1 MOBILE COMMUNICATION SYSTEM This application is a divisional of Australian Patent Application No. 2010242668, the content of which is incorporated herein by reference in its entirety. 5 TECHNICAL FIELD [0001] The present invention relates to a mobile communication system. BACKGROUND 10 [0002] A mobile communication system of the LTE scheme (Release. 8) defined by the 3GPP, as illustrated in Fig. 8, is configured such that when a handover process by a mobile station UE is carried out from a radio base station eNB#1 to a radio base station eNB#2, control signals involved in the handover process are transmitted and received between the radio base station eNB#1 and the radio base station eNB#2 via an X2 bearer Is that has been installed between the radio base station eNB#1 and the radio base station eNB#2. [0003] As illustrated in Fig. 8, the radio base station eNB#1 and the radio base station eNB#2 include a network layer 1 (NW Li) function, a network layer 2 (NW L2) 20 function, an IP (Internet Protocol) layer function, and an SCTP (Stream Control Transmission Protocol) layer function as the X2 bearer functions for establishing the X2 bearer. [0004] In the LTE-advanced mobile communication system, which is a next 25 generation communication scheme of the LTE scheme, "relay nodes (RN)" including the same functions as a radio base station eNB can establish a connection between a mobile station UE and the radio base station eNB. [0005] However, the conventional mobile communication system has a problem in 30 that there is no regulation for how handover processes by the mobile station UE are to be handled when the relay nodes RN have been connected. [0006] Therefore, the present invention has been achieved in view of the problem described above and a need to provide a mobile communication system capable of 2 implementing a handover process by a mobile station even when a relay node is connected. SUMMARY 5 [0006a] According to one aspect of the present invention, there is provided a mobile communication system in which a first relay node and a radio base station are connected via a radio bearer, a second relay node and the radio base station are connected via a radio bearer, wherein the first relay node and the second relay node comprise: as a radio bearer function of setting a Un interface with the radio base station, a physical layer function; an 10 MAC layer function provided as an upper layer function of the physical layer function; an RLC layer function provided as an upper layer function of the MAC layer function; a PDCP layer function provided as an upper layer function of the RLC layer function; and an RRC layer function provided as an upper layer function of the PDCP layer function; the first relay node and the second relay node comprise: as an upper layer function of the 15 radio bearer function, an IP layer function; an SCTP layer function provided as an upper layer function of the IP layer function; and an X2AP layer function provided as an upper layer function of the SCTP layer function; the radio base station comprise: as a radio bearer function of setting a un interface with the first relay node and the second relay node, a physical layer function; an MAC layer function provided as an upper layer 20 function of the physical layer function; an RLC layer function provided as an upper layer function of the MAC layer function; a PDCP layer function provided as an upper layer function of the RLC layer function; and an RRC layer function provided as an upper layer function of the PDCP layer function; the radio base station comprise: as an upper layer function of the radio bearer function, an IP layer function; an SCTP layer function 25 provided as an upper layer function of the IP layer function; and an X2AP layer function provided as an upper layer function of the SCTP layer function; and a control signal involved in a handover process is configured to be terminated between the X2AP layer function of the first relay node and the X2AP layer function of the radio base station, and between the X2AP layer function of the second relay node and the X2AP layer function 30 of the radio base station. OTHER DISCLOSURE [0007] The first feature of the present invention is summarized in that a mobile communication system, a first relay node and a radio base station are connected via a 35 radio bearer, a second relay node and a radio base station are connected via a radio bearer, 3 a mobile station is configured so as to conduct a handover process between a first state wherein a radio bearer is established with the first relay node in order to communicate via the first relay node and the radio base station and a second state wherein a radio bearer is established with the second relay node in order to communicate via the second relay node 5 and the radio base station and the mobile station is configured such that in the handover process, control signals involved in the handover process are transmitted and received via the radio bearer between the first relay node and the radio base station, and via the radio bearer between the second relay node and the radio base station. 10 [0008] The first feature of the present invention is summarized in that when a measurement report is received from the mobile station, the first relay node is configured so as to transfer the measurement report to the radio base station via the radio bearer between the first relay node and the radio base station and when it is determined based on the measurement report that a handover process of the mobile station from the first state is to the second state is to be initiated, the radio base station is configured so as to transmit a handover request signal giving notification of the determination as a control signal involved in the handover process to the second relay node via the radio bearer between the second relay node and the radio base station. 20 [0009] The first feature of the present invention is summarized in that when it is determined that a handover process of the mobile station from the first state to the second state is to be initiated, the first relay node is configured so as to transmit a handover request signal giving notification of the determination as a control signal involved in the handover process to the radio base station via the radio bearer between the first relay node 25 and the radio base station and the radio base station is configured so as to transfer the received handover request signal to the second relay node via the radio bearer between the second relay node and the radio base station. [0010] As has been described above, according to the present invention, it is possible 30 to provide a mobile communication system capable of implementing a handover process by a mobile station even when a relay node is connected.
