Handover method in a wireless access network

When a mobile device performs a handover from a first wireless base station to a second wireless base station, a base station controller sends a control message addressed to the second base station to notify the handover, to the first wireless base station via a wired line. The first wireless base station sends received control message to the second wireless base station using a pre-established wireless line. The wireless base stations exchange a control message to control the second wireless base station, a control message to control the mobile device, and user data of the mobile device and a communication partner, using the wireless line.

TECHNICAL FIELD

The present invention relates to a handover method in a wireless access network, and more particularly, to a handover method in a wireless access network that includes wireless links between wireless base stations.

BACKGROUND ART

In a mobile communication system, a handover is performed when a mobile device moves from a communication area of a certain wireless base station in which the mobile device is currently in communication to a communication area of another wireless base station. Various handover technologies have been proposed.

For example, Non-patent Document 1 discloses a technology related to a handover method in which a base station controller controls each wireless base station without direct transmission of signaling information or user data between wireless base stations in a mobile communication system that connects a plurality of wireless base stations to which a mobile device is connected to the base station controller with wired lines.

Specifically, the mobile device measures communication quality of a wireless line connected to a wireless base station that the mobile device is not currently communicating with. If the measured communication quality is higher than that of a wireless line connected to the wireless base station that the mobile device is currently communicating with, the mobile device sends the measured result to the base station controller.

The base station controller establishes a wired link between the wireless base station with the good result and the base station controller, and instructs the wireless base station to which the wired link has been established (a destination wireless base station) to establish a wireless link to the mobile device. After the destination wireless base station completes establishment of the wired link to the base station controller and preparation for establishment of the wireless link to the mobile device, the base station controller instructs the mobile device to establish the wireless link to the destination wireless base station via the wireless base station that the mobile device is currently communicating with.

After switching (handing over) the wireless line from the wireless base station that the mobile device is currently communicating with to the destination wireless base station, the mobile device notifies the base station controller via the destination wireless base station that the handover has been completed.

However, the handover method described in the Non-patent Document 1 involves a problem that the handover takes a long time due to a heavy processing load on the base station controller at the time of the handover because a wired line between the destination wireless base station and the base station controller is switched every time a handover of a mobile device occurs.

To solve the problem, according to the conventional technology described in Patent Document 1, a single master base station connected to public switched telephone networks (PSTN) and a plurality of slave base stations are serially connected with wired lines, and the master wireless base station comprehensively controls the slave wireless base stations. In this manner, the master wireless base station establishes the wired links among the wireless base stations and manages a location of the mobile device so that the handover is performed at a high speed.

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

However, the conventional technology described in the Patent Document 1 involves a problem that locations of the wireless base stations are restricted because the master base station and the slave base stations are connected with wired lines.

The present invention was made to solve the problems described above. It is an object of the present invention to obtain a handover method in a wireless access network, which reduces the processing load on the base station controller without restricting the locations of the wireless base stations.

Means for Solving Problem

A handover method according to one aspect of the present invention is for a wireless access network that includes a base station controller, at least one first wireless base station connected to the base station controller with a wired line, and at least one second wireless base station not connected to the base station with the wired line, where a mobile device is connected to the base station controller via the first wireless base station or the second wireless base station. The handover method includes establishing a wireless line between the first wireless base station and the second wireless base station in advance; sending including, when the mobile device performs a handover from the first wireless base station to the second wireless base station, the base station controller sending a control message addressed to the second base station to notify that the mobile device performs the handover, to the first wireless base station via the wired line; sending including the first wireless base station sending the control message addressed to the second wireless base station received from the base station controller to the second wireless base station using established wireless line; and exchanging including the first wireless base station and the second wireless base station exchanging a control message for the base station controller to control the second wireless base station, a control message for the base station controller to control the mobile device, and user data of the mobile device and a communication partner, using the wireless line.

