FIELD OF THE INVENTION

The present invention relates to a method to manage a jamming situation on-board a mobile vehicle having a predetermined trajectory.

The invention also relates to a method to manage a jamming situation in a wireless communication infrastructure of an area wherein mobile vehicles having predetermined trajectories are moving.

The invention also pertains to a module dedicated to be installed onboard of a mobile vehicle having a predetermined trajectory and to an emergency centre to interact with such modules.

BACKGROUND OF THE INVENTION

Many methods enables jamming detection for 5G. Giving that 5G will in the coming years supersede GSM-R and autonomous railway activity based on 5G will increase in importance, also jamming reaction is an important aspect for railway systems. The 5G rail-system (FRMCS) is likely to work as a 5G standalone system and hence corresponding jamming detection can be provided using known methods.

However, the related reactions, i.e. alarming or others are not sufficient as a train is bound to the rail tracks and hence, when in jamming situation, without communication to any control center. This could lead to dangerous situations or traffic jams also from non-affected trains as they are also bound to the rail track and hence cannot bypass a jammed train, which may only run at lower speed following jamming detection. For general security there is always only one train in a certain rail track area. So for rail systems the early knowledge of a jamming situation for the control center is important.

Also, according to the “first radio law” which consist in “do not transmit if you do not receive” would totally prevent a jammed train to inform the control center in case of a jamming situation.

Following this rule the train will never be able to inform the control center. On a general point of view, a device fulfills certain important points to communicate with a base station based on 5G or any other radio technology. For system such as 5G or LTE, it specifically relies on a time frequency grid as shown on figure 1 A and 1 B.

Figure 1A schematically shows a time frequency grid of LTE being based on a subcarrier SC spacing of 15kHz according to the 3GPP specification (3GPP TR 25.814). NR (New Radio) systems have in principle the same time frequency grid, where the subcarrier spacing can be 15/30 or 60kHz in FR1 , including rail frequency range, whilst time slots TS, i.e. general time duration, is reduced accordingly. It means that the frequency/time accuracy requirements may be strengthened or loosened. For train system operating on 60kHz as subcarrier spacing (SCS), a cyclic prefix (CP) against inter-symbol- interference (ISI) would anyway be reduced and hence there even would be a higher burden on TA estimate. Thus, with a short cyclic prefix (CP), a resource block has 7 symbols * 12 subcarriers SC and, with a long cyclic prefix, it has 6 symbols * 12 subcarriers.

One OFDM symbol on one subcarrier SC is called resource element RE. Twelve subcarriers versus 6/7 OFDM symbols in a time slot TS are called resource block RB.

On figure 1 B, a subframe SF comprising two resource blocks RB is shown. A resource block RB is the smallest addressable size by the scheduler when using common scheduling and no specialized subslot scheduling. Each resource block contains reference signals for measurements and MIMO. LTE reference signals are interspersed among resource elements.

It means that the signal arriving at the base station needs to fit into said time-frequency grid. It causes following problems/challenges.

First, the device needs to estimate the distance to the base station, for a so called timing advance. It means that, in large cells, the UE estimation is based on the received downlink DL and the related attenuation, i.e. signal strength, what is the distance to the base station and hence the timing advance that needs to be applied to arrive at the base station in the respective allocated time grip. Once this is done in the RACH access, the timing advance, TA, is corrected by the base station and a corresponding correction loop via uplink UL and DL is maintained.

Thus, in case of DL jamming, the signal reception is disturbed and hence the UE cannot derive any timing advance or when a timing advance is available maintain it accordingly. Due to loss of timing with respect to the base station, no transmission is possible, especially not when moving.

Also the direction of the movement, normally derived from subsequent measurements and the change in the DL signal strength, is used for TA maintenance, including BS signaling. As some examples moving in a circle around the base station causes a constant TA, moving towards the base station increasing reference signals points towards reducing timing advance and receiving the base station at a lower signal level points to increasing the distance/ timing advance.