4 BRIEF DESCRIPTION OF THE DRAWINGS [0011] [Fig. 1] Fig 1 is a diagram showing the entire configuration of a mobile communication system according to a first embodiment of the present invention [Fig. 2] Fig. 2 is a diagram of a protocol stack in the mobile 5 communication system according the first embodiment of the present invention. [Fig. 3] Fig. 3 is a sequence diagram illustrating the operation of the mobile communication system according to the first embodiment of the present invention. [Fig. 4] Fig. 4 is a diagram of the protocol stack in the mobile communication system according to a second embodiment of the present invention. 10 [Fig. 5] Fig. 5 is a sequence diagram illustrating the operation of the mobile communication system according to the second embodiment of the present invention. [Fig. 6] Fig. 6 is a diagram of the protocol stack in the mobile communication system according to a third embodiment of the present invention. 15 [Fig; 7] Fig. 7 is a sequence diagram illustrating the operation of the mobile communication system according to the third embodiment of the present invention. [Fig. 8] Fig. 8 is a diagram of the protocol stack in a current mobile communication system. 20 DETAILED DESCRIPTION [0012] (Mobile communication system according to a first embodiment of the present invention) With reference to Fig. 1 to Fig. 3, a mobile communication system according to the 25 first embodiment of the present invention is described. [0013] The mobile communication system according to the present invention is an LTE-Advanced mobile communication system including, for example, as illustrated in Fig. 1, a mobile switching center MME, relay nodes RN1 to RN4, a radio base station 30 DeNB (Donor Enb)1 that is connected to relay node RN1, a radio base station DeNB2 that is connected to the relay nodes RN2 and RN3, and a radio base station eNB 1.
4a [0014] Herein, the radio base station DeNBI and the radio base station DeNB2 are connected via an X2-C interface, and the radio base station DeNB2 and the radio base station eNB I are connected via an X2-C interface. 5 [0015] Also, the radio base station DeNB1, the radio base station DeNB2 and the radio base station eNB I are each respectively connected with the mobile switching center MME via an Sl -MME interfaces. [0016] In such a mobile communication system, the mobile station UE is configured I0 so as to establish a radio bearer between the radio base stations eNB (DeNB) and the relay nodes RN in order to perform radio communication. [0017] Also, in such a mobile communication system, as illustrated by 15 [NEXT PAGE IS PAGE 5] 5 (4) of Fig. 1, the mobile station UE is configured so as to conduct a handover process between the state in which a radio bearer is established with the relay node RN2 (the first relay node) in order to communicate via the relay node RN2 and the radio base station DeNB2 5 (the radio base station), and the state in which a radio bearer is established with the relay node RN3 (the second relay node) in order to communicate via the relay node RN2 and the radio base station DeNB2. 10 [0018] Additionally, in such a handover process, control signals (X2AP signals) involved in the handover process are configured so as to be transmitted and received via the radio bearer (Un interface) between the relay node RN2 and the radio base station DeNB2, and via the radio bearer (Un interface) between the relay node RN3 and the radio 15 base station DeNB2. [0019] Note that in the present embodiment, a radio bearer (Un interface) is configured not to be established between the relay node RN2 and the relay node RN4. 20 [0020] Specifically, as illustrated in Fig. 2, as X2-C radio bearer functions for establishing an X2-C radio bearer with the radio base station DeNB2 (Un interface), the relay node RN2 includes a physical (PHY) layer function, an MAC (Media Access Control) layer function 25 provided as an upper layer function of the physical (PHY) layer function, an RLC (Radio Link Control) layer function provided as an upper layer function of the MAC layer function, and a PDCP (Packet Data Convergence Protocol) layer function provided as an upper layer function of the RLC layer function. 30 [0021] Note that the relay node RN2 may include an RRC (Radio Resource Control) layer function provided as an upper layer function of the PDCP layer function. 