Communication apparatus and handover control method

It is provided a communication apparatus connected to first and second wireless networks which performs handover between the first and second wireless networks, including first and second wireless functional units which obtain connection states and wireless quality of the wireless networks. A transmitter and a receiver of the first wireless functional unit are activated, a transmitter of the second wireless functional unit is deactivated, a receiver of the second wireless functional unit is activated and the wireless quality of the first wireless network and the second wireless network are obtained when a connection between the first wireless functional unit and the first wireless network is in a connected state. The transmitter and the receiver of the first wireless functional unit are deactivated, the transmitter and the receiver of the second wireless functional unit are activated and the data suppression process is canceled after the completion of the handover.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent application JP 2011-089936 filed on Apr. 14, 2011, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a hybrid communication terminal capable of communication with a plurality of networks and particularly to the handover technology thereof.

A mobile communication system is about to transition from the CDMA method having been used in 3G and 3.5G networks to next-generation networks such as faster WiMAX (registered trademark) and LTE (Long Term Evolution). However, since a service area is limited at the beginning of a transition to the next-generation networks, the need for hybrid communication terminals using a combination of a conventional network such as the 3G network and the next-generation network increases.

Although various forms such as data cards to be connected to PCs (Personal Computers) and handsets which do not receive power supply from PCs have been commercialized as communication terminals, miniaturization, weight saving and power saving are required in either case.

JP 2008-236079 A discloses a communication terminal which monitors wireless communication quality between the communication terminal and a first network and is connected to a second network if the wireless communication quality falls below a threshold value.

JP 2009-49875 A discloses a communication terminal which obtains information on communication quality between the communication terminal and each network, power consumption at the time of communication with each network, a communication rate with each network, communication applications used and the like, and utilizes these pieces of obtained information for handover between a first network and a second network.

SUMMARY OF THE INVENTION

<Problem Due to a Delay in the Determination of a System>

The conventional technique of handover between conventional different networks requires a facility for handover at each network side in addition to a communication terminal.

A communication terminal includes a handover circuit and a network needs to include a handover facility. In consideration of future system migration, ease of roaming and the like, the network side facility generally utilizes a facility which supports a method specified by a standard group (e.g. 3GPP and 3GPP2 in the 3G network, IEEE, WiMAX Forum and the like in WiMAX, 3GPP in LTE).

In this case, a handover service between these networks cannot be provided until these standard groups specify the specification of handover between the WiMAX network and the 3G network and the specification of handover between the LTE network and the 3G network. Further, the network side facility is expensive and cost burden for facility investment is high. Further, networks immediately after the start of service such as WiMAX and LTE have a small service area, roaming with existing networks is generally supported, but there is a problem that a roaming service cannot be provided until use is specified.

<Problem in the Case of Dealing on the Communication Terminal Side>

Preferably, the communication terminal side is simultaneously connected to both networks, compares wireless communication quality of the both networks, selects the network with a better environment, and constantly hands the communication over to the network with a better environment. However, when the communication terminal is simultaneously connected to the both networks, circuits for connection with the respective networks need to be simultaneously operated. In such a case, about twice as much power as a normal single terminal needs to be supplied.

However, in the case of receiving power supply from a PC, there are not many general-purpose interfaces which can supply a large amount of power to be consumed. Conversely, an interface capable of supplying a large amount of power can be used in limited PCs, with the result that the spread to the market does not progress. Further, even in the case of no power supply from the PC, an operating time by a built-in battery becomes shorter.

<Technique Disclosed in Prior Art Literatures>

The communication terminal disclosed in JP 2008-236079 A is connected to the second network when the wireless communication quality with the connected first network falls below the predetermined threshold value, whereby the communication terminal is simultaneously connected to different networks and the same data is transmitted from the communication terminal to the both networks, and the first network is disconnected to hand over the communication when the wireless communication quality between the communication terminal and the second network exceeds a certain threshold value. Thus, circuits corresponding to the respective networks simultaneously operate and power consumption increases in high-speed communication such as 3G, WiMAX or LTE communication.

