GB2508734B

GB2508734B - Method and device for determining the relative distance and the relative movement of a plurality of traffic participants

Info

Publication number: GB2508734B
Application number: GB1320856.6A
Authority: GB
Inventors: Karl Matthias
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-12-05
Filing date: 2013-11-26
Publication date: 2019-07-10
Anticipated expiration: 2033-11-26
Also published as: GB2508734A; FR2999007A1; DE102012222334A1; FR2999007B1; GB201320856D0; DE102012222334B4

Description

Title

Method and device for determining the relative distance and the relative movement of a plurality of traffic participants

Field of the invention

The present invention relates to a method for determining the relative distance and/or the relative movement of at least two traffic participants, in particular at least two vehicles, in which, on the basis of the initialisation emissions of acoustic signals generated by a first traffic participant of the two traffic participants, reaction emissions of acoustic signals of a second traffic participant receiving the acoustic signals of the initialisation emissions are triggered and are received and evaluated by the first traffic participant. The invention additionally relates to a corresponding device for determining the relative distance and/or the relative movement between at least two traffic participants, in particular between at least two vehicles. The invention also relates to a vehicle assistance system having a corresponding device.

Prior art

At present, acoustic sensing of the environment of vehicles is usually performed by means of, in particular, pulse-type measuring systems that operate in the ultrasonic range. In the case of such systems, typically, acoustic pulses are emitted at approximately 50 kHz every 10 ms to 300 ms via an electroacoustic transducer. The spatial distance of the object is deduced from the pulse propagation time in relation to the transmitting and the non-transmitting converters .

It has been proposed, in previous patent applications of the applicant, not to limit the choice of acoustic medium solely to ultrasound around 50 kHz. The decision, thirty years ago, in favour of the ultrasonic range was based, on the one hand, on the fact that, in this frequency range, there is a sufficiently marked decrease in the noise power in proportion to the reciprocal of the signal frequency and, on the other hand, the attenuation caused by the medium is still kept within manageable limits, and on the fact that the first affordable electronic components for this frequency range became available at that time.

Since then, the technology has developed further: cars are becoming quieter, the problems relating to electromagnetic compatibility (EMC) are becoming more manageable and, with the signal processing currently available in every MP3 player, more efficient filtering can be achieved within the range of affordability.

In particular, with the introduction of electric vehicles, it is now necessary for these vehicles to be rendered acoustically perceptible through the use of synthesized sound, in order to alert pedestrians or other traffic participants, at least for the purpose of warning. It has therefore already been proposed, in older patent applications of the applicant, to use the entire frequency spectrum of the ultrasonic range, including that of the human auditory range as a whole, for acoustic monitoring of a vehicle environment through evaluation of the sound emitted by the vehicle itself, in particular through evaluation of the synthesized sound emitted by the vehicle and/or of the function-related sound generated by the vehicle itself, for the purpose of locating signal emitters, or signal sources, and thereby improving traffic safety.

The document DE 30 24 791 C2 describes a device for monitoring the position of a working vessel, wherein it is described as prior art that, in a known solution, four microphones are attached, at a distance from each other, to the underside of a drilling vessel, while an acoustic transponder is disposed at a particular location close to the drill-hole at the bottom of the body of water. This acoustic transponder is operated by an acoustic transmitter on the underside of the vessel and, for its part, is thereby made to emit acoustic signals. The acoustic signals emanating from a single location on the bottom of the body of water are picked up with a greater or lesser phase displacement, according to the respective position of the vessel, by three microphones, which phase displacement is processed in a computer, thereby enabling the position of the vessel to be recorrected.

The documents DE 23 35 613 A1 and DE 23 35 613 B2 describe a method for measuring distances, changes in distance and/or changes in speed of objects that are moving relative to each other, in particular for vehicles of all kinds. In this case, the acoustic signal emitted by the transmitter of a first object is received by the receiver of a second object, altered in its frequency position, and then actively reflected directly, in order to be received by the receiver of the first object. The use of acoustic beams, in particular ultrasound, is mentioned as being particularly suited to application of the measurement method in the case of land vehicles and water craft. The distance between two vehicles is thus determined on the basis of evaluation of propagation time, and the relative speed is determined from the Doppler shift. Moreover, it is stated that information can be modulated on to the signals .

In summary, it is known from the prior art, for the purpose of determining the relative distance and/or the relative movement between at least two objects, for a first object of the two objects to generate initialisation emissions of acoustic signals, which are received by a second object of the two objects and recognized as such by means of an evaluation. It is additionally known from the prior art for reaction emissions of acoustic signals of the second object to be generated as a direct response to the received acoustic signals of the initialisation emissions. In this case, the acoustic signals of the reaction emissions of the second object are received by the first object and evaluated for the purpose of determining the relative distance and/or the relative movement between the two obj ects. A disadvantage in the realization of conventional transponder methods in the sonic or ultrasonic range is the low propagation speed of the sound, or ultrasound, as compared with transmission by means of electromagnetic waves. Thus, conventional acoustic transponders start to radiate reaction emissions even before the initialisation emissions have fully arrived. Apart from this time collision that occurs in the case of such a transponder method, time collisions additionally occur with echoes from passively reflecting objects. A disadvantage in this case is the large amount of resource required to effect evaluation of the received acoustic signals of the reaction emissions, owing to the received echo signals, arriving simultaneously or quasi-simultaneously, that originate from passive reflections of the acoustic signals of the initialisation emissions on ambient objects. In normal traffic, such as road traffic, a plurality of traffic participants use one and the same transmission medium. The resource requirement increases if a plurality of traffic participants are to generate reaction emissions in reaction to one and the same initialisation emission. It is additionally disadvantageous if each electroacoustic transducer present on each traffic participant reacts in the same manner to the arrival of each initialisation emission. A further disadvantage of conventional transponder methods is that they are only suitable for few forms of initialisation signal. Frequently, inter-operability between different types of acoustic transponder method is not possible, and the use of new technology, such as more elaborate modulation methods, is not supported by already existing transponders. However, various kinds of traffic participant, frequently differing greatly in their equipment, come together, for example on public roads.

Disclosure of the invention

Provided according to the invention is a method for determining the relative distance and/or the relative movement between at least two traffic participants, wherein, upon the receipt of acoustic signals originating from initialisation emissions in the form of acoustic signals that have been emitted by a first traffic participant, reaction emissions in the form of acoustic signals, which are received and evaluated by the first traffic participant, are triggered by a second traffic participant. In this case, the reaction emissions of the second traffic participant are effected after the expiry of at least one delay that is known to the traffic participants and that is set to be of such a duration that acoustic signals received by the first traffic participant that originate from passive reflections of the initialisation emissions of the first traffic participant on ambient objects do not affect an evaluation, performed by the first traffic participant, of the reaction emissions of the second traffic participant that are received by means of at least one receiver. The signal strength and/or the signal progression of the acoustic signals of the reaction emissions of the second traffic participant have an unambiguous relationship to the signal strength and/or to the signal progression of the acoustic signals of the initialisation emissions of the first traffic participant, which have a frequency progression that varies with time. The acoustic signals of the reaction emissions also each comprise a predetermined signal segment of the acoustic signals of the initialisation emissions, the predetermined signal segments being emitted in the inverse time sequence, or in an unchanged time sequence.

