Service station for an intelligent transportation system

Abstract

The invention relates to an Intelligent Transportation System, ITS, service station (20), comprising: a receiver (34) having an area of radio coverage (35) and being configured to receive a first Collective Perception Message, CPM, (31) from a first ITS station (26) at a first position (PB) within the coverage area (35), the first CPM (31) including first sensor data (sdi) on at least one first free space area (A) perceived by the first ITS station (26); an aggregator (36) connected to the receiver (34) and configured to aggregate said first sensor data (sdi) with at least one second sensor data (sdi , sdk) on at least one second free space area (B, C) into a third sensor data (sdΣ), which second sensor data (sdi , sdk) either is received via the receiver (34) in a second CPM (32) from a second ITS station (27) at a second position (Pc) within the coverage area (35) or is determined by a sensor (28) of the ITS service station (20); and a transmitter (37) connected to the aggregator (36) and configured to broadcast said third sensor data (sdΣ) in a third CPM (33).

Description

Service Station for an Intelligent Transportation System The present invention relates to a service station for an Intelligent Transportation System (ITS). The basic ITS communication architecture is described in ETSI (European Telecommunications Standards Institute) Stand- ard EN 302 665 and related ETSI standards. A most recent de- velopment in ITS is the so-called Collective Perception Ser- vice (CPS) to share information on objects detected by one communication partner, such as a vehicle onboard unit (OBU) or a roadside unit (RSU) (generally called "ITS station", ITS-S), with another communication partner (ITS-S). The CPS in ITS is described in, e.g., ETSI Technical Report TR 103 562 and ETSI Technical Specification TS 103 324. Figs. 1a - 1c show the present concept of CPS to share "perceptions" (detections, analysis and / or trackings) of ob- jects among participants according to the above-mentioned ETSI standards. In Fig. 1a a vehicle 1 on a road 2 perceives an ob- ject 3, e.g., another vehicle, by means of an own sensor 4 such as a camera, a radar sensor, lidar sensor etc., with a field of view 5. In Fig. 1b the vehicle 1 may be additionally aware of a third vehicle 6 around a bend 7 of the road 2 which obstructs the direct view to the vehicle 6, by means of a wireless communication 8 between an ITS-S aboard the vehicle 6 and an own ITS-S aboard the vehicle 1. In Fig. 1c the third vehicle 6 around the bend 7 perceives a fourth vehicle 9 by means of an own sensor 10 with a field of view 11 and shares information about this perception over the wireless communica- tion 8 with the first vehicle 1. Vehicle 1 thus enjoys the benefit of a "Collective Perception" (CP) from other ITS-S- equipped participants so that it becomes aware of objects be- yond its own sensor range even when those objects are not equipped with an ITS-S on their own. Similarly to the perception of objects the CPS standard- ized in ETSI TR 103 562 also provides for the sharing of in- formation on free space areas a participant may move into, for example for collision avoidance or maneuvering. The messages exchanged in the CPS to share such percep- tions of objects and / or free space areas to inform the commu- nication partner about, e.g., the existence, speed, distance, position, direction etc. of a perceived object or the exist- ence, position, shape, size etc. of a perceived free space ar- ea are called Collective Perception Messages (CPMs). Fig. 2 shows the general structure of a CPM as defined in ETSI TR 103 562. The CPM 12 contains - apart from an ITS PDU (Protocol Da- ta Unit) header 13 designating the message as a "CPM package" - a set of CPM parameters 14 in the form of one or more data containers 15 - 18, in particular: - a management container 15 containing basic information about the transmitting ITS-S (in the example of Fig. 1: the vehicle 6), such as the station's type (e.g., OBU or RSU) and the station's absolute position; - a station data container 16 with further details, such as the dynamic state or map references of the transmitting ITS-S; - none, one or more sensor information containers 17 de- scribing the sensory capabilities of the transmitting ITS-S, such as range, aperture and position of the sensor / s; and - none, one or more perceived object containers 18 con- taining detailed information about the perceived objects. Each perceived object is assigned a local object identifier by the ITS-S generating the CPM which remains constant as long as the object is detected and tracked by the ITS-S. Information about perceived free space areas may be trans- ported in either one or more of the sensor information con- tainers 17 or one or more of the perceived object