Radio communication system wherein transceivers retransmit messages in synchronism

A radio communication system comprises a first transceiver (M) and a plurality of further transceivers (S1 to S6) of which some (S4 to S6) but not all are out of range of the first transceiver (M) and none of which is out of range of all the others. In operation the first transceiver (M) transmits a radio message having a pre-determined format, and each of the further transceivers (S1 to S6) receiving the message, whether directly (S1, S2 and S3) or indirectly (S4 and S5), re-transmits that message in synchronism or substantially in synchronism with all the other further tranceivers which received the message at the same time, so that in general a further transceiver out of range of the first transceiver will receive the message simultaneously from two or more sources.