Emergency Vehicle Detector

The present invention relates generally to radar detectors, and more particularly, to a method and apparatus for detecting emergency vehicles with a radar detector.

It has long been desirable to provide a system whereby drivers are alerted to the presence of emergency vehicles, such as those used by police and fire personnel, so that safe operation of passenger vehicles can be maintained.

U.S. Pat. No. 4,238,778 discloses an emergency vehicle warning system which includes an RF transmitter in the emergency vehicle and a receiver in other vehicles. The transmitter includes a single oscillator for generating a carder frequency of predetermined frequency. The receiver includes an antenna and bandpass filter, and the intensity of signals passed by the filter are compared to a predetermined intensity level to validate the signal and generate a warning.

U.S. Pat. No. 5,235,329 discloses an emergency vehicle detection system wherein a passenger vehicle includes a receiver sensitive to the frequency of a wave-borne signal generated by the emergency vehicle. The emergency vehicle transmits a signal in a broad frequency band, and the receiver located in the passenger vehicle generates an alert for any signals received within that frequency band. However, each emergency vehicle is configured to have a unique dead band somewhere in selected frequency band, and each emergency vehicle has a received designed to generate an alert only for signals it receives in that dead band. In that way, an emergency vehicle will be alerted to other emergency vehicles but will not alert based on its own signal.

Radar detectors, such as the ESCORT.RTM. and PASSPORT.RTM. radar detector products manufactured and sold by Cincinnati Microwave, Inc., assignee herein, are generally known and used by vehicle drivers for detecting the presence of police radar signals and generating an alert thereto, as disclosed in the following commonly assigned patents: U.S. Pat. No. 4,313,216; U.S. Pat. No. 4,581,769; U.S. Pat. No. 4,954,828; U.S. Pat. No. 5,049,885; U.S. Pat. No. 5,079,553; and U.S. Pat. No. 5,305,007. However, legislation has banned the use of such devices in many states and in interstate trucking. It has been proposed that such devices be used for other purposes, such as to detect emergency vehicles. However, no one has successfully developed such an application. Therefore, it would be desirable to utilize a radar detector to detect emergency vehicles and generate an alert for such detection.

According to the present invention, a system is provided for detecting emergency vehicles. A transmitter is mounted in an emergency vehicle for generating and transmitting a first signal and a second signal, wherein the first signal and the second signal are fixed at different frequencies of a preselected frequency band. In the preferred embodiment, the K band is selected. A receiver is carried in a second vehicle for detecting that the first signal and the second signal are in a predetermined location and for generating an alert upon such detection. The second signal may be selectable between two discrete frequencies such that two combinations of first and second signals are provided. In one position, the detected signals indicate a moving emergency vehicle. In the other position, the detected signals indicate a stationary emergency vehicle. Alternatively, two types of transmitters could be provided, one type to generate the first and second signal which indicate a moving emergency vehicle, and the other type to generate a second and a third signal which indicate a stationary emergency vehicle.

A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description of the invention and accompanying drawings which set forth an illustrative embodiment in which the principles of the invention are utilized.

FIG. 1 is a schematic diagram showing an emergency vehicle and a passenger vehicle equipped with the emergency vehicle detection system of the present invention.

FIG. 2 is a block diagram of a radar detector configured according to the present invention.

FIG. 3 A is a graphical representation of the transmitted signals from an emergency vehicle.

FIG. 3B is a graphical representation of the output from the quadrature detector portion of the present invention.

FIG. 4 is a simplified flow chart showing the steps performed in evaluating detected signal pairs.

Referring now to FIG. 1, an emergency vehicle 2 is equipped with a transmitter 4 having two signal sources 6A and 6B for concurrently generating and transmitting a first signal S.sub.1 and a second signal S.sub.2, respectively. Preferably, the signals S.sub.1 and S.sub.2 are continuous wave signals fixed at specified frequencies located near opposite ends of the K band, which is defined by the Federal Communications Commission as 24.15+/-0.100 GHz. At a minimum, the signals S.sub.1 and S.sub.2 must be fixed at different frequencies in a preselected frequency band and be capable of discrimination by a receiver/detector unit.

In the preferred embodiment of the invention, two different types of signal sources are provided: one for moving vehicles and the other for stationary hazards. The receiver is adapted to detect and distinguish the different types of sources and to provide an alert corresponding to each type.

For example, in moving vehicles, transmitter source 6A generates the first signal S.sub.1 as a continuous wave signal fixed at 24.110+/-0.020 GHz and transmitter source 6B generates the second signal S.sub.2 as a continuous wave signal fixed at 24.230+/-0.020 GHz. For stationary vehicles, transmitter source 6A generates the first signal S.sub.1 as a continuous wave signal fixed at 24.070+/-0.020 GHz and transmitter source 6B generates the second signal S.sub.2 as a continuous wave signal fixed at 24.230+/-0.020 GHz. Thus, in the preferred embodiment, moving vehicles will transmit the first signal type, wherein the signals differ in frequency by 120 MHz, while stationary vehicles will transmit the second signal type, wherein the signals differ in frequency by 160 MHz. Other variations will be obvious to one skilled in the art, including the addition of more types of signal sources to differentiate other types of emergency vehicles or other mobile or stationary hazards. Further, the difference in frequency between signals need only be so large as to be distinguishable by the receiver. Filter technology is well known which can reduce the distinguishable difference to the order of a few MHz or less, but utilization of such technology is generally considered based on desired resolution and cost. For example, where the receiver generates both an s-curve and its image in response to a signal, as described below, a plurality of signals S.sub.1 . . . S.sub.n could be provided wherein the difference between signals is 40 MHz, and the receiver could adequately distinguish and alert for each signal or groups of signals. Image rejection schemes are also known, such as that employed in Cincinnati Microwave'S SOLO.RTM. radar detector, wherein the distinguishable difference is on the order of 20 MHz or less.