Effect of the Invention

According to an aspect of the present invention, a wireless line is established in advance between a first wireless base station connected to a base station controller with a wired line and a second wireless base station connected to the base station controller not with the wired line, a message for the base station controller to control the second wireless base station, a control message for the base station controller to control the mobile device, and user data of the mobile device and a counterpart thereof are transmitted via the first wireless base station when the mobile device is handed over from the first wireless base station to the second wireless base station, and the wireless line established in advance is used between the first wireless base station and the second wireless base station. As a result, a handover is performed with a wireless base station that includes only the wireless interface having no restriction on the location thereof without increasing processing load on the base station controller.

EXPLANATIONS OF LETTERS OR NUMERALS

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Exemplary embodiments of a handover method in a wireless access network according to the present invention are explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments explained below.

First Embodiment

A first embodiment of the present invention is explained referring toFIGS. 1 to 8.FIG. 1is an example of a configuration of a mobile communication system that uses a handover method in a wireless access network according to the first embodiment. The mobile communication system that uses the handover method in a wireless access network according to the first embodiment includes a wireless access network6that includes wireless base stations2and5and a base station controller3that controls the wireless base stations2and5, a core network4that is connected to the wireless access network6by the base station controller3, and a mobile device1that communicates with a fixed terminal (not shown) or another mobile device (not shown) via the core network4connected to the wireless base stations2and5with wireless lines to set communication paths to the base station controller3, the fixed terminal, and the other mobile device.

The wireless base station2includes a wireless interface and a wired interface. It is connected to the base station controller3with a wired line40, and connected to the mobile device1and the adjacent wireless base station5with wireless lines. The wireless base station5includes a wireless interface alone. It is not connected to the base station controller3, and it is connected to the mobile device1and the adjacent wireless base station2with the wireless lines. The base station controller3controls the wireless base station2, and controls the wireless base station5via the wireless base station2. While the wireless access network6includes a single base station controller3inFIG. 1, there is actually a plurality of the base station controllers3. Moreover, a plurality of the wireless base stations2can be connected to the base station controller3. Furthermore, a plurality of the wireless base stations5can be connected to the wireless base station2via the wireless line.

FIG. 2is a schematic of a configuration of the mobile communication system when the mobile device1located in a cell7, which is a communication area of the wireless base station2, moves to a location in both of the cell7and a cell8, which is a communication area of the wireless base station5. When the mobile device1is located in the cell7(before moving), a wireless line10is established between the mobile device1and the wireless base station2. After the mobile device1moves to the location in both of the cells7and8and it is handed over from the wireless base station2to the wireless base station5(after moving), a wireless line12is established between the mobile device1and the wireless base station5. A wireless line11is established in advance between the wireless base station2and the wireless base station5. The wireless line11is always present between the wireless base station2and the wireless base station5regardless of presence of the mobile device1, and enables communication between the wireless base station5and the base station controller3via the wireless base station2.

FIG. 3is a schematic of a state of signal paths when the mobile device1is connected to the wireless base station2for communication. A control signal path21is used for sending and receiving a control message by which the base station controller3controls the wireless base station2, and it uses the wired line40.

A control signal path22is used for sending and receiving a control message by which the base station controller3controls the wireless base station5. The control signal path22uses the wired line40between the base station controller3and the wireless base station2, and uses the wireless line11between the wireless base station2and the wireless base station5.

A control signal path20is used for sending and receiving a control message by which the base station controller3controls the mobile device1. The control signal path20uses the wired line40between the base station controller3and the wireless base station2, and uses the wireless line10between the wireless base station2and the mobile device1.

A user data path30is used for sending and receiving user data related to communication between the mobile device1and another mobile device or a fixed terminal. The user data path30uses the wired line40between the base station controller3and the wireless base station2, and uses the wireless line10between the wireless base station2and the mobile device1.

FIG. 4is a schematic of a state of the signal paths when the mobile device1is connected to the wireless base station5for communication. The difference between the states of the communication paths when the mobile device1is connected to the wireless base station5for communication and when the mobile device1is connected to the wireless base station2for communication as shown inFIG. 3is that, because the mobile device1is connected to the wireless base station5instead of the wireless base station2, the wireless line10connected to the wireless base station2is open, whereby the control signal path20and the user data path30use the wireless line12between the mobile device1and the wireless base station5and they use the wireless line11between the wireless base station5and the wireless base station2.

