Communication system, compact base station, and communication method

TECHNICAL FIELD

0001The present invention relates to a communication system, a compact base station, and a communication method.

BACKGROUND ART

0002Communications by mobile phones use radio waves. Thus, even within a communication coverage area, in a radio shadow area where radio waves from an outdoor base station (hereinafter, referred to as a “macrocell base station”) are difficult to reach (or do not reach), communications by mobile phones cannot be performed. Hence, in order to enable communications by mobile phones even in the radio shadow area, the construction of a communication system using a compact base station is considered.

0003In this communication system, a compact base station (hereinafter, referred to as a “femtocell base station”) having, as its coverage area, a very small cell (femtocell) with a radius of the order of several meters to several tens of meters is installed in a radio shadow area. In addition, the femtocell base station is connected to a mobile communication network of a mobile service provider through a wire communication line. Therefore, mobile phones in the radio shadow area are connected to the mobile communication network through the femtocell base station and the wire communication line. As a result, even in the radio shadow area, communications by mobile phones are enabled.

0004Note that Japanese Unexamined Patent Publication No. 2004-15103 (Patent Literature 1) discloses a communication system including a radio base station installed in an optical communication subscriber's home. In this communication system, a signal from a mobile phone used in the subscriber's home is transmitted from the radio base station in the home to a local office through an optical communication cable and is then transmitted from the local office to various networks such as an IP network, a general telephone switching network, and a mobile communication switching network.

CITATION LIST

Patent Literature

0005Patent Literature 1: Japanese Unexamined Patent Publication No. 2004-15103

SUMMARY OF INVENTION

Technical Problem

0006In LTE (Long Term Evolution), a communication connection using a base station-to-base station logical interface, referred to as an X<b>2</b> interface, is established between adjacent macrocell base stations (eNodeBs). The adjacent macrocell base stations communicate information about a used frequency band, information about the movement operation of a mobile terminal, etc., with each other via the X<b>2</b> interface. This suppresses radio wave interference between the adjacent macrocells and achieves rapid inter-cell movement.

0007Here, the “movement” of a mobile terminal not only refers to a handover but also refers to making a selection of which base station is used to perform communication when a mobile terminal in an idle state starts communication from now on, i.e., when the mobile terminal starts a call or data communication.

0008However, for a femtocell base station (Home eNodeB), a communication connection using an X<b>2</b> interface is not established with a macrocell base station located in the neighborhood thereof or with another femtocell base station located in the neighborhood thereof. Therefore, since the base stations cannot communicate information about a used frequency band with each other via the X<b>2</b> interface, when the used frequency band overlaps between adjacent cells, radio wave interference between the adjacent cells increases. In addition, since the base stations cannot communicate information about movement operation with each other via the X<b>2</b> interface, it is difficult to perform rapid inter-cell movement.

0009The present invention is made in view of such circumstances, and an object thereof is to obtain a communication system, a compact base station, and a communication method that are capable of suppressing radio wave interference between adjacent cells and capable of achieving rapid inter-cell movement even in femtocell base stations.

Solution to Problem

0010A communication system according to a first aspect of the present invention includes: a mobile communication network; a fixed communication network connected to the mobile communication network; and a plurality of radio base stations capable of communicating with a mobile terminal by radio communication, and the radio base stations include: a first base station connected to the mobile communication network; and second base stations connected to the fixed communication network through wire communication lines, and a communication connection using a predetermined logical interface is established between one of the second base stations and a neighboring base station located in a neighborhood of the one of the second base stations, the neighboring base station including the first base station and/or another one of the second base stations.

0011According to the communication system according to the first aspect, a communication connection using a predetermined logical interface is established between a second base station and its neighboring base station. Therefore, since the second base station and its neighboring base station can communicate information about a used frequency band with each other via the logical interface, by setting used frequency bands such that they do not overlap with each other, overlapping of used frequency bands between adjacent cells can be avoided. As a result, radio wave interference between adjacent cells can be suppressed. In addition, since the second base station and its neighboring base station can communicate information about movement operation with each other via the logical interface, inter-cell movement can be performed rapidly.

0012A communication system according to a second aspect of the present invention is such that in the communication system according to the first aspect, particularly, a base station-to-base station logical interface is used as the predetermined logical interface.

0013Here, the “base station-to-base station logical interface” includes an X<b>2</b> interface in LTE.

0014According to the communication system according to the second aspect, since the second base station and its neighboring base station can be logically and directly connected to each other using the base station-to-base station logical interface, communication of information can be performed between the second base station and its neighboring base station without adding a change to communication management apparatuses such as MMEs.

0015A communication system according to a third aspect of the present invention is such that in the communication system according to the second aspect, particularly, each of the second base stations: makes a search for a neighboring base station; makes a request to a neighboring base station having responded to the search, for establishment of the communication connection; and establishes the communication connection with the neighboring base station having responded to the request.

0016According to the communication system according to the third aspect, a second base station makes a search for its neighboring base station, makes a request to a neighboring base station having responded to the search, for establishment of a communication connection, and establishes a communication connection with the neighboring base station having responded to the request. By the second base station making a search for its neighboring base station itself, there is no need to prepare a management server holding the location information of radio base stations, making it possible to achieve simplification of the configuration of the communication system. In addition, upon requesting establishment of a communication connection, the setting information, etc., of the second base station can be notified from the second base station to the neighboring base station, and upon responding to the request, the setting information, etc., of the neighboring base station can be notified from the neighboring base station to the second base station. By the base stations notifying each other of the setting information, a communication connection can be securely established.

0017A communication system according to a fourth aspect of the present invention is such that the communication system according to the second aspect particularly further includes: a management server that holds location information of the radio base stations, and each of the second base stations: obtains information about the neighboring base station from the management server; makes a request to the neighboring base station about which the information is obtained from the management server, for establishment of the communication connection; and establishes the communication connection with the neighboring base station having responded to the request.

0018According to the communication system according to the fourth aspect, a second base station obtains information about its neighboring base station from the management server, makes a request to the neighboring base station about which the information is obtained from the management server, for establishment of a communication connection, and establishes a communication connection with the neighboring base station having responded to the request. By the management server collectively managing the location information of radio base stations, a neighboring base station of the second base station can be accurately identified based on the location information. In addition, upon requesting establishment of a communication connection, the setting information, etc., of the second base station can be notified from the second base station to the neighboring base station, and upon responding to the request, the setting information, etc., of the neighboring base station can be notified from the neighboring base station to the second base station. By the base stations notifying each other of the setting information, a communication connection can be securely established.

0019A communication system according to a fifth aspect of the present invention is such that in the communication system according to the first aspect, particularly, a base station-to-base station logical interface using a base station-to-upper node logical interface is used as the predetermined logical interface.

0020Here, the “base station-to-upper node logical interface” includes an S<b>1</b> interface in LTE. In addition, the “base station-to-base station logical interface” includes an X<b>2</b> interface in LTE.

0021According to the communication system according to the fifth aspect, by allowing the base station-to-base station logical interface to be tunneled over the base station-to-upper node logical interface, a second base station and its neighboring base station can be logically connected to each other. As a result, without adding a new port for establishing the base station-to-base station logical interface besides the base station-to-upper node logical interface, the second base station and its neighboring base station can be logically connected to each other.

0022A communication system according to a sixth aspect of the present invention is such that the communication system according to the fifth aspect, particularly, further includes a communication management apparatus that is connected to each of the second base stations using the base station-to-upper node logical interface and collects information about the neighboring base station.

0023According to the communication system according to the sixth aspect, by the communication management apparatus, information about a neighboring base station of a second base station can be collected from another communication management apparatus, etc. By the communication management apparatus collecting information about a neighboring base station, there is no need to prepare a management server holding the location information of radio base stations, making it possible to achieve simplification of the configuration of the communication system.

0024A communication system according to a seventh aspect of the present invention is such that in the communication system according to the sixth aspect, particularly, each of the second base stations: obtains information about a neighboring base station from the communication management apparatus; makes a request through the communication management apparatus to the neighboring base station about which the information is obtained from the communication management apparatus, for establishment of the communication connection; and establishes the communication connection with the neighboring base station having responded to the request.

0025According to the communication system according to the seventh aspect, upon requesting establishment of a communication connection, the setting information, etc., of a second base station can be notified from the second base station to its neighboring base station, and upon responding to the request, the setting information, etc., of the neighboring base station can be notified from the neighboring base station to the second base station. By the base stations notifying each other of the setting information, a communication connection can be securely established.

0026A compact base station according to an eighth aspect of the present invention is used for a communication system including a mobile communication network; a fixed communication network connected to the mobile communication network; and a plurality of radio base stations capable of communicating with a mobile terminal by radio communication, and the radio base stations include: a first base station connected to the mobile communication network; and second base stations connected to the fixed communication network through wire communication lines, each of the second base stations serving as the compact base station, and a communication connection using a predetermined logical interface is established between one of the second base stations and a neighboring base station located in a neighborhood of the second base stations, the neighboring base station including the first base station and/or another one of the second base stations.

