Measurement receiver demodulator

• US 6,671,334 B1
• Filed: 11/03/1998
• Issued: 12/30/2003
• Est. Priority Date: 11/03/1998
• Status: Expired due to Term

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Deshpande, Nikhil M., Bernard, Kyle L., Chen, Xiaofen, Kuntz, Thomas L.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Lugo, David B.
• Application Number:
  US09/185,419
• Time in Patent Office: 1,883 Days
• Field of Search: 375/229, 375/316, 375/340, 375/346, 375/349, 375/350, 329/315, 329/347, 329/372, 329/316
• US Class Current: 375/340
• CPC Class Codes: H04L 2025/03382 Single of vestigal sideband
• CPC Class Codes: H04L 2025/03732 according to the convergence state
• CPC Class Codes: H04L 2027/0038 using an equaliser
• CPC Class Codes: H04L 2027/0046 Open loops
• CPC Class Codes: H04L 2027/0067 Phase error detectors
• CPC Class Codes: H04L 2027/0087 Out-of-band signals, (e.g. pilots)
• CPC Class Codes: H04L 25/0305 using blind adaptation
• CPC Class Codes: H04L 27/066 Carrier recovery circuits H04L27/2271 takes precedence
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04N 17/004 for digital television systems

Abstract

A measurement receiver demodulator has a first processing channel for producing a filtered signal sample output where the signal samples are processed through a transmission system receiver filter and a second processing channel producing an unfiltered signal sample output where the signal samples are not processed through the transmission system receiver filter. The first processing channel down converts digitally modulated IF signal samples and filters the down converted signal samples using a combined transmission system receiver filter and front end hardware compensation filter. A synchronizer produces timing phase and rate offset parameters that are applied to a resampling filter to synchronize the filtered signal samples to symbol instances of the symbol modulation. The filtered, time-aligned signal samples are scaled using a derived scaling factor. A pilot offset level, if present, is estimated and removed. The resultant signal samples are processed through an equalizer to produce filtered, time-aligned, scaled equalized signal samples that are output as filtered signal samples. The second processing channel receives the down converted signal samples and uses compensation and equalization filter coefficients, timing parameters, and the scaling from the first processing channel in compensation, resampling and equalization filters and a scaler to produce compensated, time-aligned, scaled equalized signal samples that are output as unfiltered signal samples.

Claims

1. A demodulator for a measurement receiver receiving a radio frequency signal modulated with data symbols at a symbol frequency generated by a transmission system having a transmitter filter and a receiver filter where the digitally modulated radio frequency signal is down converted to a digitally modulated intermediate frequency signal and digitized to produce signal samples of the intermediate frequency signal by hardware front end circuitry, the demodulator comprising:

a first processing channel receiving the signal samples and producing filtered signal samples using the transmission system receiver filter with the first processing channel having subchannels with one subchannel producing filtered equalized signal samples and a second subchannel producing filtered unequalized signal samples; and

a second processing channel bypassing the transmission system receiver filter receiving the signal samples and producing unfiltered signal samples with the second processing channel having subchannels with one subchannel producing unfiltered equalized signal samples and a second subchannel producing unfiltered unequalized signal samples.

2. The demodulator as recited in claim 1 wherein the first and second subchannels of the first processing channel further comprises:

a down converter receiving the intermediate frequency signal samples and producing baseband signal samples;

a digital filter having combined filter coefficients producing a transmission system receiver filter response and compensating for the hardware front end circuitry receiving the baseband signal samples and generating filtered baseband signal samples;

a symbol timing synchronizer having a resampler receiving the filtered baseband signal samples and a timing estimator receiving the combined filter coefficients and the baseband signal samples with the timing estimator generating timing and phase offset parameters that are applied to the resampler to produce time-aligned, filtered baseband signal samples;

a scaler receiving the time-aligned, filtered baseband signal samples and estimating a scaling factor that is applied to the signal samples to produce scaled, time-aligned, filtered baseband signal samples that are output as filtered unequalized signal samples from the second subchannel; and

an equalizer receiving the scaled, time-aligned, filtered baseband signal samples and generating equalizer coefficients that are applied to an equalization filter to produce equalized, scaled, time-aligned, filtered baseband signal samples that are output as filtered equalized signal samples from the first subchannel.

3. The demodulator as recited in claim 1 wherein the first and second subchannels of the first processing channel further comprises:

a down converter receiving the intermediate frequency signal samples and producing baseband signal samples;

a first digital filter having filter coefficients compensating for the hardware front end circuitry receiving the baseband signal samples and generating compensated baseband signal samples;

a second digital filter having filter coefficients producing a transmission system receiver filter response receiving the compensated baseband signal samples and generating filtered baseband signal samples;

a symbol timing synchronizer having a resampler receiving the filtered baseband signal samples and a timing estimator receiving the combined filter coefficients and the baseband signal samples with the timing estimator generating timing and phase offset parameters that are applied to the resampler to produce time-aligned, filtered baseband signal samples;

a scaler receiving the time-aligned, filtered baseband signal samples and a estimating scaling factor that is applied to the signal samples to produce scaled, time-aligned, filtered baseband signal samples that are output as filtered unequalized signal samples from the second subchannel; and

an equalizer receiving the scaled time-aligned filtered baseband signal samples and generating equalizer coefficients that are applied to an equalization filter to produce equalized, scaled, time-aligned, filtered baseband signal samples that are output as filtered equalized signal samples from the first subchannel.

