WO2021117111A1 - Base station, terminal device, and wireless communication system - Google Patents

Abstract

A base station (100) is provided with a wireless control device (110) and a wireless device (120). The wireless control device (110) has: a first processor (112) which, when a random access process by a terminal device (200) does not finish normally, determines that a random access setting in the wireless device (120) is to be changed; and a transmission path interface (113) which requests the wireless device (120) to change the random access setting in accordance with the determination by the first processor (112). The wireless device (120) has: a second processor (122) which changes the random access setting in response to the request from the wireless control device (110); and a wireless interface (123) which wirelessly provides notification of the random access setting change by the second processor.

Description

Base stations, terminal equipment and wireless communication systems

The present invention relates to a base station, a terminal device, and a wireless communication system.

In the current network, the traffic of mobile terminals (smartphones and feature phones) occupies most of the network resources. In addition, the traffic used by mobile terminals tends to increase in the future.

On the other hand, in line with the development of IoT (Internet of things) services (for example, monitoring systems for transportation systems, smart meters, devices, etc.), it is required to support services with various requirements. Therefore, in the communication standard of the 5th generation mobile communication (5G or NR (New Radio)), in addition to the standard technology of 4G (4th generation mobile communication) (for example, Non-Patent Documents 1 to 11), further There is a demand for technology that realizes high data rates, large capacities, and low delays. Regarding the 5th generation communication standard, technical studies are underway by the 3GPP working group (for example, TSG-RAN WG1, TSG-RAN WG2, etc.), and the first edition of the standard document was issued at the end of 2017. (Non-Patent Documents 12-40).

In 5G mobile networks, centralization and distribution of processing are being considered in order to cope with the increase in traffic. As a method of centralization and distribution, for example, CU (Central Unit) that distributes message processing to multiple nodes according to the protocol hierarchy and executes processing of the upper layer protocol, and DU (Distributed Unit) that executes processing of the lower layer protocol. There is a CU / DU separation that separates and. When CU / DU is separated, a combination of one CU and one DU, or a combination of one CU and a plurality of DUs becomes one logical base station. This base station is also called "gNB (g Node B)".

FIG. 1 is a diagram showing a specific configuration example of gNB10. The gNB 10 shown in FIG. 1 has one CU 10a and one DU 10b. The CU10a executes the processing of the RRC (Radio Resource Control) layer and the PDCP (Packet Data Convergence Protocol) layer. On the other hand, the DU 10b executes the processing of the RLC (Radio Link Control) layer, the MAC (Medium Access Control) layer, and the PHY (Physical) layer. The CU 10a and the DU 10b are connected by, for example, an F1 interface, and may be arranged at remote locations from each other. Although omitted in FIG. 1, the CU 10a is connected to the CU of another gNB by, for example, the Xn interface, and is connected to the device constituting the core network by, for example, the NG interface.

When the terminal device communicates with the gNB 10, the terminal device executes wireless communication with the DU 10b. When establishing an initial connection with gNB10, the terminal device receives SIB (System Information Block) transmitted from DU10b and acquires RA (Random Access) settings (RA Config) including parameters required for random access. The RA setting includes information that identifies the PRACH (Physical Random Access CHannel) used for transmitting the preamble in random access in the cell formed by the DU 10b. The terminal device transmits the preamble to the DU 10b based on the RA setting. Then, the DU 10b that has received the preamble transmits an RA response to the preamble to the terminal device. Upon receiving the RA response to the preamble transmitted by the terminal device, the terminal device starts processing of the subsequent RRC connection.

Japanese Unexamined Patent Publication No. 2015-195621

By the way, since the RA setting includes parameters required for random access for each cell, for example, when the RA settings of neighboring base stations overlap, the random access by the terminal device may not be completed normally. That is, for example, when base station A and base station B notify the same RA setting by SIB, the preamble transmitted by the terminal device to base station A is also received by base station B, and base station B transmits the RA response. I have something to do. In such a case, the processing of the subsequent RRC connection fails between the terminal device and the base station B, and it is difficult for the terminal device to start communication.

Therefore, for example, in a wireless communication system that employs LTE (Long Term Evolution), peripheral base stations may share information on RA settings to avoid duplication of RA settings between base stations. Such sharing of information on RA settings between base stations is called RACH (Random Access CHannel) optimization (RACH Optimization).

However, in a wireless communication system that adopts 5G, there is a problem that RACH optimization is not easy because CU / DU may be separated. Specifically, for example, a DU may be implemented as a virtual machine and can be easily enabled and disabled, so that it is considered that cells appear and disappear frequently. Further, it is considered that beamforming by DU is executed according to, for example, the density of the terminal device, and the shape and position of the cell are dynamically changed. In this way, when CU / DU is separated, the cell state changes frequently, so if information on RA settings is shared between base stations each time, traffic will increase and the network load will increase. It ends up. Therefore, it is not practical to perform RACH optimization every time the cell state changes.

The disclosed technology has been made in view of this point, and an object of the present invention is to provide a base station, a terminal device, and a wireless communication system capable of executing RACH optimization at an appropriate timing.

The base station disclosed in the present application is, in one embodiment, a base station including a wireless control device and a wireless device, and the wireless control device is said to be described when the random access process by the terminal device is not normally completed. It has a first processor that determines to change the random access setting in the wireless device, and a transmission line interface that requests the wireless device to change the random access setting according to the decision by the first processor. The wireless device includes a second processor that changes the random access setting and a wireless interface that wirelessly notifies the random access setting changed by the second processor in response to a request from the wireless control device. Have.

According to one aspect of the base station, the terminal device, and the wireless communication system disclosed in the present application, there is an effect that RACH optimization can be executed at an appropriate timing.

FIG. 1 is a diagram showing a configuration example of a base station. FIG. 2 is a diagram showing a configuration example of a wireless communication network. FIG. 3 is a block diagram showing a configuration of a base station according to the first embodiment. FIG. 4 is a block diagram showing the configuration of the terminal device according to the first embodiment. FIG. 5 is a sequence diagram showing a RACH optimization method according to the first embodiment. FIG. 6 is a flow chart showing the operation of the terminal device. FIG. 7 is a flow chart showing the operation of the base station. FIG. 8 is a flow chart showing the operation of other base stations. FIG. 9 is a sequence diagram showing another RACH optimization method according to the first embodiment. FIG. 10 is a sequence diagram showing still another RACH optimization method according to the first embodiment. FIG. 11 is a sequence diagram showing the RACH optimization method according to the second embodiment. FIG. 12 is a flow chart showing the operation of the base station. FIG. 13 is a sequence diagram showing another RACH optimization method according to the second embodiment.

