JP5792498B2 - Base station and mobile communication system - Google Patents

Description

  The present invention relates to a radio terminal, a base station, and a mobile communication system capable of performing multi-base station cooperative communication.

  Generally, in a mobile communication system, a wireless terminal performs communication involving data transmission with one base station having the best downlink reception state.

  In recent years, for the purpose of improving the throughput of a radio terminal located at a cell edge, attention is paid to multi-base station cooperative communication, which is a technique in which one radio terminal executes communication involving data transmission with a plurality of base stations ( Patent Document 1).

  Such coordinated communication between multiple base stations is referred to as CoMP (Coordinated Multi-Point transmission) in 3GPP (3rd Generation Partnership Project), which is a standardization project for mobile communication systems. Discussions are planned for formulation (see Non-Patent Document 1).

Special table 2008-523665 gazette

3GPP TR 36.912 V9.3.0 (2010-06), Feasibility study for Further Advancements for E-UTRA (LTE-Advanced)

  However, the multiple base station cooperative communication described above has the following problems.

  First, there is a problem that it is difficult to obtain the throughput improvement effect by the multi-base station cooperative communication in a situation where the traffic load of each of the plurality of base stations to be subjected to the multi-base station cooperative communication is increasing.

  Secondly, the multiple base station cooperative communication leads to an increase in control information and signaling to be transmitted / received, that is, an increase in overhead as compared with a case where a wireless terminal performs wireless communication with one base station. The heavy use of station cooperative communication is not preferable from the viewpoint of overhead reduction.

  Then, an object of this invention is to provide the radio | wireless terminal, base station, and mobile communication system which can perform multiple base station cooperation communication in an appropriate condition.

A feature of the base station according to the present invention is a base station (e.g., base station eNB # 1) of a mobile communication system (mobile communication system 1) that performs radio communication with a radio terminal (radio terminal UE). A plurality of base stations that perform communication units (for example, wireless communication units 111, 112, and 113) and a plurality of base stations (for example, base stations eNB # 1 and eNB # 2) including the own station for communication involving data transmission. A base station control unit (control unit 140) that controls the base station radio communication unit to transmit information for starting the multi-base station coordinated communication to the radio terminal when it is determined to perform station coordinated communication; The base station control unit includes the plurality of base stations when the total amount of surplus resources in each radio section between the radio terminal and the plurality of base stations is greater than a first threshold. When you do cooperative communication And summary to be constant.

According to such a feature, the base station performs multi-base station cooperative communication between the plurality of base stations and the wireless terminal based on the surplus amount of resources in the respective wireless sections of the plurality of base stations including the own station. Decide whether to do it. Thereby, it is possible to prevent the multi-base station cooperative communication from being performed in a situation where the surplus amount of resources in the radio section of the plurality of base stations to be subjected to the multi-base station cooperative communication is small . Further, in a situation where there is a large amount of surplus resources in the radio section of a plurality of base stations that are the targets of the multi-base station cooperative communication, the multi-base station cooperative communication can be performed. Therefore, multiple base station cooperative communication can be performed in an appropriate situation.

Another feature of the base station according to the present invention is that, in the base station according to the feature described above, the base station radio communication unit receives the measurement result of the downlink received electric field strength of each of the plurality of base stations from the radio terminal. The base station control unit is a case where the total of the surplus resources of the radio sections of the plurality of base stations is larger than the first threshold, and each of the plurality of base stations The gist is to determine that the multi-base station cooperative communication is performed when the difference in the downlink received electric field strength is smaller than a second threshold (threshold P).

  Another feature of the base station according to the present invention is that, in the base station according to the above feature, the first threshold value is set according to a communication capability of the wireless terminal and / or an application executed by the wireless terminal. This is the gist.

  Another feature of the base station according to the present invention is that, in the base station according to the above feature, the base station control unit determines that the own station performs the base station cooperative communication, and the plurality of base stations When it is confirmed that another base station included in the base station decides to perform the multi-base station cooperative communication, information for starting the multi-base station cooperative communication is transmitted to the wireless terminal. The gist is to control the base station radio communication unit.

A feature of the mobile communication system according to the present invention is a mobile communication system (mobile communication system 1) having a plurality of base stations (for example, base stations eNB # 1 and eNB # 2) and a radio terminal (radio terminal UE). In addition, each of the plurality of base stations is accompanied by data transmission when the total amount of surplus resources in the respective radio sections between the radio terminal and the plurality of base stations is greater than a first threshold value. wherein the communication wireless terminal has decided to perform a plurality of base stations cooperative communication for executing said plurality of base stations, each of said plurality of base stations, and determines that the own station performs the plurality base stations cooperative communication And when it is confirmed that another base station included in the plurality of base stations has decided to perform the multiple base station cooperative communication, for starting the multiple base station cooperative communication Wireless information To increase the transmission end to the.

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless terminal, base station, and mobile communication system which can perform multiple base station cooperation communication in an appropriate condition can be provided.

It is a whole schematic block diagram of the mobile communication system which concerns on 1st Embodiment and 2nd Embodiment. It is a figure which shows the cell structural example of the base station which concerns on 1st Embodiment and 2nd Embodiment. It is a block diagram which shows the structure of the base station which concerns on 1st Embodiment and 2nd Embodiment. It is a figure for demonstrating the calculation method of the backhaul traffic surplus amount which concerns on 1st Embodiment and 2nd Embodiment. It is a block diagram which shows the structure of the radio | wireless terminal which concerns on 1st Embodiment and 2nd Embodiment. It is an operation | movement sequence diagram which shows the whole operation | movement of the mobile communication system which concerns on 1st Embodiment. It is a flowchart which shows the determination process which concerns on 1st Embodiment and 2nd Embodiment. It is a figure for demonstrating the uplink multiple base station cooperation communication which concerns on 1st Embodiment and 2nd Embodiment. It is a figure for demonstrating the downlink multiple base station cooperation communication which concerns on 1st Embodiment and 2nd Embodiment. It is an operation | movement sequence diagram which shows the whole operation | movement of the mobile communication system which concerns on 2nd Embodiment. It is an operation | movement sequence diagram which shows the whole operation | movement of the mobile communication system which concerns on 3rd Embodiment.

