EP3259864A1

EP3259864A1 - Methods for transmitting and receiving downlink messages with implicit identification of recipients

Info

Publication number: EP3259864A1
Application number: EP16713517.7A
Authority: EP
Inventors: Lionel ZIRPHILE
Original assignee: Sigfox SA
Current assignee: Sigfox SA
Priority date: 2015-02-19
Filing date: 2016-02-19
Publication date: 2017-12-27
Also published as: FR3033105B1; CN107258062A; US10314027B2; US20180035412A1; FR3033105A1; KR102482252B1; MX2017010562A; MX369875B; WO2016132084A1; KR20170134382A

Abstract

The present invention relates to a method (50) for transmitting a downlink message on a downlink between an access network (30) and a plurality of terminals (20), the downlink message being made up of main data to be transmitted to a receiving terminal (20), the method (50) comprising the steps of: - (51) generating error detection data from the main data, - (52) modifying main data and/or error-detection data on the basis of an identifier of the receiving terminal (20), using a predefined reversible modification function, the modification being carried out at a constant spectral width and for a constant duration with respect to the aforementioned main data and/or error-detection data, and - (53) transmitting a downlink message comprising the main data and the error-detection data obtained after modification. The invention further relates to a suitable method (60) of receiving downlink messages.

Description

Methods of sending and receiving downstream messages with implicit identification of recipients

TECHNICAL AREA

The present invention belongs to the field of digital telecommunications, and more particularly relates to a method of transmitting a downlink message on a downlink between an access network and terminals, and a method of receiving said downlink message.

STATE OF THE ART

The present invention finds a particularly advantageous, though in no way limiting, application in ultra-narrowband wireless communication systems. By "ultra narrow band" ("Ultra Narrow Band" or UNB in the Anglo-Saxon literature), it is meant that the instantaneous frequency spectrum of the radio signals emitted by the terminals is of frequency width less than one kilohertz.

Such UNB wireless communication systems are particularly suitable for applications of the type M2M (acronym for machine-to-machine) or the Internet of Things ("Internet of Things" or loT in the literature Anglo-Saxon).

In such a UNB wireless communication system, the data exchanges are essentially monodirectional, in this case on a rising link between terminals and an access network of said system.

The terminals transmit uplink messages that are collected by base stations of the access network, without having to first associate with one or more base stations of the access network. In other words, the upstream messages sent by a terminal are not intended for a specific base station of the access network, and the terminal transmits its upstream messages assuming that they can be received by at least one forwarding station. based. Such provisions are advantageous in that the terminal does not need to make regular measurements, particularly greedy in terms of power consumption, to determine the most appropriate base station to receive its upstream messages. The complexity lies in the access network, which must be able to receive messages that can be transmitted at arbitrary times and on arbitrary central frequencies. Each base station of the access network receives messages from the various terminals that are within its reach.

Such a mode of operation, in which data exchanges are essentially monodirectional, is quite satisfactory for many applications, such as for example the remote reading of gas meters, water, electricity, remote monitoring of buildings or houses, etc.

In some applications, however, it may be advantageous to also be able to perform data exchanges in the other direction, namely on a downlink from the access network to the terminals, for example to reconfigure a terminal and / or control an actuator. connected to said terminal. However, it is desirable to offer such capacity by limiting the impact on the collection of upstream messages.

In particular, in such UNB wireless communication systems, the bit rates are by construction low, generally between a few tens of bits per second and a few kilobits per second. Therefore, even if the number of bits to be transmitted in a downlink message is small, the duration of said downlink message can be significant, of the order of one second.

Therefore, it is necessary to limit the number of bits in the downstream messages, in order to reduce their duration, and consequently to reduce the occupation time of the frequency band used to exchange data between the terminals and the network. 'access.

Such a limitation of the number of bits in the downstream messages is also desired because, to reduce the cost of deploying the access network, it is envisaged to use half-duplex base stations, i.e. say base stations that can receive upstream messages and send outgoing messages, but not simultaneously. By limiting the duration of downstream messages, the length of time that base stations can not receive uplink messages would also be reduced.

