Burst mode digital communications system

• US 6,493,398 B1
• Filed: 01/26/1999
• Issued: 12/10/2002
• Est. Priority Date: 10/07/1996
• Status: Expired due to Term

• Current Assignee: X-COM Systems LLC (Bird Technologies Group Incorporated)
• Original Assignee: David E. Erisman
• Inventors: Erisman, David E.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/236,669
• Time in Patent Office: 1,414 Days
• Field of Search: 375/302, 375/308, 375/300, 375/268, 375/269, 375/271, 375/279, 375/280
• US Class Current: 375/295
• CPC Class Codes: H04L 27/02 Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation H04L27/32 takes precedence
• CPC Class Codes: H04L 27/18 Phase-modulated carrier systems, i.e. using phase-shift keying H04L27/32 takes precedence

Abstract

A burst mode digital communications system which is unique in that it modulates a sinusoidal carrier with discrete cosine segments. The discrete cosine segments may contain different time and amplitude values. The discrete cosine segments may be combined with each other or with zero slope level segments in order to effectively modulate the sinusoidal carrier. Rather than employing the use of filters for controlling instantaneous voltage changes, the present communications system forces the bit edges of the discrete cosine segments to occur at the zero slope points of a cosine wave, where no voltage changes occur. The communications system utilizes direct digital synthesis in order to create a carrier signal which closely represents sinusoidal carrier signal. The present communication system may be used in conjunction with various conventional methods such as phase-shift keying and amplitude-shift keying. A device is also disclosed for demodulating the carrier signal in order to recover the original base band signal. The burst mode digital communications system may also demodulate data by employing adaptive templates for more accurately determining received digital symbols.

Claims

1. A method of modulating using a plurality of digital data blocks as carrier segments of a carrier, the method of modulating comprising the steps:

creating a table of amplitude coefficients representing predetermined shapes, each of said predetermined shapes beginning and ending with zero slope edges;

storing the table of amplitude coefficients in a read only memory look-up table;

sequentially receiving the plurality of digital data blocks, wherein each of the plurality of digital data blocks has a predetermined discrete value associated therewith out of a predetermined number of possibly assigned discrete values;

creating modulated carrier segments using each of the plurality of digital data blocks;

accessing a succession of address locations in the read only look-up table for stored amplitude coefficients corresponding to said predetermined shapes for each of the plurality of digital data blocks;

retrieving an equal number of successive stored amplitude coefficients from the read only memory look-up table that correspond to said predetermined shapes for each of the plurality of digital data blocks; and

directing the equal number of successive stored amplitude coefficients corresponding to said predetermined shapes to a digital-to-analog converter to produce a carrier waveform.

2. A method of modulating a plurality of digital data blocks as carrier segments of a carrier according to claim 1, further comprising the step of using a finite impulse response filter.

3. A method of modulating a plurality of digital data blocks as carrier segments of a carrier according to claim 1, wherein said step of sequentially receiving further comprises the step of initially receiving carrier segments and special symbols designed to provide symbol edge synchronization that can be used for a long series of data symbols to follow.

4. A method of modulating a plurality of digital data blocks as carrier segments of a carrier according to claim 3, wherein said step of sequentially receiving further comprises the step of using amplitudes of said special symbols as a standard from which voltage thresholds are derived.

5. A method of modulating a plurality of digital data blocks as carrier segments of-a carrier according to claim 1, wherein said step of sequentially receiving utilizes a digital logic controller and further comprises the step of determining the content of each of the plurality of digital data blocks.

6. A method of modulating a plurality of digital data blocks as carrier segments of a carrier according to claim 5, further comprising the step:

sending a signal from the digital logic controller to a phase accumulator indicative of a symbol to be transmitted;

determining successive address locations in the read only memory look-up table for stored amplitude coefficients corresponding to the symbol to be transmitted, and

retrieving successive stored amplitude coefficients corresponding to the symbol to be transmitted from the read only memory look-up table.

7. A method of modulating a plurality of digital data blocks as carrier segments of a carrier according to claim 6, wherein said step of sending a signal further comprises the steps:

informing the phase accumulator how many address locations to use for each symbol to be transmitted.

8. A method of modulating a plurality of digital data blocks as carrier segments of a carrier according to claim 6, further comprising the step of filtering the carrier waveform produced by said digital-to-analog converter in order to produce a low distortion carrier waveform.