An emergency vehicle is preferably equipped with both types of signal sources and a means for selecting one or the other type. For example, a two position switch (not shown) may be operated between a first position if the emergency vehicle is moving and a second position if the emergency vehicle is stationary. Alternatively, a motion sensor (not shown) or other suitable switching means could be incorporated to automatically select between the two types of signal sources. In this way, passenger vehicles properly equipped as described below can determine from the received signals whether the emergency vehicle is moving or stationary.

A passenger vehicle 8 is equipped with a radar detector 10. As shown in FIG. 2, the radar detector 10 includes a microwave receiver section 12 coupled to a microprocessor section 14. The microprocessor section 14 includes sufficient hardware and/or software to evaluate the detected signals and generate an audible or visible alert on alert indicator 15. Typically, the microprocessor 14 may be programmed with appropriate instructions to evaluate signals which are detected by the receiver section 12.

Preferably, an application specific integrated circuit (ASIC) 17 is used to perform low rate signal processing, and a digital signal processor (DSP) chip 19 is used to perform high rate signal processing. Such a configuration is known, for example, from U.S. Pat. No. 5,305,007, the text of which is expressly incorporated herein by reference. Other detection configurations are generally known, for example, those shown in the following U.S. Patents which are also expressly incorporated herein by reference: U.S. Pat. No. 4,954,828; U.S. Pat. No. 5,049,885; and U.S. Pat. No. 5,079,553.

Generally, the receiver section 12 includes an antenna 16 for receiving incoming signals. A first local oscillator 18 is driven by a sweep circuit 20 to provide a signal which sweeps across the frequency band and which is mixed by first mixer 22 with the incoming signal to generate a first intermediate frequency signal IF.sub.1. Signal IF.sub.1 is amplified by IF amplifier 24 and mixed by second mixer 26 with a fixed signal from a second local oscillator 28 to generate a second intermediate frequency IF.sub.2. Signal IF.sub.2 is then amplified by amplifier 30, passed through bandpass filter 32, then amplified, limited and demodulated by quadrature detector 34 to generate as an output a pair of s-curves for each detected signal. As explained in U.S. Pat. No. 5,049,885, the s-curves define positions in time relative to the start of the sweep which correspond to the frequency at which the incoming signal is received.

As explained in U.S. Pat. No. 5,305,007, digital signal processing may be used to effectively evaluate the s-curves to determine whether they represent "valid" detected signals. Because the preferred embodiment of the present invention uses K band sources, the time spacing between s-curve pairs will be approximately 3.4 ms. However, rather than detecting just a single pair of s-curves in the K band, as would be the case for a conventional radar detector, the present invention will discriminate for two or more pairs of s-curves, as shown in FIGS. 3A and 3B. One transmitted signal S.sub.1 will be located at one end of the frequency band, and the other transmitted signal S.sub.2 will be located at the other end of the frequency band. Likewise, the output of the quadrature detector 34 will be the s-curve pair S.sub.3 and S.sub.3, corresponding to signal S.sub.1, and the s-curve pair S.sub.4 and S.sub.4, corresponding to signal S.sub.2, separated in a time domain as shown. This can be accomplished by making simple software changes in microprocessor 14 to realize the flow chart illustrated in FIG. 4. It should be obvious that many variations in the flow chart could provide an adequate solution. For example, an illustrative copy of source code is appended hereto and has been shown to work when implemented in Texas Instruments model TMS320C15 DSP chip. Referring to FIG. 4, the microprocessor 14 receives and stores two signals in step 100. An optional step 102 (but implemented in conventional radar detectors) checks to see if the signal(s) received are within the K band. If not, the program loops back. If so, then the microprocessor evaluates the s-curve pairs in step 104 to see if one of the pairs corresponds to 24.230+/-0.020 GHz. If not, the program may perform another process in step 105 (such as conventional police radar detection) and loop back. If so, then the microprocessor evaluates the other s-curve pair in step 106 to see if it corresponds to 24.110+/-0.020 GHz. If so, then an alert corresponding to a first signal type is generated in step 107. If not, then the microprocessor checks in step 108 to see if it corresponds to 24.070+/-0.020 GHz. If so, then an alert corresponding to a second signal type is generated in step 109. If not, then the program loops back.

It should be realized that many solutions could be realized via either hardware or software to implement the present invention. However, as most broadly contemplated, the present invention allows existing radar detectors to be modified through simple software changes to recognize these new emergency classes of signals. Other solutions will be obvious to those skilled in the art.

It should be understood that the invention is not intended to be limited by the specifics of the above-described embodiment, but rather defined by the accompanying claims.