Method and device for determining the direction of travel of an emergency vehicle

Abstract

The present invention relates to a method and a device for determining a direction of travel of an emergency vehicle emitting a periodic audio signal formed of at least one fundamental frequency. The method comprises determining vehicle speeds (33, 36) and fundamental frequencies (32, 35) from consecutive time segments of an audio signal received by the vehicle. If the vehicle has slowed down and the determined fundamental frequency has decreased, or if the vehicle has accelerated and the determined fundamental frequency has increased, then the emergency vehicle and the vehicle travel in opposite directions (37), otherwise they travel in the same direction (38). Figure for abstract: Figure 4

Description

Title of the invention: Method and device for determining the direction of travel of an emergency vehicle Technical field

[0001] The present invention relates to methods and devices for determining a direction of travel of an emergency vehicle. Technological background

[0002] Legislation regarding how to react to the approach of an emergency vehicle varies from country to country and only a few countries systematically adopt the creation of an emergency corridor for priority vehicles.

[0003] Generally, these emergency lanes are not present along traffic lanes and vehicle drivers must clear the lane on which they are traveling to facilitate the passage of emergency vehicles.

[0004] It is essential that vehicle drivers are informed as soon as possible that an emergency vehicle is approaching in order to minimize the slowdown of these emergency vehicles. For this purpose, emergency vehicles are equipped with warning sirens which are particularly loud and omnidirectional so that they can be heard as far away as possible by vehicle drivers.

[0005] However, these warning sirens can be a source of stress and confusion for a driver of a vehicle because it is difficult, if not impossible, for this driver to identify whether an emergency vehicle is traveling in the same direction as his vehicle or whether this emergency vehicle is traveling in an opposite direction. If the emergency vehicle is traveling in a direction opposite to his vehicle, then the driver continues his journey but if this emergency vehicle is traveling in the same direction, the driver must then pull over to facilitate the movement of the emergency vehicle. This choice, the driver can only make it when he sees the emergency vehicle which is very often too late and the emergency vehicle must slow down until an emergency corridor is created in front of him.

[0006] To determine the direction of travel of an emergency vehicle, it is known to use a system that broadcasts an alert in a vehicle if the vehicle is positioned in a geographical area in which an emergency vehicle is traveling. This system requires the installation in the vehicle of a device for receiving audio signals corresponding to warning sirens and a device for broadcasting alerts in the passenger compartment of the vehicle as soon as an audio signal corresponding to a warning siren is received.

[0007] The receiving device may comprise a set of directional microphones or a single rotating microphone that allows the position of the emergency vehicle to be estimated by analyzing the audio signal received by this set of microphones or by this rotating microphone.

[0008] Existing solutions require the installation in vehicles of audio signal receiving devices such as microphones, whereas it would be more economical and simpler if none of these devices had to be installed in a vehicle to inform a driver as quickly as possible that an emergency vehicle is approaching.

[0009] Furthermore, a solution without installing an audio signal receiving device in the vehicle must provide the driver with an indication of the direction of travel of an emergency vehicle so that the driver can adapt his driving accordingly and thus limit his stress as soon as he hears a warning siren of an approaching emergency vehicle.

[0010] Summary of the present invention

[0011] An object of the present invention is to solve at least one of the problems of the technological background described above.

[0012] Another object of the present invention is to determine a direction of travel of an emergency vehicle approaching a vehicle.

[0013] Another object of the present invention is to warn a vehicle driver when an emergency vehicle is approaching.

[0014] Another object of the present invention is to limit the stress of a vehicle driver when an emergency vehicle is approaching.

[0015] Another object of the present invention is to improve road safety by warning a driver sufficiently in advance that an emergency vehicle is approaching and whether this emergency vehicle is traveling in the same direction as the vehicle or in an opposite direction.

