Multiple access coding for radio communications
US5353352A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Apr 10, 1992 |
| Grant date | Oct 4, 1994 |
| Priority date | — |
| Expiry date | Apr 10, 2012 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L2209/34
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.