Patent Publication Number: US-2018041324-A1

Title: Mobile communication system, base station device and relay device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the benefit of priority from U.S. application Ser. No. 13/577,522, filed on Aug. 7, 2012, which claims the benefit of prior International Application No. PCT/W2011/052720, filed on Feb. 9, 2011, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-028412, filed on Feb. 12, 2010; the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a mobile communication system in which a base station performs radio communication with a plurality of user equipments. 
     BACKGROUND ART 
     Commercial service of a wideband code division multiple access (W-CDMA) system among so-called third-generation communication systems has been offered in Japan since 2001. In addition, high speed down link packet access (HSDPA) service for achieving higher-speed data transmission using a downlink has been offered by adding a channel for packet transmission (high speed-downlink shared channel (HS-DSCH)) to the downlink (dedicated data channel, dedicated control channel). Further, in order to increase the speed of data transmission in an uplink direction, service of a high speed up link packet access (HSUPA) system has been offered. W-CDMA is a communication system defined by the 3rd generation partnership project (3GPP) that is the standard organization regarding the mobile communication system, where the specifications of Release 8 version are produced. 
     Further, 3GPP is studying new communication systems referred to as long term evolution (LTE) regarding radio areas and system architecture evolution (SAE) regarding the overall system configuration including a core network (merely referred to as network as well) as communication systems independent of W-CDMA. 
     In the LTE, an access scheme, a radio channel configuration and a protocol are totally different from those of the current W-CDMA (HSDPA/HSUPA). For example, as to the access scheme, code division multiple access is used in the W-CDMA, whereas in the LTE, orthogonal frequency division multiplexing (OFDM) is used in a downlink direction and single career frequency division multiple access (SC-FDMA) is used in an uplink direction. In addition, the bandwidth is 5 MHz in the W-CDMA, while in the LTE, the bandwidth can be selected from 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz for each base station. Further, differently from the W-CDMA, circuit switching is not provided but a packet communication system is only provided in the LTE. 
     The LTE is defined as a radio access network independent of the W-CDMA network because its communication system is configured with a new core network different from a core network (general packet radio service: GPRS) of the W-CDMA. Therefore, for differentiation from the W-CDMA communication system, a base station that communicates with a user equipment (UE) and a radio network controller that transmits/receives control data and user data to/from a plurality of base stations are referred to as an E-UTRAN NodeB (eNB) and an evolved packet core (EPC) or access gateway (aGW), respectively, in the LTE communication system. Unicast service and evolved multimedia broadcast multicast service (E-MBMS service) are provided in this LTE communication system. The E-MBMS service is broadcast multimedia service, which is merely referred to as MBMS in some cases. Bulk broadcast contents such as news, weather forecast and mobile broadcast are transmitted to a plurality of user equipments. This is also referred to as point to multipoint service. 
     Non-Patent Document 1 (Chapter 4.6.1) describes the current decisions by 3GPP regarding an overall architecture in the LTE system. The overall architecture is described with reference to  FIG. 1 .  FIG. 1  is a diagram illustrating the configuration of the LTE communication system. With reference to  FIG. 1 , the evolved universal terrestrial radio access (E-UTRAN) is composed of one or a plurality of base stations  102 , provided that a control protocol for a user equipment  101  such as a radio resource control (RRC) and user planes such as a packet data convergence protocol (PDCP), radio link control (RLC), medium access control (MAC) and physical layer (PHY) are terminated in the base station  102 . 
     The base stations  102  perform scheduling and transmission of paging signaling (also referred to as paging messages) notified from a mobility management entity (MME)  103 . The base stations  102  are connected to each other by means of an X2 interface. In addition, the base stations  102  are connected to an evolved packet core (EPC) by means of an S1 interface. More specifically, the base station  102  is connected to the mobility management entity (MME)  103  by means of an S1_MME interface and connected to a serving gateway (S-GW)  104  by means of an S1_U interface. 
     The MME  103  distributes the paging signal to a plurality of or a single base station  102 . In addition, the MME  103  performs mobility control of an idle state. When the user equipment is in the idle state and an active state, the MME  103  manages a list of tracking areas. 
     The S-GW  104  transmits/receives user data to/from one or a plurality of base stations  102 . The S-GW  104  serves as a local mobility anchor point in handover between base stations. Moreover, a PDN gateway (P-GW) is provided in the EPC, which performs per-user packet filtering and UE-ID address allocation. 
     The control protocol RRC between the user equipment  101  and the base station  102  performs broadcast, paging, RRC connection management and the like. The states of the base station and the user equipment in RRC are classified into RRC_Idle and RRC_CONNECTED. In RRC_IDLE, public land mobile network (PLMN) selection, system information (SI) broadcast, paging, cell re-selection, mobility and the like are performed. In RRC_CONNECTED, the user equipment has RRC connection, is capable of transmitting/receiving data to/from a network, and performs, for example, handover (HO) and measurement of a neighbor cell. RRC IDLE is merely referred to as IDLE or idle state as well. RRC_CONNECTED is merely referred to as CONNECTED as well. 
     The current decisions by 3GPP regarding the frame configuration in the LTE system described in Non-Patent Document 1 (Chapter 5) are described with reference to  FIG. 2 .  FIG. 2  is a diagram illustrating the configuration of a radio frame used in the LTE communication system. With reference to  FIG. 2 , one radio frame is 10 ms. The radio frame is divided into ten equally sized sub-frames. The subframe is divided into two equally sized slots. The first and sixth subframes contain a downlink synchronization signal (SS) per each radio frame. The synchronization signals are classified into a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS). Multiplexing of channels for multimedia broadcast multicast service single frequency network (MBSFN) and for non-MBSFN is performed on a per-subframe basis. Hereinafter, a subframe for MBSFN transmission is referred to as an MBSFN sub-frame. 
     Non-Patent Document 2 describes a signaling example when MBSFN subframes are allocated.  FIG. 3  is a diagram illustrating the configuration of the MBSFN frame. With reference to  FIG. 3 , the MBSFN subframes are allocated for each MBSFN frame. An MBSFN frame cluster is scheduled. A repetition period of the MBSFN frame cluster is allocated. 
     Non-Patent Document 1 (Chapter 5) describes the current decisions by 3GPP regarding the channel configuration in the LTE system. It is assumed that the same channel configuration is used in a closed subscriber group cell (CSG cell) as that of a non-CSG cell. A physical channel is described with reference to  FIG. 4 .  FIG. 4  is a diagram illustrating physical channels used in the LTE communication system. With reference to  FIG. 4 , a physical broadcast channel (PBCH)  401  is a downlink channel transmitted from the base station  102  to the user equipment  101 . A BCH transport block is mapped to four subframes within a 40 ms interval. There is no explicit signaling indicating 40 ms timing A physical control format indicator channel (PCFICH)  402  is transmitted from the base station  102  to the user equipment  101 . The PCFICH notifies the number of OFDM symbols used for PDCCHs from the base station  102  to the user equipment  101 . The PCFICH is transmitted in each subframe. 
     A physical downlink control channel (PDCCH)  403  is a downlink channel transmitted from the base station  102  to the user equipment  101 . The PDCCH notifies the resource allocation, HARQ information related to DL-SCH (downlink shared channel that is one of the transport channels shown in  FIG. 5  described below) and the PCH (paging channel that is one of the transport channels shown in  FIG. 5 ). The PDCCH carries an uplink scheduling grant. The PDCCH carries acknowledgement (Ack)/negative acknowledgement (Nack) that is a response signal to uplink transmission. The PDCCH is referred to as an L1/L2 control signal as well. 
     A physical downlink shared channel (PDSCH)  404  is a downlink channel transmitted from the base station  102  to the user equipment  101 . A DL-SCH (downlink shared channel) that is a transport channel and a PCH that is a transport channel are mapped to the PDSCH. A physical multicast channel (PMCH)  405  is a downlink channel transmitted from the base station  102  to the user equipment  101 . A multicast channel (MCH) that is a transport channel is mapped to the PMCH. 
     A physical uplink control channel (PUCCH)  406  is an uplink channel transmitted from the user equipment  101  to the base station  102 . The PUCCH carries Ack/Nack that is a response signal to downlink transmission. The PUCCH carries a channel quality indicator (CQI) report. The CQI is quality information indicating the quality of received data or channel quality. In addition, the PUCCH carries a scheduling request (SR). A physical uplink shared channel (PUSCH)  407  is an uplink channel transmitted from the user equipment  101  to the base station  102 . A UL-SCH (uplink shared channel that is one of the transport channels shown in  FIG. 5 ) is mapped to the PUSCH. 
     A physical hybrid ARQ indicator channel (PHICH)  408  is a downlink channel transmitted from the base station  102  to the user equipment  101 . The PHICH carries Ack/Nack that is a response to uplink transmission. A physical random access channel (PRACH)  409  is an uplink channel transmitted from the user equipment  101  to the base station  102 . The PRACH carries a random access preamble. 
     A downlink reference signal which is a known symbol in a mobile communication system is inserted in the first, third and last OFDM symbols of each slot. The physical layer measurement objects of a user equipment include, for example, reference symbol received power (RSRP). 
     The transport channel described in Non-Patent Document 1 (Chapter 5) is described with reference to  FIG. 5 .  FIG. 5  is a diagram illustrating transport channels used in the LTE communication system.  FIG. 5(A)  shows mapping between a downlink transport channel and a downlink physical channel.  FIG. 5(B)  shows mapping between an uplink transport channel and an uplink physical channel. A broadcast channel (BCH) is broadcast to the entire base station (cell) regarding the downlink transport channel. The BCH is mapped to the physical broadcast channel (PBCH). 
     Retransmission control according to a hybrid ARQ (HARQ) is applied to a downlink shared channel (DL-SCH). The DL-SCH enables broadcast to the entire base station (cell). The DL-SCH supports dynamic or semi-static resource allocation. The semi-static resource allocation is also referred to as persistent scheduling. The DL-SCH supports discontinuous reception (DRX) of a user equipment for enabling the user equipment to save power. The DL-SCH is mapped to the physical downlink shared channel (PDSCH). 
     The paging channel (PCH) supports DRX of the user equipment for enabling the user equipment to save power. Broadcast to the entire base station (cell) is required for the PCH. The PCH is mapped to physical resources such as the physical downlink shared channel (PDSCH) that can be used dynamically for traffic or physical resources such as the physical downlink control channel (PDCCH) of the other control channel The multicast channel (MCH) is used for broadcast to the entire base station (cell). The MCH supports SFN combining of MBMS service (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH. 
     Retransmission control according to a hybrid ARQ (HARQ) is applied to an uplink shared channel (UL-SCH). The UL-SCH supports dynamic or semi-static resource allocation. The UL-SCH is mapped to the physical uplink shared channel (PUSCH). A random access channel (RACH) shown in  FIG. 5(B)  is limited to control information. The RACH involves a collision risk. The RACH is mapped to the physical random access channel (PRACH). 
     The HARQ is described. The HARQ is the technique for improving the 
     The HARQ is described. The HARQ is the technique for improving the communication quality of a channel by combination of automatic repeat request and forward error correction. The HARQ has an advantage that error correction functions effectively by retransmission even for a channel whose communication quality changes. In particular, it is also possible to achieve further quality improvement in retransmission through combination of the reception results of the first transmission and the reception results of the retransmission. 
     An example of the retransmission method is described. In a case where the receiver fails to successfully decode the received data, in other words, in a case where a cyclic redundancy check (CRC) error occurs (CRC=NG), the receiver transmits “Nack” to the transmitter. The transmitter that has received “Nack” retransmits the data. In a case where the receiver successfully decodes the received data, in other words, in a case where a CRC error does not occur (CRC=OK), the receiver transmits “AcK” to the transmitter. The transmitter that has received “Ack” transmits the next data. 