9. A method of modulating using a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier, the method of modulating comprising the steps;

creating a table of amplitude coefficients representing predetermined shapes containing dual orthogonal frequency carrier segments;

storing the table of amplitude coefficients in a read only memory look-up table;

sequentially receiving the plurality of digital data blocks, wherein each of the plurality of digital data blocks has a predetermined discrete value associated therewith out of a predetermined number of possibly assigned discrete values;

creating modulated carrier segments using each of the plurality of digital data blocks representing two orthogonal frequency carriers;

accessing a succession of address locations in the read only memory look-up table for stored amplitude coefficients corresponding to said predetermined shapes for each of the plurality of digital data blocks;

retrieving an equal number of successive stored amplitude coefficients from the read only memory look-up table that correspond to said predetermined shapes for each of the plurality of digital data blocks; and

directing the equal number of successive stored amplitude coefficients corresponding to said predetermined shapes to a digital-to-analog converter to produce a dual orthogonal frequency carrier waveform.

10. A method of modulating a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier according to claim 9, further comprising the step of using a finite impulse response filter.

11. A method of modulating a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier according to claim 9, wherein said step of sequentially receiving further comprises the step of initially receiving carrier segments and special symbols designed to provide symbol edge synchronization that can be used for a long series of data symbols to follow.

12. A method of modulating a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier according to claim 11, wherein said step of sequentially receiving further comprises the step of using amplitudes of said special symbols as a standard from which voltage thresholds are derived.

13. A method of modulating a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier according to claim 9, wherein said step of sequentially receiving utilizes a digital logic controller, and further comprises the step of determining the content of each of the plurality of digital data blocks.

14. A method of modulating a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier according to claim 13, further comprising the step:

sending a signal from the digital logic controller to a phase accumulator indicative of a symbol to be transmitted;

determining successive address locations in the read only memory look-up table for stored amplitude coefficients corresponding to the symbol to be transmitted, and

retrieving successive stored amplitude coefficients corresponding to the symbol to be transmitted from the read only memory look-up table.

15. A method of modulating a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier according to claim 14, wherein said step of sending a signal further comprises the steps:

informing the phase accumulator how many address locations to use for each symbol to be transmitted.

16. A method of modulating a plurality of digital data blocks as carrier segments of a dual orthogonal frequency carrier according to claim 14, further comprising the step of filtering the carrier waveform produced by said digital-to-analog converter in order to produce a low distortion carrier waveform.

17. A method of digital carrier segment demodulation comprising the steps:

receiving digital carrier segment modulated data in a communication channel, the digital carrier segment modulated data comprising a plurality of carrier segments and a header of preamble carrier segments that defines a pattern for each digital state, wherein each of the carrier segments begins and ends with zero kinetic energy;

filtering the digital carrier segment modulated data;

digitally sampling and storing the received header as an adaptive template thus taking into consideration degradation that occurs in the communication channel for evaluating the digital carrier segment modulated data; and

recovering data from the plurality of carrier segments of the digital carrier segment modulated data by using the adaptive template for evaluating the digital carrier segment modulated data.

18. A method of digital demodulation as recited in claim 17, wherein said step of receiving includes subsequently receiving carrier segments which have associated digital values that are compared against the stored templates to determine how many digital values match the stored template values.

19. A method of digital carrier segment demodulation according to claim 18, further comprising the step of determining decision as to which carrier segment is received according to the template with the highest number of matches for each subsequently received carrier segment and using carrier segment amplitude values compared against stored voltage threshold values.

20. A method digital demodulation as recited in claim 18, further comprising the step of constantly updating the templates for each data burst or portion of a burst.

21. A method of digital demodulation as recited in claim 17, wherein said step of recovering is performed by detecting the presence of a carrier segment within a predetermined bit time.

22. A method of digital demodulation as recited in claim 17, wherein said step of recovering is performed by detecting the presence of a sine or cosine segment within a predetermined carrier segment duration.

