JP2020123941A - Multicast distribution system and wireless base station - Google Patents

Abstract

To provide a multicast distribution system capable of distributing multicast data received by a wireless base station from a core network to mobile terminals that do not support MBMS without any problem.SOLUTION: As a wireless bearer construction instruction for multicast data transmission to a mobile terminal 5 is received from a core network 3, a wireless base station 4 transmits to the mobile terminal 5 a substitute unicast bearer 12 setting instruction for instructing a setting of the substitute unicast bearer 12 serving as a substitute transmission path of the multicast data in a form of mapping a multicast traffic channel on a downlink shared channel. The mobile terminal 5 sets the substitute unicast bearer 12 in response to this. With the substitute unicast bearer 12 configured on a multicast traffic channel mapped on the downlink shared channel, the mobile terminal 5 receives multicast data using the substitute unicast bearer without problems.SELECTED DRAWING: Figure 1

Description

The present invention relates to a multicast distribution system including a mobile terminal such as a mobile terminal, and more particularly, in an LTE (Long Term Evolution) system or the like, a multicast data distribution function conforming to eMBMS (evolved Multimedia Broadcast Multicast Service) is further provided. The present invention relates to a multicast distribution system for realizing a simple network configuration and a wireless base station used for the same.

In 3GPP (Third Generation Partnership Project), which is a standardization project for mobile communication systems, eMBMS is specified to provide a multicast/broadcast service. In the current eMBMS, multicast data is transmitted via an MBCH (Physical Multicast Channel), which is a physical channel dedicated to multicast, in an area unit of an MBSFN (Multicast-Broadcast Single-Frequency Network) including a plurality of cells (MBSFN). transmission). In this case, a multicast bearer that is a radio bearer dedicated to multicast is constructed between the radio base station and the mobile terminal, and the multicast data is distributed to each mobile terminal via the multicast bearer (Patent Documents 1 and 2). ..

JP, 2013-146109, A JP, 2018-113706, A

However, in order to perform the multicast distribution using the multicast bearer, not only the core network and the wireless base station but also the wireless interface of the eMBMS specification including the mobile terminal, that is, the wireless interface capable of constructing the multicast bearer is provided. I won't. However, since the eMBMS service in 3GPP has not been shared for a long time, the spread of mobile terminals supporting eMBMS has not caught up, and users who have only mobile terminals that are not compatible with eMBMS have There is a problem that you can not receive delivery.

An object of the present invention is to provide a multicast distribution system that can distribute multicast data received by a wireless base station from a core network to mobile terminals that do not support eMBMS without any problem, and a wireless base station used for the multicast distribution system. ..

In order to solve the above problems, a multicast distribution system of the present invention has a core network, a radio base station connected to the core network by a physical line, and a mobile terminal wirelessly connected to the radio base station. Then, the wireless base station is configured to be able to deliver multicast data conforming to eMBMS (evolved Multimedia Broadcast Multicast Service) from the core network to the mobile terminal, and the wireless base station receives the multicast data from the core network and the multicast data receiving unit. A multicast radio bearer construction instruction receiving unit that receives a multicast radio bearer construction instruction from the core network for constructing a radio bearer for transmission with a mobile terminal, a base station side wireless transmission/reception unit, and a multicast data Direct the proxy unicast bearer setting instruction to the mobile terminal based on the multicast radio bearer construction instruction so that the proxy unicast bearer that serves as the proxy transmission path is set in the form of mapping the multicast traffic channel on the downlink shared channel. The base station side wireless transmission/reception unit is provided with a substitute unicast bearer setting instruction unit, and the mobile terminal receives the substitute unicast bearer setting instruction between the terminal side wireless transmission/reception unit and the wireless base station. And a proxy unicast bearer setting unit for setting a proxy unicast bearer, wherein the multicast data is transmitted to the mobile terminal via the core network, the radio base station and the proxy unicast bearer.

Further, the radio base station of the present invention is a multicast radio bearer construction instruction for constructing a multicast bearer for receiving multicast data from the core network and a radio bearer for transmitting the multicast data with the mobile terminal. Wireless bearer construction instruction receiving unit for receiving multicast from the core network, base station side wireless transmission/reception unit, proxy unicast bearer serving as a proxy transmission path for multicast data, and multicast traffic channel mapped on the downlink shared channel So that the proxy unicast bearer setup instruction unit for sending the proxy unicast bearer setup instruction to the mobile terminal to the base station side radio transceiver unit based on the multicast radio bearer construction instruction And

In the multicast distribution system of the present invention, as the radio base station receives the radio bearer establishment instruction for multicast data transmission to the mobile terminal from the core network, the radio base station serves as a proxy unicast bearer serving as a proxy transmission path for multicast data. , A substitute unicast bearer setting instruction for setting an instruction in the form of mapping a multicast traffic channel on the downlink shared channel is transmitted to the mobile terminal. In response to this, the mobile terminal sets up a proxy unicast bearer. Since the multicast traffic channel is set on the downlink shared channel, the mobile terminal can use the unicast bearer as an alternate unicast bearer capable of transmitting multicast data, and the multicast bearer is not set up. Can receive multicast data without any problem. The term "proxy unicast bearer" used in this specification is used to clarify that it is used for proxy transmission of multicast data, and is physically a normal "unicast bearer". There is no difference.

