WO2012137402A1 - Cell selection method, cell selection system, communication device, and base station - Google Patents

Abstract

Disclosed is a technology wherein a communication device re-sending a second connection request with a high probability of rejection to a mobile administration node over a wireless network is avoided when a first connection request from the mobile administration node is rejected. According to the technology, after receiving a reject notification via a base station (3A1) in step (S1), an MTC device (1) assesses whether a back-off timer (T) is in effect in step (S2), and if the back-off timer (T) is still in effect (Yes in S2), carries out a cell selection on the basis of the reception quality and verifies whether another cell is present (step S3). If the other cell is present (Yes in S3), the MTC device (1) acquires a TAC which is included in notification information (SIB1) which is notified from a base station which administers the cell. The MTC device (1) verifies whether the acquired TAC is the same as a TAC (A) of the base station (3A1) (step S4), returning to S3 if the TAC is the same as the TAC (A). If no other cell is present (No in S3), the MTC device (1) stands by until the notified back-off timer (T) expires (step S7).

Description

Cell selection method, cell selection system, communication device, and base station

The present invention relates to a cell selection method, a cell selection system, a communication device, and a base station for a communication device that is denied a connection request from a mobility management node via a wireless network to select another cell.

Unlike communication (H2H: Human to Human, H2M: Human to Machine), which uses users with terminals with abundant user interfaces such as mobile phones, direct operation by the user is not required. As a form of communication using a communication device that can operate independently, there is inter-machine communication (called Machine と to Machine Communication or Machine Type Communication; hereinafter referred to as M2M communication). In M2M communication, one or a plurality of communication devices (hereinafter referred to as MTC devices) that are located at the end and appropriately collect necessary information operate, and sensing functions (for example, temperature, seismic intensity, water volume, camera, Information (sensing data) detected and measured by GPS (Global Positioning System) is collected in a server (hereinafter referred to as MTC server) that manages MTC devices, and various services are provided to users (clients) based on the information. The user is provided with a service based on the information notified from the MTC device via the MTC server, and the user who has the MTC device using the information exchanged between the MTC devices. Service.

As means for establishing a communication path between the MTC device and the MTC server, not only a wired network such as a telephone line or a DSL (Digital Subscriber Line) line but also a wireless network such as a mobile phone network can be used. . In particular, when wireless is used, restrictions on the installation location of the MTC device are almost eliminated, so that it is possible to install the MTC device in a wide range, and it can be said that this is a very effective communication means.

However, a wireless communication system usually used for a mobile phone or the like is optimized for a mobile phone and is not necessarily optimal for an MTC device that provides a service specialized for M2M communication. For example, in the case of a mobile phone, it is necessary to periodically check the paging from the network side in order to receive an incoming voice call addressed to itself, but it is an MTC device that does not have a voice call function, and only from the MTC device. In the case of issuing information, it is not necessary to be in a state where it can always be subjected to paging, so such an operation is not necessary.

In addition, since MTC devices have a wide variety of installation locations and have little contact with the user, there is little possibility of being placed in a state where power is always supplied. For this reason, it is necessary to use limited power such as a battery or a battery, and it is required to suppress power consumption as much as possible and to lengthen the operation time. In particular, power consumed by a radio interface used for communication cannot be ignored, and optimizing a radio communication system for an MTC device is an indispensable problem for an MTC device using radio communication. Currently, in 3GPP (3rd Generation Generation Partnership Project), discussions for optimizing the mobile phone network for M2M communication are performed (see Non-Patent Document 1 and Non-Patent Document 2 below).

Furthermore, it is expected that the larger the installation scale, the greater the number of MTC devices that operate. For this reason, when a large number of MTC devices are simultaneously connected to the network and data transmission / reception is started, it is expected that congestion will occur in the wireless network and the core network. For this reason, a mechanism to minimize access concentration is also necessary.

Usually, when an MTC device is connected to a 3GPP network, first, a cell configured by surrounding base stations is searched, and a connection request is transmitted to the base station configuring the cell having the best reception quality. When the connection request is accepted by the base station, the connection request is transferred to a mobility management node (MME: Mobility Management Entity) to which the base station can connect. When the connection request is accepted by the MME, a data communication connection is established between the MTC device and the S-GW (Serving Gateway) and P-GW (Packet Data Gateway), and the MTC server and other MTC devices are connected. Communication becomes possible. However, when congestion (congestion) occurs in the MME due to access concentration of a large number of MTC devices, the connection request transmitted by the MTC device is rejected, and a back-off timer (back-off timer (from the MME to the MTC device via the base station) Standby time). The back-off timer is a time interval that the MTC device must wait before retransmitting the connection request, and is assigned to each MTC device so that retransmission of connection requests is not concentrated on a congested network. That can be.

In order for the MTC device from which the first connection request is rejected by the MME to connect to the network, it is necessary to retransmit the second connection request to the network. However, if the MTC device retransmits the second connection request to the same MME that rejected the first connection request due to congestion without waiting for the backoff timer to elapse, the MME is still congested. And will be rejected again. This causes a problem that unnecessary traffic is generated between the MTC device and the network.

On the other hand, there is a possibility that the second connection request is accepted by waiting for the notified back-off timer to elapse and then retransmitting the second connection request to the same MME via the same base station again. However, since the network cannot be accessed while waiting for the back-off timer to elapse, data transmission / reception is delayed.

In order to solve the above problem, the present invention provides a communication device that has been rejected by the mobility management node via the wireless network before the first connection request is rejected before the waiting time elapses. An object of the present invention is to provide a cell selection method, a cell selection system, and a communication device that can prevent a second connection request that is likely to be retransmitted from being retransmitted.
The present invention also enables a communication device that has been denied the first connection request from the mobility management node via the wireless network to access the network before the standby time elapses, thereby preventing delays in data transmission and reception. An object of the present invention is to provide a cell selection method, a cell selection system, a communication device, and a base station.

In order to achieve the above object, the present invention provides a communication device that detects a first cell configured by a first base station and is denied a first connection request transmitted to a mobility management node. A cell selection method for selecting a second cell different from a cell, comprising:
Notifying the communication device of a waiting time until the first connection request is retransmitted when the mobility management node rejects the first connection request from the communication device;
Receiving the waiting time when the communication device is denied the first connection request;
The base station group identification information of the base station notified in the cell from the base station constituting the cell is different information for each mobility management node to which the base station belongs, and receiving the base station group identification information;
When the communication device detects the second cell before the waiting time elapses, the base station group identification information of the first base station and the second cell constituting the second cell By comparing the base station group identification information of the base station, it is determined whether or not the first and second base stations belong to the same mobility management node. Transmitting the second connection request to the second base station if the second connection request does not belong to the second base station.
It was set as the structure which has.