In the context of wireless communication systems LTE (English acronym for "Long Term Evolution"), it is known from patent applications US 2013/077583 A1 and WO 2014/075239 A1 to scramble the data to be transmitted with an identifier of the destination terminal. The identifier of the destination terminal is therefore not explicitly transmitted, which makes it possible to reduce the number of bits transmitted.

However, the patent applications US 2013/077583 A1 and WO 2014/075239 A1 rely on the mechanisms of the LTE access network for the management of the identifiers of the terminals, which are difficult to implement in an access network. which we seek to reduce complexity.

STATEMENT OF THE INVENTION

The present invention aims to overcome all or part of the limitations of the solutions of the prior art, including those described above, by proposing a solution that limits the duration of the downlink messages transmitted by the base stations of the network. access.

For this purpose, and according to a first aspect, the invention relates to a method of transmitting a downlink message on a downlink between an access network and a plurality of terminals, said downlink message being formed from main data. to be transmitted to a destination terminal, said method comprising steps of:

- generation of error detection data from the main data,

modification of the main data and / or of the error detection data as a function of an identifier of said destination terminal, by means of a reversible predefined modification function, said modification being carried out with a constant spectral width and with a constant duration with respect to said main data and / or error detection data,

- transmission, by a base station of the access network, of a downlink message comprising the main data and the error detection data obtained after modification.

In addition, said descending message being sent in response to an amount message previously received from the destination terminal, the identifier of said destination terminal is a temporary identifier determined from control data included in said amount message.

Thus, according to the invention, the identifier of the destination terminal is used to modify the main data and / or the error detection data without increasing the spectral width and without increasing the duration. Consequently, the identifier of the destination terminal is not explicitly transmitted in the descending message. Indeed, the descending message does not include a field in which a receiving terminal can directly find the identifier of the destination terminal. Compared with conventional solutions of adding the identifier of the destination terminal to the transmitted data, generally as a preamble, the duration of the downstream messages is reduced by the duration of the destination terminal identifier.

Such a reduction in the duration of the downstream messages is, however, accompanied by an increase in the amount of processing to be performed by the different terminals. Indeed, when a receiving terminal receives a downlink message, said receiving terminal must first, before knowing if said downlink message is intended for it, modify said downlink message according to its identifier, by means of a reverse function of the modification function used on transmission, and then check using the error detection data if the main data contains errors. If the identifier of the receiving terminal is different from the identifier of the destination terminal, then the main data extracted by the receiving terminal will have errors, which will be detected by the error detection data, and the receiving terminal will consider that the message descendant is not intended for him.

However, the increase in the amount of processing to be performed by the terminals can be limited, if necessary, by limiting the number of downstream messages that can be detected by each terminal.

Since the identifier to be used for a destination terminal is a temporary identifier which is determined from control data extracted from the amount message in response to which the outgoing message is to be transmitted, the access network does not need to memorize identifiers for all the terminals that are in its coverage area. Such arrangements therefore make it possible to reduce the complexity of said access network.

In particular modes of implementation, the transmission method may further comprise one or more of the following characteristics, in isolation or in any technically feasible combination.

In particular modes of implementation, the identifier of the destination terminal is obtained by shifting a predefined identification code, the same identification code being used for each terminal, the offset to be applied being determined according to data. included in the amount message in response to which the descending message is to be sent.

Such arrangements are advantageous in that the access network can simply store, for all terminals in its coverage area, a single identification code that is used for all terminals. The identifier to be used for a destination terminal is then determined according to the identification code, common to all the terminals, and as a function of control data extracted from the message amount in response to which the descending message is sent, control data which in principle make it possible to distinguish said destination terminal from the other terminals.

In particular modes of implementation, the identification code is a pseudo-random sequence generated by means of a predefined pseudo-random generator, the determined offset being used as a seed of said pseudo-random generator.

In particular modes of implementation, the control data used to determine the identifier of the destination terminal include a sequence number of the amount message.

In particular modes of implementation, the main data, the error detection data and the identifier of the destination terminal being binary symbol sequences, the modification corresponds to a symbol symbol combination by means of a function " or exclusive ".

In particular modes of implementation, the descending message is sent during a predetermined time window with respect to an amount message previously received from said destination terminal.