An operation of the mobile communication system according to the first embodiment is explained referring to sequence diagrams shown inFIGS. 5 and 6. Firstly, referring to the sequence diagram inFIG. 5, the operation of the mobile communication system when the mobile device1that is communicating with the wireless base station2under the state of the signal paths shown inFIG. 3is handed over to the wireless base station5to be under the state of the signal paths shown inFIG. 4is explained.

The mobile device1measures communication quality of the wireless line10and that of a wireless line connected to a wireless base station except the wireless base station2(in this case, the wireless line12connected to the wireless base station5). To measure the communication quality, for example, a signal to noise ratio (SNR) or an error rate can be used.

If the communication quality of the wireless line12is higher that of the wireless line10, the mobile device1uses the control signal path20to send a handover requesting message to request a handover from the wireless base station2to the wireless base station5to the base station controller3via the wireless base station2(001).

The base station controller3recognizes from the handover requesting message that a destination is the wireless base station5, and uses the control signal path22to send a wireless-line-establishment requesting message to request an establishment of the wireless line12between the wireless base station5and the mobile device1to the wireless base station5via the wireless base station2(002). When the wireless base station2sends the message to the wireless base station5or the base station controller3using the control signal path22, the wireless base station2analyzes contents of the message to be sent. By analyzing the wireless-line-establishment requesting message to the wireless base station5, the wireless base station2recognizes that the wireless line12will be established, i.e., the mobile device1will be handed over to the wireless base station5. The wireless base station2performs a process for setting the control signal path20and the user data path30connected to the mobile device1to the wireless line11between the wireless base station2and the wireless base station5.

The wireless base station5performs a process for establishing the wireless line12between the wireless base station5and the mobile device1based on the wireless-line-establishment requesting message. Specifically, the wireless base station5performs a process for using the wireless line12such as startup of hardware and software related to the wireless line12. The wireless base station5sets the control signal path20and the user data path30to the wireless line11. The control signal path20and the user data path30are thereby set from the wireless base station2to the wireless base station5using the wireless line11. Because the wireless line10between the wireless base station2and the mobile device1remains established, the control signal path20and the user data path30are connected also to the mobile device1using the wireless line10.

When the process for establishing the wireless line12is completed, the wireless base station5uses the control signal path22to send a wireless-line-establishment response message indicative of completion of the process for establishing the wireless line12to the base station controller3via the wireless base station2(003).

The base station controller3uses the control signal path20to send a handover-start requesting message that permits a handover to the wireless base station5to the mobile device1via the wireless base station2(004).

Upon receiving the handover-start requesting message, the mobile device1starts transition from the wireless line10connected to the wireless base station2to the wireless line12connected to the wireless base station5. When the transition to the wireless line12is completed (when the wireless line12is established), the mobile device1uses the control signal path20that uses the wireless lines12and11to send a handover-completion response message indicative of establishment of the wireless line12to the base station controller3via the wireless base station5and the wireless base station2(005).

Upon receiving the handover-completion response message, the base station controller3uses the control signal path21to send a wireless-line-release requesting message to request release of the wireless line10to the wireless base station2(006).

Upon receiving the wireless-line-release requesting message, the wireless base station2releases resources of the wireless line10used to communicate with the mobile device1. The wireless base station2uses the control signal path21to send a wireless-line-release response message indicative of release of the wireless line10to the base station controller3(007).

In this manner, the wireless line12is established between the mobile device1and the wireless base station5as shown inFIG. 4. The control signal path20and the user data path30are set to use the wireless line12between the mobile device1and the wireless base station5, to use the wireless line11between the wireless base station5and the wireless base station2, and to use the wired line between the wireless base station2and the base station controller3. Thus, the handover from the wireless base station2to the wireless base station5is completed.

Secondly, referring to the sequence diagram shown inFIG. 6, the operation of the mobile communication system is explained assuming that the mobile device1that is communicating with the wireless base station5under the state of the signal paths shown inFIG. 4is handed over to the wireless base station2to be under the state of the signal paths shown inFIG. 3.