That is, in the above system, the multicast traffic channel is mapped on the downlink shared channel, so that the unicast bearer is treated as an alternate unicast bearer that functions in the same manner as the multicast bearer in the normal eMBMS specification when viewed from the core network. Therefore, it is easy to share the hardware with the core network of the usual eMBMS specifications. Since a unicast bearer is set up as a radio bearer for transmitting the multicast data between the radio base station and the mobile terminal, the multicast data can be received without any problem even by the mobile terminal that is not capable of establishing the multicast bearer and does not support eMBMS. Like

FIG. 1 is a block diagram of a multicast distribution system that is an embodiment of the present invention. The block diagram of eNodeB (radio|wireless base station) and UE (mobile terminal). The conceptual diagram of PDU. The figure which shows notionally the protocol stack of the control plane of 3GPP. The figure which shows notionally the protocol stack of the user plane of 3GPP. The figure which shows notionally the channel mapping of the downlink in this invention. Resource block conceptual diagram. The communication flow figure which shows the session sequence in a core network. The data flow figure which shows the sequence of the multicast data transfer process inside eNodeB. The data flow diagram in case a plurality of UEs are connected. The flowchart which shows the flow of the process in eNodeB which switches a proxy unicast bearer and a multicast bearer according to the number of connection of UE.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.
(Embodiment 1)
FIG. 1 is a block diagram showing the overall configuration of a multicast distribution system that is an embodiment of the present invention. The multicast distribution system 1 includes a core network 3 (or EPC: Evolved Packet Core), an eNodeB 4 forming a radio base station, and an E-UTRAN7 (Evolved Universal Terrestrial Radio Access Network: illustrated portion forming a physical circuit network connecting these. Is called an S1 line), and a plurality of UEs 5 (User Equipment: mobile terminals) are wirelessly connected to the eNodeB 4. Although not shown, the E-UTRAN7 includes an X2 line for handover for connecting the eNodeB4 to another eNodeB4. The core network 3 has a network structure of eMBMS (Multimedia Broadcast Multicast Service) specifications based on 3GPP (Third Generation Partnership Project). The wireless communication network that connects the eNodeB 4 and the UE 5 is constructed as a 3GPP advanced wireless communication network, specifically, an LTE system.

The core network 3 includes a BMSC (Broadcast Multicast Service Center) 8 that serves as a receiving node for multicast data from a higher-level network, an MBMS-GW (Multimedia Broadcast Multicast Service Gateway) 9 that serves as a user plane side gateway of the MBMS core network, and an MBMS. The MME (Mobility Management Entity) 2 which is the gateway on the control plane side of the core network in the above, and the MCE (Multi-cell multicast Coordination Entity) which controls the transmission control of the multicast data transmitted on the user plane side to the UE (mobile terminal) 5. ) 10 are included. The MBMS-GW 9 is connected to the eNodeB 4 via the M1 interface, connected to the MME 2 via the SM interface, and further connected to the BMSC 8 via the SG-mb and SGi-mb interfaces.

The BMSC 8 collects multicast content data from the media server 6 that is a data delivery source, manages group membership and QoS (Quality of Service) that is a delivery destination, announces multicast/broadcast sessions, and performs general multicast delivery such as security. Manage services. The MBMS-GW 9 is a gateway on the user plane (U-Plane) side and performs multicast data transmission and session control for the eNodeB 4. On the other hand, the MME 2 is a gateway on the control plane (C-Plane) side, and functions as an exchange that mediates control signals required for communication with the eNodeB 4 that is a base station. Specifically, for UE authentication control called NAS (Non Access Stratum), routing (connection path setting) request, and for exchanging data transmission/reception management information for each UE 5 between different eNodeBs 4 at the time of handover. Mediate. The MCE 10 corresponds to a multicast control device and has functions such as radio resource management and allocation of MBSFN, and specifies a radio resource to be used for data transmission between eNodeBs forming the MBSFN, thereby allowing a plurality of UEs 5 to be served by the eNodeB 4. It is responsible for synchronizing the content distribution using the multicast bearer. The eNodeB 4 is connected to the MCE 10 via the E-UTRAN 7.

The M1 interface is a user plane interface and functions as a transmission path for user data in multicast. On the other hand, the M2 interface and the M3 interface are control plane interfaces and function as control data transmission paths in multicast. Specifically, the M2 interface constitutes a control plane interface in the E-UTRAN, and the M3 interface constitutes a control plane interface between the E-UTRAN and the core network. The SGmb/SGimb interface is a shared interface of the control plane and the user plane between the BMSC 8 and the MBMS-GW 9 in the core network. Moreover, the SM interface is for forming a reference point of the control plane between the MME 2 and the MBMS-GW 9.

The above-mentioned core network configuration for eMBMS is constructed assuming a situation in which, for example, a large amount of moving image data or the like is simultaneously stream-distributed to an unspecified large number of UEs 5 on the IP network. That is, the content data distributed by multicast is transmitted to the core network 3 through the BMSC 8 for the purpose of collection and distribution management. Then, in order to realize large-capacity content processing, the multicast data forming the content is received by the MBMS-GW 9, which is the gateway device on the user plane side. On the other hand, the control data is generated by the MME 2, which is the gateway device on the control plane side, by referring to the MBMS-GW 9 via the SM interface. The control data flows to the eNodeB 4 while being separated from the user data via a transmission path (M3/M2 interface) different from the user plane.

