Multiple access coding for radio communications
First Claim
1. In a communications system for simultaneous communication of spectrally overlapping information signals, a transmitter comprising:
- means for encoding individual information signals into blocks of codewords;
means for generating a scrambling mask for each codeword from a set of scrambling masks that have optimal correlation properties;
means for combining a different scrambling mask with each codeword to obtain uniquely scrambled codewords; and
means for transmitting the scrambled codewords over a communication channel.
1 Assignment
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Accused Products
Abstract
Individual information signals encoded with a common block error-correction code are assigned a unique scrambling mask, or signature sequence, taken from a set of scrambling masks having selected correlation properties. The set of scrambling masks is selected such that the correlation between the modulo-2 sum of two masks with any codeword in the block code is a constant magnitude, independent of the mask set and the individual masks being compared. In one embodiment, when any two masks are summed using modulo-2 arithmetic, the Walsh transformation of that sum results in a maximally flat Walsh spectrum. For cellular radio telephone systems using subtractive CDMA demodulation techniques, a two-tier ciphering system ensures security at the cellular system level by using a pseudorandomly generated code key to select one of the scrambling masks common to all of the mobile stations in a particular cell. Also, privacy at the individual mobile subscriber level is ensured by using a pseudorandomly generated ciphering key to encipher individual information signals before the scrambling operation.
221 Citations
67 Claims
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1. In a communications system for simultaneous communication of spectrally overlapping information signals, a transmitter comprising:
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means for encoding individual information signals into blocks of codewords; means for generating a scrambling mask for each codeword from a set of scrambling masks that have optimal correlation properties; means for combining a different scrambling mask with each codeword to obtain uniquely scrambled codewords; and means for transmitting the scrambled codewords over a communication channel. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. In a communications system for simultaneous communication of coded, scrambled, spectrally overlapping information signals, a receiver comprising:
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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. - View Dependent Claims (37)
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38. A communications system for simultaneous communication of a plurality of coded, scrambled, spectrally overlapping information signals, comprising:
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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. - View Dependent Claims (39, 40, 41, 42)
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43. A method for simultaneously transmitting a plurality of spectrally overlapping information signals comprising the steps of:
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(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. - View Dependent Claims (44, 45, 46, 47, 48, 49, 50, 51, 52)
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53. A method for simultaneously receiving a plurality of spectrally overlapping information signals comprising the steps of:
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(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. - View Dependent Claims (54)
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55. A method for simultaneously communicating a plurality of spectrally overlapping information signals comprising the steps of:
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(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. - View Dependent Claims (56, 57, 58)
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59. In a communications system for simultaneously communicating a plurality of spectrally overlapping signals, a transmitter comprising:
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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. - View Dependent Claims (60, 61, 62, 63, 64)
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65. In a communications system for simultaneously communicating a plurality of spectrally overlapping signals, a receiver comprising:
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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. - View Dependent Claims (66)
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67. A communications system for simultaneously communicating a plurality of spectrally overlapping signals, comprising:
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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.
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Specification