Tag frequency control

A communication system comprising:

• one or more transceiver units of a first type;
• two or more transceiver units of a second type, the transceiver units of a second type being capable of communicating with the transceiver units of the first type, and each transceiver unit of the second type comprising a local frequency reference unit on which the frequency of signals transmitted by it are dependent;
• wherein at least one transceiver unit of the first type comprises:
• a frequency comparison unit configured to compare the frequency of signals received from transceiver units of the second type with a reference frequency and to form an offset signal representative of the average offset between the frequency of the received signals and the reference frequency;
• and
• a frequency adjustment unit for adjusting the reference frequency in accordance with the offset signal.

A method for adjusting the transmit and/or receive frequency of a transceiver unit in a communication system comprising one or more transceiver units of a first type, and two or more transceiver units of a second type, the transceiver units of a second type being capable of communicating with the transceiver units of the first type;

• the method comprising:
• making a comparison of the frequency of a signal received by a transceiver unit of the first type from a transceiver unit of the second type with a reference frequency;
• forming an offset signal representative of the offset between the frequency of the signal received from the transceiver unit of the second type with the reference frequency;
• storing feedback data representative of the offset signal in respect of that transceiver unit of the second type;
• and
• adjusting the transmit and/or receive frequency of the transceiver unit of the first type for communication with one of the transceiver units of the second type in accordance with feedback data stored in respect of that transceiver unit of the second type.

A method for adjusting a reference frequency of a transceiver unit in a communication system comprising one or more transceiver units of a first type, and two or more transceiver units of a second type, the transceiver units of the second type being capable of communicating with the transceiver units of the first type, each transceiver unit of the second type comprising a local frequency reference unit on which the frequency of signals transmitted by it are dependent;

• the method comprising:
• comparing the frequency of signals received from transceiver units of the second type with a reference frequency;
• forming an offset signal representative of the average offset between the frequency of the received signals and the reference frequency;
• and
• adjusting the reference frequency in accordance with the offset signal.