Technique for handling radio link failure in a communication network

The present invention generally relates to a field dealing with wireless link failures in communication networks.

Radio link failure (RLF: radio link) failure) occurs in a mobile communication network when, for example, a mobile station, such as a mobile telephone, loses its connection to the communication network in an uncontrolled manner. Wireless link failures usually do not occur randomly. Typically, radio link failures occur at a particular location. Alternatively, it occurs when a mobile station moves out of the cell's network coverage area and into another cell's network coverage area that is not properly configured. The reason for losing connectivity may be, for example, that the mobile station is rapidly moving away from the radio coverage area of the base station servicing the mobile station. In these situations, if a wireless link failure cannot be avoided, the mobile station will reconnect to the communication network as quickly as possible to minimize downtime, transmission data loss, and service degradation perceived by mobile station users. It is desirable to be able to. For this purpose, the mobile station performs multiple network reconnection procedures after losing connectivity with the communication network. These steps include selecting a new base station and cell and accessing this new base station to reconnect to the communication network.

<p> Third Generation Partnership Project (3GP) Wireless link failure for next generation mobile network (NGMN) following Long Term Evolution (LTE) It is suggested that the user equipment (UE) that detects the receipt should transition to the LTE_IDLE state, execute a service request, reconnect to the network, and recover the wireless network bearer. The LTE_IDLE state in LTE is the power conservation state for the UE. In this state, the UE is neither transmitting nor receiving data packets with the network. In the LTE_IDLE state, the context for the UE is Evolved Node B (eNodeB: evolved Node). B) That is, nothing is stored in the base station servicing the UE. Therefore, eNodeB has no information about the UE making the request to allow reconnection.</p><p> In order to reconnect the UE to the communication network, the evolved packet core (EPC) of the communication network needs to be involved in the reconnection process. That is, contextual information about the UE must be obtained by eNodeB via the EPC. The EPC is the mobile packet backbone network behind the eNodeB. It takes about 100ms to transition from the LTE_IDLE state to the LTE_IDLE active state, that is, to the state where the UE is registered in the communication network and the radio resource control (RRC) connection with eNodeB is established. There will be. Therefore, such network reconnection after a wireless link failure can take a long time and can occupy the core network elements needed for other network operations.</p><p> Therefore, there is a need for technology to deal with wireless link failures in communication networks that avoids at least some of the problems outlined above.</p>