0027According to the compact base station according to the eighth aspect, a communication connection using a predetermined logical interface is established between a second base station and its neighboring base station. Therefore, since the second base station and its neighboring base station can communicate information about a used frequency band with each other via the logical interface, by setting used frequency bands such that they do not overlap with each other, overlapping of used frequency bands between adjacent cells can be avoided. As a result, radio wave interference between adjacent cells can be suppressed. In addition, since the second base station and its neighboring base station can communicate information about movement operation with each other via the logical interface, inter-cell movement can be performed rapidly.

0028A communication method according to a ninth aspect of the present invention is for a communication system including a mobile communication network; a fixed communication network connected to the mobile communication network; and a plurality of radio base stations capable of communicating with a mobile terminal by radio communication, and the radio base stations include: a first base station connected to the mobile communication network; and second base stations connected to the fixed communication network through wire communication lines, a communication connection using a predetermined logical interface is established between one of the second base stations and a neighboring base station located in a neighborhood of the second base stations, the neighboring base station including the first base station and/or another one of the second base stations, and the one of the second base stations performs communication with the neighboring base station through the communication connection.

0029According to the communication method according to the ninth aspect, a communication connection using a predetermined logical interface is established between a second base station and its neighboring base station. Therefore, since the second base station and its neighboring base station can communicate information about a used frequency band with each other via the logical interface, by setting used frequency bands such that they do not overlap with each other, overlapping of used frequency bands between adjacent cells can be avoided. As a result, radio wave interference between adjacent cells can be suppressed. In addition, since the second base station and its neighboring base station can communicate information about movement operation with each other via the logical interface, inter-cell movement can be performed rapidly.

0030A communication system according to a tenth aspect of the present invention is such that the communication system according to the second aspect, particularly, further includes a relay apparatus connected between the mobile communication network and the fixed communication network, and the second base stations are connected to the mobile communication network through the fixed communication network and the relay apparatus, and when a communication connection using the base station-to-base station logical interface is established between the relay apparatus and the first base station, the relay apparatus and the second base stations use the base station-to-base station logical interface using the base station-to-upper node logical interface, between the relay apparatus and the second base stations.

0031According to the communication system according to the tenth aspect of the present invention, by using a base station-to-base station logical interface using a base station-to-upper node logical interface between the relay apparatus and a second base station, the communication system can be configured as if a communication connection using a base station-to-base station logical interface is established between a first base station and the second base station. By this, a communication connection using a base station-to-base station logical interface can be established in a pseudo-manner between the first base station, the relay apparatus, and the second base station.

0032A communication system according to an eleventh aspect of the present invention includes: a plurality of radio base stations, each capable of communicating with a mobile terminal by radio communication and capable of establishing a communication connection using a predetermined logical interface with another radio base station; and a communication control apparatus capable of storing information on the plurality of radio base stations and capable of communicating with the plurality of radio base stations, and when the communication control apparatus recognizes a target base station being one of the radio base stations to newly establish the communication connection with another one of the radio base stations, the communication control apparatus notifies all those radio base stations other than the target base station of a connection establishment instruction indicating an instruction to perform a connection establishment process for establishing the communication connection with the target base station, and after each of the radio base stations is notified of the connection establishment instruction from the communication control apparatus and thereby performs the connection establishment process, each of the radio base stations determines whether or not to maintain an establishment state of the communication connection with the target base station and if determined not to maintain the establishment state, then the radio base station disconnects the communication connection.

0033According to the communication system according to the eleventh aspect of the present invention, for example, when a radio base station is newly installed and a communication connection using a predetermined logical interface is established between the radio base station and another radio base station, there is no need for a human to manually perform the establishment process and thus time and trouble and cost can be reduced. In addition, without providing radio base stations with greater functionality, a process of establishing a communication connection using a predetermined logical interface can be performed with a simple process and configuration. Furthermore, by disconnecting a predetermined logical interface that does not need to be maintained, wasteful use of various resources can be prevented in the communication system.

0034A communication system according to a twelfth aspect of the present invention is such that in the communication system according to the eleventh aspect, particularly, the target base station is connected to a mobile communication network through a fixed communication network, and the communication control apparatus notifies all those radio base stations other than the target base station of the connection establishment instruction.

0035According to the communication system according to the twelfth aspect of the present invention, a process of selecting a radio base station serving as the destination of notification of a connection establishment instruction is not necessary, making it possible to achieve simplification of a process of notifying of a connection establishment instruction.

0036A communication system according to a thirteenth aspect of the present invention is such that in the communication system according to the eleventh aspect, particularly, the target base station is connected to a mobile communication network through a fixed communication network, and the communication control apparatus notifies the radio base station disposed in a neighborhood of the target base station among the radio base stations, of the connection establishment instruction.

0037According to the communication system according to the thirteenth aspect of the present invention, by a configuration in which a connection establishment instruction is notified only to a radio base station disposed in the neighborhood of a target base station, a process of establishing a communication connection using a predetermined logical interface can be more efficiently performed.

0038A communication system according to a fourteenth aspect of the present invention is such that in the communication system according to any one of the eleventh to thirteenth aspects, particularly, each of the radio base stations determines not to maintain the establishment state of the communication connection when, after the radio base station is notified of the connection establishment instruction from the communication control apparatus and thereby performs the connection establishment process, the predetermined logical interface established with the target base station has not been used for a predetermined period.

0039According to the communication system according to the fourteenth aspect of the present invention, whether or not to maintain a predetermined logical interface can be appropriately determined.

0040In addition, each of the radio base stations determines not to maintain the establishment state of the communication connection when, after the radio base station is notified of the connection establishment instruction from the communication control apparatus and thereby performs the connection establishment process, the amount of data transmitted and received during a predetermined period, using the predetermined logical interface established with the target base station is less than or equal to a predetermined value.

0041In addition, each of the radio base stations determines not to maintain the establishment state of the communication connection when, after the radio base station is notified of the connection establishment instruction from the communication control apparatus and thereby performs the connection establishment process, the radio base station transmits predetermined data to the target base station and the response time of the target base station to the predetermined data is greater than or equal to a predetermined value.

0042A communication system according to a fifteenth aspect of the present invention includes: a plurality of radio base stations, each capable of communicating with a mobile terminal by radio communication and capable of establishing a communication connection using a predetermined logical interface with another radio base station; and a communication control apparatus capable of storing information on the plurality of radio base stations and capable of communicating with the plurality of radio base stations, and when the communication control apparatus recognizes a target base station being one of the radio base stations to newly establish the communication connection with another one of the radio base stations, the communication control apparatus notifies a radio base station disposed in a neighborhood of the target base station among the radio base stations, of a connection establishment instruction indicating an instruction to perform a connection establishment process for establishing the communication connection with the target base station.

0043According to the communication system according to the fifteenth aspect of the present invention, by a configuration in which a connection establishment instruction is notified only to a radio base station disposed in the neighborhood of a target base station, a process of establishing a communication connection using a predetermined logical interface can be more efficiently performed.

0044A communication system according to a sixteenth aspect of the present invention is such that in the communication system according to the thirteenth or fifteenth aspect, particularly, the communication control apparatus selects the radio base station to be notified of the connection establishment instruction from among the radio base stations, based on information indicating installed locations of the plurality of radio base stations including the target base station.

0045According to the communication system according to the sixteenth aspect of the present invention, by a configuration using information indicating the installed locations of radio base stations, a radio base station to be notified of a connection establishment instruction can be appropriately selected.

0046A communication system according to a seventeenth aspect of the present invention is such that in the communication system according to any one of the first to seventh and tenth to sixteenth aspects, particularly, at least one of information for performing, by the mobile terminal, movement operation between the radio base stations, information indicating interference received by the radio base stations, and load information of the radio base stations is transmitted and received between the radio base stations via the predetermined logical interface.

0047According to the communication system according to the seventeenth aspect of the present invention, radio wave interference between adjacent femtocells is suppressed and rapid and appropriate inter-cell movement can be achieved.

0048A communication control apparatus according to an eighteenth aspect of the present invention is capable of storing information on a plurality of radio base stations, each capable of establishing a communication connection using a predetermined logical interface with another radio base station, and is capable of communicating with the plurality of radio base stations, and when the communication control apparatus recognizes a target base station being one of the radio base stations to newly establish the communication connection with another one of the radio base stations, the communication control apparatus notifies the plurality of radio base stations other than the target base station of a connection establishment instruction indicating an instruction to perform a connection establishment process for establishing the communication connection with the target base station, and after each of the radio base stations performs the connection establishment process in response to the connection establishment instruction, the communication control apparatus determines whether or not to maintain an establishment state of the communication connection between each of the radio base stations and the target base station, and if determined not to maintain the establishment state, then the communication control apparatus performs control to disconnect the communication connection.

