Phase modulated system with phase domain filtering

• US 4,962,510 A
• Filed: 05/13/1988
• Issued: 10/09/1990
• Est. Priority Date: 04/15/1986
• Status: Expired due to Term

• Current Assignee: Terra Marine Engineering Incorporated
• Original Assignee: Terra Marine Engineering Incorporated
• Inventors: Itani, Talal A., McDavid, William T., Bryce, William W.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Edwards, Christopher O.
• Application Number:
  US07/194,024
• Time in Patent Office: 879 Days
• Field of Search: 375/38, 375/39, 375/67, 375/52, 375/42, 375/86, 375/96, 375/83, 332/9 R, 332/1 R, 332/16, 364/721, 364/724.01, 379/418
• US Class Current: 375/308
• CPC Class Codes: H04L 27/2014 in which the phase changes in a piecewise linear manner during each symbol period, e.g. minimum shift keying, fast frequency shift keying H04L27/201 takes precedence

Abstract

A phase modulation system includes a phase mapping circuit (218) for mapping binary data into a plurality of discrete phase values in accordance with a predetermined phase modulation scheme. The discrete phase values are then filtered in the phase domain by a filter (220) to provide a filtered output. This filtered output is then digitized and input to a numerically controlled oscillator for phase modulating a carrier.

Claims

1. A phase modulation system for phase modulating a carrier with digital data, comprising:

means for receiving the digital data as a sequence of data bits at a predetermined bit rate;

a phase mapper circuit for converting the received digital data to discrete phase values in accordance with a predetermined phase modulation scheme;

phase domain filter means for cross-correlating a predetermined phase domain filter function with a predetermined number of discrete phase values about one current phase value, said one current phase value corresponding to one of said data bits, and said predetermined number of discrete phase values corresponding to a predetermined number of said data bits about one said data bit, said filter means outputting a filtered waveform in the phase domain of, said filtered waveform representing a continuous sequence in time of said discrete phase values; and

phase modulation circuitry for generating a carrier at a predetermined carrier frequency and phase modulating said carrier in accordance with said filtered waveform that is output by said phase domain filter means.

2. The phase modulation system of claim 1 wherein said phase mapper circuitry and said phase domain filter means comprise:

memory means for storing digital representation of pregenerated analog waveform segments at predetermined addressable locations, each of said waveform segments having a beginning point and an end point, each of said waveform segments corresponding to said one data bit with each of said waveform segments comprising the cross-correlation of said predetermined phase domain filter function with said predetermined number of discrete phase values about said current phase value, said predetermined number of discrete phase value and said current phase values generated in accordance with said current data bit and said predetermined number of data bits about said one data bit and said predetermined phase modulation scheme, each combination of said predetermined number of data bits and said one data bit corresponding to at least one of said waveform segments;

address means for examining said predetermined number of said data bits about said one data bit and generating an address for addressing the one of said waveform segments corresponding to said one data bit; and

means for assembling said addressed waveform segments into a filtered waveform such that one of said waveform segments has the end point thereof connected to the beginning point of the next adjacent one of said waveform segments, each of said waveform segments having a duration equal to said corresponding one data bit in the digital data.

3. The phase modulation system of claim 2 wherein the output of said phase domain filter means comprises digital values wherein each of said waveform segments is comprised of a plurality of digital values and said phase modulation circuitry is operable to receive said digital phase values for modulation of said carrier.

4. The phase modulation system of claim 3 wherein said phase modulation means comprises a numerically controlled oscillator, said numerically controlled oscillator including:

a phase incrementing circuit for periodically generating a phase increment at a predetermined phase value;

accumulator means for accumulating the phase increments over a full-cycle from zero to three hundred sixty degrees;

adder means for adding the digital output of said filter means with the value in said accumulator;

a ROM lookup table containing the trigonometric value of the output of said accumulator means and operable to receive the output of said accumulator means and address a value in said ROM lookup table corresponding to the trigonometric value of the accumulator output; and

a digital-to-analog converter for converting the output of said ROM lookup table to an analog value, the analog value comprising said carrier.