[0016] According to a first aspect, the present invention relates to a method for determining a direction of travel of an emergency vehicle emitting a periodic audio signal formed of at least one fundamental frequency, said method being implemented by at least one on-board processor of the vehicle, said method comprising the following steps: - receiving a first time segment of the audio signal transmitted at a first time instant; - determining a first fundamental frequency from the first time segment of the received audio signal; - obtaining a first vehicle speed at the first time instant; - receiving a second time segment of the audio signal transmitted at a second time instant subsequent to the first time instant; - determination of a second fundamental frequency from the second time segment of the received audio signal; - obtaining a second vehicle speed at the second time instant; - if the second vehicle speed is lower than the first vehicle speed and if the second fundamental frequency is lower than the first fundamental frequency then the emergency vehicle and the vehicle travel in opposite directions, otherwise the emergency vehicle and the vehicle travel in the same direction; - if the second vehicle speed is greater than the first vehicle speed and if the second fundamental frequency is greater than the first fundamental frequency then the emergency vehicle and the vehicle travel in opposite directions otherwise the emergency vehicle and the vehicle travel in the same direction.

[0017] The present invention determines a direction of travel of an emergency vehicle by analyzing two consecutive time segments of a received audio signal corresponding to a warning siren. Since the audio signal corresponding to a warning siren comprises at least one fundamental frequency, the present invention analyzes each of the two time segments to determine a fundamental frequency for each of these two time segments. Then, depending on whether the driver slows down or accelerates, the present invention determines the direction of travel of the emergency vehicle transmitting the audio signal by comparing the fundamental frequencies determined from the two consecutive time segments of the audio signal received by the vehicle.

[0018] The present invention does not require the installation in the vehicle of dedicated audio signal receiving devices because an audio signal corresponding to a warning siren can be received by an audio signal receiving device dedicated to a function other than determining the direction of travel of an emergency vehicle. For example, a single fixed microphone that is usually used by a hands-free system for telephoning can be used. It is also possible to use a microphone of a mobile phone that would be in the vehicle at the time of reception of the audio signal corresponding to a warning siren.

[0019] The analysis of the audio signal and the determination of the fundamental frequencies and the direction of travel of the emergency vehicle can be implemented by one or more on-board processors of the vehicle. These processors can be part of computers which are not necessarily dedicated solely to these functions of analysis and determination of fundamental frequencies and direction of travel. This allows a lower cost implementation of the present invention.

[0020] According to a variant, the determination of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal comprises a filtering of the first, respectively second, time segment of the audio signal by a band-pass filter defined by a high fundamental frequency and a low fundamental frequency of the emitted audio signal.

[0021] According to a variant, the method further comprises a step of identifying the audio signal received from among a set of audio signals corresponding to warning sirens used by emergency vehicles, each audio signal defining values of the high and low fundamental frequencies of the bandpass filter.

[0022] This variant is advantageous because it allows the method to automatically adapt to vehicles circulating in countries which would use audio signals comprising different fundamental frequencies, i.e. different warning sirens.

[0023] According to a variant, the determination of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal further comprises noise-reducing filtering of the first, respectively second, time segment of the received audio signal.

[0024] According to a variant, the determination of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal further comprises smoothing by filtering the first, respectively second, time segment of the received audio signal.

[0025] According to a variant, the first, respectively second fundamental frequency is determined by averaging a series of pitches detected from the first, respectively second, time segment of the received audio signal.

[0026] According to a second aspect, the present invention relates to a device for determining a direction of travel of an emergency vehicle, the device comprising a memory associated with a processor configured for implementing the steps of the method according to the first aspect of the present invention.

[0027] According to a third aspect, the present invention relates to a vehicle, for example of the automobile type, comprising a device according to the second aspect of the present invention.

[0028] According to a fourth aspect, the present invention relates to a computer program which comprises instructions adapted for executing the steps of the method according to the first aspect of the present invention, in particular when the computer program is executed by at least one processor.

[0029] Such a computer program may use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0030] According to a fifth aspect, the present invention relates to a support computer-readable recording medium having recorded thereon a computer program comprising instructions for carrying out the steps of the method according to the first aspect of the present invention.

[0031] On the one hand, the recording medium may be any entity or device capable of storing the program. For example, the medium may comprise a storage means, such as a ROM memory, a CD-ROM or a microelectronic circuit type ROM memory, or a magnetic recording means or a hard disk.

[0032] Furthermore, this recording medium may also be a transmissible medium such as an electrical or optical signal, such a signal being able to be conveyed via an electrical or optical cable, by conventional or hertzian radio or by self-directed laser beam or by other means. The computer program according to the present invention may in particular be downloaded from an Internet-type network.

