TITLE: Method for accessing a communication network, attachment method, terminal, base station and corresponding computer programs.

1. Field of the invention

The field of the invention is that of digital communications.

More specifically, the invention relates to the phase of attachment of a terminal to a communication network. In particular, it offers a solution for rapid network access, for example for instant messaging type applications.

The invention finds in particular, but not exclusively, applications in the field of LTE (in English “Long Term Evolution”) or 5G.

2. Prior Art

Conventionally, for a terminal to be able to communicate with another in a communication network, two phases are implemented: an attachment phase to the communication network, during which a terminal is identified, synchronized with the network and configured , and a communication phase, during which the terminal can exchange useful data with the network and/or another terminal attached to the network.

By way of example, according to the LTE standard, a random access procedure based on the use of the RACH channel (in English "Random Access Channel", in French "random access channel"), known as the RACH procedure, is implemented implemented in order to be able to attach a terminal to the network. Such a channel is “random access” because, from the point of view of the network, it is difficult to know when a terminal will seek to connect to the network.

The main objectives of the RACH procedure are to ensure the synchronization of the terminal and the base station (for example the eNB according to the LTE standard) in the uplink and to identify the terminal, so that the network can know it and configure it.

The synchronization of the base station and the downlink terminal can be ensured by the periodic broadcasting of system information carrying synchronization information.

The main steps of the RACH procedure are described below.

As illustrated in Figure 1, when the terminal UE comes out of standby mode or enters a coverage area of ​​a base station, eNodeB for example, it receives system information 11, regularly broadcast in the network by a network entity, for example the eNodeB base station. Such information identifies

in particular at least one time-frequency resource, called RACH resource, intended to be used by the terminal for the RACH procedure.

Upon receipt of this system information, the terminal UE randomly selects a preamble from a group of available preambles, and transmits, on the RACH resource, a first message 12 carrying this preamble, an identifier, denoted RA-RNTI (in English "Random Access - Radio Network Temporary Identifier”), associated with the RACH resource and therefore known to the network, as well as a possible indication of the volume to be expected for data transmission. The RA-RNTI identifier can be used in particular to detect transmission errors (CRC or "Cyclic Redundancy Check").

As the network has not yet identified the terminal, the network (or more precisely an entity of the network, for example the base station) responds with a second message 13, denoted RAR (in English “Random Access Response”), carrying the identifier of the preamble received on the RACH resource, denoted PID (in English “Preamble ID”), an estimate of a time shift to be applied for the transmission of a message by the terminal, taking into account the travel time between the terminal and the base station, denoted TA (in English “Timing Advance”), a temporary network access identifier, denoted TC-RNTI (in English “Temporary Cell Radio Network Temporary Identifier”), and an indication of the resources allocated for uplink communications, denoted “UL grant”. These different parameters can be encapsulated in packets and transmitted on the MAC layer. In particular, such packets can be coded using the RA-RNTI identifier, associated with the RACH resource and therefore known to the network. In this way, only the terminal having transmitted the first message 12 on the RACH resource can decode these packets.

Upon receipt of these packets, the terminal can therefore decode them, and check whether the PID identifier indeed corresponds to the preamble that it has selected and transmitted in the first message 12. If this is the case, it can continue to decode the different settings. Otherwise, it may interrupt the decoding.

When the terminal has verified that the received PID identifier indeed corresponds to the transmitted preamble, it knows that the network has correctly received the first message 12 with the preamble. He can therefore adjust his transmission time taking into account the TA parameter, and transmit his UEJD identifier in a third message 14, on the resources allocated for communications on the uplink “UL grant”. The UEJD identifier is for example the IMSI number (in English let "International Mobile Subscriber Identifier") of the terminal's SIM card. In particular, this third message 14 can be coded using a temporary identifier TC-RNTI generated by the base station.

Upon receipt of this request, the base station can send a fourth message 15 to the terminal, so as to resolve any collision problems. This message carries the identifier of the UEJD terminal.

If this identifier of the UEJD terminal is identical to that transmitted in the third message, this means that the terminal is known to the network. The terminal can then change the temporary identifier TC-RNTI to C-RNTI (“Cell RNTI”), which is a specific identifier used by the terminal during the communication phase with the network, after the attachment phase, for example as CRC to detect transmission errors.

Otherwise, it means that the terminal is not known to the network. The terminal must then restart the RACH procedure.

At the end of the RACH procedure, the base station therefore knows the UEJD identity of the terminal. On the other hand, the latter cannot yet transmit useful data (i.e. start the communication phase) until the network has configured the terminal by, for example, implementing an RRC-type radio resource control protocol ( in English “radio resource control”). This configuration is necessary for the terminal to effectively use the radio link provided by the base station.

The RACH and RRC procedures are therefore particularly useful for network access and terminal configuration.

However, a drawback of these techniques is that they must be implemented each time the terminal wishes to access the network, for example when the terminal comes out of standby mode or switches to a new cell of a cellular network ( handover). However, such techniques are quite long to implement and costly in terms of resources.

In particular, when the communication phase is of short duration, for example when the terminal sends instant messaging type messages (SMS, MMS, chat, sending a message via an application such as Facebook, Whatsapp, Twitter - registered trademarks - for example), the network attachment phase can be more costly in time and/or in resources than the communication phase. Indeed, such instant messages generally have a small size, of the order of

a few bytes or kilobytes, and the cost of the attachment phase becomes significant compared to the cost of the communication phase.

