Dual mode communication system, dual mode communication method and dual mode communication user equipment

A dual mode communication system, with user equipment selectively connectable to a plurality of communication systems, for switching communication systems to which the user equipment should be connected, detects that the remaining battery level fell below a first threshold in the user equipment communicating over the W-CDMA system. In the system it is determined whether or not the user equipment can communicate using the GSM system, which can be operated with lower power consumption than the W-CDMA system. When it is determined that communication can be established with the GSM system, the system switches from a connection between the user equipment and the W-CDMA system to a connection between the user equipment and the GSM system without interrupting the communication over the W-CDMA.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology for selecting a communications system to be used and switching from system to system among a plurality of different communications systems.

2. Description of the Related Art

Construction of communications infrastructure is in progress at present, and there are a plurality of systems such as W-CDMA (Wideband CDMA), CDMA2000 (Wideband CDMA one) as third generation mobile communication systems, which are becoming the mainstream among wireless communication systems. These communication systems allow high-speed and high-capacity communication; however the power consumption of mobile communication terminal user equipment (hereinafter referred to as user equipment) such as cellular phones is higher than user equipment of the conventional communication systems such as second generation mobile communication systems etc.

Currently, user equipment in general has a function for detecting the remaining battery level and, when the remaining battery level falls below a prescribed level, for notifying a user possessing the equipment of the low battery level by an alarm sound etc. However, in the case that the alarm sounds while the user equipment is in use, if it were during a voice call, for example, the call would be interrupted in several tens of seconds. In other words, although the user equipment has such a function, its alarm does not sound until the remaining battery level falls below the level insufficient to continue the call, and therefore, communication cannot be maintained with the user equipment. The user equipment, the call of which was terminated due to battery discharge, cannot be used for communication until its battery is recharged.

Technologies, which allow the battery power consumption of mobile communication user equipment to be controlled as soon as possible while maintaining communication quality to some extent, are proposed (for example, Patent Document 1). According to such technologies, the communication speed of mobile communication terminal user equipment is switched depending on the remaining battery power, and as the remaining battery level falls, the communication speed is reduced so as to extend the battery lifetime for communication.

There are other technologies proposed in which mobile communication terminal user equipment can selectively switch the communication system to use depending on the communication environment (Patent Documents 2, 3 and 4). According to such technologies, switching between W-CDMA and GSM (Global System for Mobile Communication) is performed, for example, in such a way that W-CDMA, which allows high-speed communication, is used when the remaining battery level is high, and can be switched to the battery-friendly GSM when the battery level is low.

As explained above, although one communication system among a plurality of communication systems can be selected and be switched to, the conventional art is not such that an optimum communication system can be automatically selected during a voice call. That is, in the conventional art, when the remaining battery level of the user equipment falls, the call has to be disconnected once, and the user is required to resume communication after switching communication systems to the one requiring less power consumption by manual operation. Such a case is troublesome in that the call has to be disconnected once and, in addition, resuming the communication disconnected once requires heavy battery consumption; therefore, efficiency in the use of the battery itself is reduced and, in some cases, the call cannot be resumed.

The user equipment described in the above Patent Document 2 comprises a function for selecting an optimum system in call request (at the beginning of a call). However, the user equipment only outputs an alarm sound when the battery level falls during a call.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a communication technology, of a mobile communication system, for enhancing user operation and for extending the user equipment up-time.

In order to solve the above problems, the present invention employs a dual mode communication method or system, in which dual mode user equipment switches between communication systems to which it is connected, when the remaining battery level is detected to have fallen below a first threshold in the user equipment during communication over a first communication system, determining whether or not the user equipment is able to communicate using a second communication system, which can be operated with lower power consumption than the first communication system, and switching a connection between the user equipment and the first communication system to a connection between the user equipment and the second communication system, when it is determined that communication can be established over the second communication system.

When the remaining battery level of the user equipment falls below a first threshold during communication over the first communication system, whether or not handover to the second communication system requiring less power than the first communication system is possible is determined, and if it is possible, handover to the second communication system is performed. In other words, when the remaining battery power becomes low during a voice call, automatic handover to a communication system, which can operate with lower power consumption can be performed maintaining the voice call.

It is possible that the user equipment, if communication can be established over the second communication system, transmits a message requesting a switch from the first communication system to the second communication system, and a handover control system configured on a network switches from the connection between the user equipment and the first communication system to the connection between the user equipment and the second communication system according to the message. Or it is also possible that the user equipment, if communication can be established over the second communication system, transmits measurement information, indicating that the signal level information from the second communication system is higher than the signal level information from the first communication system, to a network, and a handover control device, configured on the network, switches from the connection between the user equipment and the first communication system to a connection between the user equipment and the second communication system, according to the measurement information.

