Control channel for time division multiple access systems

Abstract

In a TDMA system a multifunction control channel is employed that carries data used for implementing channel access functionality for users and is also employed at the remote terminals in the performance of modem functionality. In other words, information necessary to accurately receive data on the user traffic channels is obtainable by processing the multifunction control channel. This is achieved by arranging the broadband channel of the TDMA system as a repeating frame having time slots in which at least one time slot is reserved for use as the multifunction control channel, and the data that is transmitted on the multifunction control channel is encoded using a spread spectrum format. To this end the data carried on the multifunction control channel is encoded in a way that uses each symbol of the multifunction control channel as if it were a so-called spread spectrum 'chip'. At least one of the remaining time slots of the frame, and preferably all of the remaining time slots, which are typically used to carry user traffic arranged as logical channels, are not spread spectrum encoded. With regard to modem functionality, the remote terminals use the received multifunction control channel to a) perform frame synchronization, i.e., frame timing, b) perform frequency offset estimation, c) obtain an estimate of the channel impulse response, and d) estimate the received signal strength for use in gain control.