The configuration of the core network 3 in the multicast distribution system 1 is the same as the standard core network of the eMBMS specification, and a multicast bearer that is a radio bearer dedicated to multicast distribution is constructed between the eNodeB 4 and the UE 5. On the premise, a communication session is established among the BMSC 8, MBMS-GW 9, MME 2, MCE 10 and eNodeB 4 (FIG. 8: described later). Specifically, when delivering the multicast data, the core network 3 transmits a multicast bearer establishment instruction to the eNodeB 4. On the other hand, the eNodeB 4 is provided with the communication function configuration peculiar to the present invention, so that the multicast bearer that should originally be constructed on the multicast traffic channel (MTCH: Multicast Traffic Channel) with the UE 5 is replaced with the proxy unicast. The cast bearer 12 is set. In addition, the MTCH is mapped to the downlink shared channel (DLSCH) instead of the normal multicast channel (MCH: Multicast Channel) in the eMBMS, so that the unicast bearer is capable of transmitting multicast data and is set. It is done (on behalf). The proxy unicast bearer 12 delivers the multicast data (content) to the UE 5. This allows the UE 5 to participate in the multicast even when it is a mobile terminal or the like that does not support eMBMS. In this embodiment, the default unicast bearer established when the UE 5 attaches to the eNodeB 4 is used as the proxy unicast bearer. The default unicast bearer is used by a logical channel mapped to a downlink shared channel (DLSCH), and is normally occupied by a dedicated traffic channel (DTCH: Dedicated Traffic Channel) for performing one-to-one communication between UEs 5. To be done. However, as described above, it is possible to set the default unicast bearer as the proxy unicast bearer by mapping the MTCH for performing the multicast communication on the DLSCH.

FIG. 2 is a block diagram showing a configuration example of the eNodeB 4 and the UE 5 (portions indicated by virtual lines (dashed and two-dot chain lines) are components of a second embodiment described later and are not used in this embodiment. ). The eNodeB 4 includes a control unit 4a configured by an MPU, an upper-side transmission/reception unit 4k for transmitting/receiving multicast data between the core network 3 and the E-UTRAN 7, and a base station-side wireless transmission/reception unit 4f. It has a hardware configuration connected to a bus. The base station side wireless transmission/reception unit 4f includes a unicast transmission/reception I/F 4g for transmitting/receiving unicast data. Further, the upper-side transmitting/receiving unit 4k receives from the core network 3 a multicast radio bearer construction instruction for setting a radio bearer for transmitting multicast data (the above-mentioned proxy unicast bearer) with the mobile terminal. It also functions as a multicast bearer establishment instruction receiving unit.

Further, the eNodeB 4 is provided with the following elements that realize functions by a software module executed by the control unit 4a or a hardware logic that operates according to a command from the control unit 4a.
Proxy unicast bearer setting instruction unit 4u: Upon connection with the UE5, the proxy unicast bearer 12 serving as a proxy transmission path for multicast data is mapped on the DLSCH based on the multicast radio bearer construction instruction received from the core network 3. The substitute unicast bearer setting instruction for instructing the setting on the MTCH is transmitted to the base station side wireless transmission/reception unit toward the mobile terminal.

In the multicast distribution system 1, the “radio bearer for multicast”, which the core network 3 instructs the eNodeB 4 to construct, originally means the multicast bearer, but the eNodeB 4 receives the instruction and is not the multicast bearer. , Instructs the UE 5 to set the proxy unicast bearer 12. That is, it can be said that the proxy unicast bearer setting instruction unit 4d of the eNodeB 4 plays a role of converting the multicast bearer establishment instruction from the core network 3 into the proxy unicast bearer setting instruction for the UE 5. In addition, when a plurality of UEs 5 are connected to the eNodeB 4, the proxy unicast bearer setting instruction unit 4u corresponds to the plurality of UEs 5 in a one-to-one relationship with the proxy unicast bearers 12 as shown in FIG. So that each of the UEs 5 is individually transmitted to the base station side wireless transmission/reception unit 4f so that each of the UEs 5 is individually set.

Multicast data copying unit 4b: copies the multicast data received from the core network 3 to a plurality of data paths for data transfer to each proxy unicast bearer constructed with a plurality of UEs 5 (mobile terminals). .. In the 3GPP unicast communication specification, if the content data received from the core network 3 is treated as unicast data, the distribution of the content data must be repeated by the number of UEs 5 in the unicast communication premised on one-to-one communication. However, by incorporating the multicast data copying unit 4b, the content data distributed as the multicast data can be copied to the data path of the proxy unicast bearer 12 which is set in a plural number corresponding to the number of UEs 5. That is, one multicast data can be distributed to each of the plurality of proxy unicast bearers 12, and a data distribution system functionally equivalent to multicast can be realized.

Retransmission control unit 4c: Controls retransmission of multicast data by the substitute unicast bearer 12 on the DLSCH. As will be described later, this function is incorporated in the MAC layer of the LTE protocol stack and performs error correction of transmission data by HARQ (Hybrid Automatic Repeat reQuest). In 3GPP, retransmission control is used in unicast communication using DLSCH, but in eMBMS multicast using MCH, retransmission control has not been performed because unidirectional data distribution is performed. As a result, there is a problem that packet loss tends to occur because the retransmission control does not function in the multicast distribution using MCH. However, by distributing the multicast data by the substitute unicast bearer 12 using the DLSCH, the retransmission control can function without problems, and the frequency of packet loss can be reduced.

-SYNC module (synchronization control unit) 4d: performs transmission synchronization control on the DLSCH of multicast data by a plurality of proxy unicast bearers 12. In the case of delivering the content to the plurality of UEs 5 using the multicast bearer, the synchronization control of the content is secured by the MCE 10 in the core network 3. However, since the multicast distribution system 1 of the present embodiment distributes the multicast data to the plurality of UEs 5 by using the individual proxy multicast bearers 12 that the synchronization control from the MCE 10 does not directly reach, the content is distributed from the eNodeB 4 to the UEs 5. May be out of sync. Therefore, by providing the above-mentioned SYNC module (synchronization control unit) 4b, transmission synchronization of multicast data (content data) to a plurality of proxy unicast bearers 12 can be easily achieved.