Secondly, the device needs to estimate the Doppler shift. The emitted frequency of the base station is seen in a moving device with a Doppler shift. The experienced Doppler frequency shift is proportional to the relative velocity of the receiver compared to the transmitter and the carrier frequency. Normally the Doppler shift is derived from subsequent DL measurements as the effect is relative to the speed of the device/train. The evaluation of the Doppler shift is important for channel estimation and hence the effect on the UL frequency accuracy.

In case of jamming situation, none of these calculations can be performed and the vehicle cannot anymore communicate with the infrastructure of the network it was in communication with. Also the predetermined trajectory may cause additional problem as, typically trains are not able to move in any desired direction except on the tracks and are not able to free/leave the rail tracks. In train area there are rules to avoid accidents, i.e. only one train per track segment, however when considering a train jammed and stopped, this would cause traffic jams and exponential problems in the network if no reaction of the network is possible. The prior art jamming alarming with blinking lights or else are just means to overcome the shortcoming of being not able to adapt to the time/frequency grid especially while being jammed as the device is further moving and hence no transmission can be done.

Also all attempts for radio devices by re-using/maintaining the latest TA and Doppler-shift evolved in connected mode only allows this for a short time, especially when considering high speed trains where said values will rapidly change and the problem of resource assignment or resource usage would remain to be handled in a reasonable resource efficient way. Thus, having a static pre-determined emergency frequency region with very loose timing and frequency accuracy to allow for simple re-use of the previously used values would be a severe impact for frequency resource giving that frequency is a scarce good also for train communication.

Further alternative and advantageous solutions would, accordingly, be desirable in the art.

SUMMARY OF THE INVENTION

The present invention thus aims to enable a jammed train to inform the communication network that it is jammed and to establish a minimal communication with the network.

The present invention is defined, in its broadest sense, as a method to manage a jamming situation on-board a mobile vehicle having a predetermined trajectory, said vehicle having stored at the departure of the mobility duration at least information relative to the predetermined trajectory, information relative to the positions of available base stations on the trajectory, an identifier for the vehicle and information about emergency resources to be used in case of emergency, said method further comprising the steps of, the vehicle moving along its predetermined trajectory:

- identifying a jamming situation;

- determining the closest available base station taking into account the current speed and the predetermined trajectory, - calculating a Doppler shift and a frequency offset taking into account the position of the determined closest available base station, the current speed and the predetermined trajectory,

- emitting repetitively an emergency message on pre-stored emergency resources taking into account the Doppler shift and the frequency offset as calculated during the move of the vehicle along the predetermined trajectory.

The invention provides the means for a necessary solution so that jammed trains can a minima inform railway security system. It allows, typically for a train scenario, a jammed train to perform the corresponding estimates on timing advance and Doppler and to transmit some emergency signals in a predetermined non-exclusive used frequency range for said purpose.

The invention enables the achievement and realization of all required uplink (UL) information for a jammed train to send an UL radio signal on an individualized pre-determined UL resource region per mobile vehicle without wasting bandwidth. The pre-determined UL resource region may also be defined per group of devices.

However for a normal device not transmitting when not receiving has reasons which can be solved or circumvented when being operated in a closed system such as rail-communication and trains following rail tracks.

In the train use case, the invention consists in a train mounted radio communication device, sending in the UL messages in pre-indicated blocks corresponding to a time frequency grid, in case DL reception is interrupted/jammed. Hence the device, evaluating the train speed on the tracks in relation to the known stored base station positions along the track, at least with the closest BS can determine the distance and the relative speed and compensate the timing advance (TA) and frequency Doppler shift accordingly. It is then able to perform transmission on the pre-indicated UL resource blocks by applying those determined values and in case of repetitions updating said transmission values if evaluated to be necessary.

According to a preferred embodiment, the method further comprises the steps of: - while sending emergency messages, perform downlink signal accumulation according to coverage enhancement mode while applying calculated Doppler shift and frequency offset,

- in case the accumulation results in a coherent message, receiving a downlink message from the base station while applying calculated Doppler shift and frequency offset.

