Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-09-16
2002-03-26
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S452200, C455S509000
Reexamination Certificate
active
06363252
ABSTRACT:
TECHNICAL FIELD
In general, the invention relates to how in a cellular radio system there is made a decision that the mobile station is handed over to a new base station. In particular, the invention relates to how the different base stations are set in a priority order for the handover.
BACKGROUND OF THE INVENTION
In cellular radio systems, there is known a so-called handover procedure, according to which a data transmission connection between a mobile station and the stationary parts of the system is routed to pass via a new base station, when the connection through the old base station becomes too weak or has too much interference. For instance in a GSM system (Global System for Mobile telecommunications), each base station transmits a signal in a given so-called BCCH channel (Broadcast Control Channel), in which case the mobile stations measure the power of the received BCCH signals and determine on the basis thereof which cell is the most profitable for the quality of the radio connection. The base stations also inform the mobile stations of the BCCH frequencies used in the adjacent cells, so that the mobile station know what frequencies they must listen to in order to find the BCCH transmissions of the adjacent cells.
FIG. 1
illustrates a second-generation cellular system comprising a mobile switching centre MSC belonging to the core network CN of the cellular system, as well as base station controllers BSC and base stations BS belonging to a radio access network RAN; the mobile stations MS are in connection with said base stations.
FIG. 2
illustrates the coverage areas
201
a-
209
a
of the base stations
201
-
209
in another second-generation cellular system.
In second-generation cellular systems, such as the GSM system, data transmission between the base stations BS and the core network CN takes place through base station controllers BSC. One base station controller normally controls a large number of base stations, so that when a mobile station moves from the area of one cell to the area of another, the base stations of both the old and the new cell are very often connected to the same base station controller. Thus the selection of a new active base station can be carried out in the base station controller. Consequently, for example in a regular GSM system there occur fairly few such inter-cell handovers where the mobile station moves from a base station connected to a first base station controller to a base station connected to a second base station controller. If this should happen, the switching centre must close the connection with the first base station controller and set up a new connection with a new base station controller. This kind of procedure includes a lot of signalling between the base station controllers and the switching centre, and because the distances between the base station controllers and the switching centre may be long, interference may occur during the selection of a new base station and a new base station controller.
A prior art arrangement for changing the active base station and base station controller is well suited to so-called second-generation digital cellular radio systems, such as GSM and its expanded version DCS1800 (Digital Communications System at 1800 MHz), IS-54 (Interim Standard 54) and PDC (Personal Digital Cellular). However, it has been suggested that in the future third-generation digital cellular radio systems, the quality of service offered by the cells for the mobile stations may considerably vary from cell to cell. Suggestions for third-generation systems are UMTS (Universal Mobile Telecommunications System) and. FPLMTS/IMT-2000 (Future Public Land Mobile Telecommunications System/International Mobile Telecommunications at 2000 MHz). In these plans, cells are divided, on the basis of their size and characteristics, for instance to pico, nano, micro and macro cells, and for example data transmission capacity can be used to describe the quality of service. The highest data transmission capacity is offered by pico cells and to the lowest in macro cells. The cells may be partly or completely superimposed, and there may be different kinds of mobile terminal devices, in which case all mobile stations cannot necessarily make use of the quality of service offered by all cells. Moreover, base stations can in different ways support services requiring real-time and non-real-time data transmission.
FIG. 3
illustrates a form of a future cellular radio system, which is not totally new for instance with respect to the known GSM system, but contains both known elements and completely new elements. The bottleneck of current cellular radio systems that hinders the offering of more advanced services to the mobile stations, is the radio access network RAN formed by the base stations and the base station controllers. The core network of the cellular radio system consists of mobile services switching centres (MSC), other network elements (in GSM for instance SGSN and GGSN connected to packet radio transmission, i.e. Serving GPRS Support Node and Gateway GPRS Support Node, where GPRS means General Packet Radio Service), and of transmission systems connected thereto. The core network is capable, in accordance with GSM+ definitions developed from GSM, of transmitting new types of services, too.
In
FIG. 3
, the core network of the cellular radio system
300
is a GSM+ core network
301
, and three parallel radio access networks are connected thereto. Among these, networks
302
and
303
are UMTS radio access networks, and network
304
is a GSM+ radio access network. Of the UMTS radio access networks, the one illustrated topmost, i.e.
302
, is for example a commercial radio access network owned by a teleoperator that offers mobile communications services and serves equally all customers who are subscribers of said operator. The lower UMTS radio access network
303
can be private, owned for instance by an enterprise in whose facilities said radio access network functions. The cells in the private radio access network
303
are typically nano and/or pico cells, and only the terminals of the employees of the owner enterprise can camp in them. All three radio access networks can contain cells that offer different types of services and vary in size. Moreover, the cells of all three radio access networks
302
,
303
and
304
can be completely or partly superimposed. The bit rate applied in each case depends among others on the radio environment, features of the employed services, the regional total capacity of the cellular radio system and the capacity needs of other users. The above mentioned new types of radio access networks are in general called generic radio access networks (GRANs). Such a network can be connected to be used in cooperation with different types of core networks CN, and particularly with the GPRS network of the GSM system. A generic radio access network GRAN can be defined as a group of such base stations BS and radio network controllers RNC controlling them where the members of the group are capable of exchanging signalling messages. In the specification below, the generic radio access network is called radio network GRAN for short.
The mobile station
305
illustrated in
FIG. 3
is most advantageously a so-called dual mode station that can function either as a second-generation GSM terminal or a third-generation UMTS terminal, according to what kind of services there are available in the area where it is located at the point of time in question and what are the data transmission needs of the user. It can also serve as a multi-mode terminal that can function as the mobile station of several different data transmission systems according to the needs and availability of services. The radio access networks and services available for the user are defined in the subscriber identity module SIM
306
.
FIG. 4
illustrates in more detail the core network CN of a third-generation cellular radio system, the CN comprising a switching centre MSC, and the radio network GRAN connected to the core network. The radio ne
Hämäläinen Seppo
Laaksonen Niina
Lappeteläinen Antti
Salonaho Oscar
Hunter Daniel
Le Lana
Nokia Mobile Phones Ltd.
Perman & Green LLP
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