35 [0022] As illustrated in Fig. 2, as an upper layer function of the X2-C 6 radio bearer functions, the relay node RN2 may include an IP layer function configured so as to perform security processes between the relay node RN2 and the radio base station DeNB2, and may include an SCTP layer function configured so as to perform keep-alive processes 5 for the X2-C radio bearer as an upper layer function of the IP layer function. [0023] The relay node RN2 may include an X2AP layer function configured to transmit and receive control signals involved in the 10 handover process, as an upper layer function of the SCTP layer function. [0024] Similarly, as X2-C radio bearer functions for establishing an X2-C radio bearer with the radio base station DeNB2 (Un interface), 15 the relay node RN3 includes a physical (PHY) layer function, an MAC layer function provided as an upper layer function of the physical (PHY) layer function, an RLC layer function provided as an upper layer function of the MAC layer function, and a PDCP layer function provided as an upper layer function of the RLC layer function. 20 [0025] Note that the relay node RN3 may include an RRC layer function provided as an upper layer function of the PDCP layer function. 25 [0026] As an upper layer function of the X2-C radio bearer functions, the relay node RN3 may include an IP layer function configured so as to perform security processes between the relay node RN3 and the radio base station DeNB2, and may include an SCTP layer functoion configured so as to perform keep-alive processes for the X2-C radio 30 bearer as an upper layer function of the IP layer function. [0027] The relay node RN3 may include an X2AP layer function configured to transmit and receive control signals involved in the handover process, as an upper layer function of the SCTP layer 35 function.
7 [0028] The radio base station DeNB2 also includes an X2-C radio bearer function for establishing an X2-C radio bearer (Un interface) with the relay node RN2 and the relay node RN3. 5 [0029] The radio base station DeNB2 also includes an IP layer function provided as an upper layer function of the X2-C radio bearer function and the bearer'function, an SCTP function provided as an upper layer function of the IP layer, and an X2AP layer function provided as an 10 upper layer function of the SCTP layer function. [0030] A description is given below with reference to Fig. 3 for the operation in the mobile communication system according to the present embodiment in which the mobile station UE hands over from the state 15 in which a radio bearer has been established with the relay node RN2 in order to communicate via the relay node RN2 and the radio base station DeNB2, to the state in which a radio bearer has been established with the relay node RN3 in order to communicate via the relay node RN3 and the radio base station DeNB2. 20 [0031] As illustrated in Fig. 3, the relay node RN2 manages the "UE Context" of the mobile station UE in step S1000, and transmits an "HO Request (handover request signal)" to the radio base station DeNB2 via the X2-C radio bearer in step S1001 to request a handover by the 25 mobile station UE from the relay node RN2 to the relay node RN3. [0032] The radio base station DeNB2, upon receiving the "HO Request" in the X2AP layer function, stores the "UE Context" of the mobile station UE in step S1002, and transfers the "HO Request" to the relay 30 node RN3 via the X2-C radio bearer in step S1003. [0033] The relay node RN3, upon receiving the "HO Request", stores the "UE Context" of the mobile station UE in step S1004, and transmits an "HO Request Ack (handover request acknowledgement 35 signal)" to the radio base station DeNB2 via the X2-C radio bearer in 8 Step S 1005. [0034] The radio base station DeNB2, upon receiving the "HO Request Ack" in the X2AP layer function, transfers the "HO Request Ack" to the relay node RN2 via the X2 5 C radio bearer in step S 1006. [00351 Instep S1007, the relay node RN2 transmits an "HO Command (a handover instruction signal" to the mobile station UE commanding a handover to the relay node RN3 by means of the RRC layer function. 