JP2018164137A - Terminal device, control method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speedily establish an alternative radio link if radio link failure occurs to a radio link which a terminal device has formed between itself and a plurality of base station devices.SOLUTION: A terminal device performs communication in a cell formed by a first base station device in parallel with communication in a cell formed by a second base station device and under control of the first base station device. The terminal device detects radio link failure of a first cell during communication in the first cell among a plurality of cells formed by the second base station device, and if radio link failure of the first cell is detected, connects to a second cell different from the first cell of the cells, ignoring the first base station device, and notifies the second cell of the occurrence of radio link failure of the first cell.SELECTED DRAWING: Figure 4

Description

  The present invention relates to connection control between a terminal device and a plurality of base station devices.

  A technique has been standardized in which a terminal device performs communication with a first base station device in parallel with communication with a second base station device under the control of the first base station device ( Non-patent document 1). In the technique described in Non-Patent Document 1, when a radio link failure (Radio Link Failure, RLF) occurs in the connection with the second base station apparatus, the terminal apparatus performs another control under the control of the first base station apparatus. A connection with the third base station apparatus can be established.

3GPP TS36.300 V12.10.0, June 2016

  In the technique described in Non-Patent Document 1, since the connection to another base station apparatus when RLF occurs is performed under the control of the first base station apparatus, the RLF from the terminal apparatus to the first base station apparatus An occurrence notification, an instruction for causing the second base station device to disconnect the terminal device from the first base station device through the backhaul line, and establishment of the connection with the terminal device to the third base station device Must be set for transmission of this instruction and connection with the third base station apparatus for the terminal apparatus. Since these processes require a lot of time, there may be a case where the delay requirement is not satisfied in a system having a severe delay requirement, for example, a next-generation wireless communication system.

  The present invention has been made in view of the above problems, and a terminal device establishes an alternative radio link at a high speed when a radio link failure occurs in a radio link formed with a plurality of base station devices. With the goal.

  A terminal apparatus according to an aspect of the present invention communicates in a cell formed by a first base station apparatus and communicates under control of the first base station apparatus in a cell formed by a second base station apparatus. And detecting a radio link failure related to the first cell during communication in the first cell among the plurality of cells formed by the second base station device. When a radio link failure relating to the first cell is detected with the detection means, the second cell different from the first cell among the plurality of cells is not routed through the first base station apparatus. Connecting means for connecting to the second cell, and notifying means for notifying the second cell that a radio link failure has occurred regarding the first cell.

  According to the present invention, when a radio link failure occurs in a radio link formed between a terminal device and a plurality of base station devices, an alternative radio link can be established at high speed.

The figure which shows the structural example of a radio | wireless communications system. The figure which shows the hardware structural example of a terminal device. The block diagram which shows the function structural example of a terminal device. The figure which shows the 1st example of the flow of the process performed with a radio | wireless communications system. The figure which shows the 2nd example of the flow of the process performed with a radio | wireless communications system. The figure which shows the 3rd example of the flow of the process performed with a radio | wireless communications system. The figure which shows the 4th example of the flow of the process performed with a radio | wireless communications system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(System configuration)
FIG. 1 shows a configuration of a wireless communication system according to the present embodiment. In this wireless communication system, a plurality of base station devices (eNB and gNB) each form one or more cells. In addition, eNB is a base station apparatus regarding 4th generation cellular communication systems, such as long term evolution (LTE), for example. Moreover, gNB is a base station apparatus regarding the 5th generation cellular communication system called what is called New Radio (NR), for example. For example, each of cell 1 to cell 3 formed by gNB can be formed by one or more beams formed by one or more transmission reception points (TRP) (not shown). A cell formed by gNB may be defined as a set of logical beams that may be uniquely specified for all terminal apparatuses or may be determined for each terminal apparatus. The cell formed by the eNB may be a cell extending in all directions around the eNB or a sector extending in a certain range of directions. Further, in this example, the eNB forms one cell and the gNB forms three cells, but is not limited thereto. For example, the eNB may form a plurality of sectorized cells (sectors), and the gNB may form two or less cells or four or more cells. Moreover, although one eNB and one gNB are shown in FIG. 1, the wireless communication system may include a plurality of eNBs or gNBs. Moreover, eNB and gNB are only examples, and can be replaced with a base station apparatus conforming to an arbitrary wireless communication standard.

