EP2617023A2 - A system for detecting and signalling a particular condition in a carriageway, in particular a danger condition - Google Patents

Abstract

A system and a method (1) for detecting a warning condition (2) in a section (7) of a roadway (5) and for notifying it to users (6) of the roadway. A row of detection and signalling devices (10) is arranged along the roadway at a interval (d) from one another, each device comprising: at least one sensor (13) to create a signal (8) of a physical quantity detected in the roadway section, a communication means (17) forming a data network for transferring the signal (8) between the devices, a computing means (14) to create a signal of warning condition (9), starting from at least one signal (8) of physical quantity coming from the device that is located at the roadway section, and/or from other devices through the respective communication means, a frame - forming means (14) for forming a frame (3) of data comprising physical quantity signals; a warning condition notifying means for notifying the warning condition to the users (6) of the roadway.

Description

TITLE

A SYSTEM FOR DETECTING AND SIGNALLING PARTICULAR CONDITIONS IN A CARRIAGEWAY, IN PARTICULAR A DANGER CONDITION

DESCRIPTION

Field of the invention

The present invention relates, in general, to a system for detecting and quickly signalling particular conditions in a section of roadway of a roadway. In particular, the system is suitable for detecting danger conditions, and for signalling such danger conditions to the drivers of vehicles running towards said section of roadway.

For example, the system is configured to detect and to signal vehicles running in the wrong direction, typically in a roadway of a motorway.

State of the Art - Technical problem

Many route accidents are caused by obstacles and hindrances such as motionless vehicles, or damaged vehicles or irregularly running and/or parked vehicles. In particular, vehicles that run in the wrong direction are seriously dangerous. Other particular dangerous cases are pile ups, and the real-time traffic radio alerts, and/or the variable message board signalling means, are not always so prompt and/or widely distributed to allow drivers to slow down or stop in time to avoid them.

WO2007039924 discloses a system for detecting and signalling the presence of obstacles or hindrances on a roadway. The system comprises devices that are arranged along the roadway. The devices comprise a detection means for detecting obstacles on the roadway, and comprise also a signalling means for locally or remotely signalling said presence of obstacles. The detection means is essentially formed by a magnetometer, an infrared ray sensor and a microphone. Such detection means is suitable for detecting motionless or particularly slow vehicles on the roadway, within a predetermined distance. Starting from the signals provided by the three types of sensors, a control unit, or CPU, of each single device determines the position and/or the speed of the obstacles or of the vehicles. If a condition is recognized as dangerous, the CPU turns the corresponding device into an alarm state. The alarm state of the device is communicated to a plurality of devices that are located upstream, with respect to the vehicle travel direction, through a transceiving means. This way, the devices that are located upstream can notify the alarm state to upcoming vehicles, through their own visual and/or acoustic signalling means.

The system disclosed in WO2007039924 is suitable for remotely detecting and signalling the presence of obstacles and/or irregularly running vehicles, and also suitable for warning very quickly the upcoming drivers. This way, the drivers can slow down in advance enough to avoid accidents such as pileups. However, this system is not suitable for detecting particular danger conditions such as cars running in the wrong direction. Furthermore, the way the devices communicate with one another is not effective as it would be required.

Summary of the invention

It is therefore a feature of the present invention to provide a system and a method for recognizing the presence of a danger condition in a roadway.

It is a particular feature of the invention to provide a system and a method for recognizing the presence of dangers such as irregularly running vehicles, crashes, traffic jams and so on, and for signalling such a condition to upcoming cars at a predetermined distance, and in advance enough to avoid accidents.

It is a particular feature of the invention to provide such a system that is more reliable than the prior art systems, and that allows recognizing, in particular, which type of obstacle is present on the roadway, and/or to recognize which event has created the obstacle.

It is another particular feature of the invention to provide a system and a method for recognizing and signalling the presence of a car running along a roadway/roadway of a motorway in a direction contrary to the carriageway or roadway direction.

These and other objects are achieved by a system for detecting a warning condition in a roadway section and for notifying this condition to users of the roadway, comprising:

a plurality of detection and signalling devices in use arranged along the roadway at a predetermined interval from one another, wherein each detection and signalling device defines a node of a data network, each detection and signalling device comprising:

- at least one sensor that is configured to detect a physical quantity in a portion of the roadway section, and to produce a physical quantity signal;

- a communication means that is configured to transfer the physical quantity signal to the detection and signalling devices that are present along the roadway, the communication means comprising a transceiving means that is configured to transceive the physical quantity signal from the detection and signalling device to/from another detection and signalling device present along the roadway;

- a computing means that is configured to create a condition signal, which describes the condition occurring in the roadway section, starting from at least one physical quantity signal which comes from the detection and signalling device that is arranged in the roadway section, and/or from other detection and signalling devices, by a corresponding communication means in each device,

- a frame-forming means for forming a data frame which includes physical quantity signals and/or condition signals that are created o received by each device;

- a notification means for notifying the warning condition to the users of the roadway,

wherein the main feature of the system is that each detection and signalling device comprises a means for executing a linear communication protocol, the linear communication protocol comprising:

defining a reception distance k as a predetermined number of intervals, i.e. of "hops", along the roadway, such that within the reception distance a corresponding number of devices is arranged along the roadway, wherein the reception distance k is selected such that a transceiving range of each device does not extend along the roadway up to devices that are arranged beyond the reception distance;

defining a distance module as a number N of intervals, greater than the reception distance, such that N>2k + 1 , wherein the distance module is selected such that two nodes that are located at the distance module from each other are allowed to contemporaneously transmit the data frame to other nodes that are arranged along the roadway at a distance within the reception distance; contemporaneously transmitting the data frame on a same transmission channel, during a predetermined transmission time, by a plurality of devices that are arranged along the roadway at the distance module from one another, towards other detection and signalling devices that are located within the reception distance with respect to respective devices of the plurality of devices, and maintaining a still stand state by all the other devices which do not belong to the plurality;

- iterating the step of transmitting for other pluralities of devices for further respective transmission times until all the detection and signalling devices that are present along the roadway have completed the step of transmitting;

cyclically repeating the steps of transmitting and iterating;

- transferring the warning condition, if the warning condition is present within the data frame for at least one of the devices in a known position, to a predetermined number of devices that are located upstream of the position according to a predetermined vehicle travel direction along the roadway.

This way, the system according to the invention allows to distribute a signal of a warning condition, which is occurring at a place of the roadway, for a potentially unlimited distance along the roadway itself. At the same time, the system allows to use a same communication channel and to avoid interferences between detection and signalling devices. Such communication channel is used for different communication processes in local areas that are defined by the distance module N.

Advantageously, each detection and signalling device is configured to carry out the step of sequentially iterating the step of transmitting according to a direction which is opposite to the vehicle travel direction of the vehicles in the roadway. This way, the system allows detecting danger conditions occurring on the roadway and/or notifying such danger conditions to drivers of upcoming vehicles. In particular, the step of transmitting is repeated in succession, in a direction which is opposite to the vehicle travel direction of the vehicles at all the nodes of the network, and for a respective transmission time T_T. This way, each node is allowed to transmit again after a repetition time or cycle time Ts=T_T*N, and at each iteration each module of size N migrates according to a direction which is opposite to the vehicle travel direction. This ensures a fusion of data which are formed by the physical quantity signals and by the condition signals that are calculated at said nodes by each device. Advantageously, the warning condition is an irregular speed condition of at least one vehicle or of an object that is comparable to at least one vehicle present on the roadway. The irregular speed condition can be selected from the group comprised of:

- a motionless vehicle, for example a damaged vehicle;

- a vehicle moving at a speed lower than a prefixed minimum value;

- a vehicle moving at a speed higher than a prefixed maximum value;

- a couple of vehicles having a relative speed higher than a prefixed maximum value;

- a traffic jam, i.e. a plurality of vehicles following one another moving at a speed lower than a prefixed minimum value;

- a vehicle moving at a speed of direction which is opposite to the prefixed vehicle travel direction of a carriageway of the roadway, i.e. a vehicle moving in the wrong direction.

The transceiving means can be:

- a cable means;

- a wireless means.

In particular, the transceiving wireless means is a radiofrequency means. In particular, the radiofrequency means is configured to transceive through channels corresponding to the ISM band (Industrial, Scientific and Medical band), i.e. through frequency bands set between 862 and 956 MHz.

In a particular exemplary embodiment, the system comprises a row of detection and signalling devices for each carriageway or each roadway of a roadway, and the transceiving wireless means of the detection and signalling devices of each row is configured to transceive through non-overlapping channels, i.e. through channels that comprise different frequencies.

Furthermore, or Alternatively, the radiofrequency transceiving means is configured to carry out a frequency-division duplexing (FDD) technique. This allows communication processes along two or more carriageways or roadways of a same roadway, which are independent from one another, by an access protocol that is simpler than the protocol which is required when using a time- division duplexing technique (TDD). Indeed, in the latter case it is necessary to coordinate the detection and signalling devices of the two or more carriageways or roadways. Advantageously, the step of maintaining a still stand state, by all the other devices which do not belong to the plurality of devices at the nodes that are carrying out the transmission, comprises a step of waiting a predetermined response time after the end of the reception of the frame, coming from one of the other nodes different from the nodes that are carrying out the transmission.

In particular, the linear communication protocol comprises furthermore, for each currently receiving node:

starting a timer immediately after a receiving step has been completed or after the step of transmitting a frame has been completed, the timer having a predetermined timeout;

- awaiting and recognizing an event, the event selected from the group consisting of:

- the timeout of the timer;

- a reception of data coming from other nodes different from the currently receiving node,

after the timeout event has expired, the linear communication protocol provides the step of transmitting, whereas after the step of receiving the linear communication protocol comprises:

stopping the timer;

- waiting for a response time to elapse, after completion of the reception of data coming from one of the nodes different from the currently receiving node.

In an exemplary embodiment, the frame, which includes the physical quantity signals and/or or the condition signals, comprises a synchronization portion that serves for signalling the beginning of the step of transmitting, and a data portion that comprises the physical quantity signals and/or the condition signals, and

the communication means of one of the currently receiving devices for transceiving the data frame is configured to generate and to notify the following to the computing means:

- a synchronization end interrupt signal as soon as the synchronization portion has been received by the receiving device;

- a reception end interrupt signal after the data portion has been received by the detection and signalling device.

