EP3942320A1

EP3942320A1 - Method for detecting a position change of a radio receiver

Info

Publication number: EP3942320A1
Application number: EP20731526.8A
Authority: EP
Inventors: Apostoslos KOUNTOURIS; Philippe SURBAYROLE
Original assignee: Orange SA
Current assignee: Orange SA
Priority date: 2019-03-20
Filing date: 2020-03-20
Publication date: 2022-01-26
Also published as: FR3094094A1; WO2020188227A1

Abstract

The invention relates to the detection of a position change of a radio receiver, characterized by: - said receiver acquiring (P1) a radio signal at a given time, - determining (P2) a set of at least one radio transmitter from the radio signal, - comparing (P3) said set of at least one radio transmitter with at least two sets of previously recorded radio transmitters, - determining (P4) whether the radio receiver has changed position on the basis of said comparison.

Description

DESCRIPTION

Method for detecting a change in the position of a radio receiver

The present invention relates to the field of the location of an object and more particularly to the detection of a change in the position of an object by analysis of the surrounding radio signal.

As part of future developments towards the Internet of Things (IoT), the number of connected objects deployed will increase considerably. A very large part of these objects will be very constrained devices on the one hand at the hardware level, with simple and inexpensive hardware to produce, and, on the other hand, at the energy consumption level so as not to have to charge them. too regularly.

However, these objects must be connected to radio networks in order to be able to communicate information on their status, measurements, state, etc. These objects may also need to know their position or, at least, position change information in order to inform a service or a third party in real time or in deferred time. Take the example of a communicating object installed on a bicycle that detects a change in position, it can trigger an alert system that can inform its owner or an operator to report this change of position.

In addition, on the one hand, access via Wifi or mobile radio communication (EDGE, UMTS and LTE etc.) is not always available and, on the other hand, these networks were not designed to optimize consumption. terminals. This therefore poses a problem for connected objects which must greatly reduce their consumption because they must remain autonomous for long periods of time. Geolocation solutions using a GPS module or even triangulation solutions via mobile base stations are therefore not recommended in these cases because they also consume too much energy.

In these cases, it would therefore be useful for the object to be able to determine on its own a change of location without necessarily having to know this change in detail and without even knowing its precise location. Indeed, it would be useful for the object to be able to answer the following question: has the object moved? Yes or no. It would even be useful to integrate a certain level of mobility status of the object linked to its past actions such as: the object is still moving, the object has just stopped moving, the object is still stationary , the object has just moved.

Solutions have been designed and implemented in order to overcome these problems and in particular by using the Bluetooth © Low Energy protocol (also called BLE) which optimizes the terminal's consumption and makes it possible to communicate with other terminals equipped with these modules. In this register, we can cite the method described in the document US 20160021499 A1 which makes it possible to determine a change of position of a terminal equipped with a BLE module by a scan of the latter towards other BLE terminals in its surroundings. The terminal therefore requests the other terminals to know their identity and their position in cases where the GPS is not available or when it is desired to save the battery of the terminal.

This solution, although effective, can still be improved in the context of the Internet of Things because it requires a number of conditions to function correctly, such as:

the implementation of protocol (s) between the nearby terminal (s) such as BLE or Wifi, which, on the one hand, limits the spectrum of terminals that can be contacted as well as the range and, on the other hand, involves the implementation of a communication protocol between the terminal seeking to determine its mobility and the surrounding terminals, which can be a factor in energy consumption and costs,

the transmission of terminal location information in the environment of the terminal seeking to determine its mobility, which further reduces the scope of use of these methods because they are dependent on external terminals having knowledge of their location coordinates, which requires that they have an automatic system for determining their location in operation or, where applicable, that they have been configured so as to know their coordinates,

the explicit identification of the terminals that are within the perimeter of the terminal seeking to know its mobility.

The invention seeks to improve the state of the art by proposing a method and a device making it possible to know whether a terminal has changed position and even to provide information on the dynamics of this terminal without prerequisites on the radio protocol used and the data. information conveyed in the radio signal of surrounding transmitters. This method does not have the disadvantages listed above because it is not restricted to one or two radio protocols, which makes its scope of use wider. This method also does not require having to activate a radio transmission module to communicate with other terminals, which makes it possible to achieve substantial savings in terms of consumption.

One of the aims of the invention is to remedy the drawbacks of the aforementioned state of the art.

To this end, an object of the present invention relates to a method for detecting a change in the position of a radio receiver, implemented by a computing device, characterized in that it comprises the following:

acquire by said receiver a radio signal at a given time,

determine a set of at least one radio transmitter from the radio signal,

compare said set of at least one radio transmitter with at least two sets of previously registered radio transmitters,

based on said comparison, determining whether the radio receiver has changed position. Thanks to the invention, it is possible to determine the presence or absence of at least one radio transmitter and to use this information in order to estimate a change in the position of a radio receiver, without this receiver needing to initiate a communication or even to request other terminals to retrieve useful information, such as the identifier of the transmitters and their location. Compared with existing solutions, the fact of not needing to initiate communication with other terminals optimizes the energy consumption of the radio receiver.

Moreover, the invention is not dependent on obtaining information of the location of surrounding terminals in order to be able to determine whether the radio receiver has moved or not. This increases its scope of use in detecting transmitters that do not necessarily have a location module or do not know their position. Thus, the invention advantageously makes it possible, following the acquisition of a radio signal by the receiver, to identify radio transmitters at a given time and to deduce a change in position therefrom.

According to a particular embodiment, said determination of a set of at least one radio transmitter comprises:

on the basis of said acquired radio signal, calculate at least one item of information characterizing at least one radio transmitter present in said set of at least one radio transmitter,

search for said at least one item of information in a plurality of items of information previously recorded,

according to the result of the search, generate and record at least one identifier associated with said at least one item of information.

