Mobile communication system, user terminal, and base station

A mobile communication system according to an embodiment supports a cellular communication in which a data path passes through a network and a D2D communication that is a direct device-to-device communication in which a data path does not pass through the network. The mobile communication system comprises: an eNB 200 included in the network and configured to transmit D2D broadcast information; and a UE 100 configured to perform the D2D communication after receiving the D2D broadcast information from the eNB 200. The D2D broadcast information is information that enables the D2D communication even though the UE 100 is in a specific state in which a connection with the network is not established. The UE 100 performs the D2D communication in the specific state on the basis of the D2D broadcast information.

TECHNICAL FIELD

The prevent invention relates to a mobile communication system, a user terminal, and a base station which support D2D communication.

BACKGROUND ART

In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, it is considered to introduce communication between devices (Device to Device: D2D) as a new function to be specified in Release 12 or subsequent versions (see Non Patent Literature 1).

In the D2D communication, a plurality of neighboring user terminals perform a direct communication without passing through a network. That is, a data path of the D2D communication does not pass through the network. On the other hand, a data path of a normal communication (cellular communication) of a mobile communication system passes through the network.

CITATION LIST

Non Patent Literature

SUMMARY OF THE INVENTION

The D2D communication is assumed to be controlled at the initiative of the network. Thus, a user terminal is considered to perform the D2D communication in a state (a connected state) in which a connection with the network has been established. However, such a method has a problem of an increase in load and signaling of the network caused by the control of the D2D communication.

Therefore, the present invention provides a mobile communication system capable of suppressing an increase in load and signaling of a network caused by the control of D2D communication.

A mobile communication system according to the embodiment supports cellular communication in which a data path passes through a network and D2D communication that is direct device-to-device communication in which a data path does not pass through the network. The mobile communication system comprises: a base station that is included in the network and transmits broadcast information; and a user terminal that performs the D2D communication after receiving the broadcast information from the base station. The broadcast information is information that enables the D2D communication even though the user terminal is in a specific state in which a connection with the network is not established. The user terminal performs the D2D communication in the specific state on the basis of the broadcast information.

DESCRIPTION OF EMBODIMENTS

Overview of Embodiment

A mobile communication system according to a first embodiment and a second embodiment supports a cellular communication in which a data path passes through a network, and a D2D communication that is a direct device-to-device communication in which a data path does not pass through the network. The mobile communication system includes a base station included in the network and configured to transmit broadcast information, and a user terminal configured to receive the broadcast information from the base station and then performs the D2D communication. The broadcast information is information that enables the D2D communication even in a specific state in which the user terminal does not establish a connection with the network. The user terminal performs the D2D communication in the specific state on the basis of the broadcast information.

In the first embodiment, the specific state is an idle state indicating a state in which the user terminal does not establish the connection in a coverage of the network.

In the second embodiment, the specific state is a state in which the user terminal exists out of the coverage of the network.

In the second embodiment, the base station is a base station that manages a termination cell included in a termination area of the coverage.

In the first embodiment and the second embodiment, the broadcast information includes resource information indicating a radio resource permitted to be used in one of the D2D communication and a terminal discovery process for starting the D2D communication.

In the first embodiment and the second embodiment, the broadcast information includes power information indicating a maximum transmission power permitted in one of the D2D communication and a terminal discovery process for starting the D2D communication.

In the first embodiment, the base station does not use the radio resource permitted to be used in one of the D2D communication and the terminal discovery process, in the cellular communication.

In the first embodiment, in the case of establishing the connection before performing the D2D communication, the user terminal performs the D2D communication after disconnecting the connection on the basis of the broadcast information.

In the first embodiment, in response to the detection of interference to the D2D communication from another user terminal, the user terminal performing the D2D communication transmits, to the network, information indicating a request to avoid the interference after establishing the connection or in the process of establishing the connection.

In the second embodiment, in response to the detection of interference to the D2D communication from another user terminal, the user terminal performing the D2D communication determines to stop the D2D communication and transmits information indicating the stop of the D2D communication to a terminal with which the user terminal communicates.