In other words, the computing means of each detection and signalling device is configured to carry out protocol steps of:

- starting a timer of duration equal to the sum of an intrinsic response time of the transceiving means of the system, and of a multiple of a data transmission time of one device. In particular, the respbnse time is a time span that is required to switch from the transmission mode to the reception mode. In particular, the multiple of the transmission time is proportional to a number of devices arranged in respective upstream nodes, to which a transmission priority is allowed before starting an own data transmission;

transmitting new own data, if at the node no transmission is correctly detected which comes from the upstream nodes, within a synchronization time starting from the beginning of its own previous transmission;

- stopping the previously started timer and transmitting own data within a time equal to the response time starting from the end of the reception of data coming from an immediately upstream node, if data are correctly received from this node;

- transmitting an own frame at the prefixed instant, unless the data transmission from an adjacent node has been detected.

In particular if a detection and signalling device at one node recognizes a reception of data coming from a sending detection and signalling device at another node, the linear communication protocol comprises furthermore:

- a step of assessing the current distance between the node of the receiving device and the transmitting node;

a step of deciding whether to start or not to start said step of waiting for a predetermined time (T_R) after said step of receiving said data coming from said transmitting node, according to whether the current distance is shorter or not shorter than the reception distance k. The current distance can be computed as number of intervals between a node and a subsequent node.

According to another aspect of the invention, the computing means can comprise a data combination means for combining data selected from the group consisting of:

- signals of the physical quantity produced by different sensors of a same detection and signalling device which defines a current node;

signals of the physical quantity, and/or condition signals, that are generated in at least one device which defines a respective node different from the current node.

Alternatively, the computing means can comprise a logical decision means for:

- defining the warning condition, for example an alarm condition;

actuating the notification means.

In particular the sensors comprise a radar Doppler device, and the detection and signalling devices comprise a signal treatment means that is configured to extract a phase shift from a signal detected by the radar Doppler device, in order to evaluate the direction and a value of the speed of an object on the roadway. In particular, this allows signalling a vehicle that is moving in the wrong direction along the roadway.

Advantageously, the data combination means is configured to:

- store radar signals coming from at least one device (11M) that is located before the predetermined device, according to the vehicle travel direction of the lane;

- signalling a traffic jam on the roadway, if a speed is detected which is lower than a predetermined limit value proximate to the predetermined device, and proximate to at least one preceding device. In other words, the traffic jam condition is detected if a slow speed is detected by a plurality of adjacent devices.

Advantageously, the sensors can comprise a device for remotely detecting a temperature, the sensors configured to produce a temperature signal, and the data combination means is configured to:

receive radar signals from at least one previous node located upstream of said predetermined node according to the vehicle travel direction of the roadway lane;

- signalling a motionless vehicle condition if the temperature signal indicates the presence of a motionless object present on the roadway proximate to the predetermined device, and if a speed is detected which is lower than a second predetermined limit value proximate to at least one preceding device.

The device for remotely detecting a temperature can be configured to detect infrared waves coming from the motionless object on the roadway.

Preferably, the sensors can comprise

- a device for detecting acoustic signals; a means for analysing the energy content of sounds detected by the device for detecting acoustic signals,

and the data combination means is configured to:

receive radar signals from at least one node located upstream of the predetermined node, according to the vehicle travel direction of the lane;

— signalling a condition of accident if:

- the acoustic signals comprise typical noise components of an event associated with an accident;

a quick reduction of speed of a vehicle is detected proximate to at least one preceding device.

Preferably, the notification means is a LED light signalling means. Such solution provides low energy consumption detection and signalling devices. In particular, the intensity, the frequency of the intermittence, or the colour of the LED light signalling means can be changed for indicating conditions of different types, and for indicating the distance of the signalling device from the event that is causing the alarm condition.

According to another aspect of the invention, a method is provided whose operative steps can be carried out by means of the above described system, and with reference to the attached claims.

Brief description of the drawings

The invention will be made clearer with the description of exemplary embodiments thereof, exemplifying but not limitative, with reference to the attached drawings, in which

— Fig. 1 is a diagrammatical view of the system according to the invention;

— Fig. 2 diagrammatically shows time and space scannings of the devices of the system;

— Fig. 3 diagrammatically shows the structure of a detection and signalling device of the system according to the invention;

— Fig. 4 shows the structure of a frame used by a protocol according to an exemplary embodiment of the system;

— Fig. 5 shows a complete time diagram according to the protocol according to an exemplary embodiment of the system;

— Fig. 6 is a block diagram that shows an exemplary embodiment of the communication protocol of the system;

— Fig. 7 is a block diagram that shows another exemplary embodiment of the communication protocol of the system;

— Figs. 8, 9 and 10 are time diagrams that describe the application of the protocol in different operating conditions;

— Fig. 11 diagrammatically shows a radar device that is configured to provide signals that are demodulated in phase and in phase-quadrature;

— Fig. 12 is a block diagram of a process carried out by the system according to the invention, for detecting the speed of an object travelling along a roadway;

— Fig. 13 is a block diagram of a process carried out by the system according to the invention, for detecting the movement direction of an object travelling along a roadway;

— Fig. 14 is a block diagram of a sensor fusion step carried out by the system according to the invention, for determining the presence of a traffic jam along a roadway;

— Fig. 15 is a block diagram of a process carried out by the system according to the invention, for detecting a motionless vehicle on a roadway;

— Fig. 16 is a block diagram of a sensor fusion step carried out by the system according to the invention which follows the procedure of Fig. 15;

— Fig. 17 is a block diagram of a process carried out by the system according to the invention, for detecting an accident that has occurred on a roadway;

— Fig. 18 is a block diagram of a sensor fusion step carried out by the system according to the invention which follows the procedure of Fig. 17;

— Fig. 19 is a block diagram of a data fusion process carried out by the system according to the invention.

Description of preferred exemplary embodiments

With reference to Fig. 1 , a system is shown 1 for detecting a condition 2, in particular a danger condition, which takes place in a section 7 of a roadway 5, and for signalling such condition 2 to users of roadway 5, typically to drivers of vehicles 6 that are approaching roadway section 7.

The system comprises a plurality of devices 10 that are cooperatively configured to detect and to signal such conditions of roadway 5. Devices 10 are indicated as "intelligent devices" or simply "devices", in analogy with guardrail reflectors that are arranged along the roadways, which have, however, only the object of signalling the border of the carriageways or of the roadways, or of signalling static danger conditions. Devices 10 of system 1 according to the invention can be used together with or instead of the conventional guardrail reflectors or devices.

Fig. 1 represents a danger condition 2 comprising motionless vehicles after an accident. In any case, the danger condition can be even a vehicle that moves at a speed lower than a minimum value or a vehicle that moves at a speed higher than a maximum value, or a traffic jam that comprises vehicles that move close to one another at a speed lower than a prefixed minimum value, or vehicles that run at an excessive relative speed, or a vehicle that moves in the wrong direction, or even other conditions.

As shown in Fig. 2, each device 10 defines a node 1 1 , of a linear network V comprising a total number of devices T (i=1...T). In other words, the nodes are progressively numbered from a first node 1 1 i to a T^th node 1 1_T, along carriageway or roadway 5. As shown in Fig. 1 , more than one row 1 ',1 " of nodes 1 1 ,, 11j ... can be provided for each carriageway or lane 5', 5" of a roadway. In Figs. 1 and 2 nodes 1 1 ,, are arranged at a same mutual distance d, i.e. a interval d is defined between nodes 1 1 ,. However, the following description can be referred more in general to a case in which the distance between a couple of adjacent nodes is different from the distance between another couple of adjacent nodes. This solution can be suggested in case of low mutual visibility between devices 10 at a predetermined place of the roadway, or can be due to particular installation reasons.

As diagrammatically shown in Fig. 3, each device 10 comprises at least one sensor 13. For example, a device 10 can comprise a radar sensor 20 (Fig. 11), and/or a temperature sensor 40 (Fig. 15), and/or an acoustic sensor 50 (Fig. 17), and/or an accelerometer 60 and/or at least one sensor of a different type.

Each device 10 comprises, furthermore, computing means 14. Starting from signals 8 received by sensors 13 and/or from condition signals 9',9",9"' coming from devices 10 arranged in other nodes, computing means 14 is configured to decide whether a warning condition 2 exists in a section of roadway 5. In particular, the computing means is configured to decide whether one of the above-indicated danger conditions exists. Computing means 14 is, furthermore configured to create a condition signal 9 that identifies the warning condition 2.

Still with reference to Fig. 3, each device 10 has a means 16 for notifying condition signal 9, which is created by de device itself, to drivers 6 that are travelling along roadway 5. A notification means for notifying signal 9 can be like that described in Italian patent application ITRM2005A000495, which is incorporated by reference, for example can be a visual signalling means, preferably a LED means, and/or it can be an acoustic signalling means. The signalling means can emit a continuous or an intermittent light or sound. In the latter case, the intermittent sound has an intensity and/or a frequency and/or a duration responsive to the distance from the driver of section 7 of the roadway 5 where condition 2 is present. In particular, the intensity and/or the frequency and/or the duration increase while approaching to section 7 of the roadway where condition 2 is present.

Each device 10 that is arranged in a node 1 , has transceiving means 17, for communicating, i.e. for transmitting and receiving signals, in particular condition signals 9, to/from devices 10 of at least one neighbouring node 11_r.

In a particular exemplary embodiment, transceiving means 17 is a wireless means. The transceiving wireless means can be typically a radiofrequency means comprising a radio subsystem. For example, radiofrequency means 17 can comprise an Analog Devices ADF7020 chip, which is configured to work as described in table 1 , for example. In any case, in an exemplary embodiment, not shown, transceiving means 17 of devices 10 can also be a cable means.

If the roadway comprises more than one lane or carriageway, for example if it comprises two carriageways 5', 5" as shown in Fig. 1 , the two different frequency bands can be used, i.e. two different channels which are influenced by communication means 17 of devices 10 of respective rows 1', 1". Otherwise, a same band of frequency can be used. This is possible in a particular exemplary embodiment of the system, in which the radiofrequency transceiving means 17 is configured to carry out a frequency-division duplexing (FDD) technique, that operates in a conventional way. The transmission channel can belong to an iSM band, to avoid any interference with other radiofrequency devices. The same applies to roadways that have more than one roadway. In the following description, for the sake of simplicity, reference is made to a single row of T devices 10, i.e. to a single row of T nodes 11 ,, where i=1 ...T. With reference to Fig. 2, H modules 12_h are defined following one another. The extension of each module ^2^ is defined by a distance N. Modules 12_h) of Fig. 2 are shown as 12_{h -}i, 12_h-, 12_{h +}i that follow each other according to the two opposite possible directions of row V of devices. Actually, modules 12_h are replicated along the whole roadway portion where row 1 ' of devices extends, until a total number T is attained. A strictly progressive ID number is assigned to each node 1 1 , of each module defined by the distance N between a first integer and a second integer that is equal to the first integer plus N. For example, the progressive number can increase according to the direction opposite to a prefixed vehicle travel direction. Apart from an integer multiple of N, the progressive ID number has a 8 bit resolution. Therefore, the progressive number can range at most between 0 and 255. The nodes can be equivalently indicated as 1 1j+hN, where h is an index referring to a particular module 12_h. This way, nodes 1 1j+hN that have the same index j are corresponding nodes of different modules 12_h.

