Enhanced vertical object detection for a vehicle radar system
A vehicle radar sensor unit ( 2 ) arranged to acquire a plurality of radar detections, and including an antenna arrangement ( 3 ), a transmitter unit ( 4 ), a receiver unit ( 5 ) and a processing unit ( 6 ). The antenna arrangement ( 3 ) has at least two transmitter antennas ( 7, 8 ) and at least two receiver antennas ( 9, 10, 11, 12 ), where two transmitter antennas ( 7, 8 ) have a vertical spacing (h) between their respective phase centers ( 17, 18 ) that exceeds half the free-space wavelength of the transmitted signal. The processing unit ( 5 ) is arranged to determine a first radial velocity of each radar detection by tracking the change of radial distance (r) to each radar detection for a plurality of radar cycles; determine a second radial velocity that best matches the first radial velocity; track a plurality of measured heights (z) as a function of radial distance (r); and to choose a measured height (z GT ) among the tracked measured heights (z) that has a minimal change from radar cycle to radar cycle.
1. A vehicle radar sensor unit comprising, an antenna arrangement, a transmitter unit, a receiver unit and a processing unit, where the antenna arrangement comprises at least two transmitter antennas and at least two receiver antennas, where the at least two transmitter antennas have a first horizontal spacing between respective phase centers and a vertical spacing between the respective phase centers, where the vehicle radar sensor unit is arranged to transmit time division multiplexed signals and to receive signals that have been reflected by one or more objects during a plurality of radar cycles, such that a plurality of radar detections is acquired, the vertical spacing exceeds half the free-space wavelength of the transmitted signal, where the processing unit is arranged to:
determine a first radial velocity of each of the radar detections by tracking the change of a radial distance to each of the radar detections for each of the radar cycles during the plurality of the radar cycles;
determine a second radial velocity by choosing a measured radial velocity that best matches the first radial velocity;
track a plurality of measured heights as a function of the radial distance for each of the radar cycles during the plurality of radar cycles; and to
choose one of the measured heights among the tracked measured heights that has a minimal change from one of the radar cycles to another of the radar cycles.
2. The vehicle radar sensor unit according to claim 1 further comprising, the processing unit is arranged to solve the equation:
dz
m
dr
=
Δ
m
·
λ
h
for Δm, where z m is the measured height, λ is a free-space wavelength of the transmitted signal, and where
Δ m =( m−m GT ),
where m denotes a geometrical ambiguity index and m GT denotes a ground truth geometrical ambiguity index that corresponds to a correct geometrical ambiguity index.
3. The vehicle radar sensor unit according to claim 2 further comprising, the processing unit is arranged to determine:
u
el
,
k
,
m
=
λ
h
(
Φ
el
,
k
2
π
+
m
)
,
where u el,k,m denotes sin el in view of k and m, where el is an elevation angle for a certain target object detection point and kϵ is an integer, where ϕ el,k is the measured phase between two channels.
4. The vehicle radar sensor unit according to claim 2 further comprising the processing unit is arranged to determine the geometrical ambiguity index m according to the inequality:
-
h
λ
-
1
≤
m
<
h
λ
.
5. A method for a vehicle radar sensor unit using an antenna arrangement with at least two transmitter antennas and at least two receiver antennas, where the transmitter antennas have a first horizontal spacing between respective phase centers, and a vertical spacing between respective phase centers, where the vehicle radar sensor unit is used for transmitting time division multiplexed signals and for receiving signals that have been reflected by one or more objects during a plurality of radar cycles, such that a plurality of radar detections is acquired, the vertical spacing exceeds half the free-space wavelength of the transmitted signal, where the method includes:
determining a first radial velocity of each of the radar detections by tracking a change of radial distance to each of the radar detections for each of the radar cycles during a plurality of the radar cycles;
determining a second radial velocity by choosing a measured radial velocity that best matches the first radial velocity;
tracking a plurality of measured heights as a function of the radial distance for each of the radar cycles during a plurality of the radar cycles; and
choosing a measured height among the tracked measured heights that has a minimal change from radar cycle to radar cycle.
6. The method according to claim 5 wherein the method further comprises, solving the equation:
dz
m
dr
=
Δ
m
·
λ
h
for Δm, where z m is the measured height, λ is the free-space wavelength of the transmitted signal, and where:
Δ m =( m−m GT ),
where m denotes a geometrical ambiguity index and m GT denotes a ground truth geometrical ambiguity index that corresponds to a correct geometrical ambiguity index.
7. The method according to claim 6 wherein the method further comprises, determining:
u
el
,
k
,
m
=
λ
h
(
Φ
el
,
k
2
π
+
m
)
,
where u el,k,m denotes sin el in view of k and m, where el is an elevation angle for a certain target object detection point and kϵ is an integer, where ϕ el,k is the measured phase between two channels.
8. The method according to claim 6 wherein the method further comprises, determining the geometrical ambiguity index m according to the inequality:
-
h
λ
-
1
≤
m
<
h
λ
.