  The terminal device can perform communication in a cell formed by at least one of the eNB and the gNB. In addition, the terminal device communicates with the cell formed by the first base station device among these base station devices, and the cell formed by the second base station device under the control of the first base station device. Can communicate in parallel. Here, the first base station apparatus is, for example, an eNB, and the second base station apparatus is, for example, gNB. However, the first base station apparatus is not limited to these. For example, both the first base station apparatus and the second base station apparatus are It may be gNB or eNB.

  Due to the movement of the terminal device or a change in the surrounding environment of the terminal device, the cell to which the terminal device can be connected may vary over time. For example, when one cell is formed by one beam formed by gNB, the terminal device can easily leave the cell by moving. In such a case, a radio link failure (RLF) may occur in a radio link established between the terminal device and the base station device in a cell in which the terminal device has been located. At this time, the terminal device can establish a radio link with another cell instead of the radio link in which the RLF has occurred.

  For example, in Dual Connectivity in LTE Release 12, RLF occurs in the radio link between the terminal device and the second base station device established under the control of the first base station device as follows. In this case, another radio link is established between the terminal device and another base station device. That is, first, when the terminal device detects RLF in the first cell formed by the second base station device, the terminal device transmits a notification that RLF has occurred and a measurement report of the radio quality to the first base station device. . And a 1st base station apparatus determines changing the cell which a terminal device should connect according to a measurement result. The first base station device may determine to simply disconnect the connection related to the second base station device when there is no appropriate base station device to switch to. When the first base station apparatus switches the connection, the first base station apparatus establishes a connection with the terminal apparatus with respect to the second base station apparatus to which the terminal apparatus was connected and the base station apparatus to which the switching is performed. Instruct. Also, the first base station apparatus can notify the terminal apparatus of setting information for connection with the switching destination base station apparatus. The terminal device can establish a connection with the base station device by executing a random access procedure with the switching destination base station device in accordance with the notification from the first base station device.

  However, in such a procedure, since the number of times that signals are transmitted and received between devices is large, the time required from the start to the completion can be prolonged. Further, for example, the backhaul line between the base station apparatuses may have a large delay, so that this time may be prolonged or unstable. For this reason, in the conventional method, when RLF occurs, the real-time property required in, for example, the fifth generation wireless communication system may not be satisfied.

  On the other hand, the terminal device of this embodiment notifies the RLF of the first base station device when the connection switching destination cell is formed by the same second base station device as the cell before switching. Without starting, the random access procedure for the switching destination cell is started. That is, when the terminal device detects the RLF for the connected cell, the terminal device searches for other connectable cells, and when the other cell found is formed by the same base station device as the connected cell, The random access procedure for the other connectable cells is started. Note that the terminal device may start the random access procedure without notifying the first base station device of the RLF even if the cells before and after switching of the connection destination are formed by different base station devices. Good. For example, the terminal device can obtain information necessary for executing a random access procedure for the base station device to be switched, such as a security key, from the first base station device at the time of switching the connection. If so, the random access procedure can be started without notifying the first base station apparatus of the RLF. When a terminal apparatus establishes a radio link in a cell connected by a random access procedure, the terminal apparatus notifies the cell that RLF has occurred. The terminal device may notify the cell that RLF has occurred during execution of the random access procedure. For example, the terminal device may notify in parallel that an RLF has occurred during transmission of a random access preamble (message 1) in a random access procedure standardized by the LTE standard of 3GPP. The notification that the RLF has occurred may be transmitted, for example, by being included as information in the random access preamble or by a signal transmitted in parallel with the random access preamble. Further, the terminal device may notify that RLF has occurred when transmitting a message (message 3) including identification information of the terminal device itself to be transmitted after receiving the random access response to the random access preamble. . For example, information indicating that RLF has occurred may be included in the message 3 or may be transmitted in parallel with the message 3. Note that the notification that RLF has occurred may include information indicating in which cell the RLF has occurred. For example, when the same base station apparatus forms cells before and after switching, Information may not be included.

  Then, the second base station apparatus can transfer data between cells so that data that has not been transmitted in the cell before switching is transmitted in the cell after switching. The base station device that forms the cell after switching may notify the first base station device that the cell to which the terminal device is connected has been switched, but in this case, the cell before and after switching is formed. Since the base station apparatus to perform is the same, this notification need not be performed. In addition, when the base station apparatus forming the cell before and after switching is different, the base station apparatus forming the cell after switching transfers data to the base station apparatus forming the cell before switching. Can be requested. In this case, the base station apparatus forming the cell after switching can notify the first base station apparatus that the connection destination of the terminal apparatus has been switched.

