Wavetronix SmartSensor HD Manual page 9

SmartSensor HD
The vertical beam width of the RVSD at the 6 dB points of the two-way pattern shall be 65 degrees or greater.
This enables the RVSD to provide simultaneous detection from a lane located at the minimum offset and a lane located at the maxi-
mum range. The vertical beam width of an RVSD determines the field of view in which it can detect traffic. If the field of view is
smaller than the distance between the minimum offset 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 offset of 6 ft. (1.8 m) to the
maximum range of 250 ft. (76.2 m).
The 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.
The 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. The RVSD shall transmit a signal with a bandwidth of at least 240 MHz.
The 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 effects 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 specified
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. The 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. The 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 Configuration.
12.1 Auto-configuration. The RVSD shall have a method for automatically defining traffic lanes or detection zones with-
out requiring user intervention. This auto-configuration process shall execute on a processor internal to the RVSD and shall
not require an external PC or other processor.
The auto-configuration process shall automatically define traffic lanes or detection zones by detecting the relative position
of vehicles within the RVSD's field of view.
The RVSD shall include a transceiver capable of detecting multiple vehicles present within its field of view. The 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 defines traffic lanes from that probability density function estimation. The probability density function estimation
represents the probability that a vehicle will be located at any range.
The RVSD auto-configuration process shall define all lanes within the detectable area of the RVSD, up to the maximum
number of lanes, during free-flow conditions; when at least 50% of a sedan is visible above any barriers; when at least 10
cars pass in each lane during configuration time; and there are less than 10% lane-changing vehicles.
12.2 Manual Configuration. The auto-configuration method shall not prohibit the ability of the user to manually adjust
the RVSD configuration.
The RVSD shall support the configuring of lanes or detection zones in 1-ft. (0.3-m) increments.
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