<p> This objective is achieved according to the first aspect of the method for dealing with wireless link failures in communication networks. The method shows a step to detect a wireless link failure for a user device, a time stamp indicating when the wireless link failure was detected, and a cell that was servicing the user device before the wireless link failure was detected. It includes a step of writing the identifier of the user device suffering from the wireless link failure in the log file together with at least one data item of the reference information.</p><p> The method can be performed by a base station such as eNodeB, or any other suitable network element. In particular, this method can be performed by the base station to which the user equipment is connected when a wireless link failure occurs. The user device may be any kind of communication terminal. For example, it is a mobile phone capable of communicating with a communication network.</p><p> From a further perspective, one method is provided for dealing with wireless link failures in communication networks. This method correlates the wireless link failure information with the reconnection information, the step of holding the wireless link failure information, the step of receiving the reconnection information after the user device is reconnected to the communication network, and the correlation result. With the steps to obtain. The wireless link failure information provided services to the user device prior to the detection of the wireless link failure, the identifier of the user device suffering from the wireless link failure, the time stamp indicating when the wireless link failure was detected, and the wireless link failure. Contains at least one of the reference information data items that indicate the cell. The reconnection information includes the identifier of the user device that has suffered a wireless link failure and has been reconnected. The correlation result may be, for example, a relationship between a cell that causes a large number of radio link failures and a cell that the mobile terminal frequently reconnects after a radio link failure occurs.</p><p> The method can be performed by a base station such as eNodeB, or any other suitable network element. In particular, this method can be performed by a base station to which the user equipment is reconnected after a wireless link failure has occurred. If the user equipment does not leave the serviced cell, the base station may be the same base station to which the user equipment was connected prior to the occurrence of the radio link failure. The method can also be implemented by non-base station network elements, such as core network elements. In this case, this network element includes wireless link failure information and reconnection information from the base station to which the user device was connected before the wireless link failure and the base station to which the user device is reconnected after the wireless link failure. To receive.</p><p> The identifier may be any kind of identification information that can identify the user device in an unambiguous manner. This identifier is a radio network temporary identifier (RNTI) such as cell RNTI (C-RNTI: Cell RNTI), random access RNTI (RA-RNTI: Random Access RNTI), paging RNTI (P-RNTI: Paging RNTI) or BCCH RNTI. : Radio Network Temporary Identity, Temporary Mobile Subscriber Identifier (TMSI) such as Packet TSMI (P-TMSI: Packet TMSI) or S-TMSI, and GUTI (Globally Unique Temporary) Identity). To correlate wireless link failure information with reconnection information for correlation results, the identifier of the user device and a time stamp or wireless link failure indicating when the wireless link failure was detected are often detected. Only reference information indicating the cell that was servicing the user device before it was done is needed. In other words, only the identifier of the user device suffering from the wireless link failure and the time stamp indicating when the wireless link failure was detected, or the identifier of the user device suffering the wireless link failure and the wireless link failure are detected. It suffices to retain only the reference information that indicates the cell that was servicing the user device before. Cell reference information is not always necessary, for example, in situations where it is possible to correlate time stamps from different base stations, indicating when a radio link failure was detected. Both the time stamp and the cell information can be retained together with the identifier in order to easily correlate the wireless link failure information and the reconnection information and obtain the correlation result.</p><p> The reconnection information is at least one of a time stamp indicating when the user device was reconnected to the communication network and reference information indicating the cell servicing the user device after being reconnected to the communication network. Can be further included. Similar to the retention of wireless link failure information, a time stamp indicating when the user device was reconnected to the communication network and reference information indicating the cell servicing the user device after being reconnected to the communication network. Only one of them can be received with the identifier of the reconnected user device. By receiving both the time stamp and the cell information, it is possible to easily obtain the correlation result by correlating the wireless link failure information and the reconnection information.</p><p> In one embodiment of the method, the correlation results can be evaluated and based on this evaluation, cells that cause a large number of radio link failures can be identified. In other words, it compares with other cells of the communication network based on the radio link failure received and entered in the log file to determine in which cell of the communication network more radio link failures occur. be able to. The result of this determination can be expressed as an absolute numerical value or a ratio.</p><p> According to a further point of view, the correlation result can be evaluated, and based on this evaluation, the cells that are frequently reconnected by the user device after the occurrence of the wireless link failure can be identified. This makes it possible to determine the relationship between disconnection and reconnection between cells in a communication network. For example, a large number of radio link failures (eg, values above a predetermined threshold per unit time) occur in cell A, and at what rate the user after the radio link failure. If the device is reconnected to cell B, their relationship can be determined. The relationship between such disconnection and reconnection can be obtained for all cells.</p><p> User device context for base stations servicing cells that the user device frequently reconnects after a wireless link failure to minimize the interruption time of the user device suffering from a wireless link failure. Information (user equipment context information) can be sent. Reconnecting frequently means, for example, that after a wireless link failure, the user device reconnects to the cell more than a predetermined number of times (or at a predetermined ratio) within a given time interval. It means that. However, the network operator can also determine the base station to which the user device context information is transmitted.</p><p> The user device context information can include data required for the base station to communicate with the user device. Such user device context information includes, for example, the user device identifier (for example, for the base station itself to investigate further information), security keying material, and radio resource control (RRC). It can be a Control (Control) context, a System Architecture Evolution (SAE) bearer context, or an S1 interface context reference.