Next, the communication terminal disclosed in JP 2009-49875 A measures power consumption in the case of connection with each network and hands over the communication to the network with less power consumption within a range that the use of an application does not become difficult. Thus, after measuring power consumption for communication with the first network, the communication terminal is connected to the second network and measures power consumption with the communication with the first network maintained. Therefore, power consumption increases.

Further, since parameters used in determining handover are measured in real time, these measuring circuits may become larger in scale and the miniaturization of the communication terminal becomes difficult.

That is, the above problems cannot be solved by the conventional technique.

The representative one of inventions disclosed in this application is outlined as follows. There is provided a communication apparatus which is connected to a first wireless network and a second wireless network and performs handover between the first wireless network and the second wireless network, including a first wireless functional unit which connects to the first wireless network, a second wireless functional unit which connects to the second wireless network, and a connection unit for connecting the first wireless functional unit and the second wireless functional unit to a computer. The first wireless functional unit obtains a connection state and wireless quality of the first wireless network. The second wireless functional unit obtains a connection state and wireless quality of the second wireless network. The handover between the first wireless network and the second wireless network is controlled in accordance with instructions from the computer based on the connection states and the wireless quality obtained by the first wireless functional unit and the second wireless functional unit. A transmitter and a receiver of the first wireless functional unit are activated, a transmitter of the second wireless functional unit is deactivated, a receiver of the second wireless functional unit is activated and the wireless quality of the first wireless network and the second wireless network are obtained in a case where a connection between the first wireless functional unit and the first wireless network is in a connected state. The first wireless functional unit checks a communication state in a case where the wireless quality of the first wireless network is less than a predetermined threshold and the wireless quality of the second wireless network is more than the predetermined threshold The first wireless functional unit starts a data suppression process in a case of carrying out communication The first wireless functional unit checks the communication state after the start of the data suppression process The first wireless functional unit performs the handover after being transitioned to a standby state in a case of carrying out communication. The transmitter and the receiver of the first wireless functional unit are deactivated, the transmitter and the receiver of the second wireless functional unit are activated and the data suppression process is canceled after the completion of the handover.

According to a representative embodiment of the present invention, it is possible to confirm the wireless quality of a second wireless network during connection to a first wireless network and perform handover while suppressing power consumption.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention are described by way of examples with reference to the drawings. Although 3G and WiMAX networks are described as examples of wireless networks, application to other networks such as LTE network is also possible.

First Embodiment

1. System Configuration

FIG. 1is a diagram showing the configuration of a wireless network1000according to a first embodiment of the present invention.

The wireless network1000of the first embodiment includes a 3G network, a WiMAX network200and a communication terminal300.

The communication terminal300is a hybrid communication terminal300capable of communication with the 3G network100and the WiMAX network200and is connected to a personal computer (PC)400. The PC400is equipped with a handover control module500which is a program (software) for controlling handover between the 3G network and the WiMAX network. The 3G network100includes a 3G base station110and the WiMAX network200includes a WiMAX base station210.

FIG. 2is a block diagram showing the configurations of the hybrid communication terminal300and the PC400of the first embodiment.

The hybrid communication terminal300includes a hub310, a 3G functional unit320and a WiMAX functional unit330.

The 3G functional unit320includes a 3G memory unit321, a 3G control unit322, a 3G wireless unit323and a 3G antenna324.

The 3G memory unit321is a nonvolatile storage device for storing a program to be executed by the 3G control unit322and data to be used at the time of executing the program. The 3G control unit322executes a protocol control (call request, incoming calls, handover, etc.) of the 3G network by executing the program stored in the 3G memory unit321. It should be noted that a part or all of the functions of the 3G control unit322may be realized by firmware or hardware.

The 3G wireless unit323generates a wireless signal for communication with the 3G base station110and receives a wireless signal from the 3G base station110. The 3G antenna324transmits and receives wireless signals to and from the 3G base station110.

The WiMAX functional unit330includes a WiMAX memory unit331, a WiMAX control unit332, a WiMAX wireless unit333and a WiMAX antenna334.