Additionally provided according to the invention is a device for determining the relative distance and/or the relative movement between at least two traffic participants, which is designed to receive, by means of at least one receiver, the initialisation emissions of acoustic signals generated by at least one traffic participant of the two traffic participants, and to recognize these initialisation emissions as such by means of an evaluation, and to generate reaction emissions of acoustic signals as a response to the received initialisation emissions of the at least one traffic participant. Moreover, the device is designed to generate the reaction emissions of acoustic signals, having at least one predetermined signal duration, after the expiry of at least one predetermined delay that is known to the traffic participants. The device is also designed to generate reaction emissions of acoustic signals that have a signal strength and/or a signal progression that have an unambiguous relationship to the signal strength and/or to the signal progression of the received acoustic signals of the initialisation emissions generated with a time-dependent frequency progression. The acoustic signals of the reaction emissions also each comprise a predetermined signal segment of the acoustic signals of the initialisation emissions, the predetermined signal segments being emitted in the inverse time sequence, or in an unchanged time sequence.

The dependent claims disclose preferred developments of the invention.

In the case of the method according to the invention, in particular, on the basis of the acoustic signals of the reaction emissions of the second traffic participant that are received by the first traffic participant, reaction emissions of acoustic signals of the first traffic participant are triggered after the expiry of at least one delay that is known to the traffic participants. In this case, this delay is fixed to be of such a duration that the acoustic signals received by the second traffic participant that originate from passive reflections of the acoustic signals of the reaction emissions of the first traffic participant on ambient objects do not affect an evaluation of the acoustic signals of the reaction emissions of the first traffic participant that are received by the second traffic participant by means of at least one receiver, which evaluation is performed by the second traffic participant for the purpose of determining the relative distance and/or the relative movement between the two traffic participants.

In other words, such reaction emissions that are generated upon the receipt of an initialisation emission and, optionally, such further reaction emissions that are generated as a reaction to the receipt of reaction emissions, of at least one traffic participant that receives and recognizes the acoustic signals of actively generated emissions (initialisation emissions and/or reaction emissions) of at least one other traffic participant and, optionally, of a sound source present in the acoustic environment, are in each case emitted after the expiry of a fixedly agreed delay that is known to the corresponding traffic participants.

Owing to the use of the fixedly agreed delay that is known at least to the traffic participants involved, there can only be collisions of reaction emissions, or of further reaction emissions, of such traffic participants that are at the same distance from the traffic participant generating the actively generated emissions of acoustic signals .

If there are a plurality of traffic participants in the traffic, the reaction emissions, or the further reaction emissions, of acoustic signals can be generated as a response to the actively generated emissions of the traffic participant, or of the sound source, generating the latter, after the expiry of a fixedly agreed delay that is known at least to the traffic participants involved and that, in particular, is different in each case.

Owing to the use of a fixedly agreed delay that is known at least to the traffic participants involved and that is different in each case, collisions of reaction emissions of such traffic participants that are at the same distance from the traffic participant generating the actively generated emissions of acoustic signals can also be easily prevented. In other words, the pseudo-random use of a delay, differing in each case, from a set of distinctly differing delays that are known to all traffic participants, has the effect of statistically reducing the collision probability of the reaction emissions, even of the traffic participants located at the same distance in respect of propagation time.

The use of a fixedly agreed delay that is known at least to the traffic participants involved enables the traffic participant that has initiated the actively generated emissions of acoustic signals to deduce the distance between the two traffic participants, in the moment of signal exchange, from the propagation time between the instant of initiation of its actively generated emissions and the instant of receipt of the acoustic signals of the reaction emissions of the other traffic participant that are generated as a response to the received acoustic signals of the actively generated emissions.

According to the invention, fixedly agreed delays are used that are of such duration that all echoes, even from potentially far distant, passively reflecting objects from the environment, are already closer to the receiving traffic participant. As a result, collisions of the acoustic signals of the corresponding reaction emissions with echoes from passively reflecting ambient objects are reduced to a minimum in a simple manner. Owing to the fact that during an evaluation, according to the invention, of the received acoustic signals of the reaction emissions, no further evaluation of echoes from passively reflecting ambient objects, received simultaneously or quasi-simultaneously, need be effected, in the case of the evaluation, according to the invention, of the acoustic signals of the reaction emissions the resource requirement for realization of a corresponding evaluation unit is reduced considerably.

Moreover, the use of the delays according to the invention reduces the loud/quiet problem (loud reaction emissions as compared with quiet echoes of the passive reflections). In this case, the corresponding evaluation units of the traffic participants that receive the acoustic signals of the initialisation emissions or reaction emissions of other traffic participants can be set first to receive quiet echoes that originate from passive reflections of the acoustic signals of these initialisation emissions or reaction emissions. Then, if no more echoes arrive, i.e. after the expiry of the delays according to the invention, the same evaluation units can additionally be set to receive loud acoustic signals of the reaction emissions generated as a reaction to the received acoustic signals of the initialisation emissions, or to receive loud acoustic signals of the further reaction emissions generated as a reaction to the received acoustic signals of the reaction emissions. This then increases the probability of detection, both of quiet echoes and of loud reaction emissions, such that the aforementioned loud/quiet problem can be reduced considerably.

Provided according to the invention, therefore, is a method for determining, by means of acoustic signals, the position and/or the movement of acoustically actively emitting traffic participants. The mobility aids may be realized, for example, as wheelchairs, Segways, bicycles, electric cars, other vehicles such as, for example, cars, buses and lorries. In this case, the operators of the mobility aid and/or other traffic participants are provided with information, or warned, concerning the traffic situation, in particular by means of acoustic and/or optical signals. Moreover, in the case of the method according to the invention, the intended spatial movement such as, for example, the speed progression in respect of a coordinate system, can be influenced automatically, at least in a supporting manner, by braking, accelerating and steering.

In addition, devices that reduce the consequences of inappropriate movements in traffic, in particular the consequences of accidents, such as, for example, seat-belt tensioners, window lifters, airbags and/or adjustment devices for engine hoods, can be influenced in their manner of operation, or activated. In particular, at least one acoustically active traffic participant recognizes at least one characteristic feature of the acoustic signals of the initialisation emissions, generated by communication means and/or as a result of function, of at least one other acoustically active traffic participant and/or of at least one other sound source present in the environment of the acoustically active traffic participant and thereupon, after a delay, emits, for a limited period of time, an acoustic reaction emission that preferably has an unambiguous relationship to the initialisation emission.

