Multiple access coding for radio communications

In a communications system for simultaneous communication of coded, scrambled, spectrally overlapping information signals, a receiver comprising:

• means for receiving a composite signal including a plurality of said overlapping information signals;
• means for combining a selected scrambling mask with said composite signal to generate a descrambled signal;
• means for decoding said descrambled signal, including means for correlating the descrambled signal with a set of codewords to produce a correlation spectrum;
• and
• means for identifying a correlation component in said correlation spectrum having a greatest magnitude and extracting said correlation component as a decoded information signal,
• wherein the selected scrambling mask is a bit sequence having a length equal to the lengths of the codewords.

A communications system for simultaneous communication of a plurality of coded, scrambled, spectrally overlapping information signals, comprising:

• means for encoding individual information signals into blocks of codewords using error correction codes;
• means for generating a scrambling mask for each coded information signal from a set of scrambling masks that have optimal correlation properties;
• means for combining a different scrambling mask with each codeword to obtain a uniquely scrambled codeword;
• means for transmitting uniquely scrambled codewords over a communication channel;
• means for receiving a composite signal including a plurality of said uniquely scrambled codewords;
• means for combining a selected scrambling mask with said composite signal to generate a descrambled signal;
• means for decoding said descrambled signal including means for correlating the descrambled signal with the error correction codewords to produce a correlation spectrum;
• and
• means for identifying a correlation component in said correlation spectrum having a greatest magnitude and extracting said correlation component as a decoded information signal.

A method for simultaneously transmitting a plurality of spectrally overlapping information signals comprising the steps of:

• (a) digitizing an information signal;
• (b) encoding blocks of binary digits of the digitized information signal into codewords;
• (c) producing a set of scrambling masks having optimal correlation properties;
• (d) combining a selected scrambling mask with a codeword to obtain a scrambled codeword;
• and
• (e) transmitting said scrambled codewords over a communications channel.

A method for simultaneously receiving a plurality of spectrally overlapping information signals comprising the steps of:

• (a) receiving a composite signal including a plurality of coded information signals;
• (b) combining a selected one of a plurality of scrambling masks with said composite signal to generate a descrambled signal;
• and
• (c) decoding said descrambled signal by correlating the descrambled signal with a plurality of error correction codewords to generate a correlation spectrum;
• identifying a correlation component in said spectrum having a greatest magnitude;
• and extracting said correlation component as a decoded information signal,
• wherein the selected scrambling mask is a bit sequence having a length equal to the lengths of the error correction codewords.

A method for simultaneously communicating a plurality of spectrally overlapping information signals comprising the steps of:

• (a) converting an information signal into digital format;
• (b) encoding blocks of binary digits of the information signal into codewords;
• (c) producing a set of scrambling masks having optimal correlation properties;
• (d) combining a selected scrambling mask with a codeword to obtain a scrambled codeword;
• (e) transmitting said scrambled codewords over a communications channel;
• (f) receiving a composite signal including a plurality of the scrambled codewords;
• (g) combining a selected scrambling mask with said composite signal to generate a descrambled signal;
• and
• (h) decoding said descrambled signal by correlating the descrambled signal with the codewords to generate a correlation spectrum;
• identifying a correlation component in said spectrum having a greatest magnitude;
• and extracting said correlation component as a decoded information signal.

In a communications system for simultaneously communicating a plurality of spectrally overlapping signals, a transmitter comprising:

• means for converting a signal into blocks of M binary digits;
• means for generating a first pseudorandom number associated with a block and for generating a second pseudorandom number;
• first means for combining said first pseudorandom number with said blocks to obtain an enciphered signal;
• means for encoding said enciphered signal using block codes to obtain a codeword;
• means for storing a set of scrambling masks having optimal correlation properties;
• means for offsetting said second pseudorandom number to obtain a scrambling mask address;
• means for retrieving a scrambling mask from said storing means based on said scrambling mask address;
• second means for combining said retrieved scrambling mask with said codeword to obtain a scrambled codeword;
• and
• means for transmitting said scrambled codeword over a communications channel.

In a communications system for simultaneously communicating a plurality of spectrally overlapping signals, a receiver comprising:

• means for receiving a composite signal including a plurality of said overlapping information signals;
• means for generating a scrambling mask address and for retrieving a scrambling mask from a memory based on the scrambling mask address;
• means for combining said retrieved scrambling mask with said composite signal to generate a descrambled signal;
• means for transforming said descrambled signal using error correction codewords to generate a correlation spectrum;
• means for identifying a correlation component in said correlation spectrum having a greatest magnitude as a decoded information signal;
• and
• means for deciphering said decoded information signal using a pseudorandom number associated with the information signal,
• wherein the retrieved scrambling mask is a bit sequence having a length equal to the lengths of the error correction codewords.

A communications system for simultaneously communicating a plurality of spectrally overlapping signals, comprising:

• means for converting a signal into blocks of M binary digits;
• means for generating a first pseudorandom number associated with a signal block and a second pseudorandom number;
• first means for combining said first pseudorandom number with said signal block to obtain an enciphered signal;
• means for encoding said enciphered signal using block codes to obtain a codeword;
• means for storing a set of scrambling masks having optimal correlation properties;
• means for offsetting said second pseudorandom number to obtain a scrambling mask address;
• means for retrieving a scrambling mask from said storing means based on said address;
• second means for combining said retrieved scrambling mask with said codeword to obtain a scrambled codeword;
• means for transmitting said scrambled codeword over a communications channel;
• means for receiving a composite signal including a plurality of said overlapping information signals;
• means for generating said scrambling mask address;
• means for combining said retrieved scrambling mask with said composite signal to generate a descrambled signal;
• means for transforming said descrambled signal using error correction codewords to generate a correlation spectrum;
• means for identifying a correlation component in said spectrum having a greatest magnitude as a decoded information signal;
• and
• means for deciphering said decoded signal using said first pseudorandom number.