containers 18, depending on the implementation of the ETSI TR 103 562 standard. In particular, according to ETSI TR 103 562 a perceived object container 18 may contain sensor data such as distance and direction or position, shape and size of a perceived free space area as measured by the ITS-S's sensor, and an indica- tion of the time of measurement of the sensor data. For some data elements, e.g., for distance, speed, angle and object di- mension values of a perceived object or for the existence of a free space area, ETSI TR 103 562 also provides for confidence measures of the respective data values. The receiving ITS-S can then assess the trustworthiness of the collectively shared perception information. In general, it is up to the receiving ITS-S to make good use of the wealth of collectively shared sensor data to appro- priately execute road safety applications, such as driver warnings or automatic braking and steering functions for mov- ing into a free space area for collision avoidance. However, the wealth of information can overload the processing capabil- ities of receiving ITS-S in heavy traffic situations, leading either to malfunctions or the need for higher processing pow- ers with increased costs. It is an object of the invention to overcome the shortcom- ings of the prior art and to provide novel devices for improv- ing CPS in ITS. To this end, the invention creates a novel ITS service station, comprising: a receiver having an area of radio coverage and being con- figured to receive a first Collective Perception Message, CPM, from a first ITS station at a first position within the cover- age area, the first CPM including first sensor data on at least one first free space area perceived by the first ITS station; an aggregator connected to the receiver and configured to aggregate said first sensor data with at least one second sen- sor data on at least one second free space area into a third sensor data, which second sensor data either is received via the receiver in a second CPM from a second ITS station at a second position within the coverage area or is determined by a sensor of the ITS service station; and a transmitter connected to the aggregator and configured to broadcast said third sensor data in a third CPM. The novel ITS service station of the invention aggregates CPMs from surrounding ITS-S into aggregated ("third") CPMs so that other ITS-S listening to these broadcasts are eased from the burden of following a multitude of ITS-S and processing a multitude of CPMs to assess free maneuvering space. The ITS service station of the invention therefore contributes to re- duce the complexity of the CPS for listening ITS-S, in partic- ular when the aggregated CPMs of the ITS service station are prioritized over "normal" CPMs during communication or re- ceipt. Listening ITS-S can thus gain a better overview about any possible free space areas in their vicinity without the need to fuse free space area information from a multitude of CPMs themselves. A preferred embodiment of the invention is characterized in that the first sensor data includes a first confidence measure of said first free space area and the at least one second sensor data includes a second confidence measure of said second free space area, wherein the aggregator is config- ured to calculate a third confidence measure from said first and at least one second confidence measures and to include said third confidence measure in the third sensor data. An aggregated ("third") data in the aggregated ("third") CPM may have a better aggregated ("third") confidence measure when it had been aggregated from multiple data sources. There- fore, any ITS-S listening to both "normal" CPMs (here: the first and second CPMs) and "aggregated" CPMs (here: the "third" CPM of the inventive ITS service station) can choose to process and consider the CPM showing the best confidence measure for a specific maneuvering space needed, leading to an implicit prioritizing of the CPMs of the ITS service station at the receiving ITS-S. The receiving ITS-S may ignore sensor data regarding the maneuvering space from other CPMs in favor of the sensor data in the aggregated CPM. Processing load in the receiving ITS-S is thus significantly reduced, in particu- lar in heavy traffic situations, e.g., at an intersection, and low-cost ITS-S with modest processing capabilities can be used without compromising safety. In one embodiment, the aggregator is configured to aggre- gate said first and second sensor data by geometrically inter- secting the first and second free space areas indicated there- in and by including the resulting intersection area in the third sensor data. The area of intersection is thus an area which is confirmed by at least two disseminating ITS-S as be- ing "free", i.e., unoccupied by another vehicle or object. This double confirmation