In particular modes of implementation, the descending message is transmitted on a predetermined central frequency with respect to a central frequency of an amount message received previously from said recipient terminal.

According to a second aspect, the present invention relates to a base station comprising means configured to implement a transmission method according to any of the embodiments of the invention.

According to a third aspect, the present invention relates to an access network comprising means configured to implement a transmission method according to any of the embodiments of the invention.

According to a fourth aspect, the present invention relates to a method of reception, by a receiving terminal, of a descending message transmitted according to a transmission method according to any of the embodiments of the invention. More particularly, the reception method comprises steps of:

detection of the descending message on the downlink,

extraction of main data and error detection data by modifying the descending message according to an identifier of the receiving terminal, by means of a function inverse to the modification function used to form the descending message, the identifier the receiving terminal being a temporary identifier determined from control data included in a rising message previously sent by said receiving terminal, in response to which a descending message must be sent,

determining, as a function of the error detection data, whether the main data comprises errors, the receiving terminal being considered to be the destination terminal of the said downward message when the main data are considered as having no errors.

In particular modes of implementation, the reception method may further comprise one or more of the following characteristics, taken separately or in any technically possible combination.

In particular modes of implementation, the receiving terminal listens to the downlink on a time window, called the "listening window", predetermined in relation to the amount message previously sent by said receiving terminal.

Such arrangements make it possible to limit the number of downstream messages that can be detected by the receiving terminal, and therefore the amount of unnecessary processing that may be performed by said receiving terminal. Indeed, the receiving terminal listening to the downlink only on the listening window of limited duration, only the descendant messages issued during this listening window will be likely to be detected.

In particular modes of implementation, the receiving terminal listens the downlink around a predetermined central frequency with respect to a central frequency of the amount message previously sent by said receiving terminal.

Such arrangements make it possible to limit the number of downstream messages that can be detected by the receiving terminal, and therefore the amount of unnecessary processing that may be performed by said receiving terminal. Indeed, since the receiving terminal only listens for the downlink on a frequency band of limited width, only the downstream messages transmitted in this frequency band will be able to be detected.

In particular modes of implementation, the identifier of the receiving terminal is obtained by shifting a predefined identification code, the same identification code being used for each terminal, the offset to be applied being determined according to data. control messages included in the amount message in response to which a descending message must be sent.

In particular modes of implementation, the control data used to determine the identifier of the receiving terminal include a sequence number of the upstream message.

According to a fifth aspect, the present invention relates to a terminal comprising means configured to implement a reception method according to any of the embodiments of the invention.

PRESENTATION OF FIGURES

The invention will be better understood on reading the following description, given by way of non-limiting example, and with reference to the figures which represent: - Figure 1: a schematic representation of a wireless communication system,

FIG. 2: a diagram illustrating the main steps of a method for transmitting a descending message,

- Figure 3: a diagram illustrating the main steps of a method of receiving a descending message.

In these figures, identical references from one figure to another designate identical or similar elements. For the sake of clarity, the elements shown are not to scale unless otherwise stated.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 schematically represents a wireless communication system 10, for example of the UNB type, comprising several terminals 20 and an access network 30 comprising several base stations 31.

The terminals 20 and the base stations 31 of the access network 30 exchange data in the form of radio signals. By "radio signal" is meant an electromagnetic wave propagating via non-wired means, the frequencies of which are included in the traditional spectrum of radio waves (a few hertz to several hundred gigahertz).

The terminals 20 are adapted to transmit uplink messages on a uplink link to the access network 30. The uplink messages are for example transmitted asynchronously. By "asynchronously transmitting" is meant that the terminals 20 autonomously determine when they transmit, without coordination of said terminals 20 to each other and to the base stations 31 of the access network 30.

Each base station 31 is adapted to receive the upstream messages of the terminals 20 which are within range. Each incoming message thus received is for example transmitted to a server 32 of the access network 30, possibly accompanied by other information such as an identifier of the base station 31 which received it, the measured power of said received message amount, the date of receipt of said amount message, etc. For example, the server 32 processes all the received messages received from the different base stations 31.

