A communication system comprising one or more transceiver units of a first type and one or more transceiver units of a second type capable of communicating with the transceiver units of the first type; each transceiver unit of the first type comprising: a frequency comparison unit for comparing the frequency...http://www.google.es/patents/US8045930?utm_source=gb-gplus-sharePatente US8045930 - Tag frequency control