When detecting that the remaining battery level of the user equipment, during communication over the second communication system, rises to or above a second threshold, the connection between the user equipment and the second communication system can be switched to a connection between the user equipment and the first communication system. In such a case, the communication over the first communication system, used before the handover to the second communication system, is resumed when the remaining battery level is recovered by charging etc.

The present invention is not limited to the above dual mode communication method or system. The present invention should be construed as including mobile communication user equipment, network systems and so on, which adopt the above communication method or system.

According to the present invention, a communication system to which user equipment, during a voice call, should connect is switched automatically depending on the remaining battery power, and thus user equipment up-time can be extended enhancing user operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, details of the preferred embodiment of the present invention are set forth with reference to drawings.

FIG. 1is a diagram explaining a usage pattern of dual mode mobile user equipment. The dual mode mobile user equipment is terminal equipment, which can be selectively connected to a plurality (usually two) of communication systems, and can perform communication with the other user equipment using the selected communication system.

In the example inFIG. 1, the dual mode mobile user equipment1(hereinafter called “user equipment” on occasion) connects to either a W-CDMA system100adopting a W-CDMA method or a GSM system200adopting a GSM method, and performs communication with the other user equipment. A BTS (Base Transceiver System)101of the W-CDMA communication100and a BTS102of the GSM system200transmit a BCCH (Broadcast Channel) or a CPICH (Common Pilot Channel) signal to user equipment located within the service area of each BTS repeatedly at a prescribed time interval. The user equipment1, based on the BCCH or the pilot signal received from the BTS101and the BTS102, recognizes the state of each network and determines a communication system to be connected to in performing communication. For example, when signal level of the BCCH from the BTS101of the W-CDMA system100is higher than a predetermined level, and signal level of the BCCH from the BTS102of the GSM system200is lower than a predetermined level, the user equipment1selects the W-CDMA system100and performs communication over the BTS101.

A network10is connected to both of the BTS101of the W-CDMA system and the BTS102of the GSM system200. That is, the network10provides a function for transferring signals between the W-CDMA system100and the GSM system200. In addition, the network10comprises a handover control system, not shown in the figures, for controlling handover between the W-CDMA system100and the GSM system200.

FIG. 2is a block diagram of the dual mode user equipment1relating to the present invention. The user equipment1comprises a W-CDMA radio frequency unit2, a GSM radio frequency unit3, a battery4, a battery voltage control unit5and a digital baseband unit6. The W-CDMA radio frequency unit2and the GSM radio frequency unit3transmit/receive radio signals to/from the communication system100and the communication system200, respectively. The battery4is a rechargeable secondary battery. The battery voltage control unit5converts the output voltage of the battery4into voltages that each of the circuit units (the W-CDMA radio frequency unit2, the GSM radio frequency unit3, and the digital baseband unit6) require. The digital baseband unit6comprises a W-CDMA modem11, a GSM modem12and a CPU (Central Processing Unit)13, and the CPU13comprises a battery voltage monitor unit14. Each of the W-CDMA modem11and the GSM modem12modulates/demodulates transmitted/received signals over its corresponding communication system. The CPU13controls various operations relating to the present invention. The battery voltage monitor unit14is connected to the battery voltage control unit5, and monitors the output voltage of the battery4in order to detect the remaining battery level.

FIG. 3is a handover sequence from the W-CDMA system100to the GSM system200.FIG. 4is also a handover sequence but is from the GSM system200to the W-CDMA system100. In the following description, an explanation of a general handover sequence is provided with reference toFIG. 3andFIG. 4.

InFIG. 3, UE (User Equipment)1was transmitting/receiving voice data over the W-CDMA system100. Then, handover from UTRAN Command-GSM is transmitted from the W-CDMA system100to the UE1. Due to this command, the UE1starts processing for switching its communication system to the GSM system200. The UE1, which received the handover from UTRAN Command-GSM, transmits a handover access message to the GSM system200of the handover destination. The GSM system200, upon receiving the handover access message, transmits a physical information message to the UE1. The physical information message that the UE1received from the GSM system200contains information related to line status statistics, utilization and so on at that point in time.