There is therefore a need for a new technique for accessing the network, which is simple to implement and inexpensive in terms of time and/or resources.

3. Disclosure of Invention

The invention proposes, according to at least one embodiment, a method for accessing a communication network, implemented by a terminal.

According to the invention, such a method comprises:

the reception of system information broadcast by said network, the system information comprising an identification of at least one time-frequency resource capable of carrying information relating to a unique terminal identifier, the transmission to the network of an access request , said access request carrying first information representative of a unique identifier of said terminal, transmitted on at least one of said time-frequency resources identified from said system information, called specific resource,

the authorization of access to said network in the event of receipt of a response to said access request carrying a second piece of information representing the unique identifier of said terminal.

The proposed solution thus makes it possible to identify, in the system information disseminated in the network, one or more specific time-frequency resources, which the terminal will be able to use from its first transmission to the network to transmit its unique identifier, which may be its physical layer identifier, its I MSI identifier, or any other unique identifier, such as for example its MSISDN identifier (in English “Mobile Station ISDN Number”).

Thus, the network access procedure according to at least one embodiment of the invention is simplified compared to the prior art, since it is based on the exchange of two main messages (an access request carrying an identifier terminal, and a response to the request), while it is based on the exchange of four main messages according to the prior art as described in relation to Figure 1.

Due to the limited number of messages exchanged, the network access procedure according to at least one embodiment of the invention is also faster than the RACH procedure described in relation to the prior art and makes it possible to optimize the spectral efficiency during the access procedure.

It is noted that such an access procedure must be implemented each time the terminal leaves the network (for example because it enters standby mode) and wishes to “enter” the network again (for example because it exits standby mode). It is therefore desirable to simplify and speed up the access procedure.

In particular, access to the network is authorized if a response to the access request is received, and if this response carries a second piece of information representing the unique identifier of the terminal. For example, the first and second pieces of information representative of the unique identifier of the terminal are identical, or correlated. These first and second pieces of information make it possible to identify the same terminal.

According to a first embodiment, the first piece of information representative of the unique identifier of the terminal can be transmitted in a dedicated resource, denoted TFR, identified from the system information.

According to a second embodiment, the first piece of information representative of the unique identifier of the terminal can be transmitted in a resource conventionally used for channel access, for example the RACH resource. According to this second embodiment, the network can reserve a greater time-frequency resource for the transmission of the first information representative of the unique identifier and conventional information for access to the channel.

According to a particular embodiment, said access request also carries a useful message intended to be transmitted to at least one other terminal. In particular, the useful message is transmitted with the first piece of information representing a unique identifier of the terminal on the specific time-frequency resource, or on another time-frequency resource capable of carrying a useful message identified in the system information.

The proposed solution thus allows the transmission of useful messages from the terminal to the network during the access procedure, i.e. without requiring the prior configuration of the terminal (based for example on the implementation of a radio resource control protocol of the CRR).

In particular, the proposed solution makes it possible to improve the spectral efficiency of the network, in particular when the terminal sends messages with an application of the instant messaging type (SMS, MMS, chat, Facebook, Twitter, Whatsapp - registered trademarks, etc.).

It should be noted in this respect that the unique identifier of the terminal allows, among other things, the identification of the sender of a useful message via an application of the social network type. It is therefore an identifier at the application level.

According to a particular embodiment, the system information identifies at least two time-frequency resources capable of carrying the useful message. According to this embodiment, the method implements the selection of at least one of the time-frequency resources taking into account the size of the useful message intended to be transmitted to at least one other terminal. In this case, the useful message can be transmitted on the selected resource.

For example, the system information identifies a first resource for the transmission of useful messages having a size of the order of a few bits, denoted TFR1, a second resource for the transmission of messages of a few bytes, denoted TFR2, and a third resource for the transmission of messages of a few kilobytes, denoted TFR3.

This optimizes the use of time-frequency resources, by adapting them to the size of the useful message.

According to a particular embodiment, the first piece of information representative of the unique identifier of said terminal and/or the useful message is transmitted to the network taking into account modulation and coding information associated with the specific time-frequency resource selected for the transmission. Such modulation and coding information is obtained from system information.

In this way, the terminal is aware of the modulation and coding schemes (MCS, in English “Modulation and Coding Scheme”) to be used in the network, in particular for the transmission of payload data, from the start of the access procedure.

According to a particular embodiment, the unique identifier of the terminal is an integer, and the transmission also transmits a reference signal obtained by applying a cyclic shift to a predefined basic sequence. Such a cyclic shift can be determined based on the terminal's unique identifier.

The reference signal transmitted from the terminal to the network therefore does not carry a classic basic sequence, but a modified version of this sequence (shifted cyclically) making it possible to transmit the unique identifier of the terminal, or part of this identifier, directly in the reference signal.

This optimizes the transmission rate, by reducing the quantity of bits necessary to transmit the unique identifier of the terminal.

For example, the reference signal is of the demod reference signal type.ulation (DMRS, in English “DeModulation Referenced Signal”). The base sequence may be network defined, standardized, or otherwise. This is a sequence known to the terminal and to at least one network entity, for example a base station.

