Dual mode subscriber terminal and a handover procedure of the du

Details Dual mode subscriber terminal and a handover procedure of the du Dual mode subscriber terminal and a handover procedure of the du

1995-06-08

1997-08-19

Bost, Dwayne

Telecommunications

Radiotelephone system

Zoned or cellular telephone system

455426, 455553, H04M 1100, H04Q 738

Patent

active

056595980

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a mobile telecommunications system including a fixed network comprising mobile exchanges, base stations for mobile stations, and cordless telephone base stations connected to and under control of the mobile exchanges. In particular, the present invention relates to a method for performing handover from the cordless telephone base stations to base stations for mobile stations.
Conventional cordless telephones operate as an extension to the Public Switched Telephone Network (PSTN). A cordless telephone system consists of a portable handset and a base station (a fixed part) connected to PSTN. The first cordless telephone systems were analog systems, such as CT1. Recently digital cordless telephone systems, such as CT2 and DECT (Digital European Cordless Telephone) have been introduced. When a cordless telephone is a subscriber of PSTN, a cordless telephone is accessed by dialing the telephone number associated with the fixed subscriber connection to which the base station is connected. Also, the subscriber has access to the PSTN only via the home base station. In CT2 and DECT, also a telepoint service is introduced, whereby a subscriber to the service can make calls away from home via a public base station. Also, a common air interface for cordless telephones was introduced to facilitate roaming between systems and so to improve service coverage for the use.
There has also been a proposal to combine a cordless telephone system with a cellular mobile telecommunications system to further improve the roaming capabilities by means of utilization of the mobility control of the cellular network. When combined with the mobile telecommunications systems, the roaming of the cordless telephone handsets within the cordless telephone systems is fully supported. However, the cordless telephone handset is not able to utilize the more extensive radio coverage of the supporting cellular network or to perform handover to or from the cellular network. This disadvantage is due to several reasons.
Firstly, the radio interfaces of cordless telephone systems and the mobile radio systems are usually incompatible.
Secondly, the handover procedures are different. In cordless telephone systems, the handover procedure is usually initiated by the portable terminal. More particularly, when a cordless telephone terminal considers it necessary to change from one base station to another, the terminal scans the frequency band and selects the appropriate base station for the handover. In most of the mobile telephone systems, the handover is controlled by the network. The mobile station only measures the quality of the radio connection and forwards the measuring results to the fixed network. One of the network elements, for example a mobile exchange, makes a decision for handover on the basis of the obtained information.


SUMMARY OF THE INVENTION

It is an object of the invention to provide a subscriber terminal capable of communicating with both a fixed part of a cordless telephone system and a base station of the mobile radio system.
It is a further object of the invention to provide a method for performing handover from a fixed part of a cordless telephone system to a base station of a mobile telecommunications system.
One aspect of the invention is, in a mobile telecommunications system including a fixed network comprising mobile exchanges, first base stations connected to the mobile exchanges, and second base stations of a cordless telephone system, the second base stations being connected to and under control of the mobile exchanges, dual mode subscriber terminals having a mobile station part for radio communication with said first base stations and a cordless telephone part for radio communication with the second base stations; a method for performing handover from one of the second base stations to one of the first base stations, comprising the steps of:
measuring field strengths of said first base stations at the mobile station part of the dual mode terminal and storing measuremen

REFERENCES:
patent: 4893327 (1990-01-01), Stern et al.
patent: 5127042 (1992-06-01), Gillig et al.
patent: 5247701 (1993-09-01), Comroe et al.
patent: 5260988 (1993-11-01), Schellinger et al.
patent: 5278991 (1994-01-01), Ramsdale et al.
patent: 5392331 (1995-02-01), Patsiokas et al.
patent: 5454028 (1995-09-01), Hara et al.

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