The present invention generally relates to the field of wireless communications systems and, more particularly, to a dual mode mobile terminal capable of functioning as either a cellular radiotelephone or a cordless telephone.
The wireless communication industry has made phenomenal strides in commercial operations in the United States and the rest of the world. A goal of wireless communication devices is to provide users with access to the public switched telephone network without restriction by location or mobility. Growth of wireless communications in major metropolitan areas has far exceeded expectations. If this trend continues, it is possible that wireless communications will provide the bulk of telecommunication services in some areas.
As a result of this growth, wireless communication services have become more affordable and customers may choose to make wireless communication devices their primary means of personal communication. The popularity of wireless communication devices is further enhanced by their ability to be used for non-voice communication, such as facsimile and data transmission.
Two implementations of wireless communications are cordless telephones and cellular radiotelephones. Cordless telephones utilize a low-power RF link between a cordless handset and a base unit. The base unit is connected to the public switched telephone network (PSTN) in the same manner as a conventional corded telephone. There are no air-time charges associated with the home-based cordless telephone systems. Cordless telephone systems (CTS) support wireless communications over a short distance from the base unit. When a cordless handset moves outside the range of coverage of the base unit, its connection to the PSTN is broken.
In a cellular radiotelephone, a handheld unit generally referred to as a mobile terminal communicates with any one of a plurality of cellular base stations, which form the interface between a Public Land Mobile Network (PLMN) and the mobile terminal. The PLMN comprises a multiplicity of base stations, each of which connect to a mobile switching circuit (MSC). The PLMN may have one or more MSCs. At least one MSC, referred to as a gateway MSC, connects to the PSTN. Cellular radiotelephones use a higher-power RF link than a cordless telephone and consequently allow greater distances to be spanned between a base station and a mobile terminal. As the mobile terminal moves out of range of one base station, the link provided by that base station is handed off to an adjacent base station without interruption of the user's connection to the PSTN through the PLMN.
In the near future, wireless communication devices, such as mobile terminals, will incorporate position-estimating devices to enhance the function and utility of the wireless communication device. The Federal Communication Commissioner has recently implemented legislation requiring service providers to give accurate position of emergency (i.e., 911) callers. This requirement can be fulfilled by including a GPS receiver in the mobile terminal. Perhaps the best-known use of position estimating technology is for navigation. Another common use for position estimating devices is to identify facilities, such as hotels or restaurants, that are nearby the current position of the mobile terminal. Position information can also be used to enhance intrinsic functions of mobile terminals. For example, position information can be used to improve cell reselection or hand-off decisions in mobile terminals. Examples of how position information may be used to enhance intrinsic functions of the mobile terminal are described in the following U.S. patent application Ser. No. 09/498,785 entitled “Position Assisted Handoff in a Wireless Communication Network”; Ser. No. 09/505,431 entitled “Position Assisted Service Selection”; and Ser. No. 09/498,772 entitled “System and Method For Improving Channel Monitoring In a Cellular System.” Position estimating devices have a broad variety of uses and can significantly enhance the utility and, therefore, the desirability of wireless communication devices.