     Examples of the HARQ system include chase combining. In chase combining, the same data sequence is transmitted in the first transmission and retransmission, which is the system for improving gains by combining the data sequence of the first transmission and the data sequence of the retransmission in retransmission. This is based on the idea that correct data is partially included even if the data of the first transmission contains an error, and highly accurate data transmission is enabled by combining the correct portions of the first transmission data and the retransmission data. Another example of the HARQ system is incremental redundancy (IR). The IR is aimed to increase redundancy, where a parity bit is transmitted in retransmission to increase the redundancy by combining the first transmission and retransmission, to thereby improve the quality by an error correction function. 
     A logical channel (hereinafter, referred to as “logical channel” in some cases) described in Non-Patent Document 1 (Chapter 6) is described with reference to  FIG. 6 .  FIG. 6  is a diagram illustrating logical channels used in an LTE communication system.  FIG. 6(A)  shows mapping between a downlink logical channel and a downlink transport channel.  FIG. 6(B)  shows mapping between an uplink logical channel and an uplink transport channel. A broadcast control channel (BCCH) is a downlink channel for broadcast system control information. The BCCH that is a logical channel is mapped to the broadcast channel (BCH) or downlink shared channel (DL-SCH) that is a transport channel. 
     A paging control channel (PCCH) is a downlink channel for transmitting paging signals. The PCCH is used when the network does not know the cell location of a user equipment. The PCCH that is a logical channel is mapped to the paging channel (PCH) that is a transport channel. A common control channel (CCCH) is a channel for transmission control information between user equipments and a base station. The CCCH is used in a case where the user equipments have no RRC connection with the network. In a downlink direction, the CCCH is mapped to the downlink shared channel (DL-SCH) that is a transport channel. In an uplink direction, the CCCH is mapped to the uplink shared channel (UL-SCH) that is a transport channel. 
     A multicast control channel (MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used for transmission of MBMS control information for one or several MTCHs from a network to a user equipment. The MCCH is a channel used only by a user equipment during reception of the MBMS. The MCCH is mapped to the downlink shared channel (DL-SCH) or multicast channel (MCH) that is a transport channel. 
     A dedicated control channel (DCCH) is a channel that transmits dedicated the uplink shared channel (UL-SCH) in uplink and mapped to the downlink shared channel (DL-SCH) in downlink. 
     A dedicate traffic channel (DTCH) is a point-to-point communication channel for transmission of user information to a dedicated user equipment. The DTCH exists in uplink as well as downlink The DTCH is mapped to the uplink shared channel (UL-SCH) in uplink and mapped to the downlink shared channel (DL-SCH) in downlink. 
     A multicast traffic channel (MTCH) is a downlink channel for traffic data transmission from a network to a user equipment. The MTCH is a channel used only by a user equipment during reception of the MBMS. The MTCH is mapped to the downlink shared channel (DL-SCH) or multicast channel (MCH). 
     GCI represents a global cell identity. A closed subscriber group cell (CSG cell) is introduced in the LTE and universal mobile telecommunication system (UMTS). The CSG is described below (see Chapter 3.1 of Non-Patent Document 3). The closed subscriber group (CSG) is a cell in which subscribers who are allowed to use are specified by an operator (cell for specific subscribers). The specified subscribers are allowed to access one or more E-UTRAN cells of a public land mobile network (PLMN). One or more E-UTRAN cells in which the specified subscribers are allowed access are referred to as “CSG cell(s)”. Note that access is limited in the PLMN. The CSG cell is part of the PLMN that broadcasts a specific CSG identity (CSG ID, CSG-ID). The authorized members of the subscriber group who have registered in advance access the CSG cells using the CSG-ID that is the access permission information. 
     The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDs exist in a mobile communication system. The CSG-IDs are used by user equipments (UEs) for making access from CSG-related members easier. The locations of user equipments are traced based on an area composed of one or more cells. The locations are traced for enabling tracing of the locations of user equipments and calling (calling of user equipments) even in an idle state. An area for tracing locations of user equipments is referred to as a tracking area. A CSG whitelist is a list stored in a universal subscriber identity module (USIM) in which all CSG IDs of the CSG cells to which the subscribers belong are recorded. The CSG whitelist is also referred to as an allowed CSG ID list in some cases. 
     A “suitable cell” is described below (see Chapter 4. 3 of Non-Patent Document 3). The “suitable cell” is a cell on which a UE camps to obtain normal service. Such a cell shall fulfill the following conditions. 
     (1) The cell is part of the selected PLMN or the registered PLMN, or part of the PLMN of an “equivalent PLMN list”. 
     (2) According to the latest information provided by a non-access stratum (NAS), the cell shall further fulfill the following conditions: 
     (a) the cell is not a barred cell; 
     (b) the cell is part of at least one tracking area (TA), not part of “forbidden LAs for roaming”, where the cell needs to fulfill (1) above; 
     (c) the cell shall fulfill the cell selection criteria; and 
     (d) for a cell specified as CSG cell by system information (SI), the CSG-ID is part of a “CSG whitelist” of the UE (contained in the CSG whitelist of the UE). 
     An “acceptable cell” is described below (see Chapter 4.3 of Non-Patent Document 3). This is the cell on which a UE camps to obtain limited service (emergency calls). Such a cell shall fulfill all the following requirements. That is, the minimum required set for initiating an emergency call in an E-UTRAN network are as follows: (1) the cell is not a barred cell; and (2) the cell fulfills the cell selection criteria. 
     Camping on a cell represents the state where a UE has completed the cell selection/reselection process and the UE has selected a cell for monitoring the system information and paging information. 
     3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, for example, household, corporation or commercial access service in UTRAN/E-UTRAN. Non-Patent Document 4 discloses three different modes of the access to the HeNB and HNB. Specifically, those are an open access mode, a closed access mode and a hybrid access mode. 
     The respective modes have the following characteristics. In the open access mode, the HeNB and HNB are operated as a normal cell of a normal operator. In the closed access mode, the HeNB and HNB are operated as a CSG cell. The CSG cell is a cell where only CSG members are allowed access. In the hybrid access mode, non-CSG members are allowed access at the same time. In other words, a cell in the hybrid access mode (also referred to as hybrid cell) is the cell that supports both the open access mode and the closed access mode. 
     3GPP discusses that all physical cell identities (PCIs) are split (referred to as PCI-split) into ones reserved for CSG cells and the others reserved for non-CSG cells (see Non-Patent Document 5). Further, 3GPP discusses that the PCI split information is broadcast in the system information from the base station to the user equipments being served thereby. Non-Patent Document 5 discloses the basic operation of a user equipment using PCI split. The user equipment that does not have the PCI split information needs to perform cell search using all PCIs (for example, using all 504 codes). On the other hand, the user equipment that has the PCI split information is capable of performing cell search using the PCI split information. 
     Further, 3GPP is pursuing specifications standard of long term evolution advanced (LTE-A) as Release 10 (see Non-Patent Document 6 and Non-Patent Document 7). 
     As one of the techniques to be studied in LTE-A, heterogeneous networks (HetNets) are added. 3GPP has decided to handle low-output-power network nodes with low output power in a local area range, such as pico eNB (pico cell), node for hotzone cells, HeNB/HNB/CSG cell, relay node, remote radio head (RRH). Networks in which one or more of the above-mentioned network nodes in a local area range are incorporated in a normal eNB (macro cell) are heterogeneous networks. 
     As to the LTE-A system, it is studied in that a relay (relay node (RN)) is supported for achieving a high data rate, high cell-edge throughput, new coverage area or the like. The relay node is wirelessly connected to the radio-access network via a donor cell (Donor eNB; DeNB). The network (NW)-to-relay link shares the same frequency band with the network-to-UE link within the range of the donor cell. In this case, the UE can also be connected to the donor cell in the specifications of Release 8 of 3GPP. The link between a donor cell and a relay node is referred to as a backhaul link, the link between the relay node and the UE is referred to as an access link, and the link between the network and the UE is referred to as a direct link. 
     As the method of multiplexing backhaul links in frequency division duplex (FDD), the transmission from DeNB to RN is done in the downlink (DL) frequency band, whereas the transmission from RN to DeNB is done in the uplink (UL) frequency band. As the method of partitioning resources at the relay, the link from DeNB to RN and link from RN to UE are time division multiplexed in a single frequency band, and the link from RN to DeNB and the link from UE to RN are time division multiplexed in a single frequency band as well. This prevents, in the relay node, the transmission of the relay node from causing interference to the reception of its own relay node. The interference caused by the transmission of a relay node to the reception of its own relay node is also referred to as self-interference in some cases. 
     As described above, in the conventional technique, the link from a donor cell to a relay node and the link from a relay node to a user equipment being served by the relay node are time division multiplexed in one frequency band, and the link from a relay node to a donor cell and the link from a user equipment being served by a relay node to the relay node are time division multiplexed in one frequency band for preventing self-interference. The time division multiplexing described above decreases the throughput, leading to a problem that the system performance degrades. 
     In order to solve this problem, Non-Patent Document 8 discloses that the access link and backhaul link are operated in different carrier frequencies or different frequency bands. According to the technique disclosed in Non-Patent Document 8, it is not required to use time division multiplexing, which improves a throughput. 
     A user equipment selects a downlink (or cell) with good reception quality through a search operation. The frequency band of an uplink with respect to the selected downlink is notified in the broadcast information (see Non-Patent Document 9). 
     PRIOR ART DOCUMENTS 
     Non-Patent Documents 
     Non-Patent Document 1: 3GPP TS36.300 V9.1.0 Chapter 4.6.1, Chapter 4.6.2, Chapter 5, Chapter 6, and Chapter 10.7 
     Non-Patent Document 2: 3GPP R1-072963 
     Non-Patent Document 3: 3GPP TS36.304 V9.0.0 Chapter 3.1, Chapter 4.3 and Chapter 5.2.4 
     Non-Patent Document 4: 3GPP S1-083461 
     Non-Patent Document 5: 3GPP R2-082899 
     Non-Patent Document 6: 3GPP TR36.814 V1.5.0 
     Non-Patent Document 7: 3GPP TR36.912 V9.0.0 
     Non-Patent Document 8: 3GPP R1-094452 
     Non-Patent Document 9: 3GPP TS36,331 V9.0.0 
     SUMMARY OF INVENTION 
     Problem to be Solved by the Invention 
     In the technique disclosed in Non-Patent Document 8, the carrier frequency differs between the direct link and access link, which increases the load of a user equipment in a search operation. This causes a control delay of a user equipment, leading to a problem that power consumption increases. 
     An object of the present invention is to provide a mobile communication system capable of preventing interference in a communication system such as interference of network nodes in a local area range as well as reducing the load of a user equipment in a search operation. 
     Means to Solve the Problem 
     A mobile communication system according to the present invention includes a base station device, a user equipment device configured to perform radio communication with the base station device, and a relay device relaying the radio communication between the base station device and the user equipment device, wherein: the relay device performs radio communication with the user equipment device using a carrier having a different frequency from that of a carrier used in radio communication with the base station device; and the base station device performs radio communication with the user equipment device using a carrier having the same frequency as that of the carrier used in the radio communication between the relay device and the user equipment device. 
     Further, a mobile communication system according to the present invention includes a base station device, a user equipment device configured to perform radio communication with the base station device, and a relay device relaying the radio communication between the base station device and the user equipment device, wherein: the relay device performs radio communication with the user equipment device using a carrier having a different frequency from that of a carrier used in radio communication with the base station device; and the base station device notifies the user equipment device of the information related to a radio communication link between the relay device and the user equipment device. 
