JP7624708B2 - Wireless devices - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act January 11, 2021, https://ieeeexplorer.ieee.org/document/9369487, Proceedings of the 2021 IEEE 18th Annual Consumer Communications & Networking Conference [Publications, etc.] January 11, 2021, https://ccnc2021.ieee-ccnc. org/, Virtual Conference at the 2021 IEEE 18th Annual Consumer Communications & Networking Conference

An embodiment of the present invention relates to a wireless device.

Mobility management is an important function in cellular networks. It is the process by which the core network (CN) tracks the location of the user equipment (UE) and has two components: registration and paging.

Registration is the process by which a user equipment UE reports its location information to the core network CN. In current 4G LTE (Long-Term Evolution) and EPC (Evolved Packet Core) systems, cells (i.e. Evolved Node Bs (eNBs)) are grouped to form tracking areas (TAs) that manage the movement of mobile objects. Each cell is assigned to one tracking area TA, and each user equipment UE registers with one tracking area TA. When a user equipment UE moves from one tracking area TA to another, the user equipment UE reports (registers) its latest location information to the core network CN.

The procedure of registering location information to the core network CN is called Tracking Area Update in LTE/EPC. The user equipment UE needs to perform the registration or tracking area update procedure when it moves to a new tracking area TA, when the tracking area update timer expires, etc. The tracking areas TA are further grouped to form a Tracking Area List. Since the Tracking Area List contains multiple Tracking Areas TA, the user equipment UE can freely move between these Tracking Areas TA without performing the Tracking Area Update procedure. When the user equipment UE moves to another Tracking Area TA that is not included in the current Tracking Area List, the user equipment UE needs to complete the Tracking Area Update procedure.

Paging (Call termination) is the procedure for routing incoming data or calls to a user equipment UE. When the core network CN (including the Mobility Management Entity (MME)) receives a call or data for the user equipment UE, the core network CN sends a paging message in all cells belonging to the tracking area TA where the user equipment UE was recently registered. When the user equipment UE receives the paging message, a connection is established through the cell where the user equipment UE responds to the paging message. The purpose of mobility management is for the core network CN to accurately track the user equipment UE. To this end, the user equipment UE periodically reports its location information.

The core network CN updates the reported information from time to time. If the location information in the core network CN is inaccurate, the core network CN cannot correctly forward calls to the user equipment UE.

Considering the case where the user equipment UE is not a so-called mobile phone but an equipment (M2M device) that performs M2M communication (Machine to Machine), an M2M network generally has a large number of M2M devices referenced in a cellular network, and refers to hundreds of M2M devices. Therefore, in an M2M network, millions of devices will be connected to the mobile communication system in addition to the current mobile subscribers. Mobility management for a large number of devices will be a significant burden for the mobile network.

One solution to reduce mobility management-related communications, especially those related to registration, is the grouping approach. In the grouping approach, M2M devices (or user equipment UE) with similar mobility patterns are grouped together, and one of the devices is selected as a group leader (GL). When the group moves to a new tracking area TA, only the group leader GL performs the registration operation on behalf of the group. In this way, this approach can reduce the concentration of communications due to registration and location updates.

However, this method has the problem of being overly dependent on the group leader GL for registration and paging functions. If the group leader GL leaves the group or if the registration procedure (or tracking area update procedure) cannot be established due to interference or insufficient terminal power, the core network CN will fail to track the entire group. In addition, the grouping method does not have a mechanism for detecting the departure of user equipment UE or devices, so if a member user equipment UE or M2M device deviates from the group's trajectory, the core network CN cannot detect the departure.

Patent Publication 2018-093537

As such, in conventional wireless devices, the core network may fail to track even when the grouping method is used. This embodiment has been made to solve this problem, and aims to provide a wireless device that allows the core network to maintain tracking even when the grouping method is used to manage moving objects.

The wireless device of the embodiment is a wireless device that connects to a base station in a core network that manages the location of the connection partner of the base station in units of a tracking area including the communication area of the base station. This wireless device includes a first wireless interface that communicates with the core network via the base station, a second wireless interface that communicates with other wireless devices located in a common tracking area, a positioning unit that generates trajectory information of the wireless device's own movement based on its own past location information, and a group management unit that generates a transmission signal including the trajectory information at a predetermined timing and transmits it via the second wireless interface, receives a response signal returned from the other wireless device in response to the transmission signal via the second wireless interface, generates a group list including the IDs of the other wireless devices that returned the response signals, and transmits a registration request for location information of the wireless device itself and the other wireless devices that returned the response signals to the core network via the first wireless interface based on the group list. The wireless device also includes a group determination unit that receives a signal including movement trajectory information of another wireless device from the other wireless device via the second wireless interface, generates correlation information indicating a correlation between the movement trajectory information of the wireless device and the movement trajectory information of the other wireless device based on the movement trajectory information of the wireless device, determines whether or not the wireless device belongs to a group formed by the other wireless device based on the correlation information, and transmits a response signal including its own ID via the second wireless interface if the determination results in the device belonging to the group.