The transmission and the reception of the signals between devices 10 is carried out according to a linear communication protocol in which transmission means 17 of devices 10 of nodes 1 1j+hN, h=1 ... H, which are arranged at a mutual distance N, and belong to different modules 12_h, influence at the same time a same transmission channel, during a predetermined transmission time TT at the longest. Predetermined transmission time Tj is set between instant tj_,n and a subsequent instant t n+Tr. On the contrary, transmission means 17' of the other devices 10 of the same module defined by the distance N are not transmitting. Transmission means 17' of devices 10 of nodes 11_a+(h+i)N_> h=1... H, which are respectively adjacent to nodes 1 1_a+hN, transmit through the same channel between instant ti,_n+T_T and subsequent instant ti,_n+2T_T, and the same applies to corresponding devices of nodes 1 1_a+(h+2)N, 1 1a+(h+3)N

Nodes 1 1 _r, which are located forwards and rearwards at a distance of not more than k intervals from nodes 1 1_a+hN, 1 1_a+(h±i )N, which are transmitting at a predetermined instant, form at this same instant receiving regions, in other words they can correctly receive the signals transmitted by nodes 11_a+hN and 11_a+(h±i )N, respectively. The number N of the nodes, and transmission time T_T define an overall cycle duration, or cycle time, or synchronization time Ts_, which is equal to N times the transmission time T_T, i.e. ts = ΝχΤτ. Cycle time Ts is preferably the same for all nodes 11

The linear communication protocol is detailed further with reference to Fig. 2a). First nodes 11|_-N,11,,11,+N (more in general 11_a, 11_A+N ■••11a+hN) are considered, which are located at respective positions x*-Nd, x*, x*+Nd, i.e. are arranged at mutual distances that are multiples (h) of interference distance module N. Starting from a first instant 6i, devices 10 at first nodes contemporaneously transmit respective condition signals 9', 9", 9"'. Condition signals 9',9",9"' last not longer than transmission time T_T. Signals 9',9",9"' are received at currently receiving nodes 11_r (11_a+_P, 11a+N+p ...11 _a+mN+p, |p|≤k), which are located at a distance shorter than reception distance k from respective first nodes 11,-1, 11,, 1i+i (11a- 11a+N ...11_a+hN)- During the whole transmission time Ττ, device 10 of first node 11,-1,11,,1 ,+i (11_a+hN) is transmitting in each module 12h only. Considering now only currently receiving nodes 1 _r, for instance the nodes that are located at positions x*-Nd+d, x*+d, x*+Nd+d (Fig. 2b), (11b, 11b+N. .11b+hN, b=a+1), respectively adjacent to first nodes 11μι11,,11_i+i (11a, 11a+N..-11a+h ) of Fig. 2a). Once transmission time Ττ has elapsed, i.e. starting from an instant +Ττ, devices 10 of nodes 11_r can propagate respective condition signals 9',9",9'", i.e. they can forward said signals to further devices of currently receiving nodes 11_r, always during a time not longer than transmission time Tj. In this step of propagation, once again, only device 0 of one transmitting node transmits in each module 12_h. Therefore, a condition signal 9 migrates for one interval d along row 1 in a time equal to transmission time T_T, in at least one of the two directions of row 1.

In another exemplary embodiment, not shown, condition signal 9 migrates for more than one interval d. In other words, the transmission of condition signals 9 can be received by more than one node proximate to a given currently transmitting node 11,. This way, a breakdown of the linear network can be prevented in case of fault of the device of one node, in particular if one device is damaged by a vehicle.

Reference will now be made to Fig.2c). Once the above defined time T_s, has elapsed, i.e. at instant 6N=6I+TS, condition signals 9 have migrated for at least the distance module. The distance module is equal to N times interval d, provided a same interval d is defined between any nodes. In fact, at instant Θ module 12_h' lies between the positions x* and x*+Nd. At instant Θ1 , module 12_h'₊i was lying between the same positions. In other words, modules 12_h migrate along row 1 of nodes, and in one cycle time Ts they scan at least N nodes, i.e. the number of nodes that defines modules 12_h.

Normally, condition signals 9 that are transmitted by transmission means 17' of device 10 of node 1 1 , can be received by reception means 17" of devices 10 of nodes 1 1 _r at a maximum distance from node 1 1 j. This maximum distance depends on the power and on the sensibility of transceiving means 17. In case of a wireless communication, the maximum distance also depends on the environment, in particular by the orographic conditions of the area where the roadway is. In particular, the maximum distance can be affected by natural and/or artificial obstacles, and by the weather. Reception distance k is defined as a number of intervals d, and is an operating parameter of system 1 . Reception distance k can be selected to ensure the reception of a signal between a device 0 of node 1 1 , and a device at a node 1 1 _r where r=i±r', and r' is lower than k or equal to k. In other words, reception distance k can be chosen, in order to ensure the reception in a reception zone 2k+1 that is centered at each node 1 , and that extends for k intervals in the two directions of linear network or row 1. In particular, reception distance k can be selected to ensure the reception in most possible operating and environmental conditions.

More in detail, still with reference to Fig. 2, two contiguous modules are considered that are currently centred at nodes 1 1 M, 1 1 j..., and that are currently transmitting. These contiguous modules, besides comprising nodes 1 1 _r, also comprise M nodes 1 _s that are at a distance longer than k intervals from nodes 1 1 ,-1 , 1 1 i_> , respectively, where M is a prefixed integer. Nodes 1 1_s cannot receive signals transmitted by any of the two next currently transmitting nodes 1 1 M, 1 1 ,. More precisely, it is possible that nodes 1 _s receive only noise in a current instant, since they are too distant from both transmitting node 1 1 M and transmitting node 1 1 ,. Otherwise, nodes 1 1_s receive signals, but these signals are discarded by control means 14 because they come from a too distant node (distance >k). On the one hand, the choice of M allows adjusting the system robustness against interference; on the other hand, the choice of M allows adjusting the efficiency of the radiofrequency means. In other words, a compromise value of M can be chosen between robustness against interference and radiofrequency means efficiency. If M=0, i.e. if modules 12_h' and 12_{h +}i are immediately adjacent, a maximum radiofrequency means efficiency is obtained, but the reliability of the transmissions is reduced towards the devices that are located exactly at a distance of k intervals from nodes 11j+hN, which all can be currently busy in a transmission. In fact, nodes 11_s at a distance of k intervals can be affected by the interference caused by transmitting device 10 of a most proximate node 11_j+(h_±i)N- Once an M value has been assigned, let's consider the integer defined by the expression 2k+M+1. Such integer corresponds to the number N of nodes of each module, i.e. the module N = 2k+M+1. The number 2k+M+1 represents then the minimum distance that must lay between two nodes that are allowed to contemporaneously transmit in order to ensure, in normal conditions, k correct receptions travelling along row 1 in a first direction, and k correct receptions travelling along row 1 in the opposite direction. In other words, there are k + k nodes, at opposite sides with respect to each currently transmitting node, where the interference is not strong enough to hinder a correct data reception. Each device 10 of a node, after "talking" for a time T_T, keeps silent and waits that all the devices at a distance k have in turn talked. Device 10 can talk again only after a time Ts=T_T ^*N has elapsed. Therefore, at each repetition of the transmission time Ττ, each module of size N migrates in a direction which is opposite to the vehicle travel direction, thus ensuring a fusion of data including the physical quantity signals and the condition signals 9 that control means 14 of each device calculate starting from the physical quantity signals. More in general, each device 10 of a node transmits again at subsequent instants of a sequence of cycles, therefore the time for repeating the transmission by each node 11, is equal to ΔΤ,_,η. Therefore, the series of repeating cycles is ti,n = i,n-i + ΔΤ,η, where ΔΤ,,η is a silence time that spans between a transmission by the device of a node 11, and the following transmission by the same device.

In an exemplary embodiment, transceiving means 17 comprises a wireless means. In this case, the distance d between nodes 11, is limited by the propagation capacity of the electromagnetic signals used by the radiofrequency means. In normal conditions, this distance is about 15 metres, but it can be adjusted if particular conditions of visibility are present between devices 10. A distance of this order of magnitude allows to consider the instant at which signals 9 are transmitted at a node 11, substantially coincident with the instant at which the same signals 9 are received at the proximate nodes 11_r, where |r-i|≤k. This can be accepted since the propagation delay in air, which is about 56 ns (nanoseconds) for each interval d, is negligible with respect to the bit time which corresponds to the system data rate R. For instance, the data rate R can be advantageously set at about 200 kbps. This value corresponds to a bit time of about 5 ps, as shown in table 1.

With reference to Figs. 4 and 5, a description is given of a frame 3 which is the object of a linear communication protocol recognized by detection and signalling devices 10 of the system according to a particular exemplary embodiment of the invention. For example, a total length L of frame 3 can be 30 Byte. Frame 3 comprises a succession of fields 3a÷3f. A first preamble field 3a is used for getting through the PLL for the reception, for setting the bit synchronization, and comprises a sequence of alternate bits 1 and 0. For example, if the RF transceiving means comprises an Analog Devices ADF7020 chip, the minimum length of preamble field 3a is 24 bit. Precautionarily, preamble field 3a can comprise 40 bits. Preamble field 3a is followed by a second synchronization field or Sync 3b, which serves as a "Start Frame Delimiter" (SFD). In other words, synchronization field 3b is used for signalling the beginning of the transmission of a frame. Therefore, field 3b has a predetermined pattern that can be recognized by reception means 17" of each device 10. The physical level, i.e. reception means 17", of each device 10, notifies the beginning of the reception of frame 3 to the MAC level, i.e. to control means 14 of device 10, only after correctly receiving field Sync 3b. To this purpose, a synchronization interrupt or INT_SYNC 3w is generated (Fig. 5). In particular, field Sync 3b can have a length of 24 bit. Therefore, in this case the overall length of the fields Preamble 3a and Sync 3b is 64 bit.

A third field ID 3c contains the indication of the node where the device that transmits the data frame 3 is arranged. A fourth field CRC ID 3d is used to check the correctness of field ID 3c of node source (or the token), by an error correction code (ECC). In particular, a conventional ECC algorithm is used, which allows recovering a 1-bit error. A fifth field, Data 3e, follows, which contains the data each device 10 transmits to other devices 10 of system 1. In particular, Data 3e field contains condition signal 9. A last data field, CRC 3f, of frame 3 is used to check the correctness of field Data 3e. In particular, the correctness of Data 3e field is verified with a conventional error correction algorithm ECC.

