Arrangement and method for location registration

A method and an arrangement for subscriber location management among a group of radio networks comprising at least two radio networks (101, PMR1, PMR2) in which at least some of the subscribers (SBR1, SBR2, SBR3) may roam away from the home network and register in another radio network over the radio path. To enable centralized subscriber location management, the subscriber database (HLR) of one radio network (101) is arranged to maintain in a centralized manner the location data of all subscribers (SBR1) that have roamed outside their home networks and registered in another radio network (PMR2) at least with an accuracy of a radio network.

FIELD OF THE INVENTION 
The invention relates to an arrangement and a method for subscriber 
location management among a group of radio networks comprising at least a 
first and a second radio network in which at least some of the subscribers 
may roam away from the first radio network, which is the subscribers' home 
network, and register in the second radio network over the radio path. 
BACKGROUND OF THE INVENTION 
The mobile telephone networks of the prior art have typically had their own 
independent location management systems, which have not communicated with 
other radio networks in respect of location management. This has been the 
case even if several radio systems have been combined to form a single 
radio network. In GSM systems, location management is standardized so that 
all GSM systems of different operators can communicate with each other as 
regards location management. In GSM systems, the location management of a 
mobile phone is performed by the home network of this mobile phone. The 
situation is more complicated when several mobile telephone networks of 
different kinds are combined, e.g. a GSM-type radio network and private 
radio networks such as PMR-type (Private Mobile Radio) networks. Networks 
of different types have usually not been able to communicate with each 
other regarding location management. 
A disadvantage of these prior art solutions is that each network requires 
its own location management system. This is naturally very expensive, as 
each radio system must have its own location management registers, which 
are continuously aware of the location of each subscriber. 
BRIEF DESCRIPTION OF THE INVENTION 
The object of the invention is to provide such an advantageous location 
management method and system for subscribers of interconnected radio 
systems by which the problems with the solutions of the prior art are 
avoided. 
This new type of arrangement for location management among radio networks 
is achieved with the arrangement according to the invention, which is 
characterized in that the subscriber database of a third radio network, 
which does not belong to the same group of radio networks as said first 
and second radio network, and in which the subscribers of said first and 
second radio network cannot register, is arranged to maintain in a 
centralized manner the location data of all the subscribers that have 
roamed away from their home network and registered in the second radio 
network at least with an accuracy of a radio network. 
The new type of method for performing location management among radio 
networks is achieved with the method according to the invention, which is 
characterized in that the subscriber database of a third radio network, 
which does not belong to the same group of radio networks as said first 
and second radio network, and in which the subscribers of said first and 
second radio network cannot register, maintains in a centralized manner 
the location data of all the subscribers that have roamed away from their 
home network and registered in the second radio network at least with an 
accuracy of a radio network. 
The invention is based on the idea that the location and subscriber data 
management in interconnected radio systems can be performed, if necessary, 
by a centralized network element. The system may comprise local registers 
for location and subscriber data management; these registers maintain 
location and subscriber data locally within the area of the subscriber's 
home network. When the subscriber roams outside the service area of his 
home network, the subscriber location management is performed by a 
location management register which is located outside the home network, 
possibly in another radio network. 
An advantage of the system and method according to the invention for 
subscriber location management among radio networks is that it allows 
construction of mobile telephone networks which do not comprise location 
and/or subscriber data management of their own, nor registers for this 
purpose. It is thus possible to utilize the properties and registers of 
the location and subscriber data management of another mobile telephone 
network, and it is therefore not necessary to implement these properties 
in the network to be constructed. This naturally reduces the costs. 
A further advantage of the invention is that if there already exists a 
radio network in the area to be constructed, it is possible to utilize the 
existing location and subscriber data management registers and functions. 
Since existing systems can be used, fewer design efforts are needed. 