FIG. 1 is a diagram showing an overview of a cellular network. FIG. 2 illustrates receiving a call in a cellular network. A diagram showing an M2M device moving in a cellular network. FIG. 13 is a diagram showing a state in which a device has left a group of M2M devices. FIG. 13 is a diagram showing a device leaving a group of M2M devices. FIG. 13 is a diagram showing how grouped devices move. FIG. 2 is a diagram showing a configuration of a device according to an embodiment. FIG. 11 is a diagram illustrating a device grouping operation according to an embodiment. FIG. 11 is a diagram illustrating a device grouping operation according to an embodiment. FIG. 11 is a diagram showing a communication procedure in a device grouping operation. FIG. 1 is a diagram showing two devices moving. 11A and 11B are diagrams illustrating effects of the device according to the embodiment. 11A and 11B are diagrams illustrating effects of the device according to the embodiment. 11A and 11B are diagrams illustrating effects of the device according to the embodiment. 11A and 11B are diagrams illustrating effects of the device according to the embodiment. 11A and 11B are diagrams illustrating effects of the device according to the embodiment.

(Cellular network overview)
A cellular network according to an embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the cellular network NW according to the embodiment has a core network CN. The core network CN is a so-called backbone network, and a user equipment UE belongs to the core network CN. The core network has a system for managing location information of the user equipment UE in order to send a paging message to the user equipment UE.

The cellular network NW of the embodiment has base stations eNB1 to eNB5. The base stations eNB1 to eNB5 are connected to a core network CN. In the example shown in FIG. 1, the communication areas (cells) of the base stations eNB1 and eNB2 each constitute a tracking area TA1. Similarly, the communication areas of the base stations eNB3 to eNB5 each constitute a tracking area TA2.

The tracking area TA is an area that is a unit for tracking user equipment UE, which is a terminal of a cellular network. Each cell, which is the communication area of each base station, is assigned to one of the tracking areas TA. The user equipment UE registers with the core network CN as being located in one tracking area TA. Even if the user equipment UE moves from the cell of base station eNB1 to the cell of base station eNB2, the user equipment UE remains located in the tracking area TA1. On the other hand, if the user equipment UE moves from the cell of base station eNB2 to the cell of base station eNB3, the user equipment UE moves from the tracking area TA1 to the tracking area TA2. The core network CN manages the location and movement of the user equipment UE in units of tracking areas.

When the user equipment UE moves, for example, from tracking area TA1 to tracking area TA2, the user equipment UE reports its latest location information to the core network CN. The location information can be expressed as the ID of the tracking area TA. In the example shown in FIG. 1, after the movement, the user equipment UE reports the tracking area TA2 to the core network CN as its latest location information.

Next, with reference to Figures 1 and 2, a call flow (incoming communication flow) received by the user equipment UE in the cellular network NW according to the embodiment will be described. When the core network CN receives a call for the user equipment UE, the core network CN transmits a call message for the user equipment UE to the base stations of all cells belonging to the tracking area TA in which the user equipment UE was last registered (dotted and dashed lines in Figure 2). When the user equipment UE receives the call message, a connection is established through the base station of the cell in which the user equipment UE responds to the call message (solid lines in Figure 2).

In the example shown in Figures 1 and 2, the user equipment UE after moving reports the tracking area TA2 to the core network CN as location information, so the call to the user equipment UE received by the core network CN is sent to all communication areas of the base stations eNB3 to eNB5 belonging to the tracking area TA2 (dotted line in Figure 2). When the user equipment UE receives the call message, it establishes a connection through the base station eNB3 of the cell to which it belongs. Subsequent communication of the user equipment UE is performed via the base station eNB3 (solid arrow in Figure 2).

(When the user equipment is an M2M device)
With reference to FIG. 3, a case where a certain number of user equipments UE move together like M2M devices will be described. Consider the case where the user equipment UE is not a so-called mobile phone, but an equipment (M2M device) that performs M2M communication (Machine to Machine). In this case, generally, the number of M2M devices referenced in the cellular network NW is large, and hundreds of M2M devices may be referenced. Therefore, in the cellular network to which the M2M devices belong, millions of M2M devices will be connected to the cellular network in addition to the current mobile subscribers. Mobility management of a large number of devices is a significant burden for the core network CN and base stations. The example shown in FIG. 3 shows a situation in which, when multiple user equipments UE move from tracking area TA1 to tracking area TA2, each user equipment UE reports its own location information to the core network CN via the base station eNB3. In this case, the burden on the base station eNB3 and the core network CN becomes extremely large.

Therefore, in the cellular network of the embodiment, the user equipment UE first forms a group represented by a group leader GL. This group is composed of user equipment UE members that have similar movement trajectories.