The UE1having received the physical information message transmits a SABM (Set Asynchronous Balanced Mode) message to the GSM system200of the handover destination. In response, the GSM system200transmits a UA (Unnumbered Acknowledgement) back to the UE1. The UE1, which received the UA, transmits a handover complete message to the GSM system200, and the handover is completed. Subsequently, the UE1continues the call over the GSM system200of the handover destination.

InFIG. 4, the UE1was transmitting/receiving voice over the GSM system200. Then, an intersystem to UTRAN handover command message is transmitted from the GSM system200to the UE1. The UE1, which received the intersystem to UTRAN handover command, transmits a handover to UTRAN complete message to the W-CDMA system100of the handover destination. Subsequently, the UE1continues the call over the W-CDMA system100of the handover destination.

InFIG. 3andFIG. 4, an example of transmitting/receiving of voice is used for the explanation; however it is not limited to the example. That is, the sequence is, for example, basically the same in handover during packet communication or in handover during data communication.

The above sequence is a standardized technology, which is heretofore known.

The above handover, in general, is performed depending on the neighbor radio wave environment the UE1. When the UE1is performing communication using the W-CDMA system100, for example, if the signal level of a signal from the BTS101of the W-CDMA system100becomes weak and the signal level of a signal from the BTS102of the GSM system200is sufficiently high, handover from the W-CDMA system100to the GSM system200is performed.

Meanwhile, in the dual mode communication method or system of the present embodiments, handover between the communication systems100and200is performed depending on the remaining battery power of the UE1. In the following description, therefore, handover operation, depending on the remaining battery power of the UE1, is explained. A system relating to the dual mode communication method or system of the present embodiments can also perform handover depending on neighbor radio wave environment the UE1.

The remaining battery level is displayed on the screen of the UE1so that a user can refer to the battery level.FIG. 5A,FIG. 5BandFIG. 5Care display examples of the remaining battery level on the screen of the UE1. The remaining battery level is generally displayed in three levels. In the present embodiment, the fully-charged state shown inFIG. 5Ais called “level3”; the half-charged state shown inFIG. 5B“level2”; and the charge-required state shown inFIG. 5C“level1”.

The UE1, basically, consumes higher electric power when using the W-CDMA system100than when using the GSM system200. In the present embodiment, therefore, when the remaining battery level falls to the Level1while the UE1communicates in the W-CDMA system, the system is switched to the GSM system, without interrupting the communication. In other words, handover from the W-CDMA system100to the GSM system200is performed. By so doing, communication time can be extended reducing power consumption of the UE1though the highest communication speed is lower compared with the case that the W-CDMA system is continuously used.

FIG. 6is a processing sequence of switching between the communication systems relating to the present embodiment. According to the example inFIG. 6, the user equipment1is able to communicate with another user equipment over either of two communication systems A or B. Here, the communication system A provides faster communication service than the communication system B. However, electric power consumption of the UE1is higher when using the communication system A than when using the communication system B. The UE1performs communication over the communication system A when the remaining battery level is the level2or the level3.

In the present embodiment, the communication system A is the W-CDMA system, for example. For the communication system B, a GSM system, a wireless LAN (wireless Local Area Network), a Bluetooth network, a PHS (Personal Handyphone System) in which the power consumption of the UE1is lower than the W-CDMA system, can be used.

Suppose the remaining battery level of the UE1communicating with another user equipment over the communication system A fell to the level1inFIG. 6. When recognizing the fall of the battery level to the level1, the UE1transmits either a communication switch request message or a measurement report message. The transmitted message is transferred to a handover control system, not shown in the figures, provided in the network10. In so doing, the handover control system provides instructions to carry out handover from the communication system A to the communication system B, based on the message, to both the communication system A and the communication system B. At that time, the instruction is transmitted to the UE1via the communication system A. By so doing, handover from the communication system A to the communication system B is performed, and the UE1continues communication over the communication system B thereafter. An explanation of the communication system switch request message and the measurement report message is provided later with reference toFIG. 7andFIG. 8.

After switching to the communication system B, the UE1transmits information required to prevent handover back to the communication system A (that is, information required to maintain the connection to the communication system B), by using the measurement report message transmitted at a prescribed interval, for example.

The UE1transmits the communication system switch notification request message or the measurement report message when the remaining battery level returns to the level2or higher because of charging the battery or due to other reasons. Then, the handover control system provides instructions to perform handover from the communication system B to the communication system A, to the communication system A, the communication system B and the UE1. By so doing, the handover from the communication system B to the communication system A is performed, and the UE1continues communication over the communication system A thereafter.

