Apparatuses, systems, and methods for communicating using MIMO and spread spectrum coding in backscatter of ambient signals

Patent metadata

Field	Value
Publication number	US-9973367-B2
Application number	US-201515118432-A
Country	US
Kind code	B2
Filing date	Feb 11, 2015
Priority date	Feb 11, 2014
Publication date	May 15, 2018
Grant date	May 15, 2018

Abstract

Apparatuses, systems, ambient RF backscatter transceivers, and methods for communicating using MIMO and spread spectrum coding of backscattered ambient RF signals are described. An example system may include an ambient RF backscatter transceiver that include an antenna configured to receive a backscattered ambient radio frequency (RF) signal, and a receiver coupled to the antenna. The receiver may be configured to demodulate the backscattered ambient RF signal using one of multiple input, multiple output multiplexing demodulation or spread spectrum code demodulation to retrieve the first data. The backscattered ambient RF signal may be generated by backscattering an ambient RF signal at a first frequency. The ambient RF signal may be configured to provide other data at a second frequency.

First claim

What is claimed is:

1. A system comprising:
an ambient RF backscatter transceiver comprising:
a first antenna configured to receive a backscattered ambient radio frequency (RF) signal;
a second antenna configured to receive the backscattered ambient radio frequency (RF) signal; and

a receiver coupled to the first antenna and the second antenna, wherein the receiver is configured to demodulate the backscattered ambient RF signal to provide output bits using at least one of: multiple input, multiple output multiplexing demodulation based on a ratio of a magnitude of the backscattered ambient radio frequency signal received via the first antenna to a magnitude of the backscattered ambient radio frequency signal received via the second antenna or spread spectrum code demodulation based on a chip duration;
wherein the backscattered ambient RF signal is generated by backscattering an ambient RF signal at a first frequency, the ambient RF signal configured to provide additional data at a second frequency.

2. The system of claim 1 , wherein the backscattered ambient RF signal received at the second antenna has a different phase offset than the backscattered ambient RF signal received at the first antenna.

3. The system of claim 2 , wherein the receiver comprises:
a first envelope detector circuit configured to filter out transitions of the backscattered ambient RF signal received at the first antenna to provide a first signal envelope;
a second envelope detector circuit configured to filter out transitions of the backscattered ambient RF signal received at the second antenna to provide a second signal envelope;
a multiple input, multiple output (MIMO) multiplexing demodulation circuit configured to determine a ratio of the first signal envelope to the second signal envelope;
a threshold circuit configured to provide an output based on a comparison of a threshold value to the ratio of the first signal envelope to the second signal envelope.

4. The system of claim 3 , wherein the MIMO multiplexing demodulation circuit comprises:
a first logarithmic amplifier configured to transform the first signal envelope from a linear domain to a logarithmic domain; and
a second logarithmic amplifier configured to transform the second signal envelope from the linear domain to the logarithmic domain.

5. The system of claim 4 , wherein the MIMO multiplexing demodulation circuit further comprises an analog subtractor circuit configured to subtract the first signal envelope in the logarithmic domain from the second signal envelope in the logarithmic domain to provide a difference signal indicative of the ratio of the first signal envelope to the second signal envelope.

6. The system of claim 5 , wherein the threshold circuit is configured to provide the output based on a comparison of the threshold value to the difference signal indicative of the ratio of the first signal envelope to the second signal envelope.

7. The system of claim 5 , wherein the MIMO multiplexing demodulation circuit further comprises an exponential amplifier configured to transform the difference signal from the logarithmic domain to the linear domain, wherein the threshold circuit is configured to provide the output based on a comparison of the threshold value to the difference signal indicative of the ratio of the first signal envelope to the second signal envelope in the linear domain.

8. The system of claim 1 , wherein, while demodulating the backscattered ambient RF signal using spread spectrum code demodulation, the receiver may demodulate the ambient backscattered RF signal based on an in-phase and quadrature-phase correlation.

