Target persistence filter for multi-frequency automotive radar system

• US 5,181,038 A
• Filed: 08/16/1991
• Issued: 01/19/1993
• Est. Priority Date: 05/06/1991
• Status: Expired due to Term

• Current Assignee: Bendix Commercial Vehicle Systems LLC (Estate of Heinz Hermann Thiele)
• Original Assignee: IVHS Technologies Incorporated
• Inventors: Davis, John W., Asbury, Jimmie
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US07/745,928
• Time in Patent Office: 522 Days
• Field of Search: 342/70, 342/71, 342/72, 342/114, 342/98, 342/99, 342/101, 342/27, 342/28
• US Class Current: 342/70
• CPC Class Codes: G01S 13/24 using frequency agility of carrier wave
• CPC Class Codes: G01S 13/53 performing filtering on a single spectral line and associated with one or more range gates with a phase detector or a frequency mixer to extract the Doppler information, e.g. pulse Doppler radar G01S13/5244 takes precedence
• CPC Class Codes: G01S 13/534 based upon amplitude or phase shift resulting from movement of objects, with reference to the surrounding clutter echo signal, e.g. non coherent MTi, clutter referenced MTi, externally coherent MTi
• CPC Class Codes: G01S 13/726 Multiple target tracking
• CPC Class Codes: G01S 13/86 Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
• CPC Class Codes: G01S 13/931 of land vehicles
• CPC Class Codes: G01S 2013/932 using own vehicle data, e.g. ground speed, steering wheel direction
• CPC Class Codes: G01S 2013/9322 using additional data, e.g. driver condition, road state or weather data
• CPC Class Codes: G01S 2013/9329 cooperating with reflectors or transponders

Abstract

A Doppler control circuit for a CW or pulse Doppler radar system for monitoring not only the phase shift between echo signals from several targets but also the amplitude difference between the several targets and to further tune the radar to a particular target among one or more targets from which echo signals return. The control circuit can be used in state of the art CW or pulse Doppler type radar systems. In a further system, a continuously generated radar signal is repeatedly transmitted at different frequencies in time division fashion to define a succession of transmit and receive frames. The receive frames are divided into a plurality of time interval windows with selected windows being used to detect received signals at the different frequencies. The remaining windows can be used for subsystems of the radar system. The rate of phase shift of received signals at a reference frequency is used to determine closing rate (positive or negative), while the phase shift difference between received signals at two frequencies is used to determine range and target direction. A target persistence and environment filter prevents the radar system from giving false alarms due to short duration target echoes resulting from birds or wayside objects.

Claims

1. In an automotive collision avoidance system in a vehicle having a Doppler radar system with means for successively transmitting a radar beam at a plurality of successive intervals and for receiving echo signals corresponding to the plurality of successive intervals from at least one target within the radar beam, a target persistence and environment filter comprising:

a. means for receiving a first and a second echo signal from at least one target, and for generating a signal indicative of the relative phase difference between the first and the second received echo signals, such relative phase difference corresponding to a change in relative distance of such at least one target with respect to the vehicle, the generated signal having a first value when such relative distance is decreasing and a second value when such relative distance is increasing;

b. persistence determination means, coupled to the generated signal, and including a programmable time delay means for determining a time period in accordance with a programmed value, for generating an output signal having a first value if the generated signal has its first value for the time period determined by the programmed value of the time delay means, and having a second value if the generated signal has its second value during the time period determined by the programmed value of the time delay means;

c. speed determination means, for determining the speed of the vehicle; and

d. programming means, coupled to the persistance determination means and to the speed determination means, for programming the time delay means with a value whereby the duratin of the time period is proportional to the speed of the vehicle.

2. The system of claim 1, wherein the persistence determination means comprises a resettable shift register.

3. The system of claim 1, wherein the persistence determination means comprises a resettable timer circuit and a resettable latch circuit.

4. In an automotive collision avoidance system in a vehicle having a Doppler radar system with means for successively transmitting a radar beam at a plurality of successive intervals and for receiving echo signals corresponding to the plurality of successive intervals from at least one target within the radar beam, a target persistence and environment filter comprising:

a. means for receiving a first and a second echo signal from at least one target, for comparing the relative phase difference between the first and the second received echo signals, and for generating a signal as a result of such comparison to indicate change in relative distance of such at least one target with respect to the vehicle, the generated signal having a first value when such relative distance is decreasing and a second value when such relative distance is increasing;

b. signal delay means, coupled to the generated signal, and including a programmable time delay means for determining a time period in accordance with a programmed value, for delaying the generated signal for a time period determined by the programmed value of the time delay means, the signal delay means generating an output signal having a first value if the generated signal has its first value for the determined period of time, and having a second value if the generated signal has its second value during the determined period of time;

c. speed determinatin means, for determining the speed of the vehicle; and

d. programming means, coupled to the signal delay means and to the speed determination means, for programming the time delay means with a value whereby the duration of the time period is proportional to the speed of the vehicle;

whereby only echo signals from targets persisting in the radar beam for the determined period of time are further processed by the radar system.

5. The system of claim 4, wherein the signal delay means comprises a resettable shift register.

6. The system of claim 4, wherein the signal delay means comprises a resettable timer circuit and a resettable latch circuit.

7. In an automotive collision avoidance system in a vehicle having a Doppler radar system with means for successively transmitting a radar beam at a plurality of successive intervals and for receiving echo signals corresponding to the plurality of successive intervals from at least one target within the radar beam, a target persistence and environment filter comprising:

a. a bistable latch for receiving a first and a second echo signal from at least one target, for comparing the relative phase difference between the first and the second received echo signals, and for generating a signal as a result of such comparison to indicate change in relative distance of such at least one target with respect to the vehicle, the generated signal having a first value when such relative distance is decreasing and a second value when such relative distance is increasing;

b. a resettable shift register, coupled to the output of the bistable latch, for delaying the generated signal a selected number of bit shifts, the shift register generating an output signal having a first value if the generated signal has its first value for the selected number of bit shifts, and being reset to a second value if the generated signal has its second value during the selected number of bit shifts;

c. speed determination means, for determining the speed of the vehicle; and

d. programming means, coupled to the resettable shift register and to the speed determination means, for programming the resettable shift register with a selected bit shift value whereby the selected number of bit shifts is proportional to the speed of the vehicle;

whereby only echo signals from targets persisting in the radar beam for the selected number of bit shifts are further processed by the radar system.

8. In an automotive collision avoidance system in a vehicle having a Doppler radar system with means for successively transmitting a radar beam at a plurality of successive intervals and for receiving echo signals corresponding to the plurality of successive intervals from at least one target within the radar beam, a target persistence and environment filter comprising:

a. a bistable latch having a clock input coupled to a first echo signal from at least one target, and a data input coupled to a second echo signal from at least one target, for generating a signal indicative of the relative phase difference between the first and the second received echo signals, such relative phase difference corresponding to a change in relative distance of such at least one target with respect to the vehicle, the generated signal having a first value when such relative distance is decreasing and a second value when such relative distance is increasing;

b. a resettable shift register, coupled to the output of the bistable latch, for delaying the generated signal a selected number of bit shifts, the shift register generating an output signal having a first value if the generated signal has its first value for the selected number of bit shifts, and being reset to a second value if the generated signal has its second value during the selected number of bit shifts;

c. speed determination means, for determining the speed of the vehicle; and

d. programming means, coupled to the resettable shift register and to the speed determination means, for programming the resettable shift register with a selected bit shift value whereby the selected number of bit shifts is proportional to the speed of the vehicle;

whereby only echo signals from targets persisting in the radar beam for the selected number of bit shifts are further processed by the radar system.