FIG. 7is an example of the communication system switch request.FIG. 7shows commands transmitted from the UE1to the network10, and a command C1is an example of a request to switch from the W-CDMA system100to the GSM system200whereas a command C2is an example of a request to switch from the GSM system200to the W-CDMA system100. These commands can be transmitted with the other messages or can be transmitted separately.

FIG. 8is an example of a measurement report. In a header section81, at least information for identifying the UE1and information for indicating the message type (in this example, information indicating measurement report) are stored. In a data section82, at least, a measurement result of the signal level of signals from the BTS101of the W-CDMA system100and/or the BTS102of the GSM system200is stored. For example, the UE1measures the signal level information (or propagation loss) of the channel being used, the signal level information of signals of other frequencies in the communication system being used by the UE1, and the signal level information of a signal in yet another communication system and so forth, and the measurement results are stored in the data section82.

The handover control system provided in the network10determines whether to perform handover or not, according to measurement result information carried by the message. This sequence is realized by a technology, which is heretofore known.

However, the UE1of the present embodiment, when requesting a handover in accordance with the fall of the remaining battery level, independently of the actual measurement result, a value higher than the signal level data of a communication system, of the UE1with high power consumption, is written in the data section82as signal level data of a communication system, of the UE1with low power consumption. In the above embodiment, when the remaining battery level of the UE1falls to the level1, information indicating that the signal level information from the GSM system200is higher than that from the W-CDMA system100is written to the data section82and is transmitted to the network10. In other words, the UE1generates measurement information in order to forcibly cause handover, and transmits the measurement information to the network10. According to the information, the handover control system provided in the network10determines whether to perform the handover or not. As a result, the handover from the W-DMA system100to the GSM system200can be performed regardless of the actual radio wave environment.

In the following description, a specific processing flow of a dual mode communication method or system of the present embodiment is explained with reference toFIG. 9throughFIG. 13.

FIG. 9is a flowchart of system switch processing based on the system switch request. In this flow, the processing inFIG. 9is repeatedly performed at a prescribed time interval in the UE1during its communication. Processing inFIG. 10throughFIG. 13, explained later, is, also in the same manner, performed at a prescribed time interval.

First, the remaining battery level is determined in step S1. When the battery level is either in the level2or the level3, the processing is terminated. On the other hand, when the battery level is in the level1, the processing proceeds to the step S2, and it is determined whether or not it is communicating over the W-CDMA system. Then, when communication is performed over a system other than the W-CDMA system, the processing is terminated.

When the UE1is communicating over the W-CDMA system, the radio wave intensity of neighbor cells the GSM system200is monitored in steps S3and S4, and it is determined whether or not a GSM cell is detected. When a GSM cell is not detected, the processing is terminated. On the other hand, when any GSM cell is detected, in step S5, a network switch request message is transmitted to the network10in order to request handover from the W-CDMA system100to the GSM system200. Due to the request message, handover processing from the W-CDMA system100to the GSM system200is performed on the network10side. In step S6, a measurement report message is transmitted and the processing is terminated.

In the measurement report message transmitted in the step S6, not information indicating the signal level actually measured by the UE1, but information for the UE1to maintain the connection with the GSM system200is stored. By so doing, even when the radio wave intensity of the W-CDMA system100is in practice higher than that of the GSM system200, switching back to the W-CDMA system100which has higher power consumption can be prevented. More specifically, information indicating that the radio field intensity received from the GSM system200is higher than the radio field intensity received from the W-CDMA system100, or measurement result information of the GSM system200alone is included in the measurement report, and is transmitted to the network10.

As described above, in the procedures shown inFIG. 9, when the remaining battery level falls during communication, a message for directly requesting handover is transmitted from the UE1to the network10. The network10performs the handover in response to the message.

FIG. 10is a flowchart of system switching processing based on the measurement report. The processing in step S11through step S14is equivalent to the processing in step S1through step S4inFIG. 9, and therefore the explanation of the processing is omitted. In the following description, processing, which is different from that ofFIG. 9, is explained.

In step S15, the measurement report message is transmitted to the network10. The measurement report message transmitted stores information used to perform handover from the W-CDMA system100to which the UE1is connected to the GSM system200. Specifically, either information, indicating that the signal level information from the GSM system200is higher than that from the W-CDMA system100, or measurement result information of the GSM system alone is set by the UE1, and is stored in a certain field of the message. In step S16, the network10, which received the measurement report, performs the handover processing. Processing of step S17is the same as that of step S6inFIG. 9.

