Abstract: A clear channel assessment procedure is described. The procedure includes setting a threshold value of signal strength. When a message is ready to transmit, the received signal strength intensity (RSSI) is measured, and compared with the threshold. If the received signal strength is less than the threshold value, the message is transmitted, otherwise the system waits before trying again. After a predetermined number of failed attempts the threshold value is increased. The threshold value may be reduced if no acknowledgement is received.