In particular, when the unique identifier of the terminal is greater than a maximum number of cyclic shifts, the first piece of information representative of the unique identifier of the terminal comprises the integer part of the ratio between the unique identifier and the maximum number of cyclic shifts, also called remaining value. The maximum number of cyclic shifts can in particular be obtained from the system information.

In this way, the quantity of bits necessary to transmit the first piece of information representative of the unique identifier of the terminal is low.

For example, the maximum number of cyclic shifts is equal to the length of said base sequence.

As a variant, the terminal can directly transmit its unique identifier to the network.

According to a particular embodiment, the access request also carries a preamble selected from a plurality of preambles, transmitted on the specific time-frequency resource or on a time-frequency resource able to carry the preamble (for example the RACH resource) identified from said system information. According to this embodiment, authorization to access the network is granted when the response to the access request carries the second piece of information representing the unique identifier of the terminal and information representing the selected preamble.

A time-frequency resource dedicated to the transmission of the preamble is also called “used RACH”. For example, such an “used RACH” resource is associated with one or more time-frequency resources capable of carrying a useful message.

According to a particular embodiment, the access request also carries at least one indicator indicating a return to standby mode of the terminal following authorization of access to the network.

For example, part of the specific time-frequency resource is reserved for the transmission of such an indicator. As a variant, part of a time-frequency resource dedicated to the transmission of a preamble is reserved for the transmission of such an indicator. As a variant, at least two types of preamble are defined, a first type of preamble to be used when the terminal wishes to switch to standby mode after having accessed the channel, a second type of preamble to be used when the terminal wishes to continue the configuration procedure after have accessed the channel. According to this variant, the indicator is therefore the type of preamble selected.

Such an indicator can in particular be used by a network entity to detect the transmission of an instant messaging type message, for which the terminal wishes to return to standby mode after the transmission of the useful message.

In particular, when the terminal has received a response to the access request and network access is authorised, the terminal can switch to standby mode. In this way, the energy consumption of the terminal sending the access request is limited.

Alternatively, when access to the network is authorized, the terminal can remain in active mode.

For example, if the access request does not carry a useful message, said method implements a configuration phase of said terminal with said network.

Indeed, if the access request carries the first piece of information relating to the unique identifier of the terminal, but does not carry any useful message, it means that the terminal is using the proposed solution to quickly access the network. In this case, the terminal does not wish to return to standby mode when network access has been authorized.

According to a particular embodiment, in the event of receipt of a response to said access request not carrying second information representative of the unique identifier of said terminal, said method comprises the retransmission of said access request, said first information representative of the unique identifier of said terminal being transmitted on a new specific time-frequency resource identified in said response.

This particular embodiment can in particular be implemented when a network entity, for example the base station, can decode the preamble of the access request transmitted on a dedicated time-frequency resource, but cannot decode the useful message and/or the first piece of information representative of the unique identifier of the terminal of the access request transmitted on a specific time-frequency resource.

According to this embodiment, rather than restarting the access procedure entirely, it is possible to allocate to the terminal a new specific resource for the transmission of the first piece of information representing the unique identifier of the terminal, and possibly the museful message.

Moreover, as the base station indicates to the terminal the new resource to be used for the transmission of the first piece of information representative of the unique identifier of the terminal, and possibly of the useful message, the risk of collision with access requests transmitted by other terminals is limited.

According to a particular characteristic, in the event of non-receipt of a response to the access request at the end of a predetermined time interval, said method comprises the retransmission of said access request.

In other words, following the transmission of the access request, the terminal remains listening for a predetermined period, denoted RAR window (“RAR window”). If it has not received a response to its access request at the end of this period, it can retransmit the access request, possibly by using other time-frequency resources.

In another embodiment, the invention relates to a corresponding terminal.

Such a terminal is in particular suitable for implementing the access method described previously. This is for example user equipment such as a mobile phone. This terminal may of course include the various characteristics relating to the method according to the invention, which may be combined or taken separately. Thus, the characteristics and advantages of this terminal are the same as those of the method described previously. Therefore, they are not further detailed.

The invention also relates, according to one embodiment, to a method for attaching a terminal to a communication network. In particular, such a method is implemented at the level of a network entity, for example a base station.

According to the invention, such a method comprises:

the dissemination of system information by said network, the system information comprising an identification of at least one time-frequency resource capable of

carry information relating to a unique terminal identifier, the verification of the reception, on at least one of said time-frequency resources identified from system information, called specific resource, of a first piece of information representing a unique identifier of the terminal carried by a request for access to said network;

if said first information representative of a unique identifier of said terminal is received, the transmission to said terminal of a response to said access request, carrying a second information representative of the unique identifier of said terminal.

Such a method is in particular suitable for receiving an access request sent by a terminal, according to the network access method described above.

As already indicated, according to at least one embodiment, it allows a terminal to quickly access the network.

According to a particular embodiment, said verification also verifies the reception, on the specific time-frequency resource used for the transmission of the first piece of information representing the unique identifier of the terminal or on another time-frequency resource capable of carrying a message useful, identified from said system information, of a useful message intended to be transmitted to at least one other terminal.

The method also comprises the transmission of said useful message to said at least one other terminal if said first piece of information representing a unique identifier of said terminal and said useful message are received.

The method according to this embodiment thus makes it possible to optimize the spectral efficiency of the network.

