Method for transmitting announcement frames, method for establishing a wireless link, electronic device and system associated therewith

Abstract

A first communication circuit installed in an electronic device transmits announcement frames to a second communication circuit installed in a vehicle. The second communication circuit operates according to consecutive periods that have a first predetermined duration and each comprise a listening phase, during which the second communication circuit is able to detect an electromagnetic signal, and an idle phase, during which the second communication circuit is inactive. This method comprises the following steps: - the first communication circuit transmitting (E4) an announcement frame (ADV1) at a first time (t1); - determining (E6) a random value; - the first communication circuit transmitting (E10) another announcement frame (ADV2) at a second time (t2) separated from the first time by a second duration (At) determined according to the random value and included strictly between two consecutive multiples of the first duration.

Description

Method for transmitting advertisement frames, method for establishing a wireless link, associated electronic device and system

[0001] The present invention generally relates to the field of wireless exchanges between an on-board system, for example equipping a vehicle, and an electronic device, for example forming an identifier associated with this vehicle.

[0002] It relates more particularly to a method for transmitting advertisement frames, a method for establishing a wireless link, as well as an associated electronic device and system. Technological background

[0003] PEPS (for "Passive Entry – Passive Start") type systems are known in which the implementation of a functionality (such as unlocking the doors of a vehicle or starting such a vehicle) is conditioned by the presence near the vehicle of an electronic device forming an identifier of the user of the vehicle (generally carried by this user).

[0004] The vehicle and the identifier may for this purpose be equipped with communication circuits designed to establish a wireless data exchange link in accordance with a communication protocol.

[0005] In this context, a method is proposed for transmitting, by a first communication circuit equipping an electronic device, announcement frames intended for a second communication circuit equipping a vehicle, in which the second communication circuit operates according to successive periods having a first predetermined duration and each comprising a listening phase, during which the second communication circuit is capable of detecting an electromagnetic signal, and a rest phase, during which the second communication circuit is inactive, the method comprising the following steps:

[0006] - transmission of an announcement frame by the first communication circuit at a first instant;

[0007] - determination of a random value;

[0008] - transmission of another announcement frame by the first communication circuit at a second instant separated from the first instant by a second duration determined as a function of the random value and strictly between two consecutive multiples of the first duration.

[0009] Thus, the transmission times of the two successive announcement frames are not separated by a duration which would be an exact multiple of the first duration (duration of the operating periods of the second communication circuit) so that an announcement frame can be transmitted during a listening phase of the second communication circuit (vernier principle).

[0010] Furthermore, the second instant, at which the announcement frame referred to above as "other announcement frame" is transmitted, depends on the aforementioned random value, and will therefore be distinct (except in exceptional cases) from a corresponding transmission instant, used by another electronic device of the same design which could be located nearby (such as when two people each equipped with a similar identifier approach the vehicle simultaneously). This avoids interference in the event of the presence of two such electronic devices near the vehicle.

[0011] Other features that may be considered, without being limiting, taken individually or in all technically possible combinations, are the following:

[0012] - the second duration, noted Δt, verifies n.T0< Δt < (n+1).T0, where T0 is the first duration and n an integer greater than or equal to 5 (or even greater than or equal to 9);

[0013] - the method comprises a step of determining the second duration by adding or subtracting, depending on the random value, the duration of the listening phase (denoted t ON in the following) to the product of the first duration T0 by an integer (which may be a predetermined integer, for example greater than or equal to 10, or an integer possibly depending on another random value);

[0014] - the method comprises a step of determining the second duration using a multiplication of the first duration T0 by a number depending on the random value (the determination of the second duration can then comprise the addition of the duration t ON of the listening phase, or a multiple of the duration of the listening phase, to the result of this multiplication);

[0015] - the method comprises a step of determining the second duration by adding, to the product of the first duration T0 by an integer (which may be a predetermined integer, for example greater than or equal to 10, or depend on another random value), the product of the duration of the listening phase t ON by a non-zero relative integer depending on the random value;

[0016] - for each of said successive periods, the listening phase has a duration of between 5% and 30% of said first duration (i.e. the duration t ON is between 0.05.T0 and 0.3.T0).