Thanks to this embodiment, it is possible to precisely characterize at least one radio transmitter from the radio signal acquired by the receiver. The techniques used for this characterization are well known to those skilled in the art such as, for example, "fingerprinting" type techniques. These techniques use artificial intelligence algorithms to identify, in the form of the radio signal, the peculiarities that characterize a transmitter. These peculiarities make it possible to differentiate one sender from another and therefore to identify it, thereafter, with almost certainty. This embodiment offers the advantage of dispensing with data external to the receiver in order to be able to identify a transmitter. The processing performed by the invention works regardless of the technology or protocols used by the radio transmitters. This embodiment also creates a database that can be queried to ensure that the sender is not already known to the receiver or not. Depending on the result of the interrogation, the embodiment makes it possible either to name an identifier on the basis of an identifier already known to the receiver, or to generate a new name if the sender is not known.

According to a particular embodiment, said determination of said set of at least one radio transmitter uses an analysis of radio frames containing at least one identifier of a radio transmitter. Thanks to this embodiment, it is thus possible to extract valuable information such as the identifier of the transmitter, its geographical position, its operating state, etc. This is done by protocol analysis of the signal according to various standards in force, such as the Bluetooth Low Energy © (BLE) or Wifi wireless communication standards. In addition, this information can be used to make reliable decision-making in the event that the processing carried out according to the previous embodiment is neither able to define reliable information on a change in position of the receiver, nor able to identify an issuer. Such processing by analysis of radio frames proves to be particularly effective with a slight increase in energy consumption.

According to a particular embodiment, said at least one item of information characterizing at least one radio transmitter is recorded in correspondence with said given instant.

Thanks to this embodiment, it is thus possible to create a database which makes it possible to follow the evolution over time of the presence of radio transmitters in the vicinity of the receiver. This temporal evolution makes it possible to complete a database used as a resource in order to calculate a new moment of acquisition of the signal adapted to the context of mobility of the receiver. This database also allows the invention to perform various data processing operations related to the temporality of acquisitions such as, for example, to select transmitters over a defined time range.

According to a particular embodiment, said at least two sets of previously recorded radio transmitters are selected in a time range between an instant prior to said given instant and said given instant.

Thanks to this embodiment, and in order to perform said comparison, it is thus possible to select only the sets of radio transmitters associated with recent acquisitions. Indeed, the results of the comparison are more efficient if the method performs the comparison with the transmitters determined recently because this makes it possible to detect recent changes of transmitters and therefore to determine with a higher probability a change in position or not of the receiver. .

According to a particular embodiment, said comparison comprises determining a second set of at least one transmitter, this second set being common to both said set of at least one radio transmitter and to said at least two sets of transmitters previously recorded radio.

Thanks to this embodiment, it is thus possible to identify the issuers common to the issuers determined during the last acquisition and to the issuers determined during prior acquisitions. It is by this type of comparison that the method of the invention can determine with a high probability a change in the position of the receiver.

According to a particular embodiment, said determination, whether the radio receiver has changed position, is a function of at least one threshold. Thanks to this embodiment, the method significantly improves the reliability of the result of the determination when the radio receiver has changed position. A first case arises if the number of shared transmitters determined in the previous embodiment is greater than or equal to a first predefined integer. In this case, the method therefore considers that the similarities are significant between the set of transmitters determined during the last acquisition and during the prior acquisitions. The sets of transmitters selected during the prior acquisitions have been judiciously chosen such as, for example, the last acquisitions made previously at said given time.

A second case arises if the number of shared transmitters determined in the previous embodiment is less than a second predefined integer. In this case, the method estimates that the probability that the receiver has changed position is very high and therefore validates a change of position without additional calculation steps. A third case arises if the number of shared transmitters determined in the previous embodiment is less than the first predefined integer and greater than or equal to the second predefined integer. In this case, the method considers that the change in position of the receiver is not determined and that this change remains to be validated. This case represents a gray area for the process which cannot decide with sufficient certainty whether the receiver has moved or not. In this case, the method can perform further steps in order to determine whether the receiver has changed position or not. The method refines its assessment of change in position to determine whether the receiver is moving slowly or is stationary. To do this, it searches for common transmitters between the last signal acquisition and each of the previous acquisitions. The evolution over time of the number of transmitters in common then allows the method to estimate whether the receiver is moving slowly or is finally stationary. Indeed, it is possible that the number of transmitters in common varies slowly but continuously over time, the determining method as well as the receiver moving slowly and therefore that it has changed position. Conversely, it is possible that the number of shared transmitters fell rapidly following a maintenance action on the transmitters which caused the displacement and replacement of two transmitters but that it was previously stable. This event is therefore analyzed as being one-off by the method and is therefore not linked to the movement of the receiver. The method therefore concludes that the receiver has not moved. The advantage of such a refinement of the evaluation of the change of position is to propose a reliable estimation method for a change of position in cases which are however not very obvious. For example, it may be that a single fixed transmitter in a set of ten fixed transmitters is not identified in the last acquisition. Is it due to a movement of the receiver or to a movement of this fixed transmitter or even to a stop in the operation of this fixed transmitter? With this method, the uncertainties can be removed by a judicious choice of the values of the first and second numbers. This choice of value for the first and second numbers can be made manually and adjusted empirically. It can also be done directly by the process by setting up rules that allow optimize these values according to the context of the radio environment around the receiver and its history (last movements of the receiver, number of fixed and mobile transmitters) and the requirements of the user or receiver manager (margin d 'error tolerated).

According to a particular embodiment, the result of said determination, if the radio receiver has changed position, defines the instant of acquisition of a next radio signal.

The invention also makes it possible to optimize the energy consumption of the receiver by performing only the acquisitions useful for determining information on the change of position of the receiver, in particular in the case where the receiver has been stationary for a certain time. As presented above in the statement of the technical issue, in the field of the Internet of Things, energy consumption is an essential factor because some objects cannot be recharged easily and therefore require high energy autonomy. Furthermore, this alternative embodiment makes it possible to make the calculations performed by the method more reliable, in particular in cases where the receiver is in motion.