The WiMAX memory unit331is a nonvolatile storage device for storing a program to be executed by the WiMAX control unit332and data to be used at the time of executing the program. The WiMAX control unit332executes a protocol control (call request, incoming calls, handover, etc.) of the WiMAX network by executing the program stored in the WiMAX memory unit331. It should be noted that a part or all of the functions of the WiMAX control unit332may be realized by firmware or hardware.

The WiMAX wireless unit333generates a wireless signal for communication with the WiMAX base station210and receives a wireless signal from the WiMAX base station210. The WiMAX antenna334transmits and receives wireless signals to and from the WiMAX base station210.

The hub310connects the 3G functional unit320and the WiMAX functional unit330to the PC400.

The PC400includes a USB IF unit410, a CPU420, a memory430, a display unit440, a storage device450, an operation unit460and an internal communication line470for connecting them.

The USB IF unit410is a serial interface and connected to the hybrid communication terminal300in this embodiment. The CPU420executes a program stored in the memory430. The handover control module500is configured by executing this program. The memory430is a volatile or nonvolatile storage device for storing the program to be executed by the CPU420and data to be used at the time of executing the program and, for example, a RAM.

The display unit440includes a display screen (e.g. liquid crystal display device) which provides information to a user. The storage device450is a nonvolatile storage device for storing the program to be executed by the CPU420and data to be used at the time of executing the program and, for example, a hard disk drive or a flash memory. The operation unit460is a human interface which receives input from the user and, for example, a keyboard, a mouse or the like.

The internal communication line470is a communication bus connecting the configurations described above.

FIG. 3is a functional block diagram of the PC400of the first embodiment.

The PC400of the first embodiment includes the handover control module500, a 3G driver510, a WiMAX driver520, a TCP/IP unit530and an application540.

The 3G driver510and the WiMAX driver520perform processes of connection, disconnection, handover, obtaining state and obtaining wireless quality with the 3G network100and the WiMAX base station210by respectively transferring signals to and from the 3G base station110and the WiMAX base station210.

The 3G driver510and the WiMAX driver520respectively transfer signals to and from the 3G control unit322and WiMAX control unit332in accordance with a command transmitted from the handover control module500.

The application540transmits and receives data via the TCP/IP unit530. The TCP/IP unit530transmits and receives data to and from the 3G driver510or the WiMAX driver520that is connected.

First, states between the hybrid communication terminal300and the 3G network100or the WiMAX network200are distinguished into a connected state, communicating state, a standby state and a waiting state.

The connected state is a state where a connection between the hybrid communication terminal300and the 3G network100or the WiMAX network200is completed, i.e. a state where a wireless session, a PPP (Point-to-Point Protocol) connection, a TCP connection are established. The connected state includes the communicating state and the standby state.

The communicating state is a state where the hybrid communication terminal300is carrying out data communication with the 3G network100or the WiMAX network200and also expressed as an active state.

The standby state is a state where a wireless connection is open between the hybrid communication terminal300and the 3G network100or the WiMAX network200, but the wireless session, the PPP connection and the TCP connection are maintained. That is, if it returns from the standby state to the communicating state, a state is set where communication can be continued. The standby state is expressed as a dormant state in the 3G network100and an idle state in the WiMAX network200.

The waiting state is a state where the hybrid communication terminal300is connected neither to the 3G network100nor to the WiMAX network200.

Next, the handover from the WiMAX network200to the 3G network100is described with reference toFIGS. 4A and 4B. It should be noted that the handover from the 3G network100to the WiMAX network200is possible by a procedure similar to that shown inFIGS. 4A and 4B.

In a case where the hybrid communication terminal300is in the communicating state with the 3G network100(3G active state) (1001), the handover control module550is so controlled that a transmitter (Tx) and a receiver (Rx) of the 3G wireless unit323are both in an active state and a transmitter (Tx) and a receiver (Rx) of the WiMAX wireless unit333are both in an inactive state (1002). Here, Tx, Rx, ON and OFF respectively denote the transmitter, the receiver, the active state and the inactive state.

