1) Field of the Invention
The present invention relates to a power supply control in a voice communication apparatus that includes a plurality of radio communication devices.
2) Description of the Related Art
In the field of portable phones (including a PHS), there are growing needs for realizing what is called IP (Internet Protocol) telephony that lowers telephone charges by using the Internet or a similar IP network in place of the Public Switched Telephone Network. The public radio network of portable phones covers a wide coverage area but has a narrow bandwidth. On the other hand, a WLAN (wireless LAN) has a wide bandwidth but covers a narrow coverage area such as corporations, homes, public hot spots. To compensate for the defects, communication terminals including a plurality of communication interfaces (such as the PHS, the WLAN) have been already suggested.
However, such a terminal needs to switch the interfaces seamlessly to allow continuation of voice communication. To meet this requirement, a technology called VoIP (Voice over IP), which means voice communication over IP, is used in the terminal. That is, a communication via every interface is connected over IP to perform a VoIP communication. Since a WLAN communication is usually connected over IP, VoIP can be used as it is, but in the PHS, it is necessary to use VoIP after IP connection by PPP. This makes it possible to realize seamless roaming disclosed in Japanese Patent Application Laid-Open No. 2003-319010 or Japanese Patent Application Laid-Open No. 2004-129024.
Since it is necessary for the terminal with a plurality of communication interfaces to supply power to every interface, power consumption increases. In particular, power consumption of the WLAN is very high. As a result, the standby time of the terminal disadvantageously becomes shorter. To reduce power consumption and lengthen the standby time, it has been already suggested, as disclosed in Japanese Patent Application Laid-Open No. 2002-135203, to stand by with a narrowband wave receiving circuit with comparatively lower power consumption, and to supply power to a mediumband or wideband wave receiving circuit upon receiving an incoming call.
In the conventional technology, however, as described in FIG. 13 which explains an eighth embodiment of the Japanese Patent Application Laid-Open No. 2002-135203, power supply to the narrowband receiving circuit is continued even during communication in the mediumband or wideband wave. As a result, extra power is consumed. Moreover, another incoming call is disadvantageously received even during communication in the mediumband or wideband wave, which makes the control complex. Furthermore, the terminal cannot receive any incoming call when the terminal is out of the coverage area of narrowband wave, even if it is in the coverage area of the mediumband or wideband wave.