Multi-protocol or multi-command RFID system

An interrogation system for communicating with backscatter transponders using a communication protocol having different commands, the interrogation system comprising;

• a plurality of interrogators, and
• a synchronization signal,
• each of the interrogators comprising a transmitter and a receiver,
• the transmitters being arranged for transmitting downlink signals in accordance with different commands over a downlink communications link to the transponders,
• the receivers being arranged for receiving respective uplink signals over an uplink communications signal link from the transponders,
• the synchronization signal being arranged for synchronizing the downlink signals for each of the plurality of interrogators,
• each of the interrogators operating in response to the synchronization signal to simultaneously transmit the downlink signals to the transponders to enable the transponders to provide their respective uplink signals after the transmission of the downlink signals, thereby enabling communication between respective ones of the interrogators and transponders without interference between the uplink signals from the transponders and the downlink signals from the interrogators.

An interrogator capable of communicating with a first set of transponders and a second set of transponders, the first and second set of transponders having different power, depth of modulation, or duty cycles, the interrogator comprising:

• a transmitter for transmitting a first downlink signal to the first set of transponders and a second downlink signal to the second set of transponders;
• a receiver for receiving a first uplink signal from the first set of transponders and a second uplink signal from the second set of transponders;
• and,
• a controller for controlling said transmitter to transmit the first and second downlink signals based on the power, depth of modulation, or duty cycle of the respective first and second sets of transponders, and for controlling said receiver to receive the first and second uplink signals based on the power, depth of modulation, or duty cycle of the respective first and second sets of transponders;
• wherein the interrogator operates in an environment with at least one additional like interrogator and all of the interrogators are responsive to a synchronization signal that enables the interrogators to simultaneously transmit downlink signals to the transponders to enable the transponders to provide their respective uplink signals after the transmission of the downlink signals, thereby enabling communication between respective ones of the interrogators and transponders without interference between the uplink signals from the transponders and the downlink signals from the interrogators.