  The first to third embodiments of the present invention and other embodiments will be described with reference to the drawings. In the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) First Embodiment Hereinafter, (1.1) Outline of mobile communication system, (1.2) Detailed configuration of mobile communication system, (1.3) Operation of mobile communication system, 1.4) Description will be given in the order of the effects of the first embodiment.

(1.1) Overview of Mobile Communication System FIG. 1 is an overall schematic configuration diagram of a mobile communication system 1 according to the first embodiment. The mobile communication system 1 is configured based on LTE (Long Term Evolution) whose specifications are established by 3GPP.

  As illustrated in FIG. 1, the mobile communication system 1 includes a radio terminal UE, a plurality of base stations eNB (eNB # 1 to eNB # 3), a plurality of mobility management devices MME, and a plurality of gateway devices S-GW. Have

  The radio terminal UE is a radio communication device possessed by a user and is also referred to as a user device. The radio terminal UE performs communication involving data transmission with one or a plurality of base stations eNB. The form in which the radio terminal UE communicates with one base station eNB is a normal communication form, and the form in which the radio terminal UE communicates simultaneously with a plurality of base stations eNB is the multiple base station cooperative communication described above.

  A plurality of base stations eNB constitutes an E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network). Each of the plurality of base stations eNB forms a communication area that should provide a service to the radio terminal UE. The communication area of each base station eNB is configured using one or a plurality of cells that are the minimum unit of the communication area. In the following description, a cell configuration in which the communication area of each base station eNB is composed of three cells will be described as an example.

  The base stations eNB adjacent to each other can communicate with each other via an X2 interface which is a logical interface that provides a communication line between base stations. Control signals used for header compression, packet management, handover control, and the like are transmitted / received via the X2 interface between adjacent base stations eNB.

  Each base station eNB is connected to the EPC via a backhaul network (see FIGS. 8 and 9). A communication line set on the backhaul network between each base station eNB and EPC is referred to as a backhaul line.

  Each of the plurality of base stations eNB communicates with the core network EPC, specifically, the mobility management device MME and the gateway device S-GW via an S1 interface that is a logical interface that provides a communication line with the core network EPC. Is possible. The mobility management device MME and / or the gateway device S-GW corresponds to a core network device.

  The mobility management apparatus MME mainly executes a control plane function for enabling user authentication, paging, interconnection with other systems, and the like. The mobility management device MME controls the base station eNB via an S1-MME interface which is a kind of S1 interface.

  The gateway device S-GW performs a bearer plane (also referred to as user plane) function for transferring user data packets. The gateway device S-GW transmits and receives user data packets to and from the base station eNB via an S1-U interface which is a kind of S1 interface.

  FIG. 2 is a diagram illustrating a cell configuration example of the base stations eNB # 1 to eNB # 3. For convenience of explanation, a regular hexagonal communication area is illustrated, but in reality, the end of each communication area overlaps with the end of another communication area.

  As illustrated in FIG. 2, the base station eNB # 1 forms a communication area including three cells, cell A to cell C. Similarly, the base station eNB # 2 forms a communication area composed of three cells D to F, and the base station eNB # 3 defines a communication area composed of three cells G to I. Forming.

  In the example of FIG. 2, the radio terminal UE is located at the boundary between the cell B of the base station eNB # 1 and the cell D of the base station eNB # 2. In such a cell boundary part, the radio terminal UE cannot obtain a good reception state for both the base station eNB # 1 and the base station eNB # 2. Therefore, as will be described later, the mobile communication system 1 has a configuration for performing multi-base station cooperative communication.

(1.2) Detailed Configuration of Mobile Communication System Next, a detailed configuration of the mobile communication system 1 will be described in the order of (1.2.1) configuration of base station and (1.2.2) configuration of radio terminal. .

(1.2.1) Configuration of Base Station FIG. 3 is a block diagram showing the configuration of the base station eNB.

  As illustrated in FIG. 3, the base station eNB includes a base station main body 100 and three radio communication units 111 to 113 corresponding to the three cells. Each of the wireless communication units 111 to 113 is connected to the base station main body 100 via, for example, a CPRI (Common Public Radio Interface). Base station main body 100 includes network communication unit 120, storage unit 130, and control unit 140.

  Each of the wireless communication units 111 to 113 is configured to perform wireless communication via an antenna. For transmission, each of the wireless communication units 111 to 113 performs up-conversion and amplification of the baseband signal input from the control unit 140 and outputs the wireless signal from the antenna. For reception, each of the wireless communication units 111 to 113 outputs a baseband signal to the control unit 140 after performing amplification and down-conversion of the reception signal input from the antenna. In addition, each of the wireless communication units 111 to 113 transmits a reference signal. The reference signal is configured to identify a transmission source (transmission source base station and / or transmission source cell).

  The network communication unit 120 is connected to a backhaul network (backhaul line), and performs communication with the gateway device S-GW and / or the mobility management device MME using the S1 interface. The network communication unit 120 performs inter-base station communication with an adjacent base station using the X2 interface.

  The storage unit 130 is configured using, for example, a memory, and stores various types of information used for control by the control unit 140 and the like. The control unit 140 is configured using, for example, a CPU, and controls various functions of the base station eNB.

  In the base station eNB configured as described above, the control unit 140 periodically measures the traffic volume of data transmitted and received by the network communication unit 120 via the backhaul line, and based on the measured traffic volume, The traffic surplus amount of the line (hereinafter referred to as “backhaul traffic surplus amount”) is periodically calculated. In addition, the control unit 140 controls the wireless communication units 111 to 113 so that information indicating the calculated backhaul traffic surplus amount is included in the broadcast information and transmitted. The wireless communication units 111 to 113 transmit broadcast information using a broadcast channel. The broadcast information is configured to identify a transmission source (transmission source base station and / or transmission source cell).