Hereinafter, embodiments of the base station, terminal device, and wireless communication system disclosed in the present application will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

(Embodiment 1)
FIG. 2 is a diagram showing a configuration example of the wireless communication system according to the first embodiment. The wireless communication system has a plurality of gNBs 100a and 100b connected to the core network, and a UE (User Equipment) 200 that wirelessly communicates with the gNBs 100a and 100b. In FIG. 2, two gNBs 100a and 100b and one UE 200 are illustrated, but the number of gNBs and UEs possessed by the wireless communication system is not limited to this.

The core network includes UPF (User Plane Function) 11, AMF (Access and Mobility Management Function) 12, SMF (Session Management Function) 13, PCF (Policy Control Function) 14, AF (Application Function) 15, and AUSF (Authentication Server). Function) 16 and UDM (Unified Data Management) 17 are arranged.

UPF11 is a device that controls the user plane and executes routing and transfer of user data. The AMF 12 is a device that controls the control plane, and terminates the control plane in a radio access network (RAN: Radio Access Network). The SMF 13 manages the session. The PCF 14 provides policy rules and the like regarding the control plane. AF15 is an application server that provides an application. The AUSF16 performs the authentication process of the UE 200. The UDM 17 stores subscriber information and the like.

The gNBs 100a and 100b are base stations, which are connected and communicate with UPF11 and AMF12 of the core network by wire, and also wirelessly communicate with the UE 200. Specifically, gNB100a and 100b have CU (Central Unit) 110a and 110b and DU (Distributed Unit) 120a and 120b, respectively. Although FIG. 2 shows a one-to-one connection in which one DU 120a and 120b are connected to one CU 110a and 110b, the connection relationship between the CU and the DU may be a one-to-many connection. Many-to-many connections are also acceptable. One combination of CU and DU connected to each other constitutes one gNB.

The CU 110a and 110b are wireless control devices that are connected to the UPF 11 and AMF 12 of the core network and control the wireless communication between the DU 120a and 120b under their respective control and the UE 200. The CU 110a and 110b execute the processing of the RRC layer and the PDCP layer. For example, the CUs 110a and 110b exchange data with the UE 200 when the RRC connection is established by the random access processing between the subordinate DUs 120a and 120b and the UE 200. Further, when the UE 200 notifies that the RRC connection failures occur frequently, the CU 110a and 110b determine that the RA settings related to the random access process are duplicated, and control the change of the RA settings in the gNB 100a and 100b. To do.

The DU 120a and 120b are wireless devices that wirelessly communicate with the UE 200 under the control of the CU 110a and 110b, which are higher in the DU 120a and 120b, respectively. The DU 120a and 120b execute the processing of the RLC layer, the MAC layer and the PHY layer. For example, when the DUs 120a and 120b form at least one or more cells and receive a preamble for random access from the UE 200 in the cells, the DU 120a and 120b transmit an RA response to the preamble to the UE 200. Then, the DU 120a and 120b establish an RRC connection between the UE 200 and the gNB 100a and 100b. Further, the DU 120a and 120b change the RA setting related to the random access process according to the control by the higher- level CU 110a and 110b, and transmit the SIB including the information of the changed RA setting.

The UE 200 is a terminal device that wirelessly communicates with the DUs 120a and 120b forming the cells when they are in the cell formed by the DUs 120a and 120b. When starting wireless communication with the DU 120a and 120b, the UE 200 receives the SIB transmitted from the DU 120a and 120b and acquires the RA setting in the cell. Then, the UE 200 transmits a preamble for random access based on the RA setting. Upon receiving the RA response to the preamble, the UE 200 establishes an RRC connection with the gNB 100a, 100b having the DU 120a, 120b of the RA response source. At this time, the UE 200 counts the number of times the establishment of the RRC connection fails, and when the RRC connection is established with any of the gNBs, notifies that the number of times the RRC connection fails is equal to or greater than a predetermined threshold value. To do.

FIG. 3 is a block diagram showing the configuration of the gNB 100 according to the first embodiment. The gNB 100 shown in FIG. 3 has the same configuration as the gNB 100a and 100b shown in FIG. 2, and has a CU 110 and a DU 120.

The CU 110 is a wireless control device like the CU 110a and 110b. The CU 110 includes a wired interface unit (hereinafter abbreviated as "wired IF unit") 111, a processor 112, a transmission line interface unit (hereinafter abbreviated as "transmission line IF unit") 113, and a memory 114.

The wired IF unit 111 has an interface for wired connection with a core network device and other gNBs. Specifically, the wired IF unit 111 is connected to UPF11 and AMF12 constituting the core network by, for example, an NG interface, and is connected to another gNB's CU, for example, by an Xn interface. Then, the wired IF unit 111 transmits / receives user data to / from UPF 11 and transmits / receives control data to / from AMF 12. Further, the wired IF unit 111 sends and receives an RA setting change request requesting a change of the RA setting to and from another gNB CU, and sends and receives a change completion notification to the effect that the change of the RA setting is completed. ..

The processor 112 includes, for example, a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array), a DSP (Digital Signal Processor), etc., and controls the entire CU 110 in an integrated manner. Specifically, the processor 112 has an RRC processing unit 115 and a RACH optimization control unit 116.

The RRC processing unit 115 executes the processing of the RRC layer. Specifically, the RRC processing unit 115 exchanges data with the UE 200 when the RRC connection is established by the random access processing by the DU 120 and the UE 200. The data exchanged with the UE 200 includes, for example, a notification that RRC connection failures occur frequently and cell identification information (for example, PCI (Physical Cell ID)) in which RRC connection failures occur frequently.

The RACH optimization control unit 116 starts the RACH optimization process when the RRC processing unit 115 receives a notification that RRC connection failures have occurred frequently. Specifically, the RACH optimization control unit 116 requests the CU of gNB, which has jurisdiction over the cell in which RRC connection failures occur frequently, to change the RA setting. The RA setting change request is transmitted to the CU of another gNB via the wired IF unit 111.