4. The demodulator as recited in claim 1 wherein the digitally modulated radio frequency signal includes a pilot signal and the first and second subchannels of the first processing channel further comprises:

a down converter receiving the intermediate frequency signal samples and producing baseband signal samples having a pilot level;

a digital filter having combined filter coefficients producing a transmission system receiver filter response and compensating for the hardware front end circuitry receiving the baseband signal samples and generating filtered baseband signal samples;

a symbol timing synchronizer having a resampler receiving the filtered baseband signal samples and a timing estimator receiving the combined filter coefficients and the baseband signal samples with the timing estimator generating timing and phase offset parameters that are applied to the resampler to produce time-aligned, filtered baseband signal samples;

a scaler receiving the time-aligned filtered baseband signal samples and producing a scaling factor that is applied to the time-aligned filtered baseband signal samples to produce scaled, time-aligned, filtered baseband signal samples with the pilot level;

a pilot level remover receiving the scaled, time-aligned, filtered baseband signal samples that estimates and removes the pilot level to produce scaled, time-aligned, filtered baseband signal samples that are output as filtered unequalized signal samples from the second subchannel; and

an equalizer receiving the scaled, time-aligned, filtered baseband signal samples and generating equalizer coefficients that are applied to an equalization filter to produce equalized, scaled, time-aligned, filtered baseband signal samples that are output as filtered equalized signal samples from the first subchannel.

5. The demodulator as recited in claim 1 wherein the digitally modulated radio frequency signal includes a pilot signal and the first and second subchannels of the first processing channel further comprises:

a down converter receiving the intermediate frequency signal samples and producing baseband signal samples having a pilot level;

a first digital filter having filter coefficients compensating for the hardware front end circuitry receiving the baseband signal samples and generating compensated baseband signal samples;

a second digital filter having filter coefficients producing a transmission system receiver filter response receiving the compensated baseband signal samples and generating filtered baseband signal samples;

a symbol timing synchronizer having a resampler receiving the filtered baseband signal samples and a timing estimator receiving the combined filter coefficients and the baseband signal samples with the timing estimator generating timing and phase offset parameters that are applied to the resampler to produce time-aligned, filtered, baseband signal samples;

a scaler receiving the time-aligned filtered baseband signal samples and producing a scaling factor that is applied to the time-aligned filtered baseband signal samples to produce scaled, time-aligned, filtered baseband signal samples with the pilot level;

a pilot level remover receiving the scaled, time-aligned, filtered baseband signal samples that estimates and removes the pilot level to produce scaled, time-aligned, filtered baseband signal samples that are output as filtered unequalized signal samples from the second subchannel; and

an equalizer receiving the scaled time-aligned filtered baseband signal samples and generating equalizer coefficients that are applied to an equalization filter to produce equalized, scaled, time-aligned, filtered baseband signal samples that are output as filtered equalized signal samples from the first subchannel.

6. The demodulator as recited in claim 1 wherein the intermediate frequency signal samples include a pilot tone and the first and second subchannels of the first processing channel further comprises:

a down converter receiving the intermediate frequency signal samples and producing baseband signal samples having a pilot level;

a digital filter having combined filter coefficients producing a transmission system receiver filter response and compensating for the hardware front end circuitry receiving the baseband signal samples and generating filtered baseband signal samples;

a symbol timing synchronizer having a resampler receiving the filtered baseband signal samples and a timing estimator receiving the combined filter coefficients and the baseband signal samples with the timing estimator generating timing and phase offset parameters that are applied to the resampler to produce time-aligned, filtered baseband signal samples;

a scaler and pilot level remover receiving the time-aligned, filtered baseband signal samples and estimating a scaling factor and a pilot level that are applied to the signal samples to produce scaled, time-aligned, filtered baseband signal samples that are output as filtered unequalized signal samples from the second subchannel; and

an equalizer receiving the scaled time-aligned filtered baseband signal samples and generating equalizer coefficients that are applied to an equalization filter to produce equalized, scaled, time-aligned, filtered baseband signal samples that are output as filtered equalized signal samples from the first subchannel.

7. The demodulator as recited in claims 2, 3, 4, 5, or 6 wherein the intermediate frequency signal samples are acquired at N times the symbol frequency where N is greater than 1 and the first subchannel of the first processing channel further comprises a down sampler having a decimation factor equal to N receiving the equalized, scaled, time-aligned, filtered baseband signal samples for generating down sampled equalized, scaled, time-aligned, filtered baseband signal samples that are output as filtered equalized signal samples from the first subchannel.

8. The demodulator as recited in claims 2, 3, 4, 5, or 6 wherein the intermediate frequency signal samples are acquired at N times the symbol frequency where N is greater than 1 and the second subchannel of the first processing channel further comprises a down sampler having a decimation factor equal to N receiving the scaled, time-aligned, filtered baseband signal samples for generating down sampled scaled, time-aligned, filtered, unequalized baseband signal samples that are output as filtered unequalized signal samples from the second subchannel.

9. The demodulator as recited in claim 1 wherein the first and second subchannels of the second processing channel further comprises:

a first digital filter receiving the baseband signal samples and filter coefficients that compensate for the hardware front end circuitry from the first processing channel that are applied to the baseband signal samples to generate compensated baseband signal samples;

a resampling filter receiving the compensated baseband signal samples and the timing and phase offset parameters from the symbol timing synchronizer that are applied to the resampling filter to produce time-aligned, compensated baseband signal samples;

a scaler receiving the time-aligned, compensated baseband signal samples and the scaling factor from the first processing channel scaler that is applied to the time-aligned, compensated baseband signal samples to generate scaled, time-aligned, compensated baseband signal samples that are output as unfiltered unequalized signal samples from the second subchannel; and

a second digital filter receiving the scaled, time-aligned, compensated baseband signal samples and equalizer coefficients from the first processing channel equalizer that are applied to the second digital filter to produce equalized, scaled, time-aligned baseband signal samples that are output as unfiltered equalized signal samples from the first subchannel.