In the first embodiment and the second embodiment, in response to the detection of interference to the D2D communication from another user terminal, the user terminal performing the D2D communication performs negotiation between terminals such that a radio resource used in a D2D terminal group including the user terminal is different from a radio resource used in a D2D terminal group including the another user terminal.

In the first embodiment and the second embodiment, in response to the detection of interference to the D2D communication from another user terminal, the user terminal performing the D2D communication changes a radio resource used in the D2D communication to another radio resource.

In the first embodiment and the second embodiment, the user terminal, which changes the radio resource used in the D2D communication to the another radio resource, broadcasts change information indicating a change to the another radio resource by using the another radio resource.

In the second embodiment, when another user terminal, which belongs to a D2D terminal group different from the D2D terminal group including the user terminal, receives the change information during the use of the another radio resource, the another user terminal notifies a serving cell of the another user terminal of the reception of the change information.

In the first embodiment and the second embodiment, when another user terminal, which belongs to a D2D terminal group different from the D2D terminal group including the user terminal, receives the change information during the use of the another radio resource, the another user terminal notifies the user terminal of the fact that the another radio resource is being used.

In a modification of the second embodiment, the user terminal performs the D2D communication by using a frequency hopping scheme. The broadcast information includes information indicating a hopping pattern permitted to be used in the D2D communication.

A user terminal according to the first embodiment and the second embodiment is used in a mobile communication system that supports a cellular communication in which a data path passes through a network, and a D2D communication that is a direct device-to-device communication in which a data path does not pass through the network. The user terminal includes a receiver configured to receive broadcast information from a base station included in the network, and a controller configured to perform the D2D communication after the receiver receives the broadcast information. The broadcast information is information that enables the D2D communication even in a specific state in which the user terminal does not establish a connection with the network. The controller performs the D2D communication in the specific state on the basis of the broadcast information.

A base station according to the first embodiment and the second embodiment is included in a network in a mobile communication system that supports a cellular communication in which a data path passes through a network, and a D2D communication that is a direct device-to-device communication in which a data path does not pass through the network. The base station includes a transmitter configured to transmit broadcast information that enables the D2D communication even in a specific state in which a user terminal does not establish a connection with the network.

First Embodiment

Hereinafter, with reference to the drawings, a description will be provided for an embodiment in a case where D2D communication is introduced to an LTE system which is one of mobile communication systems configured based on the 3GPP standards.

LTE System

FIG. 1is a configuration diagram of an LTE system according to the first embodiment. As illustrated inFIG. 1, the LTE system includes a plurality of UEs (User Equipment)100, E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network)10, and EPC (Evolved Packet Core)20. The E-UTRAN10corresponds to a radio access network and the EPC20corresponds to a core network. The E-UTRAN10and the EPC20configure a network of the LTE system.

The UE100is a mobile communication device and performs radio communication with a cell (a serving cell) with which a connection is established. The UE100corresponds to the user terminal.

The E-UTRAN10includes a plurality of eNBs200(evolved Node-B). The eNB200corresponds to a base station. The eNB200manages one or a plurality of cells and performs radio communication with the UE100which establishes a connection with the cell of the eNB200. It is noted that the “cell” is used as a term indicating a minimum unit of a radio communication area, and is also used as a term indicating a function of performing radio communication with the UE100.

The eNB200, for example, has a radio resource management (RRM) function, a function of routing user data, and a measurement control function for mobility control and scheduling.

The EPC20includes a plurality of MME (Mobility Management Entity)/S-GW (Serving-Gateway)300. The MME is a network node for performing various mobility controls and the like for the UE100and corresponds to a controller. The S-GW is a network node that performs control to transfer user data and corresponds to a mobile switching center. The EPC20including the MME/S-GW300accommodates the eNB200.

The eNBs200are connected mutually via an X2 interface. Furthermore, the eNB200is connected to the MME/S-GW300via an S1 interface.

Next, the configurations of the UE100and the eNB200will be described.