The handover control module550periodically obtains the state (connected state, communicating state, standby state, waiting state, etc.) and the wireless quality of the 3G network100from the 3G control unit322via the 3G driver510.

The handover control module550periodically requests Tx:OFF/Rx:ON to the WiMAX driver520to confirm the wireless quality of the WiMAX network200. The WiMAX driver520transfers the request of Tx:OFF/Rx:ON to the WiMAX control unit332. In a case of receiving the request of Tx:OFF/Rx:ON, the WiMAX control unit332sets the WiMAX wireless unit333in a state of Tx:OFF/Rx:ON (1003) and transmits a completion response of Tx:OFF/Rx:ON to the handover control module550via the WiMAX driver520(1004).

The handover control module550transmits a pilot acquisition request to the WiMAX control unit332via the WiMAX driver520(1005). The WiMAX control unit332obtains the wireless quality of the WiMAX network200from the WiMAX wireless unit333and notifies it to the handover control module550via the WiMAX driver520(1006).

After obtaining the wireless quality of the WiMAX network200, the handover control module550transmits a request of Tx:OFF/Rx:OFF to the WiMAX control unit332via the WiMAX driver520and sets the WiMAX wireless unit333in a state of Tx:OFF/Rx:OFF (1007,1008).

Normally, power consumption is large at the transmission side of the wireless unit in each system. Thus, as described in Steps1003to1008, it is possible to obtain the wireless quality of the other wireless network during the communicating state with one wireless network while reducing the power consumption of the hybrid communication terminal300by activating only the reception side of the system that is not connected.

The handover control module550checks whether an avoid timer is running. The avoid timer is a timer used to prevent the flapping of the handover. Since the handover is not performed while the avoid timer is running, unstable communication caused by the flapping of the handover can be prevented. Unless the avoid timer is running, the wireless quality of the 3G network100and the WiMAX network200are confirmed.

The handover control module550requests the handover to the 3G driver510(1009) in a case where the wireless quality of the 3G network100is below a reference value and that of the WiMAX network200is above a reference value.

Here, an example of wireless quality judgment is described. That the wireless quality of the 3G network100is below the reference value is judged by RSSI (Received Signal Strength Indication)≦reference value “a” or CINR (Carrier to Interference and Noise Ratio)≦reference value “b”. That the wireless quality of the WiMAX network200is above the reference value is judged by RSSI≧reference value “c” and CINR≧reference value “d”.

The 3G driver510having received a handover request checks the state of the 3G network100. As a result, in the communicating state with the 3G network100, a data suppression process is performed (1010) to prevent the missing of a packet during the handover. The data suppression process is described in detail later.

After the data suppression process, the 3G driver510checks the state of the 3G network100. As a result, in a case where the 3G network100is in the communicating state after the data suppression process, a transition to the standby state is requested to the 3G control unit322(1011).

The 3G control unit322checks whether a protocol process is in progress. As a result, in a case where the protocol process is in progress, the 3G control unit322transmits a standby state transition pending response. The 3G driver510transmits a standby state transition request again after the elapse of a predetermined time in a case of receiving the standby state transition pending response.

On the other hand, in a case where the protocol process is not in progress, the 3G control unit322transmits a connection close message to the 3G network100and transitions to the standby state (3G dormant state) (1012). The 3G control unit322transmits a standby state transition completion response to the 3G driver510(1013) after the transition to the standby state.

The 3G driver510transmits a handover completion response to the handover control module550(1014) after receiving the standby state transition completion response.

The handover control module550requests Tx:OFF/Rx:ON to the 3G control unit322via the 3G driver510after receiving the handover completion response. The 3G control unit322checks whether the protocol process is in progress. As a result, in a case where the protocol process is in progress, the 3G control unit322transmits a request pending response of Tx:OFF/Rx:ON. The handover control module550requests Tx:OFF/Rx:ON again after the elapse of a predetermined time in a case of receiving the request pending request of Tx:OFF/Rx:ON.

