Method for seat occupancy detection

Patent metadata

Field	Value
Publication number	US-12411209-B2
Application number	US-202017787833-A
Country	US
Kind code	B2
Filing date	Dec 15, 2020
Priority date	Dec 20, 2019
Publication date	Sep 9, 2025
Grant date	Sep 9, 2025

Abstract

A method for occupancy detection for at least one vehicle seat, using at least one transmit antenna and a plurality of receive antennas, includes: emitting a detection signal with each transmit antenna onto at least one vehicle seat, which detection signal is a frequency-modulated continuous-wave radar signal, and receiving with each receive antenna a reflected signal; recording sample data representing the reflected signal, the sample data having M channels, with M=N1·N2, where N1 is the number of transmit antennas and N2 is the number of receive antennas; for each channel, removing a component from the sample data that corresponds to a reflection from a static object; and applying a frequency estimation method to the sample data to at least implicitly determine at least one angle of arrival θ i corresponding to a position of an occupant on a vehicle seat.

First claim

The invention claimed is:

1. A method for occupancy detection for at least one vehicle seat, using at least one transmit antenna and a plurality of receive antennas, the method comprising:
emitting a detection signal with each transmit antenna onto at least one vehicle seat, which detection signal is a frequency-modulated continuous-wave radar signal, and receiving with each receive antenna a reflected signal;
recording sample data representing the reflected signal, the sample data having M channels, with M=N1·N2, where N1 is the number of transmit antennas and N2 is the number of receive antennas;
for each channel, removing a component from the sample data that corresponds to a reflection from a static object; and
applying a frequency estimation method to the sample data to at least implicitly determine at least one angle of arrival θ i corresponding to a position of an occupant on a vehicle seat,

wherein the frequency estimation method is a multiple signal classification (MUSIC) method and includes:
calculating a sample covariance matrix {circumflex over (R)};
calculating eigenvalues and eigenvectors of the sample covariance matrix {circumflex over (R)};
sorting the eigenvalues in descending order and, with D being a number of targets, selecting M−D smallest eigenvalues and corresponding eigenvectors to determine a noise subspace G; and
calculating roots z i of a root-MUSIC polynomial J(z) with
J ( z )= z M-1 p T ( z −1 ) GG R p ( z )

wherein

p
⁡
(
z
)

=

[

z
0

⋮

z

M
-
1

]

 and each root z i corresponds to an angle of arrival θ i ,

wherein for each seat, an associated area in the complex plane is defined and for each frame, which corresponds to a plurality of modulation periods of the detection signal, a counter for this associated area is increased if at least one root z i is located in this associated area and decreased if there is no root z i in this associated area and the seat is identified as occupied if the counter exceeds a predefined threshold.

2. The method according to claim 1 , wherein the method uses only D roots z i located inside a unit circle in the complex plane and closest to the unit circle.

3. The method according to claim 1 , wherein for each vehicle seat, an angle interval is defined and wherein the method uses only roots z i corresponding to an angle of arrival θ i within an angle interval.

4. The method according to claim 1 , wherein an inner circle having a radius of less than 1 is defined and wherein the method uses only roots z i outside the inner circle and inside the unit circle.

5. The method according to claim 1 , wherein 1 to 5 samples are used for calculating the covariance matrix {circumflex over (R)}.

6. The method according to claim 1 , wherein before applying the frequency estimation method, a range gating is performed for each channel by:
transforming the sample data into a range representation; and
only considering a portion of the sample data corresponding to a predefined range interval, which includes a potential position of an occupant.

7. The method according to claim 1 , wherein a plurality of transmit antennas is used.

8. The method according to claim 1 , wherein transmit signals from different transmit antennas are separated by time division multiplexing.

9. The method according to claim 1 , wherein the receiving antennas are arranged as a uniform linear array.

10. The method according to claim 1 , wherein the frequency estimation method is a Capon method, and comprises:
calculating the sample covariance matrix {circumflex over (R)} with

R
^

=

1
K

⁢

∑

k
=
0

K
-
1

x
[
k
]

⁢

x
H

[
k
]

wherein x[k] is an M-dimensional output vector representing the sample data in each channel in range representation and K is the number of data samples considered;
calculating an inverse sample covariance matrix {circumflex over (R)} −1 ;
generating a steering vector a(θ) for each of a plurality of scanning angles θ; and
calculating a Capon power spectrum P Cap (θ) with

P
Cap

(
θ
)

=

1

a
H

(
θ
)

⁢

R
^

-
1

⁢

a
⁡
(
θ
)

11. The method according to claim 1 , wherein the method further comprises, after determining the noise subspace G:
generating a steering vector a(θ) for each of a plurality of scanning angles θ; and
calculating a MUSIC power spectrum P MUSIC (θ) with

P
MUSIC

(
θ
)

=

a
H

(

Assignees

• Iee Sa

Inventors

• Cordie Janine
• Diewald Andreas
• Gomez Oscar
• Koehler Alan
• Landwehr Jochen
• Singh Parth Raj

Classifications

• B60N2210/16

  Electromagnetic waves · CPC title

• B60N2/267

  alerting means responsive to presence or absence of children · CPC title

• B60N2230/30

  Signal processing of sensor data · CPC title

• B60N2/0021

  characterised by the type of sensor or measurement · CPC title

• B60N2/266

  with detection or alerting means responsive to presence or absence of children; with detection or alerting means responsive to improper locking or installation of the child seats or parts thereof · CPC title