Method and apparatus for reducing receiver imposed distortion

• US 6,137,831 A
• Filed: 06/20/1997
• Issued: 10/24/2000
• Est. Priority Date: 06/20/1997
• Status: Expired due to Term

• Current Assignee: International Automated Systems
• Original Assignee: International Automated Systems
• Inventors: Johnson, Neldon P.
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US08/879,755
• Time in Patent Office: 1,222 Days
• Field of Search: 375/285, 375/295, 375/296, 375/229, 375/259, 375/230, 455/91, 455/116, 455/63, 332/107, 327/306
• US Class Current: 375/229
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation
• CPC Class Codes: H04L 27/28 with simultaneous transmission of different frequencies each representing one code element

Abstract

Method and apparatus for reducing the distortion imposed upon a combined information wave by a receiver filter or other signal processor. The method includes a step of adjusting the amplitude of the positive and negative segments of the combined information wave such that the positive and negative segments have pre-selected and equal amplitudes. The apparatus includes an adder circuit for combining the component information waves and the reference wave to form the combined information wave, a wave shaper to produce an equalized wave, and a wave multiplier for proportionally adjusting, on a half cycle basis, the amplitudes of the equalized positive and negative segments. The method further includes a step of pre-distorting the combined information wave to compensate for the distortion effect of a receiver filter or other signal processor. The apparatus for pre-distorting the combined information wave comprises a filter or other signal processor which is the same as the receiver filter or signal processor and a wave subtractor for biasing the combined information wave or comprises one or more circuits for mathematically predicting a distortion response to the filter or other signal processor and a wave subtractor for adding the inverse of the distortion response to the wave as it is transmitted.

Claims

1. Method for reducing the distortion imposed upon a combined information wave by a filter system or other signal processor, said combined information wave comprising a reference wave and one or more component information waves of known and distinct frequencies, said reference wave having positive and negative segments of known amplitudes, said combined information wave having positive and negative segments, and said method comprising adjusting the amplitudes of the positive and negative segments of the combined information wave such that the positive and negative segments have pre-selected and equal amplitudes, thereby producing an amplitude adjusted combined information wave with positive and negative segments of pre-selected and equal amplitudes.

2. Method claimed in claim 1 wherein the step of adjusting the amplitudes of the positive and negative segments comprises the steps of:

a) multiplying the positive segment of the combined information wave by a factor which adjusts the amplitude of the positive segment to a pre-set amplitude; and

b) multiplying the negative segment of the combined information wave by a factor which adjusts the amplitude of the negative segment to a pre-set amplitude which is equal to the pre-set amplitude of the positive segment.

3. Method claimed in claim 1 further comprising the steps of:

a) predicting a distortion effect that a filter system or other signal processor, through which the amplitude adjusted combined information wave will pass at a receiver, would have on the amplitude adjusted combined information wave, and

b) adding a filter correction wave, which is the inverse of the predicted distortion effect, to the amplitude adjusted combined information wave, thereby producing a filter biased wave.

4. Method for reducing the distortion imposed upon a combined information wave by a filter system or other signal processor, said combined information wave comprising a reference wave and one or more component information waves of known and distinct frequencies, said reference wave having positive and negative segments of known amplitudes, said combined information wave having positive and negative segments, said method comprising the steps of:

a) adjusting the amplitudes of the positive and negative segments of the combined information wave such that the positive and negative segments have pre-selected and equal amplitudes thereby producing an amplitude adjusted combined information wave with positive and negative segments of pre-selected and equal amplitudes;

b) passing the amplitude adjusted combined information wave prior to transmission through a filter system or signal processor which is identical to the filter system or signal processor through which the amplitude adjusted combined information wave will pass at a receiver, thereby producing a pre-filtered wave;

c) inverting the pre-filtered wave;

d) adding the inverted pre-filtered wave to the amplitude adjusted combined information wave, thereby producing a filter correction wave; and

e) adding the filter correction wave to the amplitude adjusted wave, thereby producing a filter biased wave.

5. Method claimed in claim 4 wherein the step of adjusting the amplitudes of the positive and negative segments comprises the steps of:

a) multiplying the positive segment of the combined information wave by a factor which adjusts the amplitude of the positive segment to a pre-set amplitude; and

b) multiplying the negative segment of the combined information wave by a factor which adjusts the amplitude of the negative segment to a pre-set amplitude which is equal to the pre-set amplitude of the positive segment.