Whether the protocol process is in progress is checked here because the protocol process may be performed such as by crossing a sub-network in the 3G network100, for example, in the standby state or the communicating state. If the transmitter of the 3G wireless unit323is stopped at this timing, the communication may be cut off, judging that the protocol process was interrupted halfway and session negotiation was failed at the network side. Thus, the disconnection of the communication can be prevented by keeping the handover on hold during the protocol process and starting the handover again after the protocol process is finished.

In a case where the protocol process is not in progress, the 3G control unit322sets the 3G wireless unit323in a state of Tx:OFF/Rx:ON (1015) and transmits a completion response of Tx:OFF/Rx:ON to the handover control module550via the 3G driver510(1016).

After receiving the completion response of Tx:OFF/Rx:ON, the handover control module550requests Tx:ON/Rx:ON to the WiMAX control unit332via the WiMAX driver520. The WiMAX control unit332sets the WiMAX wireless unit333in a state of Tx:ON/Rx:ON (1017) and transmits a completion response of Tx:ON/Rx:ON to the handover control module550via the WiMAX driver520(1018).

After receiving the completion response of Tx:ON/Rx:ON, the handover control module550requests a connection to the WiMAX control unit332via the WiMAX driver520(1019). The WiMAX control unit332performs a connection process with the WiMAX network200(1020). The WiMAX control unit332transmits a connection completion response to the handover control module550via the WiMAX driver520(1021).

After the completion of the connection to the WiMAX network200, the handover control module550requests a disconnection to the 3G control unit322via the 3G driver510(1022). The 3G control unit322transitions to the disconnected state by internally opening the wireless session and the like (1023). At this time, the 3G wireless unit323transmits no disconnection message to the 3G network100since the transmission side is in an inactive state. After the transition to the disconnected state, the 3G control unit322transmits a disconnection completion response to the handover control module550via the 3G driver510(1024).

The handover control module550requests Tx:OFF/Rx:OFF to the 3G control unit322via the 3G driver510. The 3G control unit322sets the 3G wireless unit323in a state of Tx:OFF/Rx:OFF (1025) and transmits a completion response of Tx:OFF/Rx:OFF to the handover control module550via the 3G driver510(1026).

In a case of receiving the completion response of Tx:OFF/Rx:OFF, the handover control module550starts the avoid timer. The hybrid communication terminal300completes the handover and continues the communication with the WiMAX network200(1027).

It should be noted that, in a WiMAX active state, the 3G wireless unit323is set in the state of Tx:OFF/Rx:ON, the 3G control unit322obtains the wireless quality of the 3G network100from the 3G wireless unit323and notifies it to the handover control module550via the 3G driver510as in Steps1003to1006.

Next, the data suppression process (1010inFIG. 4A) is described with reference toFIG. 5. In this embodiment, an explicit congestion notification (ECN) function specified in RFC 3168 is used as the data suppression process.

In a case where the hybrid communication terminal300is in the communicating state with the 3G network100(3G active state) (1031), the TCP/IP-1 unit530and a TCP/IP-2 unit531transmit data with an ECT flag of an IP header of a packet to be transmitted set on to indicate the use of ECN (1032,1033). It should be noted that in a case where the ECT (ECN Capable Transport) flag is on, it indicates that a congestion process is supported.

In a case of receiving a handover request from the handover control module550(1034), the 3G driver510checks whether the ECT flag of the IP header of the packet received from the TCP/IP-1 unit530is on. As a result, in a case where the ECT flag is on, a CE flag of this packet is set on and the packet is transferred to the TCP/IP-2 unit531(1035). Thereafter, the 3G driver510transmits the packet received from the TCP/IP-1 unit530with the CE flag thereof set on. It should be noted that in a case where the CE (Congestion Experienced) flag is on, it indicates an ongoing congestion.

In a case of receiving the packet including the CE flag being set on, the TCP/IP-2 unit531transmits an ACK in which an ECE flag of a TCP header is on to the TCP/IP-1 unit530(1036). It should be noted that in a case where the ECE (ECN Echo) flag is on, an ongoing congestion is notified.