At least one characteristic feature such as, for example, the signal strength and/or the time progression of the signal strength (for example, in the form of a pulse pattern) and/or the time progression of the signal frequency, or of the signal frequency mix, is used in this case. Optionally, the traffic participant that has emitted the initialisation emission reacts in the same manner to the receipt of at least one reaction emission, by emitting a further reaction emission. Both the acoustically actively emitting traffic participants and such traffic participants that only receive and evaluate the acoustic signals occurring in the environment can use both the emitted initialisation emissions, the emitted reaction emissions and, optionally, also the emitted further reaction emissions, generated as a reaction to the receipt of reaction emissions, and the then respectively occurring echoes from passively reflecting objects, for the purpose of determining the position and/or the movement of acoustically actively transmitting traffic participants and/or of passively reflecting objects from the environment.

Preferably, in the case of at least one evaluation of the acoustic signals of the initialisation emissions of an initialising traffic participant and/or of the reaction emissions of at least one of the two traffic participants, which evaluation is performed for the purpose of determining the relative distance and/or the relative movement between at least two traffic participants, at least one characteristic feature of the acoustic signals of these initialisation emissions and/or of these reaction emissions is used, such as, preferably, the signal strength and/or the time progression of the signal strength (for example, in the form of a pulse pattern) and/or the signal frequency and/or the time progression of the signal frequency or of the signal frequency mix of the corresponding acoustic signals.

In the case of the method according to the invention, the traffic participant generating the initialisation emissions additionally knows the delay observed between the instant of fulfilment of the at least one characteristic feature of the acoustic signals of its initialisation emissions and the start of the reaction emissions of the traffic participants receiving the acoustic signals of the initialisation emissions. The initialising traffic participant can therefore deduce the distance between the two traffic participants from the total propagation time of the acoustic signals of the initialisation emissions and of the corresponding reaction emissions.

In order to reduce the probability of collision between the reaction emissions of, in particular, a plurality of traffic participants reacting to the same emissions of a traffic participant, some differing delays, from a set of agreed delays, are preferably used for these reaction emissions .

In order to reduce the collision probability of the acoustic signals of the reaction emissions of a plurality of traffic participants, in the case of a particularly advantageous embodiment of the method according to the invention the signal duration of the acoustic signals of the reaction emissions of at least one traffic participant is less than a predetermined fraction of the signal duration of the acoustic signals of the initialisation emissions of the initialising traffic participant (first traffic participant). In particular, at least one signal duration and/or at least one frequency or at least one frequency progression of the acoustic signals of the reaction emissions of at least one traffic participant is/are known to at least the traffic participants receiving the acoustic signals of these reaction emissions.

In other words, in particular even in the case of continuous fulfilment of at least one characteristic feature of the acoustic signals of the initialisation emissions of a traffic participant, only time-limited reaction emissions of acoustic signals are generated by the receiving traffic participants. In particular, the transmission duration proportion of such reaction emissions can be less than 1%. If, for example, the characteristic feature of the acoustic signals of an initialisation emission that is to be fulfilled is the signal strength, a continuous sound source generating the initialisation emission can effect a reaction emission that includes an occasional short-time reproduction (replay) of the continuous sound source.

In order to achieve a further reduction of the probability of collision between the reaction emissions of a plurality of traffic participants reacting, in particular, to the same emissions of a traffic participant, some differing reaction emission durations, from a set of agreed reaction emission durations (replay durations) are preferably used for these reaction emissions.

In the case of a further preferred embodiment of the method according to the invention, the acoustic signals of the reaction emissions of at least one traffic participant contain modulated-on information relating to these reaction emissions, in particular information comprising the delay used for these reaction emissions and/or the signal duration and/or the signal frequency or the signal frequency progression of the corresponding acoustic signals .

In the method according to the invention, the acoustic signals of the reaction emissions of at least one traffic participant have an unambiguous relationship to the initialisation emissions of the initialising traffic participant. The signal strength and/or the signal progression of the acoustic signals of the reaction emissions of at least one traffic participant have an unambiguous relationship to the signal strength and/or to the signal progression of the acoustic signals of the initialisation emissions of the initialising traffic participant, which, in particular, have a frequency progression that varies with time.

The acoustic signals of the reaction emissions in this case each comprise a predetermined signal segment of the acoustic signals of the initialisation emissions, the predetermined signal segments being emitted in the inverse time sequence (in colloquial terms, "replayed backwards"), or in an unchanged time sequence, at the same reproduction speed, and/or at a different playback speed (and therefore at a signal frequency different from that of the acoustic signals of the initialisation emissions of the initialising traffic participant). The altered playback speed is realized by communication means by, in particular, the use of an altered sample rate, as compared with the recording. The use of a different playback speed for the acoustic signals of the reaction emissions has the advantage that the acoustic signals of the reaction emissions can be separated from each other from the acoustic signals of the initialisation emissions in a technically simple manner, by filtering. In particular, a signal form, determined by coding, that is realized, for example, by means of an assignment table or an algebra, is used for the signal form of the acoustic signals of the reaction emissions.

To enable the acoustic signals of the reaction emissions of a plurality of traffic participants, in particular reacting to the same emissions of a traffic participant, to be easily separated, some differing playback speeds, from a set of agreed playback speeds, are used for the playback speeds of the acoustic signals of these reaction emissions.

In order to achieve a further reduction of the probability of collision between the reaction emissions of a plurality of traffic participants, in particular reacting to the same emissions of a traffic participant, preferably the delay, the transmission duration proportion, the reaction emission duration, the strength of the signal, the playback sequence and/or the playback speed is varied, preferably, in dependence on the degree of utilization of the acoustic medium by other traffic participants and/or by other sound sources and/or in dependence on the emitting traffic participant's own speed and/or on the relative position and/or on the relative movement of other objects and/or traffic participants.

In the case of the method according to the invention, at least one receiving traffic participant picks up the acoustic signals of the active emissions of at least one other traffic participant, preferably by means of at least two receiving systems, and evaluates the differences of the received acoustic signals of the active emissions in respect of a relative position and/or a relative movement, in particular on the basis of the differences in propagation time, the Doppler shift, and/or the signal strength. In addition, this traffic participant can preferably also concomitantly evaluate the echoes reaching the latter, i.e. including the acoustic signals that have occurred after acoustic emissions as a result of passive reflection on reflecting objects. In this case, from the signal variations in the course of the transmission path, either at least the spatial relationship between an emitting and a receiving traffic participant and/or the passively sound-reflecting objects is determined, and/or a proposition is made concerning the relative movement between the traffic participants and/or the passively sound-reflecting objects, and/or the traffic conditions between the traffic participants are deduced, in particular the position and/or the shape of the other traffic participants, or of stationary users such as trees, that are present between said traffic participants, and/or the condition of a roadway, etc.