This embodiment typically covers a train mounted device sending the UL jamming/DI interruption emergency signal in a repetitive manner and listening to a certain pre-defined DL region and accumulating said resource blocks i.e. operating in CE mode to overcome jamming. Said DL region may especially in FDD being the area around the nominal duplex distance in FDD the same area as used for the UL transmission. It is feasible for the device to receive in train systems the entire bandwidth in parallel. However it would ease the DSP processing if resource blocks to be accumulated could be limited. A device once able to receive a DL signal through the jammed DL by accumulation, indicates early termination/success. In this way, the base station can adjust its DL repetition number accordingly for further communication.

Such an accumulation should work in case of uncorrelated noise and correlated signal for accumulation. During said accumulation the trainmounted device further compensates and adapts TA and Doppler shift, as distance and speed relative to the base station will/may change.

According to an implementation, the emergency messages are RACH based messages on pre-configured RACH resources with an indication that the downlink is disturbed.

This simple implementation enables the emergency messages to reach the closest base station while using standardized messages.

According to an implementation, an emergency RACH based message is a Msg 1/Msg A depending on 2-step/4-step RACH which comprises an emergency indication by being allocated to a special PRACH group.

This enables to use a special pre-determined message format or resource group which thus constitutes the emergency message itself. It is indeed possible to indicate in BCH which PRACH group is to be used for what purpose for Msg 1 .

According to another implementation, the emergency message are part of Msg 3/Msg B depending on 2-step/4-step RACH including a corresponding identifier.

It is advantageous as Msg 3 or Msg B could contain a device identifier, i.e. a message compared to Msg 1/Msg A.

To avoid blocking of RACH resources, which need to be commonly shared by all users, said special RACH resources for emergency could also be located in the scheduling area normally used for UL transmission.

According to a particular feature, the pre-stored emergency resources are common to a list of mobile vehicles.

This solves a resource issue as the frequency resource are limited and allocating an emergency resource to each device would be far too much resource consuming.

According to an advantageous feature, the used emergency resource, being part of a normal UL scheduling range, is derived from at least one physical identifier of the device such as: IMEI, serial number, vehicle number or a corresponding value derived with a mathematical operation thereof to group the vehicles to respective emergency frequency areas.

This enables the information on the emergency resources not to be storage-consuming. This would also allow for planning attempts that only one vehicle within a rail track range uses a certain range. Thus already the selection of the range for sending such an emergency signal would give indication on the impacted device/train, without even having analyzed/decoded the content potentially disturbed received at the base station. Here disturbance may result from the fact that said area used for emergency transmission may be assigned to other devices as their UL transmission region.

The invention also concerns a method to manage a jamming situation in a wireless communication infrastructure of an area wherein mobile vehicles having predetermined trajectories are moving, each of these vehicles having stored at the departure of their mobility duration at least information relative to the predetermined trajectory, expected speed on the predetermined trajectory, information relative to positions of available base stations on their predetermined trajectory, an identifier for the vehicle and information about emergency resources to be used in case of emergency, the method comprising the steps of: storing at least information relative to predetermined trajectories of the mobile vehicles, identifiers associated to the mobile vehicles and information about emergency resources associated to the mobile vehicles to be used in case of emergency, detecting a reception of an emergency message on an emergency resource, determining a list of mobile vehicles allocated to this emergency resource, freeing the emergency resources.

The invention also covers such a method to be implemented in a base station receiving a disturbed signal in a certain UL frequency area which could be a jamming indication from a certain device and starting resource allocation for said device in a certain pre-known frequency block/area and freeing corresponding used UL resouces. For a transmission in the uplink, even when time and frequency shift can correctly be estimated, also a resource assignment or, in general, free resources need to be available. Freeing concerned frequency is thus an essential feature. It means that, in case said frequency area is assigned to other devices for normal UL transmission, that assignment will be changed so that, on this frequency area only, the emergency jamming indication can be received and correctly understood, as no interfering signal is present. Here the interfering signal is the scheduled UL signal for other users. Hence it is under control of the base station by changing said assignment of the other user.