Next, the UE 5 has a hardware configuration in which the control unit 5a configured by the MPU and the terminal side wireless transmission/reception unit 5f are bus-connected. The terminal side wireless transmission/reception unit 5f includes a unicast transmission/reception I/F 5g. In addition, the following elements that realize functions by a software module executed by the control unit 4a or a hardware logic that operates according to a command from the control unit 5a are provided.
Proxy unicast bearer setting unit 5c: A proxy unicast bearer 12 is connected to the eNodeB 4 by receiving a proxy unicast bearer setting instruction from the eNodeB 4, and a downlink shared channel (DLSCH; described later) is provided to the terminal side wireless transceiver 5f. Use to set.

FIG. 3 is a schematic diagram showing the structure of a PDU (Protocol Data Unit) used for data transmission. The PDU 300 is composed of a header 301 and a payload 302, and a PDU identification number, a data source address 301a, a data destination address 301b, etc. are written in the header 301. Further, in the payload 302, in the case of user data, data that is the main body of the distribution content is written, and in the case of control data, various control commands and the like are written. In the case of the PDU used for the multicast packet, a unique address indicating the delivery destination of the multicast packet is written.

4 and 5 show a radio interface protocol stack in the LTE system, FIG. 5 shows a user plane protocol stack, and FIG. 4 shows a control plane protocol stack. The radio interface protocol is divided into layers 1 to 3 of the OSI reference model, and layer 1 is the PHY (physical) layer. The layer 2 includes a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, and a PDCP (Packet Data Convergence Protocol) layer. Layer 3 includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum: non-access) layer.

The role of each layer is as follows.
PHY layer: performs encoding/decoding, modulation/demodulation, antenna mapping/demapping, and resource mapping/demapping. Data and control signals are transmitted via the physical channel between the PHY layer of the UE 5 and the PHY layer of the eNodeB 4.
MAC layer: Performs data priority control, HARQ retransmission control processing, random access procedure, and the like. Data and control signals are transmitted between the MAC layer of the UE 5 and the MAC layer of the eNodeB 4 via the transport channel. The MAC layer of the eNodeB 4 includes a scheduler that determines a transport format (transport block size, modulation/coding method (MCS)) of uplink and downlink and a resource block allocated to the UE 5. As described above, since the retransmission control processing relating to the multicast data transmission on the proxy unicast bearer 12 is performed in this MAC layer, it can be considered that the retransmission control unit 4d in FIG. 2 is incorporated therein.

RLC layer: Data is transmitted to the RLC layer on the receiving side by utilizing the functions of the MAC layer and the PHY layer. Data and control signals are transmitted via a logical channel between the RLC layer of the UE 5 and the RLC layer of the eNodeB 4.
-PDCP layer: Performs PDU header compression/decompression and encryption/decryption.
RRC layer: defined only in the control plane that handles control signals. Messages for various settings (RRC messages) are transmitted between the RRC layer of the UE 5 and the RRC layer of the eNodeB 4. The RRC layer controls logical channels, transport channels and physical channels according to establishment, re-establishment and release of radio bearers (multicast bearers and unicast bearers). When there is a connection (RRC connection) between the RRC of the UE 5 and the RRC of the eNodeB 4, the UE 5 enters the RRC connected mode, and otherwise the RRC idle mode.

The above layers are used both in the control plane and the user plane. On the other hand, only in the control plane, the UE 5 and the MME 3 are provided with a NAS layer for performing session management, mobility management, and the like higher than the RRC layer.

The user data transmission interface with the core network side of the eNodeB 4 is provided with a GTP-U (GPRS (General Packet Radio Service) Tunneling Protocol for User Plane) layer and a SYNC (Synchronization) module. The roles of these layers are as follows.
-GTP-U layer: The UE 5 (mobile terminal) of the connection destination and the radio bearer to be used are identified. In the present invention, the UE 5 that is the destination of the multicast data and the unicast bearer that is the alternate transmission path for the multicast data are identified.
-SYNC module (synchronization control unit): When a plurality of UEs 5 are connected, between data paths (between bearers) when copying and transmitting multicast data to the data paths of a plurality of unicast bearers connecting them. Is responsible for the data transmission synchronization control. This is newly incorporated in the protocol stack in order to realize the function of synchronously transmitting multicast data using DLSCH that handles unicast data. In this embodiment, the SYNC module also copies the multicast data to the plurality of data paths, and it can be considered that the function of the multicast data copying unit 4b is also incorporated therein.

Next, FIG. 6 shows downlink channel mapping in the LTE system (the portion 50 surrounded by the alternate long and short dash line is a component of a second embodiment described later and is not used in this embodiment). Here, the mapping relationship among logical channels (Downlink Logical Channel), transport channels (Downlink Transport Channel), and physical channels (Downlink Physical Channel) is shown. Hereinafter, they will be described in order.
DTCH (Dedicated Traffic Channel) is a dedicated logical channel for data transmission. The DTCH is mapped to DLSCH (Downlink Shared Channel) which is a transport channel.
DCCH (Dedicated Control Channel): a logical channel for transmitting dedicated control information between the UE 5 and the network. DCCH is used when UE5 has an RRC connection. DCCH is mapped to DLSCH.
CCCH (Common Control Channel): A logical channel for transmission control information between the UE 5 and the eNodeB 4. The CCCH is used when the UE 5 does not have an RRC connection with the eNodeB 4 (network). CCCH is mapped to DLSCH.