[0017] The invention also proposes a method for establishing a wireless link between a first communication circuit equipping an electronic device and a second communication circuit equipping a vehicle, comprising the following steps:

[0018] - implementation, by the first communication circuit, of a method for transmitting announcement frames as described above;

[0019] - detection of one of said announcement frames by the second communication circuit during a listening phase;

[0020] - in response to the detected announcement frame, transmission, by the second communication circuit, of a connection request;

[0021] - establishing a connection between the first communication circuit and the second communication circuit.

[0022] Correlatively, the invention proposes an electronic device comprising a control unit and a first communication circuit designed to transmit announcement frames intended for a second communication circuit fitted to a vehicle, the second communication circuit operating according to successive periods having a first predetermined duration and each comprising a listening phase, during which the second communication circuit is capable of detecting an electromagnetic signal, and a rest phase, during which the second communication circuit is inactive, in which the control unit is designed to determine a random value and to determine, as a function of the random value, a second duration strictly between two consecutive multiples of the first duration,and wherein the first communication circuit is configured to transmit an announcement frame at a first time and another announcement frame at a second time separated from the first time by the second duration.,

[0023] Finally, the invention proposes a system comprising an electronic device as just indicated and an on-board system comprising the second communication circuit.

[0024] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the figures

[0025] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0026] On the attached drawings:

[0027] schematically represents the main elements of a system in which the invention can be implemented;

[0028] represents an example of a method of transmitting announcement frames that can be implemented within the system of the; and

[0029] represents an example of a method for establishing a wireless connection.

[0030] It schematically represents the main elements of a system in which the invention can be implemented.

[0031] Such a system comprises a vehicle 10, here a motor vehicle, and an electronic device 20 used as an identifier, for example a key or badge for access to the vehicle 10 (or, alternatively, a user terminal, such as a multifunction mobile telephone – or "smartphone" according to the commonly used English application, provided with access rights to the vehicle 10).

[0032] The vehicle 10 is equipped with an on-board system 15 comprising in particular an electronic control unit 11 and a communication circuit 12.

[0033] The electronic control unit 11 comprises, for example, a microprocessor and at least one memory, for example a rewritable non-volatile memory. The memory stores in particular program instructions which, when executed by the microprocessor, allow the electronic control unit 11 to implement the method described below with reference to the. The memory can also store values ​​or parameters used during these methods.

[0034] The memory of the electronic control unit 11 further stores a cryptographic key K (which was, for example, written into the electronic control unit 11 during its manufacture).

[0035] Alternatively, the electronic control unit 11 could be implemented in the form of an application-specific integrated circuit (or ASIC for "Application Specific Integrated Circuit").

[0036] The communication circuit 12 is designed to establish a wireless connection with other electronic devices, here a connection of the "Bluetooth Low Energy" (or "BLE") type. The communication circuit 12 is therefore designed in particular to transmit and receive electromagnetic signals (typically with a frequency greater than 1 MHz, or even 500 MHz), here in the 2.4 GHz band.

[0037] Due for example to commands received from the electronic control unit 11, the communication circuit 12 carries out successive operating periods having a predetermined duration T0 and / or each comprising a listening phase, during which the communication circuit 12 is able to detect an electromagnetic signal, and a rest phase, during which the communication circuit 12 is inactive. In other words, the operation of the communication circuit 12 is periodic, each operating period (of predetermined duration T0) comprising a listening phase and a rest phase as defined above. The rest phases make it possible to reduce the average electrical consumption of the communication circuit 12 and thus of the on-board system 15.

[0038] The predetermined duration T0 of the operating periods is for example between 10 ms and 200 ms, and here is 100 ms.

[0039] Over each operating period, the duration of the listening phase is, for example, between 5% and 30% of the operating period. In the following, we note t ON the duration of a listening phase. (The duration t ON is therefore here between 0.05.T0 and 0.3.T0.)

[0040] The electronic device 20, generally carried by a user of the vehicle 10, is used as an identifier to authorize and / or enable the control of certain functionalities of the vehicle 10 (for example the unlocking of the doors of the vehicle 10), in particular when it is approached to the vehicle 10. The electronic device 20 may optionally further comprise control buttons, using which the user can control at least some of the aforementioned functionalities or other functionalities of the vehicle 10.

[0041] The electronic device 20 comprises a control unit 21 and a communication circuit 22.

[0042] The control unit 21 is for example implemented by means of a microprocessor and at least one memory, for example a rewritable non-volatile memory. The memory stores in particular program instructions which allow, when executed by the microprocessor, the implementation by the control unit 21 of the method described below with reference to la and / or the method described below with reference to la. The memory can also store values ​​or parameters used during these methods.

[0043] The memory of the control unit 21 also stores the cryptographic key K. In the case where the electronic device forming the identifier 20 is a badge (or key) for access to the vehicle, the cryptographic key K has for example been written into the memory of the control unit 21 during the manufacture of the identifier 20. In the variant mentioned above where the electronic device forming the identifier 20 is a user terminal, the cryptographic key K has for example been received from a remote server and stored during a subscription phase to a service for controlling the vehicle functionalities by means of the user terminal.

[0044] It is noted that, in the embodiment described here, the cryptographic key K stored in the memory of the control unit 21 is identical to the cryptographic key K stored in the memory of the electronic control unit 11. However, as a variant, the cryptographic key K stored in the memory of the control unit 21 could be different from the cryptographic key K stored in the memory of the electronic control unit 11, for example in the context of the use of a public key infrastructure (or PKI for "Public Key Infrastructure").

[0045] Alternatively, the control unit 21 could be implemented as an application-specific integrated circuit.

[0046] The communication circuit 22 is designed to establish a wireless connection (here of the "Bluetooth Low Energy" or "BLE" type) with other electronic devices, in particular with the electronic control unit 11 of the vehicle 10 via the communication circuit 12 mentioned above. The communication circuit 22 is therefore also designed to transmit and receive electromagnetic signals (typically with a frequency greater than 1 MHz, or even 500 MHz), here in the 2.4 GHz band.

[0047] By means of the wireless connection which can be established between the communication circuit 12 of the on-board system 15 of the vehicle 10 and the communication circuit 22 of the electronic device 20 as described below, data can be exchanged between the electronic control unit 11 of the on-board system 15 of the vehicle 10 and the control unit 21 of the electronic device 20.

[0048] The electromagnetic signals exchanged between the communication circuits 12, 22 can further be used to evaluate the distance separating the electronic device and the vehicle 10 (precisely the distance separating the communication circuits 12, 22), as also explained below.

[0049] The represents an example of a method for transmitting announcement frames which can be implemented within the framework of the system which has just been described.

[0050] Announcement frames are electromagnetic signals, located for example in a predefined frequency band and / or having a predefined shape in accordance with the communication protocol used, here the BLE protocol.

[0051] This method begins at step E2 during which the control unit 21 commands the communication circuit 22 to send an advertisement frame ADV1 ("advertising packet" according to English terminology) at a time t1. The advertisement frame ADV1 is for example the first advertisement frame sent after a restart of the electronic device 20 (for example following its power-up) and the time t1 is for example a predefined time of the restart process.

[0052] The communication circuit 22 thus transmits in step E4 the announcement frame ADV1 at time t1 and in accordance with the BLE protocol.

[0053] The method continues in step E6 during which the control unit 21 determines a random value a, for example in the case described here by calling a dedicated function (random draw function) within the microprocessor forming the control unit 21.

[0054] The control unit 21 then commands the communication circuit 22 in step E8 to send an announcement frame ADV2 at a time t2 separated from the first time t1 by a duration Δt determined as a function of the random value a and strictly between two consecutive multiples of the predetermined duration T0 (duration of each period of operation of the communication circuit 12 as explained above).

[0055] In other words, the duration Δt separating the instant t1 of emission of the ADV1 frame and the instant t2 of emission of the ADV2 frame depends on the random value a and verifies:

[0056] n.T0< Δt < (n+1).T0, with n an integer greater than or equal to 2, and preferably greater than or equal to 5.

[0057] In practice, the duration Δt can be determined according to one of the methods proposed at present. In these examples, we consider that the random value a determined in step E6 is between 0 and 1 (i.e. obtained by random drawing on the interval [0,1]).

[0058] According to a first possible method, the duration Δt is determined as follows:

[0059] Δt = m.T0+ t ON if a>0.5,

[0060] Δt = m.T0- t ON if a≤0.5,

[0061] where m is a predetermined integer (greater than or equal to 3, and preferably greater than or equal to 6) and where t ON is as already indicated the duration of each listening phase.

[0062] According to a second possible method, the duration Δt is determined as follows:

[0063] Δt = m.T0+ 2.t ON if a>0.5,

[0064] Δt = m.T0+ t ON if a≤0.5,

[0065] where m is a predetermined integer (greater than or equal to 2, and preferably greater than or equal to 5) and where t ON is as already indicated the duration of each listening phase.

[0066] According to a third possible method, the duration Δt is determined as follows:

[0067] Δt = INT(5+5a).T0+ t ON

[0068] where INT is the "integer part" function and where t ON is as already indicated the duration of each listening phase.

[0069] According to a fourth possible embodiment, step E6 further comprises the determination of another random value b and the duration Δt is determined as follows:

[0070] Δt = INT(5+5a).T0+ t ON if b>0.5,

[0071] Δt = INT(5+5a).T0- t ON if b≤0.5

[0072] The communication circuit 22 then transmits in step E10 the announcement frame ADV2 at time t2 and in accordance with the BLE protocol.

[0073] The method can then loop back to step E6 with a view to transmitting a new announcement frame.

[0074] Using the method just described, two successive announcement frames are transmitted at respective times separated by a duration Δt which satisfies the conditions stated above regarding the announcement frame ADV2, namely that this duration Δt depends on a random value (which may be different for each frame transmitted) and is strictly between two consecutive multiples of the predetermined duration T0 (the pair of consecutive multiples concerned may be distinct from one frame to another).

[0075] Thus, for each ADVi announcement frame transmitted, the duration Δt separating the transmission of this ADVi announcement frame from the previous frame verifies:

[0076] n.T0< Δt < (n+1).T0, with n an integer greater than or equal to 2, and preferably greater than or equal to 5 (n can vary from one announcement frame to another as already indicated).

[0077] The announcement frames are thus transmitted less frequently than the listening phases of the communication circuit 12 are planned, which makes it possible to reduce the electrical consumption at the level of the electronic device 20.

[0078] Furthermore, the announcement frames are not transmitted with a period identical to the period T0 of repetition of the listening phases so as to ensure that an announcement frame occurs (possibly after transmission of several announcement frames) during a listening phase (vernier principle).

[0079] Finally, the time of transmission of the announcement frames (during step E8) depends on a random value (determined in step E6) so that two electronic devices of the type of electronic device 20 and of the same design (which is the case for example when two users of the vehicle respectively carry two similar identifiers) will transmit (except in exceptional cases) an announcement frame at distinct times, which makes it possible to avoid interference between these two electronic devices in their exchanges with the communication circuit 12 which equips the vehicle.

[0080] The ADV1, ADV2 announcement frames mentioned above are of type ADV_IND: these are announcement frames signaling availability for a connection and not specifically directed towards a communication partner (or "connectableundirectedadvertisingevent" according to Anglo-Saxon terminology).

[0081] The announcement frames ADV1, ADV2, ADVi transmitted by the communication circuit 22 of the electronic device 20 may include data, in particular identification data ID of the electronic device 20.

[0082] This represents an example of a method for establishing a wireless link between the communication circuit 12 equipping the vehicle and the communication circuit 22 of the electronic device 20 forming an identifier.

[0083] This method begins with the transmission of announcement frames by the communication circuit 22 of the electronic device 20 in accordance with what has just been described with reference to the.

[0084] When the vehicle 10 is sufficiently close to the electronic device 20 (which usually occurs when the wearer of the electronic device 20 approaches the vehicle 10), the communication circuit 12 of the on-board system 15 of the vehicle 10 detects (and therefore receives) one of the ADVi announcement frames and thus signals to the electronic control unit 11 the arrival of this ADVi announcement frame (step E12). The communication circuit 12 can also transmit at this step the data possibly included in the ADVi announcement frame (in particular the identification data ID of the electronic device 20) to the electronic control unit 11.

[0085] The electronic control unit 11 can then command the communication circuit 12 in step E14 to respond to the ADVi announcement frame sent by the electronic device 20, typically by sending a connection request CONN_REQ to the communication circuit 22 of the identifier 20 (step E16).

[0086] According to one possible embodiment, the transmission of the connection request CONN_REQ by the communication circuit 12 (on command from the electronic control unit 11) may however be conditioned by the presence of the identification data ID of the electronic device 20 within a list of previously paired identifiers (this list being stored in the memory of the electronic control unit 11, the identification data of a given electronic device being added to this list by means of a specific pairing process).

[0087] The communication circuit 22 of the electronic device 20 receives the connection request CONN_REQ in step E18. A wireless link can thus be set up between the embedded system 15 and the identifier 20 in step E20 by means of establishing a connection between the communication circuit 12 of the embedded system 15 and the communication circuit 22 of the identifier 20 in accordance with the communication protocol concerned (here the BLE protocol already mentioned).

[0088] Within the framework of this connection established according to the communication protocol concerned, there are provided, as already indicated, time slots dedicated to the exchange of data (such as for example during steps E22 to E30 described below) between the communication circuit 12 of the on-board system 15 and the communication circuit 22 of the electronic device 20.

[0089] According to one conceivable embodiment, the data exchanged between the electronic device 20 and the on-board system 15 are encrypted (typically by means of a cryptographic encryption algorithm, using for example the cryptographic key K shared by the electronic control unit 11 and the control unit 21 as already indicated) during their exchange between the communication circuit 12 of the on-board system 15 and the communication circuit 22 of the electronic device 20. The encryption used is for example that provided within the framework of the relevant data exchange protocol D, here the BLE protocol.

[0090] We now describe, still with reference to the, possible exchanges of data between the electronic device 20 and the on-board system 15.

[0091] During a step E22, the electronic control unit 11 of the on-board system 15 determines a CH value (for example by random selection) and commands the communication circuit 12 to transmit this CH value via the established wireless link (between the communication circuit 12 and the communication circuit 22), and thus to the electronic device 20 (i.e. in practice to the control unit 21). As explained below, this CH value is used as a challenge in a challenge-response type exchange (or "challenge-response" according to the English term sometimes used) to verify that the electronic device 20 indeed holds the cryptographic key K.

[0092] The control unit 21 receives the CH value via the communication circuit 22 (step E24).

[0093] During step E26, the control unit 21 applies to the value CH a cryptographic processing algorithm (for example an encryption algorithm) using the cryptographic key K so as to obtain a response RS intended for the on-board system 15.

[0094] The control unit 21 then commands (step E28) the communication circuit 22 to send the RS response via the established wireless link (between the communication circuit 12 and the communication circuit 22), and thus to the electronic control unit 11.

[0095] The electronic control unit 11 therefore receives the response RS at step E30, via the communication circuit 12.

[0096] The electronic control unit 11 can thus verify the response RS received in step E32, here by applying to the response RS a cryptographic processing algorithm, for example a decryption algorithm, using the cryptographic key K, and by verifying whether the result obtained is indeed identical to the value CH sent in step E22.

[0097] If (and only if) the verification is correctly carried out in step E32 (which demonstrates that the electronic device actually stores the cryptographic key K), the electronic device 20 is authenticated by the electronic control unit 11; the electronic control unit 11 can then authorize certain actions such as unlocking the vehicle 10.

[0098] Furthermore, the electronic control unit 11 and / or the control unit 21 can control (respectively the communication circuit 12 and / or the communication circuit 22) the emission of electromagnetic signals and / or the carrying out of measurements (step E40) so as to evaluate the distance separating the communication circuit 12 and the communication circuit 22, in accordance for example with what is described in the patent application published under the reference FR 3 081 637.

Claims

Method for transmitting, by a first communication circuit (22) equipping an electronic device (20), announcement frames intended for a second communication circuit (12) equipping a vehicle (10), in which the second communication circuit (12) operates according to successive periods having a first predetermined duration and each comprising a listening phase, during which the second communication circuit (12) is capable of detecting an electromagnetic signal, and a rest phase, during which the second communication circuit (12) is inactive, the method comprising the following steps: - transmitting (E4) an announcement frame (ADV1) by the first communication circuit (22) at a first instant (t1); - determining (E6) a random value;- transmission (E10) of another announcement frame (ADV2) by the first communication circuit (22) at a second instant (t2) separated from the first instant by a second duration (Δt) determined as a function of the random value and strictly between two consecutive multiples of the first duration.; Transmission method according to claim 1, in which the second duration, denoted Δt, verifies n.T0 < Δt < (n+1).T0, where T0 is the first duration and n an integer greater than or equal to 5. Transmission method according to claim 1 or 2, comprising a step of determining (E8) the second duration (Δt) by adding or subtracting, depending on the random value, the duration of the listening phase from the product of the first duration by an integer. Transmission method according to claim 1 or 2, comprising a step of determining (E8) the second duration (Δt) using a multiplication of the first duration by a number depending on the random value. Transmission method according to claim 1 or 2, comprising a step of determining (E8) the second duration (Δt) by adding, to the product of the first duration by an integer, the product of the duration of the listening phase by a non-zero relative integer depending on the random value. Transmission method according to one of claims 1 to 5, in which, for each of said successive periods, the listening phase has a duration of between 5% and 30% of said first duration. Method for establishing a wireless link between a first communication circuit (22) equipping an electronic device (20) and a second communication circuit (12) equipping a vehicle (10), comprising the following steps: - implementation, by the first communication circuit (22), of a method for transmitting announcement frames (ADV1, ADV2, ADVi) according to one of claims 1 to 6; - detection (E12) of one of said announcement frames (ADVi) by the second communication circuit (12) during a listening phase; - in response to the detected announcement frame (ADVi), transmission (E16), by the second communication circuit (12), of a connection request (CONN_REQ); - establishment (E20) of a connection between the first communication circuit (22) and the second communication circuit (12). Electronic device (20) comprising a control unit (21) and a first communication circuit (22) designed to transmit announcement frames (ADV1, ADV2) intended for a second communication circuit (12) fitted to a vehicle (10), the second communication circuit (12) operating according to successive periods having a first predetermined duration and each comprising a listening phase, during which the second communication circuit (12) is capable of detecting an electromagnetic signal, and a rest phase, during which the second communication circuit (12) is inactive, in which the control unit (21) is designed to determine a random value and to determine, as a function of the random value, a second duration (Δt) strictly between two consecutive multiples of the first duration,andwherein the first communication circuit (22) is designed to transmit an announcement frame (ADV1) at a first time (t1) and another announcement frame (ADV2) at a second time (t2) separated from the first time (t1) by the second duration (Δt)., A system comprising an electronic device (20) according to claim 8 and an on-board system (15) comprising the second communication circuit (12).

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