According to the invention, a general pre-known emergency frequency area is to be used for such situation. This emergency frequency area is individualized or grouped among the trains by a certain physical characteristic of the device. This determination of the emergency resource is available in the information about emergency resource as stored in the infrastructure and onboard the mobile vehicle. In average this would distribute all trains to a certain number of groups. Thus the devices within the groups and regions may not evenly be distributed. It could also be likely that all trains in an area would be from the same group, it is unlikely but possible.

The emergency resource as used by the jammed mobile vehicle can enable an emergency center to evaluate which mobile vehicle has called for emergency.

However this is not applicable when the emergency resource is shared by several mobile devices.

Thus according to an advantageous feature, the method further comprises the steps of, while an emergency message is detected while it remains non decodable: sending downlink messages to listed mobile vehicles, receiving answers to these downlink messages from any answering mobile vehicle, determining an identifier of the jammed mobile vehicle as the one that did not send an answer. and repeating the signal for said device unless early detection/detection is indicated by the UE in the herby assigned UL resources.

In a more advanced way the listed mobile devices are the devices being in said area and would use the emergency resource where the so far non- decodable signal was received.

With this feature, in case message cannot be decoded by analysing the used emergency frequency area and mapping to a train/group of devices, an emergency center of the infrastructure can identify the jammed mobile vehicle.

Hence in this more advanced approach the security system may already drive by the disturbance, i.e. collision caused by an emergency unscheduled user, with UL scheduled user, to determine his/its identity. If there are more trains belonging to same group in said area/base station the base station may contact, typically by paging, all of them to evaluate which is the disturbed train by excluding the answering once, i.e. the one not responding is the jammed train. According to an advantageous feature, the method further comprises the steps of, once a jammed vehicle is identified:

- determining a presence area where the jammed mobile vehicle is expected to be located regarding the predetermined trajectory, the expected speed of the mobile vehicle and the time of detection,

- sending downlink communication messages on the determined presence area in coverage enhancement mode to overcome jamming.

Coverage enhancement mode consists in sending in a repetitive manner. With this feature, when the train has reached the emergency system, the emergency system can then start communication with the train. This advanced feature enables the base station to switch in a pre-determined DL part to a coverage enhancement (CE) mode transmission in DL. It allows a delayed communication loop.

The seldom incidence of two parallel jammed users accessing same resource can be solved by applying random offsets when exactly to send in the UL. Collision with other users can again be circumvented by re-allocating the scheduled users and by applying individual offset in time when to send UL indication would also separate these two users. In addition to the aforementioned method, i.e. that the server would call back all devices being related to the detected used frequency range for UL emergency transmission, there would in this case two devices not answering and at least it would be known that they both are impacted/jammed. Hence, the outlined method would also solve this situation.

As an alternative leaving in general certain resource blocks/frequency chunks unused except for emergency communication to be randomly chosen by the affected device would be resource inefficient for general communication purposes and hence shows the advantage of the invention.

Advantageously, the downlink communication messages are sent in a predetermined downlink region.

It is advantageous as the DL communication to all other users needs to be continued, i.e. the DL will further be used. Moreover it needs to be used in a manner not deviating from normal usage, i.e. using it for assignment of UL and DL and also for transporting data. However, using a certain frequency chunk for downlink communication to said device would not even remarked by the other devices as it is just a frequency area not addressed to them. For the disturbed device it is important to know which area shall be processed for DL reception, as also the DL assignment is disturbed. Hence processing only a certain frequency range in a cumulative manner for overcoming the disturbance and reducing said cumulative approach to a certain region allows maintaining service for others and being resource efficient /capable also for the affected device.

According to a specific feature, the predetermined downlink region is, in FDD, the area around a nominal duplex distance in FDD the same area as used for the uplink transmission.

The duplex distance is defined as Lowest DL frequency - lowest UL frequency. In NR where the invention occurs, entire band must be received, or certain band parts during certain times, which when doing CE would be problematic. Thus a connected device in a mobile vehicle shall focus on a certain DL area, which can be pre-determined by having UL area indicated and using DL in nominal distance and around there.