increases the trustworthiness of the aggregated CPM on free space area information. Furthermore, if the aggregated (third) CPM contains a (third) confidence meas- ure for the (third) sensor data on the intersection area, then this third confidence measure can be chosen as equal to or better than the better one of the first and second confidence measures of the first and second free space areas which had been intersected. A listening ITS-S can then use the intersec- tion area with high confidence that it is empty. Alternatively the aggregator is configured to aggregate said first and second sensor data by geometrically merging the first and second free space areas indicated therein and in- cluding the resulting merged area in the third sensor data. In this embodiment, the listening ITS-S has a large merged area of free space available for manoeuvring, albeit of lower con- fidence. In particular, if confidence measures are used in the first, second and third CPMs, the third confidence measure in the aggregated CPM can be set to the worst confidence measure of all first and second free space areas from which the merged area had been built, to be on the safe side. The third sensor data may additionally include the number (count) of first and second sensor data from which the third sensor data has been aggregated, and / or may additionally in- clude the number (count) of first and second ITS-S from whose CPMs the third sensor data has been aggregated. An ITS-S re- ceiving the aggregated CPM can use this information to further assess the confidence of a sensor data indicated therein. For keeping inventory and tracking of objects in its area of coverage over time, the aggregator of the ITS service sta- tion may have a memory for storing first and second CPMs in- cluding timestamps of the sensor data therein and may be con- figured to retrieve, for aggregating said third CPM, all sen- sor data from the memory having timestamps falling within a selected period of time. Although the aggregated CPMs of the ITS service station of the invention may implicitly have priority over "normal" CPMs in that they will usually carry sensor data with higher confi- dence measures than the normal CPMs of other ITS-S, the aggre- gated CPMs of the ITS service station may additionally be flagged with a higher priority than normal CPMs. This may be done by, e.g., including a "high priority" flag in the header of the aggregated CPM. Receiving ITS-S then do not need to compare confidence measures to prioritize aggregated CPM over normal CPMs, but just will look for the high priority flag, to speed up processing. The ITS service station of the invention can either be moveable, e.g., in the form of an onboard unit on a vehicle, or stationary, such as a roadside unit or infrastructure. In a particularly preferred embodiment the ITS service station is a roadside unit at an intersection. At intersections high vehi- cle traffic and hence communication traffic is to be expected so that receiving ITS-S benefit most from the load-reducing and safety-increasing CPM aggregation service of the inventive ITS service station. The invention will now be described in further detail by means of exemplary embodiments thereof under reference to the enclosed drawings, in which show: Figs. 1a - 1c the basic concept of Collective Perception in ITS according to the state of the art in three plan views of an exemplary road section; Fig. 2 a data structure of a CPM according to the state of the art; Figs. 3a and 3b two different embodiments of an ITS ser- vice station according to the invention in a plan view each; Fig. 4 an ITS service station according to the invention in a block diagram; Fig. 5a an exemplary memory contents of the ITS service station of Fig. 4; and Fig. 5b an example of an aggregated CPM as broadcast by the ITS service station of Fig. 4. Figs. 1 and 2 referring to the CPS in ITS and the CPM data structure, respectively, have been explained at outset. Figs. 3a and 3b each show an ITS service station 20 mount- ed stationarily as a roadside unit (RSU) at a traffic area S, e.g., an intersection, a highway, a parking lot etc. Three ex- emplary vehicles 21 - 23 are shown approaching or just about to enter the traffic area S. The positions of the vehicles 21 - 23 on the area S are designated as <semantics>PA<annotation encoding="application / x-tex">P_A< / annotation>< / semantics>, <semantics>PB<annotation encoding="application / x-tex">P_B< / annotation>< / semantics> and <semantics>PC<annotation encoding="application / x-tex">P_C< / annotation>< / semantics>, respective- ly. The vehicles 21 - 23 each carry an ITS-S 25 - 27 in the form of an onboard unit (OBU). Vehicles 22, 23 are exemplarily equipped with a sensor 28 with a respective field of view, ca- pable of perceiving an object <semantics>24i<annotation encoding="application / x-tex">24_i< / annotation>< / semantics> (i = 1, 2, ...). The sensors <semantics>28<annotation encoding="application / x-tex">28< / annotation>< / semantics> may be of any kind, e.g., a camera, a radar or lidar sensor, an acoustic sensor, a vibration sensor, an infrared sensor etc. The ITS service station 20, too, may have an own sensor 28 to perceive objects <semantics>24i<annotation encoding="application / x-tex">24_i< / annotation>< / semantics> in its vicinity, although this is not obligatory. Generally speaking, each of the ITS-S 25 - 27 and ITS service station 20 may have none, one or more sensors 28, also of different sensor types. Instead of being stationarily mounted as a roadside unit, the ITS service station 20 could also be mobile, e.g., aboard a vehicle as an OBU. The objects <semantics>24i<annotation encoding="application / x-tex">24_i< / annotation>< / semantics> perceived by the sensors 28 may be of any kind, e.g., a manned or unmanned land, sea or air vehicle, a pedestrian, an animal, a machine, a traffic sign, a radio, a light or infrared beacon, and the like. In the scenarios depicted in Figs. 3a and 3b each of the ITS-S 26, 27 of the vehicles 22, 23 perceives the same exem- plarily depicted object <semantics>24i<annotation encoding="application / x-tex">24_{i}< / annotation>< / semantics>. At the same time, within their re- spective fields of views of the sensors 28, the ITS-S 26, 27 each perceive a free space area A, B which is devoid of any object <semantics>24i<annotation encoding="application / x-tex">24_{i}< / annotation>< / semantics>. Also the sensor 28 of the ITS service station 20 perceives a free space area C devoid of any object 24i. The free space areas A, B, C perceived by the stations 26, 27, 20 will have a shape and size depending on the field of view of the respective sensor 28 and the objects 24i perceived therein as well as the shadow each object 24i casts within that field of view for the respective sensor 28. The vehicles 22, 23 share their perceptions of the ob- served free space areas A, B, as detected by their sensors 28, via CPMs 31, 32 sent from their ITS-S 26, 27 (the "perceiving" or "disseminating" ITS-S) to the ITS-S 25 (the "receiving" or "listening" ITS-S) of the vehicle 21. These "normal" CPMs 31, 32 are also received by the ITS service station 20, which cre- ates an "aggregated" CPM 33 therefrom, as follows. Within the CPMs 31, 32 a perceived free space area A, B can be indicated in any possible geometric definition, e.g., as a circle, square, rectangle, sector, ellipse or polygon. For example, the free space areas A, B are defined by the cor- ner points <semantics>A1−A11<annotation encoding="application / x-tex">A_1 - A_{11}< / annotation>< / semantics> and <semantics>B1−B11<annotation encoding="application / x-tex">B_1 - B_{11}< / annotation>< / semantics>, respectively. The exemplary free space area C observed by the ITS service station 20 is defined by an ellipse. With reference to Figs. 3a, 3b and 4, the ITS service sta- tion 20 has a receiver 34 with an area of radio coverage 35 to receive the CPMs 31, 32 from the ITS-S 26, 27 in its neighbor- hood. It goes without saying that the radio coverage area 35 will be dependent both on the transmitting power of the dis- seminating ITS-S 26, 27 and the receiving sensitivity of the receiver 34. For ease of description, the various normal CPMs 31, 32 ... are designated as <semantics>CP1<annotation encoding="application / x-tex">CP_1< / annotation>< / semantics>, <semantics>CP2<annotation encoding="application / x-tex">CP_2< / annotation>< / semantics>, ..., generally <semantics>CPm<annotation encoding="application / x-tex">CP_m< / annotation>< / semantics>, in the following. An aggregator 36 connected to the receiver 34 processes the set {CPm} of the received CPMs CPm and calculates the ag- gregated CPM 33, called <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics> in the following, therefrom. The aggregated CPM <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics> is then broadcast by a transmitter 37 con- nected to the output of the aggregator 36 so that it can be received by listening ITS-S in the vicinity, such as (here) the ITS-S 25 on the vehicle 21. The transmitter 37 and the re- ceiver 34 of the ITS service station 20 can be implemented by a combined transceiver, too. To calculate the aggregated CPM CP2 from the received nor- mal CPMs CPm the aggregator 36 has a memory 38 which contains - among other programs and data as needed - a table 39 storing the CPMs <semantics>CPm<annotation encoding="application / x-tex">CP_m< / annotation>< / semantics>, shown in Fig. 5a. With reference to Figs. 2 and 5a a CPM 12, 31, 32 or <semantics>CPm<annotation encoding="application / x-tex">CP_m< / annotation>< / semantics>, respectively, contains - apart from the other data depicted in Fig. 2 - in