Multi-mode radio telephone

Details Multi-mode radio telephone Multi-mode radio telephone

1996-11-15

2004-03-16

Maung, Nay (Department: 2684)

Telecommunications

Radiotelephone system

Zoned or cellular telephone system

C455S439000, C455S552100, C455S432200

Reexamination Certificate

active

06708028

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a radio telephone, and in particular to a radio telephone operable for more than one system.
BACKGROUND OF THE INVENTION
Over the last ten years there has been a rapid growth in the use and availability of radio telephone systems. As part of this growth there has been a proliferation of different types of radio telephone system, offering the user a variety of services, geographical coverage and cost. Many of these different radio telephone systems cover the same, or a part of the same, geographical area as each other.
Typically, different radio systems operate on different radio frequencies, utilise different modulation techniques, signalling techniques and intra-system protocols etc. to each other. Thus, a radio telephone designed for one system is generally unable to be used on another system. Thus if a user wishes to have access to more than one system it is necessary to have either more than one radio telephone or a radio telephone capable of operating in more than one system. Having more than one radio telephone is inconvenient for the user. Known radio telephones capable of operating in more than one system typically consist of little more than 2 separate phones combined in a signal housing. The preference for operating in a particular system is user defined as disclosed in U.S. Pat. No. 4,989,230.
A particularly useful and appropriate environment for multi-mode radio telephones is the recently available cellular and cordless telephone systems. In the prior art, cordless telephones are typically used in the home and office to allow the user to place and receive calls at any point throughout the house via an RF link with a home base station located within the house or office. Such cordless telephones are connected via the home base station to the user's telephone landline which in turn is connected to the Public Switched Telephone Network (PSTN). Further, there are known second generation cordless telephone systems such as CT-2 or DECT which are digital systems. Such CT-2 or DECT systems extend beyond conventional domestic operation of cordless telephones by allowing the user to establish an RF link between a CT-2 or DECT radio telephone and a base station in a more publicly accessible location e.g. outside of the user's home, a railway station, shopping mall or airport. Such base stations are known as telepoint base stations and are linked to the PSTN in much the same way as a home base station. Some cordless, and in particular DECT radio telephones, are now able to receive calls via telepoint base stations whereas hitherto they were only able to place them. A description of such a system can be found in PCT international patent application WO 92/03006. Thus, placing and receiving calls whilst geographically roaming is possible in cordless telephone systems.
However, cordless telephone systems are low power systems and each base station provides telecommunications within only approximately a 150 meter radius of the base station, dependent upon the terrain and any man-made objects which could interfere with signalling between a cordless telephone and the base station. Such systems are generally only used in areas of high user density and thus tend to be limited to urban areas. This clearly restricts the geographical mobility of a CT-2, DECT or the like cordless telephone user.
In the prior art there are known so called cellular radio telephone systems having base stations which cover a wide geographical area (cell), eg 35 km diameter. However, in urban areas where the user density is high the cells are much smaller and operate at lower powers to facilitate frequency re-use thereby increasing the communication channel density.
Cellular systems have advantages over cordless systems since they allow a user to place and receive calls over a large area. Additionally they are suitable for use in moving vehicles. This is because cellular telephone systems have sophisticated handover procedures to facilitate switching between cells as a user's vehicle crosses from one cell to another. Furthermore, the cells are larger than in cordless systems and thus handovers occur less often, even if travelling in a vehicle. This ensures continuity of service and is particularly important during a call. However, the cost of a cellular telephone call is significantly greater than the cost of a cordless telephone call, since cordless telephone calls are made by way of the user's land line PSTN link and cost the same as landline calls, whilst cellular telephone calls are made by way of expensive cellular base stations and cellular switching equipment and cost much more than land line telephone calls. In order for a user to be able to utilise both cellular and cordless telephone systems via a single radio telephone handset a so-called cellular cordless telephone (CCT) has been proposed in U.S. Pat. No. 4,989,230. Both the cellular system and the cordless system are monitored by the CCT for incoming calls and the CCT automatically enters a user defined preferred mode for answering an incoming call if the system corresponding to that mode is available. When placing a call the user initiates the call as either cellular or cordless and the CCT connects the call appropriately. In order for the user to be able to make a choice the available systems can be displayed on the CCT. When using the CCT, the user has to make the decision as to which telephone system is used. Furthermore, the prior art CCT disclosed in U.S. Pat. No. 4,989,230 requires the user to select transfer of a cordless call to the cellular system should the cordless signals deteriorate (eg the user moves out of range of a cordless base station or the user's velocity increases). Additionally, optimisation of the available systems is likely not to be achieved if the user is left to decide which system is to be used. One of the disadvantages of the CCT disclosed in U.S. Pat. No. 4,989,230 is that a user might not know if a signal is deteriorating until it is too late and the ongoing call is lost. For example, a visual indication of poor signal shown on the CCT is likely to be missed by a user, since in use the CCT will be placed at the side of the user's head and thus visual indications would not be visible to the user. Other indications such as an audible tone or alarm would interfere with the user's ongoing call, and would be annoying and irritating to the user.
BRIEF SUMMARY OF THE INVENTION
A first aspect of the present invention provides a radio telephone operable in more than one radio telephone system, comprising communication means respectively associated with each of the more than one radio telephone system, monitoring means for monitoring signals of the more than one radio telephone system, and selection means responsive to said monitoring means for automatically selecting and re-selecting respective said communication means in accordance with the signals of one of the more than one radio telephone system fulfilling at least one predetermined criterion, and a second aspect of the invention provides a method for operating a radio telephone in more than one radio telephone system, comprising, monitoring signals of the more than one radio telephone system determining whether the signals of the more than one radio telephone system fulfill at least one predetermined criterion, and automatically selecting and re-selecting for which of the more than one radio telephone system the radio telephone is operable in accordance with the signals fulfilling the at least one predetermined criterion.
These have the advantage that the radio telephone is not only operable for more than one radio telephone system, but that it is able to automatically select and re-select which of the available radio systems to use. The selection can be based on any predetermined criterion or combination of criteria. For example, the radio telephone can be set to operate on the cheapest system available (e.g. cordless system). Such criteria are likely to be factory set, but optio

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