  Note that the above-described random access procedure can be, for example, a 4-step or 2-step random access procedure standardized by the LTE standard of 3GPP. The terminal device may establish a radio link in the switching destination cell using a procedure that is not a random access procedure. That is, in this embodiment, the terminal device performs communication with the first base station device and communication in the first cell formed by the second base station device under the control of the first base station device. When RLF occurs in the first cell, the connection is made to the second cell without going through the first base station apparatus. Then, the terminal device notifies the second cell that RLF has occurred. This notification may be performed during the connection process to the second cell that is performed without going through the first base station apparatus. That is, a notification that an RLF has occurred can be transmitted / received together with or in parallel with a message transmitted / received during the connection process between the terminal device and the second cell. In addition, after the terminal device establishes the connection in the switching destination cell, this notification notifies the base station device forming the switching destination cell, for example, via the first base station device. May be. In this case, notification including information indicating the switching destination cell may be performed. This is because the first base station apparatus indicates to which base station apparatus this notification should be transferred.

  As a result, the frequency with which signals related to connection switching processing are transmitted and received is reduced, so that connection destination cells can be switched at high speed. In addition, when the base station apparatuses forming the cells before and after the connection switching are the same, the connection process is not performed through the backhaul line, so that the time required for the connection process can be improved. In addition, since the RLF is notified to the switching destination cell when the connection destination of the wireless link is switched, it is possible to prevent communication continuity from being secured by switching the connection. Further, when the control of the first base station device does not change when the base station devices forming the cells before and after the connection switching are the same, the first base station device is notified of the switching of the radio link. The time required for the connection switching process can be shortened. In addition, the notification of RLF is performed in the middle of the connection process not via the first base station apparatus, so that, for example, data is transferred from the connection switching source cell to the connection switching destination cell before the connection is established. Can be transferred. In addition, since the RLF notification is performed after the radio link is established in the connection switching destination cell, for example, the above-described procedure can be performed without changing the existing random access procedure. Further, the notification of RLF may be performed via the first base station apparatus, and in this case, it is possible to notify the first base station apparatus that RLF has occurred. Also, in this case, for example, when the base station devices forming the cells before and after the connection switching are different from each other, the first base station device changes the base station device that performs communication with the terminal device in cooperation. I can know.

  Below, the structure of the terminal device which performs such a process, and the flow of the process performed are demonstrated.

(Device configuration)
FIG. 2 shows a hardware configuration example of the terminal device. For example, the terminal device has a hardware configuration as shown in FIG. 2, and includes, for example, a CPU 201, a ROM 202, a RAM 203, an external storage device 204, and a communication device 205. In the terminal device, for example, the CPU 201 executes a program for realizing each function of the terminal device, which is recorded in any of the ROM 202, the RAM 203, and the external storage device 204. The CPU 201 may be replaced by one or more processors such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), and a DSP (Digital Signal Processor).

  And a terminal device controls the communication apparatus 205, for example by CPU201, and performs communication between base station apparatuses. In FIG. 2, a schematic diagram in which the terminal device includes one communication device 205 is shown, but the present invention is not limited to this. For example, the terminal device may have two or more communication devices 205 to communicate with two or more base station devices, and further includes another communication device 205 for communication in another system. You may have.

  The terminal device may include dedicated hardware for executing each function, or may be executed by a computer that executes a part of the hardware and executes a program. All functions may be executed by a computer and a program.

  FIG. 3 is a diagram illustrating a functional configuration example of the terminal device. The function of the terminal device is a logical function realized by the hardware of FIG. 2, for example, and can be realized by the CPU 201 executing a program stored in the ROM 202 or the like. The terminal device includes, for example, a communication unit 301, an RLF detection unit 302, a connection control unit 303, and an RLF notification unit 304.

  The communication unit 301 can communicate with one or more base station apparatuses, for example, communication in a cell formed by the first base station apparatus, and the second base station under the control of the first base station apparatus Communication in any of one or more cells formed by the device can be performed in parallel. Note that such parallel communication can be performed in accordance with the definition of Data flow aggregation discussed in 3GPP, for example, but such parallel communication may be performed by other methods. A cell can also be formed including one or more beams.

  The RLF detection unit 302 detects that a radio link failure has occurred in the radio link in communication. The RLF detection unit 302 is configured to operate the cell when the terminal device performs communication under the control of the first base station device in any of the plurality of cells formed by the second base station device. Whether or not an RLF has occurred is monitored, and the RLF is detected.