0049According to the communication control apparatus according to the eighteenth aspect of the present invention, for example, when a radio base station is newly installed and a communication connection using a predetermined logical interface is established between the radio base station and another radio base station, there is no need for a human to manually perform the establishment process and thus time and trouble and cost can be reduced. In addition, without providing radio base stations with greater functionality, a process of establishing a communication connection using a predetermined logical interface can be performed with a simple process and configuration. Furthermore, by disconnecting a predetermined logical interface that does not need to be maintained, wasteful use of various resources can be prevented in the communication system.

0050A communication method according to a nineteenth aspect of the present invention is for a communication system including a plurality of radio base stations, each capable of communicating with a mobile terminal by radio communication and capable of establishing a communication connection using a predetermined logical interface with another radio base station; and a communication control apparatus capable of storing information on the plurality of radio base stations and capable of communicating with the plurality of radio base stations, the communication method comprising the steps of; when the communication control apparatus recognizes a target base station being one of the radio base stations to newly establish the communication connection with another one of the radio base stations, notifying the plurality of radio base stations other than the target base station of a connection establishment instruction indicating an instruction to perform a connection establishment process for establishing the communication connection with the target base station, and after each of the radio base stations is notified of the connection establishment instruction from the communication control apparatus and thereby performs the connection establishment process, determining whether or not to maintain an establishment state of the communication connection with the target base station and disconnecting the communication connection if determined not to maintain the establishment state.

0051According to the communication method according to the nineteenth aspect of the present invention, for example, when a radio base station is newly installed and a communication connection using a predetermined logical interface is established between the radio base station and another radio base station, there is no need for a human to manually perform the establishment process and thus time and trouble and cost can be reduced. In addition, without providing radio base stations with greater functionality, a process of establishing a communication connection using a predetermined logical interface can be performed with a simple process and configuration. Furthermore, by disconnecting a predetermined logical interface that does not need to be maintained, wasteful use of various resources can be prevented in the communication system.

Advantageous Effects of Invention

0052According to the present invention, even in femtocell base stations, radio wave interference between adjacent cells can be suppressed and rapid inter-cell movement can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

0053<figref idref="DRAWINGS">FIG. 1</figref> is a diagram showing an overall configuration of a communication system according to a first embodiment of the present invention.

0054<figref idref="DRAWINGS">FIG. 2</figref> is a diagram showing a process sequence for establishing communication connections when a femtocell base station is newly installed.

0055<figref idref="DRAWINGS">FIG. 3</figref> is a diagram showing an overall configuration of a communication system according to a second embodiment of the present invention.

0056<figref idref="DRAWINGS">FIG. 4</figref> is a diagram showing a process sequence for establishing communication connections when a femtocell base station is newly installed.

0057<figref idref="DRAWINGS">FIG. 5</figref> is a diagram showing an overall configuration of a communication system according to a third embodiment of the present invention.

0058<figref idref="DRAWINGS">FIG. 6</figref> is a diagram showing a process sequence for establishing communication connections when a femtocell base station is newly installed.

0059<figref idref="DRAWINGS">FIG. 7</figref> is a diagram showing a procedure of a process of establishing a communication connection using an X<b>2</b> interface in a communication system <b>1</b> according to a fourth embodiment of the present invention.

0060<figref idref="DRAWINGS">FIG. 8</figref> is a diagram showing a procedure of a process of disconnecting a communication connection using an X<b>2</b> interface in the communication system <b>1</b> according to the fourth embodiment of the present invention.

0061<figref idref="DRAWINGS">FIG. 9</figref> is a diagram showing a procedure of a process of establishing a communication connection using an X<b>2</b> interface in a communication system <b>1</b> according to a fifth embodiment of the present invention.

0062<figref idref="DRAWINGS">FIG. 10</figref> is a diagram showing a procedure of a process of establishing a communication connection using an X<b>2</b> interface in a communication system <b>1</b> according to a sixth embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

0063Embodiments of the present invention will be described in detail below using the drawings. Note that those components denoted by the same reference signs in different drawings indicate the same or corresponding components.

First Embodiment

0064<figref idref="DRAWINGS">FIG. 1</figref> is a diagram showing an overall configuration of a communication system <b>1</b> according to a first embodiment of the present invention. Macrocell base stations (eNodeBs) <b>41</b> and <b>42</b> are connected to a mobile communication network <b>2</b>. Femtocell base stations (Home eNodeBs) <b>51</b> and <b>52</b> are connected to a fixed communication network <b>3</b> through wire communication lines <b>61</b> and <b>62</b> such as optical fibers. The fixed communication network <b>3</b> is connected to the mobile communication network <b>2</b> through a gateway <b>9</b>. An MME (Mobility Management Entity) <b>7</b> serving as an upper node of the macrocell base stations <b>41</b> and <b>42</b> is connected to the mobile communication network <b>2</b>. In addition, an MME <b>8</b> serving as an upper node of the femtocell base stations <b>51</b> and <b>52</b> is connected to the mobile communication network <b>2</b>. The MME <b>7</b> functions as a communication management apparatus for communication performed through the macrocell base stations <b>41</b> and <b>42</b>, and performs various processes such as session setting and release and control of movement operation. Likewise, the MME <b>8</b> functions as a communication management apparatus for communication performed through the femtocell base stations <b>51</b> and <b>52</b>, and performs various processes such as session setting and release and control of movement operation.

0065The macrocell base stations <b>41</b> and <b>42</b> each are logically connected to the MME <b>7</b> via a base station-to-upper node logical interface (S<b>1</b> interface in LTE (Long Term Evolution)). Likewise, the femtocell base stations <b>51</b> and <b>52</b> each are logically connected to the MME <b>8</b> via a base station-to-upper node logical interface (S<b>1</b> interface). In addition, the macrocell base stations <b>41</b> and <b>42</b> are logically connected to each other via a base station-to-base station logical interface (X<b>2</b> interface in LTE).

0066In the following example, it is assumed that the macrocell base station <b>42</b> and the femtocell base station <b>52</b> are neighboring base stations of the femtocell base station <b>51</b>. That is, a situation is assumed in which radio waves to be transmitted and received to/by the macrocell base station <b>42</b> and the femtocell base station <b>52</b> may interfere with radio waves to be transmitted and received to/by the femtocell base station <b>51</b> because a femtocell that is a coverage area of the femtocell base station <b>51</b>, a macrocell that is a coverage area of the macrocell base station <b>42</b>, and a femtocell that is a coverage area of the femtocell base station <b>52</b> overlap with each other or are close to each other. In addition, in this situation, when a mobile terminal <b>100</b>, such as a mobile phone, communicating with the femtocell base station <b>51</b> has moved, the macrocell of the macrocell base station <b>42</b> and the femtocell of the femtocell base station <b>52</b> may become a target of a handover from the femtocell of the femtocell base station <b>51</b>.

0067As shown in <figref idref="DRAWINGS">FIG. 1</figref>, the femtocell base station <b>51</b> is logically connected to the macrocell base station <b>42</b> and the femtocell base station <b>52</b> which are neighboring base stations, via base station-to-base station logical interfaces (X<b>2</b> interfaces). That is, communication connections using the X<b>2</b> interfaces are established between the femtocell base station <b>51</b> and each of the neighboring base stations.

0068<figref idref="DRAWINGS">FIG. 2</figref> is a diagram showing a process sequence for establishing communication connections when the femtocell base station <b>51</b> is newly installed. When the femtocell base station <b>51</b> is connected to the fixed communication network <b>3</b>, first, the femtocell base station <b>51</b> makes a search for its neighboring base stations. Specifically, the femtocell base station <b>51</b> broadcasts, by radio, a search signal M<b>101</b> requesting a response when the intensity of a received radio wave is greater than or equal to a predetermined threshold value, together with self identification information such as a base station ID, to an area around the femtocell base station <b>51</b>. The search signal M<b>101</b> is received by the macrocell base stations <b>41</b> and <b>42</b> and the femtocell base station <b>52</b>.

0069Then, the macrocell base stations <b>41</b> and <b>42</b> and the femtocell base station <b>52</b> each measure the intensity of a received radio wave for the search signal M<b>101</b> and determine whether or not a response to the femtocell base station <b>51</b> is required. In the example of the present embodiment, the intensity of a received radio wave for the search signal M<b>101</b> received by each of the macrocell base station <b>42</b> and the femtocell base station <b>52</b> which are neighboring base stations is greater than or equal to the threshold value, and the intensity of a received radio wave for the search signal M<b>101</b> received by the macrocell base station <b>41</b> which is not a neighboring base station is less than the threshold value. Therefore, the macrocell base station <b>42</b> and the femtocell base station <b>52</b> each return a response signal M<b>102</b> indicating the reception of the search signal M<b>101</b>, together with self identification information such as a base station ID, to the femtocell base station <b>51</b>. Returning of the response signals M<b>102</b> may be performed by either wire communication or radio communication. The macrocell base station <b>41</b>, on the other hand, does not return a response signal M<b>102</b> to the femtocell base station <b>51</b>.

