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US-12621819-B2 - Backscattering ambient ISM band signals

US12621819B2US 12621819 B2US12621819 B2US 12621819B2US-12621819-B2

Abstract

A backscatter tag device includes, in part, a receiver configured to receive a packet conforming to a communication protocol defining a multitude of codewords, a codeword translator configured to translate at least a first subset of the multitude of codewords disposed in the packet to a second multitude of codewords defined by the protocol in response to a data the backscatter tag is invoked to transmit, and a transmitter configured to transmit the packet supplied by the codeword translator at a frequency different than the first frequency at which the packer is received. The communication protocol may optionally be the 802.11g/n, ZigBee or the Bluetooth communication protocol.

Inventors

  • Pengyu Zhang
  • Dinesh Bharadia
  • Sachin Katti

Assignees

  • THE BOARD OF TRUSTEES OF THE LELAND STANFORD JUNIOR UNIVERSITY

Dates

Publication Date
20260505
Application Date
20220907

Claims (18)

  1. 1 . A backscatter tag communication device, comprising: a receiver configured to receive a first packet comprising a first plurality of codewords, the first packet conforming to a communication protocol defining a second plurality of codewords inclusive of the first plurality of codewords, and wherein the first packet is characterized by a first frequency: a codeword translator configured to generate a second packet, for each respective codeword of the first plurality of codewords and based at least in part on data that the backscatter tag communication device is invoked to transmit, by: selecting a target codeword of the second plurality of codewords; and translating the respective codeword to the target codeword: a switch configured to generate a backscatter tag signal defining the second packet by multiplying an excitation signal defining the first packet with the data that the backscatter tag communication device is invoked to transmit, wherein to multiply the excitation signal with the data, the switch is toggled at a desired frequency offset; and a transmitter configured to transmit the backscatter tag signal.
  2. 2 . The backscatter tag communication device of claim 1 , wherein translating the respective codeword to the target codeword comprises changing a phase of the respective codeword.
  3. 3 . The backscatter tag communication device of claim 1 , wherein the communication protocol comprises one of Bluetooth, ZigBee, WiFi 802.11(g), or WiFi 802.11(n).
  4. 4 . The backscatter tag communication device of claim 2 , wherein the phase is changed based at least in part on a data rate of the transmitter.
  5. 5 . The backscatter tag communication device of claim 1 , wherein said backscatter tag communication device is configured to transmit the second packet during one of a plurality of time slots at random.
  6. 6 . The backscatter tag communication device of claim 5 , wherein a count of the plurality of time slots is a variable number.
  7. 7 . The backscatter tag communication device of claim 1 , wherein the first packet comprises a duration.
  8. 8 . The backscatter tag communication device of claim 7 , further comprising: an envelope detector configured to detect the duration of the first packet.
  9. 9 . The backscatter tag communication device of claim 1 , wherein the target codeword is different from the respective codeword.
  10. 10 . The backscatter tag communication device of claim 1 , wherein each codeword comprises a plurality of bits.
  11. 11 . A method of communication via a backscatter tag, the method comprising: receiving, by a receiver, a first packet comprising a first plurality of codewords, the first packet conforming to a communication protocol defining a second plurality of codewords inclusive of the first plurality of codewords, wherein the first packet is characterized by a first frequency; generating, by a codeword translator, a second packet, for each respective codeword of the first plurality of codewords and based at least in part on data that the backscatter tag is invoked to transmit, by: selecting a target codeword of the second plurality of codewords; and translating the respective codeword to the target codeword; generating, by a switch, a backscatter tag signal defining the second packet by multiplying an excitation signal defining the first packet with the data that the backscatter tag is invoked to transmit, wherein to multiply the excitation signal with the data, the switch is toggled at a desired frequency offset; and transmitting, by a transmitter, the backscatter tag signal.
  12. 12 . The method of claim 11 , wherein translating the respective codeword to the target codeword comprises changing a phase of the respective codeword.
  13. 13 . The method of claim 12 , wherein the phase is changed based at least in part on a data rate of a transmitter transmitting the second packet.
  14. 14 . The method of claim 11 , wherein the communication protocol comprises one of Bluetooth, ZigBee, WiFi 802.11(g), or WiFi 802.11(n).
