SmartSensor HD
9
e vertical beam width of the RVSD at the 6 dB points of the two-way pattern shall be 65 degrees or greater.
is enables the RVSD to provide simultaneous detection from a lane located at the minimum oset and a lane located at the maxi-
mum range. e vertical beam width of an RVSD determines the eld of view in which it can detect trac. If the eld of view is
smaller than the distance between the minimum oset and the farthest range, then the RVSD will be unable to detect vehicles over
the entire range. A vertical beam width of less than 65 degrees will not allow an RVSD, mounted at a typical height of 17 ft. (5.2
m), to simultaneously detect and report information when the lanes are positioned from the minimum oset of 6 ft. (1.8 m) to the
maximum range of 250 ft. (76.2 m).
e horizontal beam width of the RVSD at the 6 dB points of the two-way pattern shall be 7 degrees or less.
A narrow horizontal beam width allows the RVSD to resolve vehicles at the farthest ranges. If the horizontal beam width is too
large, a trailing vehicle may be merged with the vehicle in front.
e sidelobes in the RVSD two-way antenna pattern shall be -40 dB or less.
Low sidelobes ensure that the performance from the antenna beam widths is fully achieved.
11.3 Resolution. e RVSD shall transmit a signal with a bandwidth of at least 240 MHz.
e bandwidth of the transmit signal translates directly into radar resolution, which contributes directly to detection performance.
For example, an RVSD that transmits at a low bandwidth will have low radar resolution, which could cause it to count a single ve-
hicle as two vehicles in adjacent lanes. As another example of the adverse eects of low radar resolution, the response from a barrier
or other radar target in the roadway may spill over into the lanes of travel and desensitize the radar. In order to achieve the specied
detection accuracy in a variety of conditions, the unwindowed radar resolution cannot be larger than 2 ft. (0.6 m) at the half-power
level, which requires a bandwidth of 240 MHz. e high radar resolution reduces the problem of vehicle responses getting drowned
out by brighter vehicles in adjacent lanes and improves performance for moving and stopped vehicles near barriers.
11.4 RF Channels. e RVSD shall provide at least 4 RF channels so that multiple units can be mounted in the same
vicinity without causing interference between them.
12.0 Conguration.
12.1 Auto-conguration. e RVSD shall have a method for automatically dening trac lanes or detection zones with-
out requiring user intervention. is auto-conguration process shall execute on a processor internal to the RVSD and shall
not require an external PC or other processor.
e auto-conguration process shall automatically dene trac lanes or detection zones by detecting the relative position
of vehicles within the RVSD’s eld of view.
e RVSD shall include a transceiver capable of detecting multiple vehicles present within its eld of view. e RVSD
shall also include a processor or computer with executable instructions that estimates the position of each of the vehicles,
records the position of the vehicles, generates a probability density function estimation from each position of the vehicles,
and denes trac lanes from that probability density function estimation. e probability density function estimation
represents the probability that a vehicle will be located at any range.
e RVSD auto-conguration process shall dene all lanes within the detectable area of the RVSD, up to the maximum
number of lanes, during free-ow conditions; when at least 50% of a sedan is visible above any barriers; when at least 10
cars pass in each lane during conguration time; and there are less than 10% lane-changing vehicles.
12.2 Manual Conguration. e auto-conguration method shall not prohibit the ability of the user to manually adjust
the RVSD conguration.
e RVSD shall support the conguring of lanes or detection zones in 1-ft. (0.3-m) increments.
To Next Page
Loading...