コアネットワークＣＮの追跡エリアは、ＴＡ_１，ＴＡ_２，．．．，ＴＡ_ＮのようにＮ個に分割されているものとする。Ｍ２Ｍデバイス各々は追跡エリアＴＡ内を独立して移動し、コアネットワークＣＮにはＭ２Ｍデバイスそれぞれの過去の軌跡が記録されている。Ｍ２Ｍデバイスそれぞれの移動に関する相関は、Ｍ２Ｍデバイスの過去の軌跡をもとに推定することができる。そこで、Ｍ２Ｍデバイスは、Ｍ２Ｍデバイス相互の移動に関する相関をもとにグループ化する。 (Grouping criteria)
The criteria for grouping user equipments UE will be described below. Assume that there are M M2M devices m as shown in Equation 1.

The tracking area of the core network CN is assumed to be divided into N areas, such as _TA1 , _TA2 , ..., _TAN . Each M2M device moves independently within the tracking area TA, and the past trajectory of each M2M device is recorded in the core network CN. The correlation of the movement of each M2M device can be estimated based on the past trajectory of the M2M device. Therefore, the M2M devices are grouped based on the correlation of the movement between the M2M devices.

数式２は、時刻ｔにおいてデバイスｍ_ｘが追跡エリアＴＡ_ｉから追跡エリアＴＡ_ｊに向かうこと意味する。もしデバイスｍ_ｘが時刻［ｔ，ｔ＋Ｔ］の間においてｗ個の追跡エリアＴＡを移動すると、デバイスｍ_ｘの軌跡は数式３のようになる。

同様に、もしデバイスｍ_ｙが時刻［ｔ，ｔ＋Ｔ］の間においてｗ_２個の追跡エリアＴＡを移動すると、デバイスｍ_ｙの軌跡は数式４のようになる。

If an M2M device _{m_x} moves from a tracking area TA _i to a tracking area TA _j at time t, the movement of the device _{m_x} is expressed as in Equation 2.

Equation 2 means that at time t, device m _x moves from tracking area TA _i to tracking area TA _j . If device m _x moves through w tracking areas TA between times [t, t+T], the trajectory of device m _x is as shown in Equation 3.

Similarly, if device _my moves through _w2 tracking areas TA during time [t, t+T], the trajectory of device _my is expressed as Equation 4.

ここで、軌跡ρ_ｉ ^ｘは、時刻ｔ_ｉにおいて追跡エリアＴＡ_ｉに存在するデバイスｍ_ｘを示すツータプル（ＴＡ_ｉ ^ｘ，ｔ_ｉ ^ｘ）である。移動体ｍ_ｘおよびｍ_ｙの相関Ｃは、数式６のように推定することができる。

∈は、閾値であり、デバイスｍ_ｘおよびｍ_ｙの相関を決定するために用いられる。さらに、Ｚ（ρ_ｖ ^ｘ，ρ_ｖ ^ｙ）は、１または０の値をとる二値関数である。例えば、Ｋ＝３とおき、もしＣ_ｘ，ｙ（３）＝１であれば、デバイスｍ_ｘおよびｍ_ｙの移動の軌跡は、時刻および空間に関して三つの追跡エリアＴＡにおいて共通していることになる。それゆえ、もしＣ_ｘ，ｙ（Ｋ）＝１であれば、デバイスｍ_ｘおよびｍ_ｙが移動の相関をもつと決定できる。すなわち、グループ化可能なデバイスであると判定することができる。 If the trajectory of device m _x including K (K>0) nearest tracking areas TA visited by device m _x is denoted by ρ ^x (K), then it can be expressed as in Equation 5.

Here, the trajectory ρ _i ^x is a two-tuple (TA _i ^x , t _i ^x ) indicating a device m _x present in a tracking area TA _i at time t _i . The correlation C between mobiles m _x and _my can be estimated as shown in Equation 6.

∈ is a threshold value used to determine the correlation between devices m _x and my _y . Furthermore, Z(ρ _v ^x , ρ _v ^y ) is a binary function that takes the value of 1 or 0. For example, if K=3 and C _x,y (3)=1, the movement trajectories of devices m _x and my _y are common in the three tracking areas TA in terms of time and space. Therefore, if C _x,y (K)=1, it can be determined that devices m _x and my _y have movement correlation. In other words, it can be determined that they are groupable devices.

In the cellular network of the embodiment, the user equipment UE determines whether grouping is appropriate based on the correlation between its own trajectory and the trajectories of other user equipment.

(User Equipment UE Grouping Procedure)
Next, a grouping procedure of user equipment UE in an embodiment will be described. The grouping procedure is performed by out-of-band communication. That is, communication between M2M devices can be performed via an unlicensed communication standard (band) rather than a communication standard via a licensed base station. Any M2M device can act as a group leader GL in a group and can initiate the grouping procedure by broadcasting its movement pattern.

When an M2M device m _x starts a grouping procedure, the device m _x broadcasts a grouping message including its ID and a trajectory ρ ^x (K). When another M2M device my _y receives the message, the device my _y estimates a correlation C with the device m _x , which is the group leader GL, by comparing the received trajectory ρ ^x (K) with its own trajectory ρ ^y (K). If the result of the calculation using Equation 6 and Equation 7 is C _x,y (K) = 1, it can be determined that the device my _y is correlated with the device m _x in terms of movement.