any sensor information container 17 or, prefera- bly, in any perceived object container 18, here called <semantics>oc1<annotation encoding="application / x-tex">oc_1< / annotation>< / semantics>, <semantics>oc2<annotation encoding="application / x-tex">oc_2< / annotation>< / semantics>, ..., generally <semantics>ocn<annotation encoding="application / x-tex">oc_n< / annotation>< / semantics>, one or more sensor data <semantics>sdi<annotation encoding="application / x-tex">sd_i< / annotation>< / semantics> (<semantics>i=1,2<annotation encoding="application / x-tex">i = 1, 2< / annotation>< / semantics>, ...) on free space areas like the free space areas A, B, C ..., and optionally corresponding free space area identifiers id, usually assigned by the perceiving ITS-S 26, 27. The sensor data sdi on any free space A, B, C ... perceived by a disseminating ITS-S 26, 27 may define the respective free space area in any form of geometrical definition di, e.g., a distance, direction and orientation of the free space area to the sensor 28, a geo-referenced or map-matched region, one or more dimensions of the free space area, a shape and size of the free space area, e.g., in form of a set of polygon corner coordinates <semantics>A1−A11<annotation encoding="application / x-tex">A_1 - A_{11}< / annotation>< / semantics>, <semantics>B1−B11<annotation encoding="application / x-tex">B_1 - B_{11}< / annotation>< / semantics> etc., as determined by the sensor 28, e.g., as taken by a camera and determined by image pro- cessing, etc. For example, any of the data items in the per- ceived object container 18 of a CPM according to ETSI TR 103 562 can be used for transporting the sensor data definition di on a free space area A, B, C, ..., e.g., the data element "FreeSpaceArea" of ETSI TR 103 562. Some of the sensor data sdi which are provided by the re- spective sensor 28 or a suitable processor connected to the sensor / s 28 in the ITS-S 26, 27 or the ITS service station 20 may be provided with a confidence measure cfi, e.g., in form of the "FreeSpaceConfidence" data element according to ETSI TR 103 562. Then the sensor data <semantics>sdi<annotation encoding="application / x-tex">sd_i< / annotation>< / semantics> is a pair <semantics>(d,cf)i<annotation encoding="application / x-tex">(d, cf)_i< / annotation>< / semantics> comprised of the free space area geometrical definition di and the asso- ciated free space area confidence measure cfi. The confidence measure <semantics>cfi<annotation encoding="application / x-tex">cf_i< / annotation>< / semantics> of a free space area A, B, C, ..., or of its definition <semantics>di<annotation encoding="application / x-tex">d_i< / annotation>< / semantics>, respectively, may be any statisti- cal measure of the confidence, reliability, trustworthiness, non-error rate etc. of this free space area to be a actually empty of objects <semantics>24i<annotation encoding="application / x-tex">24_{i}< / annotation>< / semantics>. For example, the confidence measure cfi can be the 95%-confidence interval, i.e., that with a proba- bility of 95% the free space area with the definition <semantics>di<annotation encoding="application / x-tex">d_i< / annotation>< / semantics> is empty. Of course, other measures of confidence could be used as explained later on. If the ITS service station 20 has one or more own sensors 28 which generate their own sensor data <semantics>sdk<annotation encoding="application / x-tex">sd_k< / annotation>< / semantics> (k = 1, 2, ...), the output of these sensors 28 can, e.g., be stored - in the same format as the received CPMs <semantics>CPm<annotation encoding="application / x-tex">CP_m< / annotation>< / semantics> - in data records <semantics>SD1<annotation encoding="application / x-tex">SD_1< / annotation>< / semantics>, <semantics>SD2<annotation encoding="application / x-tex">SD_2< / annotation>< / semantics>, ..., generally <semantics>SDk<annotation encoding="application / x-tex">SD_k< / annotation>< / semantics>, for example in the same table 39, as shown in Fig. 5a. From at least two received CPMs CPm, or at least one re- ceived CPM CPm and at least one sensor data record SDk, the ag- gregator 36 calculates the aggregated CPM <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics> as follows. With reference to Figs. 3a, 3b and 5b, there are basically two possibilities to aggregate free space areas A, B, C, ... from at least two different CPMs CPm or at least one CPM CPm and at least one record <semantics>SDk<annotation encoding="application / x-tex">SD_k< / annotation>< / semantics> into an aggregated sensor data <semantics>sdΣ<annotation encoding="application / x-tex">sd_{\Sigma}< / annotation>< / semantics> which is to be included in the aggregated CPM CP2. As shown in Fig. 3a, two or more free space area definitions <semantics>di<annotation encoding="application / x-tex">d_i< / annotation>< / semantics>, <semantics>dk<annotation encoding="application / x-tex">d_k< / annotation>< / semantics> can be geometrically intersected, see the resulting intersection area AB of the geometric intersection of the free space areas A and B, the resulting intersection area AC of the geometric inter- section of the free space areas A and C, and the resulting in- tersection area ABC of the geometric intersection of all three free space areas A, B, C. The more free space areas are inter- sected, the better the confidence or trustworthiness of a re- sulting (intersected) free space area AB, AC, ABC is, since more participating stations 26, 27, 20 indicate that the in- tersection area is actually devoid of any objects 24i. In the aggregated CPM <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics> one, more or all of the determined intersec- tion areas AB, AC, ABC can be indicated by respective geomet- ric definitions <semantics>dΣ<annotation encoding="application / x-tex">d_{\Sigma}< / annotation>< / semantics>. An alternative possibility to calculate the aggregated CPM <semantics>𝖢𝖯Σ<annotation encoding="application / x-tex">\mathsf{CP}_\Sigma< / annotation>< / semantics> is shown in Fig. 3b. The aggregated sensor data <semantics>𝗌𝖽Σ<annotation encoding="application / x-tex">\mathsf{sd}_\Sigma< / annotation>< / semantics> can be a geometrical merger, combination or fusion D of all individu- al free space areas A, B, C, indicating for the listening ITS- S 25 the maximum area of reported free space which can be used for maneuvering without collision with any object 24i. Of course, the confidence of the trustworthiness of this result- ing merged area D will usually not be better than the worst confidence of any of the individual free space areas A, B, C. Therefore, if free space area definitions <semantics>di<annotation encoding="application / x-tex">d_i< / annotation>< / semantics>, <semantics>dk<annotation encoding="application / x-tex">d_k< / annotation>< / semantics> with re- spective confidence measures <semantics>cfi<annotation encoding="application / x-tex">cf_i< / annotation>< / semantics>, <semantics>cfk<annotation encoding="application / x-tex">cf_k< / annotation>< / semantics> are used in the aggrega- tion, the aggregated confidence measure <semantics>cfΣ<annotation encoding="application / x-tex">cf_{\Sigma}< / annotation>< / semantics> of the aggregated area AB, AC, ABC, D in the aggregated sensor data <semantics>sdΣ<annotation encoding="application / x-tex">sd_{\Sigma}< / annotation>< / semantics> with the geometrical definition <semantics>dΣ<annotation encoding="application / x-tex">d_{\Sigma}< / annotation>< / semantics> may be - in case of an intersection (AB, AC, ABC): either equal to or better than the best one of the individual confidence measures <semantics>cfi<annotation encoding="application / x-tex">cf_i< / annotation>< / semantics>, <semantics>cfk<annotation encoding="application / x-tex">cf_k< / annotation>< / semantics> of the originating areas A, B, C, or - in case of a merged area D: equal to the worst one of the individual confidence measures cfi, cfk of the originating areas A, B, C. The aggregated confidence measure <semantics>cfΣ<annotation encoding="application / x-tex">cf_{\Sigma}< / annotation>< / semantics> can also be a compo- site field or concatenation of the confidence measure <semantics>cfΣ<annotation encoding="application / x-tex">cf_{\Sigma}< / annotation>< / semantics> as calculated above and other information such as the number (count) of data sources responsible for that confidence meas- ure <semantics>cfΣ<annotation encoding="application / x-tex">cf_{\Sigma}< / annotation>< / semantics>, their positions, speeds and / or headings with respect to the free space areas A, B, C, ..., the fields of view of the respective sensors 28, etc. For example, the more different the positions of the data sources, i.e. the positions of the sensors 28 and / or the positions of the stations 20, 26, 27, with respect to an intersected free space area AB, AC, ABC are, the better the data quality and hence trustworthiness of that intersected free space area is. The aggregation performed by the aggregator 36 may take into account timing aspects. Each CPM <semantics>CPm<annotation encoding="application / x-tex">CP_m< / annotation>< / semantics> and record <semantics>SDk<annotation encoding="application / x-tex">SD_k< / annotation>< / semantics>, and in particular each perceived object container ocn or even each individual sensor data <semantics>sdi<annotation encoding="application / x-tex">sd_i< / annotation>< / semantics>, <semantics>sdk<annotation encoding="application / x-tex">sd_k< / annotation>< / semantics>, may contain a timestamp t in- dicative of the time of measurement of the respective sensor data <semantics>sdi<annotation