[0033] Alternatively, the recording medium may be an integrated circuit in which the computer program is incorporated, the integrated circuit being adapted to perform or to be used in performing the method in question. Brief description of the figures

[0034] Other characteristics and advantages of the present invention will emerge from the description of the particular and non-limiting exemplary embodiments of the present invention below, with reference to the appended figures 1 to 4, in which:

[0035] [Fig-1] schematically illustrates an environment 1, according to an example of realization particular and non-limiting use of the present invention;

[0036] [Fig.2] illustrates an example of analysis of an audio signal corresponding to a siren warning for determining fundamental frequencies according to a particular and non-limiting exemplary embodiment of the present invention;

[0037] [Fig.3] schematically illustrates a device configured to determine a direction of movement of an emergency vehicle, according to a particular and non-limiting exemplary embodiment of the present invention;

[0038] [Fig.4] illustrates a flowchart of the different stages of a determination process mination of a direction of circulation of an emergency vehicle, according to a particular and non-limiting exemplary embodiment of the present invention.

[0039] Description of the examples of embodiment

[0040] A method and a device for determining a direction of travel of an emergency vehicle will now be described in the following with joint reference to Figures 1 to 4. The same elements are identified with the same reference signs throughout the description which follows.

[0041] The present invention determines the direction of travel of an emergency vehicle at using a single fixed microphone based on the Doppler effect.

[0042] According to a particular and non-limiting example of embodiment of the present invention, the determination of a direction of travel of an emergency vehicle emitting a periodic audio signal formed of at least one fundamental frequency, comprises the determination of two fundamental frequencies from two consecutive time segments of the audio signal received by a vehicle. If the speed of the vehicle has decreased between the two time segments and if the determined fundamental frequency has decreased between the two time segments, then the emergency vehicle and the vehicle travel in opposite directions, otherwise the emergency vehicle and the vehicle travel in the same direction; if the speed of the vehicle has increased and if the determined fundamental frequency has increased then the emergency vehicle and the vehicle travel in opposite directions otherwise the emergency vehicle and the vehicle travel in the same direction.

[0043] [Fig. 1] schematically illustrates a road environment 1, according to a particular and non-limiting exemplary embodiment of the present invention.

[0044] The road environment 1 comprises a vehicle 10 and an emergency vehicle 11 traveling on a traffic lane. The vehicle 10 travels at a speed vr and the emergency vehicle 11 travels behind the vehicle 10 at a speed L.

[0045] The emergency vehicle 11 emits a warning siren which is heard by the driver of the vehicle 10. When the emergency vehicle 11 is far from the vehicle 10 and not visible, the driver of the vehicle 10 cannot precisely determine the position of the emergency vehicle 11 or whether the latter is approaching from behind the vehicle 10, i.e. in the same direction of travel as the vehicle 10, or from the front, i.e. in a direction opposite to that of the vehicle 10. It is important that the driver of the vehicle 10 knows as soon as possible whether the emergency vehicle 11 is approaching from behind because in this case the driver of the vehicle 10 must pull over to give way to the emergency vehicle 11.

[0046] The audio signals corresponding to emergency (and rescue) vehicle warning sirens are generally bitonal and have a well-defined waveform according to the traffic code of each country. For example, in Italy, a bitonal warning siren emits a sound according to a high fundamental frequency fH of 622 Hz for 750 ms followed by a low fundamental frequency fL of 466 Hz for 750 ms for a waveform period of T = 1.5 s. The transmitted audio signals that are received by the vehicle 10 are noisy and have harmonics around the fundamental frequencies fH and fL.

[0047] The original sound wave produced by the warning siren of the moving emergency vehicle 11 is affected by the Doppler effect.

[0048] At a time instant t0, the vehicle 10 observes a sound wave comprising a fundamental frequency f':

[0049] [Math 1]

[0050] in which / is a fundamental frequency (fH or fL) of the sound wave emitted by the emergency vehicle 11 and [Math.l] v is the speed of propagation of sound waves in air (343 m / s).

[0051] The speed vr is positive if the vehicles 10 and 11 come from opposite directions and negative otherwise.