Once a prefixed number of bytes has been received after INT_SYNC 3w, the means for receiving or physical level 17' notifies the end of the reception of frame 3 by a further interrupt of end of reception or INT_ENDRX 3z (Fig. 5), in particular this is made through the port SPORT of the DSP. Such number of bytes corresponds to the overall length of the consecutive fields 3c to 3f. In an exemplary embodiment of Fig. 3 the overall length is equal to 22 bytes, corresponding to 176 bit.

Fig. 5 shows schematically the timing of the transmission frame 3, as provided by the communication protocol, according to a preferred exemplary embodiment. In normal operating conditions, the device 10 of a node 1 , starts the transmission of an own frame 3 (Fig. 4) once a predetermined response time TR has elapsed since the end of the reception of frame 3, i.e. since reception end interrupt INT_ENDRX 3z was received from device 10 of an upstream node 11M. The transmission of frame 3 uses transmission means 17 of device 10 during frame time T_F, which is defined by length L of frame 3 and by the bit rate or data rate R of the system. In the above described exemplary embodiment, the transmission time is about 2 ms.

Transmission time T_T It is therefore the sum of frame time TF, and of response time TR. Frame time TF comprises a preamble time T_P which corresponds to the transmission of fields 3a and 3b, in other words it is the time between the beginning of the transmission of frame 3 and the transmission of synchronization interrupt INT_SYNC 3w. The remainder time between synchronization interrupt INT_SYNC 3w and reception end interrupt INT_ENDRX 3z is indicated as T_D.

Response time T_R represents the difference between the time Tj, during which the transmission channel is locally occupied by device 11,, and the time T_F that is actually required for transmitting frame 3. Response time T_R cannot be endlessly reduced, because communication means 17, in particular radiofrequency transceiving means 17', 17", must be switched from the reception mode to the transmission mode. This step requires a time that depends on the features of the radio subsystem. Furthermore, during response time TR, i.e. between the end of the reception of previous frame 3 from node 11,-1 and the beginning of the transmission of frame 3 by device 10 of node 11,, the application level of the latter device can be engaged in the computation that is required to create fields 3a-3f of frame 3. It is assumed then that the instant of transmission ti_,n can differ from predetermined response time T_R by a value comprised within an unreliability or tolerance range [-τ,+τ] of amplitude 2τ. This means taking into account possible latencies of synchronization interrupt 3w and of reception end interrupt 3z, and other conditions depending on the execution of the code by control means 14 of each device 10. By this tolerance range it is possible to determine transmission time Tj, which is obtained from the expected transmission time of a frame T_F increased by reception time T_R

In an advantageous exemplary embodiment, the operating parameters of the system have the values of table 1 , where the same notations are used as in Figs. 4 and 5, and as in the above description.

TABLE 1

Topoloqv

Distance between the nodes or hop d = 15 m

Distance of module N = 10

Reception distance k = 3

Region of possible interference M = 3

MAC

Length of the frame L = 30 bytes (constant)

Response time TR = 0.5 ms

Maximum incertitude on TR τ= 0.1 ms

Transmission time (or token) T_T = L / R + T_R = 2.5 ms

Synchronization time or cycle time Ts = N ^■ T_T = 25 ms

Channel and physical level

Physical Bit rate R = 200 kbps

Frame transmission time T_F = 2 ms

Preamble transmission time Tp = 0.24 ms

Propagation delay 56 ns (negligible)

Transmission frequency 868÷870 MHz

Communication means Analogue Devices ADF7020

Other

Stability of the clock 10 ppm (negligible) With reference to the block diagram of Fig. 6 a protocol 15 is described for accessing the radiofrequency transceiving means of device 10 of detection and signalling system 1 according to the invention. At an instant t^ .n-i , a device 10 arranged at a node 1 1 , starts a (n-1 )-th the step of transmitting 82" of a frame 3. At the end of the step of transmitting 82", device 10 executes a step of starting 83" a timer of timeout [T_R + (N-1 )T_T], which is equal to synchronization time T_s decreased by frame time TF. The timeout of the timer falls therefore at an instant t^TXi,_n = t^TXj,_n-i⁺Ts- At instant t^TXj,_n, said timer triggers a step 82" of transmission of a frame 3, if the other upstream devices do not receive any frame within a time Ts since the beginning of the last transmission. This way, the cycle defined by synchronization time T_s is fulfilled. Then, device 10 is set into a stand-by state or IDLE state 89. During IDLE status 89 device 10 waits for the timeout of current timer 81 'to fall, or for the reception 81 " of a frame 3, which is notified by a synchronization interrupt INT_SYNC 3w (Fig. 5).

In normal operating conditions, before timeout 81 " of a current timer, device 10 can detect reception 81 ' of a frame 3, notified by synchronization interrupt INT_SYNC 3w (Fig. 5). In this case, a step 82' is carried out of awaiting the end of the reception of ID 3c. Then, a step 83' takes place of identification and assessment of the CRC/ECC used, through two subsequent bytes, which correspond to fields 3c and 3d of frame 3 (Fig. 4). If no transmitting node identification error arise from step 83' of assessment, i.e. if field ID is correct, the receiving device carries out a step 84 of assessing the interval distance mylD-ID=q between the receiving device itself and the transmitting node that has been identified. On the contrary, if field ID is not right, device 10 is set into a stand-by state 89. If the step of assessment 84 gives q>1 , i.e. if transmitting node is located at a distance not longer than k intervals upstream of node 1 1 ,, device 10 carries out a step 85 of stopping the current timer, and is set into a reception state 86. In other words, in this case device 10 begins waiting the end of the reception of frame 3, which is signalled by reception end interrupt INT_ENDRX 3z (Fig. 5). Once the whole frame 3 has been received, device 10 carries out a step 87 of starting a timer, with a timeout set in a time when a new transmission 82" of a frame 3 is possible. The new timer is defined by the formula:

[1 ] t™i,n = Ι^,η+βΤτ, which can be generalized into:

[2] t^TXi,_n = t^H.n+jTT,

where j is set within [1 ,k], t^TX _iin can be always updated taking into account the last frame received.

Steps 81 '-87 are repeated for decreasing values of j. This means that device 10 awaits/verifies the reception of frames from other nodes 1 1 i_-r, where 1 <r<k and r has decreasing values. When a transmitted frame is received by the first upstream device (q=1), device 10 starts a last timer which has a timeout set to response time T_R.

Similarly, if timeout 81 " of the transmission timer t™ occurs before reception 81 ' of a desired frame 3, device 10 carries out a step 82" of transmitting a frame.

This way, the transmission of each frame 3 can be enabled within and not later than a period of time equal to response time T_R from the end of the reception of the data frame of 11 _, if a frame transmitted by adjacent node 1 1M is correctly received. For this reason, frame 3 contains ID 3c of source node 11M or, alternatively, ID 3c of the node that is enabled to transmit. In this case, the expression "token" is used. Ideally, a frame from node 1 1M is received at node 11 , every synchronization time Ts, which is the cycle duration. This way, a trace of correctly received transmissions is kept at least at the first node upstream of 1 1M, and preferably a trace of the transmissions received by downstream nodes is kept as well.

The above described process is a process of "carrier sensing" at a physical level that prevents a device 10 of a node 1 1 , of one linear module from transmitting a frame 3 (colliding) while a transmission from a device of a node of the same linear module is already present on the same channel. This can occur in two cases:

a) during step 81 ' of reception of the fields Preamble 3a and Sync 3b of a frame 3, since the system has not yet recognized the presence of this transmission, or

b) if the recognition of the field Sync 3b has failed, therefore the physical level has not emitted any synchronization interrupt INT_SYNC 3w. At the end of the step of transmitting 82", device 10 carries out a step 83"of starting a timer with a timeout set at a cycle time Ts after the beginning of the step of transmitting 82".

If timeout 81 " of the transmission timer is carried out during reception 81 ' of fields ID 3c and CRC-ID 3d, device 10 assumes that the current transmission can come only from the immediately upstream device. Therefore, the interrupt associated with the timer is ignored, and a stand-by step of duration equal to response time TR is programmed at the end of the reception (Fig. 5). At the end of this stand-by step, the step of transmitting 82' is started.

Protocol 15, as above described also allows to limit rhythm irregularities in the transmission at each node, which simplifies the treatment of the errors. In particular, protocol 15, creates in a completely distributed way, a sort of cyclical TDMA frame. In this frame no collision event is possible. Therefore, protocol 15 is reliable, deterministic and easy to be implemented.

The frequent data retransmission at each cycle of duration equal to synchronization time or cycle time Ts allows to compensate for a possible loss of one or more frames 3. Therefore, the correct and ready data transmission is not a critical issue. Therefore, difficult steps of rescue and/or of data reception acknowledgement can be omitted, which reduces the computational burden.

Protocol 15 comprises a step of keeping of a trace of the transmissions correctly received at the upstream nodes, or at least at the first of them, and preferably also at downstream nodes. This improves the system reliability, since the receiving of data about the activity of nodes 1 1 μ< 1 1 M during a given cycle n enables node 1 1 , to assess its own transmission time, even if one or more proximate nodes are out of order. For instance, if at node 1 j a frame 3 is received from node 11 ,-2, and if no frame is received from node 11M , however, node 1 1 j can transmit once a time T_T+T_R has elapsed since the end of the data frame that was received from 1 1 ,-2.

In an advantageous exemplary embodiment, which is described in detail hereinafter, the communication protocol comprises a procedure of elaborating and aggregating the data detected by the sensors. To this purpose, a device 10 of a generic node 1 1, must have received at least field Data 3e of frame 3 from other nodes, in particular from one or more upstream nodes 1 1 ,_-Γ, with l£r<k, and must have carried out the step of keeping of a trace of the correctly received transmissions.

In a particular exemplary embodiment, also the transmissions of devices 10 that are located downstream of node 1 1 , are detected by device 10 of node 1 1,. This way, it is possible to forward notifications and other data even in the vehicle travel direction.

As described above, the physical level, i.e. transceiving means 17, notifies the beginning of frame 3 to each device 10 only after correctly receiving synchronization field Sync 3b. Preferably, the MAC level, i.e. control means 14 of each device 10, is configured to calculate the instant when the transmission of frame 3 from node 1 1M, t^TXj.i ,_n began. In fact, this instant occurred a time Tp the above notification. Possible shifts, which can be caused by a missing interrupt, can be incorporated into the unreliability range ±τ (Fig. 5).

For example, the starting instant of a new step 82" of transmission of a frame 3 by device 10 of node 1 1 , t j,_n is obtained as the weighed average on all the correctly received frames. In other words the following formula is used:

[3] t^TXi,_n = cij - 1.