     Further, a mobile communication system according to the present invention includes a plurality of base station devices and a user equipment device configured to perform radio communication with the base station devices, wherein: each of the base station devices performs, in a downlink of radio communication to the user equipment device, radio communication using a carrier having the same frequency as that of a carrier used in a downlink of radio communication from another base station device to the user equipment device; and each of the base station devices performs, in an uplink of radio communication from the user equipment device, radio communication using a carrier having a different frequency from that of a carrier used in an uplink of radio communication from the user equipment device to the another base station device. 
     Effects of the Invention 
     According to the mobile communication system of the present invention, the relay device performs radio communication with the user equipment device using the carrier having a different frequency from that of the carrier used in radio communication with the base station device, whereby it is possible to reduce the self-interference of the relay device, that is, the interference of the radio communication between the relay device and the base station device and the radio communication between the relay device and the user equipment device. In addition, the base station device performs radio communication with the user equipment device using the carrier having the same frequency as that of the carrier used in the radio between the relay device and the user equipment device, whereby it is possible to simplify the search operation in which the user equipment device searches for the base station device or relay device as a communication target. This reduces the load of the user equipment device in a search operation. Therefore, it is possible to prevent the interference in the mobile communication system and reduce the load of the user equipment device in the search operation. 
     Further, according to the mobile communication system of the present invention, the relay device performs radio communication with the user equipment device using the carrier having a different frequency from that of the carrier used in radio communication with the base station device, whereby it is possible to reduce the self-interference of the relay device, that is, the interference of the radio communication between the relay device and the base station device and the radio communication between the relay device and the user equipment device. In addition, the base station device notifies the user equipment device of the information related to the radio communication link between the relay device and the user equipment device, whereby the user equipment device is allowed to search for the relay device based on the information related to the radio communication link between the relay device and the user equipment device that has been notified from the base station device. This simplifies the search operation in which the user equipment device searches for the base station device or relay device as a target communication device, which reduces the load of the user equipment device in a search operation. Therefore, it is possible to prevent the interference in the mobile communication system and reduce the load of the user equipment device in the search operation. 
     Further, according to the mobile communication system of the present invention, each base station device performs radio communication using the carrier having the same frequency as that of the carrier used in the downlink of radio communication from another base station device to the user equipment device in a downlink of radio communication to the user equipment device. This simplifies the search operation in which the user equipment device searches for the base station device among a plurality of base station devices as a communication target, which reduces the load of the user equipment device in a search operation. In addition, each base station device performs radio communication using the carrier having a different frequency from that of the carrier used in the uplink of radio communication from the user equipment device to another base station device in the uplink of radio communication from the user equipment device. This reduces the uplink interference that is the interference in the uplink radio communication from the user equipment device to each base station device. Therefore, it is possible to prevent the uplink interference and reduce the load of the user equipment device in the search operation. 
     These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating the configuration of an LTE communication system. 
         FIG. 2  is a diagram illustrating the configuration of a radio frame used in the LTE communication system. 
         FIG. 3  is a diagram illustrating the configuration of an MBSFN frame. 
         FIG. 4  is a diagram illustrating physical channels used in the LTE communication system. 
         FIG. 5  is a diagram illustrating transport channels used in the LTE communication system. 
         FIG. 6  is a diagram illustrating logical channels used in the LTE communication system. 
         FIG. 7  is a block diagram showing the overall configuration of an LTE mobile communication system currently under discussion of 3GPP. 
         FIG. 8  is a block diagram showing the configuration of a user equipment (user equipment  71  of  FIG. 7 ) according to the present invention. 
         FIG. 9  is a block diagram showing the configuration of a base station (base station  72  of  FIG. 7 ) according to the present invention. 
         FIG. 10  is a block diagram showing the configuration of an MME (MME unit  73  of  FIG. 7 ) according to the present invention. 
         FIG. 11  is a block diagram showing the configuration of a HeNBGW  74  shown in  FIG. 7  that is a HeNBGW according to the present invention.  FIG. 12  is a flowchart showing an outline from a cell search to an idle state operation performed by a user equipment (UE) in the LTE communication system. 
         FIG. 13  is a diagram illustrating a relay node disclosed in Non-Patent Document 7. 
         FIG. 14  is a diagram illustrating a relay node disclosed in Non-Patent Document 8. 
         FIG. 15  is a location diagram illustrating a problem of Non-Patent Document 8. 
         FIG. 16  is a conceptual diagram of the configuration of a frequency band of an LTE-A system. 
         FIG. 17  is a diagram illustrating a relay node in a case where a solution of a first embodiment is used. 
         FIG. 18  is a diagram illustrating a sequence example of a mobile communication system in a case where the solution of the first embodiment is used. 
         FIG. 19  is a location diagram for illustrating uplink interference. 
         FIG. 20  is a diagram illustrating a relay node in a case where the solution of the first embodiment is used. 
         FIG. 21  is a diagram illustrating a relay node in a case where a solution of a first modification of the first embodiment is used. 
         FIG. 22  is a diagram illustrating a sequence example of a mobile communication system in a case where the solution of the first modification of the first embodiment is used. 
         FIG. 23  is a diagram illustrating a sequence example of a mobile communication system in a case where a solution of a second embodiment is used. 
         FIG. 24  is a diagram illustrating a HeNB in a case where a solution of a third embodiment is used. 
         FIG. 25  is a flowchart showing a procedure of an operation example of setting the frequency information of a HeNB in a case where the third embodiment is used. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     First Embodiment 
       FIG. 7  is a block diagram showing an overall configuration of an LTE mobile communication system, which is currently under discussion of 3GPP. Currently, 3GPP is studying an overall system configuration including closed subscriber group (CSG) cells (Home-eNodeBs (Home-eNB; HeNB) of E-UTRAN, Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB (eNB) of E-UTRAN, NodeB (NB) of UTRAN, and BSS of GERAN) and, as to E-UTRAN, is proposing the configuration as shown in  FIG. 7  (see Chapter 4.6.1 of Non-Patent Document 1). 
       FIG. 7  is described. A user equipment device (hereinafter, referred to as “user equipment” or “UE,”)  71  is capable of performing radio communication with a base station device (hereinafter, referred to as “base station”)  72  and transmits/receives signals through radio communication. The base stations  72  are classified into an eNB  72 - 1  and a Home-eNB  72 - 2 . The eNB  72 - 1  is connected to an MME/S-GW unit (hereinafter, referred to as an “MME unit”)  73  including an MME, S-GW or MME and S-GW through an S1 interface, and control information is communicated between the eNB  72 - 1  and the MME unit  73 . A plurality of MME units  73  may be connected to one eNB  72 - 1 . The eNBs  72 - 1  are connected to each other by means of an X2 interface, and control information is communicated between the eNBs  72 - 1 . 
     The Home-eNB  72 - 2  is connected to the MME unit  73  by means of the S1 interface, and control information is communicated between the Home-eNB  72 - 2  and the MME unit  73 . A plurality of Horne-eNBs  72 - 2  are connected to one MME unit  73 . While, the Home-eNBs  72 - 2  are connected to the MME units  73  through a Home-eNB Gateway (HeNBGW)  74 . The Home-eNBs  72 - 2  are connected to the HeNBGW  74  by means of the SI interface, and the HeNBGW  74  is connected to the MME units  73  through an S1 interface. One or a plurality of Home-eNBs  72 - 2  are connected to one HeNBGW  74 , and information is communicated therebetween through an S1 interface. The HeNBGW  74  is connected to one or a plurality of MME units  73 , and information is communicated therebetween through an S1 interface. 
     Further, 3GPP is currently studying the configuration below. The X2 interface between the Home-eNBs  72 - 2  is not supported. The HeNBGW  74  appears to the MME unit  73  as the eNB  72 - 1 . The HeNBGW  74  appears to the Home-eNB  72 - 2  as the MME unit  73 . The interfaces between the Home-eNBs  72 - 2  and the MME units  73  are the same, which are the S1 interfaces, irrespective of whether or not the Home-eNB  72 - 2  is connected to the MME unit  73  through the HeNBGW  74 . The mobility to the Home-eNB  72 - 2  or the mobility from the Home-eNB  72 - 2  that spans the plurality of MME units  73  is not supported. The Home-eNB  72 - 2  supports a single cell. 
       FIG. 8  is a block diagram showing the configuration of the user equipment (user equipment  71  of  FIG. 7 ) according to the present invention. The transmission process of the user equipment  71  shown in  FIG. 8  is described. First, a transmission data buffer unit  803  stores the control data from a protocol processing unit  801  and the user data from an application unit  802 . The data stored in the transmission data buffer unit  803  is transmitted to an encoding unit  804  and is subjected to encoding process such as error correction. There may exist the data output from the transmission data buffer unit  803  directly to a modulating unit  805  without encoding process. The data encoded by the encoding unit  804  is modulated by the modulating unit  805 . The modulated data is output to a frequency converting unit  806  after being converted into a baseband signal, and then is converted into a radio transmission frequency. After that, a transmission signal is transmitted from an antenna  807  to the base station  72 . 
     The user equipment  71  executes the reception process as follows. The antenna  807  receives the radio signal from the base station  72 . The received signal is converted from a radio reception frequency to a baseband signal by the frequency converting unit  806  and is then demodulated by a demodulating unit  808 . The demodulated data is transmitted to a decoding unit  809  and is subjected to decoding process such as error correction. Among the pieces of decoded data, the control data is transmitted to the protocol processing unit  801 , while the user data is transmitted to the application unit  802 . A series of process of the user equipment  71  is controlled by a control unit  810 . This means that, though not shown in  FIG. 8 , the control unit  810  is connected to the respective units  801  to  809 . 
       FIG. 9  is a block diagram showing the configuration of the base station (base station  72  of  FIG. 7 ) according to the present invention. The transmission process of the base station  72  shown in  FIG. 9  is described. An EPC communication unit  901  performs data transmission/reception between the base station  72  and the EPCs (such as MME unit  73  and HeNBGW  74 ). A communication with another base station unit  902  performs data transmission/reception to/from another base station. The X2 interface between the Home-eNBs  72 - 2  is not intended to be supported, and accordingly, it is conceivable that the communication with another base station unit  902  may not exist in the Home-eNB  72 - 2 . The EPC communication unit  901  and the communication with another base station unit  902  respectively transmit/receive information to/from a protocol processing unit  903 . The control data from the protocol processing unit  903 , and the user data and control data from the EPC communication unit  901  and the communication with another base station unit  902  are stored in a transmission data buffer unit  904 . 
     The data stored in the transmission data buffer unit  904  is transmitted to an encoding unit  905  and is then subjected to encoding process such as error correction. There may exist the data output from the transmission data buffer unit  904  directly to a modulating unit  906  without encoding process. The encoded data is modulated by the modulating unit  906 . The modulated data is output to a frequency converting unit  907  after being converted into a baseband signal, and is then converted into a radio transmission frequency. After that, a transmission signal is transmitted from an antenna  908  to one or a plurality of user equipments  71 . 
     While, the reception process of the base station  72  is executed as follows. A radio signal from one or a plurality of user equipments  71  is received by the antenna  908 . The received signal is converted from a radio reception frequency into a baseband signal by the frequency converting unit  907 , and is then demodulated by a demodulating unit  909 . The demodulated data is transmitted to a decoding unit  910  and is then subjected to decoding process such as error correction. Among the pieces of decoded data, the control data is transmitted to the protocol processing unit  903 , EPC communication unit  901 , or communication with another base station unit  902 , while the user data is transmitted to the EPC communication unit  901  and communication with another base station unit  902 . A series of process by the base station  72  is controlled by a control unit  911 . This means that, though not shown in  FIG. 9 , the control unit  911  is connected to the respective units  901  to  910 . 