In order to achieve the above object, the present invention provides a communication device that detects a first cell configured by a first base station and is denied a first connection request transmitted to a mobility management node. A cell selection system for selecting a second cell different from the cell of
Means for notifying the communication device of a waiting time until the first connection request is retransmitted when the mobility management node rejects the first connection request from the communication device;
Means for receiving the waiting time when the communication device is denied the first connection request;
Base station group identification information of the base station notified from the base station constituting the cell in the cell is different information for each mobility management node to which the base station belongs, and means for receiving the base station group identification information;
When the communication device detects the second cell before the waiting time elapses, the base station group identification information of the first base station and the second cell constituting the second cell By comparing the base station group identification information of the base station, it is determined whether or not the first and second base stations belong to the same mobility management node. Means for transmitting the second connection request to the second base station when it does not belong to and does not belong to the second base station,
It was set as the structure which has.

In order to achieve the above object, the present invention detects the first cell configured by the first base station, and when the first connection request transmitted to the mobility management node is rejected, A communication device for selecting a second cell different from the cell,
Transmitting means for transmitting a connection request to the mobility management node;
Receiving means for receiving, from the mobility management node, a waiting time until the first connection request is retransmitted when the mobility management node rejects the first connection request transmitted by the transmission means;
Base station group identification information of the base station notified from the base station constituting the cell in the cell is different information for each mobility management node to which the base station belongs, and means for receiving the base station group identification information;
When the second cell is detected before the standby time elapses, the base station group identification information of the first base station and the base of the second base station constituting the second cell Determining means for determining whether the first and second base stations belong to the same mobility management node by comparing station group identification information;
The transmitting means does not transmit a second connection request to the second base station when the first and second base stations belong to the same mobility management node, and when the first and second base stations do not belong, The request is transmitted to the second base station.

With this configuration, when the communication device detects another cell before the standby time elapses, the base station group identification information of the first base station that has been denied the first connection request, and the other cell It is determined whether or not the first and second base stations belong to the same mobility management node by comparing the base station group identification information of the second base station to be configured, and if so, the second connection When the request is not transmitted to the second base station and the second connection request is not transmitted to the second base station, the second connection request is transmitted to the second base station. 2 can be prevented from being retransmitted, the network can be accessed before the waiting time elapses, and delays in data transmission / reception can be prevented.

In order to achieve the above object, the present invention provides a communication device connected to the second base station belonging to a mobility management node different from the mobility management node to which the first base station belongs before the waiting time elapses. When the third cell configured by the third base station that notifies the same base station group identification information as the first base station is detected, the first and third base stations The third cell reception quality measurement report including congestion information indicating that the mobility management node to which the mobile management node belongs is congested is transmitted to the second base station.

With this configuration, the second base station to which the communication device is connected before the standby time elapses is not handed over to the mobility management node that has rejected the first connection request. Can be accessed, and thus delays in data transmission and reception can be prevented.

In order to achieve the above object, the present invention is a base station to which a communication device is connected via a wireless network,
Means for receiving a reception quality measurement report of the cell from the communication device when the communication device detects a cell;
The connection of the communication device connected to the base station when the reception quality measurement report includes congestion information indicating that the mobility management node to which the base station serving as a handover candidate constituting the cell belongs is congested. Means for handing over the connection of the communication device to the base station serving as the handover candidate when the congestion information is not included in the reception quality measurement report.
It was set as the structure which has.

According to the present invention, there is a high possibility that a communication device to which the first connection request is rejected from the mobility management node via the wireless network will be rejected before the waiting time elapses for the mobility management node. It is possible to prevent the second connection request from being retransmitted.
Also, according to the present invention, a communication device that has been denied the first connection request from the mobility management node via the wireless network can access the network before the standby time elapses, and thus delays in data transmission / reception. Can be prevented.

The block diagram which shows an example of the network structure in the 1st Embodiment of this invention Explanatory drawing which shows an example of the communication sequence in the network of FIG. The flowchart for demonstrating the process of the MTC device of FIG. Explanatory drawing which shows the other example of the communication sequence in the network of FIG. The block diagram which shows the structure of the MTC device of FIG. FIG. 3 is a block diagram showing an example of a network configuration according to the second embodiment of the present invention. Explanatory drawing which shows an example of the communication sequence in the network of FIG. The flowchart for demonstrating an example of a process of the MTC device of FIG. Explanatory drawing which shows the reception quality measurement report of FIG. The flowchart for demonstrating the other example of a process of the MTC device of FIG. The block diagram which shows the structure of the MTC device of FIG. The block diagram which shows the structure of the base station of FIG. Explanatory drawing which shows an example of the communication sequence in the network in the 3rd Embodiment of this invention The flowchart for demonstrating the process of the MTC device of FIG. Explanatory drawing which shows the other example of the communication sequence in the network in the 3rd Embodiment of this invention.

Hereinafter, first to fourth embodiments of the present invention will be described with reference to the drawings. The present invention is different from the base station that was connected when the rejection was received so that the MTC device whose connection request was rejected by the MME would not reconnect to the congested MME before the back-off timer expires. When a base station is selected, it is determined whether or not the base station is connected to a congested MME, thereby preventing connection requests and handover requests from being transferred to the congested MME. It is configured as follows.

In the first embodiment of the present invention, when the MTC device performs reselection of the base station before the back-off timer elapses, the MTC device connects to the MME in which the selection candidate base station is congested. Judge whether or not. Further, in the second embodiment of the present invention, the MTC device has the reception quality of the cell of the base station after the back-off timer elapses after connecting to the different MME through the reselected base station. When the threshold value is exceeded, it is determined whether or not the base station of the cell is connected to a congested MME. In the third embodiment of the present invention, when the MTC device is connected to a different MME via the reselected base station, the MTC device increases its priority setting before the back-off timer elapses, Hand over to the MME that rejected the initial connection request. In the fourth embodiment of the present invention, the MME notifies the base station of the congestion state, and the base station receives the reception quality measurement report received from the MTC device by the base station connected to the congested MME. It is determined whether it is related to the configured cell.

Note that, as a reason why the MME cannot accept a connection request from the MTC device, it is assumed that the MME is congested, but various factors can be considered as factors causing the congestion. For example, when access from a large number of MTC devices is concentrated on the MME, or when establishment of a new connection / bearer is limited because the maximum number of connections that can be established is reached, the other in the 3GPP network In some cases, the MME is notified that a similar event has occurred in the other node.

(First embodiment)
First, a first embodiment of the present invention will be described. FIG. 1 shows a network configuration diagram according to the first embodiment of the present invention. In FIG. 1, various information is exchanged between the MTC device 1, which is a communication terminal for MTC (Machine Type Communication), the MTC server 2, the MTC user U, and the MTC device 1 via wireless communication. 3GPP network 4 to which base stations 3A1, 3A2 and 3B and MTC device 1 are connected through cellular lines (LTE (Long Term Evolution), UMTS (Universal Mobile Telecommunication System), CDMA (Code Division Multiple Access) 2000, GSM); MME (Mobility Management Entity) 5A, 5B (or SGSN: Serving GPRS Support Node), which is a component device in the 3GPP network 4 and manages location information of the MTC device 1, and connection management and user data transfer of the MTC device 1 P-GW (Packet Data Network Gateway) 7 and S-GW (Servin) g Gateway) 6 is drawn. Here, in the scenario shown in FIG. 1, the MTC device 1 is located in a place where it can communicate with any of the base stations 3A1, 3A2, and 3B.