FIG. 2is a block diagram of the UE100. As illustrated inFIG. 2, the UE100includes an antenna101, a radio transceiver110, a user interface120, a GNSS (Global Navigation Satellite System) receiver130, a battery140, a memory150, and a processor160. The memory150and the processor160configure a controller. The UE100may not have the GNSS receiver130. Furthermore, the memory150may be integrally formed with the processor160, and this set (that is, a chip set) may be called a processor160′.

The antenna101and the radio transceiver110are used to transmit and receive a radio signal. The antenna101includes a plurality of antenna elements. The radio transceiver110converts a baseband signal output from the processor160into the radio signal, and transmits the radio signal from the antenna101. Furthermore, the radio transceiver110converts the radio signal received by the antenna101into the baseband signal, and outputs the baseband signal to the processor160.

The user interface120is an interface with a user carrying the UE100, and includes, for example, a display, a microphone, a speaker, various buttons and the like. The user interface120receives an operation from a user and outputs a signal indicating the content of the operation to the processor160. The GNSS receiver130receives a GNSS signal in order to obtain location information indicating a geographical location of the UE100, and outputs the received signal to the processor160. The battery140accumulates a power to be supplied to each block of the UE100.

The memory150stores a program to be executed by the processor160and information to be used for a process by the processor160. The processor160includes a baseband processor that performs modulation and demodulation, encoding and decoding and the like on the baseband signal, and a CPU (Central Processing Unit) that performs various processes by executing the program stored in the memory150. The processor160may further include a codec that performs encoding and decoding on sound and video signals. The processor160executes various processes and various communication protocols which will be described later.

FIG. 3is a block diagram of the eNB200. As illustrated inFIG. 3, the eNB200includes an antenna201, a radio transceiver210, a network interface220, a memory230, and a processor240. The memory230and the processor240constitute a controller.

The antenna201and the radio transceiver210are used to transmit and receive a radio signal. The antenna201includes a plurality of antenna elements. The radio transceiver210converts the baseband signal output from the processor240into the radio signal, and transmits the radio signal from the antenna201. Furthermore, the radio transceiver210converts the radio signal received by the antenna201into the baseband signal, and outputs the baseband signal to the processor240.

The network interface220is connected to the neighboring eNB200via the X2 interface and is connected to the MME/S-GW300via the S1 interface. The network interface220is used in communication performed on the X2 interface and communication performed on the S1 interface.

The memory230stores a program to be executed by the processor240and information to be used for a process by the processor240. The processor240includes the baseband processor that performs modulation and demodulation, encoding and decoding and the like on the baseband signal and a CPU that performs various processes by executing the program stored in the memory230. The processor240executes various processes and various communication protocols described later.

FIG. 4is a protocol stack diagram of a radio interface in the LTE system. As illustrated inFIG. 4, the radio interface protocol is classified into a layer1to a layer3of an OSI reference model, wherein the layer1is a physical (PHY) layer. The layer2includes a MAC (Media Access Control) layer, an RLC (Radio Link Control) layer, and a PDCP (Packet Data Convergence Protocol) layer. The layer3includes an RRC (Radio Resource Control) layer.

The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. Between the PHY layer of the UE100and the PHY layer of the eNB200, data is transmitted via the physical channel.

The MAC layer performs priority control of data, and a retransmission process and the like by hybrid ARQ (HARQ). Between the MAC layer of the UE100and the MAC layer of the eNB200, data is transmitted via a transport channel. The MAC layer of the eNB200includes a transport format of an uplink and a downlink (a transport block size and a modulation and coding scheme (MCS)) and a scheduler for determining a resource block to be assigned.

The RLC layer transmits data to an RLC layer of a reception side by using the functions of the MAC layer and the PHY layer. Between the RLC layer of the UE100and the RLC layer of the eNB200, data is transmitted via a logical channel.

The RRC layer is defined only in a control plane. Between the RRC layer of the UE100and the RRC layer of the eNB200, a control message (an RRC message) for various types of setting is transmitted. The RRC layer controls the logical channel, the transport channel, and the physical channel in response to establishment, re-establishment, and release of a radio bearer. When there is an RRC connection between the RRC of the UE100and the RRC of the eNB200, the UE100is in a connected state (an RRC connected state), and when there is no RRC connection, the UE100is in an idle state (an RRC idle state).