According to a particular embodiment, the unique identifier of the terminal being an integer and a reference signal obtained by applying a cyclic shift to a predefined basic sequence being received on the specific time-frequency resource, said method implements a step of determining the unique identifier of said terminal.

To do this, knowing the base sequence and having received the reference signal, it is indeed possible to determine the number of shifts made to the base sequence, and therefore the unique identifier of the terminal.

According to a particular embodiment, the method also comprises:

the verification of the reception, on said time-frequency resource or on at least one time-frequency resource capable of carrying a preamble, identified from the system information, of a preamble carried by the access request, if said preamble is received, and that said first information representative of a unique identifier of said terminal is not received, the transmission to said terminal of a response to said access request carrying information representative of said preamble and identifying a new specific time-frequency resource (i.e. for the transmission of said first information and possibly of the useful message).

In another embodiment, the invention relates to a corresponding base station.

Such a station base is in particular suitable for implementing the attachment method described above. This is for example an eNodeB according to the LTE standard, or gNB according to 5G. The base station may of course include the various characteristics relating to the method according to the invention, which may be combined or taken separately. Thus, the characteristics and advantages of the base station are the same as those of the method described above. Therefore, they are not further detailed.

The invention also relates to one or more computer programs comprising instructions for the implementation of at least one method as described above when this or these programs are executed by at least one processor.

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

4. List of Figures

Other characteristics and advantages of the invention will appear more clearly on reading the following description of a particular embodiment, given by way of a simple illustrative and non-limiting example, and the appended drawings, among which:

[Fig 1] Figure 1 illustrates the main steps of the RACH procedure according to the prior art;

[Fig 2] Figure 2 illustrates the main steps implemented by a terminal and a base station according to one embodiment of the invention;

[Fig 3] Figure 3 illustrates the use of a specific time-frequency resource according to one embodiment of the invention;

[Fig 4] Figure 4 shows examples of cyclic shift applied to a base sequence;

[Fig 5] Figure 5 illustrates the messages exchanged between a terminal and a base station according to a first example;

[Fig 6] Figure 6 illustrates the messages exchanged between a terminal and a base station according to a second example;

[Fig 7] Figure 7 shows the simplified structure of a terminal implementing a network access method according to one embodiment of the invention;

[Fig 8] Figure 8 shows the simplified structure of a base station implementing a method of attaching to a network according to one embodiment of the invention.

5. Description of an embodiment of the invention

5. 1 General principle

The general principle of the invention is based on a new technique allowing a terminal to attach itself simply and quickly to a network. To do this, the system information conventionally broadcast by the network is modified to identify at least one time-frequency resource capable of transmitting information relating to a unique terminal identifier to the network. Such resources are therefore not reserved for a particular terminal, but can be used by any terminal wishing to access the network.

In particular, the network can reserve a time-frequency resource greater than the RACH resource conventionally reserved for the RACH procedure, so that the terminal can transmit its unique identifier (or more generally a first piece of information representative of its unique identifier) ​​with the information conventionally transmitted on the RACH resource.

As a variant, the network can reserve a distinct time-frequency resource so that the terminal can transmit at least a first piece of information representative of its unique identifier.

A terminal wishing to access the network can thus directly transmit to the network (i.e. to at least one entity of the network, for example a base station), at the level of the physical layer, its unique identifier, as well as possibly a useful message intended for another terminal, on at least one specific time-frequency resource reserved by the network.

According to the information received, the network can send a response to the terminal. The exchange of these two main messages (an access request and a response to the access request) between the terminal and the network is sufficient to authorize the terminal to access the network or not.

The terminal can then return to standby mode or remain in active mode and continue the configuration procedure.

In particular, if we place ourselves in the context of an application of the instant messaging type, according to which the terminal sends one or more short messages, the terminal can access the network and transmit a short message via the exchange of these two main messages, without requiring the implementation of a terminal configuration procedure (of the RCC type for example), and can return to standby mode after each transmission, if it does not wish to continue with a communication phase, or remain in active mode, for example if several messages have to be transmitted.

Presented below, in relation to FIG. 2, are the main steps implemented by a terminal 21 and an entity of a communication network, for example a base station 22 according to one embodiment of the invention.

Conventionally, the base station 22 broadcasts 221 system information in the network. Such system information can be broadcast periodically, and carries in particular a synchronization signal (for example of the SSB “Synchronization Signal Block” type) allowing in particular terminals wishing to access the network to synchronize with the base station.

According to the invention, the system information is modified and includes an identification of at least one time-frequency resource capable of carrying information relating to a unique terminal identifier.

When the terminal 21 comes out of standby mode or enters a coverage area of ​​the base station 22, it can therefore receive 211 the system information broadcast by the base station 22, and synchronize with the base station for the downlinks .

The terminal 21 can then transmit 212 to the base station a network access request. Such an access request notably carries first information representative of a unique identifier of the terminal. According to the invention, the first piece of information representing a unique identifier of the terminal is transmitted on at least one of said time-frequency resources identified from the system information and therefore reserved by the network, called specific resource.

The base station 22 observes an uplink channel, for example the RACH channel, and checks 222 whether the first piece of information representing a unique identifier of the terminal has been received on one of said time-frequency resources reserved by the network.