The base stations 3A1, 3A2 and 3B are eNB (evolved Node B), Node B, femto base station, pico base station, relay base station, mobile femto, mobile relay, mobile router, etc., and each of cells A1, A2 and B is configured to perform wireless communication with the MTC device 1 located in the cells A1, A2, and B. Further, the movement management of the MTC device 1 located in the cells A1 and A2 is performed by the MME 5A, and the movement management of the MTC device 1 located in the cell B is performed by the MME 5B. Furthermore, the base stations 3A1 and 3A2 belong to the same tracking area (group), and the tracking area is different from the base station 3B. Further, a TAC (Tracking Area Code) indicating a tracking area to which the base stations 3A1, 3A2, and 3B belong is notified to the terminals (MTC device 1) under the base stations 3A1, 3A2, and 3B using the broadcast channel. Yes. Here, the TAC of the base stations 3A1 and 3A2 is TAC (A), and the TAC of the base station 3B is TAC (B).

In FIG. 1, WiMAX (registered trademark), mobile WiMAX, or the like may be used instead of the cellular line, but the names of various entities in that case conform to the specifications. Further, although the communication terminal is called an MTC device here, a case where a communication terminal normally called a UE (User Equipment) is used as a device is also included. As the MTC device and the UE, various devices including a communication module such as a smartphone, a mobile phone, a car navigation, and a PND (Portable Navigation Device) are assumed. The MTC device and the UE may be a device that is carried and moved by a car or a pedestrian, or may be a device that is installed at a fixed location such as a monitoring camera or a road sensor, and does not move. Furthermore, a moving device and a fixed device may form a group.

The MTC server 2 is a server that manages the MTC device 1. The MTC server 2 collects information from the MTC device 1 and can use the information for various determinations performed by the MTC server or provide information to the MTC user U. . In FIG. 1, the MTC server 2 is depicted as an entity that exists outside the 3GPP network 4, but may be an entity within the 3GPP network 4 provided by an operator. The MTC device 1 further transmits and receives data to and from the MTC server 2 or another MTC device.

FIG. 2 is a sequence diagram illustrating processing performed when the MTC device 1 according to the present embodiment transmits a connection request to the MME 5A in the congested state (1) via the TAC (A) base station 3A1. It is an example of 1.
(2) When the MTC device 1 transmits a connection request to the base station 3A1,
(3) The base station 3A1 transfers the connection request to the MME 5A.
(4) (5) At that time, since the MME 5A is (1) in a congested state and cannot accept a connection request from the MTC device 1, a rejection notification is transmitted to the MTC device 1. The rejection notification includes a back-off timer T. Note that the message transmitted by the MTC device 1 may be another mobility management message (NAS (Network Access Stratum) message) such as a service request or a tracking / routing area update. Good. Further, the MTC device 1 may transmit a Mobility Management message (NAS message) to the MME 5A when receiving a trigger message (SMS message, NAS message, paging, etc.) from the MTC server 2.

FIG. 3 is a flowchart showing in detail the processes of (6) reception quality measurement, (7) cell discrimination, and (8) “do not select the same TAC (A) base station 3A2” in FIG. After receiving the rejection notification via the base station 3A1 in step S1, the MTC device 1 transitions to the idle mode (or detached state), and determines whether the back-off timer T is valid in step S2. If the back-off timer T does not exist or has expired (No in step S2), the MTC device 1 retransmits the connection request via the base station 3A1 (step S5). On the other hand, if the back-off timer T is still valid (Yes in step S2), a cell is selected based on the reception quality to check whether another cell exists (step S3). Note that the MTC device 1 may measure the reception quality for a cell that has received an instruction from the connected base station 3A1.

In order to avoid interference, it is desirable that the cell searched in step S3 is a cell having a frequency different from that of the cell connected when the rejection is received. For this purpose, when the MTC device 1 measures the reception quality of the cell in step S3, a frequency different from the frequency of the cell connected when the rejection is received is selected, and the reception quality of the cell of that frequency is selected. Measure. Moreover, when the problem of interference can be avoided, the cells selected may be cells having the same frequency. In this case, in step S3, when the MTC device 1 measures the reception quality of the cell, the reception quality of the cell having the same frequency as the frequency of the cell connected when the rejection is received is measured.

Further, in step S3, when the MTC device 1 specifies a cell for which reception quality is measured (cell identification), a cell of a base station different from the base station connected when the rejection is received may be specified. Good. For this purpose, the cell list (fingerprint) detected by the MTC device 1 in the past includes the physical cell ID (Physical Cell ID) and base station ID (eNB ID) of the cell connected at the time of rejection. Hold. In step S3, when the MTC device 1 detects a cell, the physical cell ID of the detected cell is collated with the physical cell ID of the cell list. As a result, if both have the same physical cell ID, it is determined that the cell is the same base station as the cell connected when the detected cell is rejected (access prohibited cell). On the other hand, if the physical cell IDs are different from each other, it is determined that the detected cell is a cell of a base station different from the cell connected when the detected cell is rejected. When it is determined that the detected cell is a cell of a base station different from the cell connected to the cell when it was rejected, the received quality of the cell is measured. It is determined that there is a cell (Yes in step S3). This enables the base station 3A1 to identify a base station 3A2 that is different from the base station 3A1 that was connected when it was rejected before measuring the reception quality. There is no need to measure reception quality for cells of different frequencies.

If no other cell exists (No in step S3), the process waits until the notified back-off timer T expires (step S7). Note that since the rejection including the back-off timer is received from the base station 3A1 in step S1 and the back-off timer is effective immediately after starting the back-off timer, the step immediately after receiving the rejection It can be considered that S2 is YES.

On the other hand, if another cell is detected (Yes in step S3), the TAC (Tracking Area) included in the broadcast information (SIB1: System Information Block 1) broadcast from the base station that manages the cell is detected. Code) is acquired, and it is confirmed whether or not the acquired TAC is the same as the TAC (A) of the base station 3A1 (step S4). If it is the same as the TAC (A) of the base station 3A1 (Yes in step S4), it is confirmed whether there is another detected cell (step S3). On the other hand, if it is different from the TAC (A) of the base station 3A1 (No in step S4), a connection request is transmitted via the base station (base station 3B in FIG. 1) constituting the cell (step S6). If it is the same as the TAC (A) of the base station 3A1 in step S4, that is, if the same TAC (A) as the base station 3A1 is received from the base station 3A2 in FIG. 1, the process returns to step S3. The MTC device 1 holds the TAC (A) of the connected base station 3A1 as a context. Instead of TAC, comparison may be made using MCC (Mobile Country Code), MNC (Mobile Network Code), and TAI (Tracking Area Identity) composed of TAC. Similarly to TAC and TAI, other IDs may be used as long as the MME to which the base station is connected can be specified.

