Multiple access coding using bent sequences for mobile radio communications
US5550809A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 16, 1994 |
| Grant date | Aug 27, 1996 |
| Priority date | — |
| Expiry date | Aug 16, 2014 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L2209/34
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.