Advantageously, freeing the emergency resources comprises a rescheduling of mobile vehicles that were scheduled on these frequency resources and no more assigning those resources to any other device.

The present invention also relates to a module dedicated to be installed onboard of a mobile vehicle having a predetermined trajectory, said module comprising at least a reception/transmission sub-module, a computing submodule and a memory adapted to store, at the departure of the mobility duration, at least information relative to positions of available base stations on the trajectory, an identifier for the vehicle and information about emergency resources to be used in case of emergency, said module being connected to a jamming situation detector installed onboard of the mobile vehicle, said computing sub-module being configured to, when a jamming situation detection is received from the jamming situation detector: - determine the closest available base station taking into account the current speed and the predetermined trajectory,

- calculate a Doppler shift and a frequency offset taking into account the position of the determined closest available base station, the current speed and the predetermined trajectory,

- request the reception/emission sub-module to send repetitively an emergency message on pre-stored emergency resources taking into account the Doppler shift and the frequency offset as calculated during the move of the vehicle along the predetermined trajectory,

- the reception/emission sub-module being configured to send repetitively an emergency message on pre-stored emergency resources taking into account the Doppler shift and the frequency offset as calculated during the move of the vehicle along the predetermined trajectory.

Such a module is a connected device where the method of the invention, when performed onboard a mobile vehicle, is advantageously implemented.

Advantageously, the computing sub-module is further configured to, while sending emergency messages, perform downlink signal accumulation while applying calculated Doppler shift and frequency offset, and, in case the accumulation results in a coherent message, request the reception/emission sub-module to send an uplink acknowledgement message to the base station while applying calculated Doppler shift and frequency offset, wherein the reception/emission sub-module being further configured to receive such a downlink message from the base station while applying calculated Doppler shift and frequency offset.

The invention also relates to a mobile vehicle having at least a jamming situation detector and a module according to the invention.

The invention also relates to an emergency center of a wireless communication infrastructure active on an area wherein mobile vehicles having predetermined trajectories are moving and are susceptible to encounter a jamming situation, said wireless communication infrastructure comprising a plurality of base stations, each of these vehicles having further stored at the departure of their mobility duration at least information relative to positions of available base stations on their predetermined trajectory, an identifier for the vehicle and information about emergency resources to be used in case of emergency, said emergency center being configured to:

- upon detection of reception of an emergency message on an emergency resource by a base station of the wireless communication infrastructure,

- determine a list of mobile vehicles allocated to this emergency resource,

- send the list of mobile vehicles allocated to this emergency resource to the base station that received the emergency message to enable this base station to send downlink messages to listed mobile vehicles and to receive answers to these downlink messages from any answering mobile vehicle, the emergency center being further configured to:

- receive information on at least one no-answering device from the base station that received the emergency message,

- determine an identifier of the jammed mobile vehicle as the one that did not send an answer.

Advantageously the emergency center is further configured to:

- determine a presence area where the jammed mobile vehicle is expected to be located regarding the predetermined trajectory, the speed of the mobile vehicle and the time of detection, and to

- send indication on the determined presence area to the base station that received the emergency message for the base station to perform downlink communication in coverage enhancement mode to overcome jamming.

The invention also relates to a base station of a wireless communication infrastructure active on an area wherein mobile vehicles having predetermined trajectories are moving and are susceptible to encounter a jamming situation, each of these vehicles having further stored at the departure of their mobility duration at least information relative to positions of available base stations on their predetermined trajectory, an identifier for the vehicle and information about emergency resources to be used in case of emergency, said base station being configured to:

- detect reception of an emergency message on an emergency resource,

- free the emergency resource, - send information on the emergency message detection to an emergency center of the invention,

- receive in answer a list of mobile vehicles allocated to this emergency resource,

- send downlink message to listed mobile vehicles,

- receive answers from any answering mobile vehicle

- send information on at least one no-answering device to the emergency center.

