GB2321162A

GB2321162A - Dual Mode Mobile Radio Telecommunications Device

Info

Publication number: GB2321162A
Application number: GB9700283A
Authority: GB
Inventors: Mark Grayson
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 1997-01-08
Filing date: 1997-01-08
Publication date: 1998-07-15
Anticipated expiration: 2017-01-08
Also published as: GB2321162B; GB9700283D0

Abstract

A mobile radio telephone device capable of being used as a cordless telephone with a cordless base station in a private network and also as a mobile station in a public network has memory for storing identity data relating to public network base stations in the vicinity of the cordless base station and acquired whilst the device is operating as a cordless telephone. The device maintains a BA list of base stations during public network operation and, it repeatedly checks the BA list for the base station, identity data for which was stored during cordless operation.

Description

Mobile Radio Telecommunications Device This invention relates to a mobile radio telecommunications device for use in both private and public radio networks. As used herein, the term "public network" means a telecommunications network to which members of the public have access on payment of a subscription or otherwise. The term "private network", on the other hand means a network to which members of the public do not normally have access. In its simplest form a private network is a single digital radio cordless telephone system in which a cordless base station is connected to a landbased public telephone network and can establish a two way radio connection with a mobile station, but the term also includes systems including multiple land line connections and multiple mobile stations.

It has already been proposed to utilise systems whereby the users of domestic digital cordless phones can use the same mobile station on a public radio network. Clearly, such users will strongly prefer to have their calls routed through the public land switched network whenever possible as this will usually be the most economical routing. Current proposals, however, make it difficult for the mobile station, once taken out of the coverage area of its private radio network, to establish when it can switch back to its preferred domestic cordless mode of operation, without repeated searching for its cordless base station at all times, which is very power consuming and shortens the available standby duration for the mobile station significantly.

It is an object of the present invention to provide a mobile station in which provision is made for the elimination of the need for frequent searching for a preferred cordless base station.

In accordance with the invention there is provided a mobile radio telephone device capable of being used as a cordless telephone with a cordless base station in a private network and also as a mobile station in a public radio network, the device comprising: memory means for storing identity data relating to public radio network base stations in the vicinity of the cordless base station; means for acquiring and storing such identity data whilst the device is operating as a cordless telephone; means for maintaining a list of the identities of nearby public radio network base stations in the vicinity of the device when it is operating as a public radio network mobile station, signals from such nearby radio network base stations being repeatedly tested by the device to ascertain which one is capable of supporting the best connection; means for repeatedly checking the identities in said list against the identity data stored in said memory; and means for causing the device to search for its cordless base station whenever there is a match found between one of the identities in said memory and one of the identities in said list.

An example of the invention is shown in the accompanying drawings in which: Figure 1 is a block diagram of a mobile radio telephone device Figure 2 is a flow chart showing operation of the device of Figure 1 during initialisation Figure 3 is a flow chart showing the operation of the device during operation as a public radio network mobile station.

As shown in Figure 1, the device has all the normal attributes of a digital cellular radio telephone, that is to say an RF section 10 which is connected through a suitable interface circuit to a digital signal processor 11 which handles analog to digital conversions (and vice-versa) and includes a processor which can perform programmed operations on the signals received from the RF section 10. These operations include all those operations required for searching for and tuning the RF stage to receive, neighbouring public network base stations and maintaining a BA list, ie a list of the neighbouring base stations identifying the frequencies used thereby, and the IDs of the base stations. The strength of the signals from the base stations are tested periodically and the entries in the BA list are maintained in order of signal strength in the usual way. The device also incorporates a CPU 12 which communicates with the DSP 11 and cooperates therewith in the control of the functioning of the device. The CPU 12 can communicate with the SIM card 14 of the device as well as with random access memory 15, read only memory 16, non-volatile read/write memory 17, a display 18, and a keypad 19.