-BCCH (Broadcast Control Channel): A logical channel for system information distribution. BCCH is mapped to BCH (Broadcast Channel) or DLSCH which is a transport channel.
PCCH (Paging Control Channel): A logical channel for notifying the change of paging information and system information. PCCH is mapped to PCH (Paging Channel) which is a transport channel.
MCCH (Multicast Control Channel): A logical channel for multicast transmission. The MCCH is used for transmitting MBMS control data from the eNodeB 4 to the UE 5 in a normal eMBMS, but when the substitute unicast bearer 12 is used as a radio bearer for transmitting multicast data, it transmits control data. CCCH or DCCH is used as a logical channel to be used, and this MCCH is not used.
MTCH (Multicast Traffic Channel): A logical channel for transmitting multicast data (content) from the eNodeB 4 to the UE 5. The MTCH is mapped to an MCH (Multicast Channel) which is a transport channel for multicast in the usual eMBMS specifications. However, in the present invention, since the multicast data is sent on the proxy unicast bearer 12 in the same manner as the unicast data, it is mapped to DLSCH which is a transport channel for unicast data (in the figure, Shown with double lines).

The mapping relationship between transport channels and physical channels is as follows.
DLSCH and PCH: Mapped to PDSCH (Physical Downlink Shared Channel). DLSCH supports HARQ, link adaptation, and dynamic resource allocation (which is also a unicast specific part).
BCH: Mapped to PBCH (Physical Broadcast Channel).
MCH: Mapped to PMCH (Physical Multicast Channel). The MCH supports MBSFN transmission by a plurality of cells, but is not used when the substitute unicast bearer 12 is used as a radio bearer for transmitting multicast data.

Next, in the LTE system, the UE 5 wirelessly connects to the eNodeB 4 by OFDM (Orthogonal Frequency-Division Multiplexing) access (OFDMA). The OFDMA method is characterized as a two-dimensional multiplexed access method that combines frequency division multiplexing and time division multiplexing. Specifically, the orthogonal frequency axis and time axis channels (subcarriers) are divided and allocated to UE5, and orthogonal subcarriers on the frequency axis are set so that the signal of each subcarrier becomes zero (point 0). To divide. By dividing the subcarriers and allocating them on the frequency axis, it is possible to select another subcarrier that is not affected even if one subcarrier is affected by fading, so that the user is better suited to the radio environment. Subcarriers can be used, and there is an advantage that radio quality is maintained.

Further, in the OFDMA method, a resource block (Resource Block: hereinafter also referred to as RB) defined on a virtual plane spanning a frequency axis and a time axis is adopted as a radio resource. As shown in FIG. 7, RB is defined as a block obtained by dividing the above plane into a matrix at 180 kHz/0.5 msec. Each block has 12 subcarriers adjacent to each other at 15 kHz intervals on the frequency axis, and on the time axis. Includes 1 slot (7 symbols) of a frame. Two RBs (1 msec) adjacent to each other on the time axis are assigned to the UE 5 as one set.

The operation of the multicast distribution system 1 of FIG. 1 will be described below. FIG. 8 is a communication flow diagram mainly showing the flow of processing in the core network 3 (portions indicated by virtual lines (dashed-dotted lines) are components of a second embodiment described later, and Not used in the form). When the eNodeB 4 is started up, as initialization processing on the control plane side, in order to make the eNodeB 4 as the activated base station to recognize the eNodeB 4 as the activated base station, a setup request and a response are sequentially sent via the M2 interface and the M3 interface. Is performed (TS101 to TS104). Further, the procedure of the session start request/response for establishing a multicast bearer, which is a signal transmission path for wireless transmission of multicast data from the BMSC8 side to the eNodeB4, is performed between the BMSC8/MBMS-GW9 (TS105, 106) and between the MBMS-GW9/MME2 ( TS107, 108) are similarly implemented. This session start request corresponds to a multicast radio bearer establishment instruction.

Subsequently, the MME 2 transmits a session start request to the MCE 10 (TS109). The session start request/response procedure is also executed between the MCE 10 and eNodeB 4 which received this (TS110). As a result, the eNodeB 4 completes the preparation for session start for multicast data (content) distribution from the core network side. Then, as the MCE 10 sequentially receives various multicast data (contents) distribution requests, the MCE 10 schedules the distribution (distribution time, distribution area, etc.) and transmits the scheduling information to the eNodeB 4 (TS 112). The eNodeB 4 receives the scheduling information and returns a response to the MCE 10 (TS113). The MCE 10 returns a session start response to the MME 2 (TS114). With the processing up to this point, the preparation for multicast data (content) distribution on the core network 3 side is completed.

In the eMBMS session in the normal LTE network, the eNodeB 4 performs RAN (radio) resource setup of the multicast bearer by the MCH in order to instruct the UE 5 to establish the multicast bearer in the eMBMS session in the normal LTE network with respect to the UE 5 as the connection destination. However, in the case of the present invention, the proxy unicast bearer is set up with the UE 5 instead of the multicast bearer, so that the RAN (radio) resource setup of the proxy unicast bearer by DLSCH is performed. Multicast data from the media server 6 (FIG. 1) is transmitted between the BMSC8/MBMS-GW9 via the SGimb interface (TS115), and between the MBMS-GW9/eNodeB4 (see also FIG. 1) via the M1 interface. And transmitted (TS116, 117). Then, the eNodeB 4 and the UE 5 are transmitted via the proxy unicast bearer 12 (see FIGS. 1 and 2) on the DLCSH (TS118).