That is, in FIG. 2, the MTC device 1 is
(7) As a result of cell discrimination, when the TAC (A) of the base station 3A2 constituting the detected cell A2 is the same as the base station 3A1,
(8) It is determined that the NAS message is not transmitted via the base station 3A2. That is, although it is connected to the base station 3A2, the NAS message is not transmitted.
(9) Therefore, before the back-off timer T elapses, the MTC device 1 sends the second connection request to the MME 5A that rejected the first connection request via the base station 3A2 of the same TAC (A). Does not resend.

FIG. 4 shows that (8) (9) the base station 3B is selected when the TAC (B) of the base station 3B constituting the detected cell B is different from the base station 3A1 as a result of the cell discrimination. The sequence in the case of resending a connection request is shown. That is, it connects to the base station 3B and transmits a NAS message. Here, since the sequences in FIGS. 4 (1) to (6) are the same as those in FIGS. 2 (1) to (6), detailed description thereof will be omitted.
(10) When this connection request is transmitted to the MME 5B via the base station 3B,
(11) (12) Accepted by MME5B.
(13) Therefore, the MTC device 1 can connect to the MME 5B that is not the congested MME 5A via the base station 3B before the back-off timer T elapses.

Thus, while the back-off timer T of the congested MME 5A is valid, the detected TAC (A) of the other cell A2 is the same as the base station 3A1 connected when the rejection was received. In some cases, since it can be determined that the detected cell A2 is not connected, transmission of an unnecessary connection request message and transmission / reception of various messages associated therewith can be eliminated. Further, if the detected TAC (B) of the other cell B is different from the base station 3A1 connected when the rejection is received, it is determined to connect to the detected cell B, and the connection request is congested. By retransmitting to the MME 5B that is not the MME 5A, it is possible to connect to an MME 5B that is different from the MME 5A in which congestion occurs even before the back-off timer T elapses.

Although not shown, the message transmitted from the MTC device 1 to the MME 5A is not limited to a connection request, but is another session management message (NAS message) such as a bearer establishment request, a bearer change request, or a PDN connection establishment request. There may be. Further, the MTC device 1 may transmit a SessionＮＡManagement message (NAS message) to the MME 5A when receiving a trigger message (SMS message, NAS message, paging, etc.) from the MTC server 2. In this case, since the MTC device 1 when receiving the rejection message from the MME 5A is in the connected mode, the reception quality of the cell B formed by the base station 3B is measured in (6), as in the case shown in FIG. Furthermore, when the TAC of the base station 3A1 and the TAC of the base station 3B are different in (7), a reception quality measurement report is transmitted to the base station 3A1 even before the back-off timer T elapses. In this case, the base station 3A1 instructs the MTC device 1 to perform handover to the base station 3A2. The MTC device 1 handed over to the base station 3A2 retransmits the rejected NAS message.

On the other hand, as shown in FIG. 2, when the TAC of the base station 3A1 is the same as the TAC of the base station 3A2 in (7), the reception quality of the cell A2 formed by the base station 3A2 with respect to the base station 3A1 Determine that no measurement report is sent. Alternatively, a cell configured by the base station 3A2 including information (MME congestion information) indicating that the base station 3A1 is congested (or that the back-off timer T when it is rejected is valid) A reception quality measurement report related to A2 is transmitted to the base station 3A1. In this case, when the MME congestion information is included in the received reception quality measurement report, the base station 3A1 does not instruct the MTC device 1 to perform handover to the base station 3A2, or to the base station 3A2. It can be determined that the handover instruction is delayed.

Thus, while the back-off timer T of the congested MME 5A is valid, the detected TAC (A) of the other cell A2 is the same as the base station 3A1 connected when the rejection was received. In some cases, it can be determined that a reception quality measurement report related to the detected cell A2 is not transmitted or a reception quality measurement report including MME congestion information is transmitted, so unnecessary transmission / reception of signaling accompanying handover between base stations is eliminated. be able to.

In addition, if the TAC of the base station 3A1 is the same as the TAC of the base station 3A2, the MTC device 1 measures the reception quality of the cell that the base station 3A2 configures after the back-off timer has elapsed, The reception quality measurement report may be transmitted to the base station 3A1. In this case, the base station 3A1 instructs the MTC device 1 to perform handover to the base station 3A2. Thereby, since the MTC device 1 can be handed over to the base station 3A2, the rejected NAS message can be retransmitted.

As another method, when it can be determined that the base station 3A2 is connected to the same MME as the base station 3A1, a normal reception quality measurement report is sent and an instruction to hand over from the base station 3A1 to the base station 3A2 (Handover Command (Or RRCConnectionReconfiguration) and hand over to the base station 3A2. After connecting to the base station 3A1, it is determined that the rejected NAS message is not transmitted until the back-off timer expires. That is, while the back-off timer is still valid, handover between base stations is executed, but if it is determined that the handover destination base station is connected to the same MME as the base station before the handover, The message is not resent. In this case, the determination as to whether or not the handover destination base station is connected to the same MME as the base station before the handover may be performed before or after the reception quality measurement report is transmitted. You may go after. In this case, as a method for knowing the TAC of the handover destination base station, the TAC may be acquired from the SIB included in the received handover instruction or may be acquired from the SIB broadcast from the base station. .

That is, after receiving a handover instruction from a connected base station and performing handover, if it is determined that the handover destination base station is connected to the same MME as the base station before handover, the backoff timer is continued. The NAS message is not transmitted until the back-off timer expires. On the other hand, when it is determined that the handover destination base station is connected to a different MME from the base station before the handover after the handover, the NAS message is transmitted without applying the back-off timer.

<MTC device>
FIG. 5 is a configuration example of the MTC device 1 according to the first embodiment of the present invention. The MTC device 1 includes an interface 11 for connecting to the 3GPP network 4, a cell selection unit 12, a cell determination unit 13, a backoff timer management unit 4, and a connection unit 15. When the terminal (that is, the MTC device 1) is in the idle mode, the cell selection unit 12 selects the cell A1, A2, or B to camp on, and the cell determination unit 13 selects the selected cell A1, A2, or B is instructed to determine whether it is possible to connect.

When receiving an instruction from the cell selection unit 12, the cell determination unit 13 refers to the back-off timer management unit 14 and checks whether there is a back-off timer T that is still valid. Note that the back-off timer T is valid indicates that the given time interval has not yet elapsed. If there is still a valid back-off timer T, whether or not the TAC of the cell notified from the cell selection unit 12 is the same as the TAC of the cell related to the valid back-off timer (cell A1 in FIG. 1). Determine whether. If the TACs are the same, the connection unit 15 is instructed not to connect to the selected cell (cell A2 in FIG. 1). On the other hand, if the TACs are different, the connection unit 15 is instructed to connect to the selected cell (cell B in FIG. 1).