5. The phase modulation system of claim 1 and further comprising:

an amplitude mapper circuit for converting the received digital data to discrete amplitude values in accordance with a predetermined amplitude modulation scheme operating in conjunction with said phase modulation scheme, each of said discrete amplitude values corresponding to said discrete phase values;

amplitude domain filter means for cross-correlating a predetermined amplitude domain filter function with said predetermined number of data bits about said corresponding one data bit to provide a filtered waveform on the output thereof; and

amplitude modulation means for amplitude modulating said carrier with the filtered output from said amplitude domain filter means.

6. A filter for filtering digital data, comprising:

means for receiving a digital data stream containing the digital data as a sequence of digital data bits;

memory means for storing digital representation of pregenerated phase domain waveform segments at predetermined addressable locations, said waveform segments corresponding to the cross-correlation of a predetermined phase domain filter function with a predetermined sequence and number of adjacent and discrete phase values, said predetermined sequence and number of adjacent phase values corresponding to the phase mapping of a corresponding sequence and number of adjacent data bits in accordance with a predetermined phase modulation scheme, which said sequence and number of adjacent data bits comprise a frame, there being a plurality of different sequences of adjacent data bits in said digital data stream with each predetermined sequence of adjacent data bits corresponding to a unique one of said phase domain waveform segments;

address means for examining the frame of adjacent data bits in said data stream, said frame equal in length to said predetermined sequence and number of adjacent data bits, said address means generating an address for addressing one of said phase domain waveform segments corresponding to said predetermined number of adjacent data bits in said frame;

assembling means for assembling said address phase domain waveform segments into a central waveform, each of said phase domain waveform segments having a duration equal to the duration of each of the data bits in said digital data stream, each increment by one data bit of said data stream providing a new frame for examining by said address means;

carrier generation circuitry for generating a carrier frequency; and

phase modulation means for modulating said carrier with the output of said assembling means.

7. The phase modulation system of claim 6 wherein the output of said assembly means comprises digital values and said phase modulation means is operable to receive digital values and modulate said carrier in accordance with the digital values.

8. The phase modulation system of claim 7 wherein said carrier generation means comprises a numerically controlled oscillator having:

phase incrementing circuitry for periodically generating phase increments of a predetermined value;

an accumulator for accumulating said phase incrementing values at a predetermined rate over phase values from zero to three hundred sixty degrees;

a ROM lookup table for storing trigonometric values of the digital values output by said accumulator means, the output of said accumulator means comprising an address for addressing said ROM lookup table, with the value stored in the addressed locations corresponding to the trigonometric value of the output of said accumulator; and

a digital-to-analog converter for converting the digital output by said ROM lookup table to an analog value to comprise said carrier.

9. The phase modulation system of claim 8 wherein said phase modulation means comprises adder circuitry for adding the digital value output by said assembling means to the value stored in said accumulator.

10. A method for phase modulating a carrier, comprising:

receiving a digital input signal having a sequence of digital data bits;

mapping the digital data into discrete phase values in accordance with a predetermined phase modulation scheme;

filtering the discrete phase values in the phase domain to provide a phase domain filtered waveform by cross-correlation of a predetermined phase domain filter function with the discrete phase values disposed about a current one of the discrete phase values, the current one of the discrete phase values corresponding to a current one of the data bits, with said predetermined phase domain filter function having a reach that reaches a predetermined number of discrete phase values about the current discrete phase value;

generating a carrier; and

phase modulating the carrier with the phase domain filtered waveform.

11. The method of claim 10 wherein the predetermined phase modulation scheme includes variation in both amplitude and phase wherein the step of mapping comprises mapping the digital data into discrete phase values and discrete amplitude values, each of the discrete phase values having a discrete amplitude value associated therewith and further comprising filtering the discrete amplitude values in the amplitude domain by cross-correlating a predetermined amplitude domain filter function with a current one of the discrete amplitude values corresponding to the current discrete phase value, with the predetermined amplitude domain filter function having a reach equal to the reach of the predetermined phase domain filter function.

12. The method of claim 10 wherein the step of generating the carrier comprises:

periodically generating a phase increment value at a predetermined rate;

accumulating the phase incremented values to provide an output value, the step of accumulating the phase incremented values operating over a range from zero to three hundred sixty degrees;

storing digital trigonometric values of each of the accumulator values and outputting the trigonometric values in response to generation of the associated accumulated phase value; and

converting the digital trigonometric output value to an analog value to provide the carrier.