The solid line frame in FIG. 9 shows the internal data transfer sequence between the layers in the protocol stack on the user plane side of the eNodeB 4. The case where there is only one connected UE (not shown in FIG. 9) is shown (in the figure, “UE1” is displayed in the corresponding data path), and the contents surrounded by the solid line frame in the upper part of the figure are shown. Shows a sequence when a substitute unicast bearer is used. An M1 packet (user data packet of content transmitted through the M1 interface) input from the core network to the GTP-U layer is converted into a SYNC PDU and transferred to the SYNC module (SYNC) (TS201).

The SYNC module converts the SYNC PDU into a PDCP PDU and transfers it to the PDCP layer according to the transfer timing indicated by the scheduling information received on the control plane side (TS202). The PDCP layer converts this into an RLC PDU. Further, the transport channel for wireless transmission is bypassed to the DLSCH to which the MTCH is mapped (TS203), and the downlink (DL) data path corresponding to the alternate unicast bearer of the UE5 is used to transmit the RLC PDU to the RLC layer and the MAC layer. And to the PHY layer. Then, finally, the substitute unicast bearer 12 (FIG. 1) corresponding to the data path on the DLSCH wirelessly transmits to the UE 5. The multicast (content) data collected by the core network 3 can be identified as a multicast PDU by using the destination address described in the header of the PDU as a unique multicast address. ..

On the other hand, on the side of the UE 5, registration of participation in content distribution by multicast is performed in advance by using the address of the UE 5 in such a manner that the multicast content desired to be distributed is specified by the multicast address. When the PDU of the multicast content is sent, the eNodeB 4 confirms the multicast address described in the header of the PDU and detects the address of the UE 5 registered in the coverage area for distribution of the content corresponding to the multicast address. Then, the proxy unicast bearer 12 is set between the UE 5 and the UE 5. The setting timing of the proxy unicast bearer 12 is controlled by the content distribution start time defined by the scheduling information received from the core network 3 by the SYNC module.

Then, once the proxy unicast bearer 12 is set up with the UE 5, the proxy unicast bearer 12 is set up so as to specify the UE 5 that is the content delivery destination, so that the multicast data is received from the core network. In this case, the eNodeB 4 can transmit the multicast data to the connected UE 5 by the proxy unicast bearer 12 regardless of the assigned destination address. That is, the multicast data received from the core network 3 can be made to flow to the proxy multicast bearer 12, so to speak, so that the distribution process can be greatly simplified.

For example, the eNodeB 4 can transmit the packet (PDU) data of the multicast data having the destination address dedicated to the multicast by the substitute unicast bearer 12 without rewriting the destination address. As a result, the rewriting process of the transmission destination address of the PDU in the PDCP layer becomes unnecessary, and the distribution process can be further simplified.

FIG. 10 shows a similar internal data transfer sequence in the eNodeB 4 when there are a plurality of UEs 5 participating in the multicast (eight UE1, UE2,..., UE8 in FIG. 10) (with the sequence of FIG. 9). Since many parts are common, the difference will be mainly described.) In the SYNC module, the SYNC PDU created from the M1 packet is copied while being converted into PDCP PDUs into a plurality of data paths individually corresponding to the participating UEs 5. (TS201). Then, when the transfer timing indicated by the scheduling information received on the control plane side arrives, it is simultaneously transferred to the copied PDCP layers (TS202). In the PDCP layer, these are respectively converted into RLC PDUs, and DL (Down Link) data paths individually corresponding to the substitute unicast bearers that are set up in a one-to-one relationship with each UE 5 are set on the DLSCH. After copying, the converted RLC PDUs are transferred to the corresponding DL data paths (TS203), pass through the RLC layer, the MAC layer, and the PHY layer, and are simultaneously sent to each UE 5 by the corresponding proxy unicast bearer 12 (FIG. 1). Wirelessly transmitted to.

That is, it can be seen that a system capable of broadcasting multicast contents to a plurality of UEs 5 is realized by a plurality of proxy unicast bearers 12. Also, the UE 5 that does not support eMBMS can receive the distribution service of the multicast content. Further, by using the unicast bearer on the DLSCH, retransmission control, which does not work with the multicast bearer using the MCH, can function, and there is an advantage that the frequency of packet loss can be reduced. At this time, the plurality of UEs 5 may not be compatible with eMBMS, or models compatible with eMBMS and models not compatible with eMBMS may be mixed. That is, in the above embodiment, the eNodeB 4 (radio base station) transmits the multicast data to the core network 3, the eNodeB 4 and the proxy unicast bearer 12 regardless of whether the UE 5 (mobile terminal) is a model compatible with eMBMS. It is configured to be transmitted to each UE 5 via. By using the function of the proxy unicast bearer, even if UE5 models compatible with eMBMS and non-compatible models are mixed, the multicast data can be delivered without problems.

The embodiments of the present invention have been described above, but they are merely examples, and the present invention is not limited to these.
(Embodiment 2)
Hereinafter, a modified embodiment of the present invention will be described with reference to FIG. That is, as shown by a virtual line in the drawing, the eNodeB 4 (radio base station) can be provided with the multicast bearer setting instruction unit 4e. Based on the multicast radio bearer construction instruction received from the core network 3, the multicast bearer setting instruction unit 4e sends a multicast bearer construction instruction for instructing the construction of the multicast bearer 11 instead of the proxy unicast bearer 12 to the UE 5 (movement). The base station side wireless transmission/reception unit 4f transmits the data to the terminal). A multicast transmission/reception I/F 4h for establishing a multicast bearer is formed in the base station side wireless transmission/reception unit 4f. The multicast bearer 11 is built on the MCH (multicast channel) mapped on the MTCH (multicast traffic channel).