The connection unit 15 transmits and receives connection messages to the base stations 3A1, 3A2, 3B and MMEs 5A, 5B. When a rejection notification is received for the transmitted connection request, the TAC of the base station (base station 3A1 in FIG. 1) connected when the rejection notification is received is held together with the notified back-off timer T The back-off timer management unit 14 is instructed to do so. The connection unit 15 performs reception quality measurement and the like when determining to connect to the base station 3A1, and acquires the TAC broadcast from the base station during the cell selection. When receiving a rejection notice, the cell selection unit 12 is instructed to search for another cell. The back-off timer management unit 14 manages the base station information (cell ID, TAC, etc.) and the back-off timer notified from the connection unit 15, and provides an effective back-up for an inquiry from the cell determination unit 13. Returns information about whether an off timer exists.

As described above, according to the first embodiment of the present invention, when the connection request transmitted by the MTC device 1 is rejected, it is determined whether another cell can be selected and connected to the cell. By doing so, it is possible to avoid sending and receiving unnecessary connection request messages. As a result, it is possible to reduce the processing load of the MTC device 1, the base station 3A2, and the MME 5A being congested, and further the network traffic.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. The MTC device 1 shown in FIG. 6 is initially located in the cell A1, and the connection request transmitted via the base station 3A1 is rejected by the MME 5A, and then can communicate with any of the base stations 3A1, 3A2, and 3B. It is shown that the mobile terminal is in a state where the mobile station is connected to the MME 5B via the base station 3B. That is, when the MTC device 1 is rejected by transmitting a NAS message (for example, a connection request, a bearer establishment request, a bearer change request, a PDN connection establishment request, etc.) via the base station 3A1, it is notified from the MME 5A. The back-off timer T and the TAC (A) of the base station 3A1 are held. At this time, if the MTC device 1 detects the reception quality of the base station 3A2 satisfying the condition as a result of measuring the reception quality of the neighboring cell A2 of the same TAC (A), the base station 3B Assume that the base station 3B determines whether or not the handover process to the base station 3A1 is necessary by transmitting the reception quality measurement report.

When the base station 3B is the same access system as the base stations 3A1, 3A2, the handover executed by the base station 3B is a handover between the same types of access systems (S1 handover or X2 handover). On the other hand, when the base station 3B is an access system different from the base stations 3A1, 3A2, the handover executed by the base station 3B is a RAT (Radio-Access-Technology) handover (Inter-RAT-Handover). For example, the base stations 3A1, 3A2 are e-UTRAN (evolved-UTRAN) eNBs, the base station 3B is a UTRAN (Universal Terrestrial Radio Access Network) RNC (Radio Network Controller), and the MME 5B is an SGSN (Serving GPRS Support Node), it is an inter-RAT handover. Also, the base station 3B may be an E-UTRAN eNB, the base stations 3A1, 3A2 may be UTRAN RNCs, and the MME 5A may be an SGSN.

FIG. 7 shows NAS messages (for example, connection requests and so on) transmitted by the MTC device 1 according to the second embodiment of the present invention via the base station 3A1 as described in FIGS. 4 (1) to (13). (Bearer establishment request, bearer change request, PDN connection establishment request, etc.) are rejected, and after holding backoff timer T of MME5A and TAC (A) of base station 3A1, it connects to MME5B via base station 3B and is connected. (6) When the reception quality of the cell A2 configured by the base station 3A2 of the same TAC (A) as that of the base station 3A1 is measured, and it is detected that a certain condition is satisfied. It is a sequence which shows the process of.

Note that the MTC device 1 acquires the back-off timer T and the TAC (A) of the base station 3A1 by connecting the base station 3A1 and transmitting the NAS message (for example, connection request or bearer establishment) to the MME 5A as described above. Request, bearer change request, PDN connection establishment request, etc.) is not limited to the method to be acquired. For example, when connecting to the MME 5B via the base station 3B, it may be acquired from the MME 5B, or acquired from another MTC device, the MTC server 2, or an ANDSF (Access Network Discovery and Selection Function) server. Also good.

Further, in FIG. 7 (6), when the cell for which the MTC device 1 performs reception quality measurement is specified (cell identification), a cell of a base station different from the base station connected when the rejection is received is specified. May be. For this purpose, the cell list (fingerprint) detected by the MTC device 1 in the past includes the physical cell ID (Physical Cell ID) and base station ID (eNB ID) of the cell connected at the time of rejection. Hold. 7 (6), when the MTC device 1 detects a cell, the physical cell ID of the detected cell is collated with the physical cell ID of the cell list. As a result, if both have the same physical cell ID, it is determined that the cell is the same base station as the cell connected when the detected cell is rejected (access prohibited cell). On the other hand, if the physical cell IDs are different from each other, it is determined that the detected cell is a cell of a base station different from the cell connected when the detected cell is rejected. As a result, before measuring the reception quality, it is possible to identify a base station 3A2 that is different from the base station 3A1 that was connected when the reception was rejected. There is no need to make measurements.

FIG. 8 is a flowchart showing a first process of FIG. 7 (7) cell discrimination and (8) reception quality measurement report transmission performed by the MTC device 1. In FIG. 8, the MTC device 1 that has detected that the reception quality of the base station 3A2 satisfies a certain condition in step S11 checks whether or not there is a valid backoff timer T (step S12). If it does not exist (No in step S12), a normal reception quality measurement report is transmitted. On the other hand, when there is a valid backoff timer T (Yes in step S12), the TAC (A) of the base station 3A1 connected when the backoff timer T is received is changed to the TAC ( It is confirmed whether it is the same as A) (step S13). If the TACs are different (No in step S13), a normal reception quality measurement report is transmitted (step S15). On the other hand, if the TAC is the same (Yes in step S13), it is determined that the MME to which the base station 3A2 is connected is the congested MME 5A (the MME 5A that rejects the connection request transmitted via the base station 3A1). A reception quality measurement report including information (MME congestion information) indicating that there is congestion (or that the back-off timer T when rejected is valid) is transmitted to the base station 3B. The MME congestion information may be indicated by setting a flag, or may include a specific value that means that congestion has occurred. Alternatively, the MTC device 1 may determine not to transmit the reception quality measurement report.

Returning to FIG.
(7) As a result of cell discrimination, when the TAC (A) of the base station 3A2 is the same as the TAC (A) associated with the valid backoff timer T,
(8) As shown in FIG. 9, a reception quality measurement report including MME congestion information is transmitted to the connected base station 3B.
(9) The base station 3B that has received the reception quality measurement report including the MME congestion information determines that the handover to the base station 3A2 is not executed even if the report indicates that the reception quality of the base station 3A2 is good. .
(10) Therefore, before the back-off timer T elapses, the MTC device 1 sends the second connection request to the MME 5A that rejected the first connection request via the base station 3A2 of the same TAC (A). Does not resend.