In the event of a positive verification, the base station transmits 223 to the terminal a response carrying a second piece of information representing the unique identifier of the terminal.

The terminal 21 checks 213 whether a response to the access request has been received.

In the event of positive verification, and more specifically in the event of receipt of a response to the access request carrying a second item of information representing the unique identifier of the terminal, the terminal considers that it has been authorized to access the network.

If he does not wish to continue the configuration procedure and the communication phase, he can switch to standby mode. Otherwise, it can remain in active mode.

5.2 Description of a particular embodiment

An example of implementation of the invention is presented below, according to which the access request carries first information representative of a unique identifier of the terminal, as well as a useful message, intended to be transmitted to another terminal.

In particular, such a useful message can be a short message, i.e. having a size of the order of a few bits or kilobits.

According to this example, it is considered that the system information, provided by the network, identifies one or more time-frequency resources capable of carrying a preamble, denoted RACH_0, as well as, for each RACH_0 resource, one or more time-frequency resources capable of carry information relating to a unique terminal identifier, denoted TFR. Moreover, according to this example, the TFR resources are also capable of carrying a useful message. For example, three resources TFR1-1 , TFR1-2 and TFR1-3 are associated with a first resource RACH_01 , two resources TFR2-1 and TFR2-2 are associated with a second resource RACH_02, etc.

The different TFR resources associated with a RACH_0 resource can be reserved to transmit useful messages of different sizes, in addition to the unique identifier of the terminal. The TFR1-1 resource can be reserved for transmitting useful messages of small size, for example less than 10 bits (generated by

example in the context of applications with low throughput: data from a sensor, M2M (“Machine-to-Machine”) communication, etc.). The TFR1-2 resource can be reserved for transmitting useful messages of medium size, for example between 10 bits and 100 bits (generated for example in the context of applications with an average bit rate: Facebook, Twitter - registered trademarks, etc.) . The TFR1-3 resource can be reserved to transmit large useful messages, for example greater than 100 bits (generated for example in the context of applications with a high bit rate).

The system information may also carry modulation and coding information, MCS, associated with each TFR resource.

Moreover, the system information can carry information relating to a maximum number of cyclic shifts that the terminal is authorized to apply to a predefined basic sequence.

As indicated in relation to FIG. 2, upon receipt of the system information, the terminal can transmit an access request to the base station, during a first phase.

To do this, it selects a preamble, for example from a group of preambles conventionally used in the RACH procedure, and a RACH_0 resource from i the RACH_0 resources identified in the system information. For example, he selects the RACH_01 resource.

The terminal must then select a TFR resource from among the TFR resources associated with the RACH_01 resource. If he wishes to transmit only his unique identifier, he can randomly select a TFR resource from among the TFR resources associated with the FtACH_01 resource. If he wishes to transmit his identifier and a useful message, he can select a TFR resource taking into account the size of the useful message that he wishes to transmit. For example, if the useful message to be transmitted has a size equal to 20 bits, the terminal selects the TFR1-2 resource.

From the system information, the terminal can also obtain the modulation and coding scheme to be used to transmit the useful message on the TFR1-2 resource. Note that if the system information identifies several TFR resources, one or more TFR resources can be used to transmit on the one hand the unique identifier of the terminal and on the other hand the useful message. If the system information identifies a single TFR resource, the unique identifier of the terminal and the useful message are transmitted on the same TFR resource.

For example, the TFR1-2 resource reserves a block comprising X time slots and Y carrier frequencies. As illustrated in FIG. 3, the resource TFR1-2 can carry a temporal succession of X OFDM symbols, each OFDM symbol carrying data modulated by Y blocks of frequency resources.

According to the example illustrated in FIG. 3, the third OFDM symbol 31 carries a reference signal, for example of the DMRS type, modulated by Y carrier frequencies.

Conventionally, such a reference signal carries a base sequence known to the terminal and to the base station. For example, such a base sequence is normalized.

According to one embodiment of the invention, the reference signal carries a version of the base sequence after cyclic shift.

Indeed, as the specific resources are not reserved for a particular terminal, but can be used by any terminal wishing to access the network, it is possible for the same resource to be used simultaneously by several terminals. The cyclic shift brought to the basic sequence notably enables the base station to differentiate between the various terminals.

In particular, the offset applied to the basic sequence is determined according to the unique identifier of the terminal.

Thus, the basic sequence can be broken down into N equal portions, with N the number of allowed cyclic shifts, defined in the system information. The number of cyclic shifts to be applied to the basic sequence to obtain the reference signal is therefore equal to the identifier of the UEJD terminal, modulo N: mod(UE_ID, N).

According to the example shown in Figure 4, the base 41 sequence can be broken down into 17 equal portions, with 17 being the number of allowed cyclic shifts defined in the system information.

If the terminal's unique identifier is equal to 1, a cyclic shift is applied to the base sequence, and a first version of the cyclically shifted base sequence 42 is obtained.

If the unique identifier of the terminal is equal to 2, we apply two cyclic shifts to the basic sequence, and we obtain a second version of the cyclically shifted basic sequence 43.

If the terminal's unique identifier is equal to 55, four cyclic shifts are applied to the basic sequence (mod (55,17)=4).

According to this last example, as the unique identifier of the terminal is greater than N, the terminal can also transmit to the base station the remaining value corresponding to the integer part of the ratio between the unique identifier and the maximum number of cyclic shifts, i.e. the value 3 according to the example above.

