Transmitting spread spectrum data with commercial radio

A method of spread-spectrum encoding at least first and second information signals, the method comprising:

• generating at least first and second code sequences having the same number of digital signals, any two of said code sequences, when compared in-phase to each other, having near-zero cross-correlation;
• producing an output code sequence having a plurality of output levels corresponding to the number of digital signals in any one of said code sequences, said output levels being formed from sums of products by repeating, for corresponding selected positions in the first and second code sequences, the steps of
• forming a first product by multiplying said first information signal with a digital signal in the selected position of the first code sequence,
• forming a second product by multiplying said second information signal with a digital signal in the selected position of the second code sequence, and
• summing the first and second products to produce an output level;
• and
• adding a synchronization pulse to said plurality of output levels.

A method of extracting first and second information signals from a received sequence of levels, the method comprising:

• generating a first code sequence comprising digital signals arranged in respective positions and having near-zero out-of-phase autocorrelation;
• generating a second code sequence comprising digital signals arranged in respective positions, the values of the digital signals having a phase shifted relation to said plurality of digital signals of said first code sequence;
• said first and second code sequences further comprising an extra predetermined digital signal in the same predetermined position within each of said code sequences such that said code sequences, when compared in-phase to each other, have exactly zero cross-correlation,
• producing first and second correlation values respectively correlating said first and second code sequences to a window of said received sequence of levels received during a time interval, said correlation values formed by
• multiplying a level in a selected position of said window of said received sequence of levels by a digital signal in the corresponding selected position of a code sequence to form a product,
• repeating said multiplying for additional selected positions in said window and said code sequence to form additional products, and
• summing the products to produce a correlation value;
• and
• determining a value for said first and second information signals from said first and second correlation values.

A method of extracting first and second information signals from a received sequence of levels including a synchronization pulse, the method comprising:

• generating at least first and second code sequences having the same number of digital signals, any two of said code sequences, when compared in-phase to each other, having near-zero cross-correlation;
• detecting said synchronization pulse to define a reference time;
• initiating a time interval at a time having a predetermined relationship to said reference time;
• and
• producing first and second correlation values respectively correlating said first and second code sequences to a window of said received sequence of levels received during said time interval, said correlation values formed by
• multiplying a level in a selected position of said window of said received sequence of levels by a digital signal in the corresponding selected position of a code sequence to form a product,
• repeating said multiplying for additional selected positions in said window and said code sequence to form additional products, and
• summing the products to produce a correlation value;
• and
• determining a value for said first and second information signals from said first and second correlation values.

Apparatus for spread-spectrum encoding at least first and second information signals, comprising:

• circuitry generating a first code sequence comprising digital signals arranged in respective positions and having values with near-zero out-of-phase autocorrelation;
• and generating a second code sequence comprising the same number of digital signals as there are in said first code sequence, arranged in respective positions, the values of the digital signals having a phase shifted relation to said digital signals of said first code sequence, said circuitry comprising
• a shift register, an input of said shift register being generated in response to a logical function of two or more outputs of said shift register, and
• circuitry for initializing said shift register with a generator code,
• an output of said shift register shifting out the digital signals in a selected position of each of said code sequences after said shift register is initialized with an appropriate generator code;
• and
• circuitry producing an output code sequence having a plurality of output levels corresponding to the number of digital signals in either of said code sequences, said output levels being formed from sums of products, including
• circuitry forming a first product by multiplying said first information signal with a digital signal in a selected position of the first code sequence, and forming a second product by multiplying said second information signal with a digital signal in a corresponding selected position of the second code sequence, comprising a single multiplier circuit responsive to said digital signals shifted out of said shift register and to said information signals, and
• circuitry summing the first and second products to produce an output level, comprising an accumulator accumulating products produced by said single multiplier.

Apparatus for spread-spectrum encoding at least first and second information signals, comprising:

• circuitry generating at least first and second code sequences having the same number of digital signals, any two of said code sequences, when compared in-phase to each other, having near-zero cross-correlation;
• circuitry producing an output code sequence having a plurality of output levels corresponding to the number of digital signals in any one of said code sequences, said output levels being formed from sums of products, including
• circuitry forming a first product by multiplying said first information signal with a digital signal in a selected position of the first code sequence, and forming a second product by multiplying said second information signal with a digital signal in a corresponding selected position of the second code sequence, and
• circuitry summing the first and second products to produce an output level;
• and
• circuitry adding a synchronization pulse to said output levels of said output code sequence.

Apparatus for extracting first and second information signals from a received sequence of levels, comprising:

• circuitry generating a first code sequence comprising digital signals arranged in respective positions and having near-zero out-of-phase autocorrelation, and generating a second code sequence comprising digital signals arranged in respective positions, the values of the digital signals having a phase shifted relation to said plurality of digital signals of said first code sequence, comprising a shift register, an input of said shift register being generated in response to a logical function of two or more outputs of said shift register, and circuitry for initializing said shift register with a generator code, an output of said shift register shifting out the digital signals of a said code sequence after said shift register is initialized with an appropriate generator code;
• circuitry producing first and second correlation values respectively correlating said first and second code sequences to a window of said received sequence of levels received during a time interval, including
• circuitry multiplying a level in a selected position of said window of said received sequence of levels by a digital signal in the corresponding selected position of a code sequence to a product, comprising a buffer for storing said window of said received sequence of levels and for sequentially producing each level in said window, and a single multiplier circuit responsive to digital signals shifted out of said shift register and to levels sequentially produced by said buffer, and
• circuitry summing products to produce a correlation value, comprising an accumulator accumulating products produced by said single multiplier to produce each correlation value;
• and
• circuitry determining a value for said first and second information signals from said first and second correlation values.

Apparatus for extracting first and second information signals from a received sequence of levels including a synchronization pulse, comprising:

• circuitry generating at least first and second code sequences having the same number of digital signals, any two of said code sequences, when compared in-phase to each other, having near-zero cross-correlation;
• circuitry producing first and second correlation values respectively correlating said first and second code sequences to a window of said received sequence of levels received during a time interval, including
• circuitry detecting said synchronization pulse to define a reference time, said time interval having a predetermined relationship to said reference time,
• circuitry multiplying a level in a selected position of said window of said received sequence of levels by a digital signal in the corresponding selected position of a code sequence to form a product, and
• circuitry summing products to produce a correlation value;
• and
• determining a value for said first and second information signals from said first and second correlation values.