FIG. 10 is a flowchart showing a second process of FIG. 7 (7) cell discrimination and (8) reception quality measurement report transmission performed by the MTC device 1. Steps S11, S12, S13, S14, and S15 in FIG. 10 are the same as those in FIG. 8, but steps S13a and S13b are added. In step S13, it is confirmed whether or not the TAC (A) of the base station 3A1 connected when the back-off timer T is received is the same as the TAC (A) of the base station 3A2, and the reception quality is determined. When the TAC (A) acquired from the satisfied base station 3A2 is the same TAC (A) as the associated back-off timer T (Yes in step S13), the remaining back-off timer T remains. Time and a certain threshold value are compared (step S13a). The threshold value may be a value stored in the MTC device 1 in advance, or may be included in the SIB referred to when the reception quality of the base station 3A2 is measured in step S11.

If the remaining time of the back-off timer T is shorter than a certain threshold value (YES in step S13a), the normal reception quality measurement report is transmitted after waiting for the back-off timer T to elapse (step S13b). (Step S15). Thus, in order to send a normal reception quality measurement report after waiting for the congestion of the MME 5A to be alleviated, the start of the handover process to the base station 3A2 by the base station 3B is delayed after the congestion of the MME 5A is alleviated. Is possible. As a result, the handover to the base station 3A2 is successful. If the remaining time of the back-off timer T is not shorter than a certain threshold (NO in step S13a), a reception quality measurement report including MME congestion information is transmitted to the connected base station 3B.

<MTC device>
FIG. 11 is a configuration example of the MTC device 1 according to the second embodiment of the present invention. The MTC device 1 includes an interface 11, a reception quality measurement unit 16 that measures reception quality, a cell determination unit 13, a back-off timer management unit 14, and a reception quality measurement report transmission unit 17 that transmits a reception quality measurement report. The connection unit 15 is configured. The cell determination unit 13, the back-off timer management unit 14, and the connection unit 15 are the same as those described with reference to FIG. The reception quality measuring unit 16 searches the neighboring cells A1, A2, and B, and measures the reception quality of the detected cells. As a result of the measurement, if the reception quality of the cell A2 satisfies a certain condition, the cell discrimination unit 13 is instructed to determine whether it is possible to connect to the cell A2 that satisfies the reception quality condition. To do.

When receiving an instruction from the reception quality measurement unit 16, the cell determination unit 13 refers to the back-off timer management unit 14 and confirms whether there is a back-off timer T that is still valid. If there is still a valid backoff timer T, whether or not the TAC of the cell A2 notified from the reception quality measurement unit 16 is the same as the TAC (A) of the cell A1 related to the valid backoff timer Judging. If the TACs are the same, the reception quality measurement report unit 17 is instructed to transmit a reception quality measurement report including MME congestion information to the base station 3B (steps S13 → S14 in FIG. 8). On the other hand, if the TACs are different, the reception quality measurement report unit 17 is instructed to transmit a normal reception quality measurement report for the cell A2 (steps S13 to S15 in FIG. 8). The reception quality measurement report transmission unit 17 receives an instruction from the cell determination unit 13 and transmits a normal reception quality measurement report or a reception quality measurement report including MME congestion information together with the measurement result of the reception quality of the cell.

<Base station 3B>
FIG. 12 is a configuration example of the base station 3B in the second embodiment of the present invention. The base station 3B includes an interface 31, a reception quality measurement report reception unit 32, a handover determination unit 34, and a handover execution unit 33. The reception quality measurement report reception unit 32 performs reception processing of the reception quality measurement report received from the MTC device 1 and passes the information included in the message to the handover determination unit 34. If it is a reception quality measurement report including MME congestion information, the handover determining unit 34 determines not to perform handover to the target cell A2. On the other hand, when a normal reception quality measurement report that does not include MME congestion information is received, the handover execution unit 33 is instructed to start the handover process to the cell A2.

As described above, according to the second embodiment of the present invention, when the MTC device 1 transmits a reception quality measurement report regarding the cell A2 that satisfies the reception quality condition to the base station 3B, the target cell A2 Is determined to be a base station connected to the same MME 5A as the base station 3A1 that was connected when the rejection notification was received in the past, the MME 5A to which the base station 3A2 is connected By notifying the connected base station 3B of the congestion by the reception quality measurement report, unnecessary handover message transmission / reception can be avoided. Thereby, it becomes possible to reduce the processing load of the MTC device 1, the base station 3B, and the MMEs 5A and 5B, and further the network traffic.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The third embodiment of the present invention will also be described with reference to FIG. 6 described in the second embodiment. The MTC device 1 shown in FIG. 6 can change the setting of its own priority, and a low priority (Low Priority) and a normal priority (Normal Priority: normal priority (or Low Priority). Not) or High Priority). When set as Low Priority, a NAS message (for example, a connection request, a bearer establishment request, a bearer change request, a PDN connection establishment request, etc.) is transmitted with a low priority indicator (Low Priority Indicator). On the other hand, in the case of Normal (normal), a connection request not including the Low Priority Indicator is transmitted. Since the connection request including the Low Priority Indicator is handled with low priority by the MMEs 5A and 5B, when the MMEs 5A and 5B are in a congested state, they are subject to rejection prior to the normal MTC device.

When the MTC device 1 in FIG. 6 transmits a connection request via the base station 3A1, the MTC device 1 receives a back-off timer notification from the congested MME 5A. This back-off timer includes two types, one is a back-off timer T1 for a low priority MTC device, and the other is a back-off timer T2 for a normal MTC device. That is, the MME 5A rejects not only the low priority MTC device but also the normal MTC device. The values of the two back-off timers T1 and T2 are different, and it is assumed that the back-off timer T1 for the low-priority MTC device is longer than the back-off timer T2 of the normal MTC device (T1> T2). This indicates that a low priority MTC device is handled with a lower priority. The two back-off timers T1 and T2 may be notified separately by a rejection message for different connection requests. That is, the back-off timer T1 for the low-priority MTC device is acquired by the rejection message for the connection request transmitted by the MTC device 1 as Low-priority priority, and then the back-off for the normal MTC device by the rejection message for the connection request transmitted as Normal. The off timer T2 may be acquired.

At this time, the MTC device 1 that has acquired the two back-off timers T1 and T2 selects the base station 3B as in the second embodiment of the present invention, and is connected to the MME 5B as a low-priority MTC device. And Note that the configuration of FIG. 6 is the same as that described in the second embodiment of the present invention.

FIG. 13 shows that the MTC device 1 according to the third embodiment of the present invention executes the sequence of FIGS. 4 (1) to (13) from the MME 5A as in the second embodiment of the present invention. When the two back-off timers T1 and T2 and the TAC of the base station 3A1 are held, the reception quality of the cell A2 formed by the base station 3A2 is measured, and a certain condition is satisfied. It is a sequence which shows a process when this is detected.

