Abstract: A communication system for communicating between a first device and a second device is disclosed. The first device includes a first processor and a first memory, while the second device includes a second processor a second memory. The processors allow communication between the devices when an identical identification code is stored in both devices. In response to a user command, the first processor replaces an old identification code with a new identification code in a first memory location of the first memory. In response to a request signal from the first device, the second processor replaces the old identification code in a first location of the second memory with the new identification code. In response to an acknowledge signal from the second device, and after verifying that the new identification code is included in the acknowledge signal, the first processor replaces the old identification code in a second memory location of the first memory.

Abstract: A method of generating a random number is disclosed for forming an identification code used for mutual identification between a base station and a mobile telephone. The method includes receiving a radio signal by the base station or the mobile telephone; performing time intervals measurements separating passages of the radio signal through a reference level; and forming the random number from the time intervals measurements.

Abstract: A channel is selected first, and immediately the received field is measured and digital Manchester code data are searched for. The digital signals are 100% Manchester code signals. After a predetermined first delay, the carrier level is tested and recorded in a memory. The smallest value among the various recorded values is selected; a fixed value is added thereto; and the value thus obtained is used as a threshold value for the level test. If the channel is free, another channel is selected. If the channel is occupied, one will wait for a second delay period, after which a test is performed to know whether data have been recognized. If nothing has been recognized, another channel is selected.