In a case of receiving the ACK including the ECE flag of the TCP header being on, the TCP/IP-1 unit530reduces a transmission window and executes a congestion avoidance algorithm as the data suppression process (1037).

The TCP/IP-1 unit530transmits a next packet to the 3G driver510after setting a CWR flag of a TCP header thereof on. It should be noted that in a case where the CWR (Congestion Window Reduced) flag is on, it indicates the execution of the congestion avoidance algorithm. The 3G driver510transmits the packet received from the TCP/IP-1 unit530after a CE flag thereof is set on (1038).

In a case where receiving the packet including the CWR flag and the CE flag being on, the TCP/IP-2 unit531transmits an ACK, in which an ECE flag is on, to the TCP/IP-1 unit530as in Step1036(1039).

The 3G driver510transmits a packet in which the CWR flag is on, determines that the data suppression process has been completed in Step1039in which the ACK is received, and starts a process such as the transmission of a standby state transition request (1011ofFIG. 4A,709ofFIG. 7).

In a case where the handover from the 3G network100to the WiMAX network200is completed and the communicating state (WiMAX active state) is set in the WiMAX network200(1040), the TCP/IP-1 unit530switches from the 3G driver510to the WiMAX driver520and transmits data. At this time, the WiMAX driver520transmits the packet received from the TCP/IP-1 unit530with the CE flag thereof kept off (1041) since receiving no handover request from the handover control module550. It should be noted that in a case where the CE (Congestion Experienced) flag is off, it indicates that the congested state is released.

The TCP/IP-2 unit531transmits an ACK in which an ECE flag is off to the TCP/IP-1 unit530(1042). It should be noted that in a case where the ECE (ECN Echo) flag is off, the release of the congested state is notified.

In a case of receiving the ACK including the ECE flag being off, the TCP/IP-1 unit530cancels the data suppression process, restores the transmission window and cancels the congestion avoidance algorithm (1043).

Although the data suppression process from the TCP/IP-1 unit530to the TCP/IP-2 unit531is described inFIG. 5, a data suppression process from the TCP/IP-2 unit531to the TCP/IP-1 unit530can be also performed in a similar manner.

Specifically, in a case of receiving a handover request from the handover control module550, the 3G driver510checks whether an ECT flag of an IP header of a packet received from the TCP/IP-2 unit531is on, and transfers this packet to the TCP/IP-1 unit530after setting a CE flag of the packet on in a case where the ECT flag is on. In this way, the data suppression process of the TCP/IP-2 unit is performed.

Further, after the handover from the 3G network100to the WiMAX network200is completed, the WiMAX driver520transfers the packet received from the TCP/IP-2 unit531to the TCP/IP-1 unit530with the CE flag of the packet kept off. In this way, the data suppression process of the TCP/IP-2 unit is canceled after the handover.

FIG. 6is a flow chart of a handover process of the first embodiment. The handover process shown inFIG. 6is performed by the handover control module550.

The handover control module550starts the handover process at a predetermined timing (e.g. repeatedly or regularly) (601).

The handover control module550checks whether the avoid timer used to prevent the flapping of the handover is running (602). As a result, in a case where the avoid timer is running, the handover process is finished (618).

On the other hand, in a case where the avoid timer is running, the handover is possible. Thus, the wireless quality of the 3G network100and that of the WiMAX network200are confirmed (603). As a result, in a case where the wireless quality do not satisfy handover criteria, the avoid timer is started (617) and the handover process is finished (618).

On the other hand, in a case where the wireless quality satisfy the handover criteria, a handover request is transmitted to a switching-source driver (604).

The handover control module550waits for a handover completion response from the switching-source driver for a predetermined time (605) and starts the avoid timer (617) and finishes the handover process (618) in a case of unable to receive the response.

On the other hand, the handover control module550transmits a request of Tx:OFF/Rx:ON to the switching-source driver (606) In a case of receiving the handover completion response.

The handover control module550checks a response message from the switching-source driver (607). As a result, in a case where a Tx:OFF/Rx:ON request pending response is received (608), Tx:OFF/Rx:ON is requested again after the elapse of a predetermined time. The handover control module550requests Tx:ON/Rx:ON to a switching-destination driver (609) In a case of receiving a completion response of Tx:OFF/Rx:ON.