  The connection control unit 303, when RLF occurs in the communication under the control of the first base station device performed in the first cell among the plurality of cells formed by the second base station device by the terminal device In addition, the communication unit 301 is controlled so as to establish a connection with, for example, the second cell among the plurality of cells without using the first base station apparatus. Note that the connection control unit 303 causes the terminal device to perform RLF in communication under control of the first base station device that is performed in any one of a plurality of cells formed by the second base station device. In addition, the communication unit 301 may be controlled so as to establish a connection with the third base station apparatus without going through the first base station apparatus. For example, in response to detection of RLF, the connection control unit 303 can measure the radio quality of surrounding cells and select a cell with a good measurement result as a switching destination cell. Note that the connection control unit 303 may preferentially select a cell formed by the same base station apparatus as the cell before switching. The connection control unit 303 controls the communication unit 301 so as to establish a connection with the switching destination cell using, for example, a random access procedure.

  The RLF notification unit 304 performs processing for notifying the connection switching destination cell that RLF has occurred. For example, the RLF notification unit 304 controls the connection control unit 303 to notify that an RLF has occurred, for example, during the connection process with the switching destination cell. For example, the RLF notification unit 304 may transmit a notification that an RLF has occurred by including information in a message to be transmitted within the random access procedure or in parallel with this message. In this procedure, the notification that the RLF has occurred is directly notified to the switching destination cell (the base station apparatus forming the cell) without going through the first base station apparatus. Also, the RLF notification unit 304 generates a notification that the RLF has occurred, and transmits the notification via the communication unit 301 after the connection processing with the switching destination cell by the connection control unit 303 is completed, for example. Also good. In this case, for example, the RLF notification unit 304 may notify the switching destination cell of the occurrence of RLF directly without passing through the first base station apparatus, or via the first base station apparatus. You may notify to the switching destination cell.

(Process flow)
Next, an example of the flow of processing executed in the wireless communication system will be described with reference to FIGS.

  First, FIG. 4 will be described. In this processing example, the terminal device, as an initial state, communicates with a first base station device (for example, an eNB, sometimes called a master eNB (MeNB)), and controls the first base station device. Below, communication in the first cell among the plurality of cells formed by the second base station apparatus (for example, gNB) is performed in parallel (S401). A cell that performs communication under the control of another base station device, such as the first cell, may be referred to as a secondary cell. In this state, the terminal device transmits the control plane (C-plane) data to the first base station device, and the user plane (U-plane) data to the first base station device and the second base station device. (S402, S403). Here, when the RLF occurs in the radio link with the first cell formed by the second base station apparatus, the terminal apparatus detects the RLF, and according to this, the radio quality of the surrounding cells is detected. Measurement is executed (S404). And a terminal device selects a cell with a favorable measurement result (S405), and performs a random access procedure (S406-S409). This random access procedure conforms to the 4-step random access procedure specified in 3GPP. However, a notification (RLF report) that RLF has occurred is included in either message 1 (random access preamble) or message 3 (message including terminal device identification information such as C-RNTI / ID). And transmitted from the terminal device to the switching destination cell (S406, S408). Note that a notification that an RLF has occurred may be included in both of these messages, or a notification that an RLF has occurred may be transmitted separately from these messages. When a radio link is established between the terminal device and the second cell formed by the second base station device by the random access procedure, the second cell acquires untransmitted data from the switching-source first cell ( S410), the data transmission to the terminal device is recovered (S411). Thereby, the terminal device can switch a secondary cell at high speed, without the 1st base station apparatus interposing.

  Next, FIG. 5 will be described. FIG. 5 shows an example in which the random access procedure of S406 to S409 in FIG. 4 is replaced with a two-step random access procedure. In addition, about the process which is common in FIG. 4, the same reference number is attached | subjected and description is abbreviate | omitted. In this case, one message corresponding to message 1 and message 3 is transmitted from the terminal device to the second cell (S501), and one message corresponding to message 2 and message 4 is transmitted from the second cell to the terminal device. (S502). In this case, the terminal device can notify the second cell of the notification that the RLF has occurred by including the notification that the RLF has occurred in the message of S501 or by a message in parallel with this message. In this way, regardless of the connection process used, it is possible to notify the switching destination cell that RLF has occurred, thereby appropriately recovering data transmission to the terminal device. .