A NAS (Non-Access Stratum) layer positioned above the RRC layer performs session management, mobility management and the like.

FIG. 5is a configuration diagram of a radio frame used in the LTE system. In the LTE system, OFDMA (Orthogonal Frequency Division Multiplexing Access) is applied to a downlink, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is applied to an uplink, respectively.

As illustrated inFIG. 5, the radio frame is configured by 10 subframes arranged in a time direction, wherein each subframe is configured by two slots arranged in the time direction. Each subframe has a length of 1 ms and each slot has a length of 0.5 ms. Each subframe includes a plurality of resource blocks (RBs) in a frequency direction, and a plurality of symbols in the time direction. The resource block includes a plurality of subcarriers in the frequency direction. Among radio resources assigned to the UE100, a frequency resource can be specified by a resource block and a time resource can be specified by a subframe (or slot).

In the downlink, an interval of several symbols at the head of each subframe is a control region used as a physical downlink control channel (PDCCH) for mainly transmitting a control signal. Furthermore, the other interval of each subframe is a region available as a physical downlink shared channel (PDSCH) for mainly transmitting user data.

In the uplink, both ends in the frequency direction of each subframe are control regions used as a physical uplink control channel (PUCCH) for mainly transmitting a control signal. Further, the central portion in the frequency direction of each subframe is a region mainly capable of being used as a physical uplink shared channel (PUSCH) for transmitting user data.

The LTE system according to the first embodiment supports the D2D communication that is direct communication between UEs. Hereinafter, the D2D communication will be described in comparison with normal communication (cellular communication) of the LTE system.

In the cellular communication, a data path passes through the EPC20that is a core network. The data path indicates a communication path of user data (a user plane). On the other hand, in the D2D communication, the data path set between the UEs does not pass through the EPC20. Thus, it is possible to reduce traffic load of the EPC20.

The UE100discovers another UE100existing in the vicinity of the UE100by a neighboring UE discovery (Discovery) process, and starts the D2D communication. The D2D communication, for example, is performed in a frequency band (a so-called licensed band) assigned to the LTE system.

The D2D communication includes a direct communication mode and a locally routed mode. In the direct communication mode, a data path does not pass through the eNB200. A UE group (a D2D UE group) including a plurality of UEs100adjacent to one another directly perform radio communication with low transmission power in a cell of the eNB200. Thus, a merit including reduction of power consumption of the UE100and decrease of interference to a neighboring cell can be obtained. On the other hand, in the locally routed mode, a data path passes through the eNB200, however, not the EPC20. The locally routed mode is able to reduce traffic load of the EPC20, however, has a smaller merit as compared with the direct communication mode. Thus, in the first embodiment, the direct communication mode is mainly assumed.

(Operation According to First Embodiment)

Next, an operation according to the first embodiment will be described.FIG. 6is a diagram for describing an operation environment according to the first embodiment. As shown inFIG. 6, UE100-1D, UE100-2D, and UE100-C exist in the cell of the eNB200. In the first embodiment, the UE100-1D and the UE100-2D perform D2D communication in the cell of the eNB200. The UE100-C performs cellular communication in the cell of the eNB200. Hereinafter, a description will be provided for an operation in which the UE100-1D and the UE100-2D perform the D2D communication. In addition, hereinafter, the UE100-1D and the UE100-2D are simply written as “UE100-D” when they are not particularly distinguished from each other.

Firstly, the eNB200secures a radio resource (hereinafter, a “D2D radio resource”) permitted to be used in the D2D communication. The D2D radio resource is designated by a time resource and/or a frequency resource. The time resource, for example, is a subframe. The frequency resource, for example, is a resource block and/or a frequency band. In the first embodiment, the D2D radio resource is a dedicated radio resource that is not commonly used together with a cellular radio resource for the cellular communication.FIG. 7is a diagram illustrating a D2D radio resource according to the first embodiment. As shown inFIG. 7, among radio resources corresponding to three subframes, several resource blocks positioned at the center in the central subframe are secured as the D2D radio resource. That is, the eNB200does not use the D2D radio resource in the cellular communication.