The detection of an emergency message can use various emergency resource. The emergency message can be decodable in case emergency resource is not used by others. However, more commonly, it can be a detection of unscheduled message, means there is something which was not scheduled or something that was scheduled is disturbed and hence cannot be decoded. It could be also be the reception of a message to a certain emergency group. If PRACH is used, resources are generally reserved for emergency calls. It can occur that freeing the emergency resource is thus inherent to the way the emergency message is detected. The evaluation of who was jammed necessitates the use of the emergency resource which has to be freed if shared for other purpose or with other mobile vehicles. A base station detecting that someone uses reserved PRACH will not necessarily need further communication to that vehicle but will call the group to identify the jammed vehicle.

Thus depending on the implementation, the base station directly receives an emergency message, or receives a transmission which could be caused by an emergency situation. In both case an emergency message is detected.

In the second case, the base station thus receives for example a message on a special PRACH resource area. In this case the base station has previously free the PRACH recourse area for the emergency need and the freeing step is thus inherent.

According to the invention, the emergency center provides group identifiers which is a list of mobile vehicle identifiers and the base station is thus enabled to send one paging message to entire group. The base station then reports to emergency center which of the mobile vehicles responded. The base station provides a message to the emergency center indicative to at least one device not responding which occurs when a mobile vehicle is jammed. To the accomplishment of the foregoing and related ends, one or more embodiments comprise the features hereinafter fully described and particularly pointed out in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the annexed drawings set forth in detail certain illustrative aspects and are indicative of but a few of the various ways in which the principles of the embodiments may be employed. Other advantages and novel features will become apparent from the following detailed description when considered in conjunction with the drawings and the disclosed embodiments are intended to include all such aspects and their equivalents.

• Figures 1A and 1 B represents a time frequency grid of LTE and a subframe of this grid ;

• Figure 2 shows a flowchart of a method of the invention as implemented in a connected device onboard a mobile vehicle;

• Figure 3 schematically a connected device of the invention ; and

• Figure 4 shows a flowchart of a method of the invention as implemented in infrastructure of a communication network.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawing. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the scope of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and as claimed hereinafter. The same elements have been designated with the same references in the different drawings. For clarity, only those elements and steps which are useful to the understanding of the present invention have been shown in the drawings and will be described.

Figure 2 is a flowchart of the method of the invention as implemented in a connected device mounted in a mobile vehicle having a predetermined trajectory, typically a train.

Figure 3 schematically represents a connected device D of the invention comprising at least a memory dMEM, a computing module CPM, communication module CNM.

In a first step SEO, the connected device D stores in the memory dMEM, at the departure of the mobility duration, at least information relative to the predetermined trajectory T, information relative to positions of available base stations on the trajectory P(BS), an identifier for the vehicle ID and information about emergency resources EFR to be used in case of emergency.

Then in a step SE1 , a 5G downlink DL jamming situation JS is detected. Also generally antenna switching fails as it is also jammed. It triggers a step SE2 where is determined the closest available base station BSc taking into account the current speed SP and the predetermined trajectory T as stored in the memory. The positions of the base stations P(BS) is also used in this step.

Such determination is advantageously done in the computing module CPM.

Then, in a step SE3, based on the knowledge of the closest base station BSc, the computing module CPM calculates a Doppler shift DS and a frequency offset FO taking into account the position of the determined closest available base station BSc, the current speed SP and the predetermined trajectory T. In the train use case, this calculation is based on actual train speed, track-direction and closest ngNB/available base station, position- Doppler shift and frequency offset is calculated. According to pre-stored information on the emergency resource, emergency resources are derived to send UL message. Typically the use of an identifier of the mobile vehicle can be used according to the information about the emergency resources.

In a step SE4, the connected device D emits, using its communication module CNM, repetitively an emergency message EM on pre-stored emergency resources EFR taking into account the Doppler shift DS and the frequency offset FO as calculated during the move of the vehicle along the predetermined trajectory T. Thus the connected device D continues sending UL emergency message on said pre-known resources.

The send indication being indicative to the situation of jammed in Dl/or facing DI interruption. The transmission to the base station is done on preconfigured/ or pre-indicated resources and repeating said message.