This way, multiple errors are less likely to occur, even if 1 _μι is very late. This enables a random starting up of the devices, with no reference to the nodes.

The communication protocol also provides a system start-up procedure. In an exemplary embodiment of the system, such system start-up procedure comprises a step of exclusive listening of a device 10, during which device 10 does not transmit any frame 3 until it has detected a transmission from a proximate node.

Always in the system start-up procedure, a leading node can be defined, where a device 10 is configured to start the frame-transmission wave by a first- time frame 3 transmission.

Preferably, each device 10, after being switched on, is configured to wait for the reception of a plurality of frames 3 before starting an own transmission of a frame 3. In particular, each device 10 is configured to wait for two frames 3 before transmitting. This way, the transmission start-up propagates from a device to another device not every TT but every TS+TT„ In other words, (table 1), the transmission start-up propagates every about 27.5ms by a standard interval, for example a 15 metres interval. This way, the transmission start-up propagates by about 1 Km of roadway in 1 second.

Advantageously, the transient system start-up procedure provides that devices 10 are started up following an increasing ID, starting from a first node. In this case, no further procedure step is required apart from the steps that are required for the steady operation of the system, which are provided by the protocol according to the invention. In fact, each node, apart from the first one, receives a frame from a precedent node, not later than a time Ts after being switched on.

Preferably, if devices 10 are started according to an increasing node order, the protocol provides a start time limit Ti_n>Ts, after which device 10 cannot be switched on. This way, the device of a node 1 1 , is prevented from being switched on exactly a time Ts after a previous node 1 1 M has been switched on. Such a condition could cause an interference of two transmissions, i.e. two frame transmission steps could be started at the same time at two nodes of a same linear module.

Furthermore, by maintaining a trace of the transmissions correctly received at a node 1 1 j during the system start-up, problems that can arise if one or more nodes are out of order from the beginning can be solved.

The block diagram of Fig. 7, represents a version of a particular exemplary embodiment of protocol 15 of Fig. 6. According to the version of Fig. 7, the result of assessment 84 of distance mylD-ID between a generic receiving node and the transmitting node is accepted only if q=1. In other words, this result is accepted only if the transmitting node is identified as a node adjacent to the receiving node, at which assessment 84 is carried out. Therefore, only the data frame coming from device 10 of node 11_M adjacent to the generic node 11, are accepted. In the embodiment of Fig. 7, once the reception of this frame has been completed, no further timers are started, in other words it is not necessary to wait for/verify the reception of any frame from another node 1 1 i_-r with 1 <r<k, unlike the case of Fig. 6. Step 87 is replaced by a step 88 of waiting the time T_R Once time T_R has elapsed, device 10 starts a step 82" of transmitting a frame 3.

The operation of a version of protocol 15 of Fig. 6 is described with reference to Figs. 8, 9 and 10. According to this different embodiment, the computing means 14 of device 10 of each node 1 1 , is configured to accept messages, in particular condition signals 9, from three preceding nodes 11,-3, 1 1 _i-2, 1 1 M, which are adjacent to one another. Fig. 8 shows an ideal operating condition, in which the data are correctly received from all the three allowed nodes 11_i-3, 1 1 _ι-2, 1 1 ι-ι. Each of these nodes corresponds to axes 11i_-3, 1 1 i-2, 11 M _, 1 1j, along which frame 3 is shown as it is received from the device of node 11 j,₃, 1 1 j_-2, 1 1 M_, 1 1 i- Moreover, frames 3 are shown along axis 1 1 , as they are received at node 1 1 ,. The transmission time of frame 3 by nodes 11,-3, 1 1 i-2, 11μι is considered coincident with the time in which the same frame 3 is received at node 1 1 ,. The instant 90 corresponds to the end of the step of transmitting 82" (Fig. 6) of frame 3 by node 1 1,. Therefore, at instant 90 computing means 14 of device 10 starts a timer 4 of duration T_r+3TT, with a timeout set at the instant t™,^ t^TXi,_n-i + Ts. In other words, the nominal duration of timer 4 is equal to nominal cycle time Ts, starting from the beginning t^ n-i of the previous frame transmission by node 1 1 ,. The timeout indicates the instant t^i.n at which a data transmission will take place at node 1 1 ,, in order to respect cycle time Ts of the system. At instant 91 , before the timeout of timer 4 elapses, the device of node 1 1 i receives interrupt INT_SYNC 3w (step 81 ', Fig. 5), which notifies a frame 3 sent by node 11,-3, which is located three intervals upstream of node 11,. Then a step 82' starts of waiting for the end of the reception of field ID 3c and of field CRC ID 3d. At instant 92, this enables a step 83' of identifying and assessing node 11 ,-3, and also enables a step 84 of assessing the distance of the transmitting node. At instant 93 both step 83' and step 84 have been completed. Since mylD-ID=3, device 10 of node 1 1 , stops timer 4 (step 85), and waits for the end of the transmission of frame 3 (step 86). The end of the transmission of frame 3 is signalled by interrupt INT_ENDRX 3z at instant 94. A new timer 4' is then started of duration T_R+2T_T, with timeout set at the instant t^TXi,n= 3T_T. In other words, the nominal duration of timer 4' is equal to 3 times the transmission time T_T, starting from the beginning of the reception of

TX

frame 3 from node 1 1 ,-3, which still coincides with the t j,_n expected according to cycle time Ts. At instant 91 ', before the timeout of timer 4' elapses, the device of node 1 i receives a new interrupt INT_SYNC 3w (step 81 ') that notifies the reception of a new frame 3, sent by node 1 1 j.2, which is located 2 intervals upstream of node 1 1 ,. Then a new step 82' starts of waiting for the end of field ID 3c and of field CRC ID 3d of new frame 3. At instant 92', this enables new steps 83' and 84 of identifying and assessing node 1 1,-2, and of assessing the distance of the transmitting node. At instant 93, steps 83' and 84 have been completed. Since mylD-ID=2, device 10 of node 1 1 , stops timer 4' (step 85) and waits for the end of the transmission of new frame 3 (step 86). The end of the transmission of new frame 3 is signalled by interrupt INT_ENDRX 3z at instant 94'. A further timer 4" is then started of duration T_R+T_T, with timeout set at the instant t^TXi,n= t^^n - 2T_T. In other words, the nominal duration of timer 4" is twice the transmission time T_T starting from the beginning of the reception of frame 3 coming from node 1 1 ,-2, which still coincides with the t¹*^ expected according to cycle time Ts. At instant 91 ", before the timeout of timer 4" elapses, the device of node 1 1 i receives a further interrupt INT_SYNC 3w that notifies the reception of a further frame 3, sent by node 1 1M , which is located immediately upstream of node 11 j. Then a further step 82' starts of waiting for the end of field ID 3c and of field CRC ID 3d of further frame 3. At instant 92", this enables further steps 83' and 84 of identifying and assessing node 1 1 M , and of assessing the distance of the transmitting node. At instant 93" steps 83' and 84 have been completed. Since mylD-ID=1 , device 10 of node 1 1 j stops timer 4" (step 85) and waits for the end of the transmission of the further frame 3 (step 86). The end of the transmission of the further frame 3 is signalled by a further interrupt INT ENDRX 3z at instant 94". Still another timer 4"' is then

TX RX

started whose duration is TR, with timeout set at the instant t ,,„= t M ,n+ τ. In other words, the nominal duration of timer 4"' is equal to one transmission time T_T starting from the beginning of the reception of still another frame 3 from

TX

node 1 1M, which still coincides with the t expected according to cycle time T_s. At instant 95, when timer 4"' elapses, device 10 of node 1 1 , carries out a step 82" of transmitting an own frame 3 once again.

With reference to Fig. 9, the case is described in which the reception of all the frames coming from nodes 1 1 j_3, 1 1 j.2, 1 1 M fails at node 1 1 ,. At the end of a the step of transmitting 82" of a frame 3 (Fig. 5'), i.e. at instant 90, device 10 of node 1 1 , starts a timer 4 of duration T_R+3T_T, with timeout set at the instant t^TXi,n= ^,,^1 + Ts. In other words, the nominal duration of timer 4 is equal to

TX

nominal cycle time Ts, starting from the beginning t ,,_η-ι of the previous frame transmission by node 11,. When timer 4 elapses, i.e. at instant 95, device 10 has not received any interrupt 3w, therefore it carries out the step of transmitting 82" an own frame 3 once again.

Fig. 10 shows the intermediate case in which the reception of the frames coming from two immediately preceding nodes 11_i-2, 11M fails at node 11, while the reception of a frame from a node 11,-3, three nodes upstream of node 11,, is carried out successfully.

Fig. 11 diagrammatically shows an exemplary embodiment of a radar sensor 20 of detection and signalling device 10 of system 1. Radar 20 is a Doppler radar that provides signals 21' and 21" at an intermediate frequency, which are respectively demodulated both in phase and in quadrature. The operation of radar 20, and of associated devices 30' and 30" for treating signals produced by the radar (Figs. 12 and 13), is described hereinafter. In particular, reference is made to the detection of the speed of a target, i.e. of an object observed by the radar, such as a vehicle, and to the detection of the travel direction of the target, which can therefore be a vehicle moving in the wrong direction.

Radar sensor 20 is based on the architecture of the quadrature-phase reception, which is necessary for detecting the vehicle travel direction of a target. More in detail, radar device 20 is configured to operate with two antennas. A transmitting antenna is used for the transmission 22' and a receiving antenna is used for the reception 22". A local oscillator 23 provides a signal 24' that is sent to transmitting antenna 22' that broadcasts it. Signal 24' is reflected by a target, the speed of which must be assessed. Then a reflected signal 24" is created, which is received by receiving antenna 22" and is amplified in an amplifier 25 of device 10. In particular, amplifier 25 can be a Low Noise Amplifier (LNA). The amplified signal produced by amplifier 25 is sent to a signal splitter 26 that sends it to mixers 27', 27". Mixers 27', 27" provide intermediate frequency signals 21' and 21", respectively in phase and in quadrature, which are obtained as the difference between original signal 24', provided by local oscillator 23, and the respective radiofrequency signal. As known, the radiofrequency signal shows an apparent frequency change due to the relative movement of the target with respect to the radar, i.e. due to the Doppler effect. In other words, radiofrequency signal 24" contains a shift- Doppler information.

Intermediate frequency signals 21' and 21" are transferred to a signal treatment device (DSP) 30. This treatment device is described by means of the block diagrams of Figs. 12 and 13. Treatment device 30 comprises a first treatment portion 30' for assessing the speed of the target, and a second treatment portion for assessing the travel direction of the target.

