Mobile communication system

The present invention relates to a mobile communication system.

A mobile communication system of the LTE scheme (Release.8) defined by the 3GPP, as illustrated in FIG. 12 , is configured such that when a handover process of 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 sent and received between the radio base station eNB# 1 and the radio base station eNB# 2 via an X2 bearer that has been set between the radio base station eNB# 1 and the radio base station eNB# 2 .

As illustrated in FIG. 12 , the radio base station eNB# 1 and the radio base station eNB# 2 include a network layer 1 (NW L1) function, a network layer 2 (NW L2) function, an IP (Internet Protocol) layer function, and an SCTP (Stream Control Transmission Protocol) layer function as the X2 bearer functions configured to establish the X2 bearer.

In an LTE-Advanced mobile communication system, which is the communication scheme that is the next-generation 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.

However, the conventional mobile communication system has been problematic in that there is no regulation for how handover processes of the mobile station UE are to be performed when the relay nodes RN have been connected.

Therefore, the present invention is intended to overcome the above-described problem. An object of the present invention is to provide a mobile communication system capable of also implementing handover processes by a mobile station even when relay nodes have been connected.

The first feature of the present invention is summarized in that a mobile communication system, a relay node and a first radio base station are connected via a radio bearer, the first radio base station and a second radio base station are connected, a mobile station is configured to perform a handover process between a state in which a radio bearer is set with the relay node so as to communicate via the relay node and the first radio base station, and a state in which a radio bearer is set with the second radio base station so as to communicate via the second radio base station, and the handover process is configured such that a radio bearer is set between the relay node and the second radio base station, and the control signals involved in the handover process are sent and received via the radio bearer that has been set between the relay node and the second radio base station.

The first feature of the present invention is summarized in that the relay node and the second radio base station include a layer function configured to perform keep-alive processes for the radio bearer, as an upper layer function of the function configured to set the radio bearer.

The first feature of the present invention is summarized in that the relay node and the second radio base station comprise a first layer function configured to perform security processes between the relay node and the second radio base station, as an upper layer function of the function configured to set the radio bearer and a second layer function configured to perform keep-alive processes for the radio bearer as an upper layer function of the first layer function.

The second feature of the present invention is summarized in that a mobile communication system, a relay node and a first radio base station are connected via a radio bearer, the first radio base station and the second radio base station are connected via a bearer, a mobile station is configured to perform a handover processes between a first state in which a radio bearer is set with the relay node so as to communicate via the relay node and the first radio base station, and a second state in which a radio bearer is set with the second radio base station so as to communicate via the second radio base station, and the handover process is configured such that control signals involved in the handover process are sent and received via a radio bearer between the relay node and the second radio base station, and via a bearer between the second radio base station and the first radio base station.

The second feature of the present invention is summarized in that the relay node, upon receiving a measurement report from the mobile station, is configured to transfer the measurement report to the first radio base station via the radio bearer between the relay node and the first radio base station, and the first radio base station, upon deciding to initiate the handover process of the mobile station from the first state to the second state based on the measurement report, is configured to send a handover request signal giving notification of this intention to the second radio base station via the bearer between the first radio base station and the second radio base station as a control signal involved in the handover process.

The second feature of the present invention is summarized in that the relay node, upon deciding to initiate the handover process of the mobile station from the first state to the second state, is configured to send a handover request signal giving notification of this intention to the first radio base station via the radio bearer between the relay node and the first radio base station as a control signal involved in the handover process, and the first radio base station is configured to transfer the received handover request signal to the second radio base station via the bearer between the first radio base station and the second radio base station.

As has been described above, according to the present invention, it is possible to provide a mobile communication system capable of also implementing handover processes by a mobile station even when relay nodes have been connected.

FIG. 1 is a diagram showing the entire configuration of the mobile communication system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the protocol stack of the mobile communication system according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the protocol stack of the mobile communication system according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the protocol stack of the mobile communication system according to the first embodiment of the present invention.

FIG. 5 is a sequence diagram illustrating the operation of the mobile communication system according to the first embodiment of the present invention.

FIG. 6 is a diagram showing the protocol stack of the mobile communication system according to a second embodiment of the present invention.

FIG. 7 is a sequence diagram illustrating the operation of the mobile communication system according to the second embodiment of the present invention.

FIG. 8 is a diagram showing the protocol stack of the mobile communication system according to a third embodiment of the present invention.

FIG. 9 is a sequence diagram showing the operation of the mobile communication system according to the third embodiment of the present invention.

FIG. 10 is a diagram showing the protocol stack of the mobile communication system according to a fourth embodiment of the present invention.

FIG. 11 is a sequence diagram showing the operation of the mobile communication system according to the fourth embodiment of the present invention.

FIG. 12 is a diagram showing the protocol stack of a current mobile communication system.

(Mobile Communication System According to a Third Embodiment of the Present Invention)

A description will be provided for the mobile communication system according to a first embodiment of the present invention, with reference to FIG. 1 to FIG. 5 .

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 RN 1 to RN 4 , a radio base station DeNB 1 (Donor eNB) that is connected to the relay node RN 1 , a radio base station DeNB 2 that is connected to the relay nodes RN 2 and RN 3 , and a radio base station eNB 1 .

Herein, the radio base station DeNB 1 and the radio base station DeNB 2 are connected via an X2-C interface, and the radio base station DeNB 2 and the radio base station eNB 1 are connected via an X2-C interface.

Also, the radio base station DeNB 1 , the radio base station DeNB 2 and the radio base station eNB 1 are respectively connected with the mobile switching center MME via S1-MME interfaces.

In such a mobile communication system, the mobile station UE is configured to set a radio bearer between the radio base stations eNB (DeNB) and the relay nodes RN in order to perform radio communication.

In addition, the mobile communication system, as illustrated in ( 2 ) of FIG. 1 , is configured such that the mobile station UE conducts a handover process between the state in which a radio bearer is set with the relay node RN 2 in order to communicate via the relay node RN 2 and the radio base station DeNB 2 (the first radio base station), and the state in which a radio bearer is set with the radio base station DeNB 1 (the second radio base station) in order to communicate via the radio base station DeNB 1 .

Further, such a handover process is configured such that an X2-C radio bearer (radio bearer) is set between the relay node RN 2 and the radio base station DeNB 1 , and control signals involved in the handover process (X2AP signals) are sent and received via the X2-C radio bearer that has been set.

For example, as illustrated in FIG. 2 to FIG. 4 , the relay node RN 2 and the radio base station DeNB 1 include a physical (PHY) layer function as an X2-C radio bearer function configured to set the X2-C radio bearer, an MAC (Media Access Control) layer function 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.

Note that the relay node RN 2 and the radio base station DeNB 1 may include an RRC (Radio Resource Control) layer function provided as an upper layer function of the PDCP layer function.

In addition, as illustrated in FIG. 2 , the relay node RN 2 and the radio base station DeNB 1 may include an IP layer function (first layer function) configured to perform security processes between the relay node RN 2 and the radio base station DeNB 2 as an upper layer function of the X2-C radio bearer function, and may include an SCTP layer function (second layer function) configured to perform keep-alive processes for the X2-C radio bearer as an upper layer function of the IP layer function.

Alternatively, as illustrated in FIG. 3 , the relay node RN 2 and the radio base station DeNB 1 may include an SCTP layer function configured to perform keep-alive processes for the X2-C radio bearer, as an upper layer function of the X2-C radio bearer function. In the example in FIG. 3 , the relay node RN 2 and the radio base station DeNB 1 do not include an IP layer function configured to perform security processes between the relay node RN 2 and the radio base station DeNB 2 .

Furthermore, as illustrated in FIG. 4 , the relay node RN 2 and the radio base station DeNB 1 may not include an SCTP layer function configured to perform keep-alive processes for the X2-C radio bearer as an upper layer function of the X2-C radio bearer, nor with an IP layer function configured to perform security processes between the relay node RN 2 and the radio base station DeNB 1 .

A description is given below with reference to FIG. 5 for the operation in the mobile communication system according to this embodiment in which the mobile station UE hands over from the state in which a radio bearer is set with the relay node RN 2 in order to communicate via the relay node RN 2 and the radio base station DeNB 2 , to the state in which a radio bearer is set with the radio base station DeNB 1 in order to communicate via the radio base station DeNB 1 .

As illustrated in FIG. 5 , in step S 1000 , the relay node RN 2 , upon deciding to perform a handover process of the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 , sets the X2-C radio bearer with the radio base station DeNb 1 by the RRC connection setting procedure.

The relay node RN 2 manages the “UE Context” of the mobile station UE in step S 1001 , and then in step S 1002 sends an “HO Request (handover request signal)” to the radio base station DeNB 1 via the X2-C radio bearer, requesting a handover of the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

The radio base station DeNB 1 , upon receiving the “HO Request” stores the “UE Context” of the mobile station UE in step S 1003 , and then in step S 1004 sends an “HO Request Ack (handover request acknowledgement signal)” to the relay node RN 2 via the X2-C radio bearer.

In step S 1005 , the relay node RN 2 sends an “HO Command (handover instruction signal)” to the mobile station UE by means of the RRC layer function, instructing a handover to the radio base station DeNB 1 .

In step S 1006 , the mobile station UE sends an “HO Complete (handover completion signal)” to the radio base station DeNB 1 by means of the RRC layer function.

In step S 1007 , the radio base station DeNB 1 sends a “Path Switch Request (path switch request signal)” to the mobile switching center MME via the S1-MME interface.

In step S 1008 , the mobile switching center MME sends a “Path Switch Request Ack (path switch request acknowledgement signal)” to the radio base station DeNB 1 via the S1-MME interface, and also switches the transfer address of signals addressed to the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

In step S 1009 , the radio base station DeNB 1 sends a “UE Context Release” to the relay node RN 2 via the X2-C radio bearer, and the relay node RN 2 terminates management of the “UE Context” of the mobile station UE in reaction to the “UE Context Release”.

Note that in FIG. 5 , the relay node RN 2 and the radio base station DeNB 1 may be interchanged.

According to the mobile communication system of this 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 LTE mobile communication system.

(Mobile Communication System According to a Third 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. 6 and FIG. 7 . The mobile communication system according to the second embodiment of the present invention will be described below by focusing on the points of difference from the mobile communication system according to the first embodiment described above.

The mobile communication system according to this embodiment is configured such that, during the handover process described above, control signals involved in the handover process are sent and received via an X2-C radio bearer (Un interface) between the relay node RN 2 and the radio base station DeNB 2 , and via a bearer (X2-C interface) between the radio base station DeNB 2 and the radio base station DeNB 1 .

Specifically, as illustrated in FIG. 6 , the relay node RN 2 includes a physical (PHY) layer function as an X2-C radio bearer function configured to establish an X2-C radio bearer (Un interface) with the radio base station DeNB 2 , 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.

Note that the relay node RN 2 may include an RRC layer function provided as an upper layer function of the PDCP layer function.

Further, as illustrated in FIG. 6 , the relay node RN 2 may include an IP layer function configured to perform security processes between the relay node RN 2 and the radio base station DeNB 2 as an upper layer function of the X2-C radio bearer functions, and may include an SCTP layer function configured to perform keep-alive processes for the X2-C radio bearer as an upper layer function of the IP layer function.

The relay node RN 2 may include an X2AP layer function configured to send and receive control signals involved in the handover process, as an upper layer function of the SCTP layer function.

The radio base station DeNB 2 further includes an X2-C radio bearer function configured to establish an X2-C radio bearer (Un interface) with the relay node RN 2 , and a bearer function of establishing a bearer (X2-C interface) with the radio base station DeNB 1 .

Herein, the radio base station DeNB 2 includes a network layer 1 (NW L1) function and a network layer 2 (NW L2) function as bearer functions.

The radio base station DeNB 2 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 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.

Furthermore, the radio base station DeNB 1 include a network layer 1 (NW L1) function and a network layer 2 (NW L2) function as bearer functions configured to set the bearer with the radio base station DeNB 2 .

The radio base station DeNB 1 also includes an IP layer function provided as an upper layer function of the bearer functions, 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.

A description is given below with reference to FIG. 7 for the operation in the mobile communication system according to this embodiment in which the mobile station UE hands over from the state in which a radio bearer is set with the relay node RN 2 in order to communicate via the relay node RN 2 and the radio base station DeNB 2 , to the state in which a radio bearer is set with the radio base station DeNB 1 in order to communicate via the radio base station DeNB 1 .

As illustrated in FIG. 7 , the relay node RN 2 manages the “UE Context” of the mobile station UE in step S 2000 , and in step S 2001 sends an “HO Request (handover request signal)” to the radio base station DeNB 2 via the X2-C radio bearer, requesting a handover of the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

The radio base station DeNB 2 , upon receiving the “HO Request” by means of the X2AP layer function, stores the “UE Context” of the mobile station UE in step S 2002 , and in step S 2003 transfers the “HO Request” to the radio base station DeNB 1 via the X2-C radio bearer.

The radio base station DeNB 1 , upon receiving the “HO Request,” stores the “UE Context” of the mobile station UE in step S 2004 , and then in step S 2005 sends an “HO Request Ack (handover request acknowledgement signal)” to the radio base station DeNB 2 via the X2-C radio bearer.

The radio base station DeNB 2 , upon receiving the “HO Request Ack” by means of the X2AP layer function, transfers the “HO Request Ack” to the relay node RN 2 via the X2-C radio bearer in step S 2006 .

In step S 2007 , the relay node RN 2 sends an “HO Command (handover instruction signal)” to the mobile station UE by means of the RRC layer function, instructing a handover to the radio base station DeNB 1 .

In step S 2008 , the mobile station UE sends an “HO Complete (handover completion signal)” to the radio base station DeNB 1 by means of the RRC layer function.

In step S 2009 , the radio base station DeNB 1 sends a “Path Switch Request (path switch request signal)” to the mobile switching center MME via the S1-MME interface.

In step S 2010 , the mobile switching center MME sends a “Path Switch Request Ack (path switch request acknowledgement signal)” to the radio base station DeNB 1 via the S1-MME interface, and also switches the transfer address of signals addressed to the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

In step S 2011 , the radio base station DeNB 1 sends a “UE Context Release” to the radio base station DeNB 2 via the X2-C radio bearer, and in step S 2012 the radio base station DeNB 2 transfers the “UE Context Release” to the relay node RN 2 via the X2-C radio bearer by means of the X2AP layer function such that the relay node RN 2 terminates management of the “UE Context” of the mobile station UE in reaction to the “UE Context Release”.

Note that in FIG. 7 , the relay node RN 2 and the radio base station DeNB 1 may be interchanged.

As described above, the X2AP layer function in the radio base station DeNB 2 is configured to convert the control signal (X2AP signal) involved in the handover process between the relay node RN 2 and the radio base station DeNB 2 , and the control signal (X2AP signal) involved in the handover process between the radio base station DeNB 1 and the radio base station DeNB 2 .

The X2AP layer function in the radio base station DeNB 2 is also configured to manage the mobile station ID that is used between the relay node RN 2 and the radio base station DeNB 2 in association with the mobile station ID that is used between the radio base station DeNB 1 and the radio base station DeNB 2 .

(Mobile Communication System According to a Third Embodiment of the Present Invention)

A description will be provided for the mobile communication system according to a third embodiment of the present invention, with reference to FIG. 8 and FIG. 9 . The mobile communication system according to the third embodiment of the present invention will be described below by focusing on the points of difference from the mobile communication system according to the first embodiment described above.

The mobile communication system according to this embodiment is configured such that, during the handover process described above, control signals involved in the handover process are sent and received via an X2-C radio bearer (Un interface) between the relay node RN 2 and the radio base station DeNB 2 , and via a bearer (X2-C interface) between the radio base station DeNB 2 and the radio base station DeNB 1 .

Specifically, as illustrated in FIG. 8 , the relay node RN 2 includes a physical (PHY) layer function as an X2-C radio bearer function configured to establish an X2-C radio bearer (Un interface) with the radio base station DeNB 2 , 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.

Note that the relay node RN 2 may include an RRC layer function provided as an upper layer function of the PDCP layer function.

As illustrated in FIG. 8 , relay node RN 2 is configured to operate as a proxy of the RRC layer function in the mobile station UE, and may not include an IP layer function configured to perform security processes between the relay node RN 2 and the radio base station DeNB 2 as an upper layer function of the X2-C radio bearer function, an SCTP layer function configured to perform keep-alive processes for the X2-C radio bearer, and an X2AP layer function configured to send and receive control signals involved in the handover process.