The mobile device1measures communication quality of the wireless line12and that of the wireless line connected to a wireless base station except the wireless base station5(in this case, the wireless line10connected to the wireless base station2). If the communication quality of the wireless line10is higher than the communication quality of the wireless line12, the mobile device1uses the control signal path20to send a handover requesting message to request a handover from the wireless base station5to the wireless base station2to the base station controller3via the wireless base station2(101).

The base station controller3recognizes from the handover requesting message that a destination is the wireless base station2, and uses the control signal path21to send a wireless-line-establishment requesting message to request an establishment of the wireless line10between the wireless base station2and the mobile device1to the wireless base station2(102).

After performing the process for establishing the wireless line10between the wireless base station2and the mobile device1based on the wireless-line-establishment request message, the wireless base station2uses the control signal path21to send a wireless-line-establishment response message indicative of completion of the process for establishing the wireless line10to the base station controller3(103).

The base station controller3uses the control signal path20to send a handover-start requesting message that permits a handover to the mobile device1via the wireless base station5and the wireless base station2(104).

Upon receiving the handover-start requesting message, the mobile device1starts transition from the wireless line12connected to the wireless base station5to the wireless line10connected to the wireless base station2. After the transition to the wireless line10is completed (the wireless line10is established), the mobile device1uses the control signal path20that uses the wireless line10to send a handover-completion response message indicative of establishment of the wireless line10to the base station controller3via the wireless base station2(105).

Upon receiving the handover-completion response message, the base station controller3uses the control signal path22to send a wireless-line-release requesting message to request release of the wireless line12to the wireless base station5via the wireless base station2(106).

Upon receiving the wireless-line-release requesting message, the wireless base station5releases resources of the wireless line12used to communicate with the mobile device1. The wireless base station5uses the control signal path22to send a wireless-line-release response message indicative of release of the wireless line12to the base station controller3via the wireless base station5(107).

On the other hand, the wireless base station2recognizes from the wireless-line-release response message sent through the control signal path22that the mobile device1will be handed over from the wireless base station5to the wireless base station2and that the wireless line12will be released. The wireless base station2resets the setting of the control signal path20and the user data path30set to the wireless line11so that the control signal path20and the user data path30use only the wireless line10.

In this manner, the wireless line10is established between the mobile device1and the wireless base station2as shown inFIG. 3. The control signal path20and the user data path30use the wired line40between the base station controller3and the wireless base station2, and use the wireless line10between the wireless base station2and the mobile device1. The wireless line12is released, and the control signal path20and the user data path30on the wireless line11are released. Thus, the handover from the wireless base station5to the wireless base station2is completed.

An operation of retransmission control particular to wireless lines is explained below. The retransmission control is often performed because the communication quality changes in a wireless line due to a multipath effect such as reflection, transmission, and diffraction. In general, the retransmission control is performed on both ends of the wireless line. In the case of the mobile communication system shown inFIG. 2, the retransmission control is performed between the mobile device1and the wireless base station2that use the wireless line10, between the wireless base station2and the wireless base station5that use the wireless line11, or between the mobile device1and the wireless base station5that use the wireless line12.

However, when the mobile device1is handed over, for example, to employ the retransmission control of the wireless line10that was performed between the wireless base station2connected before the handover and the mobile device1between the mobile device1and the wireless base station5or between the wireless base station2and the wireless base station5, information related to the retransmission such as the information that does not include a sequence number or a delivery confirmation needs to be transferred from one of the wireless base station2and the mobile device1to the wireless base station5. In such a case, the wireless base station2retains the retransmission control that was performed during the communication with the mobile device1using the wireless line10even if the mobile device1is handed over to the wireless base station5. At the same time, the wireless base station5manages no retransmission control of the communication between the mobile device1and the wireless base station2, sends data from the mobile device1to the wireless base station2, and sends other data from the wireless base station2to the mobile device1. Thus, the wireless base station5realizes the retransmission control of two-hop wireless line between the wireless base station2and the mobile device1as it was realized on the wireless lines11and12, whereby performing the retransmission control as before the handover. However, to the signals from the base station controller3to the wireless base station5, the retransmission control is applied between the wireless base station2and the wireless base station5.