This remaining value can in particular be transmitted on an OFDM symbol of the resource TFR1-2 for example.

Thanks to the cyclic shift of the base sequence, and to this remaining value, the terminal can transmit first information representative of its unique identifier to the base station.

The terminal can thus transmit the access request carrying the preamble, the first piece of information representing the unique identifier of the terminal and the useful message, to the base station. This step corresponds to step 212 of FIG. 2.

According to the example described above, the preamble can be transmitted on the RACFL01 resource, and the first piece of information representing the unique identifier of the terminal and the useful message can be transmitted on the TFR1-2 resource. In particular, the data carried by the TFR1-2 resource can be coded using an RA-RNTI identifier, associated with the RACH_01 resource. More generally, the data transmitted on the specific resources can be encoded using an identifier.nt RA-RNTI.

According to a particular embodiment, the access request can also carry an indicator indicating whether the terminal wishes to switch to standby mode upon receipt of a response to the access request, or wishes to continue the attachment phase, for example by implementing the RCC protocol. This indicator can in particular be transmitted on the TFR1-2 resource, on the RACH_01 resource, or on another time-frequency resource. As a variant, at least two types of preamble are defined, a first type of preamble to be used when the terminal wishes to switch to standby mode after having accessed the channel, a second type of preamble to be used when the terminal wishes to continue the configuration procedure after have accessed the channel. According to this variant, the indicator is therefore the type of preamble selected. According to yet another variant, the absence of a useful message in the access request signifies that the terminal wishes to remain in active mode. The presence or absence of a useful message can therefore serve as an indicator.

In particular, if the terminal only occasionally transmits useful messages, for example because it uses an application of the instant messaging type, this indicator can automatically be set to a value indicating that the terminal wishes to switch to standby mode upon receipt of a response to the access request.

Conversely, if the terminal regularly transmits useful messages, the indicator can indicate that the terminal wishes to remain in active mode upon receipt of a response to the access request.

After transmission of the access request, the terminal remains awaiting a response from the base station. It therefore listens to a dedicated downlink channel, for example the PDCCH (physical downlink control channel), during a predetermined time interval, also called the RAR window.

During a second phase, the base station therefore processes the access request and can send a response to the terminal to inform it whether or not it is authorized to access the network, i.e. if the access request has been received, or inform him of a possible conflict.

In particular, such a response can be coded using an RA-RNTI identifier, associated with the RACH_01 resource according to the previous example. In this way, only the terminal having used the RACH_01 resource for the transmission of the preamble can decode the response from the base station.

The processing implemented by the base station is described below.

The base station listens to an uplink channel, for example the RACH channel, and checks whether a preamble has been received on a dedicated resource, known to the base station (for example RACH_01, RACH_02). If a preamble has been detected (for example on the RACH_01 resource), it checks whether a unique terminal identifier has been received on at least one specific resource associated with the dedicated resource carrying the detected preamble (for example the TFR1-1 resources, TFR1-2, TFR1-3).

A distinction is made between different cases depending on whether the base station has received the access request completely, partially or has not received it.

According to a first case, illustrated in FIG. 5, it is considered that the terminal UE has received the system information 51 broadcast by the base station, for example gNB, and has transmitted an access request 52 carrying a preamble, a useful message and a first item of information representative of the unique identifier of the terminal.

Returning to the previous example, the base station receives the preamble on the RACH_01 resource, and the useful message and the first piece of information representing the unique identifier of the terminal on the TFR1-2 resource. Upon receipt of the reference signal transmitted on the TFR1-2 resource, the base station can determine the number of cyclic shifts applied to the base sequence, i.e. 4, since it knows the base sequence. The base station also receives the remaining value. Knowing this remaining value, i.e. 3, the number of cyclic shifts applied to the base sequence, i.e. 4, and the maximum allowed number of cyclic shifts, i.e. 17, the base station can determine the unique identifier of the terminal (3* 17+4 = 55).

The base station can then send the terminal a response 53 carrying information representative of the preamble transmitted on the RACH_01 resource, for example PID, and a second information representative of the unique identifier of the terminal. According to the example above, the second piece of information representing the identifier of the terminal is 55 (UEJD).

When the terminal receives the response 53 during the RAR window, if it detects that the information representative of the PID preamble indeed corresponds to the preamble that it has selected for the access request, and that the second information representative of the identifier uniqueness of the terminal corresponds to its unique identifier, it considers that access to the network has been authorized. In other words, it means that the base station has correctly identified the terminal and received the useful message. The useful message is therefore now taken over by the network and can be transmitted to the destination terminal.

According to this first case, unlike the conventional RACH procedure, the TA parameter is not transmitted from the base station to the terminal. However, the base station knows the value of this parameter.

In particular, if the access request carries an indicator indicating a return to standby mode following authorization to access the network, the terminal can switch to standby mode, for example if it has no new useful messages. to be transmitted within a predefined time interval following receipt of the response to the access request (for example 2 minutes).

According to a second case, illustrated in FIG. 6, it is considered that the terminal UE has received the system information 61 broadcast by the base station, for example gNB, and has transmitted an access request 62 carrying a preamble, a useful message and a first item of information representative of the unique identifier of the terminal.