In particular, each traffic participant can both effect initialisation emissions of acoustic signals and react, with reaction emissions of acoustic signals, to the received acoustic signals of active emissions of other traffic participants.

Also provided according to the invention is a vehicle assistance system having a device, according to the invention, for determining the relative distance and/or the relative movement between at least two traffic participants, in particular between at least two vehicles.

Brief description of the drawings

Exemplary embodiments of the invention are described in detail in the following with reference to the accompanying drawings . In the drawings :

Figure 1 shows a schematic representation of a traffic situation in which a first, initialising traffic participant generates initialisation emissions of acoustic signals, which, in turn, triggers reaction emissions of acoustic signals in the case of a second traffic participant, which receives the acoustic signals of the initialisation emissions,

Figure 2 shows a schematic representation of the position of the possible Doppler band of the acoustic signals of a reaction emission of a reacting traffic participant in comparison with the position of the Doppler band of the original acoustic signals of the initialisation emission of the initialising traffic participant, for a playback speed that is 1.5 times the recording speed.

Embodiments of the invention

Figure 1 exemplarily illustrates the method according to the invention (auto-replay protocol) for a traffic situation in which only two traffic participants T1 and T2, of many possible acoustically active traffic participants, are represented. The first traffic participant T1 comprises a signal generator 10 for generating acoustic signals 11, a transmission means 20 for emitting acoustic signals, a receiving means 30 for receiving acoustic signals 31, and at least one evaluation means 40 for evaluating the received acoustic signals 31.

The second traffic participant T2 comprises the device 100 according to the invention, having at least one receiving means 50 for receiving acoustic signals 51, a transmission means 60 for emitting acoustic signals, and at least one control means 70 for detecting the incoming acoustic signals 51 on the basis of features that characterize the acoustic signals 51 and for initiating the emission of acoustic signals 71, as a result of the received signals 51, after a delay TD. The control means 70 is realized, in particular, in such a manner that the acoustic signals 71 generated by the second traffic participant T2, which have been generated and emitted as a reaction of the second traffic participant T2 to the received acoustic signals 51 generated by the first traffic participant T1 or by an acoustic signal source present in the environment, are clearly distinguished, by the first traffic participant Tl, from the ordinary echoes on passively reflecting objects, and consequently recognized as reaction emissions 71 of the second traffic participant T2 that have been effected in reaction to the active emissions of acoustic signals 11 of the first traffic participant Tl.

In addition, the traffic participant Tl that has generated the original initialisation emission 11 may optionally comprise a control means (not represented) that, in dependence on the signals 31 received by means of the receiving means 30, generates, according to the invention, further reaction emissions (not represented), which are likewise received and evaluated by the traffic participants present in the environment such as, for example, the traffic participant T2. The generated further reaction emissions may also preferably be combined, by means of sensor data fusion, with further received acoustic signals and/or with further signals, exchanged via further media, that characterize the presence and the movement behaviour of further traffic participants and/or of passively reflecting objects.

Further, in addition to the first traffic participant Tl, the second traffic participant T2 may also have an evaluation means (not represented) for evaluating the acoustic signals 51 received by the receiving means 50.

The sound medium 80, via which the acoustically communicating traffic participants Tl, T2 are connected to each other, is represented by hatching.

In Figure 1, TP1 denotes the pulse duration of the acoustic signals 11 emitted by the first traffic participant Tl by means of the transmission means 20. T12 denotes the time required for the transmission of the acoustic signal 11 of the first traffic participant Tl until the start of the recognition of the second traffic participant T2 by the control means 70. Further, TP1 denotes the pulse duration of the acoustic signals 51 emitted by the first traffic participant Tl or an equivalent signal source (not represented), by means of the transmission means 20, and received by means of the receiving means 50 of the second traffic participant T2. Furthermore, TP2 denotes the pulse duration of the acoustic signals 71 generated by the control means 70 of the second traffic participant T2 as a reaction to the received acoustic signals 51 of the emissions of the first traffic participant Tl. TD denotes the delay that elapses between the start of the recognition of the acoustic signals 51, emitted by the first traffic participant Tl by means of the transmission means 20 and received by the second traffic participant T2 by means of the receiving means 50, and the triggering of the reaction emissions of the acoustic signals 71 of the second traffic participant T2. Further, the reference T21 denotes the time that elapses between the start of the emission of the acoustic signals 71, generated by the second traffic participant T2, and the start of receipt by means of the receiving means 30 of the first traffic participant Tl.

The pulse duration of the acoustic signals 31 emitted by the second traffic participant T2 and received by means of the receiving means 30 of the first traffic participant Tl is denoted by TP21.

In the case of a preferred attribute, the control means 70 uses the received signals 51 to control the emission of the reaction emissions 71 on the basis of features of the received signals 51 of the initialisation emissions, such as, for example, the signal strength, the time characteristic of the signal strength (for example, in the form of a pulse pattern) and/or the time progression of the signal frequency, or the signal frequency mix. In the case of a preferred, further developed attribute, the optionally additionally provided control means (not represented) may be realized to generate further reaction emissions (not represented) of the traffic participant Tl , which had originally generated the initialisation emissions 11, as a reaction to the receipt of the acoustic signals 31 of the reaction emissions 71 evaluated on the basis of characteristic features. Owing to the equivalence to the previous preferred attribute in respect of the control means 70, the following does not give any further, separate detailed description of the said further developed attribute in respect of the additional control means (not represented) .

In an example not forming part of the invention, the initialisation signals 11 may optionally originate, not from the first traffic participant Tl, but from another sound source present in the acoustic environment. The initialisation signals 11 may also comprise function-related sound such as, for example, engine noise or the squealing of brakes, or other acoustic signals such as, for example, the beeping of traffic lights, tread or travel sounds, sounds from ventilators on structures, construction noise .

In the case of a preferred attribute, the control means 70 and/or the optionally additionally provided control means are preferably designed to limit the duration TP1 or TP2 of the emitted acoustic signals 11, 71 and/or the frequency at which the acoustic signals 11, 71 are emitted, for example even if the characteristic features of received acoustic signals 31, 51, are fulfilled for a longer period or even continuously. It is advantageous in this case that the sound medium 80 is used only proportionately, and there is therefore a reduced probability of collision with acoustic signals that originate from emissions of further actively emitting traffic participants, and/or with echoes that occur as a result of reflections of acoustic signals on passively reflecting objects. The transmission-duration to transmission-pause ratio of 1% has proved satisfactory hitherto. If multiple traffic participants ΤΙ, T2 use one and the same sound medium 80, then the multiple acoustic signals 31, 51 exchanged between the traffic participants ΤΙ, T2, and the associated echoes, contain so much, mostly redundant, information that reliable monitoring of the environment is possible, even in the case of a transmission-duration to transmission-pause duration, per electroacoustic transducer, of significantly under 1%, down to under 0.1%. Even in the case of scenarios that change only slowly, as are usual, for example, in the case of driving slowly into a parking space, a low transmission rate is generally sufficient. However, in the case of high travel speeds and, in particular, if there are only few acoustically active traffic participants ΤΙ, T2 that are acoustically irradiating the medium 80, a higher rate of acoustic emissions, in particular of such electroacoustic transducers (not represented separately) whose orientation is predominantly along the prospective travel route, is also appropriate. This applies, in particular, if division of the sound medium 80, for example by frequency multiplexing, code multiplexing and/or signal-strength multiplexing, is possible. In these circumstances, an emission rate of more than 10% per electroacoustic transducer may also be appropriate.