  FIG. 4 is a diagram for explaining a method of calculating the backhaul traffic surplus.

  As shown in FIG. 4, the backhaul traffic surplus amount is a value obtained by subtracting the average traffic amount for the past one minute from the backhaul traffic upper limit value, and is expressed in units of Mbps, for example. In the present embodiment, the backhaul traffic surplus amount will be described as a surplus amount of a line including the backhaul traffic. The backhaul traffic surplus amount may be the traffic surplus amount of the S1 interface, or may be the sum of the traffic surplus amount of the S1 interface and the traffic surplus amount of the X2 interface.

  The backhaul traffic upper limit value is an upper limit value of the amount of traffic that the network communication unit 120 can transmit and receive via the backhaul line, and the physical cable material, the type of connector, and the logical setting of the network communication unit 120 Determined by. The average traffic amount for the past one minute is an average value of the traffic amount transmitted and received by the network communication unit 120 via the backhaul line in the most recent one minute.

(1.2.2) Configuration of Radio Terminal FIG. 5 is a block diagram illustrating a configuration of the radio terminal UE.

  As illustrated in FIG. 5, the radio terminal UE includes a radio communication unit 210, a user interface unit 220, a storage unit 230, a control unit 240, and a battery 250.

  The radio communication unit 210 is configured to perform radio communication with the base station eNB via an antenna. For transmission, the radio communication unit 210 performs up-conversion and amplification of the baseband signal input from the control unit 240 and outputs the radio signal from the antenna. For reception, the radio communication unit 210 performs amplification and down-conversion of the received signal input from the antenna, and then outputs a baseband signal to the control unit 240.

  The radio communication unit 210 includes a received field strength measuring unit 211 that measures the field strength of received signals from a plurality of base stations eNB (hereinafter referred to as “downlink received field strength”) for each cell. The reception field strength measurement unit 211 outputs the measurement result of the downlink reception field strength to the control unit 240.

  The user interface unit 220 is a display, a button, or the like that functions as an interface with the user. The storage unit 230 is configured using, for example, a memory, and stores various types of information used for controlling the radio terminal UE. The control unit 240 is configured using, for example, a CPU, and controls various functions included in the radio terminal UE. The battery 250 stores power to be supplied to each block of the radio terminal UE.

  In the radio terminal UE configured as described above, the control unit 240 acquires information indicating the backhaul traffic surplus amount included in the broadcast information received by the radio communication unit 210. The control unit 240 is based on the backhaul traffic surplus amount of each of the plurality of base stations eNB to be subjected to the coordinated communication of the plurality of base stations, and the downlink received electric field strength measured for each cell of the plurality of base stations eNB. Then, it is determined whether or not to perform multi-base station cooperative communication with the plurality of base stations eNB.

  Specifically, the control unit 240 is a case where the total traffic surplus amount of each of the plurality of base stations eNB is larger than the threshold S, and is measured for each cell of the plurality of base stations eNB. When the difference of the downlink received electric field strength is smaller than the threshold value P, it is determined to perform the multiple base station cooperative communication with the multiple base stations eNB. In the present embodiment, the threshold value S is stored in advance in the storage unit 130 as a value corresponding to the maximum communication speed of the radio terminal UE. The threshold value P is stored in advance in the storage unit 130 as an allowable range of the electric field strength difference value.

(1.3) Operation of Mobile Communication System Next, regarding the operation of the mobile communication system 1, (1.3.1) Overall operation, (1.3.2) Judgment processing, (1.3.3) Up direction Multi-base station cooperative communication and (1.3.4) downlink multi-base station cooperative communication will be described in this order.

(1.3.1) Overall Operation FIG. 6 is an operation sequence diagram showing the overall operation of the mobile communication system 1 according to the first embodiment. In the present embodiment, in the configuration described in FIG. 2, the wireless terminal UE receives a reference signal from the cell B of the base station eNB # 1 and a reference signal from the cell D of the base station eNB # 2. The operation will be described.

  As illustrated in FIG. 6, in step S101, the radio terminal UE receives a reference signal from the cell B of the base station eNB # 1. In step S102, the radio terminal UE receives a reference signal from the cell D of the base station eNB # 2.

  In step S103, the radio terminal UE measures the downlink received electric field strengths of the reference signal corresponding to the cell B of the base station eNB # 1 and the reference signal corresponding to the cell D of the base station eNB # 2.

  In step S104, the base station eNB # 1 calculates the backhaul traffic surplus amount of the own station. In step S105, the base station eNB # 2 calculates the backhaul traffic surplus amount of the own station.

  In step S106, the base station eNB # 1 transmits broadcast information including information indicating the backhaul traffic surplus calculated in step S104 from the cell B. In step S107, the base station eNB # 2 transmits broadcast information including information indicating the backhaul traffic surplus calculated in step S105 from the cell D. The radio terminal UE receives broadcast information from the cell B of the base station eNB # 1 and broadcast information from the cell D of the base station eNB # 2.

  In step S108, the radio terminal UE acquires the backhaul traffic surplus amount of the base station eNB # 1 and the backhaul traffic surplus amount of the base station eNB # 2 from each broadcast information received in step S107.

  In step S109, the radio terminal UE receives the downlink received field strength of the cell B of the base station eNB # 1, the downlink received field strength of the cell D of the base station eNB # 2, and the backhaul traffic surplus amount of the base station eNB # 1. On the basis of the backhaul traffic surplus of the base station eNB # 2 and whether to communicate with either the cell B of the base station eNB # 1 or the cell D of the base station eNB # 2, or the base station eNB # It is determined whether to perform multi-base station cooperative communication with one cell B and the cell D of the base station eNB # 2. Details of the determination process will be described later.

  If it is determined that the multi-base station cooperative communication is to be performed (step S110; YES), in step S111, the radio terminal UE determines that the base station eNB # 1 cell B and the base station eNB # 2 cell D Start station cooperative communication. Details of the multiple base station cooperative communication will be described later.