encoding="application / x-tex">sd_i< / annotation>< / semantics>, <semantics>sdk<annotation encoding="application / x-tex">sd_k< / annotation>< / semantics>. The timestamp t may be indicated in any suitable format, be it relatively to a time of sending the respective <semantics>CPm<annotation encoding="application / x-tex">CP_m< / annotation>< / semantics> or the time of storing the respective record <semantics>SDk<annotation encoding="application / x-tex">SD_k< / annotation>< / semantics>, or abso- lutely in terms of a systemwide reference clock. The timestamps t can also take into account the track or estimated movement of a perceived object 24i and the sensor shadow it casts in the respective sensor's field of view, i.e., its influence on the respective perceived free space ar- eas A, B, C, ..., as well as possible calculation, processing or transmission delays. In this way, the "age" of a sensor data <semantics>sdi<annotation encoding="application / x-tex">sd_i< / annotation>< / semantics>, <semantics>skk<annotation encoding="application / x-tex">sk_k< / annotation>< / semantics> can be accounted for by the aggregator 36 when calcu- lating the aggregated CPM <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics>. For example, the aggregator 36 may, when aggregating the CPM <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics>, only use sensor data <semantics>sdi<annotation encoding="application / x-tex">sd_{i}< / annotation>< / semantics>, <semantics>sdk<annotation encoding="application / x-tex">sd_{k}< / annotation>< / semantics> from its memory 38 whose timestamps t fall within a selected period of time, for example into a past cycle interval, when the ITS service station 20 cyclically sends CPMs <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics>. In the aggregated CPM <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics> the aggregator 36 may optionally include the number (count) of originating sensor data <semantics>sdi<annotation encoding="application / x-tex">sd_{i}< / annotation>< / semantics>, <semantics>sdk<annotation encoding="application / x-tex">sd_{k}< / annotation>< / semantics> from which a specific aggregated sensor data sd2 had been ag- gregated, and / or the number (count) of disseminating ITS-S 26, 27 from whose CPMs <semantics>CPm<annotation encoding="application / x-tex">CP_m< / annotation>< / semantics> that specific aggregated sensor data <semantics>sdΣ<annotation encoding="application / x-tex">sd_{\Sigma}< / annotation>< / semantics> had been aggregated. The numbers (counts) can be, e.g., at- tached as data field / s to the respective aggregated confidence value / s cf<semantics>Σ<annotation encoding="application / x-tex">_{\Sigma}< / annotation>< / semantics> in the aggregated CPM CP<semantics>Σ<annotation encoding="application / x-tex">_{\Sigma}< / annotation>< / semantics>. These numbers (counts) can then be used by a receiving ITS-S 25 to select if or which one of several received aggregated CPM CP2 is to trust most re- garding a specific sensor data. Usually, the receiving ITS station 25 will select and use that aggregated sensor data <semantics>sdΣ<annotation encoding="application / x-tex">sd_{\Sigma}< / annotation>< / semantics> which has the best confidence measure <semantics>cfΣ<annotation encoding="application / x-tex">cf_{\Sigma}< / annotation>< / semantics> attributed to it, e.g., the smallest confidence in- terval or the highest confidence level, when the confidence measure is expressed in such terms. However, with the addi- tional knowledge of the numbers (counts) of originating sensor data or ITS-S, from which the sensor data sd2 had been aggre- gated, the receiving ITS-S 25 can improve the selection, e.g., by weighting the confidence measures <semantics>cfΣ<annotation encoding="application / x-tex">cf_{\Sigma}< / annotation>< / semantics> by their respective numbers (counts) of underlying data. On the other hand, said numbers (counts) may be particularly useful for sensor data sdz which does not comprise a confidence measure <semantics>cfΣ<annotation encoding="application / x-tex">cf_{\Sigma}< / annotation>< / semantics> at all. The aggregated CPMs <semantics>CPΣ<annotation encoding="application / x-tex">CP_{\Sigma}< / annotation>< / semantics> broadcast by the ITS service sta- tion 20 as CPMs 33 may optionally contain a "high priority" flag or a flag indicating a priority which is higher than those of the "normal" CPMs CPm (CPMs 31, 32). ITS-S 24 listen- ing to the CPMs 31, 32 may prefer CPMs 33 with higher priority (or disregard CPMs 31, 32 with lower priority) so that the ag- gregated CPMs 33 of the ITS service station 20 are favored. The invention is not restricted to the specific embodi- ments disclosed herein, but encompasses all modifications, variants and combinations thereof that fall within the scope of the appended claims.

