Multiple access coding using bent sequences for mobile radio communications
First Claim
1. In a system for communicating a sequence of information symbols, a transmitter comprising:
- means for spreading each information symbol with a respective spreading sequence, thereby forming a sequence of spread symbols, wherein the spreading sequences are selected from a set of spreading sequences that are mutually orthogonal or bi-orthogonal;
means for scrambling each spread symbol with a common scramble mask, thereby producing a sequence of scrambled symbols, wherein the common scramble mask is selected from a set of scramble masks having optimal or semi-optimal correlation properties; and
means for transmitting the sequence of scrambled symbols over a communication channel.
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Accused Products
Abstract
Information symbols spread using orthogonal or bi-orthogonal codewords are assigned a unique scramble mask that is taken from a set of scramble masks having selected correlation properties. The set of scramble masks is selected such that the correlation between the modulo-2 sum of two scramble masks with any codeword is a constant magnitude, independent of the codeword 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 scramble 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
50 Claims
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1. In a system for communicating a sequence of information symbols, a transmitter comprising:
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means for spreading each information symbol with a respective spreading sequence, thereby forming a sequence of spread symbols, wherein the spreading sequences are selected from a set of spreading sequences that are mutually orthogonal or bi-orthogonal; means for scrambling each spread symbol with a common scramble mask, thereby producing a sequence of scrambled symbols, wherein the common scramble mask is selected from a set of scramble masks having optimal or semi-optimal correlation properties; and means for transmitting the sequence of scrambled symbols over a communication channel. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. In a system for communicating sequences of information symbols, a receiver comprising:
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means for receiving a composite signal including a plurality of spectrally overlapping sequences of spread, scrambled information symbols; means for descrambling the composite signal with a scramble mask selected from a set of scramble masks having optimal or semi-optimal correlation properties, thereby producing a sequence of descrambled symbols; means for despreading the sequence of descrambled symbols using spreading sequences, including means for correlating at least one shift of each descrambled symbol with at least one of the spreading sequences, thereby producing at least one correlation value for each descrambled symbol, wherein the spreading sequences are mutually orthogonal or bi-orthogonal; and means for processing the correlation values to detect at least one sequence of information symbols. - View Dependent Claims (20, 21, 22, 23, 24, 25)
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26. A method of transmitting a sequence of information symbols comprising the steps of:
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spreading each information symbol with a respective spreading sequence, thereby forming a sequence of spread symbols, wherein the spreading sequences are selected from a set of spreading sequences that are mutually orthogonal or bi-orthogonal; scrambling each spread symbol with a common scramble mask, thereby producing a sequence of scrambled symbols, wherein the common scramble mask is selected from a set of scramble masks having optimal or semioptimal correlation properties; and transmitting the sequence of scrambled symbols over a communication channel. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43)
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44. A method of detecting information symbols comprising the steps of:
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receiving a composite signal including a plurality of spectrally overlapping sequences of spread, scrambled information symbols; descrambling the composite signal with a scramble mask selected from a set of scramble masks having optimal or semi-optimal correlation properties, thereby producing a sequence of descrambled symbols; despreading the descrambled symbols using spreading sequences, including the steps of correlating at least one shift of each descrambled symbol with at least one of the spreading sequences, thereby producing at least one correlation value for each descrambled symbol, wherein the spreading sequences are mutually orthogonal or bi-orthogonal; and processing the correlation values to detect at least one sequence of information symbols. - View Dependent Claims (45, 46, 47, 48, 49, 50)
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Specification