In fact, in this case, according to the process, acquisitions are made over shorter timeframes. Depending on the dynamic state of the receiver, depending on the method, several strategies can be defined for determining the next acquisition date, such as:

the receiver has been stationary for some time (receiver stationary for several acquisitions of the signal) and, in this case, the method may decide to proceed to a next measurement within a long time since it is unlikely that the receiver will change position in a short delay,

the receiver has just changed position (stationary receiver at least during the penultimate acquisition of the signal and mobile during the last signal acquisition) and, in this case, the method may decide to proceed to a next measurement in a short delay because it is probable that the receiver will change position within a short time (it has already moved, so the probability is not negligible that it will continue to move in the near future),

the receiver has been in motion for a certain time (mobile receiver for several acquisitions) and, in this case, the method may decide to proceed to a next measurement within an even shorter time as it is very likely that the receiver will change position in a short delay (it has been moving for a while, so there is a high probability that it will continue to move in the near future),

the receiver has just stopped (mobile receiver during the penultimate acquisition but stationary during the last acquisition) and, in this case, the method may decide to increase the delay for the next measurement because it is very likely that the receiver does not change position within a short time (it has just stopped, so it is unlikely to move in the near future). The various aforementioned embodiments or characteristics can be added independently or in combination with one another, to the method of detecting a change in position of a radio receiver, as defined above.

Also disclosed is a radio receiver including a processor that is configured to implement the following:

acquire by said receiver a radio signal at a given time,

determine a set of at least one radio transmitter from the radio signal,

based on said comparison, determining whether the radio receiver has changed position.

Such a receiver is in particular able to implement the aforementioned method of detecting a change of position, according to any one of the aforementioned embodiments.

The invention also relates to a computer program comprising instructions for implementing the method for detecting a change in the position of a radio receiver, according to any one of the particular embodiments described above, when said program is executed. by a processor.

Such instructions can be stored permanently in a non-transient memory medium (of the receiver and / or of a server communicating with the receiver).

This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other. desirable shape.

The invention also relates to a recording medium or information medium readable by a computer, and comprising instructions of a computer program as mentioned above.

The recording medium can be any entity or device capable of storing the program. For example, the medium can comprise a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or else a magnetic recording means, for example a USB key or a hard disk.

On the other hand, the recording medium can be a transmissible medium such as an electrical or optical signal, which can be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded from an Internet type network.

Alternatively, the recording medium can be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the aforementioned change of position detection method. Other characteristics and advantages of the invention will emerge more clearly on reading the following description of particular embodiments, given by way of simple illustrative and non-limiting examples, and the appended drawings, among which:

- Figure 1 shows the main actions performed by the method of detecting change of position of a radio receiver according to one embodiment of the invention;

- Figure 2 shows in more detail one of the actions executed by the method of Figure 1;

- Figure 3 shows in more detail another of the actions executed by the method of Figure 1;

- Figure 4a shows in more detail another of the actions executed by the method of Figure 1;

FIG. 4b represents in more detail another of the actions executed by the method of FIG. 4;

- Figure 5 shows a temporal description of different phases of one of the embodiments of the invention;

- Figure 6 illustrates the initialization phase of the embodiment of Figure 5;

FIG. 7 illustrates the phase of determining the change in position of the receiver of the embodiment of FIG. 5;

FIG. 8 shows in detail one of the actions performed by the method in another embodiment; and

- Figure 9 shows a device for detecting a change in the position of a radio receiver, implementing the method for detecting a change in position of a radio receiver in Figure

1.

detailed description

General principle of the invention

The general principle of the invention is, by means of a radio receiver, to acquire a radio signal for a given duration, to carry out an adapted processing of this signal in order to identify the transmitters which are at the origin. of the acquired radio signal. The signal acquisition time depends on several parameters such as for example the type and the underlying protocol (s) of the acquired radio signal but also its quality or power, etc. In the remainder of the description, we will consider that the date of acquisition of the signal corresponds to a marking of time during the period of acquisition of this signal without determining this date more precisely. In addition, for technical reasons, the signal may be recorded in a memory of the receiver of the RAM (Random Access Memory) type or a permanent memory such as for example a hard disk or an SSD type disk (standing for “Solid State”). Drive ”). This will allow the processing to be carried out either on the fly, that is to say directly after the acquisition of the signal, or a posteriori. This step makes it possible to have an estimate of the transmitters in the vicinity of the receiver. To image the invention, one can apply an analogy between the radio receiver and the human being by explaining that the receiver picks up a "radio landscape" or a "radio environment map" as a human being might see a landscape or a map. The receiver performs a step of processing the acquired radio signal. The treatments which can be carried out are not described in this invention but there are no particular restrictions. The treatment to be performed is often dependent on the type and the underlying protocol of the radio signal received. Signal processing is considered to be any processing method making it possible to identify a transmitter, whether by analyzing radio frame (s) according to a defined protocol (example of Bluetooth® or Wifi protocols) up to techniques such as “Fingerprinting” of analysis of the singularities of a radio signal allowing the identification of transmitters with certainty. These techniques allow a characterization of the singularity of each transmitter by the analysis of their radio signal. The invention does not depend on a specific method for analyzing and processing the radio signal, but is compatible with each of these methods as long as they allow the transmitter of this signal to be precisely identified.

The process, after having identified and named a set of transmitters in its vicinity, registers this set in a database. It then checks if there is a similar transmitter set in its history of previously registered transmitter sets. The method first looks into the near past and delves deeper into previous recordings if it is unable to decide on a change in the position of the receiver based on the near past.

The method, after having determined a change of position or not of the receiver, calculates a new date of acquisition of a radio signal in order to take into account the frequency of changes of position or not of the receiver and thus make the estimations of determination of the receiver more reliable. his change of position.