Further, the RACH optimization control unit 116 decides to change the RA setting of the DU 120 when the RA setting change request from the CU of another gNB is received by the wired IF unit 111, and sets the RA for the DU 120. Request a change. That is, the RACH optimization control unit 116 requests the DU 120 via the transmission line IF unit 113 to change the RA setting regarding random access in the cell formed by the DU 120.

The transmission line IF unit 113 has an interface for connecting to the DU 120. Specifically, the transmission line IF unit 113 is connected to the DU 120 by, for example, the F1 interface. Then, the transmission line IF unit 113 requests the DU 120 to change the RA setting, or notifies the DU 120 that the change of the RA setting is completed.

The memory 114 includes, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory), and stores information used by the processor 112 to execute processing.

The DU 120 is a wireless device like the DU 120a and 120b. The DU 120 includes a transmission line IF unit 121, a processor 122, a wireless interface unit (hereinafter abbreviated as “wireless IF unit”) 123, and a memory 124.

The transmission line IF unit 121 has an interface for connecting to the CU 110. Specifically, the transmission line IF unit 121 is connected to the CU 110 by, for example, the F1 interface. Then, the transmission line IF unit 121 is requested by the CU 110 to change the RA setting, or notifies the CU 110 that the change of the RA setting is completed.

The processor 122 includes, for example, a CPU, FPGA, DSP, etc., and controls the entire DU 120 in an integrated manner. Specifically, the processor 122 has an RA processing unit 125 and an RA setting control unit 126.

The RA processing unit 125 executes random access processing with the UE 200. Specifically, the RA processing unit 125 acquires a preamble transmitted from the UE 200 and received by the radio IF unit 123. Then, the RA processing unit 125 generates an RA response to the preamble and transmits the RA response to the UE 200 via the radio IF unit 123. Further, the RA processing unit 125 acquires the RRC request (RRC request) transmitted from the UE 200 and generates an RRC setting (RRC Setup) for the RRC request. Then, the RA processing unit 125 transmits the RRC setting to the UE 200 via the wireless IF unit 123.

Here, the RRC request is scrambled by the identification information (for example, PCI) that identifies the cell selected by the UE 200 as the transmission destination of the preamble. Therefore, if the UE 200 selects the DU 120 as the transmission destination of the preamble and the random access process is executed, the RA processing unit 125 descrambles the RRC request received by the wireless IF unit 123 and RRC for the RRC request. Generate settings.

On the other hand, if the UE 200 selects another DU different from the DU 120 as the preamble transmission destination, but the RA settings of the DU 120 and the other DU overlap, the preamble transmitted by the UE 200 is received by the DU 120. , DU120 and UE200 may perform random access processing. In this case, when the UE 200 receives the RA response from the DU 120, it transmits an RRC request scrambled by the identification information of the cells formed by the other DU. Then, the RRC request is received by the radio IF unit 123, but the RA processing unit 125 does not detect the RRC request scrambled by the identification information of the cell formed by the other DU, and sets the RRC for the RRC request. Does not generate.

In this way, since the RRC request is scrambled by the identification information of the cell selected by the UE 200 as the transmission destination of the preamble, the RA processing unit 125 may not generate the RRC setting for the RRC request transmitted by the UE 200. is there. As a result, the RRC setting is not transmitted to the UE 200, and the establishment of the RRC connection fails. That is, if the UE 200 does not receive the RRC setting after receiving the RA response, the random access process does not end normally, and the RRC connection fails.

The RA setting control unit 126 controls the RA setting in the cell formed by the DU 120. That is, the RA setting control unit 126 determines the RA setting including the parameter related to the random access processing for each cell, and includes the information of the RA setting in the SIB to notify the SIB. The UE 200 that receives the SIB selects a cell to which the preamble is to be transmitted, and transmits the preamble according to the RA setting of the selected cell. The RA processing unit 125 acquires a preamble according to the RA setting determined by the RA setting control unit 126. Therefore, when the RA setting control unit 126 determines the same RA setting as the RA setting of the other gNB, the RA processing unit 125 acquires the preamble transmitted by the UE that has selected the other gNB as the transmission destination. Sometimes.

Further, when the RA setting control unit 126 is requested to change the RA setting by the CU 110, the RA setting is changed, and the transmission line IF unit 121 notifies the CU 110 that the change is completed.

The wireless IF unit 123 has an interface for wirelessly connecting to the UE 200. Then, the wireless IF unit 123 transmits the SIB including the RA setting, and transmits / receives various data in the random access process. Further, when the RRC connection between the gNB 100 and the UE 200 is established, the wireless IF unit 123 receives a notification that the RRC connection between the other gNB and the UE 200 has frequently failed.

The memory 124 includes, for example, a RAM or a ROM, and stores information used by the processor 122 to execute processing.

FIG. 4 is a block diagram showing a configuration of the UE 200 according to the first embodiment. The UE 200 shown in FIG. 4 has a wireless IF unit 210, a processor 220, and a memory 230.

The wireless IF unit 210 has an interface for wirelessly connecting to the gNB 100. Then, the wireless IF unit 210 receives the SIB including the RA setting, and transmits / receives various data in the random access process. Further, when the RRC connection between the gNB 100 and the UE 200 is established, the wireless IF unit 210 transmits a notification that the RRC connection between the other gNB and the UE 200 has frequently failed.

The processor 220 includes, for example, a CPU, FPGA, DSP, etc., and controls the entire UE 200 in an integrated manner. Specifically, the processor 220 has an RA processing unit 221 and an RRC processing unit 222.

RA processing unit 221 executes random access processing with DU120. Specifically, the RA processing unit 221 generates a preamble according to the RA setting notified by the SIB, and transmits the preamble to the DU 120 via the radio IF unit 210. Then, the RA processing unit 221 acquires the RA response transmitted from the DU 120 and received by the wireless IF unit 210. Further, the RA processing unit 221 transmits an RRC request to the DU 120 via the wireless IF unit 210, and acquires the RRC setting transmitted from the DU 120.