10 [0036] In step S1008, the mobile station UE transmits an "HO Complete (handover completion signal)" to the relay node RN3 by means of the RRC layer function. [0037] In step S1009, the relay node RN3 transmits a "Path Switch Request (path switch is request signal)" to the mobile switching center MME via the SI -MME interface. [0038] In step S 1010, the mobile switching center MME transmits a "Path Switch Request Ack (path switch request acknowledgement signal)" to the relay node RN3 via the SI -MME interface, and also switches the signal transfer destination addressed to the 20 mobile station UE from the relay node RN2 to the relay node RN3. [0039] In step S1011, the relay node RN3 transmits a "UE Context Release" to the radio base station DeNB2 via the X2-C radio bearer; in step S 1012, the radio base station DeNB2 transfers the "UE Context Release" to the relay node RN2 via the X2-C radio 25 bearer in the X2AP layer function, and the relay node RN2 terminates management of the "UE Context" of the mobile station UE in reaction to the "UE Context Release". [0040] Note that in Fig. 3, it is acceptable to interchange the relay node RN2 with the relay node RN3.
9 [0041] As described above, the X2AP layer function in the radio base station DeNB2 is configured so as to convert the control signal (X2AP signal) involved in the handover process between the relay node RN2 and the radio base station DeNB2, and the control signal (X2AP signal) 5 involved in the handover process between the relay node RN3 and the radio base station DeNB2. [0042] The X2AP layer function in the radio base station DeNB2 is also configured to manage such that the mobile station ID that is used 10 between the relay node RN2 and the radio base station DeNB2, and the mobile station ID that is used between the relay node RN3 and the radio base station DeNB2 are associated. [0043] According to the mobile communication system of the present 15 embodiment, it is possible to implement a handover process involving the relay nodes RN without performing a major renovation of the protocol stack of each device used in the mobile communication system of the LTE scheme. 20 [0044] (Mobile communication system according to a second embodiment of the present invention) A description will be provided for the mobile communication system according to the second embodiment of the present invention, with reference to Fig. 4 and Fig. 5. The mobile communication system 25 according to the second embodiment of the present invention will be described by focusing on the points of difference with the mobile communication system according to the first embodiment as described above. 30 [0045] Specifically, as illustrated in Fig. 4, as X2-C radio bearer functions for establishing an X2-C radio bearer with the radio base station DeNB2 (Un interface), the relay node RN2 includes a physical (PHY) layer function, an MAC layer function provided as an upper layer function of the physical (PHY) layer function, an RLC layer 35 function provided as an upper layer function of the MAC layer function, 10 and a PDCP layer function provided as an upper layer function of the RLC layer function. [0046] Note that the relay node RN2 may include an RRC layer 5 function provided as an upper layer function of the PDCP layer function. [0047] As illustrated in Fig. 4, relay ~node RN2 is configured to operate as a proxy of the RRC layer function in the mobile station UE, and may 10 not include an IP layer function configured so as to perform security processes between the relay node RN2 and the radio base station DeNB2 as an upper layer function of the X2-C radio bearer functions, an SCTP layer function configured so as to perform keep-alive processes for the X2-C radio bearer, and an X2AP layer function 15 configured so as to transmit and receive control signals involved in the handover process. [0048] Further, the protocol stack of the radio base station DeNB2 and the relay node RN3 is the same as the protocol stack of the mobile 20 communication system according to the first embodiment as illustrated in Fig. 2. [0049] A description is given below with reference to Fig. 5 for the operation in the mobile communication system according to the present 25 embodiment in which the mobile station UE hands over from the state in which a radio bearer has been established with the relay node RN2 in order to communicate via the relay node RN2 and the radio base