Method for passive wireless channel estimation in radio frequency network and apparatus for same

1. A method for estimating characteristics of a wireless communication channel between at least two passive backscattering radio frequency (RF) nodes, the method comprising:

measuring backscatter channel state information (BCSI) during communication between the at least two passive RF nodes using a multi-phase probing (MPP) signal;

aggregating, by at least one RF node of the at least two passive RF nodes, the measured BCSI; and

analyzing, by the at least one RF node, the aggregated BSCI to at least one of detect at least one activity of a plurality of activities, improve a rate of data communication, improve robustness, and reduce bit error rate.

2. The method of claim 1 ,

wherein the BCSI is a feature vector h(t)=[Θ BC A B ΔA E ], with Θ BC , A B , and ΔA E being a backscatter channel phase, a backscatter amplitude, and a change in excitation amplitude between sampling intervals, respectively.

3. The method of claim 2 ,

wherein the backscatter channel phase is Θ BC (t)=Θ B (t)−Θ E (t), and

wherein Θ B and Θ E are phases of an exciter-transmitter-receiver channel and an exciter-transmitter channel, respectively.

4. The method of claim 3 ,

wherein a backscatter modulator of a transmitter tag varies a backscatter signal phase ϕ to obtain amplitude and a phase of a backscatter signal at a receiver tag according to:

θ

BC

=

π

2

-

ϕ

❘

"\[LeftBracketingBar]"

Δ

⁢

v

R

=

0

,

A

B

=

Δ

⁢

v

R

⁢

❘

"\[LeftBracketingBar]"

ϕ

=

-

θ

BC

.

5. The method of claim 1 ,

wherein, in response to detecting an activity of the plurality of activities, a transmit (Tx) node of the plurality of nodes transmits the MPP signal for a plurality of cycles, and

wherein the MPP signal comprises a packet of data symbols, with a backscatter channel phase of the symbols within the packet being systematically varied.

6. The method of claim 5 ,

wherein a receiving (Rx) node of the plurality of nodes receives the MPP signal, and a BCSI vector is computed based on the received MPP signal.

7. The method of claim 6 , further comprising:

parsing components of the computed BCSI vector;

identifying dynamic variation patterns of the parsed components of the BCSI vector; and

detecting a signature of an event based on the identified dynamic variation patterns.

8. The method of claim 7 ,

wherein the detected signature of the event is invariant of an environment of the at least two passive RF nodes.

9. The method of claim 1 ,

wherein the communication between the at least two passive RF nodes is powered by electromagnetic energy harvested by at least one of the at least two passive RF nodes.

10. The method of claim 9 ,

wherein a rate of the aggregating is based on an energy budget of a receiving (Rx) node of the plurality of nodes.

11. The method of claim 10 ,

wherein the energy budget limits a backscatter data rate and a number of discrete reflection phases.

12. A passive radio frequency (RF) node, comprising:

a backscatter modulator; and

at least one processor configured to:

measure backscatter channel state information (BCSI) during communication with at least one other passive RF node,

aggregate the measured BCSI, and

analyze the aggregated BSCI to at least one of detect at least one activity of a plurality of activities, improve a rate of data communication, improve robustness, and reduce bit error rate.

13. The passive RF node of claim 12 ,

wherein the BCSI is a feature vector comprising a backscatter channel phase Θ BC , a backscatter amplitude A B , and a change in excitation amplitude ΔA E between sampling intervals.

14. The passive RF node of claim 13 ,

wherein the backscatter channel phase Θ BC (t) is a difference between phases of an exciter transmitter Θ B (t) and phases of a receiver channel Θ E (t).

15. The passive RF node of claim 14 ,

wherein a backscatter modulator varies a backscatter signal phase ϕ to obtain amplitude and phase of a backscatter signal at the receiver according to:

θ

BC

=

π

2

-

ϕ

❘

"\[LeftBracketingBar]"

Δ

⁢

v

R

=

0

,

A

B

=

Δ

⁢

v

R

⁢

❘

"\[LeftBracketingBar]"

ϕ

=

-

θ

BC

.

16. The passive RF node of claim 12 ,

wherein, in response to detecting an activity of the plurality of activities, the at least one processor is further configured to transmit a multi-phase probing (MPP) signal for a plurality of cycles.

17. The passive RF node of claim 16 ,

wherein the at least one other RF node of the plurality of nodes receives the MPP signal, and a BCSI vector is computed based on the received MPP signal.

18. The passive RF node of claim 17 ,

wherein the at least one processor is further configured to:

parse components of the computed BCSI vector;

identify dynamic variation patterns of the parsed components of the BCSI vector; and

detect a signature of an event based on the identified dynamic variation patterns.

19. The passive RF node of claim 18 ,

wherein the detected signature of the event is invariant of an environment of the at least two passive RF nodes.

20. The passive RF node of claim 1 ,

wherein a rate of the aggregating of the measured BCSI is based on a predefined energy budget that limits a backscatter data rate and a number of discrete reflection phases.