Radio communication system

A positioning system comprising:

• a network comprising a plurality of first-radio-protocol access points and a second-radio-protocol radio transmitter, wherein:
• each of the first-radio-protocol access points is configured for bi-directional communication, using a first radio protocol, with devices that have been associated with the first-communication radio-protocol access point by an association data exchange, wherein the first radio protocol conforms to, or is compatible with, one of the IEEE 802.11 standards;
• each of the first-radio-protocol access points is further configured to receive, at a first data rate using the first radio protocol, a multicast radio message from a wireless communication unit that is not associated with the first-radio-protocol access point, and to forward the message onto the network;
• and
• the second-radio-protocol radio transmitter is configured to send data at a second data rate which is lower than the first data rate, using a second radio protocol which is different from the first radio protocol;
• a wireless communication unit:
• comprising a first-radio-protocol radio transmitter configured to transmit a multicast radio message at the first data rate using the first radio protocol, wherein the multicast radio message comprises (i) identification information relating to the wireless communication unit, and (ii) information relating to the position of the wireless communication unit, or information from which the position of the wireless communication unit can be derived;
• and
• comprising a second-radio-protocol radio receiver configured to receive synchronization information from said second-radio-protocol radio transmitter using the second radio protocol, and configured to use said synchronization information for time synchronization;
• and
• a server configured to:
• receive and process the multicast message from the wireless communication unit, forwarded to the server by one of the first access points, to determine the position of the wireless communication unit.

A wireless communication unit comprising:

• a first radio transmitter configured to transmit a multicast radio message at a first data rate using a first radio protocol to a plurality of first access points, wherein the wireless communication unit is not associated with any of the first access points, wherein the first radio protocol conforms to, or is compatible with, one of the IEEE 802.11 standards, and wherein the multicast radio message includes (i) identification information relating to the wireless communication unit, and (ii) information relating to the position of the wireless communication unit, or from which the position of the wireless communication unit can be derived;
• a second radio transmitter, configured to transmit messages to a second access point using a second radio protocol which is different from the first radio protocol;
• and
• a radio receiver configured to receive and decode a control message, addressed to the wireless communication unit, from the second access point at a second data rate which is lower than the first data rate, using the second radio protocol, the wireless communication unit being configured to execute a function in response to receiving the control message.