Particular modes of carrying out the invention

There is described below, with reference to Figures 1 to 9, a method for detecting a change in the position of a radio receiver.

Such a process takes place as follows.

In Figure 1, there is illustrated, from P1 to P4, the main steps defining the invention. In PI, the method, via the receiver, acquires a radio signal at a given instant. In P2, the method, following processing of the received radio signal, counts the various radio signals transmitted by a set of transmitters in the vicinity of the receiver in order to determine this set. This radio transmitter set represents a radio transmitter list that may contain an empty set, one or more radio transmitters. The method then gives an identifier to each transmitter and constitutes a database containing this identifier as well as time data corresponding approximately to the instant of acquisition of the radio signal. The identifier can already be present in the radio signal or, where appropriate, the method can generate a unique identifier for each transmitter of this set of transmitters. In addition, the identifier can be formalized in any possible way allowing a reliable and simple identification of the issuer. For example, the identifier can take the form of a series of numeric or alphanumeric characters or a mixture of the two. In the case where the acquired radio signal does not allow a reliable determination of the radio transmitter assembly, the method can restart step PI to perform a new determination which confirms or invalidates the previous radio transmitter assembly determination (s) . In P3, the method compares the name or names of the transmitters of the set determined during the last acquisition with certain transmitters already recorded in the database created in P2. In P4, the method, on the basis of the comparison performed in P3, determines whether or not the position of the receiver has changed. After this determination, the method restarts the step PI of acquiring the radio signal at a new given instant. This instant being determined by the method following the result (s) of the last determination (s) of change of position of the receiver. It may be that the step in P4 does not allow a change of position to be determined with sufficient certainty. In this case, the method relaunches a step of comparison at P3 of the current set of radio transmitter with another set or other groups of sets of transmitters which have been recorded in the aforementioned database.

In FIG. 2, at P2, a set of emitters originating from said acquired radio signal is determined. In P21, an item of information I_Ex_T characterizing a transmitter Ex issuing from the signal acquired at an instant T. This item of information can be generated by “fingerprinting” type methods well known to those skilled in the art. . In R2G, another piece of information I'_Ex_T is generated which characterizes the transmitter Ex from the signal acquired at time T. This information can be extracted from the analysis of the radio frames of the acquired radio signal. For example, the information extracted can be the MAC address of the Ex transmitter which is, for example, available in the Wifi or Bluetooth® frames. The two sub-steps P21 and P21 'can be performed independently of one another or it is also possible to first perform step P21 and, in order to make the determination more reliable, also perform step P21' or in reverse order. Other methods of identifying a transmitter can be the subject of new steps P21. They can be incorporated without modifying the general principle of the invention. The information I_Ex_T and I'_Ex_T are recorded in a database BDD1 or in a memory of the random access memory RAM. In P22, a comparison is made of the information I_Ex_T and I'_Ex_T generated during the respective steps P21 and P21 'with the information already available in the database BDD1 if this database BDD1 already contains these information identifying the transmitters determined during the prior acquisitions of radio signals according to the method of the invention. Otherwise, the comparison can be carried out with another memory having information for identifying the transmitters determined during the prior acquisitions of radio signals according to the method of the invention. If one of the information I_Ex_T and I'_Ex_T is already present in the database BDD1, then the process can reuse the information already present in the memory BDD1 to name the Ex transmitter. If this is not the case, it is recorded this information in the database BDD1 and, to link the two pieces of information I_Ex_T and I'_Ex_T to a transmitter, the method can generate a name to identify the transmitter Ex which is associated with the information I_Ex_T and I '_Ex_T. This name can then also be recorded in the database BDD1 as well as the information I_Ex_T or G_Ec_T identifiers. In P23, a set of transmitter (s) E_T is formed which is either an empty set 0 if there are no determined transmitters in the radio signal, or a list of transmitters. The list of transmitters is made up of one of the items of information I_Ex_T or F_Ex_T, or of the two items of information, or of a name linked to this information, for each transmitter. This set is associated with an instant T linked to the acquisition of the signal which made it possible to constitute this set. The set E_T is then recorded in a database BDD2. The BDD1 database can also have information from the lists of transmitters.

In FIG. 3 at P3, there is a step of comparing said set of radio transmitter E_T with at least two sets of radio transmitter E_T-1, ..., E_T-j, ..., E_T-N previously recorded in the database BDD2, at respective instants Tl, ..., Tj, ..., TN. In P31, the at least two sets of radio transmitters E_T-1 ... E_T-j ... E_T-N, such as N> 2, are reduced to at least two sets of radio transmitters E_T -1, ..., E_T-C, such that N> C> 2. The information storage of at least two sets of radio transmitters E_T-1, ..., E_T-C can be done in the database BDD2 or in the RAM of the radio receiver. This reduction of the sets serves as a basis for the comparison with the set E_T. It makes it possible to compare the transmitters of the last acquisition at time T with the transmitters of the previous acquisitions over a period of time up to approximately an instant T-C. In P32, the comparison is performed in order to detect the common emitter (s) between the set E_T and each of the sets E_T-1, ..., E_T-C. A set of transmitters in common, Ec_C_T, as well as a number of transmitters in common, Nc_C_T, the result of mathematical operations of the intersection type carried out between the different sets, are recorded in a database BDD3.

