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US 5,579,345 AGranted
Carrier tracking loop for QPSK demodulator
AssigneeWestinghouse Electric Corp.
InventorsBrian W. Kroeger, Jeffrey S. Baird, Joseph B. Bronder
Life of this patent
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Abstract
A carrier tracking loop that uses a frequency locked loop (FLL) and incorporates synchronized matched filters to minimize complexity of the system. The synchronized matched filters eliminate out-of-band interference while minimizing computation. The carrier tracking loop has an improved error signal generation to extend a frequency range and by employing error signal normalization, which extends the dynamic range of the amplitude of the input signal and allows the frequency to flywheel when signal fading occurs.
Claims19
A demodulator for a mobile telecommunications system, including a carrier tracking loop receiving a series of symbol samples, comprising:
- a complex multiplier for multiplying the received symbol samples by a complex exponential value to output a near baseband signal;
- a matched filter pair, coupled to said complex multiplier, for filtering the near baseband signal to output a complex filtered signal;
- phase difference means, coupled to said matched filter pair, for determining a phase difference between two sequential symbol samples of the received symbol samples based on the complex filtered signal;
- normalized angle determining means, coupled to said phase difference means, for determining a normalized angle representative of a carrier frequency offset in the near baseband signal in accordance with the determined phase difference;
- increment phasor determining means, coupled to said normalized angle determining means, for determining an increment phasor from the determined normalized angle;
- and
- generating means, coupled to said increment phasor determining means and said complex multiplier, for generating the complex exponential value in accordance with the determined increment phasor,
- said complex multiplier, said matched filter pair, said phase difference means, said normalized angle determining means, said increment phasor determining means and said generating means forming a frequency locked loop.
5 more elements
A demodulator for a mobile telecommunications system, including a carrier tracking loop receiving a series of symbol samples, each having an inphase signal and a quadrature signal, comprising:
- a complex multiplier for multiplying the received symbol samples With a complex exponential value to output a near baseband signal;
- a matched filter pair, coupled to said complex multiplier, for filtering the near baseband signal to output a complex filtered signal;
- phase difference means, coupled to said matched filter pair, for determining a phase difference between two sequential symbol samples of the received symbol samples based on the complex filtered signal;
- normalized angle determining means, coupled to said phase difference means, for determining a normalized angle representative of a carrier frequency offset in the near baseband signal in accordance with the determined phase difference;
- increment phasor determining means, coupled to said normalized angle determining means, for determining an increment phasor from the determined normalized angle;
- and
- generating means, coupled to said increment phasor determining means and to said complex multiplier, for generating the complex exponential value in accordance with the determined increment phasor,
- said complex multiplier including
- input means for inputting the complex exponential value to said complex multiplier, and
- multiplication means for performing a complex multiplication operation on the complex exponential value and a current pair of the inphase and quadrature signals to translate the inphase and quadrature signals to the near baseband signal.
7 more elements
A carrier tracking loop comprising:
- mixing means for mixing a received signal with a local oscillator signal to translate the received signal to a near baseband signal;
- symbol synchronization means, coupled to said mixing means, for sampling the near baseband signal at an optimum symbol timing and outputting symbol samples;
- phase difference determination means, coupled to said symbol synchronization means, for determining and outputting a complex difference phasor representative of a phase difference between successive symbol samples;
- error estimating means, coupled to said phase difference determination means, for determining an instantaneous frequency error representative of a carrier frequency offset in the near baseband signal based on the complex difference phasor and for outputting an error signal indicative thereof;
- and
- oscillation means, coupled to said error estimating means, for generating the local oscillation signal in accordance with the error signal to minimize the carrier frequency offset error in the near baseband signal.
3 more elements
A method of carrier tracking comprising:
- (a) mixing a received signal with a local oscillation signal to translate the received signal to a near baseband signal;
- (b) sampling the near baseband signal at an optimum symbol timing and outputting symbol samples;
- (c) determining a complex difference phasor representative of a phase difference between successive symbol samples;
- (d) determining an instantaneous frequency error representative of a carrier frequency offset in the near baseband signal based on the complex difference phasor;
- and
- (e) generating the local oscillation signal in accordance with the instantaneous frequency error determined in said step (d) to minimize the carrier frequency offset error in the near baseband signal.
3 more elements
A method of carrier tracking comprising:
- (a) multiplying received symbol samples by a complex exponential value to provide a near baseband signal;
- (b) filtering the near baseband signal to provide a complex filtered signal;
- (c) determining a phase difference between two sequential symbol samples of the received symbol samples based on the complex filtered signal;
- (d) determining a normalized angle representative of a carrier frequency offset in the near baseband signal in accordance with the phase difference determined in said step (c);
- (e) determining an increment phasor based on the normalized angle determined in said step (d);
- and
- (f) generating the complex exponential value in accordance with the increment phasor determined in said step (e).
4 more elements
Dependencies are inferred from the claim text.