     The functions of the Home-eNB  72 - 2  currently under discussion of 3GPP are described below (see Chapter 4.6.2 of Non-Patent Document 1). The Home-eNB  72 - 2  has the same function as that of the eNB  72 - 1 . In addition, the Home-eNB  72 - 2  has the function of discovering a suitable serving HeNBGW  74  in a case of connection to the HeNBGW  74 . The Home-eNB  72 - 2  is connected only to one HeNBGW  74 . That is, in a case of the connection to the HeNBGW  74 , the Home-eNB  72 - 2  does not use the Flex function in the S1 interface. When the Home-eNB  72 - 2  is connected to one HeNBGW  74 , it is not simultaneously connected to another HeNBGW  74  or another MME nit  73 . 
     The TAC and PLMN ID of the Home-eNB  72 - 2  are supported by the HeNBGW  74 . When the Home-eNB  72 - 2  is connected to the HeNBGW  74 , selection of the MME unit  73  at “UE attachment” is performed by the HeNBGW  74  instead of the Home-eNB  72 - 2 . The Home-eNB  72 - 2  may be deployed without network planning. In this case, the Home-eNB  72 - 2  is moved from one geographical area to another geographical area. Accordingly, the Home-eNB  72 - 2  in this case is required to be connected to a different HeNBGW  74  depending on its location. 
       FIG. 10  is a block diagram showing the configuration of the MME (MME unit  73  of  FIG. 7 ) according to the present invention. A PDN GW communication unit  1001  performs data transmission/reception between the MME unit  73  and a PDN GW. A base station communication unit  1002  performs data transmission/reception between the MME unit  73  and the base station  72  by means of the S1 interface. In the case where the data received from the PDN GW is user data, the user data is transmitted from the PDN GW communication unit  1001  to the base station communication unit  1002  through a user plane communication unit  1003  and is then transmitted to one or a plurality of base stations  72 . In the case where the data received from the base station  72  is user data, the user data is transmitted from the base station communication unit  1002  to the PDN GW communication unit  1001  through the user plane communication unit  1003  and is then transmitted to the PDN GW. 
     In the case where the data received from the PDN GW is control data, the control data is transmitted from the PDN GW communication unit  1001  to a control plane control unit  1005 . In the case where the data received from the base station  72  is control data, the control data is transmitted from the base station communication unit  1002  to the control plane control unit  1005 . 
     A HeNBGW communication unit  1004  is provided in the case where the HeNBGW  74  is provided, which performs data transmission/reception by means of the interface (IF) between the MME unit  73  and the HeNBGW  74  according to an information type. The control data received from the HeNBGW communication unit  1004  is transmitted from the HeNBGW communication unit  1004  to the control plane control unit  1005 . The processing results of the control plane control unit  1005  are transmitted to the PDN GW through the PDN GW communication unit  1001 . The processing results of the control plane control unit  1005  are transmitted to one or a plurality of base stations  72  by means of the S1 interface through the base station communication unit  1002 , and are transmitted to one or a plurality of HeNBGWs  74  through the HeNBGW communication unit  1004 . 
     The control plane control unit  1005  includes a NAS security unit  1005 - 1 , an SAE bearer control unit  1005 - 2  and an idle state mobility managing unit  1005 - 3 , and performs overall process for the control plane. The NAS security unit  1005 - 1  provides, for example, security of a non-access stratum (NAS) message. The SAE bearer control unit  1005 - 2  manages, for example, a system architecture evolution (SAE) bearer. The idle state mobility managing unit  1005 - 3  performs, for example, mobility management of an idle state (LTE-IDLE state, which is merely referred to as idle as well), generation and control of paging signal in an idle state, addition, deletion, update and search of a tracking area (TA) of one or a plurality of user equipments  71  being served thereby, and TA list management. 
     The MME unit  73  begins a paging protocol by transmitting a paging message to the cell belonging to a tracking area (TA) in which the UE is registered. The idle state mobility managing unit  1005 - 3  may manage the CSG of the Home-eNBs  72 - 2  to be connected to the MME unit  73 , CSG-IDs and a whitelist. 
     In the CSG-ID management, the relationship between a user equipment corresponding to the CSG-ID and the CSG cell is managed (added, deleted, updated or searched). For example, it may be the relationship between one or a plurality of user equipments whose user access registration has been performed with a CSG-ID and the CSG cells belonging to this CSG-ID. In the whitelist management, the relationship between the user equipment and the CSG-ID is managed (added, deleted, updated or searched). For example, one or a plurality of CSG-IDs with which user registration has been performed by a user equipment may be stored in the whitelist. The above-mentioned management related to the CSG may be performed by another part of the MME unit  73 . A series of process by the MME unit  73  is controlled by a control unit  1006 . This means that, though not shown in  FIG. 10 , the control unit  1006  is connected to the respective units  1001  to  1005 . 
     The function of the MME currently under discussion of 3GPP is described below (see Chapter 4.6.2 of Non-Patent Document 1). The MME performs access control for one or a plurality of user equipments being members of closed subscriber groups (CSGs). The MME recognizes the execution of paging optimization as an option. 
       FIG. 11  is a block diagram showing the configuration of the HeNBGW  74  shown in  FIG. 7  that is a HeNBGW according to the present invention. An EPC communication unit  1101  performs data transmission/reception between the HeNBGW  74  and the MME unit  73  by means of the S1 interface. A base station communication unit  1102  performs data transmission/reception between the HeNBGW  74  and the Home-eNB  72 - 2  by means of the S1 interface. A location processing unit  1103  performs the process of transmitting, to a plurality of Home-eNBs  72 - 2 , the registration information or the like among the data transmitted from the MME unit  73  through the EPC communication unit  1101 . The data processed by the location processing unit  1103  is transmitted to the base station communication unit  1102  and is transmitted to one or a plurality of Home-eNBs  72 - 2  through the S1 interface. 
     The data only caused to pass through (to be transparent) without requiring the process by the location processing unit  1103  is passed from the EPC communication unit  1101  to the base station communication unit  1102 , and is transmitted to one or a plurality of Home-eNBs  72 - 2  through the S1 interface. A series of process by the HeNBGW  74  is controlled by a control unit  1104 . This means that, though not shown in  FIG. 11 , the control unit  1104  is connected to the respective units  1101  to  1103 . 
     The function of the HeNBGW  74  currently under discussion of 3GPP is described below (see Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW  74  relays an S1 application. The HeNBGW  74  terminates the S1 application that is not associated with the user equipment  71  though it is a part of the procedures toward the Home-eNB  72 - 2  and towards the MME unit  73 . When the HeNBGW  74  is deployed, the procedure that is not associated with the user equipment  71  is communicated between the Home-eNB  72 - 2  and the HeNBGW  74  and between the HeNBGW  74  and the MME unit  73 . The X2 interface is not set between the HeNBGW  74  and another node. The HeNBGW  74  recognizes the execution of paging optimization as an option. 
     Next, an example of a typical cell search method in a mobile communication system is described.  FIG. 12  is a flowchart showing an outline from cell search to idle state operation performed by a user equipment (UE) in the LTE communication system. When the cell search is started by the user equipment, in Step ST 1201 , the slot timing and frame timing are synchronized by a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a nearby base station. Synchronization codes, which correspond to physical cell identities (PCIs) assigned per cell one by one, are assigned to the synchronization signals (SS) including the P-SS and S-SS. The number of PCIs is currently studied in  504  ways, and these  504  ways are used for synchronization, and the PCIs of the synchronized cells are detected (specified). 
     Next, in Step ST 1202 , a reference signal RS of the synchronized cells, which is transmitted from the base station per cell, is detected and the received power is measured. 
     The code corresponding to the PCI one by one is used for the reference signal RS, and separation from another cell is enabled by correlation using the code. The code for RS of the cell is derived from the PCI specified in Step ST 1201 , which makes it possible to detect the RS and measure the RS received power. 
     Next, in Step ST 1203 , the cell having the best RS reception quality (for example, cell having the highest RS received power; best cell) is selected from one or more cells that have been detected up to Step ST 1202 . 
     In Step ST 1204 , next, the PBCH of the best cell is received, and the BCCH that is the broadcast information is obtained. A master information block (MIB) containing the cell configuration information is mapped on the BCCH over the PBCH. Accordingly, the MIB is obtained by obtaining the BCCH through reception of the PBCH. Examples of the MIB information include the downlink (DL) system bandwidth (also referred to as transmission bandwidth configuration (dl-bandwidth)), transmission antenna number and system frame number (SFN). 
     In Step ST  1205 , next, the DL-SCH of the cell is received based on the cell configuration information of the MIB, to thereby obtain a system information block (SIB)  1  of the broadcast information BCCH. The SIB 1  contains the information related to the access to the cell, information related to cell selection and scheduling information of other SIB (SIBk; k is an integer equal to or larger than two). In addition, the SIB 1  contains a tracking area code (TAC). 
     In Step ST 1206 , next, the user equipment compares the TAC of the SIB 1  received in Step ST 1205  with the TAC that has been already possessed by the user equipment. In a case where they are identical to each other as a result of comparison, the user equipment enters an idle state operation in the cell. In a case where they are different from each other as a result of comparison, the user equipment requires a core network (EPC) (including MME and the like) to change a TA through the cell for performing tracking area update (TAU). The core network updates the TA based on an identification number (such as a UE-ID) of the user equipment transmitted from the user equipment together with a TAU request signal. The core network updates the TA, and then transmits the TAU received signal to the user equipment. The user equipment rewrites (updates) the TAC (or TAC list) of the user equipment with the TAC of the cell. After that, the user equipment enters the idle state operation in the cell. 
     In the LTE and universal mobile telecommunication system (UMTS), the introduction of a closed subscriber group (CSG) cell is studied. As described above, access is allowed for only one or a plurality of user equipments registered with the CSG cell. The CSG cell and one or a plurality of user equipments that have been registered constitute one CSG. A specific identification number referred to as CSG-ID is added to the thus constituted CSG. Note that one CSG may contain a plurality of CSG cells. After being registered with any one of the CSG cells, the user equipment can access another CSG cell of the CSG to which the registered CSG cell belongs. 
     Alternatively, the Horne-eNB in the LTE or the Home-NB in the UMTS is used as the CSG cell in some cases. The user equipment registered with the CSG cell has a whitelist. Specifically, the whitelist is stored in the subscriber identity module (SIM)/USIM. The CSG information of the CSG cell with which the user equipment has been registered is stored in the whitelist. Specific examples of the CSG information include CSG-ID, tracking area identity (TAI) and TAC. Any one of the CSG-ID and TAC is adequate as long as they are associated with each other. Alternatively, GCI is adequate as long as the CSG-ID, TAC and global cell identity (GCI) are associated with each other. 
     As can be seen from the above, the user equipment that does not have a whitelist (including a case where the whitelist is empty in the present invention) is not allowed to access the CSG cell but is allowed to access the non-CSG cell only. On the other hand, the user equipment which has a whitelist is allowed to access the CSG cell of the CSG-ID with which registration has been performed as well as the non-CSG cell. 
     3GPP discusses that all physical cell identities (PCIs) are split (referred to as PCI-split) into ones reserved for CSG cells and the others reserved for non-CSG cells (see Non-Patent Document 5). Further, 3GPP discusses that the PCI split information is broadcast in the system information from the base station to the user equipments being served thereby. Non-Patent Document 5 discloses the basic operation of a user equipment by PCI split. The user equipment that does not have the PCI split information needs to perform cell search using all PCIs (for example, using all 504 codes). On the other hand, the user equipment that has the PCI split information is capable of performing cell search using the PCI split information. 