[0052] If the emergency vehicle 11 approaches the vehicle 10 then y > f. Thus, by receiving a sound wave at a given time instant, it is possible to determine the relative position of the emergency vehicle 11 with respect to the vehicle 10. On the other hand, it is not possible to instantly determine the direction of origin of the sound wave.

[0053] However, by making an assumption of the direction of travel of the emergency vehicle 11 and by confirming or not this assumption from consecutive temporal observations of the fundamental frequencies of the received sound waves, it is possible to determine the direction of travel of the emergency vehicle 11.

[0054] Let us assume that at tT = f0 + T, the emergency vehicle 11 is traveling in a direction opposite to that of the vehicle 10. The fundamental frequency f " of the received sound wave is then given by:

[0055] [Math 2]

[0056] Since the period of the sound wave T is short and the emergency vehicle 11 is approaching the vehicle 10, it can be considered that the speed L is constant unlike the speed [Math.2] v; of vehicle 10 which varies because the driver of vehicle 10 reacts to the sound of the warning siren received.

[0057] If the driver of vehicle 10 slows down, the following two conditions must be verified for the hypothesis of equation (2) to be verified:

[0058] [Math 3] f > f —false hypothesis O) f <f —hypothèse vraie

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068] En effet, si f ” > f', this means that [Math.3] which is impossible because [Math.3] vr>v; (keeping other terms constant) because the driver of vehicle 10 slowed down. So, if vehicle 10 slows down and f" > f' then the vehicle and emergency vehicle 11 are traveling in the same direction. Intuitively, if f" > f this indicates that at t y vehicle 11 is approaching vehicle 10 faster than at t0. Since vehicle 10 slows down, the only possibility is that vehicles 10 and 11 are traveling in the same direction. On the contrary, if f" < f' then inequality (3) is verified and the hypothesis is confirmed, that is to say that vehicles 11 and 10 travel in opposite directions. If the driver of vehicle 10 accelerates, the following two conditions must be verified so that the hypothesis of equation (2) is verified: [Math 4] —true hypothesis (4) ...............................................sx —false hypothesis Indeed, if f" > f, this means that [Math.4] . Inequality (4) is verified and the hypothesis is confirmed, that is, vehicles 11 and 10 travel in opposite directions. On the contrary, if f" < f then inequality (4) is not verified, that is to say that vehicles 11 and 10 travel in the same direction. The vehicle 10 includes an audio signal receiving system such as a microphone. This audio signal receiving system may be onboard the vehicle and typically used for a purpose other than determining an emergency vehicle direction of travel. For example, the audio signal receiving system is a microphone used in a hands-free telephone system. The vehicle 10 also includes a speed sensor which makes it possible to obtain a current speed of the vehicle 10 at a given time instant. The vehicle 10 further comprises means for informing the driver of the vehicle 10 whether or not an approaching emergency vehicle is traveling in the same direction as the vehicle 10.

[0069] For example, this means may be information that appears on an on-board screen of the vehicle 10, or an audio message emitted by loudspeakers of the vehicle 10 or a light that comes on on an on-board screen of the vehicle or even an audio or visual message emitted or displayed on a screen of a mobile telephone.

[0070] A process for determining a direction of travel of the emergency vehicle 11 is advantageously implemented by a device 2 on board the vehicle 10.

[0071] In a first operation, a first time segment of the periodic audio signal of period T emitted by the emergency vehicle 11 is received by the vehicle 10 at a first time instant t0.

[0072] In a second operation, a first fundamental frequency f' is determined from the first time segment of the received audio signal.

[0073] In a third operation, a first speed U of the vehicle 10 is obtained at the first time instant t0.

[0074] In a fourth operation, a second time segment of the transmitted audio signal is received at a second time instant tT=to+T after the first time instant t0.

[0075] In a fifth operation, a second fundamental frequency f" is determined from the second time segment of the received audio signal.

[0076] In a sixth operation, a second speed v'r of the vehicle 10 is obtained at the second time instant tT.

[0077] If the second speed v'r of the vehicle 10 is lower than the first speed vr of the vehicle 10 and if the second fundamental frequency f" is lower than the first fundamental frequency f' then the emergency vehicle 11 and the vehicle 10 travel in opposite directions, otherwise the emergency vehicle 11 and the vehicle 10 travel in the same direction.