The emergency resource blocks can be indicated in the stored information on the emergency resources or means to determine said resources are used depending at least on one physical parameter of the device to achieve and individualization of the pre-determined resources at least to a certain number of groups of devices. In case a 10MHz bandwidth is used with and SCS of 15kHz corresponding to 50 resource blocks, a train-mounted connected device could use IMEI/modulo(50), where 50 is the number of RBs. More generally, for various SCS and bandwidth applied, it can also be IMEI/modulo (system BW/Width of Resource block) where the resource BW is in general 12xSCS. It means that, depending on the total bandwidth for UL communication or the part of that used for UL individual traffic and the required resource block width, a number of emergency UL frequency areas are calculated. That number forms the number of available groups. The devices/trains are grouped accordingly which can be made by a modulo operation using said calculated number. The identity which undergoes said operation can be the IMEI or any other unique identity of a train.

In a different approach, also dedicated/pre-allocated RACH resources for such incident could be agreed and signalled in the broadcast to be used for said UL communication start and a corresponding new cause for RACH access could be introduced. Upon reception of a signal in said area or from said resource group with respective cause the method could also start including sending in a certain pre-agreed assignment in DL in a repetitive manner.

This is a simple approach to send a RACH based on configured RACH resources with an indication that the downlink is disturbed. This could be either Msg 1/Msg A depending on 2-step/4-step RACH. Upon said sending, procedure with reserved PRACH resources only used for that purpose is performed. The identity can be evaluated by paging all other trains in said area and evaluating the non-answering train. It also results in special DL treatment.

Advantageously, in parallel to the emission of the emergency message EM, it tries to receive DL message by accumulation, i.e. in coverage enhancement mode, while applying frequency offset and Doppler shift adaption accordingly. Thus the connected device D advantageously performs downlink signal accumulation ACC according to coverage enhancement mode.

If jamming is un-correlated noise, the accumulation of DL message should lead to reception when compensating phase and frequency error are not too large as accumulation period is only very short.

In case the accumulation results in a coherent message, the connected device D thus receives a downlink message from the base station while applying calculated Doppler shift and frequency offset and a communication loop is thus re-established. The emergency messages EM can then be stopped and replaced by other communication messages M. Typically it thus send a detection message to the base station, and follow the instructions. A communication loop with the base station BSc is then established in a step SE6. By use of early detection, i.e. indicating to the base station the number of DL receptions that were accumulated to successfully receive the message, the transmitting base station can adopt its repetitions for further communication accordingly in the DL. It means that indicating the number of DL repetitions can lead to an adapted base station behavior using said number of repetitions only to speed up communication loop.

Figure 4 is a flowchart of the method of the invention as implemented in an infrastructure of a communication network.

In a step SSO, the infrastructure stores in a memory iMEM, at least information relative to predetermined trajectories T, typically rail tracks, of the mobile vehicles, identifiers ID associated to the mobile vehicles and information about emergency resources EFR associated to the mobile vehicles to be used in case of emergency.

Then, in its normal activity, the infrastructure is adapted to monitor the emergency resources EFR as stored in memory iMEM. In the case one of the mobile vehicle sends such an emergency message, the infrastructure then detects it in a step SS1 on an active emergency resource EFRa.

A base station having knowledge of a pre-indication of resource blocks to be used for jammed/DL disturbed users in the UL in case of jamming. Said pre-indicated resource blocks can be common or individualized.

The emergency frequency range can be determined by control signalling i.e. broadcast but this would require standards change. Advantageously it is thus derived and individualized by some physical identity of the mobile vehicle and estimating corresponding resources. The base station would just know one emergency resource per default where momentarily double allocation occurs including a call from an uplink disturbed user/train that arrives in addition to the expected uplink signal.

The detection is typically the occurrence of an UL-resource clash/message reception at an nb-NB. Then the infrastructure evaluates which train based on used resources related to train/device identity, i.e it can page group members, and free resources from scheduled users to correctly receive message/clash avoidance.