On the other hand, when the UE 5 (mobile terminal) is a model compatible with eMBMS, by receiving the above multicast bearer establishment instruction, the UE 5 (mobile terminal) wirelessly transmits/receives the multicast bearer 11 to/from the eNodeB 4 on the MCH (multicast channel). A multicast bearer construction unit 5b that is constructed by the unit 5f is provided. A multicast transmission/reception I/F 5h for establishing a multicast bearer is also formed in the terminal side wireless transmission/reception unit 5f.

Then, the multicast bearer 11 and the proxy unicast bearer 12 are used by appropriately switching according to the number N of connections of the UE 5 (mobile terminal) to the eNodeB 4. Specifically, the eNodeB 4 (radio base station) uses the eMBMS via the multi-unicast bearer 12 when the number of connections N to the UE 5 (mobile terminal) compatible with eMBMS is equal to or greater than a predetermined reference number Nc. While transmitting multicast data to the UE5 (mobile terminal) corresponding to, the number of connections N is less than the reference number Nc, the multicast data is transmitted to the UE5 (mobile terminal) corresponding to eMBMS via the proxy unicast bearer 12. To do. When the UE 5 (mobile terminal) does not support eMBMS, the eNodeB 4 transmits the multicast data to the UE 5 via the proxy unicast bearer 12 regardless of the number of connections N.

FIG. 11 shows a flowchart showing the flow of processing in the eNodeB 4 in this case. When the system is activated in S201, an attach sequence is executed in S202, and a default unicast bearer is set up in S203 with the UE5 attached to the eNodeB 4 in the area. Subsequently, in S2031, the UE type identification information indicating whether the attached UE 5 is a model compatible with eMBMS or a model not compatible with eMBMS is acquired. The UE type identification information may be uploaded in advance from the UE 5 to the upper network using, for example, an application layer protocol (for example, HTTP), and the eNodeB 4 may acquire the UE type identification information via the core network 3. The UE type identification information may be incorporated into the above-mentioned RRC message and transmitted from the UE 5 to the eNodeB 4. In the latter case, specifically, the eNodeB 4 refers to the MBMS Interest Indicator included in the RRC message transmitted by the UE 5 as the UE type identification information. The MBMS Interest Indicator is 1-bit information indicating the intention of the UE5 to receive the eMBMS. If the bit is "1", it means that the UE5 wants to receive the eMBMS, and the UE5 is a model compatible with the eMBMS. Can be understood. On the other hand, when the bit is “0”, it means that the UE 5 does not want to receive eMBMS, and it can be understood that the UE 5 is a model that does not support eMBMS.

Subsequently, in S2032, the number N of the UEs 5 (UE5s that have announced that they will participate in the multicast distribution) connected to the eMBMS is confirmed. If N is less than the predetermined reference number Nc in S2033, the process proceeds to SR1 to perform the proxy unicast bearer operation in the sequence shown in the upper part of FIG. Perform the setting process. That is, in S204, the MTCH is mapped to the DLSCH, and the radio resource allocation of the default unicast bearer and the channel setting information are transmitted to each UE 5, thereby setting this as an alternate unicast bearer used for multicast data transmission. Then, in S205, the multicast data is copied to the proxy unicast bearer.

On the other hand, in S2033, when N is equal to or larger than the reference number Nc, the process of SR2 is performed for the UE5 that does not support eMBMS, and the process is performed by the proxy unicast bearer similar to SR1. On the other hand, with respect to the eMBMS-compatible UE 5, the SR3 process is performed, and a multicast bearer is constructed with the UE 5 instead of the substitute unicast bearer. In S209, a session start request for establishing a multicast bearer is transmitted to each UE 5, and in S210, a session start response from each UE 5 is received. In S211, MTCH is mapped to MCH (shown by a virtual line in FIG. 6), and radio resource allocation and channel setting information of the multicast bearer to be constructed are transmitted to each UE5. Then, in S212, a multicast bearer is constructed.

The outline of the internal sequence in the eNodeB 4 at the time of establishing the multicast bearer is the flow surrounded by virtual lines in the lower part of FIG. That is, the SYNC PDU created in the GTP-U layer based on the M1 packet is transferred to the SYNC module in TS211. In this case, only one wide-band multicast bearer for one-to-many communication is constructed, and the SYNC module immediately converts the SYNC PDU into an RLC PDU (TS212), bypassing the PDCP layer and the RLC layer, MAC layer and Through the PHY layer, the multicast bearers 11 shown by virtual lines in FIG. 2 wirelessly transmit them to all the UEs 5 simultaneously (FIG. 8: TS119).

In any of the routines, the process then proceeds to S206, and the multicast data is transmitted to the UE 5 by the proxy unicast bearer or the multicast bearer. According to this configuration, a unicast bearer with a small radio resource allocation bandwidth is used when the number of eMBMS-compatible UEs 5 is small, and a radio resource allocation bandwidth is large when the number of eMBMS-compatible UEs 5 increases to some extent. By switching to the multicast bearer, it becomes possible to effectively utilize the wireless resources.