In the case of a greatly preferred attribute, the delay TD between the start of the arrival of an initialisation signal 51 and the start of the emission of a reaction signal 71 is non-dependent on the signal strength and nondependent on a signal variation resulting from a Doppler shift. Further, this delay TD is known to all traffic participants ΤΙ, T2 that use the acoustic emissions, according to this method according to the invention, or auto-replay protocol, to determine the position and/or movement of other traffic participants ΤΙ, T2. In this way, each traffic participant ΤΙ, T2 that picks up the acoustic signals exchanged in the sound medium 80 can deduce, from the signal propagation times, in particular between an initialisation emission 11 and a reaction emission 71, if there are only two acoustically active traffic participants ΤΙ, T2 present in the sound medium 80, or also from the signal propagation times between reaction emissions 71, if there are more than two acoustically active traffic participants ΤΙ, T2 present in the sound medium 80, the spatial relationships between the acoustically actively involved traffic participants ΤΙ, T2 and/or between the passively reflecting objects (not represented) that are present in the sound medium 80.

In the case of a further preferred attribute, the signal strength of the initialisation emission, at least on the main direction of acoustic radiation of an electroacoustic transducer, has a fixed value or, alternatively, has a plurality of signal strength values that are clearly distinguishable from each other and known to all traffic participants ΤΙ, T2.

Here, in respect of the electroacoustic transducer, the spatial distribution of the signal strength is designated as the directional characteristic. In a further preferred attribute, the directional characteristic of a transmitting traffic participant ΤΙ, T2 is known to at least one receiving traffic participant ΤΙ, T2. This is achieved, for example, in that all electroacoustic transducers (not represented separately) use the same directional characteristic or, alternatively, in that the information concerning the directional characteristic used by the transmitting electroacoustic transducer (not represented separately) and/or concerning the emitted signal strength is communicated in the exchanged communications, in particular in the exchanged acoustic communications.

In the case of a further preferred attribute, the ratio of the signal strength of the received signals 51 of the initialisation emissions and of the received acoustic signals 31 of the associated reaction emission 71 and/or of a further reaction emission (not represented) generated as a reaction to a received reaction emission 71 varies according to rules that are known to at least some traffic participants ΤΙ, T2. Further, this ratio preferably varies independently of the signal variation resulting from a Doppler shift. Furthermore, information concerning the strength of the received signal 51 of the initialisation emissions is preferably contained in the reaction emissions 71. In the case of a preferred attribute, the ratio between the signal strengths of the initialisation emission 11 and the respectively associated reaction emission 71, or the further reaction emissions (not represented), generated as a reaction to received reaction emissions 71, is fixed. In the case of this realization variant, the collision probability of the reaction emissions 71 decreases with the diminution of the signal strength of the received acoustic signals 51 of the initialisation emission, and the effect of the transmission attenuation between the two traffic participants ΤΙ, T2 is already included as a quadratic value, as information, in the received signal of the first traffic participant Tl, which emitted the initialisation emission 11.

In the case of an alternative realization variant, the reaction emission 71 is always emitted with the greatest possible signal strength. The collision probability of the reaction emissions 71 is not affected by the signal strength of the received acoustic signals 51 of the initialisation emission, the transmission range is greater, in comparison with the aforementioned realization variant, because the effect of the transmission attenuation between the two traffic participants Tl, T2 is included merely as a simple, and not a quadratic, value.

In the case of known transmission characteristics of the transmission medium 80, in one of the aforementioned realization variants, geometric relationships between the traffic participants can be deduced from the signal strength, because the electroacoustic transducers used in the sensors are usually characterized by a directional characteristic. Thus, under these conditions, the total attenuation of the transmitting and of the receiving electroacoustic transducer can already be determined solely from the received-signal strength of an emitted signal 11, 71 that is picked up by a traffic participant Tl, T2 with only with one receiving electroacoustic transducer. If the receiver 30, 50 comprises at least two receiving electroacoustic transducers (not represented separately), and if the two electroacoustic transducers are distant from each other in respect of propagation time, the spatial orientation of the transmitting electroacoustic transducer of the transmitting traffic participant ΤΙ, T2 in relation to the receiving electroacoustic transducer of the traffic participant T2, Tl, of which the directional characteristic is known, can be determined from the differing strengths of the received signals in combination with the differing propagation times. If the position of the transmitting electroacoustic transducer on the transmitting traffic participant Tl, T2 is known, the spatial relationship, including the orientation of the electroacoustic transducers in relation to each other, and consequently of the traffic participants Tl, T2 in relation to each other, can thus be determined solely by means of a communication.

Insofar as the scenario does not change, or changes only at a negligibly slow rate, subsequently exchanged acoustic information includes the spatial relationships of the traffic participants Tl, T2 present in the sound medium 80, equivalently as redundant information, otherwise as new information, concerning the changing spatial conditions.

In the case of a further preferred attribute, the signals 31 of an initialisation emission 11 that are received as a result of the transmission in the sound medium 80 and/or the signals 51 of a reaction emission 71 that are received as the result of the transmission in the sound medium 80 are evaluated on the basis of characteristic features, such as the signal strength.

If, for example, the signal strength of the acoustic signals 51 of the initialisation emission of the traffic participant T1 that are received by the traffic participant T2, or of a sound source present in the acoustic environment, exceeds a predetermined threshold that is set, for example, in dependence on the signal strength of the noise, then, in a particularly preferred attribute, the traffic participant T2 picks up this acoustic signal 51 as a time-discrete signal, by sampling. After a fixedly agreed duration TD, which may be of differing lengths TD1, TD2, the second traffic participant T2 emits at least one fixedly agreed time segment, for example the start of at least one of the acoustic initialisation signal 51 previously received and picked up by the traffic participant T2. In particular, the signal segment 71 to be emitted is amplified, preferably in a time-reversed sequence, i.e. the signal segment that is received last is transmitted first. This is preferably effected at a different playback speed, i.e. the signal segment 71 to be emitted is transmitted on a different frequency. As a result, this signal segment, in turn, can be separated from the acoustic signals 11 of the emissions of the first traffic participant Tl in an inelaborate manner, by means of filtering.