</p><p> The step of sending user device context information to a base station servicing a cell to which the user device frequently reconnects after a wireless link failure causes the user device to experience a large number of wireless link failures. It can be executed every time the service is provided by the cell. This provides a security measure in cells where user equipment frequently reconnects after a wireless link failure occurs. This is because the base station already has available user device context information and does not need to request the user device context information after the user device requests network reconnection. This makes it possible to reduce the network reconnection time after a wireless link failure occurs.</p><p> The step of sending user device context information to a base station servicing a cell to which the user device frequently reconnects after a wireless link failure is also performed after the user device wireless link failure is detected. You can also do it. This uses the time interval between detecting a wireless link failure and reconnecting to the communication network to provide potentially requested user device context information to the user device frequently after a wireless link failure occurs. It can be provided to the cell to be reconnected.</p><p> Interfaces between base stations can be configured to facilitate future handover attempts. This makes it possible to reduce the time required for handover between different base stations.</p><p> Related cells (related cells) can also be defined as neighboring cells in order to facilitate future handover attempts. Such related cells can be, for example, a cell in which a wireless link failure occurs frequently and a cell in which a user device reconnects frequently after a wireless link failure occurs. Future handover attempts can be performed via the evolved packet core.</p><p> According to one aspect, the handover parameters between the cell that causes the radio link failure many times and the cell that the user device frequently reconnects after the radio link failure can be adjusted. Since it is known that loss of connection and reconnection occur frequently in a neighboring cell, the network parameters are adjusted to cause a large number of radio link failures and after a radio link failure occurs. The time required for the handover with the cell to which the user device frequently reconnects can be optimized. The handover parameters can include, for example, the same carrier frequency (intra-frequency) handover parameters. It is even possible to reduce the number of dropped calls by adjusting the handover parameters.</p><p> From a further perspective, servicing base stations servicing cells that experience a large number of radio link failures and cells that frequently reconnect user devices after a radio link failure. It is possible to specify the X2 interface with the base station. In particular, the X2 interface can support user device handover between multiple base stations in the LT_ACTIVE state.</p><p> From a further point of view, the base station arrangement is adjusted so that the cell that causes the radio link failure many times and the cell that the user equipment is frequently reconnected after the radio link failure occurs are the same base station. The service can be provided by. Such adjustment of the base station arrangement can reduce the time for reconnection after the occurrence of a wireless link failure. This is because the base station already has all the necessary user equipment context information available and does not need to request the user equipment context information when it receives the reconnection request.</p><p> According to a further aspect, a method for dealing with wireless link failures in communication networks is provided. The steps of this method are performed by the user equipment. In this method, the step of transmitting the identifier of the user device to the first base station, the step of detecting the wireless link failure, and the step of detecting the wireless link failure of the user device are detected, and the user device is reconnected to the communication network. It comprises a step of transmitting the same identifier to a first base station or a second base station later or when reconnecting. By this method, the user apparatus provides the base station with all the information required by the base station or network element to correlate the wireless link failure information with the reconnection information.</p><p> From a further point of view, the user device provides reference information indicating the cell that was servicing the user device before the wireless link failure, at least in the first base station and the second base station. Can be sent to one. After the wireless link failure occurs, the user device can reconnect to the base station to which the user device was connected before the wireless link failure occurred. Or, for example, if the user equipment has moved to the network coverage area of another cell, or if the network connection in the original cell is temporarily lost, the user equipment will be another base station. Can be reconnected to.</p><p> The present invention can be implemented in a hardware format, a software format, and a combination of hardware / software format. From a software perspective, computer program products are provided. A computer program product comprises a program code portion for performing one or more steps of the method described above when the computer program product operates on one or more network elements. Computer program products can be stored on computer-readable recording media.</p><p> From a hardware perspective, base stations are provided. The base station includes a detection unit for detecting a wireless link failure related to a user device and a logging (logging) unit. The logging unit identifies the identifier of the user device that is suffering from the wireless link failure, a time stamp that indicates when the wireless link failure was detected, and the cell that was servicing the user device before the wireless link failure was detected. A unit for filling in log files, along with at least one of the data items with the reference information shown. In particular, the base station may be eNodeB.</p><p> From a further perspective of hardware, network elements are provided. The network elements include a holding unit for holding wireless link failure information, a receiving unit for receiving reconnection information after the user device is reconnected to the communication network, and wireless link failure information and reconnection information. It is provided with a correlation unit for taking a correlation and obtaining a correlation result. Here, the wireless link failure information provides an identifier of the user device suffering from the wireless link failure, a time stamp indicating when the wireless link failure was detected, and a service to the user device before the wireless link failure is detected. Includes at least one of the reference information data items indicating the cell that was in the cell. The reconnection information includes the identifier of the user device that has suffered a wireless link failure and has been reconnected to the communication network. The network element may be a base station, eNodeB, or any other suitable network element located within, for example, the core network.</p><p> According to a further aspect of hardware, user equipment is provided. The user device includes a transmission unit for transmitting the identifier of the user device to the base station and a detection unit for detecting a wireless link failure. Here, after the wireless link failure of the user device is detected and the user device is reconnected to the communication network, the same identifier is transmitted to the same base station or another base station.</p><p> In the following, the present invention will be described with reference to the typical embodiments shown in the drawings.</p>