Secondly, the eNB200transmits broadcast information (hereinafter, D2D broadcast information) that enables the D2D communication even in a specific state in which the UE100-D does not establish an RRC connection with the network. In the first embodiment, the specific state is an idle state indicating a state in which the UE100-D does not establish the RRC connection in a coverage of the network. The eNB200may periodically transmit the D2D broadcast information, or may transmit the D2D broadcast information when detecting a predetermined trigger. The D2D broadcast information may be included in a system information block (SIB) or a master information block (MIB). The SIB or the MIB is information receivable in UE100in an idle state. The D2D broadcast information includes resource information indicating the D2D radio resource and power information indicating maximum transmission power permitted in the D2D communication. The D2D broadcast information may also include information on a signal transmitted and received in the Discovery process (details will be described later).

Thirdly, the UE100-D in a connected state or an idle state in the cell of the eNB200receives the D2D broadcast information from the eNB200, and acquires the resource information and the power information included in the D2D broadcast information. The UE100-D may receive the D2D broadcast information before the Discovery process, or receive the D2D broadcast information after the Discovery process.

Fourthly, the UE100-D in an idle state starts the D2D communication on the basis of the D2D broadcast information. When the UE100-D is in a connected state before performing the D2D communication, the UE100-D disconnects the RRC connection and then performs the D2D communication in an idle state according to an instruction from the eNB200or voluntarily. The UE100-D decides a radio resource to be used in the D2D communication from among D2D radio resources indicated by the resource information, and performs the D2D communication by using the decided radio resource. Furthermore, the UE100-D decides transmission power to be used in the D2D communication in a range of maximum transmission power indicated by the power information, and performs the D2D communication by using the decided transmission power.

As described above, the UE100-D performs the D2D communication in an idle state, so that it is possible to suppress an increase in load and signaling of the network caused by the control of the D2D communication.

However, during the D2D communication, the UE100-D may receive interference from UE100-X (a cellular UE or a D2D UE belonging to another D2D UE group) with which the UE100-D does not communicate. Hereinafter, a description will be provided for operation patterns1to3for avoiding interference during the D2D communication.

The UE100-D performing the D2D communication detects interference (interference power) to the D2D communication from the UE100-X with which the UE100-D does not communicate. When the interference is detected, the UE100-D transmits, to the eNB200, information indicating a request to avoid the interference after establishing the RRC connection or in the process of establishing the RRC connection. That is, the UE100-D transitions to a connected state and requests the eNB200to perform a process for avoiding the interference. In the case of establishing the RRC connection only in order to request the process for avoiding the interference, the UE100-D may notify the eNB200to that effect during the process for establishing the RRC connection. As the process for avoiding the interference, the eNB200allows a radio resource used by the UE100-X to be different from a radio resource used by the UE100-D, for example. Alternatively, the eNB200reduces the transmission power of the UE100-X.

The UE100-D performing the D2D communication detects interference (interference power) to the D2D communication from the UE100-X with which the UE100-D does not communicate. When the interference is detected, the UE100-D performs negotiation between UEs in order to avoid the interference while maintaining an idle state. For example, the UE100-D negotiates with the UE100-X such that a radio resource used by a D2D UE group including the UE100-D is different from a radio resource used by a D2D UE group including the UE100-X.

The UE100-D, which performs the D2D communication by using a radio resource (hereinafter, a “radio resource A”) included in the D2D radio resource, detects interference (interference power) to the D2D communication from the UE100-X with which the UE100-D does not communicate. When the interference is detected, the UE100-D changes a radio resource used in the D2D communication to another radio resource (hereinafter, a “radio resource B”) included in the D2D radio resource. Then, the UE100-D broadcasts change information indicating a change to the radio resource B by using the radio resource B.

In this case, when UE100-Y using the radio resource B receives the change information, the UE100-Y notifies a serving cell (the eNB200) of the UE100-Y of the reception of the change information. Furthermore, the UE100-Y broadcasts in-use information, which indicates that the radio resource B is being used, by using the radio resource B. When the in-use information is received from the UE100-Y, the UE100-D performs one of the following processes.The UE100-D stops a change to the radio resource B when the interference from the UE100-X is reduced, and uses the radio resource A.The UE100-D performs the process of the interference avoidance operation pattern1or2when the interference from the UE100-X is not reduced.