6. Method for reducing the distortion imposed upon a combined information wave by a filter system or other signal processor, said combined information wave comprising a reference wave and one or more component information waves of known and distinct frequencies, said reference wave having positive and negative segments of known amplitudes, said combined information wave having positive and negative segments, said method comprising the steps of:

a) adjusting the amplitudes of the positive and negative segments of the combined information wave such that the positive and negative segments have pre-selected and equal amplitudes thereby producing an amplitude adjusted combined information wave with positive and negative segments of pre-selected and equal amplitudes;

b) predicting a distortion effect that a filter system or other signal processor, through which the amplitude adjusted combined information wave will pass at a receiver, would have on the amplitude adjusted combined information wave, and

c) adding a filter correction wave, which is the inverse of the predicted distortion effect, to the amplitude adjusted combined information wave, hereby producing a filter biased wave.

7. Method claimed in claim 6 wherein the step of adjusting the amplitudes of the positive and negative segments comprises the steps of:

a) multiplying the positive segment of the combined information wave by a factor which adjusts the amplitude of the positive segment to a pre-set amplitude; and

b) multiplying the negative segment of the combined information wave by a factor which adjusts the amplitude of the negative segment to a pre-set amplitude which is equal to the pre-set amplitude of the positive segment.

8. An apparatus for reducing the distortion imposed on a combined information wave by a receiver filter or other signal processor, said combined information wave comprising a reference wave of a known wave form, frequency and amplitude, and one or more component information waves of known and distinct frequencies and known wave forms and phases, said apparatus comprising:

a) an adder circuit for combining the component information waves and the reference wave to form the combined information wave;

b) a wave shaper for multiplying each segment of the combined information wave by selected factors on a half cycle basis, thereby producing an equalized wave with positive and negatives segments of equal amplitudes;

c) a wave multiplier for proportionally adjusting the amplitudes of the equalized positive and negative segments to produce an amplitude adjusted wave with pre-selected and equal positive and negative amplitudes.

9. Apparatus as claimed in claim 8 further comprising a wave train circuit for adding successive combined information waves together to form a continuous train of combined information waves.

10. An apparatus for reducing the distortion imposed upon a combined information wave by a filter system or other signal processor, said combined information wave comprising a reference wave and one or more component information waves of known and distinct frequencies, said reference wave having positive and negative segments of known amplitudes, said combined information wave having positive and negative segments, said apparatus comprising:

a) means for equalizing the positive and negative segments of said combined information wave;

b) means for adjusting the amplitude of the equalized information wave to produce an adjusted information wave having positive and negative segments with equal and pre-selected amplitudes;

c) means for predicting a response of the filter or other signal processor to the equalized information wave; and

d) means for biasing the equalized information wave prior to transmission to compensate for said predicted response.

11. Apparatus as claimed in claim 10 wherein the means for equalizing the positive and negative segments of said information wave and the means for adjusting the amplitude of the equalized information wave comprise:

a) an adder circuit for combining the component information waves and the reference wave to form the combined information wave;

b) a wave shaper for multiplying each segment of the combined information wave by selected factors on a half cycle basis, thereby producing an equalized wave with positive and negatives segments of equal amplitudes; and

c) a wave multiplier for proportionally adjusting the amplitudes of the equalized positive and negative segments to produce an amplitude adjusted wave with pre-selected and equal positive and negative amplitudes.

12. Apparatus as claimed in claim 10 wherein the means for predicting a response of the filter or other signal processor to the information wave and the means for biasing the information wave prior to transmission to compensate for said predicted response comprise:

a) a filter or other signal processor which is the same as the receiver filter or other signal processor;

b) a wave subtracter for subtracting the information wave from a wave produced by passing the information wave through the filter or other signal processor, thereby producing the predicted response; and

c) one or more circuits for phase shifting the predicted response by one-hundred eighty degrees and adding the phase shifted response to the information wave.

13. An apparatus for reducing the distortion imposed upon a combined information wave by a filter system or other signal processor, said combined information wave comprising a reference wave and one or more component information waves of known and distinct frequencies, said reference wave having positive and negative segments of known amplitudes, said combined information wave having positive and negative segments, said apparatus comprising:

a) a reference circuit for generating a reference wave and combining the reference wave with the component information waves to form the combined information wave;

b) an equalizer circuit for equalizing the amplitudes of the positive and negative segments of the combined information wave to produce an equalized wave; and

c) a composite circuit for adjusting the amplitudes of the positive and negative segments of the equalized wave to produce an adjusted wave with positive and negative segments of equal and pre-selected amplitudes.

14. Apparatus as claimed in claim 13 further comprising a means for combining successive adjusted waves to form a continuous train of adjusted waves.