The reaction emissions 71 from the traffic participant T2 and/or from at least one further traffic participant (not represented) have an unambiguous relationship to the initialisation emissions from the traffic participant Tl. For example, in this case a signal segment of the emissions from the traffic participant Tl can be reproduced in a time-inverse sequence (colloquially, "replayed backwards") or in a changed time sequence, and optionally at the same reproduction speed, or at a different playback speed, and consequently in a different frequency position than the frequency position emitted by the traffic participant Tl, in the reaction emissions 71. Storage of signal segments can be realized, preferably, by sampling. Moreover, reproduction can then be realized in a changed frequency position, preferably by means of an altered playback speed of the sampling values. Alternatively, the signal form used in the reaction emissions 71 is determined by a coding, which can be realized, for example, by means of an assignment table or an algebra.

According to the invention, the frequency position and the pulse duration of the reaction emissions 71 of the traffic participants reacting to at least one received initialisation signal (initialisation communication) 51, such as, for example, the traffic participant T2, can be varied by varying the sampling frequency in transmission relative to the sampling frequency in receiving. For example, as a result of emitting the acoustic signals 71 of the reaction emissions of the second traffic participant T2 at twice the speed, the sound medium 80 takes only half as long as when the same signals 71 are emitted at the playback speed at which they were recorded. If, in addition to the traffic participants Tl, T2, there are also present in the medium 80, in particular, further traffic participants (not represented) that, according to the invention, each initialise the emission of reaction emissions 71 or further reaction emissions (not represented) on the basis of an evaluation of the characteristic features of the received signals 51, 31, the collision probability of the reaction emissions in the medium 80 is thus reduced, owing to the halving of the respective utilization of the medium 80. Owing to the frequency-dependent spatial attenuation, the use of a doubled signal frequency results in a lesser range of this reaction signal 71 or of a further reaction signal (not represented), and consequently also in a reduction in the spatial collision probability of reaction emissions. In addition, because of the doubling of the signal frequency of the acoustic signals 71 of the reaction emissions, relative to the acoustic signals 11 of the initialisation emissions, these signals are more easily separated from each other, by frequency filters. The same applies, correspondingly, to reaction emissions (not represented) from the traffic participant T1 resulting from initialisation emissions (not represented) from the traffic participant T2.

Owing to the fixedly agreed delay TD, collisions of reaction emissions can occur only in the case of such traffic participants that are at the same distance from the traffic participant T1 initiating the acoustic exchange.

If the traffic participants that are at the same distance are moving at differing relative speeds, the collision effect is reduced, owing to the Doppler effect.

Owing to the fixedly agreed delay TD, the traffic participant T1 that has initiated the initialisation emission can deduce the distance between the two traffic participants ΤΙ, T2, at the moment of the signal exchange, from the propagation time between the instant of generation of the initialisation emissions and the instant of receipt of the associated reaction emission.

Owing to the evaluation of acoustic signals on the basis of the simple characteristic feature "signal strength", the Doppler information, contained in the signal, concerning the relative movement of the traffic participants (e.g. vehicles) ΤΙ, T2 in relation to each other is retained.

Owing to the use of the signal strength as a simple characteristic feature in the evaluation of received signals 51, 31, inter-operability is easily achieved. The method is easily implemented. In order to realize the method according to the invention, the reacting traffic participants ΤΙ, T2 and/or the reacting further traffic participants (not represented) do not require any knowledge of the internal structure of the emitted initialisation emission 11, in particular concerning the time progression of the signal frequencies or concerning the time progression of the signal amplitude. The instant from which an incoming signal 51, 31 is recorded is defined solely by an easily realized threshold switch, after the signal strength has once exceeded a threshold value. The storage duration and the delay TD can be determined by means of easily realized time measuring means. After expiry of the fixedly agreed delay TD, the stored signal is again emitted.

It is possible to achieve inter-operability of differing methods that are realized, for example, by differing manufactures. For example, the method according to the invention functions independently of the type of modulation of the initialisation signals 11. For example, one system may use inexpensive amplitude modulation, or even amplitude keying, while other systems use frequency shift keying, or even m-ary frequency modulation or frequency-modulated signals having a continuous frequency progression or noiselike signals or phase shift keying, such as, for example, quadrature amplitude modulation. A traffic participant such as, for example, the traffic participant T2, that has generated a reaction emission 71 (replay) in reaction to any initialisation emission modulated in such a manner does not need any knowledge of the respectively used type of modulation. Consequently, even upward compatibility between differing systems is possible. For example, a system that itself uses only amplitude keying as a type of modulation of an initialisation emission 11 can also generate a reaction emission (replay) in reaction to the receipt of signals modulated in a noise-signal like manner.

In a preferred attribute, the signal frequency alters continuously with time, at least in a time segment of the initialisation emission, i.e. the initialisation emission is chirp-modulated during the said time segment.

Owing to the use of the signal strength as a simple characteristic feature in the evaluation of received signals 31, 51, in the case of the method described here a reaction emission 71 can preferably also be generated in reaction to the arrival of such acoustic signals that were not explicitly generated as measurement signals for environment monitoring and that include, iter alia, engine noise, tread noise, squealing noise, for example of bicycles, or acoustic signals of traffic lights. This effect enables further traffic participants such as, for example, the traffic participant T2, to orientate themselves, not only on the basis of such initialisation emissions 11 explicitly emitted as measurement signals for environment monitoring and on the basis of the echoes from passively reflecting objects that then occur, but also, additionally, on the basis of reaction emissions of other traffic participants such as, for example, Tl, and the echoes from passively reflecting objects that then occur.

In this way, even with few emissions 11, 71, the medium 80 that is used, in which the sound propagates, is already scanned with an abundance of signals that, owing to the contained, mostly redundant, information, enable the position and movement of the traffic participants Tl, T2 and objects present in the medium 80 to be determined in a rapid and reliable manner, even if there are only few traffic participants involved, such as, for example, the traffic participant T2, through active emission of reaction emissions 71. It is also possible in this case for such traffic participants that do not actively transmit, but only evaluate the incoming acoustic signals, such as, for example, the traffic participant T2, to determine the position and the movement of the other traffic participants present in the medium 80, such as, for example, the traffic participant Tl, and of the objects otherwise present in the medium 80.

Also possible is the use of a combination of a plurality of characteristic features (signal characteristics), such as the signal strength and/or the time progression of the signal strength (for example in the form of frequency of occupancy of the medium 80) and/or the time progression of the signal frequency or of the signal frequency mix in the evaluation of the received signals 51, 31. Thus, for example, reaction emissions 71 may be generated more frequently in reaction to such initialisation emissions 11. Such more frequency generated reaction emissions 71 may be reproduced, in particular, at a respectively different playback speed and/or generated with a respectively different delay TD and/or have a respectively different transmission duration TP2 and/or have a respectively different reproduction sequence if in addition to having, for example, a minimum signal strength, they preferably have special, further signal characteristics such as, for example, a special signal frequency progression.

