Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-04-13
2001-07-17
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S442000, C370S332000
Reexamination Certificate
active
06263203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for controlling handover of mobile terminal equipment between base stations in a communication system, such as a cellular system, and in particular to a method for seamless handover of mobile terminal equipment in such a system.
2. Description of the Prior Art
In many communication systems, terminal equipment which can serve a variety of purposes, such as a transmission of speech, video, fax, file, program and/or measurement data, is increasingly being connected wirelessly. A connection to such mobile terminal equipment is typically set up via base stations, which are coupled to the mobile terminal equipment via air interfaces. It is common to in turn couple the base stations to a switching station, via which connections to the mobile terminal equipments are switched. The switching station can be coupled to an external communication network making it possible to establish connections between the mobile terminal equipment and external terminal equipments as well.
The area around a base station in which a wireless connection of a given quality to a mobile terminal equipment is possible via this base station is designated as the radio cell of this base station. In order to supply a larger area with connection opportunities, a number of base stations are usually distributed over the area to be serviced, so that their radio cells form a network which has full coverage, i.e., the network occupies the entire area to be serviced. These radio cells are classified as picocells, microcells, or macrocells, depending on their spatial coverage. The user of mobile terminal equipment which is coupled to the switching station via a first base station can exit the radio cell of this first base station and enter the radio cell of a neighboring base station. In this case, the path of the existing connection must be relocated from the first base station to the neighboring base station. Such a change of the path of the connection is usually referred to as “connection handover”. A significant problem is that, during the change of the connection path, a loss-free data transfer within the connection must be guaranteed, and an interruption of the data transmission must be avoided, if possible. An handover without interruption is typically referred to as a “seamless handover”, meaning a change which cannot be perceived by the user.
In known methods, a handover is controlled by a central mobile switching assembly, which is provided for this purpose, this assembly functioning as an interface between the base stations and the switching station. The base stations participating in the connection handover must exchange information about the change of the radio cell, together with information for connection management, with the central mobile switching assembly, which then effects a rerouting of the data to be transmitted to the mobile terminal equipment from the base station which is handing over the connection to the base station which is taking over the connection. Arrangements and methods of this type are taught in
Cordless Telecommunications in Europe
(Tuttlebee, Wally H. W. (Ed); Springer; London, 1990: 43-48,273-275), for example.
Equipment designed for hardwired communication are frequently employed as switching stations. In these cases, the central mobile switching assembly is controlled at the switching station side in a manner like a group of hardwired terminal equipment units. This control must be converted by the connected mobile switching assembly into a suitable control for the management of wireless communication equipment at the side of the connected base stations. In particular, the central mobile switching assembly must independently control or manage all the processes specific to a wireless communication, such as the processes associated with a change of the radio cell. The functionality required for this is generally very comprehensive, and corresponding mobile switching assemblies are thus relatively expensive.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for changing a connection which is established from mobile terminal equipment to a switching station via a first base station, to a path via a second base station, which does not require the connection of a central mobile switching assembly between the base stations and the switching station.
The above object is achieved in accordance with the principles of the present invention in a method for the seamless handover of a connection which proceeds wirelessly from a switching station to mobile terminal equipment via a first base station coupled to the switching station, to a path to the mobile terminal equipment via a second base station also coupled to the switching station wherein, given an existing connection via the first base station, if it is determined that wireless data transmission between the mobile terminal equipment and the first base station no longer satisfies a predetermined quality criterion, and if there is a second base station located in radio range of the mobile terminal equipment to which a wireless data transmission of the predetermined quality is possible, then a specially dedicated control signal is transmitted from a base station to the switching station, and the control signal causes at least one performance feature of the switching station for the parallel transmission of data to a number of destinations to be activated, so that the data to be transmitted in the framework of the connection are transmitted by the switching station to the first base station as well as to the second base station. Once the data to be transmitted to the mobile terminal equipment are present at both stations, the mobile terminal equipment terminates the data exchange with the switching station via the first base station and continues data exchange with the switching station via the second base station, without an interruption of data transmission. By means of another control signal transmission from a base station to the switching station, the data transmission from the switching station to the first base station is terminated, so that only the second base station is still supplied with the data to be transmitted to the mobile terminal equipment.
In the inventive method, in a connection between mobile terminal equipment and the switching station via a first base station, a handover is prompted when it is detected by the mobile terminal equipment or by the first base station that the wireless data transmission between the mobile terminal equipment and the first base station no longer correspond to a prescribed quality criterion, and when it is also detected that a second base station is located in the radio range of the mobile terminal equipment, to which station a data transmission of a prescribed quality is possible. A handover can also be triggered given an overload of the first base station, for example.
For the handover, a control signal, such as that according to the ETSI standard definition for signaling QSIG for private networks, or DSS1 for public networks, or according to other ITU-T standard definitions, is transmitted to the switching station by a base station, preferably one of the base stations participating in the handover. On the basis of the control signal, a performance feature of the switching station for parallel transmission of data to a plurality of transmission destinations, which feature is also provided for hardwired communication, is subsequently activated. Preferably, a standardized performance feature for In an inventive method, in a connection between a mobile terminal equipment and the switching station via a first base station, a handover is prompted when it is detected by the mobile terminal equipment or by the first base station that the wireless data transmission between the mobile terminal equipment and the first base station no longer correspond to a prescribed quality criterion, and that a second base station is located in the radio range of the mobile terminal equi
Cong Le Thanh
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
LandOfFree
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