<figref num="1">It is a block diagram which shows the communication network including the embodiment of an apparatus.</figref><figref num="2">It is a block diagram which shows eNodeB which can be used in the communication network of FIG.</figref><figref num="3">It is a block diagram which shows the user apparatus which can be used in the communication network of FIG.</figref><figref num="4">It is a flowchart which shows the 1st Embodiment of this method.</figref><figref num="5">It is a flowchart which shows the 2nd Embodiment of this method.</figref><figref num="6">It is a flowchart which shows the 3rd Embodiment of this method.</figref>

In the following, specific details such as a specific sequence (order) of steps, interfaces, and configurations are described in order to provide a sufficient understanding of the present invention. This is for illustration purposes only and is not intended to be limiting. It will be apparent to those skilled in the art that the invention can be practiced in other embodiments that differ from these specific details.

Further, one of ordinary skill in the art will appreciate that the functions and processes described below herein can be performed by a programmed microprocessor, or software functions combined with a general purpose computer. Also, although embodiments are described primarily in the form of methods and devices, the present invention is performed in a computer program product and further in a computer processor and a system comprising memory coupled to the processor. Will also be understood to be possible. Here, the memory is encoded using one or more programs capable of performing the functions disclosed herein.

In the following embodiments, various typical scenarios dealing with wireless link failures in communication networks are disclosed. These typical embodiments are based on NGMN according to LTE. However, the present invention is not limited to LTE. The present invention can be similarly used in any other communication network, such as a network according to the Universal Mobile Telecommunications System (UMTS) standard.

FIG. 1 shows a block diagram of the communication network 10. The communication network 10 includes a first eNodeB (eNB1) servicing the first cell C1 and a second eNodeB (eNB2) servicing the second cell C2. The first and second eNodeBs, eNB1 and eNB2 are connected to network element 18 by lines or air interfaces 13 and 14. Network element 18 is further connected to the core network (not shown). The X2 interface 12 is provided between the first eNodeB (eNB1) and the second eNodeB (eNB2).

The user device UE is located in cell C1 and communicates with the first eNodeB (eNB1) via the air interface 16. It is assumed that the user of the user device UE is traveling on a high-speed train (not shown). The high-speed train carrying the UE leaves cell C1 while the user equipment UE is connected to the first eNodeB (eNB1), that is, while the user equipment UE is transmitting data through the air interface 16. , Invade the network coverage area of cell C2 at high speed. This is indicated by arrow 15. High-speed relocation, that is, high-speed movement from cell C1 to cell C2, causes wireless link failure. Therefore, the UE is about to lose its connection to the first eNodeB (eNB1) through the air interface 16.

