Location estimation and tracking for passive RFID and wireless sensor networks using MIMO systems

1. A method for obtaining location information using an RFID reader system, the method comprising:

generating an RFID interrogation signal waveform having a first frequency;

generating a ranging waveform having a second frequency, where the second frequency is higher than the first frequency;

combining the RFID interrogation signal and ranging waveform signal into a combined interrogation and ranging signal;

splitting the combined interrogation and ranging signal to a plurality of transmit paths through a transmit array filter bank and modifying the signal in each transmit path using at least one transmit weighting factor, where each transmit weighting factor modifies a characteristic of the signal;

transmitting a first filtered output signal from each of the transmit paths of the transmit array filter bank using one of a plurality of transmit antennas in a first interrogation round;

transmitting a combined interrogation and ranging signal from a plurality of antennas, where the ranging signal is a pseudorandom signal;

receiving a backscattered return signal from an RFID tag at one or more receive antennas;

extracting an information signal from the return signal and decoding the information signal to obtain RFID tag data;

extracting a received ranging signal from the return signal; and

estimating a range to the RFID tag based upon correlation between the ranging signal and the received ranging signal.

2. The method of claim 1 , further comprising adjusting at least one of the at least one transmit weighting factor based upon the output of the equalizer filter bank and a plurality of the calculated time-of-arrivals of the plurality of received return signals; and

transmitting a second filtered output signal from each of the transmit paths of the transmit array filter bank using one of the plurality of transmit antennas in a second interrogation round, where the second filtered output signal is modified using the adjusted at least one transmit weighting factor.

3. The method of claim 2 , wherein adjusting at least one of the at least one transmit weighting factor comprises applying machine learning to increase the correlation of the ranging signals.

4. The method of claim 2 , wherein adjusting at least one of the at least one transmit weighting factor comprises applying machine learning to increase the read rate of the RFID tag.

5. The method of claim 1 , wherein combining the RFID interrogation signal and ranging waveform signal into a combined interrogation and ranging signal comprises adding the two signals.

6. The method of claim 1 , further comprising adjusting a characteristic of the transmitted combined interrogation and ranging signal in a subsequent interrogation round to increase read rate and ranging accuracy.

7. The method of claim 1 , further comprising calculating the time-of-arrival of each of the plurality of received return signals.

8. A method for obtaining location information using an RFID reader system, the method comprising:

transmitting a combined interrogation and ranging signal from a plurality of antennas, where the ranging signal is a pseudorandom signal;

receiving a backscattered return signal from an RFID tag at one or more receive antennas;

extracting an information signal from the return signal and decoding the information signal to obtain RFID tag data;

extracting a received ranging signal from the return signal; and

estimating a range to the RFID tag based upon correlation between the ranging signal and the received ranging signal;

wherein receiving a backscattered return signal from an RFID tag at one or more receive antennas comprises receiving a plurality of backscattered return signals from an RFID tag at a plurality of antennas; and the method further comprises combining the plurality of received return signals using an equalizer filter bank to produce a combined return signal, and the combining further comprises modifying each received return signal using at least one receive weighting factor, where each receive weighting factor modifies a characteristic of the signal.

9. The method of claim 8 , further comprising adjusting a characteristic of the transmitted combined interrogation and ranging signal in a subsequent interrogation round to increase read rate and ranging accuracy.

10. The method of claim 8 , further comprising calculating the time-of-arrival of each of the plurality of received return signals.