The retransmission control can be realized between the base station controller3and the mobile device1, or it can be realized between the base station controller3and the wireless base station5.

The wireless base station2can send information related to power control between the wireless base station2and the mobile device1to the base station controller3and the base station controller3can send an instruction related to the power control based on the information related to the power control between the wireless base station2and the mobile device1to the wireless base station5so that the transmission power is stabilized early. Moreover, massages can be sent from the wireless base station2to the wireless base station5using the wireless line11.

By controlling electric power with respect to each wireless line as described above, quality of the wireless line can be retained and appropriate retransmission control can be performed.

As explained above, according to the first embodiment, the wireless line11is established in advance between the wireless base station2connected to the base station controller3with the wired line40and the wireless base station5connected to the base station controller3not with the wired line40, the control message for the base station controller3to control the wireless base station5(the wireless-line-establishment requesting message and the wireless-line-establishment response message) is transmitted via the wireless base station2connected with the wired line40when the mobile device1is handed over from the wireless base station2to the wireless base station5, and, between the wireless base station2and the wireless base station5, the wireless line11is used to send and receive the control message for the base station controller3to control the wireless base station5, the control message for the base station controller3to control the mobile device1(the handover-start requesting message, the handover-completion response message, and the handover requesting message), and the user data of the mobile device1and a counterpart. As a result, the processing load on the base station controller is reduced, and the handover can be performed with the wireless base station5that includes only the wireless interface having no restriction on the location thereof.

While the control signal path21for the base station controller3to control the wireless base station2and the control signal path22for the base station controller3to control the wireless base station5via the wireless base station2are set to the wired line40between the base station controller3and the wireless base station2according to the first embodiment, the message to control the wireless base station5can be sent to the wireless base station2using the control signal path21. In other words, the wired line40can use the control signal path21that is a logical channel for the wireless base station2instead of using the control signal path22that is a logical channel dedicated to the base station controller3and the wireless base station5. When the control signal path21is used, the wireless base station2determines whether the message from the control signal path21is addressed to the wireless base station2or the wireless base station5, and, if the message is addressed to the wireless base station5, the wireless base station2sends it to the wireless base station5using the control signal path22set to the wireless line11.

While the mobile device1starts the handover based on the handover requesting message according to the first embodiment, the mobile device1can send the measured result of the line quality of the wireless lines10and12to the base station controller3, and the base station controller3can start the handover based on the measured result. In such a case, the mobile device1sends a line-quality measured-result message that includes the measured result of the line quality instead of the handover requesting message to the base station controller3, and, if the base station controller3determines to perform the handover, the wireless-line-establishment requesting message is sent to start the handover.

While the wireless line11is established in advance between the wireless base station2and the wireless base station5and the control signal path20and the user data path30are set to the wireless line11when the mobile device1is handed over to the wireless base station5according to the first embodiment, the wireless line11used for the control signal path22and a wireless line13used for the control signal path20and the user data path30connected to the mobile device1can be established between the wireless base station2and the wireless base station5in advance, as shown inFIG. 7. In such a case, if the mobile device1is handed over to the wireless base station5, the control signal path20and the user data path30can be set to the wireless line13as shown inFIG. 8. In other words, different wireless lines are used for the communication between the base station controller3and the mobile device1and the communication between the base station controller3and the wireless base station5. In this manner, the communication quality of the control signal path22between the base station controller3and the wireless base station5can be retained without being affected by the user traffic between the base station controller3and the mobile device1.

Second Embodiment

A second embodiment of the present invention is explained referring toFIGS. 9 to 12. The mobile communication system that uses the handover method according to the second embodiment is same or similar to the mobile communication system shown inFIG. 1, and the explanation thereof is omitted here.