If the device _my determines that there is a correlation between the device mx and the device _mx in terms of movement, the device _my transmits a group registration message including its own device ID to the device _mx , whereby the device my belongs to a group with the device _mx as the group leader GL.

If many devices that meet the correlation criteria for mobility send group registration messages at the same time, message collisions will occur, making it difficult to establish grouping. To address this message collision problem, a pre-backoff window scheme can be applied.

The pre-backoff window method reduces collisions by having each device perform a random backoff before sending a group registration message. A device responding to a grouping message selects a random backoff in the range of 0 to Wb, where Wb is the backoff window for a predetermined time slot. A device responding to a grouping message transmits a group registration message with a time difference according to the backoff value selected by each device. This makes it possible to reduce collisions of group registration messages.

As mentioned above, if each grouped user equipment reports its own location information to the core network CN, the load on the network will be large. Therefore, in the cellular network of the embodiment, among the grouped user equipments UE, only the group leader GL that represents the group reports the location information of its own group to the core network CN.

Device _mx , which has become group leader GL, receives group registration messages from multiple devices distributed in time during time Wb and executes a group formation procedure. Although many devices successfully transmit group registration messages to device _mx due to the pre-backoff window scheme, device _mx may form a group by accepting only r group registration messages (r≦ _rmax ), where _rmax is a preset value that specifies the maximum number of group members.

The group leader device m _x records the group registration message and broadcasts a group acknowledgment (ACK) containing a list of the group member IDs. If a device receives the group acknowledgment and its own ID is included in the group acknowledgment, it can know that it has joined the group.

If a device receives a group acknowledgment and its ID is not included in the group acknowledgment, it cannot join the group of devices m _x . An M2M device that has sent a group registration message but is not included in the list can form a group through further grouping procedures, i.e., it can become a group leader.

(Registration and update of location information of grouped user devices)
Similar to normal mobility management, a location registration procedure is also required for grouped M2M devices, i.e., an M2M device needs to report its location information to the core network CN when (1) it moves to a new tracking area TA or (2) the timer time T _update has elapsed.

When an M2M device belonging to a group moves to a new tracking area TA while still belonging to the group, only the group leader GL of the group can execute the registration procedure or update procedure on behalf of the group. That is, when a group of M2M devices moves to a new tracking area TA, only the group leader GL executes the registration procedure or tracking area update procedure. The tracking area update message sent by the device serving as the group leader GL in the registration procedure or tracking area update procedure includes a list of the IDs of the group members. Therefore, the core network CN can register and update the location information of each device belonging to the group by receiving a tracking area update message from the group leader GL. When the core network CN receives a tracking area update message from the group leader GL, it returns a tracking area update acceptance message to the device serving as the group leader GL. The device serving as the group leader GL forwards the tracking area update acceptance message to the members of the group. By receiving the tracking area update acceptance message, the device serving as the group member knows that its location information has been registered or updated in the core network CN.

The M2M devices have an update timer that counts the time since they joined the group. When the count value of the update timer passes a certain value T _update , all M2M devices remove themselves from the group. That is, when the update timer value passes the value T _update , the M2M devices cancel their current group membership and perform the grouping procedure again. This makes it possible to detect when a group member device has left the group by periodically updating the grouping.

It is not necessary for the original group leader GL to re-execute the grouping procedure. It may be possible to re-execute the procedure immediately after removing the group affiliation. However, since there is a possibility that the grouping procedure will be delayed if the procedures to become the group leader GL are concentrated at the same time, it is desirable to have a configuration in which the grouping procedure is started with a random time difference based on the IDs of each M2M device. This makes it possible to equalize the M2M devices that become group leader GLs.

When a group is reconfigured, the new group leader GL for each group performs a registration procedure with the core network CN.

Once the registration and updating of location information on a group basis is completed, the M2M devices belonging to the group will be able to receive calls from the core network CN. The call procedure can be achieved by sending an individual call message from the core network CN to the device, or a group call message using a group call mechanism. When the M2M device receives the call message, the device establishes a connection in response to the call message.

(Detection of Disengagement)
When a group moves to a new tracking area TA, some member trajectories may leave the group. For example, as shown in Figure 4, consider the case where a group G _i moves from a tracking area TA _i to a tracking area TA _j , and a member device m _k (m _k ∈ G _i ) moves to a tracking area TA _k (k ≠ j).

Since device m _k is a member device, it does not perform the registration procedure, but waits for a tracking area update acceptance message from the group leader GL. Therefore, if device m _k does not receive an update acceptance message from the group leader GL after a certain time interval T _update , device m _k knows that it has left the group. In that case, device m _k performs a new grouping procedure by broadcasting its ρ ^k (K) and ID as the group leader GL.

Similarly, a device that has left a group or that does not belong to a group can join the group by becoming a group leader GL according to the above procedure or by responding to a group registration message from the group leader GL. After grouping, the device m _k that has become the new group leader GL sends a registration message to the core network CN.