Yet another advantage of the invention is that it allows the location data 
of subscribers locating outside their home network to be stored in a 
centralized subscriber database. The exchange of the subscriber's home 
network can then request the location data from the centralized database. 
In this way the home exchange of the subscriber obtains the routing data 
for routing a call.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates a system according to the invention. PMR2 represents a 
PMR system with no location management; the network elements, i.e. the 
exchange MX2, use the location management services provided by the home 
location register HLR of the GSM network. This PMR2 network may be, for 
example, a TETRA-type network (TETRA=Trans European Trunked Radio). When a 
subscriber SBR2 of the PMR2 network registers through the base station BS2 
and by means of the exchange MX2 in the PMR2 network, the exchange MX2 of 
the radio network updates--or in fact, requests the home location register 
HLR of the GSM network to update--the location of the mobile station, or 
the subscriber SBR2. The following is a description of establishment of a 
call when a subscriber SBR2 residing in the service area of the MX2 wishes 
to set up a connection to a subscriber SBR3 located within the service 
area of the same radio network, or to a subscriber SBR1 located within the 
service area of another radio network, e.g. another TETRA system. The 
establishment of the call begins in such a way that the subscriber SBR2 
sends a call set-up message to the exchange MX2 of its own location area. 
The MX2 requests the location data of the called subscriber SBR3 or SBR1, 
i.e. information of the location of the SBR3 or SBR1, from the subscriber 
database, or the HLR, of another radio network, in this case the GSM 
network. The home location register HLR of the GSM system responds by 
sending the location data of the called subscriber, or the B-subscriber, 
to the exchange MX2. Having received the response, the MX2 sets up a 
connection to the exchange MX1 in whose service area the called subscriber 
SBR1 is located, or if the called subscriber is located in the area of the 
PMR2 network, the exchange MX2 sets up a telecommunication connection 
between the calling SBR2 and the called SBR3. This call establishment may 
take place over a suitable signalling path. 
In the case described above, when the called subscriber SBR3 was located 
within the service area of the same exchange MX2 as the calling subscriber 
SBR2, the exchange MX2 requested the location data of the called 
subscriber, or B-subscriber, from the home location register HLR of the 
GSM network. An alternative solution is illustrated by means of the PMR1 
network. The PMR1 network maintains a local database DB1 which is a common 
local database of both the subscribers whose home network the PMR1 network 
is and the subscribers visiting the service area of that PMR1 network. If 
a telecommunication connection is to be established to a subscriber 
located within the service area of the PMR1 network, the data of the 
called subscriber are requested from the home location register HLR of the 
GSM network 101 only if they are not obtained from the local database DB1. 
The home location register HLR of the GSM network functions thus as a 
database for all the different systems, and the local database of the PMR1 
network speeds up the call establishment when the subscriber SBR1 is 
located within the service area of the same network PMR1 or exchange MX1. 
In the arrangement of the invention, the subscribers of the PMR1 and PMR2 
networks may utilize the location management mechanism of the GSM network 
so that at least some of the subscriber numbers of the PMR network are GSM 
numbers and some of them are numbers of the PMR network, e.g. a TETRA 
network. Even if a GSM number is allocated to a subscriber, it is possible 
that the subscriber is entitled to use the services of only one or more 
PMR networks. According to the invention, a PMR network is allowed to 
utilize part of the functions of the home location register HLR of another 
radio network, e.g. a GSM network. This means that part of the resources, 
i.e. the computer time and storage locations, of the home location 
register of the GSM network is dedicated solely to the subscribers of the 
PMR network such as a TETRA network; the location data stored in the part 
of the register dedicated to the PMR network cover only the subscribers of 
the PMR network, i.e. the TETRA subscribers, for example. 
If the subscriber database DB1 of the PMR1 network, shown in FIG. 1, is in 
use, the home location register HLR of the GSM network should update this 
database when the subscriber roams from one exchange to another. On the 
other hand, the HLR of the GSM network does not have to know with an 
accuracy of a base station where a subscriber is located within the area 
of a PMR network or its exchange, but this data may be stored in the local 
database DB1 of the PMR network. These database functions may be called 
virtual database functions of the GSM network. 