In FIG. 4a at P4, a determination is made whether or not a change in position of the radio receiver is made. In P41, a comparison is made of the number of common transmitters Nc_C_T and of a first number K1. If Nc_C_T is greater than or equal to K1 (Y in FIG. 4a) or as a variant, strictly greater than K1, then it is considered that the receiver has not moved and a position change value is recorded in a database BDD4 VAL_T at 0. If Nc_C_T is less than K1 (N in FIG. 4a) or as a variant, less than or equal to K1, then the method goes to step P42. In P42, a comparison is made between the number of common transmitters Nc_C_T and a second number K2. If Nc_C_T is strictly less than K2 (Y in FIG. 4a) or in a variant, less than or equal to K2, then the receiver is considered to have moved and a position change value VAL_T at 1 is recorded in the database BDD4. In the opposite case (N in FIG. 4a), a new comparison P3 is implemented over a new time range [T; TG], so as to obtain at least two sets of radio transmitters E_T-1 ,. .., E_T-C, as determined in P31, from a reduction of the sets of radio transmitters obtained between the instant T and the instant TG. The new time range [T; TG] is calculated by the method or determined manually. In P43, for each new comparison which did not allow in P41 and P42 to determine a change in position of the receiver, then the method increments a counter by one. unit Ck = k, k representing the number of increments. If Ck is greater (or greater than or equal) to a predefined number K, the method considers that it is not possible to determine a change of position at this stage and therefore launches step P44. In P44, a new instant T + l of acquisition in PI of the next radio signal is determined as a function of the history of the position change values VAL_T, VAL_T-1, VAL_T-N calculated at the instants correspondents T, Tl, ...., TN.

In Figure 4b at P44, the time T + 1 of the next PI acquisition is determined. The method, in P441, extracts from the database BDD4 N + l values 0 or 1 assigned respectively to the N + l position change values VAL_T, VAL_T-1, ..., VAL_T-N determined during the acquisition of signals between time T and time TN. This sequence of values associated with the temporal data provides an indication of the evolution of the changes in position and therefore of the displacement of the receiver. Indeed, if for example, the last 3 determinations of VAL_T that is VAL_T, VAL_T-1, VAL_T-2 each give the value 0, then the process can deduce that the receiver is in a dynamic of the type: "the receiver does not move more ". On the other hand if the last 3 determinations of VAL_T that is VAL_T, VAL_T-1, VAL_T-2 give the following values 1; 1; 0, then the method can deduce that the receiver is in a dynamic of the type: "the receiver comes from s 'stop moving'. We can thus count 4 types of dynamic types according to the information of the database BDD4. DI can represent the dynamic state "the receiver is still not moving", D2 can represent the dynamic state "the receiver has just moved", D3 can represent the dynamic state "the receiver continues to move" and D4 can represent the 'dynamic state' the receiver has just stopped moving '. Based on the 4 dynamic states D1, D2, D3, D4, the method defines rules in order to determine the instant of the next acquisition. In the case of D1, as the receiver has been stationary for some time, the method decides to increase the time between two AT acquisitions without exceeding a maximum time ATmax. This is to save the receiver battery. In the case of D2, since the receiver has just moved, the method decides to reduce the time between two AT acquisitions in order to take into account the strong probability of a rapid change of transmitters close to the receiver, due to the movement of the receiver. In the case of D3, as the receiver continues to move, the method decreases the time between two AT acquisitions without falling below a minimum time ATmin. This allows the method to be able to more accurately track transmitters close to the receiver despite it being in motion. In the case of D4, since the receiver has just stopped moving, the process decides to increase the time between two AT acquisitions in order to save the receiver's battery.

According to an alternative embodiment illustrated in FIG. 5 at P5, a specific scheduling in time of the phases of an alternative embodiment of the method according to the invention is defined, such an alternative mode being broken down into two phases: a first phase of initialization and a second phase of determining a change in position of the receiver. The initialization phase, to be operational, requires that the receiver is stationary. The objective being to determine whether the receiver has changed position, the method therefore first of all seeks to identify the fixed transmitters in the surroundings of the receiver. During this initialization phase, the receiver performs periodic measurements of the radio signal in PI and, after processing, identifies in P2 and P3 the transmitter (s) common to all of these measurements. The method therefore defines a set of transmitters in common which are very probably fixed seen from the Euclidean frame of reference of the receiver because the transmitters are identified during all of the acquisitions made in P1. Steps PI, P2 and P3 can be reproduced on a period Dinit Ti so that the method calculates a set of invariable common emitter during each radio signal acquisition in this period. This set is called the reference set. To calculate the reference set, the method carries out M acquisitions of radio signals at instants Ti-M, Ti- (Ml), ... Ti-j ..., Ti-1, Ti during the duration Dinit_Ti which must be as close as possible to a duration fixed by the method or for example a user of the receiver or an administrator of a fleet of receivers. The method calculates the reference set Ec_M_Ti by comparing, as in P32, the transmitters common to the different sets of transmitters determined during the acquisitions in Ti-M, Ti- (Ml), ... Ti-j ..., Ti- 1, Ti. If the reference set is empty (If Ec_M_Ti = 0), then the receiver determines a new acquisition date Ti according to the step described in P44. This sequence of steps represents the first initialization phase of the method according to the invention. The second phase consists in determining a change in position of the receiver. For this, the method acquires a signal at time T (subsequent to Ti), determines a set of transmitters in its vicinity and compares it with the reference set determined during the phase of initialization. If there is a substantial difference between the two sets, then it is determined at P4 that there is a high probability that the receiver has changed position. In order to improve the reliability of the process, it can be defined:

- as in P4, a minimum number of transmitters in common between the most recent acquisition and the set of transmitters in common calculated during the initialization phase, below which the method determines that there is a high probability of change of position of the receiver, and

- as in P4, also another number, greater than the minimum number of transmitters, below which the method determines that there is a doubt about a change in position of the receiver. In this case, the set of issuers identified during the most recent acquisition phase is compared with the history contained in the database BDD2 of the sets of issuers identified for each of the previous acquisitions, in order to validate or not a change of position of the receiver. In the case where the receiver was in motion previously, the method compares the sets of transmitters determined during N acquisitions of signals at instants TN, T- (Nl) ... T- j ..., Tl, T, or for the duration DT. The duration DT corresponds to the time between the instant TN of the last signal acquisition when the receiver was still stationary and the last acquisition at the instant T. After this phase of determining the change of position, if the receiver is considered as stationary, then the process restarts an initialization phase, otherwise it launches a new position change determination phase. In all cases, the method determines, as in P44, a new instant T + 1 either for launching the initialization phase or for launching a new phase for determining a change of position depending on whether the receiver is stationary or mobile.