The device is intended to be used both on a digital cellular public network and in conjunction with a cordless phone base station within a house or other limited area. The DSP 11 has parts of its software designed to enable such operation. The software involved is much simpler than that required for public network operation as there is no need for the adaptive equalisation algorithms required when the device is operating as a public network mobile station, since multipath reception effects are insignificant.

During operation as a cordless telephone handset, the DSP has relatively little processing to do and is idle much of the time. This, and the fact that the transmit power level of the RF section can be set to the lowest power setting, means that operation in cordless telephone mode requires considerably less power in both idle and connected modes than public network mobile station operation.

Figure 2 is a flow chart showing the operations which are carried out during initialisation of the device after it is switched on and powered up.

Once all the normal hardware initialisation routines have been carried out, the device selects cordless telephone mode and searches for a cordless base station broadcast signal. If a cordless base station is found, the device initiates its link with the cordless base station in the conventional way and then switches into public network mobile station mode and commences a search for neighbouring public network base stations. For each base station found, the devices acquires details of frequencies, IDs and received signal strengths by the normal procedures and stores these details in RAM for subsequent use in forming the BA list for public network mobile station use when required. If no cordless base station is found during the initial search, the device initialises in the normal manner to allow it to camp on the selected best base station.

When operation has commenced in cordless telephone mode and the device is taken out of the service area of the cordless base station, the fall in cordless base station received signal strength will be recognised by the DSP and a procedure to switch to public network mobile station operation is initiated. This procedure involves transferring the neighbouring base station ID data from RAM to a dedicated area of the non-volatile memory 17. The data stored in RAM is used to form the BA list and the DSP then goes through its procedures for synchronising with the strongest base station and, finally, breaks contact with the cordless base station.

Whilst operating on the public network, the device periodically carries out searches so that it can keep its BA list up to date as it moves through the network. Figure 3 is a flow chart of a procedure which is carried out whenever the BA list is updated. The procedure checks the IDs stored in the non-volatile memory during the switch over to the public network with the IDs of the base stations currently in the BA list. If a match is found, then data relating to the cordless base station is added to the BA list, so that each time a check is subsequently made, the device can search for its cordless base station. If the matching base station is subsequently removed from the BA list as a result of the mobile station moving away from it, then the cordless base station data is also removed from BA list.

In this way, pointless searching for the cordless base station when the device is far removed from it is avoided and power is saved, enabling a longer standby operation duration to be achieved.

It should be noted that if the device is switched off after leaving its cordless base station and switched on again whilst outside the service area of its cordless base station, the ID data stored in the non-volatile memory when the device last moved out of the service area of its cordless base station will still be available. The data is overwritten whenever the device is taken out of its cordless base station service area whilst switched on, so that if the user moves his cordless base station to a new location, for example to a different town, the data held will be updated to match the new situation. Similarly, the installation of a new public network base station near the cordless base station will result in new data be written to the non-volatile memory when the device is removed from the cordless base station service area whilst switched on.

Claims

1. A mobile radio telephone device capable of being used as a cordless telephone with a cordless base station in a private network and also as a mobile station in a public radio network, the device comprising: memory means for storing identity data relating to public radio network base stations in the vicinity of the cordless base station; means for acquiring and storing such identity data whilst the device is operating as a cordless telephone; means for maintaining a list of the identities of nearby public radio network base stations in the vicinity of the device when it is operating as a public radio network mobile station, signals from such nearby radio network base stations being repeatedly tested by the device to ascertain which one is capable of supporting the best connection; means for repeatedly checking the identities in said list against the identity data stored in said memory; and means for causing the device to search for its cordless base station whenever there is a match found between one of the identities in said memory and one of the identities in said list.

2. A mobile radio telephone device as claimed in claim 1 in which said memory is non-volatile memory.

3. A mobile radio telephone device as claimed in claim 2 in which said means for acquiring and storing base station ID data operates to store such data in said non-volatile memory when the device is taken out of the coverage area of the cordless base station whilst operating in cordless telephone mode.