Here, the RA processing unit 221 generates an RRC request scrambled by the identification information (for example, PCI) of the cell selected as the transmission destination of the preamble. Therefore, if the RA processing unit 221 transmits the preamble according to the RA setting notified by the SIB from the DU 120, the RA processing unit 221 scrambles the RRC request according to the cell identification information formed by the DU 120.

However, when the RA settings of the DU 120 and another DU overlap, the preamble transmitted by the RA processing unit 221 according to the RA setting of the DU 120, for example, may be received by the other DU, and the RA processing unit 221 may receive the preamble. , Get RA response from another DU. Then, the RA processing unit 221 scrambles the RRC request according to the cell identification information formed by the DU 120 and transmits the scrambled request. However, since it is another DU that is waiting for the reception of the RRC request, the RRC request is sent. It is not descrambled and the RRC settings in response to the RRC request are not sent. As a result, the RA processing unit 221 does not acquire the RRC setting after transmitting the RRC request.

In this way, since the RA processing unit 221 scrambles the RRC request by the identification information of the cell selected as the transmission destination of the preamble, the RA processing unit 221 does not acquire the RRC setting for the RRC request to be transmitted. is there. As a result, the random access process does not end normally, and the RRC connection fails.

When an RRC connection failure occurs, the RA processing unit 221 counts the number of failures and stores it in the memory 230. At this time, if the identification information (for example, PCI) of the cell in which the RRC connection failure has occurred is known, the RA processing unit 221 stores the cell identification information and the number of RRC connection failures in the memory 230.

The RRC processing unit 222 executes the processing of the RRC layer. Specifically, the RRC processing unit 222 exchanges data with the CU 110 when the RRC connection is established by the random access processing between the UE 200 and the DU 120. Further, the RRC processing unit 222 refers to the number of failures of the RRC connection stored in the memory 230 when the RRC connection is established, and determines whether or not the number of failures is equal to or greater than a predetermined threshold value. Then, when the number of failures is equal to or greater than a predetermined threshold value, the RRC processing unit 222 transmits a notification to the CU 110 that RRC connection failures have occurred frequently. At this time, the RRC processing unit 222 may transmit the identification information (for example, PCI) of the cell in which the RRC connection failure occurs frequently to the CU 110.

The memory 230 includes, for example, a RAM or a ROM, and stores information used by the processor 220 to execute processing. Specifically, the memory 230 stores, for example, the number of times the RRC connection has failed in the random access process for each cell.

Next, the RACH optimization method in the wireless communication system configured as described above will be described with reference to the sequence diagram shown in FIG. In the following, it is assumed that the DU 120a and 120b of the gNB 100a and 100b have the same RA setting.

The CU110a of the gNB100a generates an SIB including the RA setting information of the DU120a and transmits it from the DU120a to notify the RA setting (step S101). Similarly, the CU 110b of the gNB 100b generates an SIB including the information of the RA setting of the DU 120b and transmits it from the DU 120b to notify the RA setting (step S102). Here, since the RA settings of the DUs 120a and 120b are the same, the SIB transmitted from the DUs 120a and 120b includes information regarding the same RA settings. Further, it is assumed that the SIB transmitted from the DU 120a is not received by the UE 200 here due to, for example, the condition of the radio wave environment. That is, it is assumed that the UE 200 does not receive the SIB transmitted from the DU 120a, but receives the SIB transmitted from the DU 120b.

The UE 200 that has received the SIB transmits a preamble for random access according to the RA setting included in the SIB (step S103). At this time, if the radio wave environment between the UE 200 and the DU 120a is improved, the preamble may be received by the DU 120a. That is, since the RA settings of the DU 120a and 120b are the same, the preamble transmitted according to the RA settings may be received by the DU 120a.

The DU 120a that received the preamble generates an RA response to the preamble and transmits it to the UE 200 (step S104). Then, the UE 200 that has received the RA response scrambles the RRC request and transmits it (step S105). Specifically, the UE 200 scrambles the RRC request using the cell identification information included in the SIB received in step S102 and transmits the RRC request. Therefore, the UE 200 scrambles the RRC request not by the DU 120a during the random access process but by the cell identification information formed by the DU 120b that is the source of the SIB. As a result, the DU 120a does not detect the RRC request after transmitting the RA response, and the random access process does not end normally.

On the other hand, the UE 200 determines that the random access process does not end normally and the RRC connection fails because the RRC setting for the RRC request is not received even though the RRC request is transmitted. Therefore, the UE 200 counts the number of failures of the RRC connection and stores the number of failures together with the identification information of the cell in which the RRC connection fails. That is, here, the UE 200 stores the identification information of the cell formed by the DU 120a and the number of failures of the RRC connection in this cell. Further, the UE 200 receives the SIB again and repeats the random access process according to the RA setting.

By repeating the random access process, the preamble transmitted by the UE 200 may be received by the DU 120b, and the RRC connection between the UE 200 and the gNB 100b may be established by the random access process by the UE 200 and the DU 120b (step S106). That is, since the radio wave environment between the UE 200 and the DU 120a and between the UE 200 and the DU 120b changes, the DU that is the source of the SIB received by the UE 200 and the DU that receives the preamble transmitted by the UE 200 also change. Therefore, the DU that is the source of the SIB and the DU that receives the preamble may match, and the RRC connection between the UE 200 and the DU 120b may be successful.

When the RRC connection with the gNB 100b is established, the UE 200 compares the number of failures for each cell stored in the memory 230 with a predetermined threshold value, and if the number of failures is equal to or greater than the predetermined threshold value, the RRC connection fails. Is transmitted to gNB100b (step S107). At this time, if the identification information of the cell in which the RRC connection failure occurs frequently is known, the UE 200 also transmits the identification information of this cell to the gNB 100b.

CU110b of gNB100b notified that RRC connection failures occur frequently activates RACH optimization processing. Specifically, the CU 110b transmits an RA setting change request requesting a change of the RA setting to the CU 110a of the gNB 100a that controls the cell in which the RRC connection failure frequently occurs (step S108). When the identification information of the cell in which the RRC connection failure occurs frequently is unknown, the CU 110b may multicast the RA setting change request to the peripheral CUs including the CU 110a. The RA setting change request transmitted by the CU 110b includes, for example, information regarding the RA setting of the DU 120b.