The device m _k , which is the group leader GL that performed the new grouping procedure, sends a modified tracking area update message to the core network CN. As a result, the core network CN has two different location information for the device m _k , the location information received from the group leader of the old group Gi and the location information received from the group leader of the current group Gk. The core network CN operates to avoid confusion and false reports by prioritizing the information in the modified registration message (the newly received information). Through the above process, the location information of the device that has left is updated in the core network CN.

The same applies when the group leader GL leaves the group. For example, as shown in Fig. 5, when the group G _i moves from the tracking area TA _i to the tracking area TA _j and the group leader GL moves to the tracking area TA _k (k ≠ j), the group can be updated by the same procedure.

(Configuration of the embodiment)
Next, a wireless device according to an embodiment will be described with reference to Fig. 6 to Fig. 11. The wireless device according to the embodiment is an M2M device that performs so-called M2M communication, and multiple devices move along similar trajectories. As shown in Fig. 6, for example, multiple devices move by the same transportation means, and the devices perform operations such as registration with the core network CN.

Figure 7 shows the configuration of a wireless device of the embodiment. As shown in Figure 7, wireless devices 1a to 1e of the embodiment have at least a partial common configuration, and communicate with a base station eNB and other wireless devices. In the following description, the configuration of wireless device 1a will be described as a representative, and the common configuration of wireless devices 1b to 1e will not be illustrated or described. As shown in Figure 7, wireless device 1a of the embodiment has a wireless interface (wireless I/F) 10a, a terminal communication unit 11a, a group management unit 12a, a positioning unit 13a, a group determination unit 14a, and a memory unit 15a.

The wireless interface 10a converts data transmitted by the wireless device 1a into a transmission signal sent to the antenna ANT, and converts signals received by the antenna ANT into received data. The wireless interface 10a supports a first standard for the wireless device 1a to transmit and receive voice, data, and the like through the base station eNB, and a second standard for transmitting and receiving grouping messages, and the like, with other nearby wireless devices 1b to 1e.

The terminal communication unit 11a is a calculation block that corresponds to a first standard. The terminal communication unit 11a generates transmission data and decodes received data. The first standard that the terminal communication unit 11a complies with is, for example, a standard used in a cellular network NW, and examples of the standard include the LTE and 5G standards. The terminal communication unit 11a mainly processes transmission and reception data communicated with the base station eNB.

The group management unit 12a is a calculation block that manages the group to which the wireless device 1a belongs. The group management unit 12a executes group management procedures when it becomes the group leader GL. When communicating with other wireless devices using the group management unit 12a, the wireless interface 10a can use the second standard.

The positioning unit 13a is a calculation block that acquires the position information of the wireless device 1a. The positioning unit 13a may acquire the position information by itself using a means such as GPS, or may manage the tracking area TA to which the base station eNB with which the wireless interface 10a communicates as the position information. The positioning unit 13a calculates trajectory information relating to the trajectory of its own movement based on its own past position information, and stores the information in the memory unit 15a.

The group determination unit 14a is a calculation block that, when receiving a grouping message sent by another wireless device 1b to 1e as the group leader GL, determines whether or not the device belongs to the group related to the grouping message. The group determination unit 14a performs a comparison calculation between its own trajectory information generated by the positioning unit 13a and the trajectory information included in the received grouping message to determine whether or not the device belongs to a group. When communicating with another wireless device using the group determination unit 14a, the wireless interface 14a can use the second standard.

The storage unit 15a is a non-volatile memory. The storage unit 15a stores information about the group managed by the group management unit 12a, and location information and trajectory information managed by the positioning unit 13a.

Next, the operation of the wireless device of the embodiment will be described with reference to Figures 7 to 10. Here, the description will be made assuming that wireless device 1a executes a grouping procedure and determines whether wireless device 1b belongs to the group of wireless device 1a.

The positioning unit 13a acquires information on the base station cell to which the wireless device 1a belongs and the tracking area TA via the wireless interface 10a. The positioning unit 13a generates a trajectory ρ ^x (k) by associating the acquired tracking area TA information with time information, and stores the trajectory ρ x (k) in the memory unit 15a (S100). The trajectory ρ ^x (k) stored in the memory unit 15a constitutes trajectory information on the movement of the wireless device 1a.

The group management unit 12a manages whether the wireless device 1a belongs to a group. If a predetermined time has passed while the wireless device 1a does not belong to a group, or if the wireless device 1a is removed from the group to which it belonged, the group management unit 12a reads out trajectory information about its own movement stored in the memory unit 15a, and generates a transmission signal including the trajectory information and its own ID. The wireless interface 10a transmits the generated transmission signal based on the second standard (S110). As shown in FIG. 10, the transmission signal transmitted by the wireless device 1a is received by the other wireless devices 1b to 1e.

The group manager 12a waits for responses from the other wireless devices 1b to 1e until a predetermined time T _W has elapsed. If there is no response, the wireless interface 10a repeats transmitting a transmission signal including its own ID and trajectory information (No in S120).