  On the other hand, when it is determined to perform communication with either the cell B of the base station eNB # 1 or the cell D of the base station eNB # 2 (step S110; NO), in step S112, the radio terminal UE Communication between the cell B of the eNB # 1 and the cell D of the base station eNB # 2 having a relatively high downlink reception electric field strength is started.

(1.3.2) Determination Process FIG. 7 is a flowchart showing details of the determination process executed by the radio terminal UE, that is, step S109 of FIG.

  As shown in FIG. 7, in step S201, the radio terminal UE receives the backhaul traffic surplus amount m [Mbps], which is information from the cell B of the base station eNB # 1, and the cell D of the base station eNB # 2. The sum of the backhaul traffic surplus amount n [Mbps] as information is calculated, and the value is compared with a threshold value S [Mbps] corresponding to the maximum communication speed of the radio terminal UE.

  When the sum of the backhaul traffic surplus amounts is smaller than the threshold S (step S201; NO), both the base stations eNB # 1 and eNB # 2 have a small backhaul traffic surplus amount. The UE determines to perform data communication by selecting the higher downlink reception electric field strength. On the other hand, when the sum of the backhaul traffic surplus amounts is greater than or equal to the threshold S (step S201; YES), the radio terminal UE advances the process to step S203.

  In step S203, the radio terminal UE receives the downlink received electric field strength x [dBm] measured for the cell B of the base station eNB # 1, and the downlink received electric field strength y [dBm] measured for the cell D of the base station eNB # 2. Is calculated, and it is determined whether or not the value is equal to or less than the threshold value P.

  When the difference in downlink received electric field strength is larger than the threshold value P (step S203; NO), it can be considered that the radio terminal UE is located near one of the base stations eNB # 1 and eNB # 2, In step S202, the radio terminal UE determines to perform data communication by selecting a higher downlink reception electric field strength. On the other hand, when the difference in downlink received electric field strength is equal to or less than the threshold value P (step S203; YES), the radio terminal UE advances the process to step S204.

  In step S204, the radio terminal UE determines to perform data communication using both the cell B of the base station eNB # 1 and the cell D of the base station eNB # 2, that is, multi-base station cooperative communication.

(1.3.3) Uplink Multiple Base Station Cooperative Communication FIG. 8 is a diagram for explaining uplink multiple base station cooperative communication.

  As shown in FIG. 8, first, the radio terminal UE divides uplink user data generated by the application being executed, stores the divided data i in the payload of the packet for the cell D, and divides the divided data ii. Stored in the payload of the packet for cell B.

  The packet for cell D includes, as header information, transmission destination cell information “D”, division partner cell information “B”, and division packet combination identifier “Θ” in addition to the transmission destination IP address and the like. The packet for cell B includes, as header information, transmission destination cell information “B”, division partner cell information “D”, and division packet combination identifier “Θ” in addition to the transmission destination IP address and the like.

  The divided packet combining identifier is an identifier for identifying a packet to be combined. The radio terminal UE gives a new divided packet combination identifier for each pair of packets to be combined. The radio terminal UE transmits a packet for cell D and a packet for cell B.

  Secondly, when receiving the packet for cell D, the base station eNB # 2 relays the received packet for cell D to the gateway device S-GW of the core network EPC via the backhaul line. Similarly, when receiving the packet for cell B, the base station eNB # 1 relays the received packet for cell B to the gateway device S-GW of the core network EPC via the backhaul line.

  Third, when the gateway device S-GW receives the packet for the cell D and the packet for the cell B, the gateway device S-GW collates the header information of each of the packet for the cell D and the packet for the cell B. Specifically, the gateway device S-GW checks whether the destination cell information “D” of the packet for the cell D matches the division partner cell information “D” of the packet for the cell B, and the cell D Cell packet destination packet information “B” and cell B packet destination cell information “B” match, and cell D packet split packet combination identifier “Θ” and cell It is confirmed whether or not the divided packet combination identifier “Θ” of the packet for B matches. When all the confirmation results are OK (match), the gateway device S-GW determines that the packet for the cell D and the packet for the cell B should be combined.

  When determining that the packets should be combined, the gateway device S-GW extracts and combines the divided data i and ii included in the packets. The gateway device S-GW transfers the original user data obtained by the combination to the Internet or another mobile communication system according to the destination IP address or the like.

(1.3.4) Downlink Multiple Base Station Cooperative Communication FIG. 9 is a diagram for explaining downlink multiple base station cooperative communication. The processing procedure of downlink multi-base station cooperative communication is the same as that of uplink multi-base station cooperative communication, but the differences will be described here.

  As shown in FIG. 9, first, when the gateway device S-GW receives downlink user data transferred from the Internet or another mobile communication system, the gateway device S-GW divides the user data and divides the user data i ′. Is stored in the payload of the packet for the cell B, and the divided data ii ′ is stored in the payload of the packet for the cell D.

  The packet for cell B includes, as header information, destination cell information “B”, split partner cell information “D”, and split packet combination identifier “Δ” in addition to the destination IP address and the like. The packet for cell D includes, as header information, transmission destination cell information “D”, division partner cell information “B”, and division packet combination identifier “Δ” in addition to the transmission destination IP address and the like.

  The divided packet combining identifier is an identifier for identifying a packet to be combined. The gateway device S-GW gives a new divided packet combination identifier for each pair of packets to be combined. The gateway device S-GW transmits the packet for the cell D and the packet for the cell B.

  Secondly, when the base station eNB # 1 receives the cell B packet via the backhaul line, the base station eNB # 1 transmits the received cell B packet to the radio terminal UE. Similarly, when the base station eNB # 2 receives the packet for cell D via the backhaul line, the base station eNB # 2 transmits the received packet for cell D to the radio terminal UE.