Upon receiving the RA setting change request, the CU 110a decides to change the RA setting of the DU 120a and requests the DU 120a to change the RA setting (step S109). Then, when the DU 120a changes the RA setting, the CU 110a receives a notification that the change is completed (step S109). In this way, in the gNB 100a that has received the RA setting change request, a signal is transmitted and received between the CU 110a and the DU 120a, and the RA setting of the DU 120a is changed.

When the RA setting is changed, the CU 110a sends a change completion notification to the CU 110b (step S110). As a result, the CU 110b is notified that the RA settings of the DU 120a have been changed, and the duplication of the RA settings of the DU 120a and 120b is eliminated. The CU 110b decides to change the RA setting of the DU 120b if the change completion notification is not received even after a predetermined time has elapsed after transmitting the RA setting change request, and changes the RA setting for the DU 120b. You may request it (step S111). Then, when the DU 120b changes the RA setting, a notification that the change is completed may be received (step S111). Thereby, even if the RA setting of the DU 120a is not changed, the RA setting of the DU 120b can be changed and the duplication of the RA setting of the DU 120a and 120b can be eliminated.

In this way, when the UE 200 notifies that RRC connection failures occur frequently, the CU 110b activates the RACH optimization process to change the RA setting of the DU 120a via the CU 110a, or the RA setting of the DU 120b. To change. Therefore, since signal transmission / reception for changing the RA setting occurs only when RRC connection failures occur frequently, it is possible to suppress an increase in traffic. Further, when the RRC connection failure occurs frequently, the RACH optimization process is started as soon as the RRC connection between the UE 200 and the gNB 100b is established, so that the duplication of RA settings can be quickly eliminated. In other words, RACH optimization can be performed at the right time.

Next, the operation of the UE 200 in RACH optimization will be described with reference to the flow chart shown in FIG.

The wireless IF unit 210 receives the SIB notified in the cell in which the UE 200 is located (step S201). Since the SIB contains information regarding the RA setting, the RA processing unit 221 transmits the preamble according to the RA setting (step S202). Since the preamble is transmitted according to the RA setting, if there are a plurality of DUs having the same RA setting, the preamble may be received by another DU that is not the source of the SIB. Even in this case, the other DUs generate and transmit an RA response to the preamble.

After the preamble is transmitted, the RA processing unit 221 waits for the reception of the RA response (step S203), and if the RA response is not received (step S203No), the process is repeated from the reception of the SIB again. On the other hand, when the RA response is received (step S203Yes), the RA processing unit 221 generates and transmits an RRC request (step S204). At this time, the RRC request is scrambled using the cell identification information included in the SIB. Therefore, an RRC request that can be detected only by the DU that is the source of the SIB is transmitted.

After the RRC request is transmitted, the RA processing unit 221 waits for the reception of the RRC setting (step S205), and if the RRC setting is not received (step S205No), the number of RRC connection failures for each cell is incremented to the memory 230. Be remembered. That is, the number of RRC connection failures is counted for each cell (step S206). Then, when the RRC connection fails, the process is repeated from the reception of the SIB again. Since each SIB is transmitted from the gNB 100 around the UE 200 and the radio wave environment changes, the random access process is not always executed with the same gNB 100 every time the process is repeated from the reception of the SIB. Absent. Therefore, while the process is repeated, the random access process with any gNB 100 may succeed and the RRC setting may be received.

When the RRC setting is received (step S205Yes), the RRC processing unit 222 refers to the number of RRC connection failures stored in the memory 230, and determines whether or not the number of failures is equal to or greater than a predetermined threshold value (step S205Yes). Step S207). As a result of this determination, when the number of failures is less than a predetermined number (step S207No), since the RA settings are not duplicated and the RACH optimization is unnecessary, the UE 200 is connected to the RRC-connected gNB 100. Continue normal communication.

On the other hand, when the number of failures is equal to or greater than a predetermined number (step S207Yes), the gNB100 connected to the RRC is notified that many failures of the RRC connection have occurred (step S208). That is, when the number of RRC connection failures is large, the RA settings are duplicated and the RACH needs to be optimized. Therefore, the UE 200 frequently fails the RRC connection with respect to the gNB 100 connected by the RRC. Notify that. This notification may include identification information of the cell in which the RRC connection failed. The gNB 100, which is notified of the frequent occurrence of RRC connection failures, activates the RACH optimization process to eliminate the duplication of RA settings.

FIG. 7 is a flow chart showing the operation of the gNB 100 in which it is notified that RRC connection failures occur frequently. This gNB 100 corresponds to, for example, the gNB 100b shown in FIG.

When the wireless IF unit 123 of the DU 120 receives a notification of frequent RRC connection failures from the UE 200 (step S211), this notification is transferred from the transmission line IF unit 121 to the CU 110 and acquired by the RRC processing unit 115 of the CU 110. Will be done. Then, the RACH optimization control unit 116 transmits the RA setting change request requesting the change of the RA setting from the wired IF unit 111 to the CU of the gNB that controls the cell in which the RRC connection failure frequently occurs (step S212). .. At this time, if the cell in which the RRC connection failure frequently occurs is not specified, the RA setting change request may be multicast to the CU of the surrounding gNB.

After that, when the RACH optimization control unit 116 waits for the change completion notification to the effect that the RA setting change is completed (step S213) and receives the change completion notification from the CU to which the RA setting change request is sent, the change completion notification is received. (Step S213Yes), the RACH optimization process is completed. On the other hand, when the change completion notification is not received (step S213No), the RACH optimization control unit 116 determines that the RA setting of the DU 120 is changed, and the RA setting is changed from the transmission line IF unit 113 to the DU 120. Is requested (step S214).

In the DU 120 that received this request, the RA setting is changed by the RA setting control unit 126 (step S215). The RA setting may be changed to any RA setting different from the current RA setting, or information on the RA setting of the surrounding DU may be collected from the SIB receivable by the wireless IF unit 123. The RA settings may be changed to different from these RA settings. Further, the CU 110 may instruct the DU 120 to collect information on RA settings from the CUs of the surrounding gNBs and change the RA settings to different from these RA settings. When the RA setting is changed by the RA setting control unit 126, the CU 110 is notified via the transmission line IF unit 121 that the change has been completed (step S216).