0070Then, the femtocell base station <b>51</b> saves the information received from the macrocell base station <b>42</b> and the femtocell base station <b>52</b> and thereafter transmits a request signal M<b>103</b> requesting establishment of a communication connection, together with self setting information such as a port number used for an X<b>2</b> interface and location information, to the macrocell base station <b>42</b> and the femtocell base station <b>52</b>. Transmission of the request signal M<b>103</b> may be performed by either wire communication or radio communication.

0071Then, the macrocell base station <b>42</b> and the femtocell base station <b>52</b> having received the request signals M<b>103</b> each return a response signal M<b>104</b> to the request for establishment of a communication connection, together with self setting information such as a port number used for the X<b>2</b> interface and location information, to the femtocell base station <b>51</b>. Returning of the response signals M<b>104</b> may be performed by either wire communication or radio communication.

0072Then, by the macrocell base station <b>42</b> and the femtocell base stations <b>51</b> and <b>52</b> completing a process for port setting, etc., a communication connection using the X<b>2</b> interface is established between the femtocell base station <b>51</b> and the macrocell base station <b>42</b> and between the femtocell base station <b>51</b> and the femtocell base station <b>52</b>. The communication connections may be either wired or radio ones. Thereafter, the femtocell base station <b>51</b> and the macrocell base station <b>42</b> and the femtocell base station <b>52</b> communicate self setting information M<b>105</b> such as a frequency band to be used, with each other through the communication connections. In addition, when there arises the need for movement operation of the mobile terminal <b>100</b>, the base stations communicate information about the movement operation with each other through the communication connections.

0073As such, according to the communication system <b>1</b> according to the present embodiment, communication connections using a predetermined logical interface are established between the femtocell base station <b>51</b> and each of its neighboring base stations (the macrocell base station <b>42</b> and the femtocell base station <b>52</b>). Therefore, since the femtocell base station <b>51</b> and its neighboring base stations can communicate information about a used frequency band with each other via the logical interface, by setting used frequency bands such that they do not overlap with each other, overlapping of used frequency bands between adjacent cells can be avoided. As a result, radio wave interference between adjacent cells can be suppressed. In addition, since the femtocell base station <b>51</b> and its neighboring base stations can communicate information about movement operation with each other via the logical interface, intercell movement can be performed rapidly compared to the case in which the information is communicated via the MMEs <b>7</b> and <b>8</b>, etc.

0074In addition, according to the communication system <b>1</b> according to the present embodiment, since the femtocell base station <b>51</b> and its neighboring base stations can be logically and directly connected to each other using an X<b>2</b> interface, communication of information can be performed between the femtocell base station <b>51</b> and each of its neighboring base stations without adding a change to communication management apparatuses such as the MMEs <b>7</b> and <b>8</b>.

0075In addition, according to the communication system <b>1</b> of the present embodiment, the femtocell base station <b>51</b> makes a search for its neighboring base stations, makes a request to neighboring base stations having responded to the search, for establishment of a communication connection, and establishes communication connections with the neighboring base stations having responded to the request. By the femtocell base station <b>51</b> making a search for its neighboring base stations itself, there is no need to prepare a management server <b>10</b> (see <figref idref="DRAWINGS">FIG. 3</figref>) holding the location information of radio base stations, making it possible to achieve simplification of the configuration of the communication system <b>1</b>. In addition, upon requesting establishment of a communication connection, the setting information, etc., of the femtocell base station <b>51</b> can be notified from the femtocell base station <b>51</b> to its neighboring base stations, and upon responding to the request, the setting information, etc., of the neighboring base stations can be notified from the neighboring base stations to the femtocell base station <b>51</b>. By the base stations notifying each other of the setting information, communication connections can be securely established.

Second Embodiment

0076<figref idref="DRAWINGS">FIG. 3</figref> is a diagram showing an overall configuration of a communication system <b>1</b> according to a second embodiment of the present invention. A management server <b>10</b> such as an HLR (Home Location Register) is added to the configurations shown in <figref idref="DRAWINGS">FIG. 1</figref> and other configurations are the same as those in <figref idref="DRAWINGS">FIG. 1</figref>. The management server <b>10</b> is connected to a fixed communication network <b>3</b>. Note, however, that the management server <b>10</b> does not necessarily need to be connected to the fixed communication network <b>3</b> and may be installed in any location in the communication system <b>1</b>. In the management server <b>10</b>, pieces of location information about the installed locations of existing radio base stations (in the example of the present embodiment, macrocell base stations <b>41</b> and <b>42</b> and a femtocell base station <b>52</b>) are stored so as to be associated with pieces of identification information such as base station IDs.

0077<figref idref="DRAWINGS">FIG. 4</figref> is a diagram showing a process sequence for establishing communication connections when a femtocell base station <b>51</b> is newly installed. When the femtocell base station <b>51</b> is connected to the fixed communication network <b>3</b>, first, the femtocell base station <b>51</b> transmits a request signal M<b>201</b> for requesting self registration, together with identification information thereof such as a base station ID and self location information, to the management server <b>10</b> through the fixed communication network <b>3</b>.

0078Then, the management server <b>10</b> having received the request signal M<b>201</b> registers the femtocell base station <b>51</b> and identifies neighboring base stations of the femtocell base station <b>51</b> based on the location information of the femtocell base station <b>51</b>. In the example of the present embodiment, the management server <b>10</b> identifies the macrocell base station <b>42</b> and the femtocell base station <b>52</b> as the neighboring base stations of the femtocell base station <b>51</b>. Then, the management server <b>10</b> transmits a registration completion notification M<b>202</b> indicating the completion of registration of the femtocell base station <b>51</b>, together with information about the identified neighboring base stations, to the femtocell base station <b>51</b> through the fixed communication network <b>3</b>.

0079Then, the femtocell base station <b>51</b> saves the information received from the management server <b>10</b> and thereafter transmits a request signal M<b>203</b> requesting establishment of a communication connection, together with self setting information such as a port number used for an X<b>2</b> interface and location information, to the macrocell base station <b>42</b> and the femtocell base station <b>52</b>. Transmission of the request signal M<b>203</b> may be performed by either wire communication or radio communication.

0080Then, the macrocell base station <b>42</b> and the femtocell base station <b>52</b> having received the request signals M<b>203</b> each return a response signal M<b>204</b> to the request for establishment of a communication connection, together with self setting information such as a port number used for the X<b>2</b> interface and location information, to the femtocell base station <b>51</b>. Returning of the response signals M<b>204</b> may be performed by either wire communication or radio communication.

0081Then, by the macrocell base station <b>42</b> and the femtocell base stations <b>51</b> and <b>52</b> completing a process for port setting, etc., a communication connection using the X<b>2</b> interface is established between the femtocell base station <b>51</b> and the macrocell base station <b>42</b> and between the femtocell base station <b>51</b> and the femtocell base station <b>52</b>. The communication connections may be either wired or radio ones. Thereafter, the femtocell base station <b>51</b> and the macrocell base station <b>42</b> and the femtocell base station <b>52</b> communicate self setting information M<b>205</b> such as a frequency band to be used, with each other through the communication connections. In addition, when there arises the need for movement operation of a mobile terminal <b>100</b>, the base stations communicate information about the movement operation with each other through the communication connections.

0082As such, according to the communication system <b>1</b> of the present embodiment, communication connections using a predetermined logical interface are established between the femtocell base station <b>51</b> and each of its neighboring base stations (the macrocell base station <b>42</b> and the femtocell base station <b>52</b>). Therefore, since the femtocell base station <b>51</b> and its neighboring base stations can communicate information about a used frequency band with each other via the logical interface, by setting used frequency bands such that they do not overlap with each other, overlapping of used frequency bands between adjacent cells can be avoided. As a result, radio wave interference between adjacent cells can be suppressed. In addition, since the femtocell base station <b>51</b> and its neighboring base stations can communicate information about movement operation with each other via the logical interface, inter-cell movement can be performed rapidly compared to the case in which the information is communicated via MMEs <b>7</b> and <b>8</b>, etc.

0083In addition, according to the communication system <b>1</b> of the present embodiment, since the femtocell base station <b>51</b> and its neighboring base stations can be logically and directly connected to each other using an X<b>2</b> interface, communication of information can be performed between the femtocell base station <b>51</b> and each of its neighboring base stations without adding a change to communication management apparatuses such as the MMEs <b>7</b> and <b>8</b>.

