Communications: directive radio wave systems and devices (e.g. – Determining velocity
Reexamination Certificate
2002-04-09
2002-12-31
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
C342S114000, C342S115000
Reexamination Certificate
active
06501418
ABSTRACT:
BACKGROUND OF THE INVENTION
Police Doppler radars need to acquire the patrol speed of the police car in various moving modes to be able to calculate the target speed of a tracked target in either moving, same lane mode or moving, opposite lane mode. In moving, opposite lane mode, the speed of the patrol car must be subtracted from the Doppler closing speed of the target being tracked to correctly calculate the speed of the target. In moving, same lane mode, the speed of the patrol car must be added to the Doppler closing speed found from the radar returns to derive the actual speed of the target. Obviously if the patrol speed is wrong, the calculated speed of the target will be wrong.
In the prior art Doppler radars such as the Applied Concepts Stalker Dual and the Kustom Eagle series as well as other Doppler police radars, the patrol speed was acquired by searching the Fourier components of the Doppler return signal for radar reflections from stationary objects such as billboards, trees, the ground, etc. Usually, the strongest signal component represented a return from the ground or another stationary object. However, that is not always true, and false patrol speed signals could be locked onto and tracked if another signal from, for example, a truck with a large radar cross section is the strongest signal in the spectrum. In other words, the fact that a radar return signal is the strongest signal in the spectrum does not guarantee that it is from a stationary object and represents the patrol speed.
To resolve that ambiguity, radars like the Kustom Eagle series use complicated digital signal processing to examine the shape of the Fourier component spectrum around the peak which the radar thinks is the patrol speed return from a stationary object. Patrol speed returns typically have an asymmetrical shape around the peak, and the Eagle series radars took advantage of this fact by examining the shape of the spectrum around each peak which is suspected of being a patrol speed return to determine if the characteristic asymmetric shape was present. This complicates the software unnecessarily and increases the cost to design it, and is not foolproof anyway. Further, it is hardly worth using this methodology since it does not help in many cases.
Another problem with deriving the patrol speed from radar returns is that when the patrol car comes to a stop. Typically, after a patrol speed return from a stationary object is found, the radar tracks that return even at a lower amplitude to maintain continuity due to traffic in the antenna beam that reduces the reflected return from stationary objects. Problems arise however when the police vehicle comes to a stop, and the lock on the patrol speed return is lost. The software of these prior art radars goes into a search mode when lock is lost on the patrol speed return in an attempt to find a new patrol speed return. The radar will then often lock onto a return from another vehicle instead of a return from a stationary object and will conclude that the speed of that other vehicle is the patrol speed.
This is called “shadowing” and frequently occurs when a patrol car has its radar operating in moving mode and pulls to a stop at a stop sign behind another car. When the other car takes off from the stop sign, the radar will often lock onto the speed of that car as the patrol speed and fail to lock onto the actual patrol car speed when the patrol car starts moving again.
When the patrol car is stopped, the radar needs to be manually switched into stationary mode to prevent this “shadowing problem” from happening. When the patrol car starts moving again, the radar must be manually switched back to moving mode. This is inconvenient to the officer, and if he forgets, a bad patrol speed can be locked which leads to errors in the tickets he writes.
Early attempts to use speedometer interfaces to find patrol speed are represented by U.S. Pat. No. 4,335,382 to Brown and assigned to Decatur. That patent taught a traffic radar system in which the speed of a target vehicle is determined by measuring the difference in frequency between a component of a doppler signal which has a frequency proportional to the relative speed of the target vehicle and a moving patrol vehicle and a reference signal having a frequency proportional to the speed of the patrol vehicle. The reference signal is developed from a tachometer device which generates a periodic signal having a frequency proportional to the rotational speed of a vehicle wheel and phase-locked loop arrangements including adjustable dividers are provided for locking an oscillator to the tachometer signal and generating a reference signal at a frequency proportional to the actual speed of the patrol vehicle. For calibration, a component of the doppler signal produced from reflections from stationary objects is used.
More recently, Kustom Signals obtained U.S. Pat. No. 6,023,236 for Speedometer Assisted Patrol Speed Search For DSP Traffic Radar. This patent demonstrates an operator sequence to synchronize the speedometer input to the radar return. Synchronization is typically done upon initial installation or when the radar is moved to another vehicle.
In U.S. Pat. No. 5,525,996 owned by the assignee of the present patent application and covering the Stalker Dual, a method of automatically rejecting the patrol speed determined from the ground return on the basis of too high a difference from a speed determined from a speedometer interface was taught. Specifically, the '996 patent taught,
“The DSP also has an optional speedometer interface 424 in some embodiments through which the DSP can read the actual patrol car speed for purposes of comparing this speed to the “patrol speed” derived from the radar returns of stationary objects. The software of Appendix 1 does not use the actual speedometer speed as the patrol speed because this is not accurate enough. Instead, the patrol speed is derived from the Doppler shifted radar returns from the ground. This is done by using the strongest radar return over time and assuming this is the return from the ground. Basically, the ground return is usually the strongest radar return although when targets get close, their returns become stronger for a short time than the ground return but then the target return goes away altogether. The software therefore assumes that the strongest return over an interval which is longest enough to distinguish over transitory target returns, is the return from which the patrol speed is derived. The software also includes the ability to compare the calculated patrol speed from the return selected in the above described manner to the speed read from the speedometer, and, if the difference is greater than 3 MPH, to discard the calculated patrol speed and re-calculate it from a different radar return.
None of these prior art attempts was completely satisfactory. Therefore, a need has arisen for a process and apparatus to use speedometer pulses to steer the DSP search for a patrol speed which automatically calibrates itself on every powerup and does not need to have a speedometer input to operate so that it can be moved from a car with a speedometer output to a car without a speedometer output with no setup needed.
SUMMARY OF THE INVENTION
The invention is a process and apparatus for using speed pulses from a speedometer to steer a search by a digital signal processor on an Fourier transform based police Doppler radar to find the correct patrol speed from stationary object returns. The system automatically calibrates itself (finds the correct ratio between speed sensor output frequency and true vehicle ground speed) so that it can be moved easily from one car to another with different speed versus frequency characteristics of their speedometers. No human input is needed of any sort to complete this automatic calibration process.
Further, in some embodiments, the radar can also operate like the prior art radars to find the ground speed without any speedometer input at all. If installed in a car with no speedometer output coupled to the radar,
Applied Concepts Inc.
Fish Ronald Craig
Ronald Craig Fish A Law Corporation
Sotomayor John B.
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