[0078] If the second speed v'r of the vehicle 10 is greater than the first speed of the vehicle 10 and if the second fundamental frequency f " is greater than the first fundamental frequency f' then the emergency vehicle 11 and the vehicle 10 travel in opposite directions, otherwise the emergency vehicle 11 and the vehicle 10 travel in the same direction.

[0079] According to a variant, the determination of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal comprises a filtering of the first, respectively second, time segment of the audio signal by a bandpass filter defined by a high fundamental frequency and a low fundamental frequency of the transmitted audio signal.

[0080] The band-pass filter is applied to the received audio signal to reduce the signal spectrum to a frequency interval [ ^ gf + 1 with 5 a value that [ Lmv ' high j compensates for the Doppler effect for increases or decreases in fundamental frequency. Typically δ = 50 Hz

[0081] According to a variant, in a seventh operation, the audio signal is identified (characterized) among a set of audio signals corresponding to warning sirens used by emergency vehicles. Each audio signal defining values of the high and low fundamental frequencies of the bandpass filter.

[0082] According to a variant, the determination of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal further comprises noise-reducing filtering of the first, respectively second, time segment of the received audio signal.

[0083] According to an exemplary embodiment, pitches are detected from the first, respectively second time segment of the audio signal by a pitch detection method based on a short-time Fourier transform (or sliding window). This method is known to those skilled in the art (Julius O. Smith. Spectral Audio Signal Processing. W3K Publishing, Stanford University, accessed 3-11-20. online book, 2011 edition, pages 4).

[0084] According to a variant, the determination of the first, respectively second, frequency from the first, respectively second, time segment of the received audio signal further comprises smoothing by filtering the first, respectively second, time segment of the received audio signal.

[0085] According to an exemplary embodiment, the smoothing filter is a low-pass Butterworth filter of order 3.

[0086] According to a variant, the first (respectively second) fundamental frequency is obtained by averaging a series of pitches of the audio signal detected from the first, respectively second, time segment of the received audio signal.

[0087] [Fig.2] illustrates an example of analysis of an audio signal corresponding to a siren warning for determining fundamental frequencies according to a particular and non-limiting exemplary embodiment of the present invention.

[0088] [Fig.2] represents a time evolution diagram of frequencies associated with samples of the received audio signal. These samples are collected according to a sampling frequency of the received audio signal.

[0089] According to Figure 2, the received audio signal is a bitonal signal comprising two theoretical fundamental frequencies fH and fL. During a first time segment extending over a period T from a first time instant t0, samples of the received audio signal (represented by triangles) are collected to form a first time segment of the received audio signal. These samples are filtered and processed as explained previously according to different variants. A fundamental frequency f is then determined from the samples collected during the first time segment according to the variants explained previously. Here, the determined fundamental frequency corresponds to the theoretical fundamental frequency fH of the received audio signal. But the method can also be based on the determination of fundamental frequencies corresponding to the low frequency fL of the received audio signal. Similarly, a second fundamental frequency f' is determined during a second time segment of the received audio signal formed by samples collected during a second time segment extending from a time instant tT to a time instant tT+T.

[0090] It can be noted that when the increase in the determined fundamental frequencies (zone A) corresponds to the emergency vehicle 11 moving closer to the vehicle 10 and that a decrease in the determined fundamental frequencies (zone B) corresponds to the emergency vehicle moving away from the vehicle 10.

[0091] [Fig.3] schematically illustrates a device 2 configured to determine a direction of travel of an emergency vehicle, according to a particular and non-limiting exemplary embodiment of the present invention.

[0092] The device 2 is for example configured for the implementation of the operations described with regard to [Fig.l] and / or the steps of the method described with regard to [Fig.4]. Examples of such a device 2 include, but are not limited to, on-board electronic equipment such as an on-board computer of a vehicle, an electronic calculator such as an ECU (“Electronic Control Unit”), a smartphone, a tablet, a laptop. The elements of the device 2, individually or in combination, can be integrated into a single integrated circuit, into several integrated circuits, and / or into discrete components. The device 2 can be produced in the form of electronic circuits or software (or computer) modules or even a combination of electronic circuits and software modules.