First treatment portion 30' (Fig. 12) comprises a band-pass filter 31', which can be a conventional one, and a following sequence 32' of digital filters. The digital filters can be conventional as well. Filters 32' are configured to preliminarily treat signals 21' and 21", which provides a filtered signal 33'. In a particular exemplary embodiment, as shown in Fig. 12, filtered signal 33' is treated by a fast Fourier transform in a computing means 34'. Accordingly, computing means 34' creates a frequency-domain transformed signal 35'.

Therefore, the signal analysis can be carried out both in the frequency domain and in the time domain.

In a particular exemplary embodiment, as shown in Fig. 12, an inertial finite-state machine 36' is provided for filtering transformed signal 35'. This cuts off the noise due to unavoidable mechanical vibrations, to the wind and to false targets, and a filtered transformed signal 37' is obtained. A means 38' is also provided for carrying out an frequency spectral analysis of filtered transformed signal 37'. Such analysis provides the speed of the target as this is "seen" by radar device 20. With the available radar devices, target speed values between 5 and 255 Km/h can be detected.

Second treatment portion 30" (Fig. 13) is in turn provided with a band-pass filter 31", which can be a conventional one, and of a following series 32" of digital filters. The digital filters can be conventional as well. Filters 32" provide phase filtered signals 33" and quadrature-phase filtered signals 35". An analysis means 38" is also provided for calculating and analysing the phase of the Doppler signal from signals 33" and 35". This way, the travel direction of the target can be determined.

More in detail, for a quadrature-phase demodulator:

I = A cos(cp),

Q = A sin((p),

from which:

φ = arctan(Q/l)

where φ is the phase of the signal received at the antenna and reflected by the target. If phase φ is positive, the target is approaching to radar 20, whereas if phase φ is negative, the target is moving away from radar 20.

As shown in Fig. 14, radar devices 20 of devices 0 also allow to detect a traffic jam along a roadway lane. To this purpose, control means 14 of each device 10 comprises a means 39 for carrying out a step of data fusion of radar data 37' (Fig. 12), as computed in a device 10 of a node 11, and data coming from devices 10 of preceding nodes 11j, where j<i, and of following nodes 1j, where j>i, with respect to the travel direction of carriageway 5', 5" or of roadway 5. For example, the radar data involved in the step of fusion 39 are obtained by an analysis procedure 30', as shown in Fig. 12 and as described above. A traffic jam condition is assessed only if:

- a speed lower than a predetermined limit value is detected at a node 11, and at a predetermined number c' of nodes 11,_-C' that precede node 11,,

at a predetermined number c" of nodes I that follow it, the speed is not lower than said predetermined limit value, c',c">0.

This means that there are many slow vehicles close to one another between node 11i and node 11i_-m, with m<c'.

As diagrammatically shown in Fig. 15, in a particular exemplary embodiment system 1 comprises devices 10 that are provided with a temperature sensor 40 that can remotely detect, with no contact, the temperature of a body. In particular, the sensor can be a radiation temperature sensor, that is configured to detect the position of the body by means of an electromagnetic wave emitted by the body itself, whose power and wavelength depend on the temperature of the body.

Alternatively, the radiation temperature sensor 40 can be a pyrometer, i.e. a sensor that is configured to detect a change of a visible light wave. Alternatively, the radiation temperature sensor 40 can be an infrared temperature sensor, which can detect the infrared waves emitted by a body such as a car or a living being. More in particular, reference will be made hereinafter to the use of a thermopile 40. It is however to be understood that any suitable temperature sensor of known type can be used. More in detail, thermopile 40 consists of an array of pixels or elementary infrared sensors that are arranged to obtain a field of vision 41. The thermopile also includes a sensor for detecting the room temperature and a microcontroller that can provide the detected data directly on a digital interface. Temperature sensors 40, in cooperation with radar devices 20, allow to detect the presence of bodies like a motionless car 42 on roadway 5, proximate to a node 1 1 ,. As Fig. 15 also indicates, temperature sensor 40 is configured to provide a temperature signal from objects like a motionless car 42, within its field of vision 41. A temperature signal treating means 45 is associated to temperature sensor 40, for treating signals of temperature 43 that are produced by sensor 40 and that are influenced in case a plurality of objects is present within field of vision 41. Treating means 45 is configured to execute an algorithm that provides an average value of temperature signals 43 in at least two different time windows, in order to find out temperature differences that indicate the presence of a body such as motionless vehicle 42. This way, false targets can be quite reliably discriminated. Furthermore, control means 14 of each device 10 comprises a data fusion means 39 for executing a step of fusion of data comprising treated temperature signals 44, as provided by thermopile 40 of device 10 of node 1 1 ,, and the signals provided by radar sensors 20 (Fig. 1 1) of devices 10 of nodes 1 1_j, j<i, upstream of node 1 1 ,. In fact, the presence of motionless vehicle 42 is necessarily preceded by a deceleration of the vehicle 42, detected by radar 20 in upstream nodes 1 Ί_]. Therefore, the presence of motionless vehicle 42 is recognized by the computing means 14 of a device 10 of node 1 1 , only if its own thermopile 40 detects a motionless object in its own field of vision, and if radar sensors 20 of a certain number of devices in the preceding nodes 1 j<i have detected a target that travelled at a speed lower than a predetermined threshold.

Fig. 17 diagrammatically shows an exemplary embodiment of system 1 in which devices 10 are provided with an acoustic sensor 50, such as a microphone. For example, acoustic sensor 50 can be a conventional passive sensor of "electret" type, which is suitable for detecting capacity variation, such as condenser microphones. In any case, they do not require any electric supply, due to the material in which they are made. This reduces the energy costs of system 1.

Acoustic sensors 50, together with radar devices 20, allow to detect an event 52, such as an accident on roadway 5, proximate to node 1 1 j. As Fig. 15 also indicates, the audio signal received by microphone 50 is treated in a bandpass filter 51 ', which produces a filtered signal 53. The band-pass filter can be a conventional band-pass filter. This allows to enhance the frequency components which relate to events of interest, such as the passage of a vehicle, the collision between vehicles or the collision of a vehicle with an obstacle or with an element of the roadway. Also a screeching sound of tyres during a sharp braking can be recognized, which normally precedes and/or characterizes an accident. An analysis means 55 is also provided for analysing filtered signal 53, which is configured to carry out an algorithm that, starting from the amplitude of the signal in the domain time, assesses its energy content and supplies a treated signal 54. A finite-state machine 56 analyses treated acoustic signals 54 and allows to assess the presence of one of the above mentioned events of interest, and of other events of interest. Control means 14 of each device 10 also comprises a means 39 for executing a step of fusion of data comprising treated acoustic signals 54, as provided by acoustic sensor 50 of device 10 of node 11,, and the signals provided by radar sensors 20 (Fig. 11) of devices 10 of nodes 11_j, j<i, upstream of node 11,. The condition of accident (Fig. 12), is recognized only if:

- the elaboration of the acoustic signals detected by acoustic sensor 50 of node 11 i indicates a particular audio event comprising corresponding frequencies;

radar devices 20 of a certain number of devices 10 of nodes 11j, j<i, 1 , upstream of node 11, have detected a deceleration such as a sharp braking before a collision.

For example, the frequencies can be the typical frequencies of an event of interest such as the above mentioned events.

A further exemplary embodiment of the system, not shown, comprises a plurality of devices 10 comprising respective accelerometers. An accelerometer is a device suitable for assessing whether the device itself has a particular acceleration, for example an acceleration higher than a predetermined value. The devices also comprise a means for treating the signals provided by the accelerometer. This exemplary embodiment allows detecting an event such as an impact of a vehicle against the device, which can affect the performances and the reliability of the latter. It also allows to treat in a particular way, or even to ignore, data which come from the sensors of the device.

As described above, transceiving means 17 is configured to notify condition signals 9, referred to a local, variably extended status of roadway 5, or to forward messages provided by computing means 14 of a device 10 of a node 11j, to other devices 10 of nodes 11i.j, until a predetermined distance is covered. In particular, transceiving means 17 is configured to notify condition signals 9 to devices 10 of a plurality of nodes 11₄ which precede alarmed node 11i, according to the vehicle travel direction of the supervised carriageway or roadway.

Besides alarm indications, condition signals 9 can contain:

— various information, such as weather conditions, presence of fog banks, and the like;

— messages of data useful to detect critical conditions;

— polling messages, where in particular polling messages are useful for determining critical conditions that can be detected by a remote central operating unit, not shown.

As shown in Fig. 19, and as anticipated when describing Figs. 14, 16 and 18, computing means 14 of each device 10 is configured to carry out a data fusion algorithm. This algorithm, using the data provided by sensors 13 after the elaboration by the CPU of the same device 10 of a node 11,, as well as the data provided by upstream and/or downstream devices, decides whether a relevant condition, i.e. a warning condition 2 is present, by carrying out the above described logical step. The data can come from a sensor such as a radar device 20 and/or a temperature sensor 40 and/or an acoustic sensor 50 and/or an accelerometer. The combination, i.e. the fusion, of the data is carried out by a decision logical process which does a combination of the data detected by sensors 13 of device 10 of node 11, and those provided by the other nodes 11_j, where j≠i, which are received along with condition signals 9 through transceiving means 17.

The procedure of data fusion 70 in device 10 of node 11, is automatically started whenever a reception 71 of data occurs. In other words, data fusion 70 takes place whenever a condition signal 9 is received, for example as a data package or frame 3, from another device 10 of node 11j. Data fusion procedure 70 comprises a verification step 72 for checking the presence of an alarm condition within condition signal 9.

If an alarm condition is detected, computing means 14 of device 10 start an alarm step 73 in which they actuate optical and/or acoustic signalling means 16 for notifying the alarm condition to the users of roadway 5. Then, computing means 14 carries out verification steps for checking the presence of further conditions of alarm that can be deducted by condition signal 9 and by the physical quantity signals 8 obtained by sensors 13 of the same device. In particular, computing means 14 can carry out:

— a step 74 of checking the presence of a motionless vehicle 42 (Figs. 15 and 16), where a physical quantity signal is acquired from temperature sensor 40 of the device of node 1 1 and/or

a step 75 of checking if an accident 52 has occurred (Figs. 17 and 18), where a physical quantity signal is acquired from acoustic sensor 50 of device 10 which defines node 1 1 i.

If at verification step 72 no alarms are present in the data packages that reach node 1 1j, steps 76, 77, 78 are started of checking particular danger conditions by a step of fusion of data coming from device 10 that is arranged at node 1 1 , with data coming from devices that are located at upstream nodes 1 1j, where j<l, and/or at downstream nodes 1 1j, where j>i.