  Thirdly, when receiving the packet for cell B and the packet for cell D, the radio terminal UE collates the header information of the packet for cell B and the packet for cell D, respectively. When determining that each packet is to be combined, the radio terminal UE extracts and combines the divided data i ′ and ii ′ included in each packet, and passes them to the application being executed.

(1.4) Effects of the First Embodiment As described above, according to the first embodiment, the radio terminal UE receives the respective back signals of the base stations eNB # 1 and eNB # 2 in addition to the downlink received electric field strength. Whether or not to perform multi-base station cooperative communication with the base stations eNB # 1 and eNB # 2 is determined based on the excess amount of whole traffic.

  Thereby, in the situation where the backhaul traffic load of base station eNB # 1 and eNB # 2 is increasing, it can determine not to perform multiple base station cooperation communication. Moreover, in a situation where the backhaul traffic load of the base stations eNB # 1 and eNB # 2 is low, it is possible to determine to perform multi-base station cooperative communication. Therefore, multiple base station cooperative communication can be performed in an appropriate situation.

  In 1st Embodiment, radio | wireless terminal UE is a case where the sum total of each backhaul traffic surplus of base station eNB # 1 and eNB # 2 is larger than threshold value S, and cell of base station eNB # 1 When the difference between the downlink received electric field strengths measured for each cell B of B and the base station eNB # 2 is smaller than the threshold P, it is determined that the multi-base station cooperative communication is performed. That the sum of the backhaul traffic surplus amounts of the base station eNB # 1 and the base station eNB # 2 is larger than the threshold value S means that a throughput improvement effect by multi-base station cooperative communication can be obtained. Further, the difference in downlink received electric field strength measured for each of the cell B of the base station eNB # 1 and the cell D of the eNB # 2 is smaller than the threshold P means that the cell B and the base station eNB # of the base station eNB # 1 The downlink received electric field strengths of the two cells D are equal, which means that the radio terminal UE is located near the intermediate point between the base station eNB # 1 and the base station eNB # 2. Such a situation is a situation suitable for performing multi-base station cooperative communication, and multi-base station cooperative communication can be performed in an appropriate situation.

(2) Second Embodiment In the first embodiment described above, the radio terminal UE determines whether or not to perform multi-base station cooperative communication. In the second embodiment, the determination is performed by the base station eNB. Assumed to be performed. Hereinafter, a difference between the second embodiment and the first embodiment will be described.

(2.1) Configuration of Mobile Communication System The radio terminal UE according to the second embodiment has the configuration shown in FIG. The control part 240 of the radio | wireless terminal UE which concerns on 2nd Embodiment controls the radio | wireless communication part 210 so that the measurement result by the received electric field strength measurement part 211 may be transmitted to a serving cell. Such a measurement result report may be referred to as a measurement report. In addition, the control unit 240 controls the wireless communication unit 210 to transmit information indicating the capability (maximum communication speed) of the terminal itself to the serving cell. Such capability information may be referred to as a UE category or a UE class.

  The base station eNB according to the second embodiment has the configuration shown in FIG. The network communication unit 120 of the base station eNB according to the second embodiment receives information indicating the backhaul traffic surplus amount of the adjacent base station from the adjacent base station via the X2 interface. Further, the radio communication unit 111, 112, or 113 of the base station eNB according to the second embodiment receives the measurement results of the downlink received electric field strengths of the own station and the adjacent base station from the radio terminal UE. Further, the control unit 140 is a case where the total traffic surplus of each of the own station and the adjacent base station is larger than the threshold S, and the downlink received electric field strength of each of the own station and the adjacent base station base station. When the difference is smaller than the threshold value P, it is determined that the base station and the adjacent base station base station and the radio terminal UE perform multi-base station cooperative communication.

(2.2) Operation of Mobile Communication System FIG. 10 is an operation sequence diagram showing the overall operation of the mobile communication system 1 according to the second embodiment. Here, the operation under the situation where the radio terminal UE uses the cell B of the base station eNB # 1 as a serving cell and the radio terminal UE receives a reference signal from the cell D of the base station eNB # 2.

  As illustrated in FIG. 10, in step S301, the radio terminal UE receives a reference signal from the cell B of the base station eNB # 1. In step S302, the radio terminal UE receives a reference signal from the cell D of the base station eNB # 2.

  In step S303, the radio terminal UE measures the downlink received field strengths of the reference signal corresponding to the cell B of the base station eNB # 1 and the reference signal corresponding to the cell D of the base station eNB # 2.

  In step S304, the radio terminal UE transmits a measurement report including information indicating the downlink received electric field strength of the cell B of the base station eNB # 1 and information indicating the downlink received electric field strength of the cell D of the base station eNB # 2 on the serving cell. Transmit to a certain cell B. Further, the radio terminal UE notifies the cell B of the UE category indicating the capability (maximum communication speed) of the terminal itself.

  In step S305, the base station eNB # 1 obtains the downlink received field strength of the cell B of the base station eNB # 1 and the downlink received field strength of the cell D of the base station eNB # 2 from the measurement report from the radio terminal UE. To do.

  In step S306, the base station eNB # 1 transmits a transmission request for information indicating the backhaul traffic surplus amount to the base station eNB # 2 having the cell D using the X2 interface. In step S307, the base station eNB # 1 calculates the backhaul traffic surplus amount of the own station.

  In step S308, the base station eNB # 2 calculates its own backhaul traffic surplus in response to a request from the base station eNB # 1. In step S309, the base station eNB # 2 transmits information indicating the backhaul traffic surplus amount to the base station eNB # 1 using the X2 interface.

  In step S310, the base station eNB # 1 acquires the backhaul traffic surplus calculated in step S307 and the backhaul traffic surplus received in step S309.

  In step S311, the base station eNB # 1 determines the downlink received field strength of the cell B of the base station eNB # 1, the downlink received field strength of the cell D of the base station eNB # 2, and the backhaul traffic of the base station eNB # 1. Whether the radio terminal UE performs communication with one of the cell B of the base station eNB # 1 or the cell D of the base station eNB # 2 based on the surplus amount and the backhaul traffic surplus amount of the base station eNB # 2 The base station eNB # 1 determines whether or not the radio terminal UE is to perform multi-base station cooperative communication with the cell B of the base station eNB # 1 and the cell D of the base station eNB # 2. The procedure of the determination process is the same as that in the first embodiment (see FIG. 7).