Meanwhile, when the in-use information is not received from the UE100-Y, the UE100-D notifies UE with which the UE100-D communicates, of a change to the radio resource B. Then, the UE100-D and the UE with which the UE100-D communicates perform the D2D communication by using the radio resource B.

FIG. 8is a diagram illustrating a specific example 1 of the interference avoidance operation pattern2. InFIG. 8, a cell A is a cell belonging to a frequency band A included in the D2D radio resource, and a cell B is a cell belonging to a frequency band B included in the D2D radio resource.

As shown inFIG. 8(A), UE100-1and UE100-2constitute a D2D UE group, and UE100-3and UE100-4constitute another D2D UE group. These two D2D UE groups are adjacent to each other and use the same frequency band, resulting in the occurrence of interference between the D2D communications. Hereinafter, the case, in which the UE100-4detects interference from the UE100-1, is considered.

As shown inFIG. 8(B), when interference is detected, the UE100-4changes a frequency band (a cell), in which D2D communication is performed, from the frequency band A (the cell A) to the frequency band B (the cell B). Then, the UE100-D broadcasts change information, which indicates a change to the frequency band B (the cell B), in the frequency band B (the cell B).

As shown inFIG. 8(C), since no in-use information is received, the UE100-4notifies the UE100-3of a change to the frequency band B (the cell B). Then, the UE100-3and the UE100-4perform the D2D communication in the frequency band B (the cell B).

FIG. 9is a diagram illustrating a specific example 2 of the interference avoidance operation pattern2. Hereinafter, the difference relative to the specific example 1 will be described.

As shown inFIG. 9(A), the UE100-4detects interference from the UE100-1in the frequency band A (the cell A). Meanwhile, the UE100-3and the UE100-4perform the D2D communication in the frequency band B (the cell B).

As shown inFIG. 9(B), the UE100-4broadcasts change information, which indicates a change to the frequency band B (the cell B), in the frequency band B (the cell B). UE100-6receives the change information from the UE100-4, and broadcasts (or notifies) in-use information, which indicates that the frequency band B (the cell B) is being used, in the frequency band B (the cell B). The UE100-4receives the in-use information from the UE100-6.

As shown inFIG. 9(C), since the interference from the UE100-2is not reduced, the UE100-4which has received the in-use information performs the process of the interference avoidance operation pattern1or2.

Second Embodiment

Next, a second embodiment will be described. In the second embodiment, the specific state is a state (hereinafter, an “out-of-service state”) in which the UE100-D exists out of a coverage of the network. The coverage is not limited to a coverage of an LTE network, and may be coverages of all networks operated by the same communication provider. Furthermore, out-of-coverage indicates both an area in which radio waves from the network do not reach, and an area in which the radio waves from the network are severely weak. An area out of the coverage is called an “out-of-range area”.

In the second embodiment, the eNB200, which transmits D2D broadcast information, manages a termination cell included in a termination area of the coverage. In the termination cell, at least a part of a periphery thereof is the out-of-range area. That is, the eNB200transmits the D2D broadcast information in the termination cell. The eNB200may be notified of information regarding whether the cell of the eNB200is the termination cell from the EPC20.

Hereinafter, an operation according to the second embodiment will be explained while focusing on the difference relative to the first embodiment.

The eNB200transmits D2D broadcast information that enables D2D communication even though the UE100-D is in the out-of-service state. The D2D broadcast information includes information (termination cell information) indicating that the D2D communication is permitted in the out-of-range area, in addition to resource information indicating a D2D radio resource and power information indicating maximum transmission power permitted in the D2D communication.

The UE100-D in a connected state or an idle state in the cell of the eNB200receives the D2D broadcast information from the eNB200. Then, the UE100-D transitioned to the out-of-service state performs a Discovery process on the basis of the D2D broadcast information, and then performs the D2D communication.

As described above, the UE100-D performs the D2D communication in the out-of-service state, so that it is possible to effectively utilize the D2D communication and to enable communication even in the out-of-service state.

