Multiple access coding for radio communications
First Claim
1. A terminal for a communication system including a base station and the terminal, information being exchangeable between the terminal and the base station by direct sequence spread spectrum communication, the terminal comprising:
- means for converting information for transmission to digital words;
means for converting digital words to corresponding Walsh-Hadamard words;
means for combining Walsh-Hadamard words with a coding sequence to produce coded words;
a modulator, wherein the modulator uses coded words to modulate a carrier signal; and
a code generator, wherein the code generator generates the coding sequence by clocking through a plurality of internal states based on a binary mask that is known only to the terminal and the base station.
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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.
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Citations
9 Claims
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1. A terminal for a communication system including a base station and the terminal, information being exchangeable between the terminal and the base station by direct sequence spread spectrum communication, the terminal comprising:
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means for converting information for transmission to digital words; means for converting digital words to corresponding Walsh-Hadamard words; means for combining Walsh-Hadamard words with a coding sequence to produce coded words; a modulator, wherein the modulator uses coded words to modulate a carrier signal; and a code generator, wherein the code generator generates the coding sequence by clocking through a plurality of internal states based on a binary mask that is known only to the terminal and the base station.
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2. In a communications system using direct sequence spread spectrum multiple access for communication between a communications network and a terminal, a terminal providing communications privacy when communicating with the network, comprising:
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a sequence generator that supplies a spread spectrum sequence and a cipher sequence, the cipher sequence being dependent on a first bit pattern that is known only to the terminal and the network and the spread spectrum sequence being dependent on a second bit pattern; a coder that converts speech for communication to digital words, each digital word having a first number of bits; a cipherer that combines digital words with the cipher sequence to produce ciphered words, each ciphered word having a second number of bits; a spread spectrum coder that combines ciphered words with the spread spectrum sequence to produce a digital spread spectrum signal; and means for generating a radio frequency carrier signal that is modulated with the digital spread spectrum signal for communication to the network. - View Dependent Claims (3)
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4. In a mobile communications system using direct sequence spread spectrum multiple access for communication between a communications network and a plurality of mobile terminals, a receiver in the network for signals transmitted by a mobile terminal, comprising:
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a radio receiver that produces a stream of baseband digital samples; a sequence generator that supplies a spread spectrum sequence and a cipher sequence, the cipher sequence being dependent on a first bit pattern that is known only to the network and the mobile terminal and the spread spectrum sequence being dependent on only a second bit pattern; a spread spectrum decoder that combines the stream of digital samples with the spread spectrum sequence to produce sample groups, each sample group including a first number of decoded digital samples; a decipherer that combines sample groups with the cipher sequence to produce deciphered words, each deciphered word having a second number of bits; and a decoder that converts deciphered words to a speech signal for transmission over the communications network. - View Dependent Claims (5)
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6. In a mobile communications system using direct sequence spread spectrum multiple access for communication between a communications network and a plurality of mobile terminals, a base station in the communications network for providing communications privacy when in communication with a mobile terminal, comprising:
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a sequence generator that supplies a spread spectrum sequence and a cipher sequence, the cipher sequence being determined by a first bit pattern that is known only to the communications network and the mobile terminal and the spread spectrum sequence being determined by a second bit pattern; coding means for converting speech for transmission to the mobile terminal to a sequence of digital words, each digital word having a first number of bits; ciphering means for combining digital words with the cipher sequence to produce ciphered words, each ciphered word having the first number of bits; a converter that converts ciphered words to codewords using at least one Walsh-Hadamard codeword, each codeword having a second number of bits and the second number being greater than the first number; means for generating a spread spectrum signal based on the codewords and the spread spectrum sequence; and means for generating a radio frequency carrier signal modulated with the spread spectrum signal for transmission to the mobile terminal. - View Dependent Claims (7)
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8. In a mobile communications system using direct sequence spread spectrum multiple access for communication between a communications network and a plurality of mobile terminals, a receiver in a mobile terminal for signals transmitted by a base station in the communications network, comprising:
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a sequence generator that supplies a cipher sequence that depends on a first bit pattern and a spread spectrum sequence that depends on a second bit pattern, the first bit pattern being known only to the mobile terminal and communications network; a radio receiver that produces a stream of digital samples that represent a radio signal transmitted by the base station; means for generating sample groups based on digital samples and the spread spectrum sequence, each sample group containing a first number of decoded digital samples; a converter that converts sample group to symbols using at least one Walsh-Hadamard codeword, each symbol containing at least one bit; deciphering means for combining symbols with the cipher sequence to produce deciphered symbols; and decoding means for converting deciphered symbols to a speech signal. - View Dependent Claims (9)
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Specification