[0093] The device 2 comprises one (or more) processor(s) 20 configured to execute instructions for carrying out the steps of the method and / or for executing the instructions of the software(s) embedded in the device 2. The processor 20 may include integrated memory, an input / output interface, and various circuits known to those skilled in the art. The device 2 further comprises at least one memory 21 corresponding for example to a volatile and / or non-volatile memory and / or comprises a memory storage device which may comprise memory volatile and / or non-volatile, such as EEPROM, ROM, PROM, RAM, DRAM, SRAM, flash, magnetic or optical disk.

[0094] The computer code of the embedded software(s) comprising the instructions to be loaded and executed by the processor is for example stored in the memory 21.

[0095] According to various particular and non-limiting embodiments, the device 2 is coupled in communication with other similar devices or systems and / or with communication devices, for example a TCU (from the English “Telematic Control Unit” or in French “Telematic Control Unit”), for example via a communication bus or through dedicated input / output ports.

[0096] According to a particular and non-limiting exemplary embodiment, the device 2 comprises a block 22 of interface elements for communicating with external devices, for example an audio signal receiver such as a microphone on board the vehicle or a microphone of a mobile device such as a mobile telephone. The interface elements of the block 22 comprise one or more of the following interfaces: - RF radio frequency interface, for example Wi-Fi® type (according to IEEE 802.11), for example in the 2.4 or 5 GHz frequency bands, or Bluetooth® type (according to IEEE 802.15.1), in the 2.4 GHz frequency band, or Sigfox type using UBN (Ultra Narrow Band) radio technology, or LoRa in the 868 MHz frequency band, LTE (LTE) “Long-Term Evolution” or in French “Long-Term Evolution”), LTE-Advanced (or in French LTE-advanced); - USB interface (from the English “Universal Serial Bus” or “Universal Serial Bus” in French); - HDMI interface (from the English “High Definition Multimedia Interface” or “High Definition Multimedia Interface” in French); - LIN interface (from the English “Local Interconnect Network”).

[0097] Data representative of audio signals are for example loaded to the device 2 via the interface of the block 22 using a Wi-Fi® network such as according to IEEE 802.11, an ITS G5 network based on IEEE 802.1 lp or a mobile network such as a 4G (or 5G) network based on the LTE (Long Term Evolution) standard defined by the 3GPP consortium, in particular an LTE-V2X network.

[0098] According to another particular and non-limiting exemplary embodiment, the device 2 comprises a communication interface 23 which makes it possible to establish communication with other devices (such as other computers) via a communication channel 24. The communication interface 23 corresponds for example to a transmitter configured to transmit and receive information and / or data for example representative of audio signals and / or fundamental frequencies and / or vehicle traffic direction via the communication channel 24. The communication interface 23 corresponds for example to a wired network of the CAN type (from the English “Controller Area Network” or in French “Network of controllers”), CAN FD (from the English “Controller Area Network Flexible Data-Rate” or in French “Flexible data rate controller network”), FlexRay (standardized by the ISO 17458 standard) or Ethernet (standardized by the ISO / IEC 802-3 standard).

[0099] According to a particular and non-limiting exemplary embodiment, the device 2 can provide output signals to one or more external devices, such as a display screen 25, touch-sensitive or not, one or more loudspeakers 26 and / or other peripherals 27 (projection system) via output interfaces 28, 29 and 30 respectively. These output signals can be representative of a direction of travel of the emergency vehicle 11 determined by the process of [Fig. 1] and / or by the method of [Fig. 4],

[0100] [Fig.4] illustrates a flowchart of the different stages of a determination process mination of a direction of travel of an emergency vehicle emitting a periodic audio signal formed of at least one fundamental frequency, according to a particular and non-limiting exemplary embodiment of the present invention. The method is for example implemented by a device on board the vehicle 10 or by the device 2 of [Fig.3].

[0101] In a first step 31, the first time segment of the transmitted audio signal is received at the first time instant t0.

[0102] In a second step 32, the first fundamental frequency f' is determined from the first time segment of the received audio signal.

[0103] In a third step 33, the first speed of the vehicle vr is obtained at the first time instant t0.

[0104] In a fourth step 34, the second time segment of the transmitted audio signal is received at the second time instant tT.