Claims

1. Intelligent Transportation System, ITS, service sta- tion comprising: a receiver having an area of radio coverage and being con- figured to receive a first Collective Perception Message, CPM, from a first ITS station at a first position within the cover- age area, the first CPM including first sensor data on at least one first free space area perceived by the first ITS station; an aggregator connected to the receiver and configured to aggregate said first sensor data with at least one second sen- sor data on at least one second free space area into a third sensor data, which second sensor data either is received via the receiver in a second CPM from a second ITS station at a second position within the coverage area or is determined by a sensor of the ITS service station; and a transmitter connected to the aggregator and configured to broadcast said third sensor data in a third CPM.

2. ITS service station according to claim 1, character- ized in that the first sensor data includes a first confidence measure of said first free space area and the at least one second sensor data includes a second confidence measure of said second free space area, wherein the aggregator is config- ured to calculate a third confidence measure from said first and at least one second confidence measures and to include said third confidence measure in the third sensor data.

3. ITS service station according to claim 1 or 2, char- acterized in that the aggregator is configured to aggregate said first and second sensor data by geometrically intersect- ing the first and second free space areas indicated therein and by including the resulting intersection area in the third sensor data.

4. ITS service station according to claim 1 or 2, char- acterized in that the aggregator is configured to aggregate said first and second sensor data by geometrically merging the first and second free space areas indicated therein and by in- cluding the resulting merged area in the third sensor data.

5. ITS service station according to any one of claims 1 to 4, characterized in that the third sensor data includes a count of first and second sensor data from which the third sensor data has been aggregated.

6. ITS service station according to any one of claims 1 to 5, characterized in that the third sensor data includes a count of first and second ITS stations from whose CPMs the third sensor data has been aggregated.

7. ITS service station according to any one of claims 1 to 6, characterized in that the aggregator has a memory for storing first and second CPMs including timestamps of the sen- sor data therein and is configured to retrieve, for aggregat- ing said third CPM, all sensor data from the memory having timestamps falling within a selected period of time.

8. ITS service station according to any one of claims 1 to 7, characterized in that the third CPM is flagged with a higher priority than the first and second CPMs.

9. ITS service station according to any one of claims 1 to 8, characterized in that the ITS service station is a road- side unit.

10. ITS service station according to claim 9, character- ized in that the ITS service station is a roadside unit at an intersection.