     Further, 3GPP has determined that the PCIs for hybrid cells are not contained in the PCI range for CSG cells (see Chapter 10.7 of Non-Patent Document 1). 
     The HeNB and HNB are required to support various types of service. For example, an operator causes the predetermined HeNB and HNB to register user equipments therein and permits only the registered user equipments to access the cells of the HeNB and HNB, so that the user equipments increase the available radio resources for performing high-speed communication. In such service, the operator sets a higher accounting fee compared with normal service. 
     In order to achieve the above-mentioned service, the closed subscriber group cell (CSG) cell accessible only to the registered (subscribed or member) user equipments is introduced. It is required to install a large number of closed subscriber group cell (CSG) cells in shopping malls, apartment buildings, schools, companies and the like. For example, the CSG cells are required to be installed for each store in shopping malls, for each room in apartment buildings, for each classroom in schools, and for each section in companies in such a manner that only the users who have registered with the respective CSG cells are permitted to use those CSG cells. The HeNB/HNB is required not only to complement the communication outside the coverage of the macro cell but also to support various types of service as described above. This leads to a case where the HeNB/HNB is installed within the coverage of the macro cell. 
     As one of the techniques to be studied in LTE-A, heterogeneous networks (HetNets) are added. 3GPP handles low-output-power network nodes in a local-area range (local area range nodes, local area nodes and local nodes), such as pico eNB (pico cell), node for hotzone cells, HeNB/HNB/CSG cell, relay node and remote radio head (RRH). Accordingly, it is required to deploy networks in which one or more of the above-mentioned local area range nodes are incorporated. The networks in which one or more of the above-mentioned local area range nodes are incorporated in a normal eNB (macro cell) are referred to as heterogeneous networks, where the interference reduction method, capacity enhancement method and the like are studied. 
     3GPP is pursuing specifications standard of long term evolution advanced (LTE-A) as Release 10 (see Non-Patent Document 6 and Non-Patent Document 7). 
     As to the LTE-A system, it is discussed that a relay (relay node (RN)) is supported for achieving a high communication rate, high cell-edge throughput, new coverage area or the like. 
     The following has been decided regarding the relay node. The relay node is described with reference to  FIG. 13 .  FIG. 13  is a diagram illustrating a relay node disclosed in Non-Patent Document  7 . A relay node  1302  is connected to a donor cell (Donor eNB; DeNB)  1301  via a link  1305 . The link  1305  is referred to as a backhaul link. The donor cell  1301  has a user equipment  1304  being served thereby. The donor cell  1301  is connected to the user equipment  1304  via a link  1307 . The link  1307  is referred to as a direct link. The link  1305  and the link  1307  share the same frequency band within the range of the donor cell  1301 . Further, it is also possible to connect the user equipment  1304  supporting the Release 8 specifications of 3GPP to the donor cell  1301 . The relay node  1302  has a user equipment  1303  being served thereby. The relay node  1302  is connected to the user equipment  1303  via a link  1306 . The link  1306  is referred to as an access link. 
     As the method of multiplexing backhaul links in FDD, the transmission from the donor cell  1301  to the relay node  1302  is performed in the downlink (DL) frequency band, whereas the transmission from the relay node  1302  to the donor cell  1301  is performed in the uplink (UL) frequency band. As the method of partitioning the resource at the relay node  1302 , the link  1305  from the donor cell  1301  to the relay node  1302  and the link  1306  from the relay node  1302  to the user equipment  1303  are time division multiplexed in a single carrier frequency, and the link  1305  from the relay node  1302  to the donor cell  1301  and the link  1306  from the user equipment  1303  to the relay node  1302  are time division multiplexed in a single carrier frequency as well. This prevents the transmission of the relay from causing interference to the reception of its own relay in the relay. 
     Further, Non-Patent Document 8 discloses that a problem described below occurs in the decisions as to the relay nodes by 3GPP. In a conventional technique, for preventing the transmission of a relay node from causing interference to the reception of its own relay node, the link from a donor cell to a relay node and the link from a relay node to a user equipment being served by the relay node are time division multiplexed in a single frequency band, and the link from a relay node to a donor cell and the link from a user equipment being served by a relay node to the relay node are time division multiplexed in a single frequency band as well. The interference caused by the transmission of a relay node to the reception of its own relay node is also referred to as self-interference in some cases. The time division multiplexing decreases a throughput, leading to a problem that the system performance degrades. 
     A solution disclosed in Non-Patent Document 8 is described below. In the solution disclosed in Non-Patent Document 8, the access link and backhaul link are operated in different carrier frequencies or different frequency bands. A specific method for the solution disclosed in Non-Patent Document 8 is described with reference to  FIG. 14 .  FIG. 14  is a diagram illustrating a relay node disclosed in Non-Patent Document 8. The portions of  FIG. 14  corresponding to those of  FIG. 13  are denoted by the same reference numerals, which are not described. 
     First,  FIG. 14( a )  is described. In the direct link  1307 , a frequency band A is used. In the backhaul link  1305 , the frequency band A is used. In the access link  1306 , among the carrier frequencies of the frequency band A, a carrier frequency different from the carrier frequency used in the backhaul link  1305  is used. In this manner, the configuration is made such that the carrier frequency differs between the access link and backhaul link. 
     Next,  FIG. 14( b )  is described. In the direct link  1307 , the frequency band A is used. In the backhaul link  1305 , the frequency band A is used. In the access link  1306 , a frequency band B is used. In this manner, the configuration is made such that the frequency band differs between the access link and backhaul link. 
     Then,  FIG. 14( c )  is described. In the direct link  1307 , the frequency band A is used. In the backhaul link  1305 , the frequency band B is used. In the access link  1306 , among the carrier frequencies of the frequency band B, a carrier frequency different from the carrier frequency used in the backhaul link  1305  is used. In this manner, the configuration is made such that the carrier frequency differs between the access link and backhaul link. 
     Then,  FIG. 14( d )  is described. In the direct link  1307 , the frequency band A is used. In the backhaul link  1305 , the frequency band  13  is used. In the access link  1306 , among the carrier frequencies of the frequency band A, a carrier frequency different from the carrier frequency used in the backhaul link  1305  is used. In this manner, the configuration is made such that the frequency band differs between the access link and backhaul link. 
     Next,  FIG. 14( e )  is described. In the direct link  1307 , the frequency band A is used. In the backhaul link  1305 , the frequency band B is used. In the access link  1306 , a frequency band C is used. In this manner, the configuration is made such that the frequency band differs between the access link and backhaul link. 
     As a result of the use of different carrier frequencies or different frequency bands between in the case where a donor cell schedules backhaul and in the case where a relay node schedules an access link as described above, it is not required to use time division multiplexing. Accordingly, the improvement of a throughput is aimed in the technique disclosed in Non-Patent Document 8. 
     However, a problem described below occurs even in a case of using the technique disclosed in Non-Patent Document 8. In the direct link and access link, the load of a user equipment in a search operation increases due to different carrier frequencies. This causes a control delay of a user equipment, leading to a problem that power consumption increases. 
     A specific example in which the above-mentioned problem occurs is described with reference to  FIG. 15 .  FIG. 15  is a location diagram illustrating a problem of Non-Patent Document 8. A donor cell  1501  has a coverage  1502 . A relay node  1503  is installed in the vicinity of a cell edge of the donor cell  1501 . The relay node  1503  has a coverage  1504 . A user equipment  1505  in an idle state is present in the coverage of the donor cell. Considered here is the case where the user equipment  1505  moves from the vicinity of the donor cell  1501  to the vicinity of the relay node  1503 . Upon the moving, the user equipment  1505  performs cell reselection to the relay node  1503  based on the measurement results of neighboring cells. The outline of a cell search operation is as shown in  FIG. 12 . 
     In the technique disclosed in Non-Patent Document 8, the carrier frequency differs between the direct link and access link, and accordingly in  FIG. 15 , cell reselection to the relay node  1503  cannot be achieved if the cell search operation is not performed in a carrier frequency different from the carrier frequency of the donor cell  1501  being a serving cell. The user equipment  1505  is not able to ascertain the carrier frequency used by the relay node  1503  in the access link. As described above, a problem that the load of a user equipment in a search operation increases occurs in the technique of Non-Patent Document 8. 
     In specific method for the solution described in  FIG. 14( c ) ,  FIG. 14( d )  and  FIG. 14( e ) , three different carrier frequencies are required for installing a relay node. This causes a problem that the frequency use efficiency decreases in a mobile communication system. 
     Therefore, in the present embodiment, the access link and direct link are configured to use the same frequency baud, same carrier, same component carrier or same frequency layer. This eliminates the need for a search operation in a different frequency band, different carrier, different component carrier or different frequency layer, leading to an effect that the load of a user equipment in a search operation is reduced. 
     Further, in the present embodiment, only the backhaul link is configured to use a different frequency band, different carrier, different component carrier or different frequency layer. This achieves an effect that self-interference of a relay node is prevented. 
     The frequency band is described below. The systems such as UMTS terrestrial radio access (UTRA), LTE and LTE-A are designed such that an operation is made in a frequency band (merely referred to as band in some cases) consisting of several successive frequencies in the uplink as well as downlink. Each frequency band as described above is referred to as a frequency band or operating band at times. 
     The component carrier is described below (see Chapter 5 of Non-Patent Document 6). A user equipment supporting LTE-A is considered to have the capability for carrier aggregation to simultaneously receive and transmit on a plurality of component carriers, only receive on those or only transmit on those. 
       FIG. 16  is a conceptual diagram of the configuration of a frequency band of the LTE-A system. In  FIG. 16 , a reference numeral  1601  denotes a physical downlink control channel (PDCCH).  FIG. 16  shows an example in which a physical downlink control channel is mapped for each of all component carriers, which is not limited thereto. As another example, it is conceivable that the component carrier to which a physical downlink control channel is mapped and a component carrier to which a physical downlink control channel is not mapped may coexist. 
     In  FIG. 16 , reference numerals  1602 ,  1603 ,  1604 ,  1605  and  1606  denote a downlink synchronization signal (SS) and a physical broadcast channel (PBCH).  FIG. 16  shows the example in which the downlink synchronization signal and physical broadcast channel (or broadcast information) are mapped per component carrier, which is not limited thereto. As another example, it is conceivable that a component carrier to which a downlink synchronization signal and a physical broadcast channel are mapped and a component carrier to which a downlink synchronization signal and a physical broadcast channel are not mapped may coexist. 
     A base station having the bandwidth of 20 MHz as a component carrier and including five such component carriers in an LIE-A system is considered with reference to  FIG. 16 . The carrier frequencies of the respective component carriers are fa, fb, fc, fd and fe. That is, considered here is a base station having a downlink transmission bandwidth of 100 MHz. The bandwidth of a component carrier is not limited to 20 MHz, and 3GPP is discussing the bandwidth of 20 MHz or smaller at a meeting. In addition, the bandwidth of a component carrier supported by one base station is not limited to one type. The downlink transmission bandwidth of a base station in the LTE-A system is not limited to 100 MHz, and 3GPP is discussing the bandwidth of 100 MHz or smaller at a meeting.  FIG. 16  shows the case of the successive component carriers, which is not limited thereto, and carrier aggregation is enabled by a receiver even in the case of non-successive component carriers. 
     An example of a specific method for a solution of the first embodiment is described with reference to  FIG. 17 .  FIG. 17  is a diagram illustrating a relay node in a case where the solution of the first embodiment is used. The portions of  FIG. 17  corresponding to those of  FIG. 13  are denoted by the same reference numerals, which are not described. In  FIG. 17 , the donor cell  1301  corresponds to a base station device, the relay node  1302  corresponds to a relay device, and the user equipments  1303  and  1304  correspond to user equipment devices. The mobile communication system includes the donor cell  1301 , relay node  1302 , and user equipments  1303  and  1304 . 
     In the present embodiment, each of carriers having the same frequency is used in the direct link  1307  and the access link  1306 , and a carrier having a different frequency from that of the carrier used in the direct link  1307  and the access link  1306  is used in the backhaul link  1305 . The frequency of the carrier used in the direct link, access link and backhaul link may be set on a frequency band, component carrier or frequency layer basis. 
     For example, the frequency band A is used in the direct link  1307 . The frequency band B is used in the backhaul link  1305 . The same frequency band A as that of the direct link  1307  is used in the access link  1306 . In this manner, the configuration is made such that the same frequency band is used in the access link and direct link and a different frequency band is used only in the backhaul link. 
     3GPP is discussing the self organized network (SON) for allowing automatic operation of a network. The present embodiment discloses the method of allowing automatic operation of a network below. A donor cell notifies the frequency information for a relay node. The donor cell may notify the frequency information for a relay node using a direct link, using a backhaul link, or using both of them. The notification of the frequency information for a relay node using a direct link allows a relay node to obtain the frequency information for a relay node even in a case where the relay node camps on the direct link in, for example, installation. The notification of the frequency information for a relay node using a backhaul link allows a relay node to obtain the frequency information for a relay node even in a case where the relay node camps on the backhaul link in, for example, installation. 
     Three specific examples of the frequency information for a relay node in a case where notification is made using a direct link are disclosed below. 
     (1) A frequency band, carrier or component carrier can be used in a backhaul link. Alternatively, it may be a frequency band, carrier or component carrier that is not used in a direct link. 
     (2) A frequency band, carrier or component carrier can be used in an access link. It may be a frequency band, carrier or component carrier used in a direct link. Alternatively, for example, by setting that the carrier having the same frequency as that of the direct link may be used in the access link, the information may be omitted. Accordingly, an effect that radio resources are effectively used is achieved. 
     (3) Both of (1) and (2) described above. 
     Four specific examples of the frequency information for a relay node in a case where notification is made using a backhaul link are disclosed below. 
     (1) Notification that the link is backhaul. Alternatively, notification that priority is given to backhaul in the link. The notification allows a user equipment being served by a donor cell to reselect another cell even in a case where the user equipment selects a backhaul link as the best cell in cell selection, cell reselection, handover or the like. 
     (2) A frequency band, carrier or component carrier used in a direct link. 
     (3) A frequency band, carrier or component carrier can be used in an access link. Alternatively, for example, by setting that the carrier having the same frequency as that of the direct link may be used in the access uplink, the information may be omitted. Accordingly, an effect that radio resources are effectively used is achieved. 
     (4) Notification of the combination of (1), (2) and (3) described above. 
     Two specific examples of the method of notifying the frequency information for a relay node from a donor cell to a relay node are disclosed below. (1) Notification is made as the broadcast information. (2) Notification is made as the dedicated control information. In a case where notification is made as the dedicated control information, the donor cell and relay node perform, for example, RRC connection. The RRC connection may be performed upon a request from a relay node. The relay node may notify the donor cell of “indication for a relay node” using the RRC connection. After the notification, the donor cell may notify the relay node of the frequency information for a relay node. 
     Next, a sequence example of a mobile communication system in a case of using the solution of the first embodiment is described with reference to  FIG. 17  and  FIG. 18 .  FIG. 17  has been described above, which is not described here.  FIG. 18  is a diagram illustrating a sequence example of a mobile communication system in a case of using the solution of the first embodiment and also in the case where the relay node performs cell selection to the direct link (band A in the example of  FIG. 17 ) in, for example, installation. In Step ST 1800 , the relay node  1302  performs cell selection to the direct link  1307  of the donor cell  1301 . That is, the relay node  1302  camps on the direct link. In Step ST 1801 , the donor cell  1301  notifies the relay node  1302  being served thereby of the frequency band can be used in the backhaul link  1305  and the frequency band can be used in the access link  1306  using the direct link  1307 . 
     In Step ST 1802 , the relay node  1302  sets the frequency band of the backhaul link  1305  as the frequency band can be used in the backhaul link  1305  that has been received in Step ST 1801 . In a case where a plurality of frequency bands have been received in Step ST 1801 , the relay node  1302  selects one from the plurality of frequency bands and sets the selected one. 
     In Step ST 1803 , the relay node  1302  sets the frequency band of the access link  1306  as the frequency band can be used in the access link  1306  that has been received in Step ST 1801 . In a case where a plurality of frequency bands have been received in Step ST 1801 , the relay node  1302  selects one from the plurality of frequency bands and sets the selected one. 
     In Step ST 1804 , the relay node  1302  re-camps on the backhaul link  1305  (performs cell reselection) using the frequency band can be used in the backhaul link that has been received in Step ST 1801 . 
     The first embodiment achieves the effects below. The frequency of a carrier to be used, specifically, frequency band, carrier, component carrier or frequency layer is the same between the access link  1306  and the direct link  1307 , and accordingly the search operation of a user equipment is simplified. This reduces the load of a user equipment, which contributes to lower power consumption. 
     The frequency of a carrier to be used differs between the backhaul link  1305  and the access link  1306 , specifically, a different frequency band or the like is used therebetween, and accordingly self-interference of the relay node  1302  is reduced. 
     Therefore, in the present embodiment, it is possible to prevent the interference in a mobile communication system as well as reduce the load of a user equipment in the search operation. 
     Further, the installation of the relay node  1302  requires only two different carriers, which improves the frequency use efficiency. 
     First Modification of First Embodiment 
     A first modification of the first embodiment is described. In the first embodiment described above, the same frequency band or the like is used in the uplink (direct link) from a user equipment being served by a donor cell and the uplink (access link) from a user equipment being served by a relay node, and accordingly, uplink interference occurs in the coverage of the donor cell at times. Uplink scheduling is performed by the serving cell. That is, the donor cell and relay node individually perform uplink scheduling on user equipments being served thereby. Accordingly, for reducing the uplink interference through uplink scheduling, a control delay increases and a mobile communication system is complicated as well. 
     The uplink interference is described with reference to  FIG. 19 .  FIG. 19  is a location diagram for illustrating the uplink interference. The portions of  FIG. 19  corresponding to those of  FIG. 15  are denoted by the same reference numerals, which are not described. A user equipment  1901  is located in the vicinity of the cell edge of the relay node  1503  and is also located in the coverage  1502  of the donor cell  1501 . The user equipment  1901  performs transmission/reception with the donor cell  1501 . Another user equipment  1902  is located in the coverage  1504  of the relay node  1503  and is also located in the coverage  1502  of the donor cell  1501 . The user equipment  1902  performs transmission/reception with the relay node  1503 . 
     The uplinks of the two user equipments  1901  and  1902  are studied. The user equipment  1901  communicates with the donor cell  1501  using an uplink  1903 . The uplink  1903  is a direct link. The another user equipment  1902  communicates with the relay node  1503  using an uplink  1905 . The uplink  1905  is an access link. In a case of using the first embodiment, the frequency band or the like is the same between the direct link and access link. Due to the communication between the user equipment  1901  and the donor cell  1501 , uplink interference  1904  occurs for the relay node  1503  in some cases. Further, due to the communication between the another user equipment  1902  and the relay node  1503 , uplink interference  1906  occurs for the donor cell  1501  in some cases. In  FIG. 19 , the interference is indicated by a broken line. 
     A solution in the first modification of the first embodiment is described below. The portion different from the solution of the first embodiment described above is mainly described here. The portion that is not descried here is similar to the first embodiment. 
     In the present modification, a different frequency band, different carrier, different component carrier or different frequency layer is used in the direct uplink and access uplink. This enables to divide the frequency of uplink (direct link) from a user equipment being served by a donor cell to the donor cell and the frequency of uplink (access link) from a user equipment being served by a relay node to the relay node. Accordingly, it is possible to reduce the uplink interference. 
     As a specific example, the frequencies of carriers to be used, specifically, the frequency bands, carriers, component carriers or frequency layers of a backhaul link and an access link are changed only in the uplink. Therefore, the configuration is made such that the frequency of a carrier to be used in the uplink differs between the direct uplink and access uplink, that is, a different frequency band, different carrier, different component carrier or different frequency layer is used therebetween. This enables to divide the frequency of uplink (direct link) from a user equipment being served by a donor cell to the donor cell and the frequency of uplink (access link) from a user equipment being served by a relay node to the relay node. Accordingly, it is possible to reduce the uplink interference. 
     A specific example of the solution of the first modification of the first embodiment is described with reference to  FIG. 20  and  FIG. 21 . The solution of the first embodiment is described again with reference to  FIG. 20 .  FIG. 20  is a diagram illustrating a relay node in the case of using the solution of the first embodiment. The portions of  FIG. 20  corresponding to those of  FIG. 13  are denoted by the same reference numerals, which are not described. In a direct downlink  2005  being a downlink of direct links, for example, a frequency band A_DL is used. In a direct uplink  2006  being an uplink of the direct links, for example, a frequency band A_UL is used. In  FIG. 20 , the donor cell  1301  corresponds to a base station device, the relay node  1302  corresponds to a relay device, and the user equipments  1303  and  1304  correspond to user equipment devices. The mobile communication system includes the donor cell  1301 , relay node  1302 , and user equipments  1303  and  1304 . The uplink corresponds to an uplink of radio communication, and the downlink corresponds to a downlink of radio communication. 
     In a backhaul downlink  2001  being a downlink of backhaul links, for example, a frequency band B_DL is used. In a backhaul uplink  2002  being an uplink of the backhaul links, for example, a frequency band B_UL is used. In an access downlink  2003  being a downlink of access links, for example, a frequency band A_DL is used. In an access uplink  2004  being an uplink of the access links, for example, a frequency band A_UL is used. Therefore, the configuration is made such that the access links  2003  and  2004  and the direct links  2005  and  2006  use the same frequency band A and only the backhaul links  2002  and  2001  use the different frequency band B. 
     Next, the solution of the first modification of the first embodiment is described with reference to  FIG. 21 .  FIG. 21  is a diagram illustrating the relay node in a case of using the solution of the first modification of the first embodiment. The portions of  FIG. 21  corresponding to those of  FIG. 13  and  FIG. 20  are denoted by the same reference numerals, which are not described. In the present modification, the frequency bands or the like of the backhaul link and access link are changed only in the uplink. In  FIG. 21 , the donor cell  1301  corresponds to a base station device, the relay node  1302  corresponds to a relay device, and the user equipments  1303  and  1304  correspond to user equipment devices. 
     That is, in a backhaul uplink  2101 , for example, the frequency band B_UL used in the first embodiment is changed to the frequency band A_UL used in the access uplink  2004  in the first embodiment. In an access uplink  2102 , for example, the frequency band A_UL used in the first embodiment is changed to the frequency band B_UL used in the backhaul uplink  2002  in the first embodiment. In the uplink  2006  from the user equipment  1304  being served by the donor cell  1301  to the donor cell  1301 , for example, the frequency band A_UL is used as in the first embodiment. 
     This enables to divide the frequency of uplink  2006  from the user equipment  1304  being served by the donor cell  1301  to the donor cell  1301  and the frequency of uplink  2102  from the user equipment  1303  being served by the relay node  1302  to the relay node  1302 . Accordingly, it is possible to reduce the uplink interference. 