  15. 15 . The method of claim 11 , further comprising: transmitting the second packet during one of a plurality of time slots at random.
  16. 16 . The method of claim 15 , wherein a count of the plurality of time slots is a variable number.
  17. 17 . The method of claim 11 , wherein the first packet has a duration.
  18. 18 . The method of claim 17 , wherein the backscatter tag comprises an envelope detector configured to detect the duration of the first packet.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a continuation of U.S. application Ser. No. 16/344,983, titled “BACKSCATTERING AMBIENT ISM BAND SIGNALS,” filed Apr. 25, 2019, which is a U.S. National Stage of PCT/US2017/058371, filed Oct. 25, 2017, which claims the benefit under 35 U.S.C. § 119 (e) of U.S. Provisional Application No. 62/412,712, filed Oct. 25, 2016, entitled “FREERIDER: BACKSCATTERING AMBIENT ISM BAND SIGNALS,” filed Oct. 25, 2016, the contents of all which are incorporated herein by reference in their entirety for all purposes. The present invention is related to application Ser. No. 15/676,474, filed Aug. 14, 2017, the content of which is incorporated herein by reference in its entirety. FIELD OF THE INVENTION The present invention relates to communication systems and methods, and more particularly to a low power WiFi backscattering communication system and method. BACKGROUND OF THE INVENTION Backscatter communication has attracted interest for applications such as implantable sensors, wearables, and smart home sensing because of its ability to offer low power connectivity to these sensors. Such applications have severe power constraints. Implantable sensors for example have to last for years, while even more traditional smart home monitoring applications may benefit from sensors and actuators that can last several years. Backscatter communication can satisfy the connectivity requirements while consuming such low power as to be energized by harvesting energy, or with batteries that could last several years. Current backscatter systems require specialized hardware to generate the excitation RF signals that backscatter radios can reflect, as well as to decode the backscattered signals. Recent research such as Wi-Fi backscatter to BackFi and passive WiFi have reduced the need for specialized hardware. Passive WiFi for example can decode using standard WiFi radios, however it still requires a dedicated continuous wave signal generator as the excitation RF signal source. BackFi needs a proprietary full duplex hardware add-on to WiFi radios to enable backscatter communication. Consequently, a need continues to exist for a backscatter system that can be deployed using commodity devices such as access points, smartphones, watches and tablets. BRIEF DESCRIPTION OF THE INVENTION FIG. 1 is a simplified view of a backscatter communication system 100, in accordance with one embodiment of the present invention. FIG. 2 shows a number of OFDM symbols modulated on different subcarriers, as known in the prior art. FIG. 3 shows the durations of a number of packets collected on a channel. FIG. 4 shows the rate of decoding success as a function of distance, in accordance with one exemplary embodiment of the present invention. FIG. 5 is a simplified high-level block diagram of a backscatter tag, in accordance with one embodiment of the present invention. FIG. 6 shows various block diagrams of an 802.11g/n transmission and reception blocks FIG. 7 is a more detailed view of the scrambler shown in FIG. 6. FIG. 8 shows the frequency spectrum of a backscattered Bluetooth signal. FIG. 9A shows an experimental setup for testing a backscatter tag deployed in a line-of-sight, in accordance with one embodiment of the present invention. FIG. 9B shows an experimental setup for testing a backscatter deployed in a non-line-of sight setup, in accordance with one embodiment of the present invention. FIG. 10A shows the throughput of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and the receiver in a LOS deployment. FIG. 10B shows the bit-error rate of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and the receiver in a LOS deployment. FIG. 10C shows the received signal strength indicator of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and the receiver in a LOS deployment. FIG. 11A shows the throughput of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and the receiver in an NLOS deployment. FIG. 11B shows the bit-error rate of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and the receiver in an NLOS deployment. FIG. 11C shows the received signal strength indicator of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and the receiver in an NLOS deployment. FIG. 12A shows the throughput of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and a ZigBee receiver. FIG. 12B shows the bit-error rate of a tag, in accordance with one embodiment of the present invention, as a function of distance between the tag and a ZigBee receiver. FIG. 12C shows the received signal strength indicator of a ta