In particular, steps are provided of:

— assessing 76 the presence of a traffic jam proximate to node 1 1 ,, where the radar data produced by the device of node 1 1 , are analysed along with the radar data produced by the devices of the upstream and downstream nodes, in particular of nodes 1 1 M and 1 1 ,+i adjacent to node 1 1 ,;

— assessing 77 the presence of a motionless vehicle proximate to node 11 ,, where the data produced by temperature sensor 40 of the device of node 1 1 j are analysed along with the radar data produced by the devices of the upstream nodes, in particular by the devices of the fifth node 1 1 _i-5 and of the sixth node 1 1 _i-6, starting from node 1 1 ,;

— assessing 78 whether an accident has occurred proximate to node 11,, where the data produced by acoustic sensor 50 of the device of node 1 1 , are analysed along with the radar data produced by the devices of the upstream nodes, in particular by the devices of the fourth node 1 1 _i-4 and of the fifth node 1 1i_-5, starting from node 1 1 ,.

Furthermore, a subsequent step 79 can be provided of assessing the presence of a specific danger condition as detected by steps 76, 77, 78. In a verification step 79 at least one danger condition of the above-indicated type can be recognized, or also another danger condition such as a vehicle moving in the wrong direction. In this case, the system starts an alarm step 80 in which the optical and/or acoustic signalling means is actuated to notify the danger condition to users 6 of roadway 5. The values produced in the process of data fusion are coded in a message that is sent by transmission means 17" of device 10 of node 11 j, such that it can be received by a predetermined number of devices 10 of adjacent nodes 11j.

The data used by the logical blocks for defining condition 2, diagrammatically shown in Figs. 9, 10" and 11", are chosen in a way depending on the position of nodes 11, and on the extension of the fields of vision of sensors 13.

In a particular exemplary embodiment, system 1 is also an interface means providing an interface with a remote central operating unit, not shown as well. This interface means is not represented, but is preferably localized in a subset of nodes 11 i. In particular, the interface means can be a cabled means, or a wireless means. In an exemplary embodiment, the wireless interface means can comprise LAN or WLAN data networks. The interface means allows:

- transmitting data to the central operating unit and notifying them to addressees who are different from users 6, for example a roadway or motorway manager;

- checking the status of the system by operators of the central operating unit.

Preferably, the central operating unit is configured to generate an alarm status, and the interface means is configured to transfer this alarm status to devices 10, in a form that is similar to condition signal 9.

In another particular exemplary embodiment, the devices comprise or are associated with an in situ electric energy generating means, such as solar cells, for electrically supplying the active components of the system.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

1. A system (1) for detecting a warning condition (2) in a section (7) of a roadway (5) and for notifying said condition (2) to users (6) of the roadway

(5) , in particular for detecting a danger condition (2) on the roadway (5) and/or signalling said danger condition (2) to drivers of vehicles (6) running towards said section (7) of roadway (5), comprising a plurality (T) of detection and signalling devices (10) in use arranged along the roadway (5) at a predetermined interval (d) from one another, wherein each detection and signalling device (10) defines a node (11,, i=1...T) of a data network, each of said detection and signalling devices (10) comprising:

- at least one sensor (13) that is configured to detect a physical quantity in a portion of said section (7) of roadway (5), and to produce a signal (8) of said physical quantity;

a communication means (17) that is configured to transfer said signal (8) of said physical quantity between said detection and signalling devices (10) that are present along the roadway (5), said communication means comprising a transceiving means (17717") that is configured to transceive said signal of said physical quantity (8) from said detection and signalling device (10) to/from another detection and signalling device (10) different from said detection and signalling device (10) that is present along the roadway (5);

a computing means (14) that is configured to create a condition signal (9), which describes said condition occurring in said section (7) of roadway (5), starting from at least one physical quantity signal (8) which comes from said detection and signalling device (10) that is arranged at said section (7) of roadway (5), and/or from other detection and signalling devices (10) by said communication means (17),

a frame-forming means (14) for forming a frame (3) of data which includes physical quantity signals (8) and/or condition signals (9) that are created o received by each detection and signalling device (10);

- a notification means for notifying said warning condition to said user

(6) of the roadway (5), characterised in that each detection and signalling device (10) comprises a means for executing a linear communication protocol (15), said linear communication protocol comprising:

- defining a reception distance k as a predetermined number (k) of intervals (d) along the roadway (5), such that ,said reception distance comprises a corresponding number of devices (10) that are arranged along the roadway (5), said reception distance k selected such that a transceiving range of one of said detection and signalling devices (10) does not extend along the roadway (5) up to devices (10) that are arranged beyond said reception distance k;

- defining a distance module as a number N of intervals (d), said distance module greater than said reception distance k, such that N>2k + 1 , said distance module selected such that two of said nodes (11_a, 11₃+N) that are distant from each other as said distance module are allowed to contemporaneously transmit said frame to other nodes (11_a+p, 11_a+N+p|p|≤k) that are arranged along the roadway (5) at a distance shorter than said reception distance (k);

contemporaneously transmitting (82") said data frame (3) on a same transmission channel, during a predetermined transmission time (T_T), by a plurality of detection and signalling devices (10) that are arranged along the roadway (5) at nodes (11_a, 11_a+N - -Ha+hN) that are distant from each other as said distance module, towards other detection and signalling devices (10) that are located at nodes (11_a+_P, 1 _a+N+p -Ha+mN+p |p|≤k) within the reception distance (k) from each detection and signalling devices (10) of said plurality, and maintaining a still stand state by all the other detection and signalling devices (10) which do not belong to said plurality;

- iterating said step of transmitting for other pluralities of detection and signalling devices (10) for further respective transmission times until all the detection and signalling devices (10) that are present along the roadway (5) have carried out said step of transmitting;

- cyclically repeating said steps of transmitting and iterating;

transferring said warning condition if the warning condition is present within said data frame (3) for at least one of said detection and signalling devices (10) in a known position, to a predetermined number of detection and signalling devices (10) that are located upstream of said position according to a predetermined vehicle travel direction along said roadway.

2. A system according to claim 1 , wherein each detection and signalling device (10) is configured to carry out said step of sequentially iterating said step of transmitting (82") according to a direction which is opposite to the vehicle travel direction of said vehicles (6) in the roadway (5), such that the step of transmitting (82") for all the nodes (1 1 ,) of the network lasts a respective transmission time (T_T), such that each node is allowed to transmit again after a repetition time Ts=T_T ^*N, and at each iteration after the transmission time (T_T), each module of size N migrates according to a direction which is opposite to said vehicle travel direction (5), allowing a data fusion which consist of said physical quantity signals (8) and of said condition signals (9) that are calculated at said nodes by each detection and signalling device (10).

3. A system according to claim 1 , wherein said protocol comprises, during said step of maintaining a still stand state by all the other devices (10) which do not belong to the plurality of devices at said nodes (1 1j) that are carrying out the transmission, a step of waiting (86) a predetermined response time (T_R) after the end of a reception condition of said frame, coming from one of said other nodes (1 1j._j) which are different from said nodes (1 1 ,).

4. A system according to claim 3, wherein said linear communication protocol (15), comprises furthermore for each currently receiving node (1 1 i):

- starting (83", 87) a timer immediately after a receiving step (86) has been completed or after said step of transmitting (82") a frame has been completed, said timer having a predetermined timeout;

- awaiting and recognizing (89) an event, said event selected from the group consisting of:

said timeout (81") of said timer;

a reception (81 ') of data coming from other nodes (1 1₄) which are different from said currently receiving node (11,); and, after said timeout event (81 ") has expired, said protocol is configured to carry out said step of transmitting (82"), whereas after said step of receiving (81 ') said protocol is configured to carry out steps of:

stopping (85) said timer;

waiting (86) for said response time (T_R) to elapse, after completion of said reception of data coming from one of said nodes (1 1 ^) which are different from said currently receiving node (1 1 j).

5. A system according to claim 1 , wherein said frame (3), which includes said physical quantity signals (8) and/or said condition signals (9), comprises a synchronization portion (3b), which serves for signalling the beginning of said step of transmitting (82"), and a data portion (3e), which comprises said physical quantity signals and/or said condition signals, and said communication means (17) of one of said devices (10) for transceiving said frame is configured to generate and notify to said computing means (14):

- a synchronization end interrupt signal (3w) as soon as said synchronization portion has been received by said receiving device (10);

- a reception end interrupt signal (3z) after said data portion 3e has been received by said detection and signalling device (10).

6. A system according to claim 3, wherein said linear communication protocol (8) is configured furthermore for:

- recognizing, by a detection and signalling device (10) which defines one of said nodes (1 1 ,), a reception (81 ') of data coming from a sending detection and signalling device which defines a node (1 1j);

if said recognition has occurred:

- assessing (84) the current distance between said node (1 1 ,) of said receiving and signalling device and said transmitting node (1 1j)

- deciding whether to start or not to start said step of waiting (86) for a predetermined time (T_R) after said step of receiving said data coming from said transmitting node (1 1_j), according to whether said current distance is shorter or not shorter than a predetermined maximum distance.

7. A system according to claim 1 , wherein said computing means (14) comprises a data combination means (39) for combining data selected from the group consisting of:

signals of said physical quantity produced by different sensors (20,40,50,60) of a same detection and signalling device (10) which defines a current node (11,);

- signals of said physical quantity and/or condition signals produced in at least one detection and signalling device (10) which define a respective node (11,) different from said current node (11,).

8. A system according to claim 1 , wherein said computing means (14) comprises a logical decision means that is configured for:

- defining the warning condition, such as an alarm condition, and activating said means;

- notifying said warning condition to said users (6) of the roadway (5).

9. A system according to claim 7, wherein said sensors comprise a radar Doppler device (20), and said detection and signalling devices comprise a signal treatment means (30', 30") that is configured to extract a phase shift (φ) from a signal detected by said radar Doppler device (20), in order to evaluate the direction and a value of said speed (v) of an object (2) on the roadway (5),

in particular, to signal a vehicle moving in the wrong direction along the roadway (5).

10. A system according to claim 9, wherein said data combination means (39) is configured to:

- store radar signals coming from at least one device (11M) that is located before said predetermined device, according to said vehicle travel direction of said lane; i

- signalling a traffic jam on the roadway (5) if a speed (v) is detected which is lower than a predetermined limit value proximate to said predetermined device (11,), and proximate to at least one preceding device (11,-1 ).

11. A system according to claim 7, wherein

- said sensors comprise a device (40) for remotely detecting a temperature, said sensors configured to produce in use a temperature signal; said data combination means (39) is configured to:

- receive radar signals from at least one node (11M) located upstream of said predetermined node according to said vehicle travel direction of said carriageway (5);

signalling a motionless vehicle condition (2) if said temperature signal indicates the presence of a motionless object present on the roadway (5) proximate to said predetermined device (11,), and if a speed (v) is detected which is lower than a second predetermined limit value proximate to at least one preceding device (11_M).