In FIG. 6, there is illustrated an initialization phase such as implemented in the alternative embodiment of FIG. 5. For a good understanding of the figure, the mobile transmitters are recognizable by their white background and by their small arrows representing their motion vector. Stationary transmitters are recognizable by their black background. The receiver is represented by a cross on a black background and contains a small arrow when it is mobile. The method performs a step as defined in PI of acquiring a radio signal at Ti-2. The determination step defined in P2 determines the presence of 8 transmitters E1, E2, E3, E4, E6, E7, E8, E9 from the radio signal acquired at the instant Ti-2. The method performs an acquisition step as defined in PI of a new radio signal at the instant Ti-1. The determination step defined in P2 allows the method to determine the presence of 10 transmitters El, E2, E3, E4, E5, E6, E7, E8, E9, E10 from the radio signal acquired at the instant Ti-1. The method carries out an acquisition step as defined in PI of a new radio signal at the instant Ti. The determination step defined in P2 allows the method to determine the presence of 7 transmitters E3, E4, E5, E6, E7, E8, E10 from the radio signal acquired at the instant Ti. The method considers that the Dinit duration corresponding to the duration between Ti-2 and Ti is sufficiently long to constitute the initialization phase. As defined in P3, the method compares the 3 sets of transmitters determined during the 3 determination steps with one another and determines a set of transmitters Ec_3_Ti which is common to these 3 sets and which comprises E3, E4, E6, E7, E8, in the example shown. This set Ec_3_Ti is recorded in P3 in a database (like the database BDD3 in FIG. 3) and constitutes the reference set which will then be compared with various sets determined subsequently, in order to determine a change of position or not from the receiver.

