Using Fractional Delay Computations to Improve Intermodulation Performance

An apparatus, comprising at least one processor;

• and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following:
• determining, estimating, or computing a coarse time delay represented by an integer T1;
• determining or selecting a current reference point for a transmitted signal waveform of an RF power amplifier;
• shifting the transmitted signal waveform by a set of offsets comprising a plurality of non-integer fractional steps from (T1−Xd) to (T1+Xd) where T1 is the integer and Xd is a non-integer fractional step size value for defining the plurality of non-integer fractional steps about the integer T1 such that the non-integer fractional steps progress in a positive direction as well as a negative direction from the integer T1;
• at each of the plurality of non-integer fractional steps, correlating the transmitted signal waveform with a feedback signal waveform to obtain a respective correlation value for each of corresponding fractional steps of the plurality of non-integer fractional steps;
• obtaining a correct fractional delay value by selecting a fractional step of the plurality of non-integer fractional steps having a highest respective correlation value;
• applying the obtained correct fractional delay value to the transmitted signal waveform to provide a compensated transmitted signal waveform, and
• combining the compensated transmitted signal waveform with the feedback signal waveform to reduce or eliminate at least one intermodulation product of the RF power amplifier.

A computer readable medium tangibly encoded with a computer program executable by a processor to perform actions comprising:

• determining, estimating, or computing a coarse time delay represented by an integer T1;
• determining or selecting a current reference point for a transmitted signal waveform of an RF power amplifier;
• shifting the transmitted signal waveform by a set of offsets comprising a plurality of non-integer fractional steps from (T1−Xd) to (T1+Xd) where T1 is the integer and Xd is a non-integer fractional step size value for defining the plurality of non-integer fractional steps about the integer T1 such that the non-integer fractional steps progress in a positive direction as well as a negative direction from the integer T1;
• at each of the plurality of non-integer fractional steps, correlating the transmitted signal waveform with a feedback signal waveform to obtain a respective correlation value for each of corresponding fractional steps of the plurality of non-integer fractional steps;
• obtaining a correct fractional delay value by selecting a fractional step of the plurality of non-integer fractional steps having a highest respective correlation value;
• applying the obtained correct fractional delay value to the transmitted signal waveform to provide a compensated transmitted signal waveform, and
• combining the compensated transmitted signal waveform with the feedback signal waveform to reduce or eliminate at least one intermodulation product of the RF power amplifier.