In addition, the access network 30 is also adapted to transmit, via the base stations 31, descendant messages on a downlink to the terminals 20, which are adapted to receive them. The downstream messages are for example issued at the initiative of the access network 30. In such a case, the terminals 20 must constantly listen to the downlink, waiting for a possible downlink message. The access network 30 can also send a downlink message in response to each received amount message, or send down messages only in response to certain upstream messages. For example, the access network 30 may respond only after having received a predefined number of upstream messages from the same terminal 20, or responding only to upstream messages comprising a request for this purpose, etc.

In the remainder of the description of the description, one places oneself in a nonlimiting manner in the case where the access network 30 sends outgoing messages only in response to all or part of the upstream messages sent by terminals 20, so that the terminals 20 should in principle listen to the downlink, waiting for a downward message, only after sending a message to the upright access network 30.

To reduce the cost of deploying the access network 30, the base stations 31 may be of the half-duplex type. In other words, these base stations 31 may receive upstream messages and send down messages, but not simultaneously. Thus, each base station 31 can be alternately placed in:

a reception mode, in which said base station 31 can receive upstream messages on a reception window but can not send outgoing messages,

a transmission mode, in which said base station 31 can send downgoing messages on a transmission window but can not receive upstream messages.

In the remainder of the description, one places oneself in a nonlimiting manner in the case where each terminal 20 can receive a downlink message only during a predetermined time window, called "listening window". compared to the last amount message sent by said terminal 20.

Because they do not have to transmit and receive simultaneously, such terminals 20 are, in preferred embodiments, of the half-duplex type, in order to reduce their manufacturing costs.

The listening window of a terminal 20 can begin immediately after sending a rising message, in particular if the response times of the access network 30 are short. However, in preferred embodiments, each terminal 20, after having sent a rising message, is configured to go into a standby mode on a standby window of predetermined duration also known to the access network 30. Conventionally, the sleep mode is an operating mode optimized to reduce the power consumption, in which said terminal 20 can not in particular receive messages downward, or issue messages up. For example, the duration of the idle window is chosen equal to or greater than the minimum response time of the access network 30.

After the idle window, the terminal 20 leaves the standby mode to listen to the downlink waiting for a downward message, on a listening window of predetermined duration equal to or greater than the duration of the descending message to be received. access network. Since the terminal 20 only listens for the downlink on a listening window of limited duration, the number of downstream messages that can be detected by said terminal 20, including downlink messages that are not intended for it, is greatly reduced compared to the case where the terminal 20 could receive messages descending at any time.

It should be noted that, if a terminal 20 knows a priori that no downlink message will be transmitted by the access network 30 (for example because the amount message it has sent does not include a request for this purpose ), then said terminal 20 does not listen to the downlink, and preferably remains in standby mode, for example until the transmission of the next upstream message.

When a terminal 20 listens to the downlink waiting for a message down, it can listen to a frequency band more or less wide. If the terminal 20 does not know a priori on which central frequency the message descendant must be sent, it must listen to all the frequencies possible central units for the downlink.

In the remainder of the description, one places oneself in a nonlimiting manner in the case where each terminal 20, when it must receive a descending message, knows a priori on which central frequency this descending message will be sent. Thus, the terminal 20 can listen to a frequency band centered on this central frequency, of limited width of the order of the spectral width of the descending message, for example twice as large as the spectral width of said downward message (to take account of a inaccuracy on the synthesis of the central frequency, the frequency drift of the frequency synthesis means, a possible Doppler effect, etc.). Since the terminal 20 only listens for the downlink on a frequency band of limited width, the number of downstream messages that can be detected by said terminal 20, including downlink messages that are not intended for it, is strongly reduced compared to the case where the terminal 20 could receive messages descending on any center frequency of the downlink.

In preferred embodiments, the central frequency of the downlink message is determined from the central frequency of the upstream message in response to which said downstream message is to be transmitted. Therefore, at the access network 30, the central frequency of the upstream message is measured, and the central frequency on which the downstream message is to be transmitted is determined according to the measurement of the central frequency of the upstream message, for example according to a predefined frequency offset for the terminal having sent the rising message. A) Method of sending a descending message

FIG. 2 diagrammatically represents the main steps of a method 50 for sending a downlink message to a particular terminal among all the terminals, called the "destination terminal".

As illustrated in FIG. 2, the transmission method 50 mainly comprises the following steps, which will be described in more detail below:

Generation of error detection data from main data for the destination terminal,

- 52 modification of the main data and / or data of detecting errors according to an identifier of said destination terminal,

Transmitting, by a base station 31 of the access network 30, a descending message comprising the main data and the error detection data obtained after modification.

Of the various steps illustrated in FIG. 2, only the step 53 of sending the downlink message must necessarily be executed at least partially by a base station 31. The other steps illustrated in FIG. 2 can be executed by a base station 31 and / or by the server 32 of the access network 30. In particular, all the steps illustrated in FIG. 2 can be executed by the base station 31 used to issue the downlink message on the downlink.

In the remainder of the description, reference is made in a nonlimiting manner in the case where the generation step 51 and the modification step 52 are executed by the server 32, which then transmits the main data and the detection data. errors obtained after modification to the base station 31, which then executes the transmission step 53.

In this case, the base stations 31 and the server 32 comprise respective processing modules (not shown in the figures), each processing module comprising for example one or more processors and storage means (magnetic hard disk, electronic memory , optical disk, etc.) in which is stored a computer program product, in the form of a set of program code instructions to be executed to implement the various steps of the transmission method 50. In a variant, each processing module comprises one or more programmable logic circuits of the FPGA, PLD, etc. type, and / or specialized integrated circuits (ASICs) adapted to implement all or part of said transmission process steps. .

Each base station 31 further comprises wireless communication means, considered as known to those skilled in the art, allowing said base station to receive uplinks and to issue messages descending. The base stations 31 and the server 32 also comprise respective network communication means, considered as known to those skilled in the art, allowing the server 32 to exchange data with each base station 31.

In other words, the access network 30 comprises a set of means configured in software (specific computer program product) and / or hardware (FPGA, PLD, ASIC, etc.) to implement the different steps of the emission process 50.

Nonlimiting examples of implementation of the generation step 51, the modification step 52 and the emission step 53 are now described in more detail.

A.1) Step of generating error detection data

The main data is, from a protocol layer view of the communication systems, physical layer level data.

Conventionally, the main data may comprise useful data and control data that can be used to decode said useful data. The useful data may be of any known type, and in principle come from protocol layers above the physical layer, which are outside the scope of the invention. The control data, added to the useful data at the level of the physical layer, can also be of any known type, except that they do not include an identifier of the destination terminal.

Step 51 aims to generate error detection data from the main data to be transmitted to the destination terminal. The error detection data are intended to make it possible to check, at each terminal 20, the integrity of the main data extracted from a descending message.

Said error detection data can be obtained according to any method known to those skilled in the art, for example by a cyclic redundancy check ("Cyclic Redundancy Check" or CRC in the English literature), by a function hash, etc.

Conventionally, the same method is then used at each terminal 20 to obtain, from the main data extracted from the descending message, error detection data which is compared with that extracted from the descending message to verify the integrity. said main data extracted. A.2) Main data modification step and / or error detection data

In step 52, the main data and / or the error detection data is changed according to an identifier of the destination terminal, by means of a reversible predefined modification function. This modification is also carried out with a constant spectral width and a constant duration with respect to the main data and / or the error detection data. In other words, the change does not increase:

the spectral width of the modified data, namely the main data and / or the error detection data: the modification therefore does not introduce spreading of the frequency spectrum of the descending message with respect to the case where the step 52 of modification would not be executed,

the duration of the modified data, namely the main data and / or the error detection data: the modification therefore does not introduce an extension of the duration of the descending message with respect to the case where the modification step 52 would not be executed.

In the remainder of the description, one places oneself in a nonlimiting manner in the case where the main data and the error detection data are previously assembled so as to obtain data assembled. The modification step 52 is therefore performed on the assembled data. However, according to other examples, nothing makes it possible to directly modify the main data and / or the error detection data, possibly to assemble them after modification.

Any assembly method known to those skilled in the art can be implemented, and the assembly method is known from each terminal 20, to allow each terminal 20 to separate the main data and the detection data. errors extracted from a descendant message.

In the remainder of the description, one places oneself in a nonlimiting manner in the case where the assembly consists of adding the error detection data following the main data, so that the duration of the assembled data corresponds to the sum respective durations of main data and error detection data. Nothing precludes, according to other examples, to consider other methods of assembly. In particular, if the main data and the error detection data are in the form of real (i.e. non-complex) symbol sequences, then they can be assembled so as to obtain assembled data presenting itself. in the form of a sequence of complex symbols, the real part of which for example corresponds to the main data and the complex part of which corresponds to the error detection data.

Different modification functions can be implemented, and the choice of a particular modification function is only a variant of implementation of the invention. The modification function must however be reversible. "Reversible" means that:

for each possible terminal identifier 20: there exists a single sequence of assembled data making it possible to obtain each possible downlink message (the correspondence between the assembled data sequences and the descending messages obtained by modification is therefore one-to-one),

for each possible sequence of assembled data, the descendant messages obtained as a function of different identifiers of terminals 20 are necessarily different.

The inverse function of the modification function used during the modification step 52 is known from each terminal 20, or can be determined by each terminal 20. By "inverse function" is meant the function which makes it possible to recover, at from the descending message, the assembled data actually used to obtain this downward message, when the identifier considered is the same as that used during the modification step 52. In other words, if we denote by F the function of modification and by G the inverse function, then:

G (F (B, ID), ID) = B

expression in which:

- B corresponds to the sequence of data assembled, - ID corresponds to the destination terminal identifier.

In addition, by construction, we have:

G (F (B, ID), ID ') ≠ B

an expression in which ID 'corresponds to a terminal identifier different from the identifier ID used during the modification step 52.

For example, if the assembled data and the identifier of the destination terminal are binary symbol sequences, then the editing function of the assembled data may advantageously correspond to a symbol symbol combination between said assembled data and said destination terminal identifier. means of an "exclusive" function.

Indeed, such a modification function is particularly simple to implement, and has the further advantage that the modification function and its inverse function are the same function. Thus, at the destination terminal, the assembled data can be retrieved by combining symbol to symbol the downlink message and the identifier of said destination terminal by means of an "exclusive" function.

The identifier of the destination terminal 20, used to modify the data assembled during the step 52 of editing the assembled data, is a temporary identifier, which must be able to be determined by both the access network 30 and the terminal 20 recipient.

In preferred implementation modes, the temporary identifier of the destination terminal 20 is determined from control data extracted from the amount message previously received from the destination terminal. For example, the control data used to determine said temporary identifier is a permanent identifier of the destination terminal, a sequence number of the upstream message (i.e., a counter of upstream messages incremented by said destination terminal at each destination terminal). new issue of a rising message), etc.

In preferred embodiments, the temporary identifier of the destination terminal is obtained by shifting a predefined identification code known to both the access network 30 and the destination terminal 20. Preferably, the same identification code is used for all terminals 20, which are optionally distinguished by the offset introduced, which is for example determined as a function of control data included in the amount message previously issued by said destination terminal.

By "shifting" of the identification code is meant the starting point from which the identification code is scanned to modify the assembled data. If the end of the identification code is reached before having finished modifying the assembled data, then the journey of the identification code is continued by resuming from the beginning of said identification code. Thus, different identifiers are obtained, from the same identification code, by browsing said identification code from different starting points.

Preferably, the same calculation function of the offset to be applied to obtain the temporary identifier is used for all the terminals 20, and is therefore known from said terminals 20. For example, it is possible to multiply the permanent identifier of the terminal 20 destination by the sequence number of the amount message, in response to which the descending message must be sent, the offset to be applied corresponding to the result of this multiplication modulo the length of the identification code.

In preferred embodiments, the identification code is a pseudo-random, for example binary, sequence generated by means of a predefined pseudo-random generator, and the calculated offset is used as a seed of said pseudo-random generator. . Where appropriate, on the side of the terminals 20, the same pseudo-random generator is implemented, and the same function of calculating the offset (seed) to be applied is implemented. A.3) Step of issuing the descending message

As indicated above, the transmission step 53 is performed at least partially by a base station 31 of the access network. More particularly, several operations may possibly be performed on the descending message, which are outside the scope of the invention.

In particular, the assembled data obtained after modification are, for example, in baseband, and the base station 31 can translate them into frequencies in order to transmit the descending message on a central frequency determined for example from the measured central frequency of the uplink message. response to which said downlink message is to be transmitted. B) Method of receiving the descending message

FIG. 3 schematically represents the main steps of a method 60 for receiving a downlink message transmitted in accordance with any of the modes of implementation of the transmission method 50 described above. In the remainder of the description, the term "receiver terminal" denotes the terminal which implements the reception method 60, which does not know a priori whether it is the destination terminal of the descending message, it being understood that said method 60 of reception can be implemented by each terminal 20.

For example, each terminal 20 comprises a processing module (not shown in the figures), comprising one or more processors and storage means (magnetic hard disk, electronic memory, optical disk, etc.) in which a program product is stored. computer, in the form of a set of program code instructions to be executed to implement the different steps of the receiving method 60. In a variant, each processing module comprises one or more programmable logic circuits, of the FPGA, PLD, etc. type, and / or specialized integrated circuits (ASIC) adapted to implement all or part of said steps of the reception method 60. Each terminal 20 furthermore comprises wireless communication means, considered as known to those skilled in the art, enabling said terminal to send up messages and to receive descendant messages.

In other words, each terminal 20 comprises a set of means configured in software (specific computer program product) and / or hardware (FPGA, PLD, ASIC, etc.) to implement the various steps of the method 60 reception.

As illustrated by FIG. 3, the reception method 60 firstly comprises a step 61 for the receiver 20 detecting the downlink message. The detection step 61 is mainly intended to find, in a radio signal measured on the downlink, a downlink message transmitted by the access network 30. Any detection method known to those skilled in the art can be implemented. artwork.

The method 60 then comprises a step 62 of extracting data assembled by modifying the message downward according to a identifier of the receiver terminal 20, by means of the inverse function of the modification function used on transmission.

By denoting by B the sequence of assembled data transmitted by the access network 30, and by ID the identifier of the destination terminal 20, then if the receiving terminal 20 is the destination terminal 20, its identifier corresponds to the identifier ID, and the sequence B of assembled data is found (in the absence of transmission errors) according to the expression:

G (F (B, ID), ID) = B

If, on the other hand, the receiving terminal 20 is not the destination terminal, then the identifier of said receiving terminal, designated by ID ', is different from the identifier ID of said destination terminal. At the end of the extraction step 62, a sequence B 'of assembled data is obtained, different from the sequence B transmitted by the access network 30:

G (F (B, ID), ID ') = B' ≠ B

As indicated above with reference to the transmission method 50, the identifier of the receiving terminal 20 is a temporary identifier, which the receiving terminal 20 determines in the same way as the access network 30, for example as a function of data. control messages included in the amount message previously sent by said receiving terminal, in response to which a descending message must be sent.

At the end of the extraction step 62, therefore, there is assembled data, comprising main data and error detection data which can be separated by the receiving terminal which knows the method of assembly used. on the show.

At this stage, the receiving terminal 20 still does not know if the downlink message is intended for it. The fact that the receiver terminal only listens for the downlink on a predetermined listening window and / or around a predetermined central frequency makes it possible to reduce the probability for the receiving terminal to detect several downstream messages. . However, this does not ensure that only the descendant message intended for it will be detected. It is therefore necessary to determine, for each downlink detected by the receiver 20, whether this message detected descendant is intended for him.

For this purpose, the reception method 60 comprises a step 63 of determining, as a function of the error detection data, whether the main data comprises errors. Indeed, if the identifier of the receiving terminal 20 corresponds to the identifier ID of the destination terminal, then the data sequence formed corresponds to the sequence B transmitted by the access network 30. Therefore, the main data and the data error detection of the sequence B are by construction coherent with each other, and no error is detected. On the other hand, if the identifier ID 'of said receiving terminal is different from the identifier ID of said destination terminal, then the sequence B' of assembled data is different from the sequence B transmitted by the access network 30. In such a case , the main data and the error detection data extracted from the sequence B 'have no reason to be coherent with each other, and errors will in principle be detected.