The MTC device 1 acquires the back-off timers T1 and T2 and the TAC (A) of the base station 3A1 when the connection request transmitted to the MME 5A by connecting to the base station 3A1 is rejected as described above. It is not limited to the acquisition method. For example, when connecting to the MME 5B via the base station 3B, it may be acquired from the MME 5B, or acquired from another MTC device, the MTC server 2, or an ANDSF (Access Network Discovery and Selection Function) server. Also good.

In FIG. 13 (6), when the cell for which the MTC device 1 measures the reception quality is specified (cell identification), the cell of the base station different from the base station connected when the rejection is received is specified. May be. For this purpose, the cell list (fingerprint) detected by the MTC device 1 in the past includes the physical cell ID (Physical Cell ID) and base station ID (eNB ID) of the cell connected at the time of rejection. Hold. In FIG. 13 (6), when the MTC device 1 detects a cell, the physical cell ID of the detected cell is collated with the physical cell ID of the cell list. As a result, if both have the same physical cell ID, it is determined that the cell is the same base station as the cell connected when the detected cell is rejected (access prohibited cell). On the other hand, if the physical cell IDs are different from each other, it is determined that the detected cell is a cell of a base station different from the cell connected when the detected cell is rejected. As a result, before measuring the reception quality, it is possible to identify a base station 3A2 that is different from the base station 3A1 that was connected when the reception was rejected. There is no need to make measurements.

FIG. 14 is a flowchart showing a case where the MTC device 1 performs the processing after (7) cell determination in FIG. FIG. 13 (6) As a result of the reception quality measurement, when it is detected in step S11 that the reception quality of the base station 3A2 satisfies the condition, the MTC device 1 still has a valid low-priority backoff timer T1 (> Whether or not T2) exists is confirmed (step S12a), and if it does not exist (No in step S12a), a normal reception quality measurement report is transmitted (step S15). On the other hand, if it exists (Yes in step S12a), it is confirmed whether the TAC (A) of the base station 3A1 associated with the back-off timer T1 is the same as the TAC (A) of the base station 3A2 (step S13). . If the TAC is different (No in step S13), a normal reception quality measurement report is transmitted to the base station 3B (step S15).

On the other hand, if TAC is the same (Yes in step S13), it is confirmed whether the backoff timer T2 (<T1) acquired together with the backoff timer T1 exists and is valid (step S16). If the back-off timer T2 does not exist or has expired (No in step S16), the MTC device 1 performs processing for changing its priority setting in the network 4 from Low４Priority to Normal. (Step S17), a normal reception quality measurement report is transmitted to the base station 3B (Step S15). If a normal reception quality measurement report is transmitted without changing the priority setting, the MME 5A rejects the handover process as a low-priority MTC device, but the normal reception quality is changed after changing to Normal. When the measurement report is transmitted, since the handover process is performed as a normal MTC device, it is accepted by the MME 5A. On the other hand, if the back-off timer T2 is valid in step S16, a reception quality measurement report including MME congestion information is transmitted to the base station 3B (step S14).

Returning to FIG.
(7) As a result of cell discrimination, when the low-priority long back-off timer T1 is still valid, but the normal short back-off timer T2 has already expired,
(8) The MTC device 1 transmits a reception quality measurement report and a handover request to the base station 3B after executing processing for changing its own priority setting to Normal.
(9) Upon receiving this, the base station 3B executes the handover process to the base station 3A1 using the MTC device 1 as a normal MTC device.
(10) For this reason, the MTC device 1 can be connected to the MME 5A where congestion has ended via the base station 3A1 after the normal shorter back-off timer T2 has elapsed.

The reason for changing the priority setting of the MTC device 1 to Normal is that there is an application in which the MTC device 1 wants to perform transmission / reception using a cell with better reception quality, or the base station 3A2 is an eNB and the base station 3B In the case of RNC, there are cases where there is an application that wants to transmit / receive on E-UTRAN rather than on UTRAN, but is not limited thereto. Further, as a process for changing the priority setting of the MTC device 1 to Normal, for example, a method of once disconnecting (detaching) from the network 4 and then connecting (attaching) as a normal MTC device again, or TAU (Tracking Area) When sending NAS (Non-Access Stratum) messages addressed to MME such as Update (Update) and RAU (Routing-Area-Update), the priority setting in network 4 is set to Normal by sending without setting Low-Priority-Indicator. There is a method of changing, but it is not limited to these.

Instead of changing the priority setting from Low to Normal in FIG. 13 (8) and transmitting the reception quality measurement report in FIG. 13 (9), in the reception quality measurement report transmitted in FIG. 15 (8). As shown in FIG. 9, information indicating that a normal handover is requested (Normal handover request) may be transmitted to the base station 3B. In this case, if the received reception quality measurement report includes a Normal handover request, the base station 3B executes the handover process as a Normal MTC device even if it is a Low Priority MTC device.

As described above, according to the third embodiment of the present invention, before the MTC device 1 transmits a reception quality measurement report for the cell A2 that satisfies the reception quality condition, its own priority setting is changed from Low１Priority. By changing to Normal, handover as a normal MTC device can be executed, so that handover processing can be started earlier than a Low Priority MTC device.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. The fourth embodiment of the present invention will also be described with reference to FIG. 1 described in the first embodiment. The MME 5A notifies the base station 3A1 that the MME 5A is in a congestion state. On the other hand, when the MTC device 1 transmits a NAS message to the MME 5A via the base station 3A1, a rejection message including a back-off timer is returned. Assume that the MTC device 1 does not have a cell discrimination function as described in the first embodiment of the present invention. That is, the MTC device 1 transmits a normal reception quality measurement report regarding the base station 3A2 to the base station 3A1. The base station 3A1 determines whether or not the base station 3A2 is connected to the congested MME 5A based on the cell ID of the base station 3A2 included in the received reception quality measurement report. When the cell ID indicates that it is connected to the MME 5A, the reception quality measurement report is ignored and it is determined that the MTC device 1 is not instructed to perform handover to the base station 3A2.

As described above, according to the fourth embodiment of the present invention, even if the MTC device 1 transmits a normal reception quality measurement report, the base station that receives the normal reception quality measurement report is connected to the MME in the congestion state. Since it is possible to determine whether or not it is a reception quality measurement report for the base station being used, unnecessary transmission / reception of a handover message can be avoided.

As described above, according to the first to third embodiments of the present invention, the newly selected base station 3A2 is connected to an MME different from the MME 5A to which the base station 3A1 connected when the rejection notification is received is connected. Since it can be determined whether or not to connect to the newly selected base station 3A2, it is possible to reduce unnecessary signaling and reduce power consumption. Further, according to the fourth embodiment of the present invention, the base station receives a notification about congestion from the MME, whereby the reception quality measurement report received from the MTC device is connected to the congested MME. By confirming whether or not it is related to a base station, it can be determined whether or not the base station should be handed over. Therefore, unnecessary signaling can be reduced and power consumption can be suppressed. In the first to fourth embodiments of the present invention described above, the case where the present invention is applied in the MTC technique has been mainly described. However, the scope of the present invention is limited to the MTC technique. It is not a thing. The present invention is applicable to any other communication technology.

