Radio communication system

A radio communication system comprises a radio transmitter (2), and a radio receiver (12) configured to receive radio transmissions from the transmitter. The transmitter (2) uses a transmitter clock signal to transmit a succession of connection-event data packets (22a′, 22b′, 22c′) according to a predetermined schedule. The receiver (12) enters a sleep state between receiving successive connection-event data packets from the transmitter (2), in which it does not receive and process radio transmissions from the transmitter. It uses a receiver clock signal to determine when a predetermined number of receiver clock cycles has elapsed after receiving one of the connection-event data packets (22b′), and then enters a ready state. The predetermined number of receiver clock cycles is the number of receiver clock cycles (34a) that elapsed between the respective receipts of two of the connection-event data packets (22a′, 22b′) received by the receiver (12) minus a correction factor (38).