0084In addition, according to the communication system <b>1</b> according to the present embodiment, the femtocell base station <b>51</b> obtains information about its neighboring base stations from the management server <b>10</b>, makes a request to the neighboring base stations, about which the information has been obtained from the management server <b>10</b>, for establishment of a communication connection, and establishes communication connections with the neighboring base stations having responded to the request. By the management server <b>10</b> collectively managing the location information of radio base stations, neighboring base stations of the femtocell base station <b>51</b> can be accurately identified based on the location information. In addition, upon requesting establishment of a communication connection, the setting information, etc., of the femtocell base station <b>51</b> can be notified from the femtocell base station <b>51</b> to its neighboring base stations, and upon responding to the request, the setting information, etc., of the neighboring base stations can be notified from the neighboring base stations to the femtocell base station <b>51</b>. By the base stations notifying each other of the setting information, communication connections can be securely established.

Third Embodiment

0085<figref idref="DRAWINGS">FIG. 5</figref> is a diagram showing an overall configuration of a communication system <b>1</b> according to a third embodiment of the present invention. A femtocell base station <b>51</b> is connected to each of a macrocell base station <b>42</b> and a femtocell base station <b>52</b> which are neighboring base stations, via a base station-to-base station logical interface (X<b>2</b> interface) tunneled over a base station-to-upper node logical interface (S<b>1</b> interface). That is, a communication connection using an X<b>2</b> interface tunneled over an Si interface (hereinafter, referred to as an “X<b>2</b> over S<b>1</b> interface”) is established between the femtocell base station <b>51</b> and each of its neighboring base stations. MMEs <b>7</b> and <b>8</b> and a gateway <b>9</b> can interpret the X<b>2</b> over S<b>1</b> interface and thus can appropriately perform routing. Other configurations are the same as those in <figref idref="DRAWINGS">FIG. 1</figref>.

0086<figref idref="DRAWINGS">FIG. 6</figref> is a diagram showing a process sequence for establishing communication connections when the femtocell base station <b>51</b> is newly installed. When the femtocell base station <b>51</b> is connected to the fixed communication network <b>3</b>, the femtocell base station <b>51</b> establishes an S<b>1</b> interface with the MME <b>8</b> and thereafter transmits a request signal M<b>301</b> for requesting information about its neighboring base stations, together with self location information, to the MME <b>8</b> through the fixed communication network <b>3</b> and the gateway <b>9</b>. Note that S<b>1</b> interfaces between the macrocell base stations <b>41</b> and <b>42</b> and the MME <b>7</b>, an S<b>1</b> interface between the femtocell base station <b>52</b> and the MME <b>8</b>, and an S<b>1</b> interface (or an S<b>10</b> interface) between the MME <b>7</b> and the MME <b>8</b> are already established. Note also that the MME <b>8</b> holds information about the MME <b>7</b> located in its neighborhood.

0087Then, the MME <b>8</b> having received the request signal M<b>301</b> collects information about a neighboring base station of the femtocell base station <b>51</b>, based on the location information of the femtocell base station <b>51</b>. In the example of the present embodiment, the MME <b>8</b> identifies the femtocell base station <b>52</b> as a neighboring base station of the femtocell base station <b>51</b>. In addition, the MME <b>8</b> transmits to the MME <b>7</b> a request signal M<b>302</b> for requesting information about a neighboring base station of the femtocell base station <b>51</b>, together with the location information of the femtocell base station <b>51</b>. The MME <b>7</b> having received the request signal M<b>302</b> collects information about a neighboring base station of the femtocell base station <b>51</b>, based on the location information of the femtocell base station <b>51</b>. In the example of the present embodiment, the MME <b>7</b> identifies the macrocell base station <b>42</b> as a neighboring base station of the femtocell base station <b>51</b>. Then, the MME <b>7</b> returns a response signal M<b>303</b> including information about the macrocell base station <b>42</b> identified as a neighboring base station, to the MME <b>8</b>.

0088The MME <b>8</b> having received the response signal M<b>303</b> returns a response signal M<b>304</b> including information about the macrocell base station <b>42</b> and the femtocell base station <b>52</b> identified as neighboring base stations, to the femtocell base station <b>51</b> through the gateway <b>9</b> and the fixed communication network <b>3</b>.

0089Then, the femtocell base station <b>51</b> saves the information received from the MME <b>8</b> and thereafter transmits a request signal M<b>305</b> requesting establishment of a communication connection to the femtocell base station <b>52</b> through the MME <b>8</b>, and to the macrocell base station <b>42</b> through the MMEs <b>8</b> and <b>7</b>. The request signal M<b>305</b> includes the setting information of the femtocell base station <b>51</b> such as a port number used for the S<b>1</b> interface and location information.

0090Then, the macrocell base station <b>42</b> having received the request signal M<b>305</b> returns a response signal M<b>306</b> to the request for establishment of a communication connection, to the femtocell base station <b>51</b> through the MMEs <b>8</b> and <b>7</b>. The response signal M<b>306</b> includes the setting information of the macrocell base station <b>42</b> such as a port number used for the S<b>1</b> interface and location information. Likewise, the femtocell base station <b>52</b> having received the request signal M<b>305</b> returns a response signal M<b>306</b> to the request for establishment of a communication connection, to the femtocell base station <b>51</b> through the MME <b>8</b>.

0091Then, by the macrocell base station <b>42</b> and the femtocell base stations <b>51</b> and <b>52</b> completing a process for port setting, etc., a communication connection using the X<b>2</b> over S<b>1</b> interface is established between the femtocell base station <b>51</b> and the macrocell base station <b>42</b> and between the femtocell base station <b>51</b> and the femtocell base station <b>52</b>. Thereafter, the femtocell base station <b>51</b> and the macrocell base station <b>42</b> and the femtocell base station <b>52</b> communicate self setting information M<b>307</b> such as a frequency band to be used, with each other through the communication connections. In addition, when there arises the need for movement operation of the mobile terminal <b>100</b>, the base stations communicate information about the movement operation with each other through the communication connections.

0092As such, according to the communication system <b>1</b> of the present embodiment, communication connections using a predetermined logical interface are established between the femtocell base station <b>51</b> and each of its neighboring base stations (the macrocell base station <b>42</b> and the femtocell base station <b>52</b>). Therefore, since the femtocell base station <b>51</b> and its neighboring base stations can communicate information about a used frequency band with each other via the logical interface, by setting used frequency bands such that they do not overlap with each other, overlapping of used frequency bands between adjacent cells can be avoided. As a result, radio wave interference between adjacent cells can be suppressed.

0093In addition, according to the communication system <b>1</b> according to the present embodiment, by allowing the X<b>2</b> interface to be tunneled over the S<b>1</b> interface, the femtocell base station <b>51</b> and its neighboring base stations can be logically connected to each other. As a result, without adding a new port for establishing the X<b>2</b> interface besides the S<b>1</b> interface, the femtocell base station <b>51</b> and its neighboring base stations can be logically connected to each other.

0094In addition, according to the communication system <b>1</b> according to the present embodiment, information about a neighboring base station of the femtocell base station <b>51</b> can be collected from the MME <b>7</b> by the MME <b>8</b>. By the MMEs <b>7</b> and <b>8</b> collecting information about neighboring base stations, there is no need to prepare a management server <b>10</b> (see <figref idref="DRAWINGS">FIG. 3</figref>) holding the location information of radio base stations, making it possible to achieve simplification of the configuration of the communication system <b>1</b>.

0095In addition, according to the communication system <b>1</b> of the present embodiment, upon requesting establishment of a communication connection, the setting information, etc., of the femtocell base station <b>51</b> can be notified from the femtocell base station <b>51</b> to its neighboring base stations, and upon responding to the request, the setting information, etc., of the neighboring base stations can be notified from the neighboring base stations to the femtocell base station <b>51</b>. By the base stations notifying each other of the setting information, communication connections can be securely established.

Fourth Embodiment

0096<figref idref="DRAWINGS">FIG. 7</figref> is a diagram showing a procedure of a process of establishing a communication connection using an X<b>2</b> interface in a communication system <b>1</b> according to a fourth embodiment of the present invention.

0097Referring to <figref idref="DRAWINGS">FIG. 7</figref>, in the communication system <b>1</b>, a gateway (communication control apparatus) <b>9</b> and femtocell base stations <b>51</b> and <b>52</b> are installed. A femtocell base station <b>53</b> is a femtocell base station to be newly installed.

0098As with a communication system <b>1</b> shown in <figref idref="DRAWINGS">FIG. 1</figref>, the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> are connected to a mobile communication network <b>2</b> through a fixed communication network <b>3</b>.

0099The femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> can communicate with a mobile terminal by radio communication and can establish a communication connection using an X<b>2</b> interface with another femtocell base station.

0100The gateway <b>9</b> can store various information of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> and can communicate with the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>. In addition, the gateway <b>9</b> performs control to establish a communication connection using an X<b>2</b> interface between the femtocell base stations.

0101For example, information for performing, by a mobile terminal, movement operation between femtocell base stations is transmitted and received between the femtocell base stations via an X<b>2</b> interface.