The handover control module550transmits a connection request to the switching-destination driver (610).

Thereafter, the handover control module550checks a response message from the switching-destination driver (611). As a result, in a case where a connection failure response is received, Tx:OFF/Rx:OFF is requested to the switching-destination driver (612), Tx:ON/Rx:ON is requested to the switching-source driver (613) and a switchback request is made to the switching-source driver (614). Thereafter, the handover control module550starts the avoid timer (617) and finishes the handover process (618). In this case, the communication is continued in the switching-source system.

On the other hand, in a case of receiving a connection completion response in Step611, the handover control module550requests a disconnection to the switching-source driver (615) and requests Tx:OFF/Rx:OFF to the switching-source driver (616). Thereafter, the handover control module550starts the avoid timer (617) and finishes the handover process (618).

FIG. 7is a flow chart of a process performed when the 3G driver510and the WiMAX driver520of the first embodiment receive a handover request. Although the process performed by the 3G driver510is described below with reference toFIGS. 7 and 8, the process performed by the WiMAX driver520is also the same.

In a case of receiving a handover request, the 3G driver510starts this process (701) and first checks whether the communicating state is set (702). As a result, in a case where the communicating state is not set, the handover is possible. Thus, the 3G driver510transmits a handover completion response to the handover control module550(712). On the other hand, in a case of the communicating state, the 3G driver510starts a data suppression waiting timer (703).

The 3G driver510checks whether the data suppression process has been completed until time of the data suppression waiting timer elapses (704). The 3G driver510checks an ECT flag of an IP header of a packet received from the TCP/IP-1 unit530and the TCP/IP-2 unit531(705). As a result, in a case where the ECT flag is off, the process proceeds to Step708without the data suppression process being performed. On the other hand, in a case where the ECT flag is on, a CE flag of the received packet is set on (706). The CE flag is kept on until a handover completion response is transmitted in Step712.

Thereafter, the 3G driver510checks whether an ACK in which an ECE flag is on has been received (707) after transmitting the packet in which a CWR flag of a TCP header is on. In Step707, data are checked in both directions, i.e. from the TCP/IP-1 unit530to the TCP/IP-2 unit531and from the TCP/IP-2 unit531to the TCP/IP-1 unit530.

In a case where the ACK including the ECE flag being on is received in Step707, it is determined that the data suppression has been completed and the process proceeds to Step708. It should be noted that the process proceeds to Step708also In a case where time of the data suppression waiting timer elapses.

In Step708, the 3G driver510checks whether the communicating state is set. As a result, in a case where the communicating state is not set, the 3G driver510transmits a handover completion response to the handover control module550(712). On the other hand, in a case of the communicating state, the 3G driver510transmits a standby state transition request to the 3G control unit322(709).

It should be noted that, in Step709, the WiMAX driver520transmits a standby state transition request to the WiMAX control unit332.

The 3G driver510checks a response message from the 3G control unit322(or WiMAX control unit332) (710).

It should be noted that the WiMAX driver520transmits the standby state transition request to the WiMAX control unit332in Step709and checks the response message from the WiMAX control unit332in Step710.

As a result, in a case where the received response message is a standby state transition pending response, a standby state transition is requested again (709) after the elapse of a predetermined time (711). On the other hand, in a case where the received response message is a standby state transition completion response, a handover completion response is transmitted to the handover control module550(712).

FIG. 8is a flow chart of a process performed when the 3G driver510and the WiMAX driver520of the first embodiment receive a switchback request. Although the process performed by the 3G driver510is described below, the process performed by the WiMAX driver520is also the same.

In a case of receiving a switchback request, the 3G driver510starts this process (801) and first cancels the data suppression process (802). Specifically, even if a packet is received from the TCP/IP-1 unit530and the TCP/IP-2 unit531, a CE flag of the received packet is not set on. In this way, the data suppression process is canceled in the TCP/IP-1 unit530and the TCP/IP-2 unit531.