23. A carrier segment communications system comprising:

means for sequentially receiving a plurality of digital data blocks, each of said digital data blocks having a predetermined discrete value associated therewith, said predetermined discrete value being chosen from a predetermined number of possibly assigned discrete values;

means for modulating said plurality of digital data blocks in order to construct a carrier signal having a plurality of carrier segments representing a predetermined set of shapes, said means for modulating including an input and an output;

means for determining completion of each of the plurality is of carrier segments of the carrier signal constructed by said means for modulating, said means for determining being coupled to the output of said means for modulating; and

a controller for producing a control signal indicative of a predetermined shape to be selected in accordance with a predetermined discrete value associated with said plurality of digital data blocks, said controller further including;

a first input coupled to said means for sequentially receiving;

a second input coupled to said means for determining; and

an output coupled to the input of said means for modulating.

24. A carrier segment communications system as recited in claim 23, wherein said means for sequentially receiving further includes means for determining initial carrier segments and special symbols designed to provide bit edge synchronization that can be used for a long series of data symbols to follow.

25. A carrier segment communications system as recited in claim 23, wherein said means for sequentially receiving further includes means for using amplitudes of said special symbols as a standard from which voltage thresholds are derived.

26. A cosine segment communications system as recited in claim 23, wherein said means for sequentially receiving further includes means for initially receiving a sequence of preamble symbols which are digitally sampled and stored for use as templates uniquely defining the pattern for each digital state.

27. A carrier segment communications system as recited in claim 26, wherein said means for sequentially receiving further includes means for subsequently receiving symbols that have associated digital values that are compared against the stored templates to determine how many digital values match the stored template values.

28. A carrier segment communications system as recited in claim 27, wherein said means for sequentially receiving further comprises means for determining a decision as to which symbol is received according to the template with the highest number of matches for each subsequently received symbol and using symbol amplitude values compared against stored voltage threshold values.

29. A carrier segment communications system as recited in claim 27, wherein said means for sequentially receiving further comprises means for constantly updating the templates for each data burst or portion of a burst.

30. A carrier segment communications system as recited in claim 23 further comprising:

means for transmitting said carrier signal to a remote destination;

means for remotely receiving said carrier signal; and

means for demodulating said carrier signal.

31. A carrier segment communications system as recited in claim 23 wherein said means for modulating further comprises:

a phase accumulator coupled to the output of said controller for receiving said control signal and generating a succession of phase address locations in accordance with said control signal; and

a read only memory look-up table having carrier segment coefficients stored therein in a successive manner corresponding to said phase address locations, thereby producing a succession of carrier segment coefficients.

32. A carrier segment communications system as recited in claim 23 wherein said means for modulating further includes:

a digital-to-analog converter coupled to said read only memory look-up table, said digital-to-analog converter being capable of converting said succession of carrier segment coefficients into analog signals; and

a filter capable of receiving said analog signals from said digital-to-analog converter and producing a low distortion sinusoidal waveform.

33. A carrier segment communications system as recited in claim 23 wherein said means for demodulating includes:

a first filter for removing unwanted noise and interference from the carrier signal transmitted to said means for receiving;

a first oscillator having a predetermined frequency corresponding to a frequency of one of said carrier segments;

a mixer having a first and second input for respectfully mixing signals from said first filter and said first oscillator, and an output for directing a resultant signal;

a second filter coupled to the output of said mixer for removing unwanted noise and interference from the resultant signal; and

means for recovering a carrier segment from said resultant signal.

34. A carrier segment communication system as recited in claim 33, wherein said first filter includes a predetermined number of outputs corresponding to said predetermined number of discrete values and said means for modulating further comprises:

a second oscillator having a predetermined frequency corresponding to the frequency of another one of said segments;

a second mixer having a first and second input for respectively receiving the signals from said first filter and said second oscillator, and an output for directing the resultant signal;

a third filter coupled to the output of said second oscillator for removing noise from the resultant signal;

a first peak detector coupled to the output of said second filter;

a second peak detector coupled to the output of said third filter;

a first carrier segment energy detector coupled to the output of said first peak detector;

a second carrier segment energy detector coupled to the output of said second peak detector; and

a comparator having two inputs and an output, each of said inputs being respectively coupled to said first and second carrier segment energy detectors.

35. A carrier segment communication system as recited in claim 34 wherein said peak detectors each include:

an operational amplifier having its inverted input coupled to said filter; and

a delay circuit having an input coupled to said filter, and an output coupled to the normal input of said operational amplifier.