Ramped interrogation power levels
A method for communicating with a plurality of radio frequency (RF) devices includes transmitting a first signal at a first power level, interrogating RF devices responding to the first signal, instructing the responding RF devices to change state, and transmitting a second signal at a second power level higher than the first power level. The RF devices responding to the first signal do not respond to the second signal upon changing state.
1. A method for communicating with a plurality of radio frequency identification (RFID) devices by, comprising:
transmitting a series of signals comprising a first signal and a second signal, using a first RFID reader, the second signal being transmitted at an increased power level relative to the first signal;
transmitting a third signal having a power level increasing from a first power level to a second power level in a continuous analog manner where a rate of the continuous increasing slows as the power level of the third signal increases;
interrogating RFID devices responding to at least one signal in the series of signals;
receiving a selection of each power level from a backend system, at least some of the power levels being selected by the backend system based on response from the first RFID reader and one or more other RFID readers in communication with the backend system so that the selected power levels do not interfere with a query being conducted by a second RFID reader simultaneously with the transmitting of the series of signals, the first and the second RFID readers being connected to the backend system; and
at each power level:
singulating RFID devices responding to the signal via backscatter communications;
instructing the responding RFID devices to change state to an unresponsive state;
wherein the first signal is transmitted at the first power level,
wherein the second signal is transmitted at the second power level,
wherein the transmitting the series of signals, the interrogating the RFID devices, and the instructing the responding RFID devices to change state are performed by the first RFID reader,
wherein one or more of the RFID devices responding to the first signal do not respond to the second signal upon changing state in response to the instruction to change state to the unresponsive state; and
wherein a variation in a backscattering power level of the RFID devices located within a maximum effective communication range is less than about 100:1.
2. The method of claim 1 , wherein the unresponsive state is a sleep mode.
3. The method of claim 1 , wherein a time period of transmission of each signal is about the same.
4. The method of claim 1 , wherein a time period of transmission of each signal is different.
5. The method of claim 1 , wherein a time period of transmission of each signal is dependent upon a result of a protocol search.
6. The method of claim 1 , wherein the backend system selects an amount of time to remain at each of the first and second power levels.
7. The method of claim 1 , wherein the RFID devices are RFID tags.
8. The method of claim 1 , wherein a time period of transmission of each of the series of signal is about the same,
wherein a speed at which the continuous increasing slows is varied based on a number of backscatter responses received from the RFID devices, and
wherein the second power level is a maximum power level allowed by law.