In FIG. 7, there is illustrated a phase for determining whether or not to change the position of the receiver, as implemented in the alternative embodiment of FIG. 5. For a good understanding of the figure, the mobile transmitters are recognizable by their white background and their small arrows representing their motion vector. Stationary transmitters are recognizable by their black background. The receiver is represented by a cross on a black background and contains a small arrow if it is mobile. In this determination phase, the method carries out a first step as defined in PI of acquisition of a radio signal at T-2. The determination step defined in P2 determines an E_T-2 set comprising 7 transmitters E2, E3, E4, E6, E7, E8, E10. This set E_T-2 is then compared in P3 with the reference set Ec_3_Ti determined in the aforementioned initialization phase. The result of this comparison makes it possible to determine a set Ec_i_T-2 which is common to the set E_T-2 and to the reference set Ec_3_Ti. In the example shown, the EC_i_T-2 set includes the transmitters E3, E4, E6, E7, E8 and a number Nc_i_T-2 of 5 transmitters. The common set Ec_i_T-2 is similar to the set Ec_3_Ti. In addition, as defined in the step of determining the change in position of a receiver at P4, the first number K1 is fixed at 5. However, since Nc_i_T-2 is greater than or equal to K1, the method therefore considers that the receiver has not changed position and therefore assigns VAL_T-2 the value 0 corresponding to a stationary state of the receiver. The method then determines a new time Tl for the next phase. This next phase is still a phase of determining a change in the position of the receiver because the method considers that the initialization phase is too recent to carry out a subsequent one. In this second determination phase, the method carries out a first step as defined in PI of acquisition of a radio signal at T1. The determination step defined in P2 determines a set E_T-1 comprising 8 transmitters El, E2, E4 , E5, E6, E7, E8, E10. This set E_T-1 is then compared in P3 with the reference set Ec_3_Ti. The result of this comparison makes it possible to determine a set Ec_i_T-1 which is common to the set E_T-1 and to the reference set Ec_3_Ti. In the example shown, the set EC_i_T-l comprises the transmitters E4, E6, E7, E8 and a number Nc_i_T-l of 4 transmitters. The common set Ec_i_T-l is not similar to the set Ec_3_Ti because it lacks the emitter E3. In addition, as defined in the step of determining the change in position of a receiver at P4 (FIG. 4), the first number K1 is fixed at 5. In this example, the second number K2 defined at P4 is fixed at 4. However, since Nc_i_T-1 is less than K1 but greater than or equal to K2, the method is not able to determine a change of position. In this case, the method compares in P3 the current set E_T-1 with other previous sets such as E_T-2, E_Ti, E_Ti-1 in order to be able to determine a change of position. In this example, this new step will not make it possible to determine the change in position as defined in step P43 of FIG. 4. The method therefore carries out a new phase of determining a change in position of the receiver by proceeding the acquisition of a new radio signal at the instant T in accordance with step P44 of FIG. 4. In this third phase of determination, the method carries out a first step as defined in PI of acquisition of a signal radio to T. The determination step defined in P2 makes it possible to determine a set E_T comprising 7 transmitters E2, E5, E6, E7, E8, E10, El i. The set E_T formed is then compared in P3 with the reference set Ec_3_Ti. The result of this comparison makes it possible to determine a set Ec_i_T which is common to the set E_T and to the set of reference Ec_3_Ti. In the example shown, the set EC_i_T comprises the transmitters E6, E7, E8 and a number Nc_i_T of 3 transmitters. The common set Ec_i_T is not similar to the set Ec_Ti because it lacks the emitters E3 and E4. Now, since Nc_i_T is less than K2, the method considers, as defined in P42 in FIG. 4, that the receiver has changed position and therefore assigns VAL_T the value 1 corresponding to a change in position of the receiver. The method determines, as in P44 in FIG. 4, a new instant T + 1 either for launching the initialization phase or for the phase for determining a change of position depending on whether the receiver is stationary or mobile respectively. In FIG. 8, in PA1, another embodiment of the initialization phase described in FIGS. 5 and 6 is defined, in which the transmitters are exclusively of the Bluetooth® type. In addition, the receiver has a module for receiving Bluetooth® signals. In PAU, a step of acquiring a radio signal at an instant Ti is carried out. In this embodiment, the acquired signal is a Bluetooth® Low Energy type signal (referred to as BLE in the remainder of the document). However, the acquired signal can be of any type such as a Wifi, UMTS or LTE signal or even an FM type radio signal. In PA12, there is a step of recording a signal S_T in a memory such as for example a BDDO database. Recording of the radio signal will allow the receiver to process the signal a posteriori. It may be considered to record the radio signal acquired in equipment external to the receiver for reasons of limited storage capacities of the receiver or for other reasons. It can also be envisaged to record the acquired radio signal in server type equipment connected to the receiver via a telecommunications network. However, these last two alternatives require that the receiver has a communication module in order to be able to exchange data with other equipment. As this module is a source of energy consumption, it is preferable to record the signal directly on the receiver. In PA13, a step of processing the acquired radio signal is carried out. This step aims to apply filtering-type processing to the radio signal and to analyze the radio signal in order to extract therefrom relevant information for the correct implementation of the method. The essential information to be extracted is the presence of the characteristic signals of the BLE transmitters in the radio signal acquired by the receiver. In the example of a transmitter equipped with a BLE communication module, the receiver listens to radio signals on the useful frequency band of the BLE, filters the signal and analyzes the radio frames in order to retrieve information allowing identify the issuer. These steps are well known to those skilled in the art and are described in the Bluetooth® specifications as Service Discovery. The information identifying the sender can be its MAC address or its Universal Unique Identifier (called UUID in the rest of the document) or any other information allowing it to be identified with certainty. As the BLE transmitter transmits a signal frequently, the receiver analyzes the same frames several times containing the same identifier. The method records, at least during the signal processing time, this identifier in memory and ensures that it is not stored several times. The method, in order to perform more precise measurements, can retrieve information related to the strength of the received signal called “Received Signal Strength Indication” (RSSI) in the Bluetooth® specifications. The method therefore has an indication of the power of the received signal by averaging the RSSIs received to define an average power of the received signal. A specific embodiment of this embodiment is to take into account the power of the signal received in order to exclude certain transmitters because the acquired radio signal is too weak. In addition, the signal strength level gives an indication of the distance between the transmitter and the receiver. The method therefore analyzes all the BLE radio frames and extracts a set of unique identifiers. These identifiers each correspond to an issuer different. This set E_Ti which represents the presence or not of at least one radio transmitter contains the information necessary for the correct implementation of the method such as an identifier for each transmitter and a date of acquisition of the associated radio signal. For generic processing needs of the invention, the identifier, which is initially an IMAC address or the UUID, can be reformulated according to a predefined naming rule and in any possible form if necessary. The set can also contain additional information such as an average RSSI level for each transmitter, the duration of the signal acquisition etc. It is also possible that the receiver does not determine the presence of another transmitter, in this case all the transmitters are empty. The set E_Ti is then stored in memory. In PA14, there is a step of comparing the set E_Ti recently formed and recorded with a group of N sets E_Ti-1, E_Ti-2, ..., E_Ti-N formed during acquisitions prior to N different dates. Each set E_Ti-1, E_Ti-2 ... E_Ti-N corresponds to a list of transmitters or to an empty set of which the method has determined the presence during old acquisitions or not. The comparison step PA14 amounts to comparing the transmitters in common between the set E_Ti-N and the set E_Ti- (Nl). The transmitters resulting from this operation are then compared with the set E_Ti (N-2) and so on until the comparison with the set E_Ti. This therefore amounts to making N + 1 comparisons. The set Ec_N_Ti of the determined common transmitters represents the identifiers associated with the fixed transmitters in the environment of the receiver. The time period described in the above chapter is called Dinit Ti in FIG. 5. Dinit_Ti is determined either by the method or by a user of the receiver or an administrator of a fleet of receivers. It must represent a substantial duration to ensure that the transmitters in the vicinity of the receiver do not move very slowly and would therefore be seen as fixed elements if the analysis duration was too short. To determine Dinit_Ti, the method can perform historical analyzes of old Dinit Ti times to determine an average Dinit Ti duration. In PA15, there is a step of recording the Ec_N_Ti set of fixed transmitters. This Ec_N_Ti set is saved in a BDD3 database even if the set is empty (no emitters determined). If the method considers that the receiver is in motion or not stationary enough or that the surrounding transmitters are not stationary, then the method cannot constitute a reference frame of transmitters in common. In this case, the method restarts step PA11 to carry out new acquisitions and analyzes during the Dinit Ti period.

According to a particular embodiment of the invention shown in FIG. 9, the actions executed by the determination method are implemented by a radio receiver REC. The REC radio receiver is for example a digital motion sensor. For this, the radio receiver REC has the classic architecture of a computer and includes in particular a MEM_REC memory, a UT_REC processing unit, equipped for example with a PROC_REC processor, and controlled by a computer program PG_REC stored in memory MEM_REC. The computer program PG_REC comprises instructions for implementing the actions of the method for determining the change in position of the radio receiver as described above, when the program is executed by the PROC_REC processor. On initialization, the code instructions of the computer program PG_REC are for example loaded into a RAM memory (not shown) before being executed by the processor PROC_REC. The PROC_REC processor of the UT_REC processing unit notably implements the actions of the method for determining the change in position of the radio receiver described above, according to the instructions of the computer program PG_REC.