If a response signal dID is received as a group registration message from another wireless device before a predetermined time T _W has elapsed (Yes in S120), the group management unit 12a generates a list of IDs of other wireless devices that have issued response signals (group list) based on the received response signal dID and stores the list in the storage unit 15a (S130). In the example shown in Fig. 10, response signals dID are transmitted from the wireless devices 1b to 1d, but no response signal is issued from the wireless device 1e. This means that the wireless device 1e has been determined not to belong to a group because there is a low correlation between the trajectory information of the wireless device 1a and the trajectory information of the wireless device 1e.

When the group list is generated, the wireless interface 10a transmits a group acknowledgment (ACK) to the other wireless devices that have issued response signals (S140). This group acknowledgment indicates that the other wireless devices have joined the group as group members. In the example shown in FIG. 10, the wireless device 1a transmits a group acknowledgment to the wireless devices 1b to 1d that have transmitted the response signal dID.

At this stage, the wireless device 1a becomes the group leader GL of the group whose members are the wireless device 1a itself and the other wireless devices 1b to 1d. The group management unit 12a transmits a tracking area update message including a list of IDs of the wireless devices 1b to 1d that are group members to the base station eNB (S150). The base station eNB transfers the received group update information to the core network CN. The core network CN is the backbone of the network and includes a database that manages the wireless devices under the tracking network TA, so it updates the tracking area TA information in the database using the received group update information. When the tracking area update is completed, the core network CN sends update acceptance information to the base station eNB, and the base station eNB transfers the update acceptance information to the wireless device 1a.

When the update reception information is received, the wireless interface 10a transfers the update reception information to the other wireless devices 1b to 1d that are group members (S160). When the update reception information is received, the other wireless devices 1b to 1d become aware that they have been registered as group members.

In this embodiment, the wireless device that becomes the group leader GL transmits its own trajectory information to the other wireless devices, and grouping is performed based on the response signals returned by the wireless devices that are determined to be appropriate for grouping based on the trajectory information. Therefore, since it is highly likely that the grouped wireless devices will move along similar trajectories, movement management by the core network CN is performed appropriately. Furthermore, since the grouping procedure is triggered by the group leader GL issuing its own trajectory information, grouping can proceed autonomously without the involvement of the core network CN or the like. Furthermore, since a tracking area update message is transmitted by the wireless device that becomes the group leader GL after grouping, concentration of communication due to updates of location information, etc. can be suppressed.

Next, we will explain the operation of wireless device 1b, which represents wireless devices 1b to 1e that are group members in the grouping procedure.

The positioning unit 13b acquires information on the base station cell to which the wireless device 1b belongs and the tracking area TA via the wireless interface 10b. The positioning unit 13b generates a trajectory ρ ^y (k) by associating the acquired tracking area TA information with time information, and stores the trajectory ρ y (k) in the memory unit 15b (S200). The trajectory ρ ^y (k) stored in the memory unit 15b constitutes trajectory information on the movement of the wireless device 1b.

When the wireless interface 10b receives a grouping message including trajectory information (trajectory ρ ^x (k)) from the wireless interface 10a (Yes in S210), the group determination unit 14b calculates the correlation C x,y (k) between itself and the wireless device 1a that transmitted the grouping message, based on the acquired trajectory information (trajectory ρ ^x (k)) and its own trajectory information (trajectory _ρ ^y (k)) stored in the memory unit 15b (S220).

If the calculated correlation C _x,y (k) is "0" (No in S230), the group determination unit 14b does not generate a response signal, and the wireless interface 10b ends the process without transmitting anything. This is because the correlation with the wireless device 1a is low, and it is not appropriate for them to belong to the same group. In the example shown in Fig. 10, this corresponds to the wireless device 1e, which ends the process without transmitting a response signal dID.

If the calculated correlation C _x,y (k) is "1" (Yes in S230), the group determination unit 14b generates a response signal dID, and the wireless interface 10b transmits the response signal dID to the wireless device 1a (S240). This means that the wireless device 1b has a high correlation with the wireless device 1a, and it is appropriate for them to belong to the same group. In the example shown in Fig. 10, the wireless devices 10b to 10d transmit response signals dID to the wireless device 1a.

After transmitting the response signal dID, the wireless interface 10b waits to receive a group acknowledgment (S250). If the group acknowledgment is not received within a certain time _Tw , the wireless interface 10b retransmits the response signal dID (No in S250).

When the group reception notification is received (Yes in S250), the group determination unit 14b stores the ID of the wireless device 1a as the group leader GL in the storage unit 15b (S260). This allows the wireless device 1b to know that it has joined a group in which the wireless device 1a is the group leader GL.

Then, the wireless interface 10b receives the tracking area update acceptance information (S270). This allows the group determination unit 14b to know that it has been recorded in the core network CN that wireless device 1b belongs to a group whose group leader GL is wireless device 1a.