The characteristic features of the reaction emissions 71 realized in this manner thus have properties that are easy to comprehend. Thus, the total propagation time between the emission of the initialisation emission 11 and the receipt of the reaction emission 71, taking account of the delay TD known to all traffic participants ΤΙ, T2, is a measure of the distance of the traffic participants ΤΙ, T2. In the consideration of the rules, known to all traffic participants ΤΙ, T2, of the changed playback speeds, the frequency changes are a measure of the relative movement of the traffic participants ΤΙ, T2 in relation to each other, and in the consideration of the instantaneous propagation attenuation in the medium 80, the change in the signal strength is a measure of the orientation of the traffic participants (communication partners) ΤΙ, T2 in relation to each other.

In order to prevent collisions of the reaction emissions with reflections from non-active objects, i.e. from reflecting objects, either a long delay TD should be used, such that all echoes from potentially far distant objects are already closer to the receiver 30 and, in particular, at least one signal form of the actively emitted acoustic signals 71 of the reaction emissions is used that differs significantly from the signal form of the echoes from passively reflecting objects. The acoustic signals 71 of the reaction emissions can be distinguishable from the echoes from passively reflecting objects on the basis, for example, of the time progression of the signal frequency in the case of frequency-modulated signal forms and/or on the basis of the signal frequency, which can be generated, in particular, by means of a changed playback speed.

For a number of applications, a lesser frequency shift, or change in the playback speed, is already sufficient for a good signal separation between the acoustic signals 11 of initialisation emissions and the acoustic signals 71 of reaction emissions by frequency filters. If there are, for example, two vehicles ΤΙ, T2, having absolute speeds of 60 km/h, i.e. 17 m/s, in a region of the sound medium 80, the maximum relative speed of the two meeting vehicles Tl, T2 can be 34 m/s, which results in a Doppler shift of approximately 10% of the signal frequency of the acoustic signals 11 of the initialisation emissions in the case of the reaction receiver Tl.

Figure 2 shows the position of the possible Doppler band DR of a reaction emission in the case of the reacting traffic participant (reactor) T2, in comparison with the position of the Doppler band DI of the corresponding initialisation emission in the case of the originally initialising traffic participant Tl, with a 1.5 times playback speed.

In this context, the ratio of playback speed to recording speed in the case of the reactor T2 is designated as the relative playback speed RA.

It becomes clear that the two bands DI, DR do not overlap each other, even with consideration of extreme values. It is even better for the relationship between an initialisation emission and an associated reaction emission, since the two bands change in the same direction.

In traffic situations in which only few acoustically traffic participants Tl, T2 must share a region of the sound medium 80, however, it is also advisable that the acoustic signals of the reaction emissions be emitted at a lower playback speed, this corresponding to a shift towards lower signal frequencies. Owing to the small number of traffic participants Tl, T2, the collision probability of the reaction emissions is low, despite the pulse duration being longer in comparison with the initialisation emissions. The choice of the lower signal frequency can be advantageous if it is necessary to achieve greater ranges, since the spatial attenuation increases with the signal frequency.

Alternatively, a change of the signal frequencies makes sense, in order to avoid noise sources. This applies both to the initialisation emissions of the initialising traffic participant T1 and to the reaction emissions of the reacting traffic participant T2.

Preferably, therefore, the method is executed in such a manner that the choice of the signal frequencies of the initialisation emissions and also the relative playback speed RA in the reproduction (replay) are adapted to the situation, but such that the respective traffic participant (communication partner) ΤΙ, T2 can recognize again the change of acoustic signals, on the basis of previously agreed rules. For example, this is achieved by selecting only significantly distinguishable steps of the relationships to the initialisation emission 11 that are contained in the reaction emission 71, for example of the relative playback speed, and/or the differing delay TD and/or the signal length.

If one takes into account the fact that, in acoustic environment detection, a traffic participant ΤΙ, T2 usually picks up the active emissions of at least one other traffic participant T2, T1 by means of at least two receiving systems, which are spatially distributed on the traffic participant ΤΙ, T2, the spatial differences of the received emissions, in particular the propagation-time differences and/or the signal strength and/or the signal variations in the course of the transmission path, can be used as a basis for determining at least the spatial relationship between the emitting and the receiving traffic participant ΤΙ, T2, a proposition can be made concerning the relative movement between the emitting and the receiving traffic participant ΤΙ, T2, and the traffic conditions between the emitting and the receiving traffic participant ΤΙ, T2, in particular the position and/or the shape of the other traffic participants and/or fixed objects, such as trees, that are present between them, and/or the condition of the carriageway can be deduced.

In the case of a preferred attribute, at least one traffic participant T2, in the case of which a plurality of electroacoustic transducers (not represented separately) are oriented to a region of the medium, does not emit a reaction emission 71 via each electroacoustic transducer. For example, following the receipt of an initialisation emission 11, a corresponding reaction emission 71 may be emitted via the electroacoustic transducer via which the acoustic signals 51 of the initialisation emission were received with a greatest signal strength, and simultaneously or time-shifted, i.e. after another delay TD at least one further corresponding reaction emission 71 is emitted via the electroacoustic transducer via which the acoustic signals 51 of the initialisation emission were received with a least signal strength. Further combinations are possible.

In the case of a further preferred attribute, at least one traffic participant of the traffic participants ΤΙ, T2 present in the medium 80 alternately assumes differing functions of the aforementioned functions, i.e. this traffic participant, for example, behaves one time as an initiating traffic participant (initiator) T1 of the acoustic exchange, and another time behaves as a reacting traffic participant (reactor), such as, for example, the traffic participant T2, which reacts with reaction emissions 71 to the receipt of the acoustic signals 51 of an initialisation emission. In a preferred attribute, an initiating traffic participant (initiator) T1 confirms the receipt of the acoustic signals 31 of a reaction emission 71 previously emitted by a reacting traffic participant (reactor) T2, likewise by emitting a further reaction emission (not represented). In this way, the initiating traffic participant T1 receives a confirmation that the reacting traffic participant T2 has received the acoustic signals 51 of its initialisation emission, and the reacting traffic participant T2 receives a confirmation of the receipt of the acoustic signals 31 of its reaction emission by the initiating traffic participant Tl. Such confirmed transmissions help to meet the increasing demands in respect of reliability in environment monitoring.

In addition to containing the information for realization of the method according to the invention (replay protocol), both the reaction emissions 71 and the initialisation emissions 11 may also contain further information such as, for example, relating to the status of the vehicle in respect of travel dynamics, and/or to the vehicle identification.

