SYSTEMS AND METHODS FOR ASYMMETRIC BACKSCATTER COMMUNICATIONS

• US 20180032768A1
• Filed: 07/31/2017
• Published: 02/01/2018
• Est. Priority Date: 07/29/2016
• Status: Active Grant

• Current Assignee: University Of Massachusetts
• Original Assignee: University Of Massachusetts
• Inventors: Ganesan, Deepak, HU, Pan, Zhang, Pengyu
• Granted Patent: US 10,452,876 B2
• Time in Patent Office: Days
• CPC Class Codes: G06K 19/0709 the source being an interrogation field
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/10069 the collision being resolved in the frequency domain, e.g. by hopping from one frequency to the other frequency hopping or spread spectrum techniques H04B7/00
• CPC Class Codes: G06K 7/10158 methods and means used by the interrogation device for reliably powering the wireless record carriers using an electromagnetic interrogation field
• CPC Class Codes: G06K 7/10297 arrangements for handling protocols designed for non-contact record carriers such as RFIDs NFCs, e.g. ISO/IEC 14443 and 18092 cryptographic protocols H04L9/00; network security protocols H04L63/00; real-time communication protocols in data switching networks H04L65/00; network protocols for data switching network services H04L67/00

Abstract

Systems and methods for backscatter communications are provided that employ a backscatter reader to transmit a carrier signal to multiple backscatter tags having heterogeneous hardware and specifications. In response to receiving the carrier, the tags encode data into the received signal and, concurrently, transmit their respective backscattered signal to the reader. The concurrent signals are received by the reader as a combined signal. The reader detects edges in the received signal, based on the corresponding in-phase (I) and quadrature (Q) signals. The edges are then assigned to streams based on the offset or transmission rate of the tags. In some cases, the reader can detect edge collisions. These collisions can be resolved by causing the colliding signals to be retransmitted or by separating the colliding signals. The individual streams corresponding to each of the tags can then be decoded to identify the originally transmitted data from each tag.

Claims

1. A method for decoding concurrent signals, comprising:

transmitting a carrier signal to a plurality of backscatter tags;

receiving a combined signal comprising respective backscattered signals transmitted by the backscatter tags, wherein the backscattered signals are transmitted at least partially concurrently by the backscatter tags, and wherein the plurality of backscatter tags transmit the backscatter signals starting at respective offsets and transmission rates;

detecting edges in the received combined signal based on in-phase (I) and quadrature (Q) signals corresponding to the received combined signal;

assigning each of the detected edges to streams corresponding to the plurality of backscatter tags, based on one or more of the offsets and transmission rates of the backscatter tags; and

decoding the streams of detected edges by assigning one of a plurality of values to each of the detected edges of the streams corresponding to the plurality of backscatter tags, wherein the plurality of values correspond to the possible edge states of the detected edges.

2. The method of claim 1, wherein the transmitting of the carrier signal:

(1) is initiated by re-starting a carrier wave generator, and

(2) causes the backscatter tags to start transmitting the backscattered signals.

3. The method of claim 1, wherein the backscattered signals are transmitted over a single frequency channel.

4. The method of claim 1, wherein the plurality of backscatter tags include backscatter tags having different sampling rates and transmission rates.

5. The method of claim 1, wherein the carrier signal includes power for powering the backscatter tags.

6. The method of claim 1,

wherein data is encoded into the carrier signal by the backscatter tags to create the backscattered signals, the data being encoded by toggling the transistors of the backscatter tags, and

wherein toggling the transistors causes the edges to be created in the combined signal, the edges representing a transition from one edge state to another edge state.

7. The method of claim 1, wherein the detecting of the edges comprises:

measuring a background signal, the background signal indicating a frequency during a time when none of the plurality of backscatter tags are transmitting; and

identifying instances in the combined signal in which a positive or negative change in frequency is larger than the frequency of the background signal and/or a predetermined threshold,

wherein each of the identified instances represents an edge.

8. The method of claim 1, wherein the assigning each of the detected edges to streams corresponding to the plurality of backscatter tags includes, for each of the detected edges:

determining if an edge time at which the identified edge occurs is equal to the offset of any of the backscatter tags; and

/or

determining if the edge time at which the identified edge occurs overlaps with any anticipated state transition times of the backscatter tags, the anticipated state transition times being calculated based on the transmission rates and the offsets of the backscatter tags.

9. The method of claim 8, wherein one of the detected edges is assigned to one of the streams corresponding to one of the plurality of backscatter tags if the one of the detected edges occurs at an edge time that is equal to the offset of the one of the backscatter tags and/or if the one of the detected edges occurs at an edge time that overlaps with an anticipated state transition time of the one of the backscatter tags.

10. The method of claim 1, further comprising:

detecting the presence of colliding edges among the detected edges, the colliding edges indicating that two or more of the streams have overlapping edges caused by the respective backscatter tags transitioning between edge states at a same time; and

resolve the colliding edges by (1) causing the backscattered signals corresponding to the colliding edges to be retransmitted, or (2) separating the colliding edges,

wherein detecting the presence of colliding edges includes;

plotting the I and/or Q signals corresponding to the received combined signal on respective IQ plots; and

identifying the number of clusters in each of the IQ plots,

wherein the colliding edges are deemed to be present among the detected edges if the number of identified clusters in any of the IQ plots exceeds the number of possible edge states.