Through this series of operations, a group is formed with wireless device 1a as group leader GL and wireless devices 1a to 1d as group members, and the group information is recorded in the core network CN. This allows the core network CN to track the locations of wireless devices 1a to 1d, and makes it possible for wireless devices 1a to 1d to receive calls from the core network.

ここで、ＴＡは追跡エリアＴＡのＩＤ、ｔは対応する追跡エリアに入った時刻である。 (Determination of correlation)
The determination of correlation between M2M devices in the embodiment will be described with reference to Fig. 11. Two devices are defined as being correlated when they take a similar movement path (trajectory) in terms of time and location. For example, if the trajectories of a device _mx that is a group leader GL candidate and a device _my for which correlation is to be determined are ^Jx and ^Jy , respectively, then the following can be expressed:

Here, TA is the ID of the tracking area TA, and t is the time when the corresponding tracking area is entered.

The trajectory ρ(k) is represented as a set of k tracking areas TA visited by the device.

ここで、

Ｚは１または０を取る二値関数なので、Ｃの結果は１か０の二値となる。もし時刻ｔｉにおけるデバイスｍ_ｘの追跡エリアとデバイスｍ_ｙの追跡エリアとが同一であり、かつ当該追跡エリアＴＡに入った両者の時刻の差が所定の値を下回る場合、Ｃ＝１（相関あり）となる。この条件を満たさない場合はＣ＝０（相関なし）となる。ｋ＝３でＣ＝１であれば、デバイスｍ_ｘとデバイスｍ_ｙの移動は最後の３つの追跡エリアＴＡについて時間的・位置的に同等ということができる。 Denoting device m _x that enters TA _i at time t _i as ρ _i ^x , the correlation of two users can be estimated as follows:

Where:

Since Z is a binary function that takes 1 or 0, the result of C is a binary value of 1 or 0. If the tracking area of device m _x and the tracking area of device _my are the same at time ti, and the difference in the time when the two entered the tracking area TA is less than a predetermined value, C = 1 (correlation exists). If this condition is not met, C = 0 (no correlation exists). If k = 3 and C = 1, it can be said that the movements of device m _x and device _my are equivalent in time and position for the last three tracking areas TA.

The M2M device _{m_x} broadcasts its ρ ^x (k) to neighboring devices. At this time, the device _{m_x} declares itself to be the group leader. The neighboring device _{m_y} receives ρ ^x (k) broadcast by the device _{m_x} .

Device my _y calculates the correlation with device m _x . If C=1, device my _y determines that there is a correlation between device m _x and a moving object. Device my _y transmits a response signal ID to device m _x and joins the group.

When a group enters a new tracking area TA, only the device that is the group leader GL performs registration (TAU procedure). The tracking area update message that the device that is the group leader GL sends to the core network CN contains the IDs of the member devices. Grouping is performed at every predetermined timing T _update . At that time, any device that was a member may start the grouping procedure. When the grouping procedure is executed again, the group leader GL at that time sends updated registration information to the core network CN.

The core network CN records the location information of each device that makes up the group in units of tracking area TA. When the core network CN receives a call or data for a specific device, it forwards it to the device via the corresponding tracking area TA.

ここで、Ｒ_ｎは、グループ化されていないデバイスにより登録された登録メッセージ総数、Ｒ_ｇは、グループ化したデバイスにより登録された登録メッセージ総数である。大きいＳＳＲは、高い登録メッセージ負担を低減することを示す。 (Evaluation of the embodiment)
The embodiment was evaluated using two methods. The first method was a signal reduction ratio (SSR) that is expressed by the following formula:

where R _n is the total number of registration messages registered by ungrouped devices and R _g is the total number of registration messages registered by grouped devices. A large SSR indicates a reduction in the high registration message burden.

ここで、Ｐ_{ｔｏｔａｌ}は、コアネットワークＣＮによりなされた呼出総数、Ｐ_ｍｉｓｓは、呼出総数のうち呼び出しに失敗した数である。大きいＰＭＲは、呼出手順における高いリスクの存在を示している。 The second is the page miss ratio (PMR), which is expressed by the following formula:

where _Ptotal is the total number of calls made by the core network CN, and _Pmiss is the number of failed calls out of the total number of calls. A large PMR indicates the presence of a high risk in the call procedure.

Simulations were performed for two movement models. The first movement model is a random walk model. In the random walk model, devices move independently and randomly to adjacent tracking areas TA, and there is no correlation between the movements of individual devices. The second movement model is a planned transportation model. In the transportation model, multiple devices are loaded onto a moving object such as a vehicle or container. Instead of being able to individually determine the tracking area TA to which they will move and the length of time they will stay, the moving object moves along a predetermined trajectory such as on a road. There is a strong correlation between the movements of devices loaded onto the same moving object.

(Effect of K)
FIG. 12 shows the influence of the index K. The index K is a criterion for grouping. When two devices are grouped, the number of past changes (changes) in the tracking area TA that they have in common is the index K. A large index K indicates that devices with higher correlation are grouped together. A large index K also means less dropouts, and the PMR value is also small. In the random walk model, when the index K is large, the SRR is also small, and there is little benefit in grouping the SRR.

