Random body movement cancellation for non-contact vital sign detection
A method and system for cancelling body movement effect for non-contact vital sign detection is described. The method begins with sending on a first electromagnetic wave transceiver a first electromagnetic signal with a first frequency to a first side of a body, such as a person or animal. Simultaneously using a second electromagnetic wave transceiver a second electromagnetic signal is sent with a second frequency to a second side of a body, wherein the first frequency and the second frequency are different frequencies. A first reflected electromagnetic signal reflected back in response to the first electromagnetic wave on the first transceiver is received and a first baseband complex signal is extracted. Likewise a second reflected electromagnetic signal reflected back in response to the second electromagnetic wave on the second transceiver is received and a second baseband complex signal is extracted. The first baseband complex signal is mathematically combined with the second baseband complex signal to cancel out a Doppler frequency drift therebetween to yield a periodic Doppler phase effect.
1. A method for cancelling body movement effect for non-contact vital sign detection, comprising:
sending a first electromagnetic signal with a first frequency to a first side of a body from a first transceiver and a second electromagnetic signal with a second frequency to a second side of the body from a second transceiver, where the first frequency of wavelength λ 1 and the second frequency of wavelength λ 2 are close to each other so that (λ 1 ≈λ 2 ≈λ);
receiving at least a first reflected electromagnetic signal reflected back in response to the first electromagnetic signal via the first transceiver and receiving at least a second reflected electromagnetic signal reflected back in response to the second electromagnetic signal via the second transceiver;
generating an angular information output by combining a first angular information signal extracted from the first reflected electromagnetic signal with a second angular information signal extracted from the second reflected electromagnetic signal to cancel out a Doppler frequency drift therebetween, where the first and second angular information signals are combined by arctangent demodulation as expressed by:
ψ
f
(
t
)
=
4
π
x
h
1
(
t
)
λ
+
4
π
x
r
1
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
1
and
ψ
b
(
t
)
=
4
π
x
h
2
(
t
)
λ
+
4
π
x
r
2
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
2
,
where x h1 (t) and x r1 (t) are heartbeat-induced and respiration-induced physiological movements on the first side of the body, x h2 (t) and x r2 (t) are heartbeat-induced and respiration-induced physiological movements on the second side of the body, φ 1 , φ 2 are residual phases of the first transceiver and the second transceiver, and y(t) is a body movement, where the y(t) term in the angular information output ψ fb (t)=ψ f (t)+ψ b (t) is cancelled out by adding ψ f (t) and ψ b (t), while terms of physiological movement X h1 (t), x h2 (t), x r1 (t) and x r2 (t) are enhanced as expressed by:
ψ
fb
(
t
)
=
4
π
[
x
h
1
(
t
)
+
x
h
2
(
t
)
]
λ
+
4
π
[
x
r
1
(
t
)
+
x
r
2
(
t
)
]
λ
+
ϕ
1
+
ϕ
2
;
and displaying a vital sign of the body extracted from the angular information output.
2. The method of claim 1 , further comprising extracting at least one of respiration rate and heart rate from the angular information output.
3. The method of claim 2 , further comprising sending the at least one of the respiration rate and the heart rate to a display.
4. The method of claim 2 , further comprising sending the at least one of the respiration rate and the heart rate to a wireless output device for display.
5. The method of claim 1 , wherein a DC offset of in-phase (I) and quadrature (Q) baseband components of at least one of the first and second reflected electromagnetic signals is calibrated out.
6. The method of claim 1 , wherein a DC offset associated with at least one of the first and second reflected electromagnetic signals is calibrated using a trajectory-fitting procedure.
7. The method of claim 1 , wherein the first transceiver and the second transceiver are anyone of:
5.8 GHz quadrature radar transceivers; and
24 GHz quadrature radar transceivers.
8. The method of claim 1 , wherein the first and second angular information signals are based upon corresponding in-phase (I) and quadrature (Q) baseband components of the first and second reflected electromagnetic signals.
9. The method of claim 1 , wherein the first side is a front of the body and the second side is a back of the body.
10. A system for cancelling body movement effect for non-contact vital sign detection, comprising:
a first transceiver configured to send a first electromagnetic signal with a first frequency to a first side of a body and receive a first reflected electromagnetic signal reflected back in response to the first electromagnetic signal;
a second transceiver configured to send a second electromagnetic signal with a second frequency to a second side of the body, where the first frequency and the second frequency are different frequencies, and receive a second reflected electromagnetic signal reflected back in response to the second electromagnetic signal, where the first frequency of wavelength λ 1 and the second frequency of wavelength λ 2 are close to each other so that (λ 1 ≈λ 2 ≈λ);
a processing system configured to generate an angular information output by combining a first angular information signal extracted from the first reflected electromagnetic signal with a second angular information signal extracted from the second reflected electromagnetic signal to cancel out a Doppler frequency drift therebetween, where the first and second angular information signals are combined by arctangent demodulation as expressed by:
ψ
f
(
t
)
=
4
π
x
h
1
(
t
)
λ
+
4
π
x
r
1
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
1
and
ψ
b
(
t
)
=
4
π
x
h
2
(
t
)
λ
+
4
π
x
r
2
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
2
,
where x h1 (t) and x r1 (t) are heartbeat-induced and respiration-induced physiological movements on the first side of the body, x h2 (t) and x r2 (t) are heartbeat-induced and respiration-induced physiological movements on the second side of the body, φ 1 , φ 2 are residual phases of the first transceiver and the second transceiver, and y(t) is a body movement, where the y(t) term in the angular information output ψ fb (t)=ψ f (t)+ψ b (t) is cancelled out by adding ψ f (t) and ψ b (t), while terms of physiological movement x h1 (t), x h2 (t), x r1 (t) and x r2 (t) are enhanced as expressed by:
ψ
fb
(
t
)
=
4
π
[
x
h
1
(
t
)
+
x
h
2
(
t
)
]
λ
+
4
π
[
x
r
1
(
t
)
+
x
r
2
(
t
)
]
λ
+
ϕ
1
+
ϕ
2
;
and display a vital sign of the body extracted from the angular information output.
11. The system of claim 10 , wherein the processing system is further configured to extract at least one of respiration rate and heart rate from the angular information output.
12. The system of claim 11 , further comprising a display that displays the at least one of the respiration rate and the heart rate.
13. The system of claim 11 , wherein the at least one of the respiration rate and the heart rate is communicated to a wireless output device for display.
14. The system of claim 11 , wherein the at least one of the respiration rate and the heart rate is communicated to a storage device for subsequent access.
15. The system of claim 11 , wherein a DC offset of in-phase (I) and quadrature (Q) baseband components of at least one of the first and second reflected electromagnetic signals is calibrated out.
16. The system of claim 10 , wherein a DC offset associated with at least one of the first and second reflected electromagnetic signals is calibrated using a trajectory-fitting procedure.
17. The system of claim 10 , wherein the first transceiver and the second transceiver are anyone of:
5.8 GHz quadrature radar transceivers; and
24 GHz quadrature radar transceivers.
18. The system of claim 10 , wherein the first and second angular information signals are based upon corresponding in-phase (I) and quadrature (Q) baseband components of the first and second reflected electromagnetic signals.
19. The system of claim 18 , wherein the I and Q baseband components are sampled by a digital acquisition module for subsequent processing.
20. The system of claim 10 , wherein the first side is a front of the body and the second side is a back of the body.