11. The method of claim 10, wherein each cluster in the IQ plots represents a possible edge state.

12. The method of claim 11, wherein, when colliding edges are deemed to be present among the detected edges, the number of clusters in any of the IQ plots is equal to Nk, where N is equal to the number of tags colliding in the colliding edges, and k is equal to the number of possible edge states.

13. The method of claim 12, wherein the possible edge states comprise:

(1) rising, (2) falling, and (3) constant.

14. The method of claim 11, wherein the separating of the colliding edges includes:

identifying an origin cluster in the IQ plots, the origin cluster representing a constant edge state;

identifying midpoint clusters by;

locating groups of the clusters that are co-linear; and

locating the midpoint clusters among each of the groups of co-linear clusters; and

identifying edge differentials based on the located midpoint clusters, the edge differentials indicating signal changes relative to the signal at the origin cluster.

15. A backscatter reader, comprising:

one or more antennas configured to communicate with a plurality of backscatter tags by;

(1) transmitting a carrier signal, and (2) receiving a combined signal that includes backscattered signals transmitted by the plurality of backscatter tags at least partly concurrently, wherein the backscattered signals are transmitted by the plurality of backscatter tags at respective offsets and transmission rates; and

a microcontroller operable to process transmission logic configured to decode the receive the combined signal by;

detecting edges in the received combined signal based on in-phase (I) and quadrature (Q) signals corresponding to the received combined signal;

assigning each of the detected edges to streams corresponding to the plurality of backscatter tags, based on one or more of the offsets and transmission rates of the plurality of backscatter tags; and

decoding the streams of detected edges by assigning one of a plurality of values to each of the detected edges of the streams corresponding to the plurality of backscatter tags, wherein the plurality of values correspond to the possible edge states of the detected edges.

16. The backscatter reader of claim 15, wherein the backscattered signals are transmitted over a single frequency channel.

17. The backscatter reader of claim 15, wherein the plurality of backscatter tags include backscatter tags having different sampling rates and transmission rates.

18. The backscatter reader of claim 15, wherein the carrier signal includes power for powering the backscatter tags.

19. The backscatter reader of claim 15,

wherein data is encoded into the carrier signal by the backscatter tags to create the backscattered signals, the data being encoded by toggling the transistors of the backscatter tags, and

wherein toggling the transistors causes the edges to be created in the combined signal, the edges representing a transition from one edge state to another edge state.

20. The backscatter reader of claim 15, wherein the detecting of the edges comprises:

measuring a background signal, the background signal indicating a frequency during a time when none of the plurality of backscatter tags are transmitting; and

identifying instances in the combined signal in which a positive or negative change in frequency is larger than the frequency of the background signal and/or a predetermined threshold,

wherein each of the identified instances represents an edge.

21. The backscatter reader of claim 15, wherein the assigning each of the detected edges to streams corresponding to the plurality of backscatter tags includes, for each of the detected edges:

determining if an edge time at which the identified edge occurs is equal to the offset of any of the backscatter tags; and

/or

determining if the edge time at which the identified edge occurs overlaps with any anticipated state transition times of the backscatter tags, the anticipated state transition times being calculated based on the transmission rates and the offsets of the backscatter tags.

22. The backscatter reader of claim 21, wherein one of the detected edges is assigned to one of the streams corresponding to one of the plurality of backscatter tags if the one of the detected edges occurs at an edge time that is equal to the offset of the one of the backscatter tags and/or if the one of the detected edges occurs at an edge time that overlaps with an anticipated state transition time of the one of the backscatter tags.

23. The backscatter reader of claim 15,

wherein the transmission logic is further configured to:

detect the presence of colliding edges among the detected edges, the colliding edges indicating that two or more of the streams have overlapping edges caused by the respective backscatter tags transitioning between edge states at a same time; and

resolve the colliding edges by (1) causing the backscattered signals corresponding to the colliding edges to be retransmitted, or (2) separating the colliding edges,

wherein the detecting the presence of colliding edges includes;

plotting the I and/or Q signals corresponding to the received combined signal on respective IQ plots; and

identifying the number of clusters in each of the IQ plots, and

wherein the colliding edges are deemed to be present among the detected edges if the number of identified clusters in any of the IQ plots exceeds the number of possible edge states.

24. The backscatter reader of claim 23, wherein each cluster in the IQ plots represents a possible edge state.

25. The backscatter reader of claim 24, wherein, when colliding edges are deemed to be present among the detected edges, the number of clusters in any of the IQ plots is equal to Nk, where N is equal to the number of tags colliding in the colliding edges, and k is equal to the number of possible edge states.

26. The backscatter reader of claim 25, wherein the possible edge states comprise:

(1) rising, (2) falling, and (3) constant.

27. The backscatter reader of claim 24, wherein the separating of the colliding edges includes:

identifying an origin cluster in the IQ plots, the origin cluster representing a constant edge state;

identifying midpoint clusters by;

locating groups of the clusters that are co-linear; and

locating the midpoint clusters among each of the groups of co-linear clusters; and

identifying edge differentials based on the located midpoint clusters, the edge differentials indicating signal changes relative to the signal at the origin cluster.

28. A backscatter tag comprising:

a transistor; and

one or more antennas configured to;

receive a carrier signal from the backscatter reader; and

transmit a backscattered signal to the backscatter reader, the backscattered signal being made up of bits encoded into the carrier signal,

wherein the transmitting of the backscattered signal is triggered by the receiving of the carrier signal.

29. The backscatter tag of claim 28, wherein the backscattered signal is transmitted to the backscatter reader at a transmission rate that is a multiple of a base rate.