[0105] In a fifth step 35, the second fundamental frequency f" is determined from the second time segment of the received audio signal.

[0106] In a sixth step 36, the second speed of the vehicle v'r is obtained at the second time instant tT.

[0107] If the second speed v'r of the vehicle is lower than the first speed vr of the vehicle and if the second fundamental frequency f" is lower than the first fundamental frequency f' then the emergency vehicle and the vehicle travel in opposite directions (37), otherwise the emergency vehicle and the vehicle travel in the same direction (38).

[0108] If the second speed v'f of the vehicle is greater than the first speed vr of the vehicle and if the second fundamental frequency f" is greater than the first fundamental frequency f' then the emergency vehicle and the vehicle travel in opposite directions (37) otherwise the emergency vehicle and the vehicle travel in the same direction (38).

[0109] According to a variant, in a ninth step 39, the received audio signal is identified (characterized) among a set of audio signals corresponding to warning sirens used by emergency vehicles, each audio signal defining values of the high and low fundamental frequencies of the bandpass filter.

[0110] According to a variant, the variants and examples of the operations described in relation to [Fig.l] apply to the steps of the method of [Fig.4].

[0111] Of course, the present invention is not limited to the exemplary embodiments described above but extends to a method for determining a direction of travel of an emergency vehicle which would include secondary steps without thereby departing from the scope of the present invention. The same would apply to a device configured for implementing such a method.

[0112] The present invention also relates to a vehicle, for example an automobile or more generally an autonomous vehicle with a land motor, comprising the device 2 of [Fig.3].

Claims

Claims

1. Method for determining a direction of travel of an emergency vehicle emitting a periodic audio signal formed of at least one fundamental frequency, said method being implemented by at least one on-board processor of the vehicle, said method comprising the following steps: - receiving (31) a first time segment of the audio signal emitted at a first time instant; - determining (32) a first fundamental frequency from the first time segment of the received audio signal; - obtaining (33) a first speed of the vehicle at the first time instant; - receiving (34) a second time segment of the audio signal emitted at a second time instant subsequent to the first time instant; - determining (35) a second fundamental frequency from the second time segment of the received audio signal; - obtaining (36) a second speed of the vehicle at the second time instant;- if the second speed of the vehicle is lower than the first speed of the vehicle and if the second fundamental frequency is lower than the first fundamental frequency then the emergency vehicle and the vehicle travel in opposite directions (37), otherwise the emergency vehicle and the vehicle travel in the same direction (38); - if the second speed of the vehicle is higher than the first speed of the vehicle and if the second fundamental frequency is higher than the first fundamental frequency then the emergency vehicle and the vehicle travel in opposite directions (37) otherwise the emergency vehicle and the vehicle travel in the same direction (38).;

2. Method according to claim 1, wherein the determination (32,35) of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal comprises a filtering of the first, respectively second, time segment of the audio signal by a bandpass filter defined by a high fundamental frequency and a low fundamental frequency of the transmitted audio signal.

3. A method according to claim 2, which further comprises a step of identifying (39) the received audio signal from among a set of signals audio corresponding to warning sirens used by emergency vehicles, each audio signal defining values of the high and low fundamental frequencies of the bandpass filter.

4. Method according to claim 3, wherein the determination (32,35) of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal further comprises a noise-reducing filtering of the first, respectively second, time segment of the received audio signal.

5. Method according to claim 4, wherein the determination (32,35) of the first, respectively second, fundamental frequency from the first, respectively second, time segment of the received audio signal further comprises smoothing by filtering the first, respectively second, time segment of the received audio signal.

6. Method according to one of claims 1 to 5, in which the first, respectively second fundamental frequency is determined (32, 35) by averaging a series of pitches detected from the first, respectively second, time segment of the received audio signal.

7. Computer program comprising instructions for implementing the method according to any one of the preceding claims, when these instructions are executed by a processor.

8. A computer-readable recording medium on which is recorded a computer program comprising instructions for carrying out the steps of the method according to one of claims 1 to 6.

9. Device (2) for determining a direction of travel of an emergency vehicle, said device (2) comprising a memory (21) associated with at least one processor (20) configured for implementing the steps of the method according to any one of claims 1 to 6.

10. Vehicle (10) comprising the device (2) according to claim 9.

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