  When it is determined that the multi-base station cooperative communication is to be performed (step S312; YES), in steps S314 to S316, the base station eNB # 1 sends a start request for the multi-base station cooperative communication to the gateway device S-GW, the base station It transmits to station eNB # 2 and radio | wireless terminal UE.

  In step S317, the radio terminal UE starts multi-base station cooperative communication with the cell B of the base station eNB # 1 and the cell D of the base station eNB # 2. The details of the multiple base station cooperative communication are the same as in the first embodiment (see FIGS. 8 and 9).

  On the other hand, when it is determined to perform communication with one of the cell B of the base station eNB # 1 or the cell D of the base station eNB # 2 (step S312; NO), in step S313, the cell B of the base station eNB # 1 or The radio terminal UE is instructed to start communication with the cell D of the base station eNB # 2 having a relatively high downlink received electric field strength.

(2.3) Effects of the Second Embodiment As described above, according to the second embodiment, the base station eNB # 1 has the base station eNB # 1 and the eNB # 2 in addition to the downlink received electric field strength. Whether or not to perform base station eNB # 1 and eNB # 2 and multi-base station cooperative communication with the radio terminal UE is determined based on the backhaul traffic surplus amount.

  Thereby, in the situation where the backhaul traffic load of base station eNB # 1 and eNB # 2 is increasing, it can be made not to perform multi-base station cooperative communication. In addition, in a situation where the backhaul traffic load of the base stations eNB # 1 and eNB # 2 is low, multiple base station cooperative communication can be performed. Therefore, multiple base station cooperative communication can be performed in an appropriate situation.

  In the second embodiment, the base station eNB # 1 is a case where the sum of the backhaul traffic surplus amounts of the base stations eNB # 1 and eNB # 2 is larger than the threshold S, and the base station eNB # 1 When the difference between the downlink received electric field strengths measured for each cell B and each cell D of the base station eNB # 2 is smaller than the threshold value P, it is determined that the multi-base station cooperative communication is performed. That the sum of the backhaul traffic surplus amounts of the base station eNB # 1 and the base station eNB # 2 is larger than the threshold value S means that a throughput improvement effect by multi-base station cooperative communication can be obtained. Further, the difference in downlink received electric field strength measured for each of the cell B of the base station eNB # 1 and the cell D of the eNB # 2 is smaller than the threshold P means that the cell B and the base station eNB # of the base station eNB # 1 The downlink received electric field strengths of the two cells D are equal, which means that the radio terminal UE is located near the intermediate point between the base station eNB # 1 and the base station eNB # 2. Such a situation is a situation suitable for performing multi-base station cooperative communication, and multi-base station cooperative communication can be performed in an appropriate situation.

(3) Third Embodiment In the above-described second embodiment, whether or not to perform multi-base station cooperative communication is determined by one base station eNB, but in the third embodiment, the determination is performed by a plurality of base stations. This is performed in each of a plurality of base stations eNB to be subjected to base station cooperative communication. Since the configuration of the mobile communication system according to the third embodiment is the same as that of the second embodiment, the operation of the mobile communication system according to the third embodiment will be described below.

  FIG. 11 is an operation sequence diagram showing an overall operation of the mobile communication system 1 according to the third embodiment. In the present embodiment, in the configuration described in FIG. 2, the wireless terminal UE receives a reference signal from the cell B of the base station eNB # 1 and a reference signal from the cell D of the base station eNB # 2. The operation will be described.

  As illustrated in FIG. 11, in step S401, the radio terminal UE receives a reference signal from the cell B of the base station eNB # 1. In step S402, the radio terminal UE receives a reference signal from the cell D of the base station eNB # 2.

  In step S403, the radio terminal UE measures the downlink received field strengths of the reference signal corresponding to the cell B of the base station eNB # 1 and the reference signal corresponding to the cell D of the base station eNB # 2.

  In step S404, the radio terminal UE transmits information indicating the downlink received field strength of the cell B of the base station eNB # 1 and information indicating the capability (maximum communication speed) of the terminal to the base station eNB # 1. The base station eNB # 1 receives and stores these pieces of information.

  In step S405, the radio terminal UE transmits information indicating the downlink received field strength of the cell D of the base station eNB # 2 and information indicating the capability (maximum communication speed) of the terminal to the base station eNB # 2. . The base station eNB # 2 receives and stores these pieces of information.

  In step S406, the base station eNB # 1 calculates the backhaul traffic surplus amount of the own station (base station eNB # 1) using the calculation method described in the first embodiment. In step S407, the base station eNB # 2 calculates the backhaul traffic surplus amount of the own station (base station eNB # 2) using the calculation method described in the first embodiment.

  In step S408, the base station eNB # 1 transmits information indicating the downlink received electric field strength of the cell B obtained from the radio terminal UE in step S404 and the backhaul traffic surplus amount of the own station obtained by calculation in step S406. Is transmitted to the base station eNB # 2 using the X2 interface. The base station eNB # 2 receives and stores these pieces of information.

  In step S409, the base station eNB # 2 receives information indicating the downlink received electric field strength of the cell D obtained from the radio terminal UE in step S405, and the backhaul traffic surplus amount of the own station obtained by calculation in step S407. Is transmitted to the base station eNB # 1 using the X2 interface. The base station eNB # 1 receives and stores these pieces of information.