9. The system of claim 2 , wherein, while the receiver configured to demodulate the ambient backscattered RF signal based on an in-phase and quadrature-phase correlation comprises addition of in-phase and quadrature phase components.

10. The system of claim 1 , wherein the receiver comprises:
an envelope detector circuit configured to filter out transitions of the backscattered ambient RF signal received at the first and second antennas to provide a signal envelope;
a spread spectrum code demodulation circuit configured to determine an in-phase and quadrature-phase correlation of the signal envelope;
a threshold circuit configured to provide an output based on a comparison of a threshold value to the in-phase and quadrature-phase correlation of the signal envelope.

11. The system of claim 10 , wherein the backscattered ambient RF signal is modulated at a chip rate and a chip length, wherein a chip of the backscattered ambient RF signal having a first value is alternative ones and zeroes, and a chip of the backscattered ambient RF signal having a second value is all zeroes, wherein the spread spectrum code demodulation circuit comprises:
a first switch configured to be modulated between the signal envelope and an inverted signal envelope at a period equal to the chip length multiplied by the chip rate;
a first accumulator circuit configured to accumulate a signal from the first switch to generate an in-phase component;
a first absolute value circuit configured to extract a magnitude of the in-phase component;
a second switch configured to be modulated with a ninety degree offset from the first switch between the signal envelope and the inverted signal envelope at a period equal to the chip length multiplied by the chip rate;
a second accumulator circuit configured to accumulate a signal from the second switch to generate an quadrature-phase component; and
a second absolute value circuit configured to extract a magnitude of the quadrature-phase component.

12. The system of claim 11 , wherein the spectrum code demodulation circuit further comprises a summation circuit configured to add the magnitude of the in-phase component and the magnitude of the quadrature-phase component to produce a sum signal.

13. The system of claim 12 , wherein the threshold circuit is configured to provide the output based on a comparison of the threshold value to the sum signal.

14. An ambient RF backscatter transceiver comprising:
a first antenna configured to receive a backscattered ambient radio frequency (RF) signal and to provide a first backscattered signal, the backscattered ambient RF signal encoded with first data via backscatter modulation of an ambient RF signal at a first frequency, the ambient RF signal modulated to provide second data at a second frequency;
a second antenna configured to receive the backscattered ambient radio frequency (RF) signal and to provide a second backscattered signal having a phase offset relative to the first backscattered signal,
a receiver coupled to the first antenna and the second antenna, wherein the receiver is configured to demodulate the backscattered ambient RF signal using multiple input, multiple output multiplexing demodulation based on a ratio of a magnitude of the first backscattered signal to a magnitude of the second backscattered signal to provide output bits; and
a microcontroller coupled to the receiver and configured to decode the output bits to retrieve data that is transmitted via the backscattered ambient RF signal.

15. The ambient RF backscatter transceiver of claim 14 , wherein the receiver comprises a multiple input, multiple output (MIMO) multiplexing demodulation circuit configured to determine the ratio of the magnitude of the first backscattered signal to the magnitude of the second backscattered signal.

16. The ambient RF backscatter transceiver of claim 15 , wherein the MIMO multiplexing demodulation circuit comprises:
a first logarithmic amplifier co

Assignees

• Univ Washington

Inventors

• Gollakota Shyamnath
• Smith Joshua R
• Parks Aaron N
• Liu Angli

Classifications

• H04B7/0413

  MIMO systems · CPC title

• H04K2203/20

  for contactless carriers, e.g. RFID carriers · CPC title

• H04B1/40

  Circuits · CPC title

• H04L27/2649 Primary

  Demodulators · CPC title

• H04K3/25 Primary

  based on characteristics of target signal or of transmission (as countermeasure against surveillance H04K3/827), e.g. using direct sequence spread spectrum or fast frequency hopping (spread spectrum techniques H04B1/69) · CPC title