0102For example, this information is an ID for identifying, by the X<b>2</b> interface, the mobile terminal, a UE Context, etc. The UE Context is basic information of the mobile terminal such as an UE ID, UE (mobile terminal)-to-base station state information indicating an idle state or a connected state, and security information. The security information is security information between the mobile terminal and a base station and between the base station and a network, and information such as an algorithm and a security key that are used for security.

0103In addition, information indicating interference received by each femtocell base station is transmitted and received between femtocell base stations via the X<b>2</b> interface.

0104This interference information is, for example, in LTE, interference information in connection with a time axis direction, specifically, information indicating which one of a plurality of time slots in a radio frame transmitted from the femtocell base station to the mobile terminal suffers from interference.

0105In addition, the interference information transmitted and received using the X<b>2</b> interface is interference information in connection with a frequency axis direction, together with or separately from the interference information in connection with the time axis direction. Specifically, the interference information is information indicating which one of a plurality of subcarriers of a radio signal transmitted from the femtocell base station to the mobile terminal suffers from interference.

0106In addition, load information of each femtocell base station is transmitted and received between femtocell base stations via the X<b>2</b> interface.

0107Here, a communication connection using an X<b>2</b> interface is established between the femtocell base station <b>51</b> and the femtocell base station <b>52</b>.

0108Note that data compliant with the X<b>2</b> interface is physically transmitted and received between femtocell base stations through, for example, the gateway <b>9</b> or other apparatuses.

0109When the gateway <b>9</b> recognizes a femtocell base station (hereinafter, also referred to as a target base station) to newly establish a communication connection using an X<b>2</b> interface with another femtocell base station, the gateway <b>9</b> notifies this another femtocell base station of a connection establishment instruction indicating an instruction to perform a connection establishment process for establishing a communication connection using the X<b>2</b> interface with the target base station.

0110Furthermore, in the communication system <b>1</b>, the gateway <b>9</b> simultaneously instructs all femtocell base stations under control thereof to perform X<b>2</b> interface establishment.

0111Namely, the gateway <b>9</b> notifies all femtocell base stations under control thereof, i.e., all those femtocell base stations other than the target base station, of a connection establishment instruction.

0112Specifically, first, when the femtocell base station <b>53</b> is newly installed (step SQ<b>1</b>), the femtocell base station <b>53</b> transmits a base station registration request to the gateway <b>9</b>. The base station registration request includes identification information unique to the femtocell base station, e.g., a Cell Global ID, in order for the gateway <b>9</b> to identify the femtocell base station. Alternatively, a USIM (Universal Subscriber Identity Module) card may be installed on the femtocell base station and an IMSI (International Mobile Subscriber Identity) saved in the USIM card may be included in the base station registration request (step SQ<b>2</b>).

0113Then, when the gateway <b>9</b> receives the base station registration request from the femtocell base station <b>53</b> and thereby recognizes that the femtocell base station <b>53</b> has been newly installed, the gateway <b>9</b> simultaneously notifies, for example, all femtocell base stations under control thereof, here, the femtocell base station <b>51</b> and the femtocell base station <b>52</b>, of a connection establishment instruction indicating an instruction to perform an X<b>2</b> interface establishment procedure (step SQ<b>3</b>). The X<b>2</b> interface establishment procedure is, for example, a procedure obtained by changing a procedure such as that shown in <figref idref="DRAWINGS">FIG. 2</figref> such that the existing femtocell base stations transmit a request signal requesting establishment of a communication connection, etc., to the newly installed femtocell base station.

0114Then, in response to the connection establishment instruction from the gateway <b>9</b>, the femtocell base station <b>51</b> and the femtocell base station <b>52</b> each perform an X<b>2</b> interface establishment procedure with the femtocell base station <b>53</b> in order to establish a communication connection using an X<b>2</b> interface with the newly installed femtocell base station <b>53</b> (step SQ<b>4</b>).

0115<figref idref="DRAWINGS">FIG. 8</figref> is a diagram showing a procedure of a process of disconnecting a communication connection using an X<b>2</b> interface in the communication system <b>1</b> according to the fourth embodiment of the present invention.

0116Referring to <figref idref="DRAWINGS">FIG. 8</figref>, after the femtocell base stations <b>51</b> and <b>52</b> are notified of a connection establishment instruction from the gateway <b>9</b> and thereby perform a connection establishment process, the femtocell base stations <b>51</b> and <b>52</b> each determine whether or not to maintain an establishment state of a communication connection using an X<b>2</b> interface with the femtocell base station <b>53</b>. Then, if the femtocell base stations <b>51</b> and <b>52</b> determine not to maintain the establishment states of their respective communication connections, then the femtocell base stations <b>51</b> and <b>52</b> disconnect their respective communication connections.

0117Specifically, when the femtocell base station <b>51</b> and the femtocell base station <b>52</b> each establish a communication connection using an X<b>2</b> interface with the newly installed femtocell base station <b>53</b> (step SQ<b>4</b>), the femtocell base station <b>51</b> and the femtocell base station <b>52</b> each monitor whether or not the X<b>2</b> interface with the femtocell base station <b>53</b> is used, e.g., whether or not predetermined data compliant with the X<b>2</b> interface is periodically transmitted and received between the femtocell base station and the femtocell base station <b>53</b>.

0118Then, if the femtocell base station <b>51</b> and the femtocell base station <b>52</b> each detect that the X<b>2</b> interface with the femtocell base station <b>53</b> has not been used for a certain period of time (step SQ<b>5</b>), then the femtocell base station <b>51</b> and the femtocell base station <b>52</b> each disconnect the communication connection using the X<b>2</b> interface with the femtocell base station <b>53</b> (step SQ<b>6</b>).

0119As described previously, in the communication system <b>1</b> according to the fourth embodiment of the present invention, performance of an X<b>2</b> interface establishment procedure is instructed to each femtocell base station by a simultaneous notification. Hence, it is considered that a communication connection using an X<b>2</b> interface may be established even between femtocell base stations that are not adjacent to each other.

0120Hence, in the communication system <b>1</b>, when, after establishment of a communication connection using an X<b>2</b> interface, for example, it is detected that femtocell base stations have not used the X<b>2</b> interface for a certain period of time, the communication connection is disconnected. This can suppress a waste of resources such as the throughput of a CPU (Central Processing Unit), etc., and the amount of memory in the femtocell base stations.

0121Note that as the case in which an X<b>2</b> interface between a given femtocell base station and another femtocell base station is not used, for example, the case is considered in which movement operation of a mobile terminal is not performed between the femtocell base stations for the reason, for example, that the installed locations of the femtocell base stations are away from each other or there is a shield between the femtocell base stations.

0122Meanwhile, when a femtocell base station is newly installed, a communication connection using an X<b>2</b> interface is established between the newly installed femtocell base station and another femtocell base station. Manual performance of an X<b>2</b> interface establishment procedure by a human to establish this communication connection not only has poor efficiency but also incurs cost. In addition, when a communication connection using an X<b>2</b> interface between a femtocell base station and another femtocell base station is disconnected due to, for example, power-off of the femtocell base station, too, the efficiency is poor and it takes cost.

0123Here, for a method of establishing a communication connection between a newly installed femtocell base station and another femtocell base station in the communication system, the adoption of an SON (Self-Organizing Network) as in the case of a communication system according to the first embodiment of the present invention is considered. The SON is a technique in which a femtocell base station automatically adjusts and sets only required parameters in a communication system.

0124However, in a process of establishing an inter-base station interface using the SON, for example, a femtocell base station or a mobile terminal measures a radio signal transmitted from its neighboring femtocell base station and performs various adjustment and setting processes based on the result of the measurement. Hence, there arises the need to provide femtocell base stations with the function.

0125On the other hand, in the communication system according to the fourth embodiment of the present invention, when the gateway <b>9</b> recognizes a target base station which is a femtocell base station to newly establish a communication connection using an X<b>2</b> interface with another femtocell base station, the gateway <b>9</b> notifies a plurality of femtocell base stations other than the target base station of a connection establishment instruction indicating an instruction to perform a connection establishment process for establishing a communication connection using the X<b>2</b> interface with the target base station. Then, after each femtocell base station is notified of the connection establishment instruction from the gateway <b>9</b> and thereby performs a connection establishment process, each femtocell base station determines whether or not to maintain an establishment state of a communication connection using the X<b>2</b> interface with the target base station. If determined not to maintain the establishment state, then the femtocell base station disconnects the communication connection using the X<b>2</b> interface.

0126By such a configuration, when a femtocell base station is newly installed and a communication connection using an X<b>2</b> interface is established between the femtocell base station and another femtocell base station, there is no need for a human to manually perform the establishment process and thus time and trouble and cost can be reduced. In addition, there is no need to provide femtocell base stations with the SON function. Furthermore, by disconnecting an X<b>2</b> interface that does not need to be maintained, wasteful use of various resources can be prevented in the communication system.