In this way, when the UE 200 notifies the gNB 100 that RRC connection failures occur frequently, the gNB that controls the cell in which the failures occur frequently is requested to change the RA setting, and if there is no response to the request, , RA setting is changed in DU120 of gNB100. Therefore, when the RRC connection fails due to the duplication of RA settings, the duplication of RA settings can be eliminated, and RACH optimization can be executed at an appropriate timing.

FIG. 8 is a flow chart showing the operation of the gNB 100 in which the RA setting is required to be changed. This gNB 100 corresponds to, for example, the gNB 100a shown in FIG.

When the RA setting change request is received by the wired IF unit 111 of the CU 110 (step S221), the RACH optimization control unit 116 determines that the RA setting of the DU 120 is changed, and the transmission line IF unit 113 to the DU 120. , You are asked to change the RA settings (step S222).

In the DU 120 that received this request, the RA setting is changed by the RA setting control unit 126 (step S223). The RA setting may be changed to any RA setting different from the current RA setting, or information on the RA setting of the surrounding DU may be collected from the SIB receivable by the wireless IF unit 123. The RA settings may be changed to different from these RA settings. Further, the CU 110 may instruct the DU 120 to collect information on RA settings from the CUs of the surrounding gNBs and change the RA settings to different from these RA settings. When the RA setting is changed by the RA setting control unit 126, the CU 110 is notified via the transmission line IF unit 121 that the change has been completed (step S224). Then, the RACH optimization control unit 116 generates a change completion notification notifying that the change of the RA setting is completed, and transmits the change completion notification to the CU of the transmission source of the RA setting change request via the wired IF unit 111 (step). S225).

In this way, when the RA setting change request is received by the CU 110, the CU 110 requests the DU 120 to change the RA setting, and the RA setting in the DU 120 is changed. Therefore, when the RRC connection fails due to the duplication of RA settings, the duplication of RA settings can be eliminated, and RACH optimization can be executed at an appropriate timing.

As described above, according to the present embodiment, the UE counts the number of RRC connection failures, and when the RRC connection with the gNB is established, it notifies that the RRC connection failures have occurred frequently. Then, the gNB requests the CU of the gNB that controls the cell in which the RRC connection failure occurs frequently to change the RA setting. The gNB CU requested to change the RA setting requests the DU to change the RA setting, and the DU changes the RA setting. Therefore, since signal transmission / reception for changing the RA setting occurs only when RRC connection failures occur frequently, it is possible to suppress an increase in traffic related to RACH optimization. Further, when RRC connection failures occur frequently, the RACH optimization process is started as soon as the RRC connection between the UE and gNB is established, so that the duplication of RA settings can be quickly eliminated. In other words, RACH optimization can be performed at the right time.

In the first embodiment, the gNB 100 (gNB 100b) notified by the UE 200 that RRC connection failures occur frequently transmits a RA setting change request to another gNB 100 (gNB 100a). However, the gNB 100 (gNB 100b) notified of frequent failures may change the RA setting without transmitting the RA setting change request. A sequence diagram showing the RACH optimization method in this case is shown in FIG. In FIG. 9, the same parts as those in FIG. 5 are designated by the same reference numerals.

As shown in FIG. 9, when the UE 200 transmits a notification to the gNB 100b that RRC connection failures occur frequently (step S107), the CU 110b of the gNB 100b activates the RACH optimization process. Here, the CU 110b decides to change the RA setting of the DU 120b instead of transmitting the RA setting change request to the CU 110a, and requests the DU 120b to change the RA setting (step S121). Then, when the DU 120b changes the RA setting, the CU 110b receives a notification that the change is completed.

In this way, when the RA setting in the gNB100a where RRC connection failures occur frequently and the RA setting in the gNB100b which receives the notification that the RRC connection failure occurs frequently overlap, the gNB100b changes the RA setting by itself. Thereby, the duplication of RA settings can be eliminated.

Further, in the first embodiment, it is assumed that the gNB100b having the same RA setting as the RA setting in the gNB100a in which the RRC connection failure occurs frequently is notified that the RRC connection failure occurs frequently. This is because the random access process is repeated every time the UE 200 fails the RRC connection with the gNB 100a to establish the RRC connection with the gNB 100b. However, as a result of the UE 200 repeating the random access process, an RRC connection may be established with the gNB having an RA setting different from the RA setting in the gNB 100a.

FIG. 10 is a sequence diagram showing a RACH optimization method when the UE 200 establishes an RRC connection with a gNB100c having a RA setting different from that of the gNB100a and 100b. In FIG. 10, the same parts as those in FIG. 5 are designated by the same reference numerals.

As shown in FIG. 10, the UE 200 acquires the RA setting of each gNB by the SIB, and repeats the random access process according to the RA setting while the RRC connection fails (steps S101 to S105). Then, when the SIB is received from the gNB 100c whose RA setting is different from that of the gNB 100a and 100b and the RA setting of the gNB 100c is acquired by the UE 200, the UE 200 executes the random access process according to the RA setting of the gNB 100c. As a result, an RRC connection between the UE 200 and the gNB 100c may be established (step S131).

When the RRC connection with the gNB 100c is established, the UE 200 compares the number of failures for each cell stored in the memory 230 with a predetermined threshold value, and if the number of failures is equal to or greater than the predetermined threshold value, the RRC connection fails. Is transmitted to the gNB 100c (step S132). At this time, if the identification information of the cell in which the RRC connection failure occurs frequently is known, the UE 200 also transmits the identification information of this cell to the gNB 100c.

The gNB100c notified that the RRC connection failure occurs frequently sends an RA setting change request requesting the RA setting change to the CU110a of the gNB100a that controls the cell in which the RRC connection failure occurs frequently (step S133). ). When the identification information of the cell in which the RRC connection failure occurs frequently is unknown, the gNB 100c may multicast the RA setting change request to the surrounding gNB including the CU110a.

The CU 110a that has received the RA setting change request requests the DU 120a to change the RA setting, and when the DU 120a changes the RA setting, it receives a notification that the change is completed (step S109). Then, the CU 110a transmits a change completion notification to the gNB 100c (step S134). As a result, the gNB 100c is notified that the RA setting of the DU 120a has been changed, and the duplication of the RA setting of the DU 120a and 120b is eliminated.