Referring to a sequence diagram shown inFIG. 9and a schematic of a state of signal paths when the mobile device1is connected to the wireless base station5for communication shown inFIG. 10, an operation of the mobile communication system according to the second embodiment is explained based on an example of the state of the signal paths shown inFIG. 10when the mobile device1, which is currently connected to the wireless base station2for communication under the state of the signal paths as shown inFIG. 3, is handed over to the wireless base station5.

The mobile device1measures the communication quality of the wireless line10and that of the wireless line connected to a wireless base station except the wireless base station2(in this case, the wireless line12connected to the wireless base station5). If the communication quality of the wireless line12is higher than that of the wireless line10, the mobile device1uses the control signal path20to send a handover requesting message to request a handover from the wireless base station2to the wireless base station5to the base station controller3via the wireless base station2(201).

The base station controller3recognizes from the handover requesting message that a destination is the wireless base station5, and uses the control signal path21to send a wireless-line-establishment requesting message to request an establishment of a wireless line14between the wireless base station2and the wireless base station5to be used for the user data path30connected to the mobile device1to the wireless base station2(202).

The base station controller3uses the control signal path22to send a wireless-line-establishment requesting message to request the establishment of the wireless line14to the wireless base station5via the wireless base station2(203).

Upon receiving the wireless-line-establishment requesting message, the wireless base stations2and5establish the wireless line14. After the wireless line14is established, the wireless base stations2and5uses the control signal paths21and22to send a wireless-line-establishment response message indicative of establishment of the wireless line14to the base station controller3(204,205).

Upon receiving the wireless-line-establishment response message from the wireless base stations2and5, the base station controller3uses the control signal path22to send a wireless-line-establishment requesting message to request the establishment of the wireless line12connected to the mobile device1to the wireless base station5via the wireless base station2(206).

After the process for establishing the wireless line12connected to the mobile device1is completed based on the wireless-line-establishment requesting message, the wireless base station5uses the control signal path22to send a wireless-line-establishment response message indicative of completion of the process for establishing the wireless line12to the base station controller3via the wireless base station2(207).

The base station controller3uses the control signal path20to send a handover-start requesting message that permits a handover to the mobile device1via the wireless base station2(208).

Upon receiving the handover-start requesting message, the mobile device1starts transition from the wireless line10connected to the wireless base station2to the wireless line12connected to the wireless base station5. After the transition to the wireless line12is completed (after the wireless line12is established), the mobile device1uses the control signal path20to send a handover-completion response message indicative of establishment of the wireless line12to the base station controller3via the wireless base station5and the wireless base station2(209). At this time, the wireless base station5uses the wireless line11to which the control signal path20is set to send the handover-completion response message received from the mobile device1to the wireless base station5, and the wireless base station2uses the wired line40to send the handover-completion response message. Because the user data of the mobile device1and the counterpart is sent and received through the user data path30, the wired line40is used between the base station controller3and the wireless base station2, the wireless line14is used between the wireless base station2and the wireless base station5, and the wireless line12is used between the wireless base station5and the mobile device1.

Upon receiving the handover-completion response message, the base station controller3uses the control signal path21to send a wireless-line-release requesting message to request release of the wireless line10to the wireless base station2(210).

Upon receiving the wireless-line-release requesting message, the wireless base station2releases resources of the wireless line10used to communicate with the mobile device1. The wireless base station2uses the control signal path21to send a wireless-line-release response message indicative of release of the wireless line10to the base station controller3(211).

In this manner, the wireless line12is established between the mobile device1and the wireless base station5, and the wireless line14is established between the wireless base station2and the wireless base station5, as shown inFIG. 10. The control signal path20is set to use the wired line40between the base station controller3and the wireless base station2, the wireless line11between the wireless base station2and the wireless base station5, and the wireless line12between the wireless base station5and the mobile device1. The user data path30is set to use the wired line40between the base station controller3and the wireless base station2, the wireless line14between the wireless base station2and the wireless base station5, and the wireless line12between the wireless base station5and the mobile device1. The control signal path20and the user data path30on the wireless line10are released, and the handover from the wireless base station2to the wireless base station5is completed.

