Backscatter estimation using progressive self interference cancellation
Techniques for estimating one or more backscatter signals reflected from one or more objects are disclosed. In one example, a backscatter sensor includes, in part, a receiver for receiving a composite signal comprising one or more reflections of a transmitted signal, each reflection being reflected by one of a plurality of objects; and a processor configured to estimate at least a first backscatter component of the composite signal using a progressive interference cancellation technique. The first backscatter component of the composite signal corresponds to a reflection of the transmitted signal from a first object. In one embodiment, the backscatter sensor includes multiple receivers and/or one or more transmitters.
1. A backscatter sensor, comprising:
a receiver for receiving a composite signal comprising one or more reflections of a transmitted signal, each reflection being reflected by one of a plurality of objects; and
a processor configured to:
estimate at least a first backscatter component of the composite signal using a progressive interference cancellation technique, wherein the first backscatter component of the composite signal corresponds to a reflection of the transmitted signal from a first object;
remove the estimated first backscatter component from the composite signal to generate a second signal; and
estimate a second backscatter component using the second signal, the second backscatter component corresponding to a reflection of the transmitted signal from a second object.
2. The backscatter sensor of claim 1 , wherein the receiver further comprises:
a plurality of receive antennas, each receive antenna being coupled to a receive chain, wherein each receive chain receives a modified copy of the composite signal.
3. The backscatter sensor of claim 1 , further comprising:
a transmitter for transmitting the transmitted signal, and wherein the processor further receives a sample of the transmitted signal.
4. The backscatter sensor of claim 3 , wherein the transmitter comprises one or more transmitters, each transmitter transmitting a signal.
5. The backscatter sensor of claim 1 , wherein the processor is further configured to estimate at least one of an amplitude of the first backscatter component, a phase of the first backscatter component and a time delay between transmission of the transmitted signal and reception of the first backscatter component.
6. The backscatter sensor of claim 1 , wherein the first object is the closest object to the receiver among the plurality of objects.
7. The backscatter sensor of claim 1 , wherein the processor is further configured to estimate one or more parameters associated with at least the first backscatter component using a linear optimization technique.
8. The backscatter sensor of claim 7 , wherein the processor is further configured to estimate the one or more parameters in accordance with the following expression:
minimize
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wherein {tilde over (h)} represents an estimated channel response, M represents number of antennas, L represents number of reflected backscatter components, α k represents an attenuation undergone by the k th backscatter component, ν k represents a phase rotation seen by the k th backscatter component, τ k represents a delay between the k th backscatter component and a corresponding transmitted signal, and Θ k represents an angle of arrival of k th backscatter component.
9. The backscatter sensor of claim 1 , wherein the receiver is further configured to receive the composite signal during a plurality of consecutive non-overlapping time windows, and the processor is further configured to:
estimate one or more parameters of the first backscatter component based at least on a first portion of the composite signal received in a first window; and
iteratively estimate parameters of a next backscatter component based on a second portion of the composite signal received in a next consecutive window.
10. The backscatter sensor of claim 9 , wherein the consecutive non-overlapping windows have a variable size.
11. The backscatter sensor of claim 1 , wherein the processor is further configured to estimate the at least the first backscatter component using a Sequential Convex Programming (SCP) algorithm.
12. The backscatter sensor of claim 11 , wherein the processor is further configured to generate an initial estimate for the SCP algorithm using a continuous basis pursuit (CBP) algorithm.
13. The backscatter sensor of claim 1 , wherein the processor is further configured to estimate the at least the first backscatter component using a continuous basis pursuit (CBP) algorithm.
14. The backscatter sensor of claim 1 , wherein the processor is further configured to estimate a Doppler frequency corresponding to each object.
15. A method for sensing backscatter signals, comprising:
receiving a composite signal comprising one or more reflections of a transmitted signal, each reflection being reflected by one of a plurality of objects; and
estimating at least a first backscatter component of the composite signal using a progressive interference cancellation technique, wherein the first backscatter component of the composite signal corresponds to a reflection of the transmitted signal from a first object;
removing the estimated first component from the composite signal to generate a second signal; and
estimating a second backscatter component using the second signal, the second backscatter component corresponding to a reflection of the transmitted signal from a second object.
16. The method of claim 15 , further comprising:
receiving a plurality of composite signals by a plurality of receive antennas, each receive antenna being coupled to a receive chain.
17. The method of claim 15 , further comprising:
transmitting one or more signals using one or more transmit antennas; and
estimating one or more backscatter components corresponding to each transmitted signal.
18. The method of claim 15 , wherein estimating at least a first backscatter component comprises estimating at least one of an amplitude of the first backscatter component, a phase of the backscatter component, and a time delay between transmission of the transmitted signal and reception of the first backscatter component, time of flight of the first backscatter component.
19. The method of claim 15 , wherein the first object is the closest object to the receiver among the plurality of objects.
20. The method of claim 15 , further comprising:
estimating one or more parameters associated with at least the first backscatter component using a linear optimization technique.
21. The method of claim 20 , wherein the linear optimization technique comprises solving the following expression:
minimize
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m
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n
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m
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n
]
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h
~
m
[
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2
subject
to
τ
k
≥
0
,
α
k
≤
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,
θ
k
∈
[
-
π
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]
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v
k
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k
=
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1
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}
,
n
=
{
-
N
,
…
,
N
}
,
m
=
{
1
,
…
,
M
}
wherein {acute over (h)} represents an estimated channel response, M represents number of antennas, L represents number of reflected backscatter components, α k represents an attenuation undergone by the k th backscatter component, ν k represents a phase rotation seen by the k th backscatter component, τ k represents a delay between the k th backscatter component and a corresponding transmitted signal, and Θ k represents an angle of arrival of k th backscatter component.
22. The method of claim 15 , further comprising:
receiving the composite signal during a plurality of consecutive non-overlapping time windows; and
estimating one or more parameters of the first backscatter component based at least on a first portion of the composite signal received in a first window; and
iteratively estimating parameters of a next backscatter component based on a second portion of the composite signal received in a next consecutive window.
23. The method of claim 22 , wherein the consecutive time windows correspond to different sizes.
24. The method of claim 15 , further comprising:
estimating the at least the first backscatter component using a Sequential Convex Programming (SCP) algorithm.
25. The method of claim 24 , further comprising:
generating an initial estimate for the SCP algorithm using a continuous basis pursuit (CBP) algorithm.
26. The method of claim 15 , further comprising:
estimating the at least the first backscatter component using a continuous basis pursuit (CBP) algorithm.
27. The method of claim 15 , further comprising:
estimating a Doppler frequency corresponding to each object.