(Embodiment 2)
The feature of the second embodiment is that the DU detects that the random access process does not end normally and starts RACH optimization led by gNB.

Since the configuration of the wireless communication system according to the second embodiment is the same as that of the wireless communication system (FIG. 2) according to the first embodiment, the description thereof will be omitted. Further, since the configurations of the gNB 100 and the UE 200 according to the second embodiment are the same as those of the gNB 100 (FIG. 3) and the UE 200 (FIG. 4) according to the first embodiment, the description thereof will be omitted. However, in the second embodiment, the operation of the gNB 100 and the UE 200 when the RRC connection between the gNB 100 and the UE 200 fails is different from that of the first embodiment.

FIG. 11 is a sequence diagram showing the RACH optimization method according to the second embodiment. In FIG. 11, the same parts as those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted. In the following, it is assumed that the DU 120a and 120b of the gNB 100a and 100b have the same RA setting.

DU120a and 120b of gNB100a and 100b transmit SIBs including RA setting information (steps S101 and S102). Here, since the RA settings of the DUs 120a and 120b are the same, the SIB transmitted from the DUs 120a and 120b includes information regarding the same RA settings. Further, it is assumed that the SIB transmitted from the DU 120a is not received by the UE 200 here due to, for example, the condition of the radio wave environment.

The UE 200 that has received the SIB transmits a preamble for random access according to the RA setting included in the SIB (step S103). At this time, if the radio wave environment between the UE 200 and the DU 120a is improved, the preamble may be received by the DU 120a.

The DU 120a that received the preamble generates an RA response to the preamble and transmits it to the UE 200 (step S104). Then, the UE 200 that has received the RA response scrambles the RRC request using the cell identification information included in the SIB received in step S102 and transmits it (step S105). As a result, the DU 120a does not detect the RRC request after transmitting the RA response, and the random access process does not end normally. Further, although the UE 200 has transmitted the RRC request, the RRC setting for the RRC request is not received, so the UE 200 receives the SIB again and repeats the random access process according to the RA setting.

While the random access process is repeated, the DU 120a detects that the random access process does not end normally, and counts and stores the number of RRC connection failures. That is, the DU 120a counts the number of times that the subsequent RRC request is not detected even though the RA response is transmitted, as the number of times the RRC connection has failed. Then, the DU 120a compares the number of failures stored in the memory 124 with a predetermined threshold value, and requests the CU 110a to optimize the RACH when the number of failures is equal to or greater than the predetermined threshold value (step S301). At this time, the DU 120a notifies the CU 110a of the current RA setting.

Then, the CU 110a notifies the CU of the surrounding gNB including the CU 110b of the RA setting of the DU 120a (step S302). The CU110b notified of the RA setting compares the RA setting of the notified DU120a with the RA setting of the DU120b, and if the RA setting overlaps, it is determined to change the RA setting of the DU120b, and the RA is set to the DU120b. Request a change in settings (step S303). When the DU 120b changes the RA setting in response to the request from the CU 110b, the DU 120b notifies the CU 110b that the change is completed (step S303). In this way, in the gNB100b notified of the RA setting, when the notified RA setting and the RA setting of the gNB100b overlap, a signal is transmitted and received between the CU 110b and the DU 120b, and the RA setting of the DU 120b is changed. ..

When the RA setting is changed, the CU110b sends a change completion notification to the CU110a (step S304). As a result, the CU 110a is notified that the RA settings of the DU 120b have been changed, and the duplication of the RA settings of the DU 120a and 120b is eliminated. The CU 110a determines that the RA setting of the DU 120a is changed if the change completion notification is not received even after a predetermined time has elapsed after notifying the surrounding CUs of the RA setting of the DU 120a, and RAs the DU 120a. You may request a change in the settings (step S305). Then, when the DU 120a changes the RA setting, a notification that the change is completed may be received (step S305). Thereby, even if the RA setting of the DU 120b is not changed, the RA setting of the DU 120a can be changed and the duplication of the RA setting of the DU 120a and 120b can be eliminated.

In this way, when the DU120a notifies that the RRC connection with the UE 200 frequently fails, the CU110a causes the RA setting of the DU120b to be changed via the CU110b, or the RA setting of the DU120a to be changed. Therefore, since signal transmission / reception for changing the RA setting occurs only when RRC connection failures occur frequently, it is possible to suppress an increase in traffic. Further, when RRC connection failures occur frequently, the DU120a detects the frequent failures and activates the RACH optimization process, so that the duplication of RA settings can be quickly eliminated. In other words, RACH optimization can be performed at the right time.

FIG. 12 is a flow diagram showing the operation of the gNB 100 in which RRC connection failures frequently occur with the UE 200. This gNB 100 corresponds to, for example, the gNB 100a shown in FIG.

When the preamble according to the RA setting of the gNB 100 is received by the radio IF unit 123 (step S401), the RA processing unit 125 generates an RA response to the preamble and transmits it from the radio IF unit 123 (step S402). After the RA response is transmitted, the RA processing unit 125 waits for the reception of the RRC request (step S403), and if the descrambleable RRC request is received by the cell identification information of the gNB 100 (step S403Yes), the RRC request is transmitted. The RRC settings are sent back and the RRC connection is established.

On the other hand, if a descrambleable RRC request is not received by the identification information of the cell of gNB100 after the RA response is transmitted (step S403No), the number of RRC connection failures is incremented and stored in the memory 124. That is, the number of RRC connection failures is counted (step S404). Then, the RA processing unit 125 refers to the number of failures of the RRC connection stored in the memory 124, and determines whether or not the number of failures is equal to or greater than a predetermined threshold value (step S405). As a result of this determination, if the number of failures is less than a predetermined number (step S405No), the random access process is repeated from the reception of the preamble according to the RA setting of gNB100.

On the other hand, when the number of failures is equal to or greater than a predetermined number (step S405 Yes), the CU 110 is notified via the transmission line IF unit 121 that RRC connection failures occur frequently (step S406). At this time, the current RA setting of the DU 120 is also notified to the CU 110. Then, the RACH optimization control unit 116 of the CU 110 generates an RA setting change request including the RA setting of the DU 120, which is transmitted from the wired IF unit 111 to the CU of the surrounding gNB (step S407).