0127The communication system according to the fourth embodiment of the present invention can be considered to be a different approach than a process of establishing an inter-base station interface using the SON. Specifically, in the communication system according to the fourth embodiment of the present invention, assuming that there is a possibility of causing waste, all femtocell base stations that are presumed to need to establish a communication connection using an X<b>2</b> interface with a newly installed target femtocell base station are allowed to perform an X<b>2</b> interface establishment procedure and thereafter an unnecessary X<b>2</b> interface(s) is (are) deleted.

0128By such a configuration, a process of establishing a communication connection using an inter-base station interface can be performed with a simple process and configuration.

0129In addition, in the communication system according to the fourth embodiment of the present invention, the gateway <b>9</b> notifies all those femtocell base stations other than a target base station that are associated with the stored information, of a connection establishment instruction.

0130By such a configuration, a process of selecting a femtocell base station serving as the destination of notification of a connection establishment instruction is not necessary, making it possible to achieve simplification of a process of notifying of a connection establishment instruction.

0131In addition, in the communication system according to the fourth embodiment of the present invention, when, after the femtocell base stations <b>51</b>, <b>52</b> are notified of a connection establishment instruction from the gateway <b>9</b> and thereby perform a connection establishment process, an X<b>2</b> interface established with a target base station has not been used for a predetermined period, the femtocell base stations <b>51</b>, <b>52</b> determine that an establishment state of a communication connection using the X<b>2</b> interface with the target base station does not need to be maintained.

0132By such a configuration, whether or not to maintain an X<b>2</b> interface can be appropriately determined.

0133In addition, in the communication systems according to the first to fourth embodiments of the present invention, at least one of information for performing, by a mobile terminal, movement operation between femtocell base stations, information indicating interference received by femtocell base stations, and load information of femtocell base stations is transmitted and received between femtocell base stations via a predetermined logical interface.

0134By such a configuration, radio wave interference between adjacent femtocells is suppressed and rapid and appropriate inter-cell movement can be achieved.

0135Note that although the communication system according to the fourth embodiment of the present invention is configured such that a communication connection using an X<b>2</b> interface is established between femtocell base stations, the configuration is not limited thereto. The configuration may be such that a communication connection using an X<b>2</b> interface is established between a femtocell base station and a macrocell base station or between macrocell base stations. In this case, for example, the MMEs <b>7</b> and <b>8</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> serve as communication control apparatuses and notify macrocell base stations and femtocell base stations of a connection establishment instruction.

0136Note that by a configuration in which a connection establishment instruction and a connection disconnection process are performed for an X<b>2</b> interface established with a femtocell base station which may be moved or whose power may be turned off due to user's circumstances, advantageous effects such as a reduction in time and trouble and cost and suppression of wasteful use of various resources can be more remarkably obtained.

0137In addition, although the communication system according to the fourth embodiment of the present invention is configured such that the gateway <b>9</b> notifies a plurality of femtocell base stations other than a target base station of a connection establishment instruction, the configuration is not limited thereto. The configuration may be such that the MME <b>7</b> or the MME <b>8</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> serves as a communication control apparatus and notifies a connection establishment instruction, or the configuration may be such that a macrocell base station or a femtocell base station serves as a communication control apparatus and notifies of a connection establishment instruction.

0138In addition, although in the communication system according to the fourth embodiment of the present invention, an X<b>2</b> interface is being established between existing femtocell base stations other than a femtocell base station to be newly installed, the configuration is not limited thereto. The configuration may be such that among the existing femtocell base stations there is a femtocell base station whose communication connection using an X<b>2</b> interface with another femtocell base station has not been established and an instruction to establish an X<b>2</b> interface with a target base station is given also to the femtocell base station.

0139In addition, although the communication system according to the fourth embodiment of the present invention is configured such that the femtocell base stations <b>51</b>, <b>52</b>, by its own determination, disconnect a communication connection using an X<b>2</b> interface with the femtocell base station <b>53</b>, the configuration is not limited thereto. The configuration may be such that the femtocell base stations <b>51</b>, <b>52</b> detect that the X<b>2</b> interface with the femtocell base station <b>53</b> has not been used for a certain period of time and reports it to the gateway <b>9</b>, and the gateway <b>9</b> determines that the communication connection using the X<b>2</b> interface between each of the femtocell base stations <b>51</b>, <b>52</b> and the femtocell base station <b>53</b> does not need to be maintained, and thus, controls the femtocell base stations <b>51</b>, <b>52</b> to disconnect the communication connection.

0140In addition, although the communication system according to the fourth embodiment of the invention is configured such that the gateway <b>9</b> recognizes a newly installed femtocell base station as a target base station, and allows a communication connection using an X<b>2</b> interface to be established between the target base station and another femtocell base station, the configuration is not limited thereto. The configuration may be any as long as the gateway <b>9</b> recognizes, as a target base station, a femtocell base station that needs for some reason to establish a communication connection using an X<b>2</b> interface with another femtocell base station, such as a femtocell base station whose power has been turned off for a long period of time.

0141In addition, although the communication system according to the fourth embodiment of the invention is configured such that when a femtocell base station detects that an X<b>2</b> interface with a target base station has not been used for a certain period of time, the femtocell base station disconnects a communication connection using the X<b>2</b> interface with the target base station, the configuration is not limited thereto. The configuration may be such that when movement operation of a mobile terminal is performed only occasionally between a femtocell base station and a target base station and the amount of data transmitted and received between the femtocell base station and the femtocell base station <b>53</b> using an X<b>2</b> interface during a predetermined period is less than or equal to a predetermined value, the femtocell base station determines that an establishment state of a communication connection using the X<b>2</b> interface with the target base station does not need to be maintained, and thus disconnects the communication connection.

0142In addition, when, after a femtocell base station performs a process of establishing a communication connection using an X<b>2</b> interface with a target base station, the femtocell base station transmits predetermined data to the target base station and the response time of the target base station to the predetermined data is greater than or equal to a predetermined value, the femtocell base station determines that an establishment state of the communication connection does not need to be maintained. For example, after a femtocell base station establishes a communication connection using an X<b>2</b> interface with a target base station, the femtocell base station transmits a packet to the target base station by a PING (Packet Internet Groper) command and measures response time of the target base station. Then, if the response time is greater than or equal to a predetermined value, then the femtocell base station determines that the necessity for the communication connection is low, and thus disconnects the communication connection.

0143Other configurations and operations are the same as those of a communication system according to the first embodiment and thus a detailed description is not repeated here.

Fifth Embodiment

0144<figref idref="DRAWINGS">FIG. 9</figref> is a diagram showing a procedure of a process of establishing a communication connection using an X<b>2</b> interface in a communication system <b>1</b> according to a fifth embodiment of the present invention.

0145Referring to <figref idref="DRAWINGS">FIG. 9</figref>, in the communication system <b>1</b>, a gateway (communication control apparatus) <b>9</b>, femtocell base stations <b>51</b> and <b>52</b>, an MME <b>8</b>, and an HLR (communication control apparatus) <b>10</b> are installed. The gateway <b>9</b> performs control to establish a communication connection using an X<b>2</b> interface between femtocell base stations. A communication connection using an X<b>2</b> interface is being established between the femtocell base station <b>51</b> and the femtocell base station <b>52</b>.

0146The HLR <b>10</b> stores information such as location information indicating the installed location of each femtocell base station in the communication system <b>1</b>, and manages each apparatus in the communication system <b>1</b>. Here, the location information is, for example, an address requested by a user to a telecommunications carrier as the installed location of a femtocell base station when the user makes a contract with the telecommunications carrier.

0147In the communication system <b>1</b>, the gateway <b>9</b> instructs a femtocell base station adjacent to a newly installed femtocell base station to establish a communication connection using an X<b>2</b> interface.

0148Specifically, when the gateway <b>9</b> recognizes a femtocell base station <b>53</b> which is a target base station to newly establish a communication connection using an X<b>2</b> interface with another femtocell base station, the gateway <b>9</b> notifies a femtocell base station disposed in the neighborhood of the femtocell base station <b>53</b> among all femtocell base stations under control thereof, i.e., those femtocell base stations associated with the stored information, of a connection establishment instruction.

0149More specifically, the gateway <b>9</b> selects a femtocell base station to be notified of a connection establishment instruction from among the femtocell base stations <b>51</b> and <b>52</b>, based on the information indicating the installed locations of the femtocell base stations <b>51</b> and <b>52</b> and the femtocell base station <b>53</b> which is the target base station.

0150Specifically, first, when the femtocell base station <b>53</b> is newly installed (step SQ<b>11</b>), the femtocell base station <b>53</b> transmits a base station registration request to the HLR <b>10</b> via the gateway <b>9</b> and the MME <b>8</b> (step SQ<b>12</b>).