1 Multicast distribution system 2 MME
3 Core network 4 eNodeB (radio base station)
4a Control unit (MPU)
4e Multicast bearer setting instruction unit 4u Substitute unicast bearer setting instruction unit 4f Base station side wireless transmission/reception unit 4g Unicast transmission/reception I/F
4h Multicast transmission/reception I/F
5 UE (mobile terminal)
5b Multicast bearer construction unit 5c Substitute unicast bearer setting unit 5f Terminal side wireless transmission/reception unit 6 Media server 7 E-UTRAN
8 BMSC
9 MBMS-GW
10 MCE
11 multicast bearer 12 proxy unicast bearer

Claims (10)

An eMBMS (evolved Multimedia Broadcast Multicast Service) is provided from the core network to the mobile terminal, which has a core network, a radio base station connected to the core network by a physical line, and a mobile terminal wirelessly connected to the radio base station. ) Compliant multicast data can be delivered,
The radio base station has a multicast data receiver for receiving the multicast data from the core network, and a multicast radio bearer construction instruction for constructing a radio bearer for transmitting the multicast data with the mobile terminal. A radio bearer construction instruction receiving unit for multicast, which receives from the core network, a radio transceiver unit on the base station side, a proxy unicast bearer serving as a proxy transmission path for the multicast data, and a multicast traffic channel mapped on the downlink shared channel. In order to be set in the form, a substitute unicast bearer setting instruction unit for transmitting a substitute unicast bearer setting instruction based on the multicast radio bearer construction instruction to the base station side radio transceiver unit toward the mobile terminal, Prepare,
The mobile terminal includes a terminal-side wireless transceiver, and a proxy unicast bearer setting unit configured to set the proxy unicast bearer with the wireless base station by receiving the proxy unicast bearer setting instruction. ,
A multicast distribution system, wherein the multicast data is transmitted to the mobile terminal via the core network, the radio base station, and the proxy unicast bearer. The core network has a BMSC (Broadcast Multicast Service Center) serving as a receiving node of multicast data from a higher-level network and a user plane of the core network in eMBMS, as a network structure of the MBMS specification conforming to 3GPP (Third Generation Partnership Project). MBMS-GW (Multimedia Broadcast Multicast Service Gateway) which is a gateway on the side, MME (Mobility Management Entity) which is a gateway on the control plane side of the core network in eMBMS, and the multicast data transmitted on the user plane side. The multicast distribution system according to claim 1, further comprising an MCE (Multi-cell multicast Coordination Entity) that controls transmission to the mobile terminal. When the wireless base station receives the multicast data from the core network, the wireless base station transmits the multicast data to the connected mobile terminal by the proxy unicast bearer regardless of the assigned destination address. Alternatively, the multicast distribution system according to claim 2. When the wireless base station receives a packet of the multicast data having a destination address dedicated to multicast from the core network, the wireless base station transmits the multicast data to the connected mobile terminal without rewriting the destination address. The multicast distribution system according to claim 3, wherein transmission is performed by a substitute unicast bearer. The wireless base station is provided with a retransmission control unit that controls retransmission of the multicast data by the proxy unicast bearer on the downlink shared channel. Multicast distribution system. The proxy unicast bearer setting instruction unit of the radio base station, when the mobile terminal is connected to the radio base station in a plurality, the proxy unicast in a one-to-one correspondence with the plurality of mobile terminals. As a cast bearer is individually set, the proxy unicast bearer setting instruction is to individually transmit to each of the mobile terminals to the base station side wireless transmission/reception unit,
Further, the multicast data received from the core network is copied to a plurality of data paths for data transfer to each of the proxy unicast bearers set between the wireless base station and the plurality of mobile terminals. The multicast distribution system according to any one of claims 1 to 5, further comprising a multicast data copying unit. 7. The multicast distribution system according to claim 6, wherein the radio base station is provided with a synchronization control unit that controls transmission synchronization of the multicast data by the plurality of proxy unicast bearers on the downlink shared channel. The radio base station sends the multicast data to each mobile terminal via the core network, the radio base station and the proxy unicast bearer regardless of whether the mobile terminal is a model compatible with eMBMS. The multicast distribution system according to any one of claims 1 to 7, which transmits. The radio base station constructs a multicast bearer for instructing to construct a multicast bearer in place of the proxy unicast bearer based on the received multicast radio bearer construction instruction in a form in which a multicast traffic channel is mapped to a multicast channel. A multicast bearer setting instruction unit for transmitting an instruction to the base station-side wireless transmission/reception unit for the mobile terminal compatible with eMBMS,
The eMBMS-compatible mobile terminal receives the multicast bearer establishment instruction, thereby causing the terminal-side radio transceiver unit to establish a multicast bearer with the radio base station on the multicast traffic channel. Section and
The radio base station, when the number of connections of the mobile terminal corresponding to the eMBMS is equal to or more than a predetermined reference number, while transmitting the multicast data to the mobile terminal corresponding to the eMBMS via the multicast bearer, 8. When the number of connections of the mobile terminals compatible with eMBMS is less than the reference number, the multicast data is transmitted to each of the mobile terminals via the proxy unicast bearer. The multicast distribution system described in. It is connected to a core network by a physical line, and is configured to be capable of wirelessly delivering, to a mobile terminal, multicast data compliant with eMBMS (evolved Multimedia Broadcast Multicast Service) from the core network,
A multicast radio bearer construction instruction for constructing a multicast bearer for receiving the multicast data from the core network and a radio bearer for transmitting the multicast data with the mobile terminal from the core network. A multicast radio bearer construction instruction receiving unit, a base station side wireless transmission/reception unit, and a proxy unicast bearer serving as a proxy transmission path for the multicast data are set in a form in which a multicast traffic channel is mapped on a downlink shared channel. As described above, a substitute unicast bearer setting instruction unit for transmitting a substitute unicast bearer setting instruction based on the multicast radio bearer construction instruction to the base station side radio transceiver unit toward the mobile terminal is provided. Wireless base station.

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