On the other hand, taking the previous example, the base station only receives the preamble on the RACH_01 resource, but does not receive the useful message and/or the first piece of information representing the unique identifier of the terminal on the TFR1-2 resource. (for example following a transmission problem on this time-frequency resource, a decoding problem, a synchronization problem, etc.).

The base station can then send the terminal a response 63 carrying information representative of the preamble, for example PID, and identifying at least one new time-frequency resource (for example in the form of the “UL grant” parameter) so that the terminal can retransmit the first piece of information representative of its unique identifier, as well as the useful message according to this example of implementation. In addition, such a response may possibly carry other parameters conventionally used in the RACH procedure, such as the TA and TC-RNTI parameters. Such parameters may be passed in the response, or in a separate message.

When the terminal receives the response 63 during the RAR window, if it detects that the information representative of the PID preamble indeed corresponds to the preamble that it has selected for the access request, but that it does not detect any second information representative of the unique identifier of the terminal, it considers that the base station has only received the preamble, but not the useful message and/or the first item of information representative of the unique identifier of the terminal.

The terminal must therefore retransmit 64 the useful message and the first piece of information representing the unique identifier of the terminal.

To do this, the terminal uses the new specific time-frequency resource identified in the response. The TA parameter can be used by the terminal to adjust its instant of transmission of the useful message and of the first piece of information representing the unique identifier of the terminal, and thus facilitate synchronization with the base station.

In particular, the useful message and the first piece of information representing the unique identifier of the terminal can be coded using the temporary identifier TC-RNTI generated by the base station.

As the useful message and the first piece of information representative of the unique identifier of the terminal are transmitted on a new time-frequency resource, specifically allocated to the terminal for this transmission by the base station, the probability that the base station receives the message useful and first information is higher.

The base station can then respond 65 with a confirmation message if it has received the useful message and the first piece of information representing the unique identifier of the terminal. In this case, the terminal considers that access to the network has been authorized, i.e. that the base station has correctly identified the terminal and received the useful message.

Otherwise, the base station may respond with an error message. In this case, the terminal must restart the access procedure, and send a new access request.

According to a third case, not illustrated, it is considered that the terminal UE has received the system information broadcast by the base station gNB, and has transmitted an access request carrying a preamble, a useful message and a first piece of information representative of the unique device identifier.

On the other hand, the terminal did not receive a response to the access request during the RAR window. In this case, the terminal considers that the access procedure has failed. The terminal must therefore restart the access procedure and send a new access request.

In the example above, we considered the transmission of an access request carrying a preamble, a first piece of information representing the unique identifier of the terminal, and a user message.e, for illustrative purposes. However, it is recalled that only the transmission of the first piece of information representative of the unique identifier of the terminal on a time-frequency resource identified by the system information is necessary for the terminal to be able to quickly access the network, as illustrated in FIG. 2. The transmission of the preamble and the transmission of the useful message are both optional.

In particular, the use of a preamble allows the base station to detect that a terminal has entered the network. However, other techniques can be implemented, in particular the simple transmission, by the terminal, of its unique identifier.

Furthermore, in the example above, we considered the transmission of the preamble on the RACH_01 resource, and of the first piece of information representing the unique identifier of the terminal on the TFR1-2 resource. Note that the first piece of information representing the unique identifier of the terminal, as well as possibly the useful message, can be transmitted on the RACH_01 resource, if the size of the time-frequency resource reserved by the network is sufficient.

5.3 Devices

Finally, in relation to FIGS. 7 and 8, we present the simplified structures of a terminal and of a network entity, for example a base station, according to at least one embodiment described above.

As illustrated in FIG. 7, a terminal according to at least one embodiment of the invention comprises at least one memory 71 and at least one processing unit 72, equipped for example with a programmable calculating machine or a dedicated calculation, for example a processor P, and driven by the computer program 73, implementing steps of the method for accessing a communication network according to at least one embodiment of the invention.

On initialization, the code instructions of the computer program 73 are for example loaded into a RAM memory before being executed by the processor of the processing unit 72.

The processor of the processing unit 72 implements steps of the method of accessing a communication network, according to the instructions of the computer program 73, for:

receive system information broadcast by the communication network to which the terminal wishes to access, the system information comprising an identification of at least one time-frequency resource capable of carrying information relating to a unique terminal identifier,

- transmitting an access request to the network, said access request carrying first information representative of a unique identifier of said terminal, transmitted on one of said time-frequency resources identified from said system information, called specific resource,

receive a response to said access request, access of the terminal to said network being authorized in the event of receipt of a response to said access request carrying a second piece of information representing the unique identifier of said terminal. As illustrated in FIG. 8, a base station according to at least one embodiment of the invention comprises at least one memory 81 and at least one processing unit 82, equipped for example with a programmable calculating machine or a dedicated computing machine, for example a processor P, and controlled by the computer program 83, implementing steps of the network attachment method according to at least one embodiment of the invention.

On initialization, the code instructions of the computer program 83 are for example loaded into a RAM memory before being executed by the processor of the processing unit 82.

