Connecting a multimode terminal to the network in a mobile...

Telecommunications – Radiotelephone system – Zoned or cellular telephone system

Reexamination Certificate

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Details

C455S426100, C455S436000, C455S438000, C455S552100, C455S553100

Reexamination Certificate

active

06487410

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the handover method and a method for the selection of the base station for connection of a multimode terminal in a mobile communication system which consists of an MSC (Mobile Services Switching Center), at least one first base station and at least one second base station controlled by the MSC, and multimode terminals which consist of a first part for establishing a radio connection with the first base station and a second part for establishing a radio connection with the second base station.
The invention also relates to the multimode terminal.
BACKGROUND OF THE INVENTION
FIG. 1
a
, attached, shows the block diagram of a mobile communication system the exchange of which controls the BSSs (Base Station Sub-systems) of the digital cordless telephone system DECT (Digital Enhanced Cordless Telecommunications) and the GSM (Global System for Mobile communications) mobile communication system. The MSC (Mobile Services Switching Centre) usually controls several base station systems BSS/FP. The MSC is connected to other MSCs and to other networks, such as the PSTN (Public Switched Telephone Network), PLMN (another mobile communication network), ISDN network, or IN (Intelligent Network). A multimode terminal that operates in several radio systems makes it possible to use several different radio systems for telecommunications traffic. The dualmode terminal PP/MS shown in
FIG. 1
a
operates both as a cordless telephone of the DECT system (PP, Portable Part) and as an MS (Mobile Station) of the GSM system. The cordless telephone part of the dualmode terminal, PP, is connected in the DECT system to a DECT base station RFP (Radio Fixed Part), as shown in
FIG. 1
a
, to the DECT base station RFP
2
. The fixed part of the base station system of the DECT system DECT FP (Fixed Part) consists of the base station controller CCFP (Common Control Fixed Part) which controls one or more DECT base stations RFP. The fixed part of the DECT system DECT FP is connected to the MSC via an adapter part IWU (Interworking Unit). The adapter part IWU performs, among other things, the necessary protocol conversions. In the GSM system the mobile station part MS of the dualmode terminal PP/MS is connected via radio path to a BTS (Base Transceiver Station). The BSS (Base Station System) consists of a BSC (Base Station Controller) and the base stations BTS controlled by it. The operation of the entire system is monitored by the OMC (Operation and Maintenance Centre).
In the DECT/GSM system it is also known that the functionality of the base station controller BSC and that of the DECT base station controller CCFP are connected into a single, so-called dualmode base station controller, as shown in
FIG. 1
b
. This kind of a dualmode base station controller BSC/CCFP also includes the adapter part IWU. Otherwise the block diagram of
FIG. 1
b
corresponds with
FIG. 1
a
described above.
For use in call setup terminating in the terminal the registers of the cordless telephone system/mobile communication system contain the information about the geographic location of the terminal. In the GSM mobile communication system and the DECT cordless telephone system the coverage area of the network is divided into location areas which consist of the coverage areas of one or more base stations. The location of the terminal is defined by using these location areas. When the terminal has moved from one location area to another the terminal performs a location update to notify the network about its new location area.
FIG. 2
shows the location update signalling for the DECT system. The cordless telephone PP sends the location update request to the base station to which it is listening by using the LOCATE REQUEST (message
21
) to which is attached the identifier of the new location area. The fixed part of the network FP acknowledges the location update by using the LOCATE_ACCEPT (message
22
), when the location area in the network register has been replaced with the stated new location area.
FIG. 3
a
attached, shows the call setup originating in the terminal PP in the DECT network. When the cordless telephone PP wants to make a call, it sends the CC_SETUP (message
31
) to the base station RFP of the fixed part FP, which the network acknowledges by sending the CC_SETUP_ACK (message
32
). If the cordless telephone PP has not indicated the number of the called subscriber to the network in the CC_SETUP (message
31
), the telephone PP is requested for it in the CC_SETUP_ACK (message
32
), in which case the terminal PP sends the number requested by using the CC_INFO (message
33
). If the number of the called subscriber was indicated in the CC_SETUP (message
31
), messages
32
and
33
are not sent at all. The traffic connection is established by using the CC_CALL_PROC (message
34
). The CC_ALERTING (message
35
) is used to send the line alert tone to the terminal PP. After this the call is continued in the normal fashion.
FIG. 3
b
attached, shows the call setup terminating in the terminal PP in the DECT network. The fixed part FP of the DECT network sends the call message LCE_REQUEST_PAGE (message
37
) to reach the terminal PP. The cordless telephone PP answers this call by sending the LCE_PAGE_RESPONSE (message
38
) after which the network notifies the terminal PP about the incoming call by sending the CC_SETUP (message
39
). During the CC_ALERTING (message
40
) the network is being sent the line alert tone, and after the subscriber has answered the terminal, the CC_CONNECT (message
41
) is sent to establish the connection which the network acknowledges by sending the CC_CONNECT_ACK (message
42
).
During the call, it may be necessary to hand over the radio connection between the terminal and base station from one radio channel to another, for example, because of a poor radio signal. Usually such a handover is performed from the serving base station to the radio channel of another base station. In cordless telephone systems, such as the DECT system, the handover process originates usually in the cordless terminal PP which measures the base station signals over the entire usable frequency band and selects a base station with a suitable radio signal as the target cell for the handover. In mobile communication systems, such as the GSM system, the handover originates usually in the side of the fixed network, for example, in the base station controller BSC.
FIG. 4
attached, shows a signaling diagram for the handover between two base station systems FP in the DECT system. Before starting the actual handover process, the terminal PP must receive the data about the possible target cells for the handover from the network. If the terminal PP has not received this data earlier, for example, during the call, the PP requests the data from the network by using the MM_INFO_REQUEST (message
43
). The network transmits to the terminal PP via the serving base station, as shown in
FIGS. 1
a
and
1
b
via the base station RFP
2
, in the MM_INFO_ACCEPT (message
44
) the identifiers of those fixed parts FP into which the handover from the serving base station is possible. The terminal PP continuously measures the quality of the base station signal for these handover target cells and compares the measurement results to one another and to the quality of the signal of the serving base station RFP
2
. When the terminal PP detects that the signal quality of some other base station is better than the signal quality of the serving base station, it usually initiates the handover process. The terminal PP informs the serving base station system FP
1
in the MM_INFO_REQUEST (message
45
) about the initiation of the handover and about the target cell selected for the handover. When FP
1
receives this information, it sends the HANDOVER_REQlIRED (message
46
) to the mobile services switching center MSC, which requests the fixed part FP
2
selected as the target cell for the handover to prepare for the handover by using the HANDOVER_REQUEST (message
47
). The fixed part FP
2
notifies the mobile ser

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