  In step S410, the base station eNB # 1 receives the downlink received field strength of cell B and the capability (maximum communication speed) of the radio terminal UE obtained from the radio terminal UE in step S404, and the base station eNB # 2 from the base station eNB # 2 in step S409. The obtained downlink received electric field strength of the cell D, the backhaul traffic surplus amount of the base station eNB # 1 calculated in step S406, and the base station eNB # obtained from the base station eNB # 2 in step S409 The base station eNB # 1 cell B or the base station eNB # 2 cell D to communicate with the radio terminal UE based on the backhaul traffic surplus of 2 or the base station eNB # 1 cell B determines whether or not the radio terminal UE is to perform multi-base station cooperative communication with the cell D of the base station eNB # 2. The procedure of the determination process is the same as that in the first embodiment (see FIG. 7).

  In step S411, the base station eNB # 2 receives the downlink reception field strength of the cell B obtained from the base station eNB # 1 in step S408, the downlink reception field strength of the cell D obtained from the radio terminal UE in step S405, and The capability (maximum communication speed) of the radio terminal UE, the backhaul traffic surplus of the base station eNB # 1 obtained from the base station eNB # 1 in step S408, and the base station eNB # obtained by calculation in step S407 The base station eNB # 1 cell B or the base station eNB # 2 cell D to communicate with the radio terminal UE based on the backhaul traffic surplus of 2 or the base station eNB # 1 cell B determines whether or not the radio terminal UE is to perform multi-base station cooperative communication with the cell D of the base station eNB # 2. The procedure of the determination process is the same as that in the first embodiment (see FIG. 7).

  When the base station eNB # 1 determines that the radio terminal UE performs multi-base station cooperative communication (step S412; YES), in step S413, the base station eNB # 2 sends a notification message to that effect using the X2 interface. Send to. The notification message includes identification information of a radio terminal UE that is to perform multi-base station cooperative communication, and a cell of the base station eNB # 1 that is to cooperate with another cell in the multi-base station cooperative communication (in this embodiment, cell B). ) Identification information. The base station eNB # 2 receives the notification message.

  In addition, when the base station eNB # 2 determines that the radio terminal UE performs multi-base station cooperative communication (step S414; YES), in step S415, the base station eNB uses a notification message to that effect using the X2 interface. Send to # 1. The notification message includes identification information of a radio terminal UE that should perform multi-base station cooperative communication, and a cell of the base station eNB # 2 that should cooperate with another cell in the multi-base station cooperative communication (in this embodiment, cell D ) Identification information. The base station eNB # 1 receives the notification message.

  In step S416, the base station eNB # 1 determines, based on the notification message obtained from the base station eNB # 2 in step S415, the other base station eNB to be coordinated with respect to the radio terminal UE that is to perform multi-base station cooperative communication. It is confirmed whether or not the # 2 cell (cell D in this embodiment) is determined to perform the coordinated base station communication. When the confirmation result is OK (step S416; YES), in step S417, the base station eNB # 1 transmits a split transmission start instruction to the radio terminal UE.

  In step S418, the base station eNB # 2 determines, based on the notification message obtained from the base station eNB # 1 in step S413, the other base station eNB to be coordinated with respect to the radio terminal UE that is to perform multi-base station cooperative communication. Whether or not the # 1 cell (cell B in this embodiment) is determined to perform the multi-base station cooperative communication is also confirmed. When the confirmation result is OK (step S418; YES), in step S419, the base station eNB # 2 transmits a split transmission start instruction to the radio terminal UE.

  When the radio terminal UE receives a split transmission start instruction from each of the cell B of the base station eNB # 1 and the cell D of the base station eNB # 2, the radio terminal UE performs a split transmission process in step S420. For example, in step S420, the radio terminal UE divides uplink user data, stores the divided data i in the payload of the packet for the cell D, and stores the divided data ii in the payload of the packet for the cell B. As described in the first embodiment, the packet for cell D includes, as header information, transmission destination cell information “D”, division partner cell information “B”, and division packet combination identifier in addition to the transmission destination IP address and the like. Includes “Θ”. The packet for cell B includes, as header information, transmission destination cell information “B”, division partner cell information “D”, and division packet combination identifier “Θ” in addition to the transmission destination IP address and the like.

  In step S421, the radio terminal UE transmits a packet for cell B to the base station eNB # 1. In step S422, the base station eNB # 1 relays the packet for cell B received from the radio terminal UE to the gateway device S-GW of the core network EPC via the backhaul line. In step S423, the radio terminal UE transmits a packet for cell D to the base station eNB # 2. In step S424, the base station eNB # 2 relays the packet for the cell D received from the radio terminal UE to the gateway device S-GW of the core network EPC via the backhaul line.

  In step S425, the gateway device S-GW receives the packet for the cell D and the packet for the cell B, and collates the header information of each of the packet for the cell D and the packet for the cell B. For example, the gateway device S-GW checks whether the destination cell information “D” of the packet for the cell D matches the division partner cell information “D” of the packet for the cell B, and It is confirmed whether or not the cell information “B” to be divided matches the destination cell information “B” of the packet for the cell B, and the divided packet combination identifier “Θ” of the packet for the cell D and the packet for the cell B It is confirmed whether or not the divided packet combination identifier “Θ” in FIG. When all the confirmation results are OK (match), the gateway device S-GW determines that the packet for the cell D and the packet for the cell B should be combined, and is included in each packet. The divided data i and ii are extracted and combined. The gateway device S-GW transfers the original user data obtained by the combination to the Internet or another mobile communication system according to the destination IP address or the like.

  In step S426, the gateway device S-GW receives downlink user data transferred from the Internet or another mobile communication system, divides the user data, and divides the divided data i ′ into the payload of the packet for the cell B And the divided data ii ′ is stored in the payload of the packet for the cell D. As described in the first embodiment, the packet for cell B includes, as header information, transmission destination cell information “B”, division partner cell information “D”, and division packet combination identifier in addition to the transmission destination IP address and the like. Includes “Δ”. The packet for cell D includes, as header information, transmission destination cell information “D”, division partner cell information “B”, and division packet combination identifier “Δ” in addition to the transmission destination IP address and the like.