Claims

1. Method for determining the relative distance and/or the relative movement between at least two traffic participants (ΤΙ, T2), wherein, upon the receipt of acoustic signals (51) originating from initialisation emissions in the form of acoustic signals (11) that have been emitted by a first traffic participant (Tl), reaction emissions in the form of acoustic signals (71), which are received and evaluated by the first traffic participant (Tl), are triggered by a second traffic participant (T2), characterized in that the reaction emissions of the second traffic participant (T2) are effected after the expiry of at least one delay (TD) that is known to the traffic participants (Tl, T2) and that is set to be of such a duration that acoustic signals received by the first traffic participant (Tl) that originate from passive reflections of the initialisation emissions of the first traffic participant (Tl) on ambient objects do not affect an evaluation, performed by the first traffic participant (Tl), of the reaction emissions (71) of the second traffic participant (T2) that are received by means of at least one receiver (30), characterized in that: the signal strength and/or the signal progression of the acoustic signals (71) of the reaction emissions of the second traffic participant (T2) have an unambiguous relationship to the signal strength and/or to the signal progression of the acoustic signals (11) of the initialisation emissions of the first traffic participant (Tl), which have a frequency progression that varies with time; and the acoustic signals of the reaction emissions each comprise a predetermined signal segment of the acoustic signals of the initialisation emissions, the predetermined signal segments being emitted in the inverse time sequence, or in an unchanged time sequence .

2. Method according to Claim 1, characterized in that, on the basis of the acoustic signals (31) of the reaction emissions of the second traffic participant (T2) that are received by the first traffic participant (Tl), reaction emissions of acoustic signals of the first traffic participant (Tl) are triggered, after the expiry of at least one delay that is known to the traffic participants (Tl, T2) and that is of such a duration that the acoustic signals received by the second traffic participant (T2) that originate from passive reflections of the acoustic signals of the reaction emissions of the second traffic participant (T2) on ambient objects do not affect an evaluation of the acoustic signals of the reaction emissions of the first traffic participant (Tl) that are received by the second traffic participant (T2) by means of at least one receiver (50), which evaluation is performed by the second traffic participant (T2) for the purpose of determining the relative distance and/or the relative movement between the two traffic participants (Tl, T2) .

3. Method according to either one of the preceding claims, characterized in that the signal duration of the acoustic signals of the reaction emissions of at least one traffic participant is less than a predetermined fraction of the signal duration (TP1) of the acoustic signals of the initialisation emissions of the first traffic participant (Tl) .

4. Method according to any of claims 1-3 wherein at least one signal duration of the acoustic signals of the reaction emissions of at least one traffic participant is known to the traffic participants (ΤΙ, T2).

5. Method according to any of claims 1-4 wherein at least one frequency of the acoustic signals of the reaction emissions of at least one traffic participant is known to the traffic participants (ΤΙ, T2).

6. Method according to any of claims 1-5 wherein at least one frequency progression of the acoustic signals of the reaction emissions of at least one traffic participant is known to the traffic participants (ΤΙ, T2).

7. Method according to any one of the preceding claims, characterized in that the acoustic signals of the reaction emissions of at least one traffic participant contain modulated-on information relating to these reaction emissions, the modulated-on information comprising the at least one delay (TD) used for these reaction emissions and/or the signal duration and/or the signal frequency or the signal frequency progression of the corresponding acoustic signals.

8. Method according to any one of the preceding claims, characterized in that, in the case of at least one evaluation of the acoustic signals (11) of the initialisation emissions of the first traffic participant and/or of the acoustic signals of the reaction emissions of at least one traffic participant, which evaluation is performed for the purpose of determining the relative distance and/or the relative movement between the traffic participants (ΤΙ, T2), at least one characteristic feature of the acoustic signals (11) of these initialisation emissions and/or of the acoustic signals of these reaction emissions is used.

9. Method according to claim 8 wherein the at least one characteristic feature of the acoustic signals (11) of these initialisation emissions and/or acoustic signals of these reaction emissions is the signal frequency and/or the signal frequency mix of the corresponding acoustic signals .

10. Device (100) for determining the relative distance and/or the relative movement between at least two traffic participants (Tl, T2), which is designed to receive, by means of at least one receiver (50), the initialisation emissions of acoustic signals (11) generated by at least one traffic participant (Tl) of the two traffic participants, and to recognize these initialisation emissions as such by means of an evaluation, and to generate reaction emissions of acoustic signals (71) as a response to the received acoustic signals (51) of the initialisation emissions of the at least one traffic participant (Tl), characterized in that the device (100) is designed to generate the reaction emissions of acoustic signals (71), having at least one predetermined signal duration (TP2), after the expiry of at least one predetermined delay (TD) that is known to the traffic participants, characterized in that: the device (100) is designed to generate reaction emissions of acoustic signals (71) that have a signal strength and/or a signal progression that have an unambiguous relationship to the signal strength and/or to the signal progression of the received (51) acoustic signals (11) of the initialisation emissions generated with a time-dependent frequency progression; and the acoustic signals of the reaction emissions each comprise a predetermined signal segment of the acoustic signals of the initialisation emissions, the predetermined signal segments being emitted in the inverse time sequence, or in an unchanged time sequence .

11. Device (100) according to Claim 10, characterized in that the device (100) is designed to generate initialisation emissions of acoustic signals having at least one predetermined signal duration, which are recognizable as such, by the at least one traffic participant (Tl), by means of an evaluation, and to receive, by means of the at least one receiver (50), the reaction emissions of acoustic signals generated by the at least one traffic participant (Tl) as a response to the initialisation emissions generated by the device (100), after the expiry of at least one predetermined delay (TD) that is known to the traffic participants, and to recognize these reaction emissions as such on the basis of an evaluation.

12. Device (100) according to any one of Claims 10 or 11, characterized in that the device (100) is designed to generate, as a response to the received reaction emissions of acoustic signals generated by the at least one traffic participant, further reaction emissions of acoustic signals, having at least one predetermined signal duration, after the expiry of at least one predetermined delay (TD) that is known to the traffic participants (Tl, T2).

13. Device (100) according to any one of Claims 10 to 12, characterized in that the device is designed to generate reaction emissions of acoustic signals (71), having at least one signal duration (TP2) that is known to the traffic participants (ΤΙ, T2) and/or having at least one frequency that is known to the traffic participants (Tl, T2) or having at least one frequency progression that is known to the traffic participants (Tl, T2).

14. Device (100) according to any one of Claims 10 to 13, characterized in that the device (100) is designed to generate reaction emissions of acoustic signals (71) having modulated-on information relating to these reaction emissions.

15. Device (100) according to any one of Claims 10 to 14, characterized in that the device (100) is designed to evaluate the received acoustic signals (51) of the initialisation emissions and/or the received acoustic signals, at least of the further traffic participant (Tl), on the basis of at least one characteristic feature of these received acoustic signals.

16. Vehicle assistance system having a device (100) according to any one of Claims 10 to 15.