In-service measurement of transmitter nonlinearities

A method for performing in-service nonlinear error measurements on a digitally modulated radio frequency signal generated by a transmission system having a transmitter filter and a receiver filter wherein signal samples are generated representative of the digitally modulated radio frequency signal and filtered signal samples are generated by filtering the signal samples through a transmission system receiver filter, unfiltered signal samples are generated by bypassing the transmission system receiver filter, reference signal samples are generated from estimated transmitted digital symbols of the digital modulation that are time-aligned with the unfiltered signal samples, and magnitude values are calculated from the reference signal samples comprising the steps of:

• a) generating nonlinear error values using the reference signal samples and the unfiltered signal samples;
• b) removing largely deviated nonlinear error values that exceed boundary values in error versus magnitude space;
• c) deriving coefficients for a nonlinear behavior function using the nonlinear error values within the boundary values;
• and
• d) estimating nonlinear error values as a function of the reference magnitude values using the derived coefficients in the nonlinear behavior function.

A method for performing in-service nonlinear error measurement on a digitally modulated radio frequency signal generated by a transmission system having a transmitter filter and a receiver filter wherein signal samples are generated representative of the digitally modulated radio frequency signal and filtered signal samples are generated by filtering the signal samples through a transmission system receiver filter and unfiltered signal samples are generated by bypassing the transmission system receiver filter comprising the steps of:

• a) generating reference signal samples from estimated transmitted digital symbols of the digital modulation using either the filtered or unfiltered signal samples;
• b) calculating magnitude values for the reference signal samples;
• c) time-aligning the unfiltered signal samples with the reference signal samples;
• d) generating nonlinear error values using the reference signal samples and the unfiltered signal samples;
• e) removing nonlinear error values that exceed boundary values in error versus magnitude space;
• f) deriving coefficients for a nonlinear behavior function using the nonlinear error values within the boundary values;
• and
• g) estimating nonlinear error values as a function of the reference magnitude values using the derived coefficients in the nonlinear behavior function.

A method for performing in-service nonlinearity error measurements on a digitally modulated radio frequency signal generated by a transmission system having a transmitter filter and a receiver filter where the digitally modulated radio frequency signal is down converted to an intermediate frequency signal and digitized to produce intermediate frequency signal samples comprising the steps of:

• a) demodulating the intermediate frequency signal samples to filtered baseband signal samples using a transmission system receiver filter for filtering signal samples wherein the filtered demodulation process produces estimated carrier offsets values, timing phase and rate offset parameters, gain factor, pilot level estimation value, and equalizer coefficients;
• b) down converting the intermediate frequency signal samples to baseband using the estimated carrier offset values;
• c) resampling the down converted signal samples using the estimated timing phase and rate parameters;
• d) applying the estimated gain factor to the resampled signal samples;
• e) equalizing the resampled signal samples by using the estimated equalizer coefficients for generating unfiltered signal samples;
• f) generating reference signal samples from estimated transmitted digital symbols of the digital modulation using either the filtered or unfiltered signal samples;
• g) calculating magnitude values for the reference signal samples;
• h) time-aligning the unfiltered signal samples with the reference signal samples;
• j) generating nonlinear error values using the reference signal samples and the unfiltered signal samples;
• k) removing nonlinear error values that exceed boundary values in error versus magnitude space;
• l) deriving coefficients for a nonlinear behavior function using the nonlinear error values within the boundary values;
• and
• m) estimating nonlinear error values as a function of the reference magnitude values using the derived coefficients in the nonlinear behavior function.

An apparatus for performing in-service nonlinear error measurements on a digitally modulated radio frequency signal wherein a measurement receiver generates signal samples representative of the received digitally modulated radio frequency signal with the receiver generating reference signal samples that represent estimated transmitted digital symbols of the digital modulation that are time-aligned with the received signal samples comprising:

• means for generating nonlinear error values using the reference signal samples and the received signal samples;
• means for removing largely deviated nonlinear error values that exceed boundary values in error versus magnitude space;
• means for deriving coefficients for a nonlinear behavior function using the nonlinear error values within the boundary values;
• and
• means for estimating nonlinear error values as a function of the reference magnitude values using the derived coefficients in the nonlinear behavior function.

An apparatus for performing in-service nonlinear error measurements on a digitally modulated radio frequency signal generated by a transmission system having a transmitter filter and a receiver filter wherein a measurement receiver generates signal samples representative of the digitally modulated radio frequency signal that are processed to include filtering by a transmission system receiver filter to produce filtered signal samples and that are processed with the transmission system receiver filter being bypassed to produce unfiltered signal samples, with the receiver generating reference signal samples that represent estimated transmitted digital symbols of the digital modulation that are time-aligned with the unfiltered signal samples comprising:

• means for generating nonlinear error values using the reference signal samples and the unfiltered signal samples;
• means for removing largely deviated nonlinear error values that exceed boundary values in error versus magnitude space;
• means for deriving coefficients for a nonlinear behavior function using the nonlinear error values within the boundary values;
• and
• means for estimating nonlinear error values as a function of the reference magnitude values using the derived coefficients in the nonlinear behavior function.

An apparatus for performing in-service nonlinear error measurements on a digitally modulated radio frequency signal generated by a transmission system having a transmitter filter and a receiver filter wherein a measurement receiver generates signal samples representative of the digitally modulated radio frequency signal that are processed to include filtering by a transmission system receiver filter to produce filtered signal samples and that are processed with the transmission system receiver filter being bypassed to produce unfiltered signal samples comprising:

• means for generating reference signal samples from estimated transmitted digital symbols in the modulation data using either the filtered or unfiltered signal samples;
• means for calculating magnitude values for the reference signal samples;
• means for time-aligning the unfiltered signal samples with the reference signal samples;
• means for generating nonlinear error values using the reference signal samples and the unfiltered signal samples;
• means for removing nonlinear error values that exceed boundary values in error versus magnitude space;
• means for deriving coefficients for a nonlinear behavior function using the nonlinear error values within the boundary values;
• and
• means for estimating nonlinear error values as a function of the reference magnitude values using the derived coefficients in the nonlinear behavior function.

A machine readable medium having stored thereon a series of instructions which, when executed by a processor of a measurement receiver, performs in-service nonlinear error measurements on a digitally modulated radio frequency signal generated by a transmission system having a transmitter filter and a receiver filter wherein signal samples are generated representative of the digitally modulated radio frequency signal and filtered signal samples are generated by filtering the signal samples through a transmission system receiver filter, unfiltered signal samples are generated by bypassing the transmission system receiver filter, reference signal samples are generated from estimated transmitted digital symbols of the digital modulation that are time-aligned with the unfiltered signal samples, the instructions causing the processor to:

• generate nonlinear error values using the reference signal samples and the unfiltered signal samples;
• remove largely deviated nonlinear error values that exceed boundary values in error versus magnitude space;
• derive coefficients for a nonlinear behavior function using the nonlinear error values within the boundary values;
• and
• estimate nonlinear error values as a function of the reference magnitude values using the derived coefficients in the nonlinear behavior function.