As explained above, according to the second embodiment, the wireless line11is established in advance between the wireless base station2connected to the base station controller3with the wired line40and the wireless base station5connected to the base station controller3not with the wired line40, and the wireless line14is established between the wireless base station2and the wireless base station5when the mobile device1is handed over from the wireless base station2to the wireless base station5. Between the wireless base station2and the wireless base station5, the control message for the base station controller3to control the wireless base station5and the control message for the base station controller3to control the mobile device1are transmitted using the wireless line11, and the user data of the mobile device1and the counterpart is transmitted using the wireless line14. As a result, the processing load on the base station controller3is reduced, and the handover can be performed with the wireless base station5that includes only the wireless interface having no restriction on the location thereof.

Moreover, between the wireless base station2and the wireless base station5, the wireless line used to transmit the control message for the base station controller3to control the wireless base station5and the control message for the base station controller3to control the mobile device1is separate from the wireless line used to transmit the user data of the mobile device1and the counterpart. As a result, the quality of the wireless line used to transmit the control messages can be higher than that of the wireless line used to transmit the user data, whereby preventing occurrence of the retransmission control of a control message.

While the wireless-line-establishment requesting message to request the establishment of the wireless line14between the wireless base station2and the wireless base station5is sent to the wireless base station2before it is sent to the wireless base station5according to the second embodiment, the wireless-line-establishment requesting message can be sent to the wireless base station5before it is sent to the wireless base station2.

While the base station controller3sends the wireless-line-establishment requesting message to request an establishment of the wireless line12between the wireless base station5and the mobile device1and the wireless-line-establishment requesting message to request an establishment of the wireless line14between the wireless base station5and the wireless base station2separately to the wireless base station5according to the second embodiment, the request for the establishment of the wireless line12and the request for the establishment of the wireless line14can be included in a single wireless-line-establishment requesting message. In such a case, the wireless base station5can send the wireless-line-establishment requesting message to the base station controller3after the wireless lines12and14are established.

While the control signal path20between the base station controller3and the mobile device1uses the wireless line11between the wireless base station2and the wireless base station5where the control signal path22between the base station controller3and the wireless base station is set according to the second embodiment, a wireless line15can be established between the wireless base station2and the wireless base station5to be used for the control signal path20, as shown inFIG. 11. The wireless line15can be established by the base station controller3sending a wireless-line-establishment requesting message to establish the wireless line14that includes a request for the establishment of the wireless line15to the wireless base station2and the wireless base station5. Naturally, the wireless lines14and15can be established by sending the wireless-line-establishment requesting message to request the establishment of the wireless line14and the wireless-line-establishment requesting message to request the establishment of the wireless line15separately.

Because the control signal path22connected to the wireless base station5and the control signal path20connected to the mobile device1use different wireless lines11and15between the wireless base station2and the wireless base station5, use of resource of the wireless line11used for the wireless base station5can be reduced.

Moreover, because the control signal path22connected to the wireless base station5and the control signal path20connected to the mobile device1use different wireless lines11and15between the wireless base station2and the wireless base station5, the communication quality of the wireless line11used for the control signal path22is higher than that of the wireless line15used for the control signal path20, and the wireless base station5is controlled with high quality by preventing occurrence of the retransmission control of the control message for the base station controller3to control the wireless base station5using the control signal path22.

Furthermore, as shown inFIG. 12, a wireless line16can be established between the wireless base station2and the wireless base station5to set the control signal path20and the user data path30. By setting the control signal path20and the user data path30for the mobile device1to the wireless line16between the wireless base station2and the wireless base station5, the establishment of the wireless line16for the mobile device1between the wireless base station2and the wireless base station5is limited to the times of the handover or call setup of the mobile device1. As a result, the wireless lines between the wireless base station2and the wireless base station5are effectively used.

Third Embodiment

A third embodiment of the present invention is explained referring toFIGS. 13 and 14. The mobile communication system that uses the handover method according to the third embodiment is same or similar to the mobile communication system shown inFIG. 1, and the explanation thereof is omitted here.

