a control channel in a communication system transmits messages in a one or multiple - slot format . to assure consistency of a message , a content quality indicator is included in the message . because a terminal receiving the message does not know the number of slots comprising the message , the terminal performs blind format determination by testing hypothesis for all slot formats . unfortunately , the content of certain control messages results in control messages that appear to be valid in a sense that , the computed crc is equal to the interpreted crc . consequently , the mobile station declares a valid control message , and a false - alarm event occurs . moreover , the same control messages always result in the same false - alarm events . to prevent such repetitive incorrect determination , the content of the message is scrambled by a time - dependent scrambling sequence before transmission . re - generating the scrambling sequence , and performing inverse to the scrambling then unscrambles the received message .