station DeNB2, to the state in which a radio bearer has been established with the relay node RN3 in order to communicate via the 30 relay node RN3 and the radio base station DeNB2. [0050] As illustrated in Fig. 5, the relay node RN2, upon receiving a "Measurement Report (measurement report)" from the mobile station UE in step S2000, acquires the "UE Context" of the managing mobile 35 station UE in step S2001 in order to then transfer the "Measurement I I Report", which includes the "UE Context" of the mobile station UE, to the radio base station DeNB2 by means of the RRC layer function in step S2002. [0051] The radio base station DeNB2 decides to perform a handover process of the s mobile station UE from the relay node RN2 to the relay node RN3 based on the received "Measurement Report", and, in step S2003, stores the "UE Context" of the mobile station UE and then, in step S2004, transmits to the relay node RN3 an "HO Request (handover request signal)" requesting a handover of the mobile station UE from the relay node RN2 to the relay node RN3, via the X2-C radio bearer. 10 [0052] The relay node RN3, upon receiving the "HO Request" stores the "UE Context" of the mobile station UE in step S2005, and transmits an "HO Request Ack (handover request acknowledgement signal)" to the radio base station DeNB2 via the X2-C radio bearer in step S2006. 15 [0053] The radio base station DeNB2, upon receiving the "HO Request Ack" transmits an "HO Command (handover instruction signal)" to the relay node RN2 commanding a handover to the relay node RN3 by means of the RRC layer function in step S2007. 20 [0054] In step S2008, the relay node RN2 transfer the received "HO Command" to the mobile station UE by means of the RRC layer function. [0055] In step S2009, the mobile station UE transmits an "HO Complete (handover completion signal)" to the relay node RN3 by means of the RRC layer function. 25 [0056] In step S2010, the relay node RN3 transmits a "Path Switch Request (path switch request signal)" to the mobile switching center MME via the S I-MME interface.
12 [0057] In step S2011, the mobile switching center MME transmits a "Path Switch Request Ack (path switch request acknowledgement signal)" to the relay node RN3 via the S I -MME interface, and also switches the signal transfer destination addressed to the mobile station UE from the relay node RN2 to the relay node RN3. 5 [0058] In step S20 12, the relay node RN3 transmits a "UE Context Release" to the. radio base station DeNB2 via the X2-C radio bearer. [0059] In step S2013, the radio base station DeNB2 transfers an "RRC Connection to Release" to the relay node RN2 in the RRC layer function, and then the relay node RN2 terminates management of the "UE Context" of the mobile station UE in reaction to the "RRC Connection Release". [0060] (Mobile communication system according to a third embodiment of the present 15 invention) A description will be provided for the mobile communication system according to the third embodiment of the present invention, with reference to Fig. 6 and Fig. 7. The mobile communication system according to the third embodiment of the present inv3ention will be described by focusing on the points of difference with the mobile 20 communication system according to the first embodiment as described above. [0061] Specifically, as illustrated in Fig. 6, the radio base station DeNB2 includes an X2-C radio bearer function for establishing an X2-C radio bearer (Un interface) with the relay node RN2 and the relay node RN3. 25 [0062] The radio base station DeNB2 also includes an IP layer function provided as an upper layer function of the X2-C radio bearer function, but does not include an SCTP function of X2AP layer function provided as upper layer functions of the IP layer function. 30 13 [0063] Note that the protocol stack of the relay node RN2 and the relay node RN3 is the same as the protocol stack of the mobile communication system according to the first embodiment as illustrated 5 in Fig. 2. [0064] A description is given below with reference to Fig. 7 for the operation in the mobile communication system according to the present embodiment in which the mobile station UE hands over from the state 10 in which a radio bearer has been established with the relay node RN2 in order to communicate via the relay node RN2 and the radio base station DeNB2, to the state in which a radio bearer has been established with the relay node RN3 in order to communicate via the relay node RN3 and the radio base station DeNB2. 