Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-08-30
2003-05-20
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S436000, C370S331000, C370S333000
Reexamination Certificate
active
06567670
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a subscriber station, a network control means and a method for triggering inter-frequency measurements in a mobile communication system. The invention also relates to a mobile communication system in which such a subscriber station, such a network control means and such a method are employed.
As will be explained with more details below, in a mobile communication system transmission conditions on a connection (communication connection or signaling connection) between a subscriber station and a base transmitter station are monitored and the need for an inter-frequency or inter-system handover is detected, e.g. when the transmission conditions deteriorate. When the need for an inter-frequency or inter-system handover is detected, an inter-frequency measurement trigger signal is generated to indicate the need for an inter-frequency or inter-system handover and to initiate inter-frequency measurements on a different frequency than currently used. In response to the trigger signal inter-frequency measurements are carried-out on one or more different frequencies and if a suitable new frequency has been found the actual an inter-frequency or inter-system handover takes place. Hereinafter, the term “handover” is used to designate an inter-frequency handover or an inter-system handover, even if not explicitly stated.
When a connection is established between the base transceiver station and the subscriber station, even if only a signaling connection is established with the subscriber station being in an active-mode of operation, there always exists some data traffic on the connection and the subscriber station and the network must must carry out inter-frequency measurements when no data is transmitted, since otherwise some of the communicated data on the connection will be lost. Another important aspect is when and how the inter-frequency measurement trigger signal should be generated by the network to initiate the inter-frequency measurements. It should be noted that the inter-frequency measurements themselves are, however, always carried out in the subscriber station in response to the inter-frequency measurement trigger signal.
The present invention in particular addresses the problem which conditions should be used to generate the trigger signal for triggering such inter-frequency measurements.
Hereinafter inter-frequency will be abbreviated with “IF”.
BACKGROUND OF THE INVENTION
With respect to a conventional method for triggering IF-measurements in a mobile communication system,
FIG. 1
shows a general overview of a telecommunication system TELE which comprises at least two different mobile communication systems T
1
, T
2
. A subscriber station, e.g. a mobile station MS, which is operable in the first mobile communication system T
1
, may also be operable in the second mobile communication system T
2
. Within each mobile communication system T
1
, T
2
the mobile station MS can move around different cells S
1
, S
2
, S
3
, S
1
′, S
3
′ and C
1
-C
6
. Due to different handover criteria the mobile station MS may perform an inter-frequency handover within the same system or an inter-system handover to/from the other system. It should be noted that the present invention is equally well applicable for triggering an inter-frequency handover within the same system and/or an inter-system handover and
FIG. 1
only shows two mobile communication systems T
1
, T
2
as an example where both such handover procedures may take place.
FIG. 1
shows as an example for the first mobile communication system T
1
a WCDMA (Wideband Code Division Multiple Access) or CDMA (Code Division Multiple Access) communication system comprising a network control means RNC (Radio Network Controller), at least one base transceiver station RBS, RBS′ (in WCDMA called radio base station), at least one subscriber station MS (Mobile Station) as well as a number of (possibly) overlapping cells S
1
, S
2
, S
3
, S
1
′, S
3
′.
An example for the second mobile communication system T
2
is a communication system according to the GSM (Global System for Mobile Communications), PDC (Personal Digital Cellular) and D-AMPS (Digital-Advanced Mobile Personal Service) standards.
In
FIG. 1
an example of a GSM system is shown for the second mobile communication system T
2
. However, it should be noted that the invention can in principle be applied to any type of digital mobile telephone system and is as such not restricted to the aforementioned systems. The GSM system shown in
FIG. 1
comprises the conventional units of a base station controller BSC, at least one mobile switching center MSC as well as a gateway mobile switching center GMSC. The mobile stations MS are served by a plurality of base transceiver stations BTS within the cells C
1
-C
6
in which the mobile station MS can move around.
The network control means RNC of the WCDMA system in
FIG. 1
is connected via a UMSC unit to the gateway mobile switching center GMSC of the GSM system.
Depending on the geographical layout of the first and second mobile communication systems T
1
, T
2
the cells S
1
, S
2
, S
3
, S
1
′, S
3
′ of the first mobile communication system T
1
may also completely or partially overlap with the cells C
1
-C
6
of the second mobile communication system T
2
. Of course, if the mobile station MS is to carry out an inter-system handover—then the mobile station MS will be able to operate according to the specifications of the first and the second mobile communication system.
One reason for performing inter-frequency or inter-system handovers in the telecommunication system TELE in
FIG. 1
may be due to coverage reasons. This is due to the fact that neither the first communication system nor any other system has a complete coverage in all geographical areas, e.g. hot spots in UMTS. Furthermore, some cells within the mobile communication system may operate on frequencies which are not applicable in adjacent cells. Therefore, by letting the mobile station MS or the network control means RNC perform either an inter-frequency handover of an inter-system handover, the mobile station MS can be used in a larger area without interruptions in the communication.
Another reason for the handover may be capacity reasons. Either the mobile communication system or other mobile communication systems may become heavily loaded at times, so that an inter-system handover may be required. Analogously, the mobile station MS may have established a connection on a particular frequency and it may be necessary that another frequency is to be used. This other frequency may be present within the same cell or in another cell and both are generally termed inter-frequency handover. As indicated in
FIG. 1
, the inter-frequency measurements (necessary for an inter-frequency handover/or an inter-system handover) is always carried-out by an inter-frequency measurement means IFMM situated in a mobile station MS.
The network control means RNC comprises a paging flag sending means PFSM for sending a paging flag to the mobile station MS when a signalling communication link has already been established between the subscriber station MS and the network. For example, when the mobile station MS has been switched on and has been registered in the network, the subscriber station is in a registered and non-active mode of operation. A standby operation means SOM holds the subscriber station in such a non-active mode of operation. In such a non-active mode of operation the operation of the subscriber station MS is invoked by receiving the paging flag PF from the network control means RNC, namely when a call is pending for the subscriber station SS and when a communication connection is to be set up to the subscriber station MS.
FIG. 2
shows a general flow chart of a method for carrying-out an inter-frequency or inter-system handover in a mobile communication system when a signaling connection or a communication connection is set up. In step ST
11
a handover means HORM (HandOveR Means) situated in the networ
Afshar Kamran
Chin Vivian
Jenkens & Gilchrist P.C.
Telefonaktiebolaget LM Ericsson (publ)
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