Referring to a sequence diagram shown inFIG. 13and a schematic of a state of signal paths when the mobile device1is connected to the wireless base station5for communication shown inFIG. 14, an operation of the mobile communication system according to the third embodiment is explained based on an example of the state of the signal paths shown inFIG. 14when the mobile device1, which is currently connected to the wireless base station2for communication under the state of the signal paths as shown inFIG. 3, is handed over to the wireless base station5.

The mobile device1measures the communication quality of the wireless line10and that of the wireless line connected to a wireless base station except the wireless base station2(in this case, the wireless line12connected to the wireless base station5). If the communication quality of the wireless line12is higher than that of the wireless line10, the mobile device1uses the control signal path20to send a handover requesting message to request a handover from the wireless base station2to the wireless base station5to the base station controller3via the wireless-base station2(301).

The base station controller3recognizes from the handover requesting message that a destination is the wireless base station5, and uses the control signal path21to send a wireless-line-establishment requesting message to the wireless base station5via the wireless base station2to request that the wireless line10currently used between the mobile device1and the wireless base station2is used between the wireless base station2and the wireless base station5(302).

After the process for establishing the wireless line10between the wireless base station5and the wireless base station2is completed based on the wireless-line-establishment requesting message, the wireless base station5uses the control signal path21to send a wireless-line-establishment response message indicative of completion of the process for establishing the wireless line10to the base station controller3via the wireless base station2(303).

The base station controller3uses the control signal path22to send a wireless-line-establishment requesting message to request the establishment of the wireless line12connected to the mobile device1to the wireless base station5via the wireless base station2(304).

After the process for establishing the wireless line12connected to the mobile device1is completed based on the wireless-line-establishment requesting message, the wireless base station5uses the control signal path22to send a wireless-line-establishment response message indicative of completion of the process for establishing the wireless line12to the base station controller3via the wireless base station2(305). The wireless base station5associates the wireless line10established between the wireless base station5and wireless base station2with the wireless line12established between the wireless base station5and the mobile device1, i.e., stores therein the fact that data received from the wireless line10should be sent to the wireless line12and data received from the wireless line12should be sent to the wireless line10.

The base station controller3uses the control signal path20to send a handover-start requesting message that permits a handover to the mobile device1via the wireless base station2(306).

Upon receiving the handover-start requesting message, the mobile device1starts transition from the wireless line10connected to the wireless base station2to the wireless line12connected to the wireless base station5. After the transition to the wireless line12is completed (after the wireless line12is established), the mobile device1uses the control signal path20to send a handover-completion response message indicative of establishment of the wireless line12to the base-station controller3via the wireless base station5and the wireless base station2(307).

As explained above, according to the third embodiment, the wireless line11is established in advance between the wireless base station2connected to the base station controller3with the wired line40and the wireless base station5connected to the base station controller3not with the wired line40, and the wireless line10that was used between the wireless base station2and the mobile device1is established between the wireless base station2and the wireless base station5when the mobile device1is handed over from the wireless base station2to the wireless base station5. Between the wireless base station2and the wireless base station5, the control message for the base station controller3to control the wireless base station5is transmitted using the wireless line11, and the control message for the base station controller3to control the mobile device1and the user data of the mobile device1and the counterpart are transmitted using the wireless line10. As a result, the processing load on the base station controller3is reduced, and the handover can be performed with the wireless base station5that includes only the wireless interface having no restriction on the location thereof.

Moreover, the wireless line10that was used between the mobile device1and the wireless base station2is used for transmission of the control message for the base station controller3to control the mobile device1between the wireless base station2and the wireless base station5. As a result, the wireless base station2does not need to establish a new wireless line, and thereby the size of sequence in the handover process is reduced.

INDUSTRIAL APPLICABILITY

As described above, the handover method in the wireless access network according to an aspect of the present invention is advantageous to a wireless access network in which a base station controller comprehensively controls wireless base stations in the network to hand over a mobile device, and especially suitable for a wireless access network including a wireless base station that includes only a wireless interface and cannot be directly connected to the wireless base station controller using a wired line.