15 [0065] As illustrated in Fig. 7, the relay node RN2 manages the "UE Context" of the mobile station UE in step S3000, and transmits an "HO Request (handover request signal)" to the radio base station DeNB2 via the X2-C radio bearer in step S3001 to request a handover by the 20 mobile station UE from the relay node RN2 to the relay node RN3. [0066] The radio base station DeNB2, upon receiving the "HO Request" in step S3002 by means of the IP layer function, transfers the "HO Request" to the relay node RN3 via the X2-C radio bearer in step 25 S3003. [0067] The relay node RN3, upon receiving the "HO Request", stores the "UE Context" of the mobile station UE in step S3004, and transmits an "HO Request Ack (handover request acknowledgement 30 signal)" to the radio base station DeNB2 via the X2-C radio bearer in step S3005. [0068] The radio base station DeNB2, upon receiving the "HO Request Ack" by means of the IP layer function, transfers the "HO Request Ack" 35 to the relay node RN2 via the X2-C radio bearer in step S3006.
14 [0060] In step S3007, the relay node RN2 transmits and "HO Command (a handover instruction signal)" to the mobile station UE commanding a handover to the relay node RN3 by means of the RRC layer function. 5 [0070] In step S3008, the mobile station UE transmits an "HO Complete (handover completion signal)" to the relay node RN3 by means of the RRC layer function. [0071] In step S3009, the relay node RN3 transmits a "Path Switch Request (path switch request signal)" to the mobile switching center MME via the SI -MM interface. 10 [0072] In step S3010, the mobile switching center MME transmits a "Path Switch Request Act (path switch request acknowledgement signal)" to the relay node RN3 via the SI -MME interface, and also switches the signal transfer destination addressed to the mobile station UE from the relay node RN2 to the relay node RN3. 15 [00731 In step S3011, the relay node RN3 transmits a "UE Context Release" to the radio base station DeNB2 via the X2-C radio bearer. [0074] The radio base station DeNB2, upon receiving the "UE Context Release" by 20 means of the I layer function in step S3012, transfers the "UE Context Release" to the relay node RN2 via the X2-C radio bearer in step S3013, and the relay node RN2 terminates the management of the "UE Context" of the mobile station UE in reaction to the "UE Context Release". 25 [0075] Note that operation of the above described the mobile station UE, the relay node RN, the radio base station eNB and the mobile switching center MME may be implemented by means of hardware, a software module executed by a processor, or a combination of both. 30 [0076] The software module may be provided in any type of storage 15 medium such as an RAM (Random Access Memory), a flash memory, a ROM (Read Only Memory), an EPROM (Erasable Programmable ROM), an EEPROM (Electronically Erasable and Programmable ROM), a register, a hard disk, a removable disk, or a CD-ROM. 5 [0077] The storage medium is connected to the processor so that the processor can read and write information from and to the storage medium. Also, the storage medium may be integrated into the processor. Also, the storage medium and the processor may be 10 provided in an ASIC. The ASIC may be provided in the mobile station UE, the relay node RN, the radio base station eNB and the mobile switching center MME. Also, the storage medium and the processor may be provided in the mobile station UE, the relay node RN, the radio base station eNB and the mobile switching center MME as a discrete 15 component. [0078] Hereinabove, the present invention has been described in detail using the above embodiment; however, it is apparent to those skilled in the art that the present invention is not limited to the embodiment 20 described herein. Modifications and variations of the present invention can be made without departing from the spirit and scope of the present invention defined by the description of the scope of claims. Thus, what is described herein is for illustrative purpose, and has no intention whatsoever to limit the present invention. 25