As described above, in the procedures shown inFIG. 10, fake measurement information to cause handover is generated, and handover is performed based on the measurement information.

FIG. 11is a flowchart of system switch processing comprising other processing in order to prevent the communication system from switching after handover. InFIG. 11, processes in the step S21through step S24are the same as the processes in the step S1through step S4ofFIG. 9, and thus the explanation of such processing is omitted.

In step S25, switch from the W-CDMA system100to the GSM system200is performed. This processing is equivalent to that of step S5inFIG. 9or that of step15and step S16inFIG. 10.

In step S26, a measurement function in the W-CDMA system is deactivated. By so doing, the signal level information of the W-CDMA system100is not transmitted to the network10, and handover from the GSM system200to the W-CDMA system100will not be performed even though the actual signal level information from the W-CDMA system100is higher than that of the GSM system200. In other words, communication is maintained in the communication system with lower power consumption.

FIG. 12is a flowchart including return processing by recovery of battery power of the UE1. In the processing shown inFIG. 12, the processing from step S31to S37is mostly the same as of the explanation provided usingFIG. 9throughFIG. 11before. However, processing for setting “1” in a switch flag GHO, which indicates a communication system to which the UE1is connected, is added as step S36. The switch flag GHO identifies “1: a state in which the GSM system200is used in response to a fall of the remaining battery level” and “0: a state in which the W-CDMA system100is used”. The switching flag GHO can be also set at the same processing timing as step S36in processing ofFIG. 9throughFIG. 11.

When the battery is charged during communication using the UE1, the remaining battery level rises from the level1to the level2and to the level3shown inFIG. 5. In such a case, the result of step S31is determined to be “No”, and the processing proceeds to step S38.

Step S38checks the switch flag GHO. That is, it is determined whether or not switching of the communication systems is performed in accordance with the remaining battery level. When “GHO=0”, it is determined that switching of systems in accordance with the battery level is not performed, and the processing is terminated. When “GHO=1”, the processing proceeds to step S39.

In step S39, by transmitting the network switch request message to the network10, handover from the GSM system200to the W-CDMA system100is requested. At the request, handover processing from the GSM system200to the W-CDMA system100is performed on the network10side. In step S40, the switch flag GHO is canceled (i.e. is set “0”), and the processing is terminated.

As described above, after handover from the W-CDMA system100to the GSM system200is performed in accordance with the remaining battery level, if battery power is recovered during the same communication, communication use of the W-CDMA system100is automatically resumed. Thus, when the battery power recovers, high-speed communication service can be provided immediately without interrupting the line.FIG. 13is a modification of the flowchart shown inFIG. 12. Among processing shown inFIG. 13, steps S51through S57corresponds to the steps S31through S37inFIG. 12, respectively, and step S58corresponds to the step S38inFIG. 12. Thus, explanation of the processing in these steps is omitted.

In step S59, the measurement report message is transmitted to the network10. The measurement report transmitted stores information for handover of the system to which the UE1is connected from the GSM system200to the W-CDMA system100. Specifically, information indicating that the radio field intensity received from the W-CDMA system100is higher than the radio field intensity received from the GSM system200or information of the W-CDMA system100alone is set by the UE1, and is stored in a prescribed location of the message. In step S60, handover processing is performed, and the UE1is connected to the W-CDMA system100. In step S61, the switch flag GHO is canceled.

As explained above, according to a dual mode communication method or system relating to the present embodiment, when the remaining battery level falls below the prescribed level during communication, handover to a communication system, which reduces electric power consumption of the UE1is automatically performed without interrupting communication. Therefore, the battery lifetime for communication after the remaining battery level is low can be extended. At that time, a user does not have to disconnect the communication once and resume the call after switching the communication system to be used, and therefore convenience is improved through the method or system. In addition, because communication disconnection processing and call resumption processing requires relatively high power consumption, elimination of such processing allows further reduction of the power consumption. Moreover, when the remaining battery level recovers to a prescribed level or above, by charging of the UE1, even if the UE1is in the middle of communication, the connected communication system can be automatically switched to a communication system, which enables higher-speed and higher-capacity communication, without disconnecting the communication.

In the above embodiment, the explanations of two communication systems and dual mode user equipment, which can be connected to both communication systems, are provided; however, the present invention is not limited to the above embodiment. In other words, the present invention can be adopted in three or more communication systems and dual mode user equipment connectable to the communication systems. In such a case, depending on the remaining battery power, the communication system to be used is selected so that the optimal balance between communication performance and available communication time period can be attained.