COMMUNICATIONS SYSTEMS AND TRANSMITTERS AND RECEIVERS INCLUDING SCRAMBLING DEVICES

摘要

Pseudo-random number (PN) sequence generators used in scrambling and descrambling circuits at separate locations are periodically preset to the same start value in order to maintain synchronism, with the preset value being also periodically changed. The preset value can be transmitted to the scrambling and descrambling circuits over a privacy channel once per frame and stored in storage registers (20) associated with each of the scrambling and descrambling circuits (22, 24). The stored starting state values can be loaded into the PN sequence generators (22) as often as desired to maintain proper synchronization, with the stored values themselves being changed at a rate dependent on the desired degree of security.