Each functional block used in the description of the above embodiment is typically realized as an LSI that is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. Although referred to as LSI here, it may be referred to as IC, system LSI, super LSI, or ultra LSI depending on the degree of integration. Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI, or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used. Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. For example, biotechnology can be applied.

According to the second aspect of the present invention, there is a high possibility that a communication device to which the first connection request is rejected from the mobility management node via the wireless network is rejected before the standby time elapses for the mobility management node. The communication device that has been refused the first connection request from the mobility management node via the wireless network accesses the network before the waiting time elapses. Therefore, it is possible to prevent a delay in data transmission / reception, and it can be applied to a communication technology for exchanging information between a communication node and a server or between communication nodes, in particular, an MTC technology. .

Claims (10)

1. A communication device that detects a first cell configured by the first base station and is denied the first connection request transmitted to the mobility management node selects a second cell different from the first cell. A cell selection method,
   Notifying the communication device of a waiting time until the first connection request is retransmitted when the mobility management node rejects the first connection request from the communication device;
   Receiving the waiting time when the communication device is denied the first connection request;
   The base station group identification information of the base station notified in the cell from the base station constituting the cell is different information for each mobility management node to which the base station belongs, and receiving the base station group identification information;
   When the communication device detects the second cell before the waiting time elapses, the base station group identification information of the first base station and the second cell constituting the second cell By comparing the base station group identification information of the base station, it is determined whether or not the first and second base stations belong to the same mobility management node. Transmitting the second connection request to the second base station if the second connection request does not belong to the second base station.
   A cell selection method.
2. When the communication device is connected to the second base station belonging to a mobility management node different from the mobility management node to which the first base station belongs before the standby time elapses, the first base That the mobility management node to which the first and third base stations belong is congested when the third cell configured by the third base station that notifies the same base station group identification information as the station is detected. The cell selection method according to claim 1, further comprising a step of transmitting a reception quality measurement report of the third cell including congestion information to the second base station.
3. When the communication device is connected to the second base station belonging to a mobility management node different from the mobility management node to which the first base station belongs, the same base station group identification information as the first base station Determining whether or not the remaining time of the waiting time is equal to or less than a predetermined value when detecting a third cell configured by the third base station notifying
   If the mobility management node to which the first and third base stations belong is not congested, a reception quality measurement report of the third cell including congestion information indicating that the mobility management node belongs to the second base station. And transmitting a reception quality measurement report of the third cell not including the congestion information to the second base station after elapse of the waiting time when it is equal to or less than a predetermined value. Item 2. The cell selection method according to Item 1.
4. A communication device that detects a first cell configured by the first base station and is denied the first connection request transmitted to the mobility management node selects a second cell different from the first cell. A cell selection system,
   Means for notifying the communication device of a waiting time until the first connection request is retransmitted when the mobility management node rejects the first connection request from the communication device;
   Means for receiving the waiting time when the communication device is denied the first connection request;
   Base station group identification information of the base station notified from the base station constituting the cell in the cell is different information for each mobility management node to which the base station belongs, and means for receiving the base station group identification information;
   When the communication device detects the second cell before the waiting time elapses, the base station group identification information of the first base station and the second cell constituting the second cell By comparing the base station group identification information of the base station, it is determined whether or not the first and second base stations belong to the same mobility management node. Means for transmitting the second connection request to the second base station when it does not belong to and does not belong to the second base station,
   Having cell selection system.
5. When the communication device is connected to the second base station belonging to a mobility management node different from the mobility management node to which the first base station belongs before the standby time elapses, the first base That the mobility management node to which the first and third base stations belong is congested when the third cell configured by the third base station that notifies the same base station group identification information as the station is detected. The cell selection system according to claim 4, further comprising means for transmitting a reception quality measurement report of the third cell including congestion information to the second base station.
6. When the communication device is connected to the second base station belonging to a mobility management node different from the mobility management node to which the first base station belongs, the same base station group identification information as the first base station Means for determining whether or not the remaining time of the waiting time is equal to or less than a predetermined value when detecting a third cell configured by the third base station notifying
   If the mobility management node to which the first and third base stations belong is not congested, a reception quality measurement report of the third cell including congestion information indicating that the mobility management node belongs to the second base station. Means for transmitting a reception quality measurement report of the third cell not including the congestion information to the second base station after elapse of the waiting time when it is equal to or less than a predetermined value;
   The cell selection system according to claim 4, further comprising:
7. Communication for selecting a second cell different from the first cell when the first cell configured by the first base station is detected and the first connection request transmitted to the mobility management node is rejected A device,
   Transmitting means for transmitting a connection request to the mobility management node;
   Receiving means for receiving, from the mobility management node, a waiting time until the first connection request is retransmitted when the mobility management node rejects the first connection request transmitted by the transmission means;
   Base station group identification information of the base station notified from the base station constituting the cell in the cell is different information for each mobility management node to which the base station belongs, and means for receiving the base station group identification information;
   When the second cell is detected before the standby time elapses, the base station group identification information of the first base station and the base of the second base station constituting the second cell Determining means for determining whether the first and second base stations belong to the same mobility management node by comparing station group identification information;
   The transmitting means does not transmit a second connection request to the second base station when the first and second base stations belong to the same mobility management node, and when the first and second base stations do not belong, A communication device that transmits a request to the second base station.
8. The same base station as the first base station when connected to the second base station belonging to a different mobility management node from the mobility management node to which the first base station belongs before the standby time elapses Congestion information indicating that the mobility management node to which the first and third base stations belong is congested when a third cell configured by a third base station that notifies group identification information is detected. The communication device according to claim 7, further comprising means for transmitting a reception quality measurement report of the third cell to the second base station.
9. When the communication device is connected to the second base station belonging to a mobility management node different from the mobility management node to which the first base station belongs, the same base station group identification information as the first base station Means for determining whether or not the remaining time of the waiting time is equal to or less than a predetermined value when detecting a third cell configured by the third base station notifying
   If the mobility management node to which the first and third base stations belong is not congested when it is not less than a predetermined value, a reception quality measurement report of the third cell including congestion information indicating congestion is sent to the second base station. Means for transmitting the third cell reception quality measurement report not including the congestion information to the second base station after the waiting time has elapsed when the transmission time is less than or equal to a predetermined value;
   The communication device according to claim 7, further comprising:
10. A base station to which a communication device is connected via a wireless network,
    Means for receiving a reception quality measurement report of the cell from the communication device when the communication device detects a cell;
    The connection of the communication device connected to the base station when the reception quality measurement report includes congestion information indicating that the mobility management node to which the base station serving as a handover candidate constituting the cell belongs is congested. Means for handing over the connection of the communication device to the base station serving as the handover candidate when the congestion information is not included in the reception quality measurement report.
    Having a base station.

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