When a wireless link failure occurs, eNB1 detects the wireless link failure. The first eNodeB (eNB1) is the UE identifier, a time stamp indicating when a wireless link failure was detected, and reference information indicating cell C1 that was servicing the UE before the wireless link failure was detected. Fill in the log file with at least one of. The first eNodeB (eNB1) provides this log information to network element 18.

After the radio link failure occurs, the UE is located in the network coverage area of the second eNodeB (eNB2), that is, in cell C2. Therefore, the UE selects this cell to reconnect with the communication network 10 and attempts to reconnect with the second eNodeB (eNB2) via the air interface 17. The reconnection is successful. The second eNodeB (eNB2) writes the UE identifier in the log file. It also optionally includes a time stamp indicating when the UE was connected to the second eNodeB (eNB2) and reference information indicating cell C2 servicing the UE after being reconnected to communication network 10. Fill in the log file. The second eNodeB (eNB2) provides this information to network element 18 via connection 14.

Therefore, the network element 18 can acquire the wireless link failure information from the first eNodeB (eNB1) and the reconnection information from the second eNodeB (eNB2). The network element 18 can also receive corresponding information from other eNodeBs (not shown) of the communication network 10. As a result, the network element 18 correlates the wireless link failure information with the reconnection information to obtain a correlation result. After that, the network element 18 evaluates each correlation result to identify the cell that causes a large number of radio link failures and the cell that the user device frequently reconnects after the radio link failure occurs. Based on this information, network parameters between certain cells (between cell C1 and cell C2 in this embodiment) can be optimized.

In an embodiment according to FIG. 1, the network element 18 causes a radio link failure to occur frequently in cell C1, and the user device enters the communication network 10 in cell C2 after a radio link failure occurs. Reconnection with high frequency was determined based on the correlation result. Therefore, whenever a UE is located in cell C1, the user device context information for this UE is transmitted from the first eNodeB (eNB1) to the second eNodeB (eNB2), thereby causing cells C1 and C2. Network parameters between and are optimized. A radio link failure is likely to occur in cell C1 and the UE will reconnect to the second eNodeB (eNB2) in cell C2 after a radio link failure in cell C1. Since the deafness is also high, the second eNodeB (eNB2) will already have the user device context information of the available UE. Therefore, the second eNodeB (eNB2) does not need to obtain or request further reconnection information from, for example, the communication network 10, thus accelerating the reconnection of the UE to the communication network 10.

Furthermore, it is desirable that the user device context information be transmitted from the first eNodeB (eNB1) to the second eNodeB (eNB2) before the wireless link failure occurs, in which case the detection of the wireless link failure and It is possible to avoid the delay due to the reconnection request. Although not shown in FIG. 1, the UE can also reconnect to the same eNodeB, i.e. eNB1, after the occurrence of a radio link failure in cell C1. This can happen, for example, when the first eNodeB (eNB1) is temporarily unable to provide services.

FIG. 2 shows a block diagram of eNodeB (eNB). eNodeB can be used in the communication network 10 shown in FIG. The eNodeB includes an antenna 29 for communicating with a plurality of user devices. In addition, eNodeB (eNB) has a detection unit 20 and a logging unit (logging). It includes a unit) 22, a holding unit 24, a receiving unit 26, and a correlation unit 28. The detection unit 20 is a unit for detecting a wireless link failure related to the user device. The logging unit 22 provides the identifier of the user device suffering from the wireless link failure, a time stamp indicating when the wireless link failure was detected, and the cell that provided the service to the user device before the wireless link failure was detected. A unit for filling in log files, along with at least one of the reference information that indicates. The retention unit 24 includes an identifier of the user device suffering from a wireless link failure, a time stamp indicating when the wireless link failure was detected, and a cell that served the user device before the wireless link failure was detected. A unit for holding radio link failure information including at least one of the reference information indicating. The receiving unit is a unit for receiving the reconnection information after the user device is reconnected to the communication network, and the reconnection information includes the identifier of the user device that has suffered a wireless link failure and is reconnected. The correlation unit 28 is a unit for obtaining a correlation result by correlating the wireless link failure information and the reconnection information.