After that, the RACH optimization control unit 116 waits for the change completion notification that the RA setting change is completed (step S408), and the change completion notification is received from any CU of the destination of the RA setting change request. In the case (step S408Yes), the RACH optimization process ends. On the other hand, when the change completion notification is not received (step S408No), the RACH optimization control unit 116 requests the DU 120 to change the RA setting via the transmission line IF unit 113 (step S409).

In the DU 120 that received this request, the RA setting is changed by the RA setting control unit 126 (step S410). The RA setting may be changed to any RA setting different from the current RA setting, or information on the RA setting of the surrounding DU may be collected from the SIB receivable by the wireless IF unit 123. The RA settings may be changed to different from these RA settings. Further, the CU 110 may instruct the DU 120 to collect information on RA settings from the CUs of the surrounding gNBs and change the RA settings to different from these RA settings. When the RA setting is changed by the RA setting control unit 126, the CU 110 is notified via the transmission line IF unit 121 that the change has been completed (step S411).

In this way, when gNB100 detects that RRC connection failures occur frequently, the CU110 of gNB100 notifies the surrounding gNBs of the RA setting of gNB100, and if they have the same RA setting, the RA setting is set. Request to change. If there is no response to the request, the RA setting is changed in the DU 120 of the gNB 100. Therefore, when the RRC connection fails due to the duplication of RA settings, the duplication of RA settings can be eliminated, and RACH optimization can be executed at an appropriate timing.

As described above, according to the present embodiment, the DU counts the number of failures of the RRC connection, and when the number of failures exceeds a predetermined threshold value, the CU is notified that the number of failures of the RRC connection has occurred frequently. Then, the CU requests the peripheral gNB having the same RA setting as the RA setting of the DU to change the RA setting. The gNB CU requested to change the RA setting requests the DU to change the RA setting, and the DU changes the RA setting. Therefore, since signal transmission / reception for changing the RA setting occurs only when RRC connection failures occur frequently, it is possible to suppress an increase in traffic related to RACH optimization. In addition, the DU monitors the number of RRC connection failures, and RACH optimization is executed as soon as failures occur frequently, so that duplication of RA settings can be quickly eliminated. In other words, RACH optimization can be performed at the right time.

In the second embodiment, the CU 110 (CU 110a) notified by the DU 120 that RRC connection failures occur frequently sends a RA setting change request to another CU 110 (CU 110b). However, the CU 110 (CU 110a) notified of the frequent occurrence of failures may request the DU 120 (DU 120a) in the gNB 100 to change the RA setting without transmitting the RA setting change request. A sequence diagram showing the RACH optimization method in this case is shown in FIG. In FIG. 13, the same parts as those in FIGS. 5 and 11 are designated by the same reference numerals.

As shown in FIG. 13, when the DU 120a requests the CU 110a to optimize the RACH (step S301), the CU 110a activates the RACH optimization process. Here, the CU 110a determines that the RA setting of the DU 120a is changed instead of transmitting the RA setting change request to the peripheral CUs including the CU 110b, and requests the DU 120a to change the RA setting (step S321). ). Then, when the DU 120a changes the RA setting, the CU 110a receives a notification that the change is completed.

In this way, when the RA setting in the gNB100a where RRC connection failures occur frequently and the RA setting in the surrounding gNB100b overlap, the gNB100a changes the RA setting by itself to eliminate the duplication of the RA setting. Can be done.

110, 110a, 110b CU
111 Wired IF unit 112, 122, 220 Processor 113, 121 Transmission line IF unit 114, 124, 230 Memory 115, 222 RRC processing unit 116 RACH optimization control unit 120, 120a, 120b DU
123, 210 Wireless IF unit 125, 221 RA processing unit 126 RA setting control unit

Claims (8)

1. A base station equipped with a wireless control device and a wireless device,
   The wireless control device is
   A first processor that determines to change the random access setting in the wireless device when the random access process by the terminal device is not completed normally.
   It has a transmission line interface that requests the wireless device to change the random access setting according to the determination by the first processor.
   The wireless device is
   A second processor that changes the random access setting in response to a request from the wireless control device, and
   A base station having a wireless interface that wirelessly notifies the random access setting changed by the second processor.
2. The wireless control device is
   It also has a wired interface that receives the random access setting change request from other base stations.
   The first processor is
   The base station according to claim 1, wherein when the change request is received by the wired interface, it is determined to change the random access setting.
3. The first processor is
   The base according to claim 1, wherein when the terminal device notifies that the random access process does not end normally with another base station, it is determined to change the random access setting. Station.
4. The wireless control device is
   Further having a wired interface for transmitting a request for changing the random access setting to the other base station when the terminal device notifies that the random access process does not end normally with the other base station. ,
   The first processor is
   The base station according to claim 1, wherein when the change completion notification is not received in response to the change request transmitted by the wired interface, it is determined to change the random access setting.
5. The wireless device is
   Further having a transmission line interface that requests the wireless control device to optimize the random access processing when it is detected that the random access processing by the terminal device does not end normally.
   The first processor is
   The base station according to claim 1, wherein when the wireless device requests optimization regarding random access processing, it is determined to change the random access setting.
6. The first processor is
   Claim 1 is characterized in that it is determined to change the random access setting in the wireless device when the number of failures of the RRC (Radio Resource Control) connection executed during the random access process is equal to or greater than a predetermined threshold value. The listed base station.
7. A wireless interface that receives information on random access settings related to random access processing,
   It has a processor that executes random access processing according to the random access setting and counts the number of failures that random access processing does not end normally.
   The wireless interface is
   A terminal device characterized in that when the number of failures counted by the processor is equal to or greater than a predetermined threshold value, a base station in which random access processing has succeeded is notified that random access processing has frequently failed.
8. A wireless communication system including a terminal device, a wireless control device, and a wireless device.
   The wireless control device is
   A first processor that determines to change the random access setting in the wireless device when the random access process by the terminal device is not completed normally.
   It has a transmission line interface that requests the wireless device to change the random access setting according to the determination by the first processor.
   The wireless device is
   A second processor that changes the random access setting in response to a request from the wireless control device, and
   A wireless communication system comprising a wireless interface for wirelessly notifying the random access setting changed by the second processor.

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