Thus, indeed, in case of detecting a collision in said resource blocks, the base station interrupts the communication with the scheduled user and receive the jamming indication emergency signal by a jammed UE. It can occur at said pre-indicated resources for a jamming/DL interruption issue can be used for the communication of non-emergency traffic and in case of signal clash the base station interrupts or re-schedules the scheduled user, for resource efficiency.

As outlined above, a base station of the invention also reacts when receiving a RACH with corresponding DL interfered/jammed indication.

The base station can thus, in reaction, re-schedule the scheduled user and free the resource. For this purpose it indicates a NACK as the previously sent block was disturbed by the jammed user and assigns new resources, with only minimum delay for said user. Said user would repeat the affected block and continue, HARQ NACK can also occur for other purposes hence does not negatively impact overall system.

Then, in a step SS2, it determines a list L of mobile vehicles allocated to this emergency resource EFRa. This list typically comprises the identifiers of the mobile vehicles that are susceptible to use this emergency resource EFRa.

In a step SS3, the infrastructure frees the concerned emergency resource EFRa. It will ease the establishment of a communication with the mobile vehicle in trouble as far as possible.

It can occur that the emergency message EM is then decodable. In this case, the infrastructure accesses the identifier of the mobile vehicle in trouble and can take the measures to establish contact specifically with the jammed vehicle or to take measures for other mobile vehicles that may be in danger due to the jamming situation on the jammed mobile vehicle.

It can also occur that the infrastructure cannot decode the emergency message EM. In this case, the method of the invention further comprises a step SS4 of sending downlink messages DLM to the mobile vehicles as listed in the list L requesting an answer from them.

All the devices, which answer, are not the mobile vehicle in emergency. Thus the infrastructure receives answers A of any of those non jammed mobile vehicles in a step SS5. From the answers, it then determines an identifier IDj of the jammed vehicle as the one that did not send any answer in a step SS6.

The infrastructure is then able to try to re-establish a communication loop with the jammed vehicle and to proceed to any measures to prevent problems due to the jamming situation.

To re-established a communication loop with the identified jammed vehicle IDj, in a step SS7, the infrastructure advantageously determine a presence area PA where the jammed mobile vehicle IDj is expected to be located regarding the predetermined trajectory T, the expected speed SP of the mobile vehicle and the time of detection. Then, in a step SS8, it sends downlink communication messages DLCM on the determined presence area PA in coverage enhancement mode to overcome jamming. A DL-message is thus sent in CE mode to overcome jamming on pre-known DL area, taking into account nominal duplex-distance. For FDD a nominal duplex distance can be derived for any band by taking the lowest UL frequency subtracted from the lowest DI frequency.

It enables the jammed vehicle to use enhanced coverage mode to extract a coherent signal out of the noise generated by the jammer. A communication loop can thus be re-established.

The invention enables to derive/calculate TA values and Doppler shift, normally derived from subsequent radio measurements, from the train speed, which can be evaluated by a train also without GPS, as the onboard connected device has stored information on rail track and base stations along the track in combination with pre-allocated resources, generally non-exclusive, for enabling an initial post interfered communication setup in the UL.

In response, the base station advantageously activates CE mode communication in the DL and hence communication loop can tried to be setup again.

The pre-determined UL range to be used by a user equipment, here the claimed module which is a connected device, in case of jamming is advantageously an UE individual frequency area derived from certain parameters of the UE or indicated in advance in the DL. Thus, based on an access clash, already the identity of the device in trouble can be evaluated according to the invention.

The security system behavior, which is to derive the identity of an interfered user by evaluating all trains in said area belonging to the same group which would use said interfered frequency area, is also an original feature of the invention.

It is here noted that, in case of indication of pre-determined frequency areas for emergency UL transmissions are agreed, there is a need for it to be announced/indicated somehow. Also when DL CE is supposed to be used by the base station once emergency occurs, DL area could be determined in case of an FDD band by the nominal duplex of the used UL of the device for the emergency call or in its proximity in case of TDD same frequency resources could be used when corresponding DL slots occur.

In the above detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. The above detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted.