Abstract:
A method for controlling interference between base stations in a radio communication system in which an indirect interface for indirectly connecting the base stations exists and an direct interface for directly connecting the base stations does not exist, the method includes: converting a first interference control message used in the direct interface into a format of a protocol of the indirect interface to thereby generate a second interference control message; and transmitting the second interference control message through the indirect interface.

Description:
CROSS-REFERENCE(S) TO RELATED APPLICATION(S) 
     The present invention claims priority of Korean Patent Application No. 10-2009-0127908, filed on Dec. 21, 2009, which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for controlling interference between base stations, and, more particularly, to a method and apparatus for controlling interference between femtocell base stations which can control the interference between the femtocell base stations using an existing X2 interference control message, in a femtocell environment where no X2 interface exists. 
     BACKGROUND OF THE INVENTION 
     In next generation multimedia radio communication systems which have been actively studied in recent years, It is required that a variety of information (e.g., video and radio data) beyond the early voice-oriented services is processed at a higher data transfer rate. 
     Accordingly, orthogonal frequency division multiplexing (OFDM) capable of having a high data transfer rate has attracted attention. The OFDM is a multi-carrier modulation scheme in which data transmission is achieved by dividing a frequency band into a plurality of orthogonal subcarriers. Orthogonal frequency division multiple access (OFDMA) provides multi-user multiplexing by combining the OFDM with frequency division multiple access (FDMA), time division multiple access (TDMA) or code division multiple access (CDMA). 
     A radio communication system includes a base station (BS) and at least one user equipment (UE). The UE may be fixed or mobile and can also be referred to as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, and the like. 
     The base station commonly refers to a fixed station which communicates with the user equipment, and it can also be referred to as a Node-B, a base transceiver system (BTS), an access point (AP), and the like. Hereinafter, an uplink (UL) refers to a transmission from the user equipment to the base station, and a downlink (DL) refers to a transmission from the base station to the user equipment. 
     Meanwhile, as the use of privately owned base stations or private-purpose base stations increases in addition to the use of existing service provider-owned base stations or public-purpose base stations, femtocell base stations have been used. 
     A femtocell is a service area of an ultra-small communication base station (a femtocell base station) used indoors, for example, in private homes or offices. The femtocell has advantages in that it can provide a fixed mobile convergence (FMC) service at a low cost by connecting the mobile terminal to the Internet, and can efficiently provide a variety of FMC services by expanding an indoor coverage and improving a call quality. 
     The demand for femtocell standardization was proposed as a standardization item in the 3rd Generation Partnership Project (3GPP) in the early 2007, and femtocell standardization activities have been carried out as a main issue in the 3GPP2 since June 2007. The femtocell is referred to as a home node B (HNB) in the 3GPP. TSG-RAN WG4 (Technical Specification Group-Radio Access Network Working Group 4) has led the discussion about the standardizations of 3G HNB based on wideband CDMA (WCDMA) and Long Term Evolution (LTE) Home evolved Node B (HeNB) based on LTE. 
     Also, in the 3GPP2, methods for minimizing the influence of the existing networks and the interfaces between macrocells have become a main issue. While various problems such as a network architecture for circuit switched/packet switched (CS/PS) service, an interface management, a handover scheme, an access system selection, a synchronization, and the like, have been under discussion, the 3GPP2 having first carried out the standardization activities took the leading position in the femtocell standardization over the 3GPP. 
     The femtocell can provide a high-capacity service, which has been provided in an existing wired broadband service, at a low cost under radio environments by configuring cells in a small size and remarkably increasing a frequency reuse rate, to thereby provide a high-speed data service regardless of places of users. Hence, such a femtocell technology has showed a possibility as the foundation for introduction of new services and expansion of next generation mobile communication markets following 3G. 
     However, since such femtocell base stations are installed in an uncoordinated, random and dense fashion, interference may occur more than in the existing macrocell base stations. 
     The interference between the femtocell base stations may degrade the quality of service (QoS) provided to the mobile terminal and also cause a call drop. Therefore, there is a need for technologies which can minimize interference occurring between the femtocell base stations in order for the femtocell base stations to successfully operate. 
     An Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) architecture in which no femtocell base stations are included will be first described. The base stations (Evolved Node-Bs (eNBs)) are connected through interfaces to Evolved Packet Cores (EPCs) which are upper nodes. The EPCs may include a Mobility Management Entity (MME) and/or a Serving-GateWay (S-GW). 
     In the E-UTRAN architecture, an interface between the eNBs is referred to as an X2 interface, and an interface between the EPC and the eNB is referred to as an S1 interface. That is, the X2 interface refers to an interface which directly connects the eNBs to each other, and the S1 interface refers to an interface which indirectly connects the eNBs to each other passing through the MME and/or the S-GW. 
     In general, interference between the macrocell base stations can be reduced by exchanging an interference control message between the macrocell base stations. In this case, the interference control message is exchanged through the X2 interface. 
     However, the interference control message having been used in the existing X2 interface cannot be exchanged in a femtocell environment where no X2 interface exists, and the interference-related messages associated with the S1 interface have to be newly defined. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides a method and apparatus for controlling interference between femtocell base stations in a femtocell environment where no X2 interface exists by using an existing X2 interference control message, without newly defining an interference control message in an S1 interface. 
     In accordance with a first aspect of the present invention, there is provided a method for controlling interference between base stations in a radio communication system in which an indirect interface for indirectly connecting the base stations exists and an direct interface for directly connecting the base stations does not exist, the method including: 
     converting a first interference control message used in the direct interface into a format of a protocol of the indirect interface to thereby generate a second interference control message; and 
     transmitting the second interference control message through the indirect interface. 
     In accordance with a second aspect of the present invention, there is provided an apparatus for controlling interference between base stations in a radio communication system in which an indirect interface for indirectly connecting the base stations exists and an direct interface for directly connecting the base stations does not exist, the apparatus including: 
     a generation unit for converting a first interference control message used in the direct interface into a format of a protocol of the indirect interface to thereby generate a second interference control message; and 
     a transmission unit for transmitting the second interference control message through the indirect interface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows an E-UTRAN architecture including a Home eNB GateWay in accordance with an embodiment of the present invention; 
         FIG. 2  shows an interference control message in accordance with the embodiment of the present invention; 
         FIG. 3  shows procedures of transferring an interference control message by using an S1 interface between femtocell base stations in accordance with the embodiment of the present invention; 
         FIG. 4  shows an X2 message container information element (IE) in accordance with the embodiment of the present invention; 
         FIG. 5  is a flowchart showing a schematic flow of an interference control method in accordance with the embodiment of the present invention; and 
         FIG. 6  is a block diagram showing a schematic architecture of an interference control apparatus in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings which form a part hereof. 
       FIG. 1  shows an E-UTRAN architecture including a Home eNB GateWay (HeNB GW) in accordance with an embodiment of the present invention. Evolved Node-Bs (eNBs)  130 ,  140  and  150  are macrocell base stations which support macrocells. The eNBs  130 ,  140  and  150  are connected through interfaces to Evolved Packet Cores (EPCs)  110  and  120  which are upper nodes. The EPCs  110  and  120  may include a Mobility Management Entity (MME) and/or a Serving GateWay (S-GW). 
     An interface which directly connects the eNBs  130 ,  140  and  150  to one another is referred to as an X2 interface, and an interface which connects the eNBs  130 ,  140  and  150  to the EPCs  110  and  120  is referred to as an S1 interface. 
     Meanwhile, Home evolved Node-Bs (HeNBs)  170 ,  180  and  190  are femtocell base stations which support femtocells. A Home eNB GateWay (HeNB GW)  160  having the S1 interface may be provided between the HeNBs  180  and  190  and the EPC  120  (including the MME and/or the S-GW) in order to support the expansion to a large number of HeNBs. The S1 interface is divided into two traffic planes known as a C-plane (control plane) and a U-plane (user plane). The C-plane carries control (signal) traffic, and the U-plane carries user data. 
     The HeNB GW  160  simply operates as a concentrator with regard to the C-plane. An interface between the HeNB GW  160  and the HeNBs  180  and  190  with regard to the C-plane is referred to as an S-MME interface, and an interface between the HeNB GW  160  and the HeNBs  180  and  190  with regard to the U-plane may be referred to as an S1-U interface. The S1-U interface may be disconnected in the HeNB GW  160 , or may be forwarded by the HeNB GW  160  and disconnected in the EPC  120 . The HeNB GW  160  may look like an MME to the HeNBs  180  and  190  and may look like a HeNB to the MME  120 . 
     As mentioned above, regarding the macrocell base stations, the X2 interfaces are defined between the eNBs  130 ,  140  and  150  and the S1 interfaces are defined between the eNBs  130 ,  140  and  150  and the EPCs  110  and  120 . However, regarding the femtocell base stations, no X2 interfaces may be defined between the HeNBs  170 ,  180  and  190 , and only the S1 interfaces may be defined between the HeNB GW  160  and the HeNBs  180  and  190 . 
     In this case, since the HeNBs  170 ,  180  and  190  are installed in a highly dense form, interference may occur more than in existing macrocell base stations. Thus, the interference must be controlled by exchanging an interference control message between the HeNBs. However, newly defining the interference control message in the S1 interface under a femtocell environment where no X2 interface exists may cause waste of processing and resources. Therefore, the present invention provides a method which uses an existing X2 interference control message in an S1 interface. 
       FIG. 2  shows an interference control message  200  in accordance with the embodiment of the present invention. The interference control message  200  is an interference control message exchanged on an existing X2 interface and may include load information in order to control interference between neighboring base stations. The load information may include an UL interference overload indicator  210 , an UL high interference indicator  220 , and a relative narrowband Tx power  230 . 
     Also, the interference control message  200  may include a noise and interference level of a corresponding base station, allowing a Tx power to be determined within a range where adjacent base stations are not interfered. In addition, the interference control message  200  may include information about an user equipment located at an edge of a cell, or information about power control of the user equipment. 
     Furthermore, the interference control message  200  may include a variety of information necessary to control interference between the base stations. 
       FIG. 3  shows procedures of transferring an interference control message by using an S1 interface between femtocell base stations in accordance with the embodiment of the present invention. The interference between a HeNB 1   310  and a HeNB 2   330  can be controlled by transferring an interference control message  340  from the HeNB 1   310  to a HeNB GW  320  through the S1 interface and transferring an interference control message  350  from the HeNB GW  320  to the HeNB 2   330  through the S1 interface. 
     In this regard, in a case where an interference control message used in an existing X2 interface is converted into a format of an S1 Application Protocol (S1AP) which is a C-plane protocol of an S1 interface, the interference control message can be transferred through the S1 interface. In the embodiment, the interference control message used in the X2 interface is inserted into an X2 message container information element (IE) and transferred in the format of S1AP. 
     Meanwhile, the X2 message container IE may be transferred through the existing S1 interface by using a piggyback scheme which inserts a plurality of information into a single frame and transmits it. 
     That is, when the HeNB 1   310  intends to perform an interference control with respect to the neighboring HeNB 2   330 , the X2 interference control message having been used in the X2 interface is encoded and inserted in the X2 message container IE. The X2 message container IE including the X2 interference control message is transferred to the HeNB GW  320 , and then to the HeNB 2   330  through the S1 interface. 
       FIG. 4  shows an X2 message container IE in accordance with the embodiment of the present invention. The X2 message container IE  400  may include an ID field  410 , a length field  420 , and a content field  430 . The ID field  410  is a field which represents an ID regarding what X2 message is encoded in the content field  430 . 
     The ID field  410  of the X2 message container IE  400  is also called an X2 message container IE ID (IEI) and has a unique value in a message used in the S1 interface and a message used in the X2 interface. The length field  420  is a field which represents a total length of the content field  430 . The content field  430  is a field into which an X2 message to be actually transferred is inserted. In this embodiment, the interference control message is stored in the content field  430 . In  FIG. 4 , the ID field  410  has a length of 1 octet, and the length field  420  has a length of 2 octets. 
       FIG. 5  is a flowchart showing a schematic flow of an interference control method in accordance with an embodiment of the present invention. In order to control interference between base stations, the X2 interference control message used in the X2 interface is converted into a format of a protocol of the S1 interface to thereby generate an S1 interference control message to be used in the S1 interface. To this end, the X2 interference control message is inserted into the X2 message container IE  400  in step  510 . Then, the X2 message container IE  400  including the X2 interference control message is transmitted through the S1 interface by using a piggyback scheme in step  520 . The interference between the base stations can be controlled by the X2 message container IE  400  transmitted through the S1 interface, i.e., the S1 interference control message. 
       FIG. 6  is a block diagram showing a schematic architecture of an interference control apparatus in accordance with the embodiment of the present invention. The interference control apparatus  600  includes a generation unit  610  and a transmission unit  620 . The generation unit  610  generates the S1 interference control message by converting an X2 interference control message  630  used in an X2 interface into a format of a protocol of the S1 interface. In one embodiment, the generation unit  610  inserts the X2 interference control message  630  into the X2 message container IE  400 . 
     Thereafter, the S1 interference control message  640  which is outputted from the generation unit  610  and is transmittable through an S1 interface is inputted to the transmission unit  620 . The transmission unit  620  transmits the S1 interference control message  640  through the S1 interface. The S1 interference control message  640  may be transmitted by using a piggyback scheme. 
     The interference control apparatus  600  may further include a control unit  650  which controls the interference between the base stations, based on the interference control message transmitted through the S1 interface. 
     In accordance with the embodiment of the present invention, since the interference between the femtocell base stations is controlled by using the existing X2 interference control message in the femtocell environment where no X2 interface exists, the efficient interference control can be achieved even in the femtocell environment where no X2 interface exists. 
     Further, since the interference control message is not newly defined in the S1 interface, the waste of communication resources can be prevented and a rapid processing can be provided. 
     While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.