  Next, FIG. 6 will be described. In FIG. 6, the fact that RLF has occurred in the random access procedure is not notified, and after the random access procedure (S601 to S602) is completed, the fact that RLF has occurred is notified to the second cell (S603). According to this, it is possible to notify that RLF has occurred in a state where it is confirmed that the connection has been established and the connection destination can be switched reliably, and unnecessarily between the cells before and after switching. Can prevent data transfer. FIG. 6 shows an example in which a two-step random access procedure is used, but it is obvious that the same processing can be executed even if a four-step random access procedure is used.

  Finally, FIG. 7 will be described. In FIG. 7, as in FIG. 6, after the random access procedure (S601 to S602) is completed, the second cell is notified that RLF has occurred, but this notification is sent via the first base station apparatus. Perform (S701 to S702). For example, after the connection with the second cell is established, the terminal device notifies the first base station device of information indicating that RLF has occurred and that the connection with the second cell has been established. (S701). Then, the first base station apparatus transfers information indicating that the RLF has occurred and information indicating the cell in which the RLF has occurred to the second cell (S702). Since the 1st base station apparatus has acquired the information on the 2nd cell from the terminal unit, it can transfer the notice that RLF occurred to the 2nd cell. In addition, since the first base station apparatus performs control when the first cell operates as a secondary cell, the first base station apparatus determines that RLF has occurred in the first cell only by notification that RLF has occurred. be able to. In this way, the terminal device notifies the second cell via the first base station device that RLF has occurred, thereby realizing detailed control in units of cells by the first base station device. be able to. In addition, by using such a notification method, for example, it is possible to appropriately switch the secondary cell under various conditions such as when base station apparatuses forming the first cell and the second cell are different. It becomes possible.

  As described above, according to the present embodiment, the terminal device performs communication in the cell formed by the first base station device and the first base station device in the cell formed by the second base station device. When communication under control is performed in parallel, if a radio link failure occurs in a cell formed by the second base station apparatus, an alternative radio link can be established at high speed.

  301: Communication unit 302: RLF detection unit 303: Connection control unit 304: RLF notification unit

Claims (10)

A terminal device that concurrently performs communication in a cell formed by a first base station device and communication under control of the first base station device in a cell formed by a second base station device. And
Detecting means for detecting a radio link failure related to the first cell during communication in the first cell among the plurality of cells formed by the second base station device;
A connection for connecting to a second cell different from the first cell among the plurality of cells without passing through the first base station device when a radio link failure relating to the first cell is detected. Means,
Notifying means for notifying the second cell that a radio link failure has occurred with respect to the first cell;
The terminal device characterized by having. The connection means connects to the second cell using a random access procedure;
The terminal device according to claim 1. The notification means performs the notification while the connection means is performing connection processing to the second cell.
The terminal device according to claim 1, wherein the terminal device is a terminal device. The notifying means notifies that the radio link failure has occurred during transmission of a random access preamble;
The terminal device according to claim 3, which is dependent on claim 2. The notifying means notifies that the radio link failure has occurred when transmitting the identification information of the terminal device to be transmitted after receiving a random access response from the second cell;
The terminal device according to claim 3 or claim 4, which is dependent on claim 2. The notification means performs the notification after the connection means completes the connection process to the second cell.
The terminal device according to claim 1. The notification means performs the notification through the first base station device.
The terminal device according to claim 6. Each of the plurality of cells includes one or more beams formed by the second base station apparatus.
The terminal device according to claim 1, wherein the terminal device is a terminal device. Control of a terminal apparatus that performs communication in the cell formed by the first base station apparatus and communication under the control of the first base station apparatus in the cell formed by the second base station apparatus in parallel A method,
A detecting step for detecting a radio link failure related to the first cell during communication in the first cell among the plurality of cells formed by the second base station device;
When the connection means detects a radio link failure related to the first cell, the connection means does not pass through the first base station apparatus to the second cell different from the first cell among the plurality of cells. A connection step to connect to,
A notifying step for notifying the second cell that a radio link failure has occurred with respect to the first cell;
A control method characterized by comprising: Provided in a terminal apparatus that performs communication in the cell formed by the first base station apparatus and communication under the control of the first base station apparatus in the cell formed by the second base station apparatus in parallel Computer
During communication in a first cell among a plurality of cells formed by the second base station device, a radio link failure related to the first cell is detected,
When a radio link failure related to the first cell is detected, the second cell different from the first cell among the plurality of cells is connected without going through the first base station device,
Notifying the second cell that a radio link failure has occurred with respect to the first cell;
Program for.

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