Subsequently, the 3G driver510transmits a communicating state transition request to the 3G control unit322(803). Finally, a switchback completion response is transmitted to the handover control module550(804).

FIG. 9is a flow chart of a process performed when the 3G control unit322and the WiMAX control unit332of the first embodiment receive an RF switch request. In a case of receiving an RF switch request, the 3G control unit322and the WiMAX control unit332activate or deactivate the Tx and Rx. Although the process performed by the 3G control unit322is described below, the process performed by the WiMAX control unit332is also the same.

In a case of receiving an RF switch request, the 3G control unit322starts this process (901) and first checks whether the communicating state or the standby state is set (902). In a case where neither the communicating state nor the standby state is set, the operations of the transmitter and the receiver are switched in accordance with a requested switch content (905) and an RF switch completion response is transmitted (907).

On the other hand, in a case where the communicating state or the standby state is set, it is checked whether the RF switch request is Tx:OFF/Rx:ON (903). Unless the RF switch request is Tx:OFF/Rx:ON, the operations of the transmitter and the receiver are switched in accordance with the requested switch content (905) and an RF switch completion response is transmitted (907).

In a case where the RF switch request is Tx:OFF/Rx:ON, it is checked whether the protocol process is in progress. The RF switch is not performed and an RF switch pending response is transmitted (906) in a case where the protocol process is in progress. On the other hand, unless the protocol process is in progress, the operations of the transmitter and the receiver are switched in accordance with the requested switch content (905) and an RF switch completion response is transmitted (907).

Second Embodiment

Although the hybrid communication terminal300and the PC400are connected by the USB interface in the first embodiment described above, the hybrid communication terminal300and the PC400may be integrally configured in one chassis. In this case, the HUB310and the CPU420are connected by an internal bus (e.g. PCI bus or the like) of the PC400.

As described above, since the handover is performed between different networks while being led by the hybrid communication terminal300in the embodiments of the present invention, it is not necessary to change the configurations of the network sides. Thus, it is not necessary to bear cost for facility investment and a time until the start of the service can be shortened. Further, since the handover can be performed within the range of the conventional specification, it is not necessary to specify a new standard in standard groups and the like.

Further, in the embodiments of the present invention, either one of the transmitter of the first wireless functional unit and that of the second wireless functional unit is deactivated at the time of the handover. This can suppress power consumption during the handover. This has an advantage of being able to support a versatile interface and being usable in a general PC in a data card type hybrid communication terminal which is connected to a PC and operates by power supplied from the PC. Further, in a handset type communication terminal which does not receive power supply from a PC, a battery usage time can be extended by suppressing power consumption.

Further, since only the receiver of the second wireless functional unit is activated at a predetermined timing (e.g. regularly) and the wireless quality of the second wireless network is confirmed even during the connection to the first wireless network in the embodiments of the present invention, it is possible to confirm the wireless quality of the second wireless network during the connection to the first wireless network while suppressing power consumption.

Further, since the data suppression process is performed to set the first wireless network in the standby state during the execution of the handover in the embodiments of the present invention, the handover to the second wireless network can be performed without missing a packet even during the communication with the first wireless network.

Further, since the handover is performed with the first wireless network set in the standby state in the embodiments of the present invention, the first wireless network can be set in the communicating state again to continuously communicate in a case where the handover to the second wireless network fails.

Further, in the embodiments of the present invention, whether the protocol process is in progress is checked during the execution of the handover and the handover is kept on hold in a case where the protocol process is in progress. For example, the protocol process may be performed due to the crossing of a subnetwork in the first wireless network during the communication with the first wireless network. In a case where the transmitter of the first wireless functional unit is stopped at this timing, it may be judged at the network side that session negotiation has failed and the communication may be disconnected. Thus, the disconnection of the communication can be prevented by keeping the handover on hold during the protocol process and starting the handover again after the protocol process is finished.

Further, since the timer used to prevent the flapping of the handover is started after the handover and the handover is not performed while the timer is running in the embodiments of the present invention, unstable communication caused by the flapping of the handover can be prevented.