     Meanwhile, the same frequency band or the like is used in the uplink  2006  from the user equipment  1304  being served by the donor cell  1301  to the donor cell  1301  and the uplink  2101  from the relay node  1302  to the donor cell  1301 . The donor cell  1301  performs uplink scheduling for the user equipment  1304  and the relay node  1302 . Therefore, it is possible to easily reduce the uplink interference due to scheduling, with a small control delay. 
     Put the solution in the first modification of the first embodiment another way, the downlinks  2001  and  2005  from the donor cell  1301  use a different frequency band or the like in the direct link  2005  and the backhaul link  2001 . Meanwhile, in the uplinks  2006  and  2101  to the donor cell, the same frequency band or the like is allocated as the uplink frequency band for the direct link  2006  (also referred to as a pair band with the direct downlink  2005 ) and the uplink frequency band for the backhaul link  2101 . That is, in the present modification, the donor cell  1301  allocates different frequency bands to the direct downlink  2005  and the backhaul downlink  2001  and allocates the same frequency band to the pair band with the direct downlink  2005  and the pair band with the backhaul downlink  2001 . 
     The method of enabling the automatic operation of a network in the first modification of the first embodiment is disclosed below. A donor cell notifies the frequency information for a relay node. The donor cell may notify the frequency information for a relay node using a direct link, using a backhaul link, or using both of them. The notification of the frequency information for a relay node using a direct link allows a relay node to obtain the frequency information for a relay node even in a case where the relay node camps on the direct link in, for example, installation. The notification of the frequency information for a relay node using a backhaul link allows a relay node to obtain the frequency information for a relay node even in a case where the relay node camps on the backhaul link in, for example, installation. 
     Four specific examples of the frequency information for a relay node in a case where notification is made using a direct link are disclosed below. 
     (1) A frequency band, carrier or component carrier can be used in a backhaul downlink. Alternatively, it may be a frequency band, carrier or component carrier that is not used in a direct downlink. 
     (2) A frequency band, carrier or component carrier can be used in an access downlink. It may be a frequency band, carrier or component carrier used in a direct downlink. Alternatively, for example, by setting that the carrier having the same frequency as that of the direct downlink may be used in the access downlink, the information may be omitted. Accordingly, an effect that radio resources are effectively used is achieved. 
     (3) A frequency band, carrier or component carrier can be used in an access uplink. Alternatively, for example, by setting that the carrier having the different frequency from that of the direct uplink may be used in the access uplink, the information may be omitted. Accordingly, an effect that radio resources are effectively used is achieved. 
     (4) (1), (2) and (3) described above may be combined and notified. 
     Four specific examples of the frequency information for a relay node in a case where notification is made using a backhaul link are disclosed below. 
     (1) Notification that the link is backhaul. Alternatively, notification that priority is given to backhaul in the link. The notification allows a user equipment being served by a donor cell to reselect another cell even in a case where the user equipment selects a backhaul link as the best cell in cell selection, cell reselection, handover or the like. 
     (2) A frequency band, carrier or component carrier can be used in an access downlink. Alternatively, it may be a frequency band, carrier or component carrier used in the direct downlink. 
     (3) A frequency band, carrier or component carrier can be used in an access uplink. Alternatively, it may be a frequency band, carrier or component carrier used in the direct uplink Still alternatively, for example, by setting that the carrier having the different frequency from that of the backhaul uplink may be used in the access uplink, the information may be omitted. Accordingly, an effect that radio resources are effectively used is achieved. 
     (4) (1), (2) and (3) described above may be combined and notified. 
     Two specific examples of the method of notifying the frequency information for a relay node from a donor cell to a relay node are disclosed below. (1) Notification is made as the broadcast information. (2) Notification is made as dedicated control information. In a case where notification is made as the dedicated control information, the donor cell and relay node perform, for example, RRC connection. The RRC connection may be performed upon a request from a relay node. The relay node may notify the donor cell of “indication of a relay node” using the RRC connection. After the notification, the donor cell may notify the relay node of the frequency information for a relay node. 
     Next, the sequence example of a mobile communication system in the case of using the solution of the first modification of the first embodiment is described with reference to  FIG. 21  and  FIG. 22 .  FIG. 21  has been described above, which is not described here.  FIG. 22  is a diagram illustrating a sequence example of a mobile communication system in a case of using the solution of the first modification of the first embodiment and also in a case where the relay node performs cell selection to the direct link (band A_DL in the example of  FIG. 21 ) in, for example, installation. 
     In Step ST 2200 , the relay node  1302  performs cell selection to the direct downlink  2005  of the donor cell  1301 . That is, the relay node  1302  camps on the direct link. In Step ST 2201 , the donor cell  1301  notifies the relay node  1302  being served thereby, using the direct downlink  2005 , of the frequency band can be used in the backhaul downlink  2001 , the frequency band can be used in the access downlink  2003 , and the frequency band can be used in the access uplink  2102 . 
     In Step ST 2202 , the relay node  1302  sets the frequency band of the backhaul downlink  2001  as the frequency band can be used in the backhaul downlink  2001  that has been received in Step ST 2201 . In a case where a plurality of frequency bands have been received in Step ST 2201 , the relay node  1302  selects one from the plurality of frequency bands and sets the selected one. 
     In Step ST 2203 , the relay node  1302  selects the same frequency band as that of the direct uplink  2006  being a pair band with the direct downlink  2005  and set as the frequency band of the backhaul uplink  2101 . 
     In Step ST 2204 , the relay node  1302  sets the frequency band of the access downlink  2003  as the frequency band can be used in the access downlink  2003  that has been received in Step ST 2201 . In a case where a plurality of frequency bands have been received in Step ST 2201 , the relay node  1302  selects one from the plurality of frequency bands and sets the selected one. 
     In Step ST 2205 , the relay node  1302  sets the frequency band of the access uplink  2102  as the frequency band can be used in the access uplink  2102  that has been received in Step ST 2201 . In a case where a plurality of frequency bands have been received in Step ST 2201 , the relay node  1302  selects one from the plurality of frequency bands and sets the selected one. 
     In Step ST 2206 , the relay node  1302  re-camps on the backhaul link (performs cell reselection) using the frequency band can be used in the backhaul downlink that has been received in Step ST 2201 . 
     In the present modification, the donor cell notifies the relay node of, for example, the frequency different from that of the carrier used in the backhaul downlink  2001  and same as that of the carrier used in the direct downlink  2005  as the frequency information of the carrier used in the access downlink  2003 . Further, the donor cell notifies the relay node of, for example, the frequency different from that of the carrier used in the backhaul uplink  2101  and also different from that of the carrier used in the direct uplink  2006  as the frequency information of the carrier used in the access uplink  2102 . The relay node sets the frequencies of the carriers used in the uplink and downlink of the access link based on the frequency information notified from the donor cell. 
     The first modification of the first embodiment achieves an effect below in addition to the effects of the first embodiment. It is possible to divide the frequency of uplink from a user equipment being served by a donor cell to the donor cell and the frequency of uplink from a user equipment being served by a relay node to the relay node. Accordingly, it is possible to reduce the uplink interference. 
     Second Embodiment 
     A second embodiment of the present invention discloses a solution different from that of the first embodiment for the problem of the present invention. The solution in the second embodiment is disclosed below. The donor cell notifies a user equipment being served thereby of the information of the access link used in a relay node being served thereby. The user equipment that has received the information performs a search operation using the carrier used in the access link. 
     Alternatively, the relay node may notify a user equipment being served thereby of the information of the direct link used in the donor cell. The user equipment that has received the information performs a search operation using the carrier used in the direct link. 
     As a result, the user equipment can ascertain the carrier frequency that is used in the access link by the relay node. Therefore, it is possible to reduce the load of a user equipment in a search operation. 
     Specific examples of the information of the access link include the frequencies of carriers to be used, more specifically, the frequency bands, carriers, component carriers and frequency layers. As a specific example of the notification method, notification is made as the broadcast information. This enables to notify a user equipment being served thereby without using a dedicated channel. Accordingly, radio resources can be effectively used. Further, notification can be made irrespective of the state (connected state, idle state) of a user equipment being served thereby. 
     Three specific examples of the broadcast information are disclosed below. 
     (1) Mapping is performed to an SIB 3 . The information common to intra-frequency cell reselection, inter-frequency cell reselection and inter-system cell reselection is mapped to the SIB 3  (see Non-Patent Document 9). Accordingly, through mapping of the “information of access link” to the SIB 3 , a user equipment is allowed to receive the “information of access link” being the information related to the cell reselection together with the conventional “information common to cell reselection”. This reduces the load of the processing in cell reselection by a user equipment and also reduces a control delay. 
     (2) Mapping is performed to an SIBS. The information related to inter-frequency cell reselection is mapped to the SIBS (see Non-Patent Document 9). Accordingly, through mapping of the “information of access link” to the SIB 5 , a user equipment is allowed to receive the “information of access link” being the information related to the inter-frequency cell reselection together with the conventional “information related to the inter-frequency cell reselection”. This reduces the load of the processing in inter-frequency cell reselection by a user equipment and also reduces a control delay. 
     (3) Mapping is performed to neighboring cell setting. The neighboring cell setting is also referred to as “neighCellConfig” (see Non-Patent Document 9). Accordingly, through mapping of the “information of access link” to the neighboring cell setting, a user equipment is allowed to receive the “information of access link” being the information related to a neighboring cell of a serving cell (donor cell) together with the conventional “neighboring cell setting”. This reduces the load of the processing for receiving the neighboring cell information by a user equipment and also reduces a control delay. 
     A specific operation example using the second embodiment is described with reference to  FIG. 14( b )  described above and  FIG. 23 .  FIG. 14( b )  has been described above, which is not described here.  FIG. 23  is a diagram illustrating a sequence example of a mobile communication system in a case of using a solution of the second embodiment. In Step ST 2301 , the donor cell  1301  broadcasts the information of the access link of the relay node  1302  to user equipments including the user equipment  1304  being served thereby. For example, in  FIG. 14( b ) , the donor cell  1301  broadcasts the band B as the information of the access link of the relay node  1302  to user equipments including the user equipment  1304  being served thereby. 
     In Step ST 2302 , the user equipment  1304  performs the cell search operation using the information of the access link that has been received in Step ST 2301 . 
     The second embodiment achieves an effect below. A user equipment can ascertain, for example, the carrier frequency used in the access link by the relay node. This simplifies the search operation of a user equipment. Therefore, the load of a user equipment can be reduced, which contributes to lower power consumption. 
     Third Embodiment 
     A problem to be solved by a third embodiment is described below. In a case where a HeNB is installed in the coverage of a cell or in the vicinity thereof, interference occurs in the uplink, similarly to a donor cell and a relay node. 
     A solution of the third embodiment is described below. A HeNB uses a carrier of a frequency different from that of a carrier used in the uplink of a neighboring cell in the uplink. Specifically, a HeNB uses a frequency band, carrier, component carrier or frequency layer, which is different from a frequency band, carrier, component carrier or frequency layer used in the uplink of a neighboring cell, in an uplink. This enables to divide the frequency of uplink from a user equipment being served by a neighboring cell to the neighboring cell and the frequency of uplink from a user equipment being served by a HeNB to the HeNB. Accordingly, it is possible to reduce the uplink interference. 
     Alternatively, a HeNB may use the same frequency band, carrier, component carrier or frequency layer as a frequency band, carrier, component carrier or frequency layer used in the downlink of a neighboring cell. This makes the downlink of a neighboring cell and the downlink of a HeNB have the same carrier or the like, which simplifies the search operation of a user equipment. Accordingly, it is possible to reduce the load of a user equipment, which contributes to lower power consumption. 