0151Then, the HLR <b>10</b> receives the base station registration request from the femtocell base station <b>53</b> and outputs a location registration response including the stored location information of the femtocell base stations <b>51</b> and <b>52</b>, to the femtocell base station <b>53</b> via the MME <b>8</b> and the gateway <b>9</b> (step SQ<b>13</b>).

0152Then, the gateway <b>9</b> recognizes, based on the location registration response received from the HLR <b>10</b>, the new installation of the femtocell base station <b>53</b> and the installed locations of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> and notifies the femtocell base station <b>52</b> disposed in the neighborhood of the femtocell base station <b>53</b> of a connection establishment instruction indicating an instruction to perform an X<b>2</b> interface establishment procedure (step SQ<b>14</b>).

0153Then, in response to the connection establishment instruction from the gateway <b>9</b>, the femtocell base station <b>52</b> performs an X<b>2</b> interface establishment procedure with the femtocell base station <b>53</b> in order to establish a communication connection using an X<b>2</b> interface with the newly installed femtocell base station <b>53</b> (step SQ<b>15</b>).

0154Then, as with a communication system according to the fourth embodiment of the present invention, when the femtocell base station <b>52</b> establishes a communication connection using an X<b>2</b> interface with the newly installed femtocell base station <b>53</b> (step SQ<b>15</b>), the femtocell base station <b>52</b> monitors whether or not the X<b>2</b> interface with the femtocell base station <b>53</b> is used, e.g., whether or not predetermined data compliant with the X<b>2</b> interface is periodically transmitted and received between the femtocell base station <b>52</b> and the femtocell base station <b>53</b>. Then, if the femtocell base station <b>52</b> detects that the X<b>2</b> interface with the femtocell base station <b>53</b> has not been used for a certain period of time, then the femtocell base station <b>52</b> disconnects the communication connection using the X<b>2</b> interface with the femtocell base station <b>53</b>.

0155As such, in the communication system according to the fifth embodiment of the present invention, when the gateway <b>9</b> recognizes a target base station to newly establish a communication connection using an X<b>2</b> interface with another femtocell base station, the gateway <b>9</b> notifies a femtocell base station disposed in the neighborhood of the target base station among those femtocell base stations associated with the stored information, of a connection establishment instruction indicating an instruction to perform a connection establishment process for establishing a communication connection using an X<b>2</b> interface with the target base station.

0156By a configuration in which a connection establishment instruction is thus notified only to a femtocell base station disposed in the neighborhood of the target base station, a process of establishing a communication connection using an inter-base station interface can be more efficiently performed.

0157In addition, in the communication system according to the fifth embodiment of the present invention, the gateway <b>9</b> selects, based on information indicating the installed locations of femtocell base stations including a target base station, a femtocell base station to be notified of a connection establishment instruction from among those femtocell base stations associated with the stored information.

0158By a configuration thus using information indicating the installed locations of femtocell base stations, a femtocell base station to be notified of a connection establishment instruction can be appropriately selected.

0159Other configurations and operations are the same as those of communication systems according to the second and fourth embodiments and thus a detailed description is not repeated here.

Sixth Embodiment

0160<figref idref="DRAWINGS">FIG. 10</figref> is a diagram showing a procedure of a process of establishing a communication connection using an X<b>2</b> interface in a communication system <b>1</b> according to a sixth embodiment of the present invention.

0161Referring to <figref idref="DRAWINGS">FIG. 10</figref>, in the communication system <b>1</b>, a gateway (relay apparatus) <b>9</b>, femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>, a macrocell base station <b>41</b>, and MMEs <b>7</b> and <b>8</b> are installed.

0162The installed location of the gateway <b>9</b> is the same as that in a communication system <b>1</b> shown in <figref idref="DRAWINGS">FIG. 1</figref>. Namely, the gateway <b>9</b> is connected between a mobile communication network <b>2</b> and a fixed communication network <b>3</b>. The femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> are also connected to the mobile communication network <b>2</b> through the fixed communication network <b>3</b> and the gateway <b>9</b>, as with the communication system <b>1</b> shown in <figref idref="DRAWINGS">FIG. 1</figref>.

0163A communication connection using an S<b>1</b> interface is established between the macrocell base station <b>41</b> and the MME <b>7</b>. In addition, a communication connection using an X<b>2</b> interface is established between the macrocell base station <b>41</b> and the gateway <b>9</b>.

0164Here, the gateway <b>9</b> looks to the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> as the MME <b>8</b> due to communication connections. Namely, the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> perform communication with the upper node side, regarding the gateway <b>9</b> as the MME <b>8</b>. Hence, a communication connection using an S<b>1</b> interface is established among each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>, the gateway <b>9</b>, and the MME <b>8</b>.

0165Due to this, when data compliant with the X<b>2</b> interface is transmitted and received between the macrocell base station <b>41</b> and each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>, the gateway <b>9</b> requires a conversion process between the X<b>2</b> interface and the S<b>1</b> interface. Thus, there is a possibility that, for the throughput of the communication system <b>1</b>, an advantageous effect brought about by setting up the X<b>2</b> interface between the macrocell base station <b>41</b> and the gateway <b>9</b> may be reduced by half.

0166Meanwhile, a configuration may be considered in which a communication connection using an X<b>2</b> interface is established between each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> and the gateway <b>9</b>; however, the gateway <b>9</b> looks to the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> not only as the MME <b>8</b> but also as the macrocell base station <b>41</b>, which makes it difficult for the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> to perform communication with the upper node side.

0167Hence, in the communication system according to the sixth embodiment of the present invention, when a communication connection using a base station-to-base station logical interface, e.g., an X<b>2</b> interface, is established between the gateway <b>9</b> and the macrocell base station <b>41</b>, the gateway <b>9</b> and the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> use a base station-to-base station logical interface using a base station-to-upper node logical interface, e.g., an S<b>1</b> interface, between the gateway <b>9</b> and each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>.

0168More specifically, the gateway <b>9</b> receives data compliant with the X<b>2</b> interface from the macrocell base station <b>41</b> and transmits the data to the femtocell base station <b>51</b>, <b>52</b>, or <b>53</b> using the S<b>1</b> interface. Specifically, the gateway <b>9</b> transmits data compliant with the X<b>2</b> interface to the femtocell base station <b>51</b>, <b>52</b>, or <b>53</b> such that the data is included, as a single message, in a predetermined field of a frame defined by the S<b>1</b> interface.

0169In addition, the gateway <b>9</b> transmits data compliant with the X<b>2</b> interface received from the femtocell base station <b>51</b>, <b>52</b>, or <b>53</b> using the S<b>1</b> interface, to the macrocell base station <b>41</b>. Specifically, the gateway <b>9</b> monitors a header of a frame defined by the S<b>1</b> interface from the femtocell base station <b>51</b>, <b>52</b>, or <b>53</b> and when the header indicates that data compliant with the X<b>2</b> interface is included, the gateway <b>9</b> extracts data compliant with the X<b>2</b> interface from the frame and transmits the data to the macrocell base station <b>41</b>.

0170As such, in the communication system according to the sixth embodiment of the present invention, by establishing a communication connection using an X<b>2</b> over S<b>1</b> interface between the gateway <b>9</b> and each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>, the communication system can be configured as if a communication connection using an X<b>2</b> interface is established between the macrocell base station <b>41</b> and each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>.

0171Namely, for communication connections among the macrocell base station <b>41</b>, the gateway <b>9</b>, and each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>, while a communication connection between the macrocell base station <b>41</b> and the gateway <b>9</b> uses an X<b>2</b> interface, a communication connection between the gateway <b>9</b> and each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b> uses an X<b>2</b> over S<b>1</b>. By this, a communication connection using an X<b>2</b> interface can be established in a pseudo-manner among the macrocell base station <b>41</b>, the gateway <b>9</b>, and each of the femtocell base stations <b>51</b>, <b>52</b>, and <b>53</b>.

0172Other configurations and operations are the same as those of communication systems according to the third and fourth embodiments and thus a detailed description is not repeated here.

0173The above-described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the appended claims rather than by the foregoing meanings, and all changes that come within the meanings and range of equivalency of the claims are therefore intended to be embraced therein.

REFERENCE SIGNS LIST

0174<b>1</b>: COMMUNICATION SYSTEM

0175<b>2</b>: MOBILE COMMUNICATION NETWORK

0176<b>3</b>: FIXED COMMUNICATION NETWORK

0177<b>7</b> and <b>8</b>: MME

0178<b>9</b>: GATEWAY

0179<b>10</b>: MANAGEMENT SERVER and HLR

0180<b>41</b> and <b>42</b>: MACROCELL BASE STATION

0181<b>51</b>, <b>52</b>, and <b>53</b>: FEMTOCELL BASE STATION

0182<b>61</b> and <b>62</b>: WIRE COMMUNICATION LINE

0183<b>100</b>: MOBILE TERMINAL