The radio base station DeNB 2 further includes an X2-C radio bearer function configured to establish an X2-C radio bearer (Un interface) with the relay node RN 2 , and a bearer function configured to establish a bearer (X2-C interface) with the radio base station DeNB 1 .

Herein, the radio base station DeNB 2 includes a network layer 1 (NW L1) function and a network layer 2 (NW L2) function as bearer functions.

The radio base station DeNB 2 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 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.

Moreover, the radio base station DeNB 1 includes a network layer 1 (NW L1) function and a network layer 2 (NW L2) function as bearer functions of setting the bearer (X2-C interface) with the radio base station DeNB 2 .

The radio base station DeNB 1 also includes an IP layer function provided as an upper layer function of the bearer functions, 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.

A description is given below with reference to FIG. 9 for the operation in the mobile communication system according to this embodiment in which the mobile station UE hands over from the state in which a radio bearer is set with the relay node RN 2 in order to communicate via the relay node RN 2 and the radio base station DeNB 2 , to the state in which a radio bearer is set with the radio base station DeNB 1 in order to communicate via the radio base station DeNB 1 .

As illustrated in FIG. 9 , the relay node RN 2 , upon receiving a “Measurement Report (measurement report)” from the mobile station UE in step S 3000 , acquires the “UE Context” of the mobile station UE under management in step S 3001 , and then transfers the “Measurement Report” including the “UE Context” of the mobile station UE to the radio base station DeNB 2 by means of the RRC layer function in step 3002 .

The radio base station DeNB 2 decides to conduct a handover process of the mobile station UE from the relay node RN 2 to the radio base station DeNB 2 based on the received “Measurement Report”, stores the “UE Context” of the mobile station UE in step S 3003 , and then sends an “HO Request (handover request signal)” to the radio base station DeNB 1 via the X2-C radio bearer in step S 3004 , requesting a handover of the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

The radio base station DeNB 1 , upon receiving the “HO Request,” stores the “UE Context” of the mobile station UE in step S 3005 , and then in step S 3006 sends an “HO Request Ack (handover request acknowledgement signal)” to the radio base station DeNB 2 via the X2-C radio bearer.

The radio base station DeNB 2 , upon receiving the “HO Request Ack,” sends an “HO Command (handover instruction signal)” to the relay node RN 2 by means of the RRC layer function in step S 3007 , instructing a handover to the radio base station DeNB 1 .

In step S 3008 , the relay node RN 2 transfers the received “HO Command” to the mobile station UE by means of the RRC layer function.

In step S 3009 , the mobile station UE sends an “HO Complete (handover completion signal)” to the radio base station DeNB 1 by means of the RRC layer function.

In step S 3010 , the radio base station DeNB 1 sends a “Path Switch Request (path switch request signal)” to the mobile switching center MME via the S1-MME interface.

In step S 3011 , the mobile switching center MME sends a “Path Switch Request Ack (path switch request acknowledgement signal)” to the radio base station DeNB 1 via the S1-MME interface, and also switches the transfer address of signals addressed to the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

In step S 3012 , the radio base station DeNB 1 sends a “UE Context Release” to the radio base station DeNB 2 via the X2-C radio bearer such that, in step S 3013 , the radio base station DeNB 2 transfers an “RRC Connection Release” to the relay node RN 2 by means of the RRC layer function, and the relay node RN 2 terminates management of the “UE Context” of the mobile station UE in reaction to the “RRC Connection Release”.

(Mobile Communication System According to a Fourth Embodiment of the Present Invention)

A description is provided for the mobile communication system according to a fourth embodiment of the present invention, with reference to FIG. 10 and FIG. 11 . The mobile communication system according to the fourth embodiment of the present invention will be described below by focusing on the points of difference from the mobile communication system according to the first embodiment described above.

The mobile communication system according to this embodiment is configured such that, during the handover process described above, control signals involved in the handover process are sent and received via an X2-C radio bearer (Un interface) between the relay node RN 2 and the radio base station DeNB 2 , and via a bearer (X2-C interface) between the radio base station DeNB 2 and the radio base station DeNB 1 .

Specifically, as illustrated in FIG. 10 , the relay node RN 2 includes a physical (PHY) layer function as an X2-C radio bearer function configured to set an X2-C radio bearer (Un interface) with the radio base station DeNB 2 , 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.