     A specific example of the solution of the third embodiment is described with reference to  FIG. 24 .  FIG. 24  is a diagram illustrating a HeNB in a case of using the solution of the third embodiment. A neighboring cell, for example, a macro cell  2401  is connected to a HeNB  2402  by means of an S1 interface  2405 . The neighboring cell  2401  has a user equipment  2404  served thereby. The neighboring cell  2401  is connected to a user equipment  2404  via a downlink  2408  and an uplink  2409 . For example, the frequency band A is used in the downlink  2408  and the frequency band A is used in the uplink  2409 . 
     In  FIG. 24 , the macro cell  2401  and the HeNB  2402  correspond to base station devices, and user equipments  2403  and  2404  correspond to user equipment devices. The mobile communication system includes the macro cell  2401 , HeNB  2402  and user equipments  2403  and  2404 . 
     The HeNB  2402  has the user equipment  2403  being served thereby. The HeNB  2402  is connected to the user equipment  2403  via a downlink  2406  and an uplink  2407 . In the uplink  2407 , a carrier of a frequency different from that of the uplink  2409  of the neighboring cell  2401  is selected as a carrier to be used and set. Specifically, for example, a frequency band different from that of the uplink  2409  of the neighboring cell  2401  is selected and set. In  FIG. 24 , for example, the frequency band B is used in the uplink  2407 . 
     In the downlink  2406 , a carrier having the same frequency as that of the downlink  2408  of the neighboring cell  2401  is selected as a carrier to be used, and then is set. Specifically, for example, the same frequency band as that of the downlink  2408  of the neighboring cell  2401  is selected and set. In  FIG. 24 , for example, the frequency band A is used in the downlink  2406 . 
     This enables to divide the frequency of uplink  2409  from the user equipment  2404  being served by the neighboring cell  2401  to the neighboring cell  2401  and the frequency of uplink  2407  from the user equipment  2403  being served by the HeNB  2402  to the HeNB  2402 . 
     Two specific examples of the method of allowing a HeNB to ascertain the frequency information of the neighboring cell are disclosed below. 
     (A1) A neighboring cell notifies a neighboring node of the frequency information of own cell using the S1 interface  2405 . 
     (A2) A HeNB measures a surrounding radio environment in initialization, turning-on of power or turning-off of transmission at times. Specific examples of the surrounding radio environment include the measurement results of neighboring cells. In measuring neighboring cells, a HeNB stores the frequency information used in the downlink of the neighboring cell. In addition, a HeNB receives the broadcast information of the neighboring cell, decodes the broadcast information, ascertains the frequency information used in the uplink of a neighboring cell that is included in the broadcast information, and stores the frequency information used in the uplink of the neighboring cell. 
     Specific examples of the frequency information include the frequency information used in the uplink and the frequency information used in the downlink, and further include a frequency band, carrier, component carrier and frequency layer. It is conceivable that specific examples of the frequency information used in the uplink in LTE and LTE-A may include a carrier frequency (ul-CarrierFreq) and an uplink bandwidth (ul-bandwidth). 
     Disclosed below is one specific example of the method of determining, by a serving cell, a neighboring node that is notified of the frequency information of own cell in a case where the specific example described in (A1) above is used in the specific example of the method of allowing a HeNB to ascertain the frequency information of the neighboring cell. One or a plurality of nodes may be notified of the frequency information of own cell. The selection of a node that is notified of the frequency information of own cell by a method described below enables to select a neighboring node. This eliminates the need to notify also an unnecessary node of the frequency information of own cell, whereby the load of the processing by a serving cell is reduced. 
     (B) 3GPP is currently discussing that in a case where a HeNB is installed, the network is notified of the location information of the HeNB. A serving cell determines a neighboring node that is notified of the frequency information of own cell based on the location of the own cell and the location information of the HeNB. As a specific example, a serving cell obtains the distance between own cell and the HeNB from the locations thereof. If the distance is equal to or larger than a certain threshold (or is larger than a threshold), a serving cell selects that node as the node that is notified of the frequency information of own cell. 
     Disclosed below is a specific example of the method of determining, by a HeNB, a neighboring cell that stores the frequency information broadcast information used in a downlink and a neighboring cell that decodes the broadcast information and stores the frequency information used in an uplink in a case where the specific example described in (A2) above is used in the specific example of allowing the HeNB to ascertain the frequency information of the neighboring cell. 
     Based on the measurement results of a surrounding radio environment of the HeNB, the HeNB determines a neighboring cell that stores the frequency information broadcast information used in a downlink, decodes the broadcast information and stores the frequency information used in an uplink. Specific examples of the surrounding radio environment include the measurement results of a neighboring cell. Specific examples of the measurement results of a neighboring cell include the reception quality, received power and path loss. 
     If the reception quality or received power of a certain node is equal to or larger than a certain threshold (or is larger than a threshold) in the measurement results of a surrounding radio environment, a HeNB selects that cell as the neighboring cell that stores the frequency information broadcast information used in a downlink, receives the broadcast information, decodes the broadcast information and stores the frequency information used in an uplink. Alternatively, if the path loss of a certain node is smaller (or is equal to or smaller) than a certain threshold in the measurement results of a surrounding radio environment, a HeNB selects that cell as the neighboring cell that stores the frequency information broadcast information used in the downlink, receives the broadcast information, decodes the broadcast information, and stores the frequency information used in an uplink. 
     One or a plurality of neighboring cells may receive the broadcast information, decode the broadcast information and store the frequency information. The selection of a neighboring cell that receives the broadcast information, decodes the broadcast information and stores the frequency information enables to select a neighboring cell. This eliminates the need to receive the broadcast information, decode the broadcast information and store the frequency information wastefully by a neighboring cell, which reduces the load of the processing of a HeNB. 
     Disclosed below is a specific example of the method of selecting the frequency information used in a downlink in a case where a plurality of neighboring cells receive the broadcast information, decode the broadcast information and store the frequency information or in a case where a plurality of neighboring cells have notified the frequency information, as a result of the measurement results of a surrounding radio environment of a HeNB. 
     In the case where a plurality of neighboring cells receive the broadcast information, decode the broadcast information and store the frequency information, a HeNB determines the frequency information used in a downlink based on the measurement results of the surrounding radio environment of a HeNB. Specific examples of the surrounding radio environment include the measurement results of a neighboring cell. Specific examples of the measurement results of a neighboring cell include the reception quality, received power and path loss. 
     In the measurement results of a surrounding radio environment, a HeNB uses the same frequency band, carrier, component carrier or frequency layer as the frequency band, carrier, component carrier or frequency layer used in a downlink of the cell having the best reception quality, the cell having the largest received power, or the cell having the smallest path loss. 
     This enables to make the frequency information identical to that of the downlink of a neighboring cell which is considered to be located in the closest vicinity thereof. That is, it is possible to make the frequency information identical to that of the downlink of a neighboring cell that has a user equipment being served thereby, the user equipment being highly expected to reselect own HeNB cell. In addition, it is possible to make the frequency information identical to that of the downlink of a neighboring cell highly expected to be selected as a cell reselection destination by a user equipment being served by own HeNB cell. Therefore, it is the most effective cell selection method from the viewpoint of a load reduction of a user equipment in a sell reselection operation. 
     Disclosed below are two specific examples of the method of selecting the frequency information used in an uplink in a case where a plurality of neighboring cells receive the broadcast information, decode the broadcast information and store the frequency information or in a case where a plurality of neighboring cells have notified the frequency information, as a result of the measurement results of a surrounding radio environment of a HeNB. In the case where a plurality of neighboring cells receive the broadcast information, decode the broadcast information and store the frequency information, a HeNB determines the frequency information used in an uplink based on the measurement results of a surrounding radio environment of a HeNB. Specific examples of the surrounding radio environment include the measurement results of a neighboring cell. Specific examples of the measurement results of a neighboring cell include the reception quality, received power and path loss. 
     (1) In the measurement results of a surrounding radio environment, a HeNB uses a frequency band, carrier, component carrier or frequency layer different from the frequency band, carrier, component carrier or frequency layer used in an uplink of the cell having the best reception quality, the cell having the largest received power or the cell having the smallest path loss. This enables to make the frequency information different from that of the uplink of a neighboring cell which is considered to be located in the closest vicinity thereof. Therefore, it is the most effective cell selection method from the viewpoint of a reduction of uplink interference. 
     (2) A HeNB uses a frequency band, carrier, component carrier or frequency layer different from the frequency bands, carriers, component carriers or frequency layers used in the uplink of all neighboring cells. It is possible to make the frequency information different from that of the uplinks of a large number of neighboring cells. Accordingly, it is possible to reduce the uplink interference between a large number of cells. 
     A specific operation example using the third embodiment is described with reference to  FIG. 24  and  FIG. 25 .  FIG. 24  has been described above, which is not described here. Next, an example of the operation of setting the frequency information of a HeNB in a case where the third embodiment is used is described with reference to  FIG. 25 .  FIG. 25  is a flowchart showing the procedure of the example of the operation of setting the frequency information of a HeNB in the case of using the third embodiment. The case where the above-mentioned specific example of the method (A2) of allowing a HeNB to ascertain the frequency information of a neighboring cell is disclosed in the operation example of the flowchart shown in  FIG. 25 . 
     In Step ST 2501 , the HeNB  2402  measures neighboring cells. In Step ST 2502 , the HeNB  2402  determines and stores the cell that stores the frequency information. In Step ST 2503 , the HeNB  2402  judges whether or not one cell stores the frequency information. In a case of one, the HeNB  2402  moves to Step ST 2505  or moves to Step ST 2504  in a case of other than one. 
     In Step ST 2504 , the HeNB  2402  selects the cell that has the best reception quality in the measurements of neighboring cells performed in Step ST 2501 . In the example of  FIG. 24 , the neighboring cell  2401  is selected. 
     In Step ST 2505 , the HeNB  2402  sets the same frequency information as that of the neighboring cell selected in Step ST 2504  in the downlink to a user equipment being served thereby. In the example of  FIG. 24 , the HeNB  2402  sets the frequency band A, which is the same frequency information as that of the downlink  2408  of the neighboring cell  2401  selected in Step ST 2504 , in the downlink  2406  to the user equipment  2403  being served thereby. 
     In Step ST 2506 , the HeNB  2402  sets the frequency information different from that of the neighboring cell selected in Step ST  2504  in the uplink from a user equipment being served thereby. In the example of  FIG. 24 , the HeNB  2402  sets the frequency band B, which is the different frequency information from that of the uplink  2409  of the neighboring cell  2401  selected in Step ST 2504 , in the uplink  2407  from the user equipment  2403  being served thereby. 
     The third embodiment achieves the effects below. The frequency of a carrier to be used, specifically, frequency band, carrier, component carrier or frequency layer is the same between the downlink of a neighboring cell and the downlink of a HeNB, and accordingly the search operation of a user equipment is simplified. This reduces the load of a user equipment, which contributes to lower power consumption. 
     The frequency of a carrier to be used, specifically, a frequency band, carrier, component carrier or frequency layer differs between the uplink of a neighboring cell and the uplink of a HeNB, which enables to divide the frequencies. This reduces the uplink interference. Accordingly, the present embodiment enables to prevent the interference in a mobile communication system and reduce the load of a user equipment in a search operation. 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. 
     DESCRIPTION OF REFERENCE SYMBOLS 
       1301  donor cell (Donor eNB, DeNB),  1302  relay node,  1303 ,  1304 ,  2403 ,  2404  user equipment,  1305  backhaul link,  1306  access link,  1307  direct link,  2001  backhaul downlink,  2002 ,  2101  backhaul uplink,  2003  access downlink,  2004 ,  2102  access uplink,  2005  direct downlink,  2006  direct uplink,  2401  macro cell,  2402  HeNB,  2406 ,  2408  downlink,  2407 ,  2409  uplink.