Cryptography – Communication system using cryptography – Time segment interchange
Patent
1992-04-10
1994-10-04
Swann, Tod R.
Cryptography
Communication system using cryptography
Time segment interchange
375 1, 380 34, H04K 100
Patent
active
053533526
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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Bottomley Gregory E.
Dent Paul W.
Ericsson - GE Mobile Communications Inc.
Swann Tod R.
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