Furthermore, in the second embodiment, among the interference avoidance operations according to the first embodiment, an interference avoidance operation, other than the operation (that is, the interference avoidance operation pattern1) to request the eNB200to avoid the interference, is applicable.

Moreover, in the second embodiment, instead of the aforementioned interference avoidance operation pattern1, an operation for stopping the D2D communication may be performed. In this case, in response to the detection of interference to the D2D communication from the UE100-X, the UE100-D determines to stop the D2D communication and transmits information indicating the stop of the D2D communication to a communication destination.

[Modification of Second Embodiment]

In the second embodiment, since it is difficult to request the eNB200to avoid the interference, D2D communication may be performed using a frequency hopping scheme in order to attenuate the influence of interference.

In the present modification, the D2D broadcast information includes information on a hopping pattern (candidates of the hopping pattern) permitted to be used in the D2D communication. However, the UE100-D may hold the candidates of the hopping pattern in advance.FIG. 10is a diagram illustrating a specific example of the candidates of the hopping pattern. InFIG. 10, a horizontal axis denotes a time axis and indicates 10 subframes corresponding to one radio frame. A vertical axis denotes a frequency axis and indicates a bandwidth corresponding to six resource blocks.

The UE100-D selects a hopping pattern to be used in the D2D communication from the candidates of the hopping pattern, and notifies a communication destination of the selected hopping pattern. The UE100-D performs the D2D communication by using the selected hopping pattern.

When the UE100-D detects interference from the UE100-X using the same hopping pattern, the UE100-D may decide the right of use of the hopping pattern by negotiation between UEs. When it is not possible to use the selected hopping pattern, the UE100-D reselects another hopping pattern from the candidates of the hopping pattern, and notifies the communication destination of the selected hopping pattern. The UE100-D performs the D2D communication by using the reselected hopping pattern.

In addition, as well as the case of selecting (or reselecting) a hopping pattern from the candidates of the hopping pattern, the corresponding UE may hold a UE-specific hopping pattern and perform the D2D communication by using the UE-specific hopping pattern. The hopping pattern may be calculated from a UE-specific ID, an ID of a cell in which the UE exists, a temporary ID (C-RNTI) assigned from the corresponding cell to the UE, and so on.

Other Embodiments

In each of the aforementioned embodiments, the D2D broadcast information may include information on a signal (Discovery signal) transmitted and received in the Discovery process. The Discovery signal is a signal for discovering neighboring UE or a signal for being discovered by the neighboring UE. The information on the Discovery signal includes resource information indicating radio resources (Discovery radio resources) permitted to be used in the Discovery process, and power information indicating maximum transmission power (Discovery maximum transmission power) permitted in the Discovery process. In this case, the UE100-D decides a radio resource used in the transmission of the Discovery signal from the Discovery radio resources indicated by the resource information, and transmits the Discovery signal by using the decided radio resource. Furthermore, the UE100-D decides transmission power of the Discovery signal in a range of the Discovery maximum transmission power indicated by the power information, and transmits the Discovery signal by using the decided transmission power.

Each the embodiments and the modification mentioned above may be performed separately and independently and may also be performed through a combination thereof.

In the aforementioned second embodiment and the modification thereof, a parameter (a radio resource, maximum transmission power and so on) necessary for the D2D communication may be statically decided and the UE100-D may hold information (the parameter) thereof. In this case, the UE100-D can perform the D2D communication by using the held parameter regardless of the D2D broadcast information (and the termination cell information).

Each of the aforementioned embodiments has described an example in which the present invention is applied to the LTE system. However, the present invention may also be applied to systems other than the LTE system, as well as the LTE system.

Thus, the present invention includes a variety of embodiments not described herein as a matter of course. Further, it is possible to combine embodiments and modifications described above. Therefore, the technical scope of the present invention is defined only by the matters according to claims based on the above description.

The entire contents of U.S. Provisional Application No. 61/766,548 (filed on Feb. 19, 2013) are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a mobile communication system, a user terminal, and a base station capable of suppressing an increase in load and signaling of a network caused by the control of D2D communication.