In this embodiment according to FIG. 2, the eNodeB (eNB) receives the wireless link failure information and the reconnection information, and the correlation result can be obtained by correlating the information. The embodiment according to FIG. 2 is different from the embodiment according to FIG. In the embodiment according to FIG. 1, the network element 18 correlates the wireless link failure information with the reconnection information. However, in the embodiment according to FIG. 2, eNodeB (eNB) provides this correlation. It is also possible that both network element 18 and eNB provide correlation results.

FIG. 3 shows a block diagram of the user device UE. The user device UE includes an antenna 34 for communicating with a base station such as eNodeB (not shown) via an air interface. Further, the user apparatus UE includes a transmission unit 30 for transmitting the identifier of the user apparatus UE to the base station and a detection unit 32 for detecting a wireless link failure. The user equipment UE may use the same base station or another base station with the same identifier, depending on whether the user equipment has already reconnected to the communication network or has reconnected to the communication network after the wireless link failure of the user equipment UE has been detected. Send to the base station.

FIG. 4 is a flowchart 400 showing a first embodiment of the method according to the present invention. This embodiment of the method relates to the handling of wireless link failures in a communication network and is performed by the eNodeB (eNB1) shown in FIG. 1, the eNodeB (eNB) shown in FIG. 2, or another device. Can be done.

The method begins in step 405, where it detects a wireless link failure with respect to the user equipment. In the next step 410, the identifier of the user device suffering from the wireless link failure is serviced to the user device before the wireless link failure is detected and the time stamp indicating when the wireless link failure was detected. Enter at least one of the reference information indicating the cell in the log file.

FIG. 5 shows a flowchart 500 of a further embodiment of the method. This embodiment of the method relates to the handling of wireless link failures in a communication network and is performed by the eNodeB (eNB1) shown in FIG. 1, the eNodeB (eNB) shown in FIG. 2, or another device. Can be done.

As shown in FIG. 5, the method is started in step 505. In step 505, the wireless link failure information is retained. The wireless link failure information provided services to the user device prior to the detection of the wireless link failure, the identifier of the user device suffering from the wireless link failure, the time stamp indicating when the wireless link failure was detected, and the wireless link failure. Contains at least one of the reference information indicating the cell. Next, in step 510, the reconnection information including the identifier of the user device that has been reconnected due to the wireless link failure is received after the user device is reconnected to the communication network. After that, as shown in step 515, the radio link failure information and the reconnection information are correlated to obtain a correlation result.

FIG. 6 shows a flowchart 600 of a further embodiment of the method. This embodiment relates to the handling of wireless link failures in a communication network and can be performed by the user device UE shown in FIG. 1 or FIG. 3 or another device.

The method is started in step 605, where the user device identifier is transmitted to the base station. This step of transmitting the identifier to the base station can be performed during normal operation, i.e., while the user equipment is in normal communication with the base station. Then, in step 610, the user device detects a wireless link failure. In the next step 615, the same identifier is transmitted to the same base station or another base station after a wireless link failure of the user equipment is detected and the user equipment is reconnected to the communication network. The identifier is transmitted to this same base station if the user equipment is still located within the network coverage area of the same base station. However, if the user equipment has moved to another base station's network coverage area, i.e., another cell, the user equipment sends the same identifier to this other base station.

As will be apparent from the above embodiments, the present technology for dealing with wireless link failures in communication networks provides the advantage of minimizing the downtime interval after a wireless link failure has occurred. This allows data loss during the downtime to be minimized or avoided. Then, the service deterioration felt by the user of the user device can be reduced. The network parameters of the communication network can be optimized, and the user of the user device does not recognize the call dropout due to the wireless link failure.

Although embodiments of the invention are illustrated in the accompanying drawings and described by description, it will be appreciated that the invention is not limited to the embodiments disclosed herein. In particular, the invention is capable of many reconstructions, modifications, and substitutions without departing from the scope of the invention described and defined by the claims set forth below.