As shown in Figure 3, when no error is detected

(reference 631 in FIG. 3), the receiving terminal 20 is considered to be the destination terminal of the said downward message, and the processing of the main data continues, for example to extract useful data.

On the other hand, when errors are detected (reference 632 in FIG. 3), the receiving terminal 20 is not considered to be the destination terminal, and the processing of the downward message may stop.

Claims

A method (50) for transmitting a downlink message on a downlink between an access network (30) and a plurality of terminals (20), said downlink message being formed from primary data to be transmitted to a terminal ( 20), said method (50) comprising steps of:

- (51) generating error detection data from the main data,

- (52) modifying the main data and / or the error detection data according to an identifier of said destination terminal (20) by means of a reversible predefined modification function, said modification being carried out with a constant spectral width and of constant duration with respect to said main data and / or error detection data,

- (53) transmission, by a base station (31) of the access network (30), of a downlink message comprising the main data and the error detection data obtained after modification, characterized in that, said downlink message being sent in response to an amount message previously received from the destination terminal (20), the identifier of said destination terminal (20) is a temporary identifier determined from control data included in said amount message.

A method (50) according to claim 1, wherein the identifier of the destination terminal is obtained by shifting a predefined identification code, the same identification code being used for each terminal (20), the offset to be applied being determined based on control data included in the amount message.

The method (50) of claim 2, wherein the identification code is a pseudo-random sequence generated by means of a predefined pseudo-random generator, the determined offset being used as a seed of said pseudo-random generator.

Method (50) according to one of the preceding claims, wherein the control data used to determine the identifier of the terminal recipient have a sequence number of the amount message. The method (50) according to one of the preceding claims, wherein, the main data, the error detection data and the destination terminal identifier being binary symbol sequences, the modification corresponds to a symbol symbol combination at the means of an "exclusive" function.

Method (50) according to one of the preceding claims, wherein the descending message is transmitted during a predetermined time window with respect to the previously received amount message of said destination terminal.

Method (50) according to one of the preceding claims, wherein the descending message is transmitted on a predetermined central frequency with respect to a central frequency of the amount message previously received from said destination terminal.

Base station (31) characterized in that it comprises means configured to implement a method (50) of emission according to one of the preceding claims.

Access network (30) characterized in that it comprises means configured to implement a transmission method (50) according to one of claims 1 to 7.

- Method (60) for reception, by a receiver terminal (20), of a downlink message transmitted in accordance with a transmission method (50) according to one of claims 1 to 7, characterized in that it comprises steps of:

- (61) detection of the descending message on the downlink,

- (62) extracting main data and error detection data by modifying the descending message according to an identifier of the receiver terminal (20), by means of a function inverse to the modification function used to form the downlink message, the identifier of the receiver terminal (20) being a temporary identifier determined from control data included in a rising message previously sent by said receiving terminal, in response to which a descending message must be issued,

- (63) determining, based on the error detection data, whether the main data has errors, the receiving terminal (20) being considered to be the receiving terminal (20) of said downward message when the main data is considered as with no errors.

1 1 - Method (60) according to claim 10, wherein the receiving terminal (20) listens to the downlink on a time window, called "listening window", predetermined with respect to the amount message previously issued by said receiving terminal.

12 - Method (60) according to one of claims 10 to 1 1, wherein the terminal (20) receiver listens the downlink around a predetermined central frequency with respect to a central frequency of the amount message previously issued by said terminal receiver.

13 - Method (60) according to one of claims 10 to 12, wherein the identifier of the receiving terminal is obtained by shifting a predefined identification code, the same identification code being used for each terminal (20). ), the offset to be applied being determined as a function of control data included in the amount message.

14 - Method (60) according to one of claims 10 to 13, wherein the control data used to determine the identifier of the receiving terminal include a sequence number of the message amount.

15 - Terminal (20) characterized in that it comprises means configured to implement a method (60) of receiving according to one of claims 10 to 14.