  In step S427, the gateway device S-GW transmits the packet for cell B to the base station eNB # 1. In step S428, the base station eNB # 1 transmits the packet for cell B received via the backhaul line to the radio terminal UE. In step S429, the gateway device S-GW transmits the packet for cell D to the base station eNB # 2. In Step S4230, the base station eNB # 2 transmits the packet for cell D received via the backhaul line to the radio terminal UE.

  In step S430, the radio terminal UE receives the packet for cell B and the packet for cell D, and collates the header information of each of the packet for cell B and the packet for cell D. When determining that the packets are to be combined, the radio terminal UE extracts and combines the divided data i ′ and ii ′ included in the packets.

  According to the third embodiment, in addition to the effects described in the second embodiment, the following effects can be obtained. Specifically, the determination whether or not to perform multi-base station cooperative communication can be performed more strictly by performing determination at each of the plurality of base stations eNB to be subjected to the multi-base station cooperative communication. .

(4) Other Embodiments As described above, the present invention has been described according to each embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In each embodiment described above, the threshold value S is set to a value corresponding to the communication capability of the radio terminal UE, specifically, the maximum communication speed of the radio terminal UE. However, the threshold value S may be set according to an application executed by the radio terminal UE. For example, when the application executed by the radio terminal UE is a voice call application or a streaming application that requires a low delay, the base station cooperative communication is performed by setting the threshold S lower than the standard value. You may make it carry out preferentially. In addition, when the application executed by the radio terminal UE is a file transfer application or the like that does not require a low delay, by setting the threshold value S higher than the standard value, the multi-base station cooperative communication is not performed as much as possible. It may be. Note that the threshold S may be set in consideration of both the communication capability (maximum communication speed) of the radio terminal UE and the application executed by the radio terminal UE.

  In each of the above-described embodiments, multi-base station cooperative communication using two base stations eNB has been described as an example. However, the present invention can also be applied to multi-base station cooperative communication using three or more base stations eNB. is there.

  In the first embodiment described above, each of the plurality of base stations eNB transmits information including backhaul traffic surplus information included in the broadcast information. However, the serving base station uses the base station cooperative communication to transmit back information. Information indicating the amount of excess hall traffic may be collected from adjacent base stations, and the collected information may be collectively reported to the radio terminal UE.

  In each of the above-described embodiments, the backhaul traffic surplus amount is used as a criterion for determining whether or not to perform multi-base station cooperative communication, but instead of the backhaul traffic surplus amount, another criterion that reflects the traffic load state is used. May be used. For example, instead of the backhaul traffic surplus amount, the resource surplus amount of the radio section (for example, the surplus amount of the resource block which is an allocation unit of the time frequency resource) may be used, and the surplus amount of hardware resources (for example, CPU surplus capacity or memory capacity surplus) may be used. However, in base stations that form multiple cells, the backhaul line is more likely to be a bottleneck than the radio section, and as a high-speed wireless communication service in the true sense that the backhaul side is not fast, no matter how much wireless resources are secured Since this does not hold, it is preferable to use the backhaul traffic surplus amount as a criterion for determining whether or not to perform multi-base station cooperative communication.

  In each of the embodiments described above, the base station eNB that forms a communication area composed of three cells has been described as an example. However, the present invention is also applied to an omni-type base station eNB that forms a communication area composed of one cell. Applicable.

  In each of the above-described embodiments, the determination process when starting multi-base station cooperative communication has been mainly described. However, the determination process according to each embodiment described above can also be applied to a determination of whether to continue or end the multi-base station cooperative communication after the multi-base station cooperative communication is started.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  MME ... mobility management device, S-GW ... gateway device, UE ... wireless terminal, eNB ... base station, 1 ... mobile communication system, 100 ... base station main body, 111, 112, 113 ... wireless communication unit, 120 ... network communication unit DESCRIPTION OF SYMBOLS 130 ... Memory | storage part 140 ... Control part 210 ... Wireless communication part 211 ... Received electric field strength measurement part 220 ... User interface part 230 ... Memory | storage part 240 ... Control part, 250 ... Battery

Claims (5)

A base station for a mobile communication system,
A base station wireless communication unit that performs wireless communication with a wireless terminal;
When the wireless terminal determines to perform multi-base station cooperative communication that executes communication involving data transmission with a plurality of base stations including its own station, information for starting the multi-base station cooperative communication is transmitted to the wireless terminal. A base station control unit that controls the base station radio communication unit to transmit to
With
The base station control unit performs the multi-base station cooperative communication when a total amount of surplus resources in each radio section between the radio terminal and the plurality of base stations is larger than a first threshold value. To decide ,
A base station characterized by that. The base station wireless communication unit receives the measurement result of the downlink received electric field strength of each of the plurality of base stations from the wireless terminal,
The base station control unit is a case where a total of surplus resources of the radio sections of the plurality of base stations is larger than the first threshold, and the base station control unit When the difference in downlink received electric field strength is smaller than the second threshold, it is determined to perform the multiple base station cooperative communication;
The base station according to claim 1 . The first threshold is set according to communication capability of the wireless terminal and / or an application executed by the wireless terminal.
The base station according to claim 1. The base station control unit determines that the own station performs the multi-base station cooperative communication, and when another base station included in the plurality of base stations performs the multi-base station cooperative communication. When it is confirmed that it has been determined, the base station radio communication unit is controlled to transmit information for starting the multi-base station cooperative communication to the radio terminal,
The base station according to claim 1. A mobile communication system having a plurality of base stations and wireless terminals,
Each of the plurality of base stations performs communication involving data transmission when the total amount of surplus resources in the respective wireless sections between the wireless terminal and the plurality of base stations is greater than a first threshold. wherein are determined with the wireless terminal performs multiple base stations cooperative communication for executing said plurality of base stations,
Each of the plurality of base stations is a case where the own station has decided to perform the multiple base station cooperative communication, and another base station included in the multiple base stations performs the multiple base station cooperative communication. When it is confirmed that it is determined to be performed, information for starting the multi-base station cooperative communication is transmitted to the wireless terminal,
A mobile communication system.

Images