According to a particular embodiment of the invention shown in FIG. 9, the actions executed by the determination method are implemented partially by a server SERV. The SERV server is for example a network server equipped with a database solution. For this, the SERV server has the conventional architecture of a computer and includes in particular a MEM_SERV memory, a UT_SERV processing unit, equipped for example with a PROC_SERV processor, and controlled by a computer program PG_SERV stored in MEM_SERV memory. . The computer program PG_SERV comprises instructions for implementing the actions of the method for determining the change of position of the radio receiver as described above, when the program is executed by the processor PROC_SERV. On initialization, the code instructions of the computer program PG_SERV are for example loaded into a RAM memory (not shown) before being executed by the processor PROC_SERV. The PROC_SERV processor of the UT_SERV processing unit notably partially implements the actions of the method for determining the change in position of the radio receiver described above, according to the instructions of the computer program PG_SERV. As regards step PI, in conjunction with FIG. 1, as already explained above, it makes it possible to acquire a radio signal. This step is performed by the REC receiver via the MPI radio acquisition module. The radio signal acquisition data by the MPI module can be stored in the MEM_REC memory in real time and more particularly in the BDDO database. Concerning step P2, in conjunction with FIG. 2, as already explained above, it makes it possible to determine a set of transmitters originating from the radio signal. This step can be carried out by the receiver REC via the processing unit UT_REC according to the instructions commanded by the program PG_REC. The data from step P2 are stored in the databases BDD1 and BDD2 as described in FIG. 2. Regarding step P3, in conjunction with FIG. 3, as already explained above, it makes it possible to compare the 'set of transmitters determined with at least two other sets of transmitters already determined. This step is carried out by the receiver REC via the processing unit UT_REC according to the instructions commanded by the program PG_REC. The data used in this step come from the database BDD2 and the result of the comparison is stored in the database BDD3. Concerning step P4, in conjunction with FIGS. 4 and 4a, as already explained above, it makes it possible to determine whether the receiver REC has changed position. This step is carried out by the receiver REC via the processing unit UT_REC according to the instructions commanded by the program PG_REC. The data used in this step are from the BDD3 database and the results of the comparison are stored in the BDD3 and BDD4 databases. The databases BDDO, BDD1, BDD2, BDD3, BDD4 defined in the invention can be merged into a single database or into as many databases as possible as there are possible combinations between these 5 databases.

In a particular embodiment, and from step P2 of Figure 1, all of the calculations performed to implement the position change detection method can be performed by the REC receiver alone. In this embodiment, the SERV server is not called upon. In this case, the MEM_REC memory includes all of the process databases.

As a variant of this embodiment, for greater flexibility, one or more of these bases are separate from the receiver REC and can be managed by the server SERV. Likewise, one or more of the steps from P2 to P4 can be carried out by the server SERV. In this case, as provided in FIG. 9 (cf. the dotted drawings), the receiver can be in communication with a SERV server. Depending on the embodiment, the REC receiver and the SERV server can be interconnected and exchange data over one or more communication link (s), using one or more networks of different types ("Network" in Figure 9) and different protocols. Examples of networks are a fixed network, a cellular network (for example according to the 2G standard (GSM, GPRS, EDGE), 3G (UMTS), 4G (LTE), LTE-A, LTE-M, WCDMA, CDMA2000, HSPA , 5G, or their variants or evolutions), another type of radio network (eg WiFi® or Bluetooth®), an IP network, a combination of several of these networks, etc. For this, the REC receiver and the SERV server will be configured with suitable data communication means (COM_REC and COM_SERV respectively in FIG. 9). In order to generalize the different possibilities of calculating the steps of the method for detecting a change of position, and according to respectively different particular embodiments of the invention not represented by a diagram, each step of calculating the method, except the step PI carried out by the receiver REC, can be carried out respectively by the receiver REC or the server SERV so as to represent all the possible combinations of calculation configurations between the receiver REC and the server SERV.

It goes without saying that the embodiments which have been described above have been given purely as an indication and in no way limiting, and that many modifications can be easily made by those skilled in the art without departing from the scope. of the invention.

Claims

1. A method of detecting change of position of a radio receiver (REC), characterized in that it comprises the following:

acquire (PI) by said receiver a radio signal at a given instant,

determine (P2) a set of at least one radio transmitter from the radio signal, compare (P3) said set of at least one radio transmitter with at least two sets of previously registered radio transmitters,

based on said comparison, determining (P4) whether the radio receiver has changed position.

2. The method of claim 1, wherein determining a set of at least one radio transmitter (E_T) comprises:

on the basis of said acquired radio signal, calculate (P21 or P21 ’) at least one item of information (I_Ex_T) characterizing at least one radio transmitter present in said set of at least one radio transmitter,

search (P22) for said at least one item of information in a plurality of items of information previously recorded,

according to the result of the search, generating and recording (P23) at least one identifier associated with said at least one item of information.

3. A method according to claim 1 or claim 2, wherein determining a set of at least one radio transmitter (E_T) uses a radio frame analysis containing at least one identifier of a radio transmitter (R2G).

4. Method according to claim 2 or 3, wherein said at least one item of information (I_Ex_T) characterizing at least one radio transmitter is recorded in correspondence with said given instant (P23).

5. The method of claim 1, wherein said at least two sets of previously registered radio transmitters are selected in a time range between an instant prior to said given instant and said given instant (P31).

6. The method of claim 1, wherein said comparison (P32) comprises determining a second set of at least one transmitter, this second set being common to both said set of at least one radio transmitter and to said at least one radio transmitter. at least two sets of previously registered radio transmitters.

7. The method of claim 1, wherein said determination, if the radio receiver has changed position, is a function of at least one threshold (P41 or P42).

8. The method of claim 1, wherein the result of said determination, whether the radio receiver has changed position, defines a time of acquisition of a next radio signal (P44).

9. Radio receiver (REC) comprising a processor (PROC_REC) which is configured to implement the following:

acquire (PI) by said receiver a radio signal at a given instant,

10. Computer program (PG_REC) comprising program code instructions for executing the steps of the detection method according to any one of claims 1 to 8, when executed on a computer.

11. Information medium (MEM_REC) readable by a computer, and comprising instructions of a computer program according to claim 10.