12. A system according to claim 11 , wherein said device for remotely detecting a temperature (40) is configured to, detect infrared waves coming from said motionless object on the roadway (5),

13. A system according to claim 11 , wherein

said sensors comprise a device (50) for detecting acoustic signals;

- a means is provided for analysing (55) the energy content of sounds detected by said device (50) of detecting acoustic signals;

- said data combination means (39) is configured to:

- receive radar signals from at least one node located upstream of said predetermined node according to said vehicle travel direction of said lane;

signalling a condition of accident (2) if: _:

- said acoustic signals comprise typical noise components of an event associated with an accident,

- a quick reduction of speed of a vehicle is detected proximate to at least one preceding device.

14. A method (1) for detecting a warning condition (2) in a section (7) of a roadway (5) and for notifying said condition (2) to users (6) of the roadway (5), in particular for detecting a danger condition (2) on the roadway (5) and/or signalling said danger condition (2) to drivers of vehicles (6) running towards said section (7) of roadway (5), comprising the steps of:

- arranging a plurality (T) of detection and signalling devices (10) along the roadway (5) at a predetermined interval (d) from one another,

- making a data network, wherein each detection and signalling device (10) defines a node (11,, i=1...T) of said data network,

- detecting a physical quantity in a portion of said section (7) of roadway (5), by means of a sensor (13) that is arranged in each of said detection and signalling devices (10), and producing a signal (8) of said physical quantity;

transferring said signal (8) of said physical quantity between said detection and signalling devices (10) that are present along the roadway (5) by communication means (17) of each of said detection and signalling devices (10), said step of transferring comprising steps of transmitting/receiving said signal of said physical quantity (8) from said detection and signalling device (10) to/from another detection and signalling device (10) different from said detection and signalling device (10) that is present along the roadway (5);

- creating, by a computing means (14) of each of said detection and signalling devices (10), a condition signal (9) that describes said condition occurring in said section (7) of roadway (5), starting from at least one physical quantity signal (8) coming from said detection and signalling device (10) that is arranged at said section (7) of a roadway (5), and/or from other detection and signalling devices (10), by said communication means (17),

- forming, by a computing means (14), a frame (3) of data which includes physical quantity signals (8) and/or condition signals (9) that are created o received by each detection and signalling device (10);

- notifying said warning condition to said user (6) of the roadway (5) by a signalling means of each of said detection and signalling devices (10), characterised in that each detection and signalling device (10) recognizes a linear communication protocol (15) that provides the steps of:

defining a reception distance k as a predetermined number (k) of intervals (d) along the roadway (5), such that said reception distance comprises a corresponding number of devices (10) that are arranged along the roadway (5), said reception distance k selected such that a transceiving range of one of said detection and signalling devices (10) does not extend along the roadway (5) up to devices (10) that are arranged beyond said reception distance k;

defining a distance module as a number N of intervals (d) that is longer than said reception distance k, such that N>2k + 1 , said distance module selected such that two of said nodes (11a, 11a+N) that are located distant from each other as said distance module are allowed to contemporaneously transmit said frame to other nodes (1 1 a+p, 1 1 a+N+p|p|≤k) that are arranged along the roadway (5) at a distance shorter than said reception distance (k);

- contemporaneously transmitting (82") said data frame (3) on a same transmission channel, during a predetermined transmission time (Ττ), through a plurality of detection and signalling devices (10) that are arranged along the roadway (5) at nodes (11_a, 11_a+N - - 1 1 a+hN) that are distant from each other as said distance module, towards other detection and signalling devices (10) that are located at nodes (11 a+p, 11_a+N₊p- - 11_a+mN+p |p|≤k) within the reception distance (k) from each detection and signalling devices (10) of said plurality, and maintaining a still stand state by all the other detection and signalling devices (10) which do not belong to said plurality;

- iterating said step of transmitting for other pluralities of detection and signalling devices (10) for further respective transmission times until all the detection and signalling devices (10) that are present along the roadway

(5) have carried out said step of transmitting;

- cyclically repeating said steps of transmitting and iterating;

- transferring said warning condition if the warning condition is present within said data frame (3) for at least one of said detection and signalling devices (10) in a known position, to a predetermined number of detection and signalling devices (10) that are located upstream of said position according to a predetermined vehicle travel direction along said roadway.

A method according to claim 14, wherein said step of sequentially iterating said step of transmitting (82") is carried out according to a direction which is opposite to the vehicle travel direction of said vehicles

(6) in the roadway (5), and said step of transmitting is iterated such that said step of transmitting (82") for all the nodes (11,) of the network lasts a transmission time (T_T), such that each node is allowed to transmit again after a repetition time T_S=T_T ^*N, and at each iteration after the transmission time (TV), each module of size N migrates according to a direction which is opposite to said vehicle travel direction (5), allowing a data fusion which consist of said physical quantity signals (8) and of condition signals (9) that are calculated at said nodes by each detection and signalling device (10).

16. A method according to claim 14, wherein said warning condition is an irregular speed condition of a vehicle (6) or of an object that is comparable to a vehicle present on the roadway (5).

17. A method according to claim 14, wherein said irregular speed condition is selected from the group consisting of:

- a motionless vehicle (2), in particular a damaged vehicle (2,42);

- a vehicle moving at a speed lower than a prefixed minimum value;

- a vehicle moving at a speed higher than a prefixed maximum value;

- a couple of vehicles having a relative speed higher than a prefixed maximum value;

- a traffic jam, i.e. a plurality of vehicles following one another at a speed lower than a prefixed minimum value;

- a vehicle moving at a speed of direction which is opposite to the prefixed vehicle travel direction of a carriageway of said roadway, i.e. a vehicle moving in the wrong direction.

18. A method according to claim 14, wherein said step of maintaining a still stand state by all the other devices (10) which do not belong to the plurality of devices at said nodes (1 1,) that are carrying out the transmission, comprises a step of waiting (86) a predetermined response time (TR) after the end of a reception condition of said frame, coming from one of said other nodes (11 ,-_j) which are different from said nodes (1 1 ,).

19. A method according to claim 18, wherein said linear communication protocol (15), for each currently receiving node (1 1 ,), comprises the steps of:

- starting (83", 87) a timer immediately after a receiving step (86) has been completed or after said step of transmitting (82") a frame has been completed, said timer having a predetermined timeout;

awaiting and recognizing (89) an event, said event selected from the group consisting of:

said timeout (81 ") of said timer;

a reception (81 ') of data coming from other nodes (11^) which are different from said currently receiving node (1 1 ,);

wherein after said timeout event (81 ") has expired, said step of transmitting (82") is activated, whereas after said step of receiving (81 ') the steps are provided of:

stopping (85) said timer;

waiting (86) for said response time (TR), after completion of said reception of data coming from one of said nodes (1 1j._j) which are different from said currently receiving node (1 1 ,).

20. A method according to claim 17, wherein said step of forming said frame (3), which includes said physical quantity signals (8) and/or said condition signals (9), comprises a step of creating a synchronization portion (3b) of said frame (3) that serves for signalling the beginning of said step of transmitting (82"), and a data portion (3e) of said frame (3) that comprises said physical quantity signals and/or said condition signals, and steps are provided of generating and notifying to said computing means (14):

- a synchronization end interrupt signal (3w), as soon as said synchronization portion has been received by said receiving device (10);

- a reception end interrupt signal (3z), after said data portion (3e) has been received by said detection and signalling device (10).

21. A method according to claim 18, wherein said linear communication protocol (8) comprises the steps of:

- recognizing, by a detection and signalling device (10) which defines one of said nodes (1 1 j), a reception (81 ') of data coming from a sending detection and signalling device which defines a node (1 1_j);

if said recognition has occurred:

- assessing (84) the current distance between said node (1 1,) of said receiving and signalling device and said transmitting node (1 1_j)

- deciding whether to start or not to start said step of waiting (86) for a predetermined time (T_R) after said step of receiving said data coming from said transmitting node (1 1_j), according to whether said current distance is shorter or not shorter than a predetermined maximum distance.

22. A method according to claim 21 , wherein in said step of assessing (84) said current distance is computed as a number (q) of intervals (d) between a node and a subsequent node.

23. A method according to claim 14, wherein a step is provided of combining data by said computing means (14), said data selected from the group consisting of:

- signals of said physical quantity produced by different sensors (20,40,50,60) of a same detection and signalling device (10) which defines a current node (1 ,);

- signals of said physical quantity and/or condition signals produced in at least one detection and signalling device (10) which defines a respective node (1 1 ,) different from said current node (1 1 ,).

24. A method according to claim 14, comprising the steps of:

- deciding i.e. recognizing the warning condition such as an alarm condition, by said computing means (14);

- notifying said alarm condition to said users (6) of the roadway (5).

25. A method according to claim 23, comprising the steps of:

- radar Doppler detection by radar Doppler means (20) of said detection and signalling devices (10);

- treating said signal of said physical quantity (8) for extracting a phase shift (φ) from said signal of said physical quantity detected by said radar Doppler device (20), in order to assess the direction and the value of said speed (v) of an object (2) on the roadway (5),

In particular, in order to signal a vehicle that is running in the wrong direction along the roadway (5).

26. A method according to claim 25, comprising the steps of:

storing radar signals coming from at least one preceding device (11j.i) upstream of said predetermined device according to said vehicle travel direction of said lane, by said means and signalling a traffic jam condition on the roadway (5), if a speed (v) is detected which is lower than a predetermined limit value proximate to said predetermined device (1 1,), and proximate to at least one preceding device (1 1 M).

27. A method according to claim 23, comprising the steps of:

- remotely detecting the temperature (40) in said section (7) of roadway (5);

- creating a temperature signal of an object in said section (7) of roadway;

- receiving a radar signal from at least one node (1 1M) that is located upstream of said predetermined node according to said vehicle travel direction of said carriageway (5);

- signalling a motionless vehicle condition (2) if said temperature signal indicates the presence of a motionless object present on the roadway (5) proximate to said predetermined device (1 1 ,), and if a speed (v) is detected which is lower than a second predetermined limit value proximate to at least one preceding device (1 1 M).

28. A method according to claim 27, wherein said step of remotely detecting the temperature (40) comprises a step of detecting infrared waves coming from said motionless object present on the roadway (5),

29. A method according to claim 27, comprising the steps of:

- detecting acoustic signals by an acoustic device (50) of said sensors;

- analysing (55) the energy content of sounds detected during said step of detecting acoustic signals;

- receiving radar signals from at least one preceding node located upstream of said predetermined node according to said vehicle travel direction of said lane;

- signalling a condition of accident (2) if:

said acoustic signals comprise typical noise components of an event associated with an accident,

- a quick reduction of speed of a vehicle is detected proximate to at least one preceding device.