulated carrier comprising:
- receive circuitry for receiving the phase modulated carrier with the phase modulated carrier operating at a first frequency;
- a local clock for generating a local carrier clock operating at a second frequency, said second frequency proximate in frequency to said first frequency and independent of said first frequency;
- means for determining the phase difference as a function of time between the phase modulated carrier and said local carrier clock to provide a composite phase signal, said composite phase signal comprised of the phase due to phase modulation on the phase modulated carrier and the free-running phase difference between the modulated carrier and said local carrier clock;
- means for discriminating the free-running phase from the composite phase signal to provide a phase error, which phase error signal is a function of time;
- a subtraction circuit for subtracting the phase error signal from said composite phase signal to provide the phase modulation on the phase modulated carrier;
- a bit clock;
- circuitry for determining when the zero crossings in the phase modulation on aid carrier occur, the zero crossings corresponding to data transitions;
- and
- circuitry for synchronizing the clock edges of said bit clock to the zero crossings of the phase modulation.
6 more elements
Dependencies are inferred from the claim text.