(Effect of T _update )
Fig. 13 shows the influence of the grouping update timing. In the transportation model, all devices update their groups at each update timing. As shown in Fig. 13, in the embodiment, the PMR is a small value in both the random walk model and the transportation model, and it can be seen that the mechanism of periodically updating the grouping is working effectively.

(Effect of average visit duration)
Fig. 14 shows the influence of the average stay time obtained by averaging the stay time in a certain tracking area TA. If the average stay time is short, the device frequently changes the tracking area TA. As shown in Fig. 14, in the embodiment, the PMR is a small value regardless of the length of the stay time in the tracking area TA.

(Effect of paging message arrival rate)
Figure 15 shows the effect of the arrival rate of the paging from the core network CN. As shown in Figure 15, the paging message arrival rate is not related to the grouping registration. In the embodiment, the PMR is small regardless of the paging message arrival rate, which is due to the effective operation of the departure detection function.

(Maximum effect of SSR on acceptable PMR)
As shown in FIG. 16, by appropriately setting the index K and the communication timing T _update , the number of registered messages can be significantly reduced.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

1a to 1e...wireless devices,
10a to 10b...wireless interface,
11a to 11b... terminal communication unit,
12a to 12b: group management department,
13a to 13b...positioning unit,
14a to 14b... group determination unit,
15a-15b...storage section,
eNB...base station,
CN: Core Network,
TA...Tracking Area.

Claims (6)

A wireless device connected to a base station in a core network that manages a location of a connection partner of the base station in units of a tracking area including a communication area of the base station, comprising:
a first radio interface for communicating with the core network via the base station;
a second wireless interface for communicating with other wireless devices located in the common tracking area;
a positioning unit that generates trajectory information of the user's own movement based on past position information of the user;
generating a transmission signal including the trajectory information at a predetermined timing and transmitting the transmission signal to the other wireless device via the second wireless interface;
receiving, via the second wireless interface, a response signal sent back from the other wireless device in response to the transmission signal;
generating a group list including IDs of the other wireless devices that have returned the response signals;
transmitting a registration request for location information of the wireless device itself and the other wireless device that has returned the response signal to the core network via the first wireless interface based on the group list;
Group Management Department and
receiving a signal including trajectory information of a movement of the other wireless device from the other wireless device via the second wireless interface;
generating correlation information indicating a correlation between the trajectory information of the own movement and the trajectory information of the other wireless device based on the trajectory information of the movement of the own wireless device and the trajectory information of the movement of the other wireless device;
determining whether the wireless device belongs to a group including the other wireless device based on the correlation information;
If the result of the determination indicates that the device belongs to the group, the device transmits a response signal including its own ID via the second wireless interface.
A group determination unit;
A wireless device comprising: A wireless device connected to a base station in a core network that manages a location of a connection partner of the base station in units of a tracking area including a communication area of the base station, comprising:
a first radio interface for communicating with the core network via the base station;
a second wireless interface for communicating with other wireless devices located in the common tracking area;
a positioning unit that generates trajectory information of the user's own movement based on past position information of the user;
generating a transmission signal including the trajectory information at a predetermined timing and transmitting the transmission signal to the other wireless device via the second wireless interface;
receiving, via the second wireless interface, a response signal sent back from the other wireless device in response to the transmission signal;
generating a group list including IDs of the other wireless devices that have returned the response signals;
transmitting a registration request for location information of the wireless device itself and the other wireless device that has returned the response signal to the core network via the first wireless interface based on the group list;
Group Management Department and
A wireless device comprising: A wireless device connected to a base station in a core network that manages a location of a connection partner of the base station in units of a tracking area including a communication area of the base station, comprising:
a first radio interface for communicating with the core network via the base station;
a second wireless interface for communicating with other wireless devices located in the common tracking area;
a positioning unit that generates trajectory information of the user's own movement based on past position information of the user;
receiving a signal including trajectory information of a movement of the other wireless device from the other wireless device via the second wireless interface;
generating correlation information indicating a correlation between the trajectory information of the own movement and the trajectory information of the other wireless device based on the trajectory information of the movement of the own wireless device and the trajectory information of the movement of the other wireless device;
determining whether the wireless device belongs to a group including the other wireless device based on the correlation information;
If the result of the determination indicates that the device belongs to the group, the device transmits a response signal including its own ID via the second wireless interface.
A group determination unit;
A wireless device comprising: The wireless device according to any one of claims 1 to 3, characterized in that the positioning unit acquires, as the location information, identification information of a tracking area including the communication area of the base station connected via the first wireless interface. The wireless device according to claim 1 or 3, characterized in that after transmitting the response signal, the group determination unit receives update acceptance information indicating that its own location information has been registered in the core network. The wireless device according to claim 1 or 2, characterized in that after transmitting the registration request, the group management unit regenerates the transmission signal after a predetermined period of time has elapsed and transmits it to the other wireless device via the second wireless interface.

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