Multiplex communications – Wide area network – Packet switching
Patent
1994-08-16
1996-08-27
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 22000, 375205000, H04J 1300
Patent
active
055508090
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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Bottomley Gregory E.
Dent Paul W.
Ericsson Ge Mobile Communications, Inc.
Olms Douglas W.
Ton Dang
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