Note that the relay node RN 2 may include an RRC layer function provided as an upper layer function of the PDCP layer function.

Further, as illustrated in FIG. 10 , the relay node RN 2 may include an IP layer function configured to perform security processes between the relay node RN 2 and the radio base station DeNB 2 as an upper layer function of the X2-C radio bearer functions, and may include an SCTP layer function configured to perform keep-alive processes for the X2-C radio bearer as an upper layer function of the IP layer function.

The relay node RN 2 may include an X2AP layer function configured to send and receive control signals involved in the handover process, as an upper layer function of the SCTP layer function.

The radio base station DeNB 2 further includes an X2-C radio bearer function configured to establish an X2-C radio bearer (Un interface) with the relay node RN 2 , and a bearer function of establishing a bearer (X2-C interface) with the radio base station DeNB 1 .

Herein, the radio base station DeNB 2 includes a network layer 1 (NW L1) function and a network layer 2 (NW L2) function as bearer functions.

The radio base station DeNB 2 also includes an IP layer function as an upper layer function of the X2-C radio bearer function and the bearer function, but does not include an SCTP layer function nor an X2AP layer function as an upper layer function of the IP layer.

Furthermore, the radio base station DeNB 1 includes a network layer 1 (NW L1) function and a network layer 2 (NW L2) function as bearer functions of setting the bearer with the radio base station DeNB 2 .

The radio base station DeNB 1 also includes an IP layer function provided as an upper layer function of the bearer functions, 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.

A description is given below with reference to FIG. 11 for the operation in the mobile communication system according to this embodiment in which the mobile station UE hands over from the state in which a radio bearer is set with the relay node RN 2 in order to communicate via the relay node RN 2 and the radio base station DeNB 2 , to the state in which a radio bearer is set with the radio base station DeNB 1 in order to communicate via the radio base station DeNB 1 .

As illustrated in FIG. 11 , the relay node RN 2 manages the “UE Context” of the mobile station UE in step S 4000 , and sends in step S 4001 an “HO Request (handover request signal)” to the radio base station DeNB 2 via the X2-C radio bearer, requesting a handover of the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

The radio base station DeNB 2 , upon receiving the “HO Request” in step S 4002 by means of the IP layer function, transfers the “HO Request” to the radio base station DeNB 1 via the X2-C radio bearer in step S 4003 .

The radio base station DeNB 1 , upon receiving the “HO Request,” stores the “UE Context” of the mobile station UE in step S 4004 , and then in step S 4005 sends an “HO Request Ack (handover request acknowledgement signal)” to the radio base station DeNB 2 via the X2-C radio bearer.

The radio base station DeNB 2 , upon receiving the “HO Request Ack” by means of the IP layer function, transfers the “HO Request Ack” to the relay node RN 2 via the X2-C radio bearer in step S 4006 .

In step S 4007 , the relay node RN 2 sends an “HO Command (handover instruction signal)” to the mobile station UE by means of the RRC layer function, instructing a handover to the radio base station DeNB 1 .

In step S 4008 , the mobile station UE sends an “HO Complete (handover completion signal)” to the radio base station DeNB 1 by means of the RRC layer function.

In step S 4009 , the radio base station DeNB 1 sends a “Path Switch Request (path switch request signal)” to the mobile switching center MME via the S1-MME interface.

In step S 4010 , the mobile switching center MME sends a “Path Switch Request Ack (path switch request acknowledgement signal)” to the radio base station DeNB 1 via the S1-MME interface, and also switches the transfer address of signals addressed to the mobile station UE from the relay node RN 2 to the radio base station DeNB 1 .

In step S 4011 , the radio base station DeNB 1 sends a “UE Context Release” to the radio base station DeNB 2 via the X2-C radio bearer, such that the radio base station DeNB 2 , upon receiving the “UE Context Release” by means of the I layer function in step S 4012 , transfers the “UE Context Release” to the relay node RN 2 via the X2-C radio bearer in step S 4013 , and the relay node RN 2 terminates management of the “UE Context” of the mobile station UE in reaction to the “UE Context Release”.

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.

The software module may be provided in any type of storage 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.

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 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 component.

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 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.