The processor of the processing unit 82 implements steps of the method of attaching to the network described previously, according to the instructions of the computer program 83, for:

broadcast system information comprising an identification of at least one time-frequency resource capable of carrying information relating to a unique terminal identifier,

- check the reception, on at least one of said time-frequency resources identified from said system information, called specific resource, of a first piece of information representing a unique identifier of said terminal, carried by a request for access to said network,

- transmitting to said terminal a response to said access request carrying a second piece of information representing the unique identifier of said terminal, if said first piece of information representing a unique identifier of said terminal is received.

CLAIMS

1. Method for accessing a communication network, implemented by a terminal, comprising:

the reception (21 1) of system information broadcast by said network, the system information comprising an identification of at least one time-frequency resource capable of carrying information relating to a unique terminal identifier,

the transmission (212) to said network of an access request, said access request carrying first information representative of a unique identifier of said terminal transmitted on at least one of said time-frequency resources identified from said system information, called specific resource,

the authorization (213) of access to said network in the event of receipt of a response to said access request carrying a second piece of information representing the unique identifier of said terminal.

2. Method according to claim 1, wherein said access request also carries a useful message intended to be transmitted to at least one other terminal, transmitted on said specific resource or on at least one time-frequency resource able to carry a message useful, identified from said system information.

3. Method according to claim 2, according to which, said system information identifying at least two time-frequency resources capable of carrying the useful message, said method implements the selection of at least one of said time-frequency resources taking into account the size of said useful message intended to be transmitted to at least one other terminal.

4. Method according to any one of claims 1 to 3, according to which, the unique identifier of said terminal being an integer, said transmission also transmits a reference signal obtained by applying a cyclic shift to a predefined base sequence, determined according to the unique identifier of said terminal.

5. Method according to claim 4, according to which, when the unique identifier of said terminal is greater than a maximum number of cyclic shifts, said first piece of information representative of the unique identifier of said terminal comprises the integer part of the ratio between the unique identifier and the maximum number of cyclic shifts, the maximum number of cyclic shifts being obtained from said system information.

6. Method according to any one of claims 1 to 5, wherein said access request also carries at least one indicator indicating a return to standby mode of said terminal following authorization of access to said network.

7. Method according to any one of claims 1 to 6, according to which said access request also carries a preamble selected from a plurality of preambles, transmitted on said specific resource or on a time-frequency resource capable of carrying the preamble, identified from said system information, according to which authorization to access said network is granted when said response to the access request carries the second information representative of the unique identifier of said terminal and information representative of said selected preamble

and according to which, in the event of receipt of a response to said access request not carrying second information representative of the unique identifier of said terminal, said method comprises the retransmission of said access request, said first information representative of the unique identifier of the terminal being transmitted on a new specific time-frequency resource identified in said response.

8. Method according to any one of claims 1 to 7, wherein said useful message is an instant messaging type message.

9. Method according to any one of claims 1 to 8, according to which said first information and/or said useful message according to claim 2 are transmitted to said network taking into account modulation and coding information associated with the time- corresponding frequency, said modulation and coding information being obtained from said system information.

10. Method for attaching a terminal to a communication network, comprising: the broadcasting (221) of system information by said network, the system information comprising an identification of at least one time-frequency resource capable of carrying a information relating to a unique terminal identifier,

the verification (222) of the reception, on at least one of said time-frequency resources identified from said system information, called specific resource, of a first piece of information representing a unique identifier of said terminal, carried by an access request to said network,

if said first information representative of a unique identifier of said terminal is received, the transmission (223) to said terminal of a response to said access request carrying a second information representative of the unique identifier of said terminal.

11. Process according to claim 10, according to n wherein said verification also verifies the reception, on said specific resource or on at least one time-frequency resource capable of carrying a useful message, identified from said system information, of a useful message intended to be transmitted to at least one other terminal, and according to which the method comprises the transmission of said useful message to said at least one other terminal if said first piece of information representing a unique identifier of said terminal and said useful message are received.

12. Method according to any one of claims 10 and 1 1, also comprising:

the verification of the reception, on said specific resource or on at least one time-frequency resource capable of carrying a preamble, identified from said system information, of a preamble carried by said access request,

if said preamble is received, and said first information representative of an identifier of said terminal is not received, the transmission to said terminal of a response to said access request carrying information representative of said preamble and identifying a new time resource -specific frequency.

13. Terminal comprising at least one processing unit configured for:

receive (211) system information broadcast by a communication network to which the terminal wishes to access, the system information comprising an identification of at least one time-frequency resource capable of carrying information relating to a unique terminal identifier,

transmitting (212) to said network a request for access to said network, said access request carrying first information representative of a unique identifier of said terminal, transmitted on at least one of said time-frequency resources identified from said system information, called specific resource,

receive (213) a response to said access request, the access of the terminal to said network being authorized in the event of receipt of a response to said access request carrying a second piece of information representing the unique identifier of said terminal.

14. Base station of a communication network, comprising at least one processing unit configured to

broadcast (221) system information comprising an identification of at least one time-frequency resource capable of carrying information relating to a unique terminal identifier,

check (222) the reception, on at least one of said time-frequency resources identified from said system information, called specific resource, of a first piece of information representative of a unique identifier of said terminal, carried by a request for access to said network ,

transmit (223) to said terminal a response to said access request carrying a second piece of information representing the unique identifier of said terminal, if said first piece of information representing an identifier of said terminal is received.

15. Computer program comprising instructions for implementing a method according to any one of claims 1 to 12 when this program is executed by a processor.