A transmission procedure for use in a communication system including a base station and one or more terminals. The base station transmits a signal to a terminal, and provides the terminal with possible characteristics of a further signal for transmission from the terminal to the base station, the possible characteristics including at least one of: one or more locations for transmission of the further signal in the time domain; and one or more locations for the transmission of the further signal in the frequency domain; and wherein transmission of the further signal from the terminal, with one or more characteristics selected by the terminal from the possible characteristics, indicates further information relating to the terminal.