<p>A first communication unit comprises a signature generator which generates a signal by spreading a first signature using a first spread spectrum code A transmitter transmits the signal in a first frequency interval at a first transmit power level The first frequency interval is a frequency interval assigned to the first communication unit for transmissions A second communication unit comprises a receiver which receives the signal in the first frequency interval A signature receiver generates a received signature by de-spreading the signal using the first spread spectrum code and a comparison processor determines if the received signature corresponds to the first signature If so, a transmitter is allowed to transmit in the first frequency interval and otherwise no transmissions are made by the second communication unit in the first frequency interval</p>