At least if the exchange of a PMR network, a TETRA network, does not 
comprise a local location database DB1, even the visitor location register 
VLR of the GSM network is used in respect of visiting subscribers. In this 
case, a visiting subscriber is a subscriber not known by the home location 
register HLR of the GSM network. It is thus assumed that all the PMR 
networks that are connected to the GSM network form separate addressing 
domains, i.e. sub-domains, in the HLR of the GSM network, but are equal in 
other respects; if a subscriber roams from one connected PMR1 network to 
another connected PMR2 network, the subscriber data do not therefore have 
to be stored in the visitor location register VLR of the GSM network. 
According to the invention, the home network of the subscriber is 
considered to be the network which recognizes the subscriber as one of its 
own subscribers. This may be implemented in such a manner that the 
subscribers whose home network a certain radio network is are indicated in 
the subscriber database of that radio network. 
FIG. 2 illustrates the operation of the system according to the invention 
in a situation where a subscriber SBR1 moves from a first network PMR1 to 
a second network PMR2. The subscriber is at first registered in the 
service area of his own PMR1, or TETRA, network. The home location 
register HLR of the GSM network 101 contains the subscriber data of this 
subscriber and information about the fact that the subscriber is located 
within the service area of the exchange MX1 of his own PMR network PMR1. 
In addition, the local location database DB1 of the TETRA network contains 
data on the actual, accurate location area of the subscriber (LAI=Location 
Area Identification) or on the base station BS1 in the coverage area of 
which the subscriber is located. The subscriber SBR1 roams 110 to the area 
of the second PMR network PMR2, and transmits a registration message to a 
base station of this network, e.g. to base station BS2. The base station 
BS2 transmits the data on the registration of the new subscriber to its 
exchange MX2. The exchange MX2 detects that the PMR2 network is not the 
home network of the subscriber SBR1. Thereafter the exchange MX2 requests 
the subscriber data of the subscriber from the home location register HLR 
of the GSM network. If, on the basis of the subscriber data, the 
subscriber SBR1 is entitled to use the services of the PMR2 network, the 
exchange MX2 sends the subscriber SBR2 an acknowledgement of the 
registration, stores the data on the base station or location area LAI 
used by the subscriber in a local register, i.e. in database DB2, or this 
data is sent to the home location register HLR of the GSM network. The HLR 
of the GSM network informs the PMR network PMR1 from which the subscriber 
has come that the subscriber has left the service area of that network, 
and that the subscriber can now be reached on the basis of the data stored 
in the HLR of the GSM network. Thereafter the PMR1 removes the location 
data of the subscriber SBR1 from its own local database DB1 and possibly 
acknowledges this to the HLR of the GSM network. 
A feature of the present invention is that, in addition to the location 
data of a subscriber, the centralized database also maintains other 
subscriber data, for example data on the services which the subscriber is 
entitled to use. Such data may include, for instance, information on which 
networks the subscriber is allowed to register in, and which networks the 
subscriber is allowed to call to. They may also include information on 
which additional services or service restrictions apply to the subscriber. 
Another feature of the invention is that the centralized database which 
maintains the location data of a subscriber and possibly the subscriber 
data of the subscriber is a database of a radio network which is not one 
of the above-mentioned group of radio networks and in which the 
subscribers of the above-mentioned radio networks cannot register over the 
radio path. 
The drawings and the description relating thereto are intended merely to 
illustrate the inventive concept. In its details, the arrangement and 
method of the invention for subscriber location management among radio 
networks may vary within the scope of the appended claims. Even though the 
invention has been described above mainly with reference to GSM and TETRA 
networks, the invention may also be applied to other kinds of mobile 
telephone and radio networks.