FI90182C - Cellular radio network - Google Patents

Description

! 90182

The cellular radio network

The invention relates to a cellular radio network comprising mobile subscriber radio stations, fixed radio stations, at least one exchange and an associated subscriber register, the central area covered by said at least one exchange being divided into traffic areas, each of which is further divided into a plurality of radio cells each comprising at least one fixed radio station 10 capable of establishing a radio connection with the currently active subscriber stations in the radio cell, and wherein said subscriber register stores the location information of each subscriber with the accuracy of one traffic area.

Various cellular radio or mobile telephone systems are currently in use and designed, in which the geographical area covered by the system is divided into smaller separate radio areas, i.e. cells so that while in the cell the radiotelephone or mobile telephone communicates with the fixed network via a fixed radio station 20. The mobile phones included in the system are free to move from one cell to another within the system. One such system is the digital mobile phone system GSM. When a subscriber in the same system or in an external system wants to call the mobile subscriber (MS) of such a system, the fixed network must know the actual location of the MS in order to route the call to the correct mobile switching center MSC. For example, in GSM, the number dialed by the calling subscriber does not contain any information about the actual location of the called MS. Therefore, in order to establish a complete connection, it is necessary to find out the location of the MS and the routing address required for the call. Typically, the cellular network knows the location of the MS with the accuracy of a larger area formed by several cells, commonly referred to as a traffic area. When the MS moves to a new traffic area, it is registered as a visiting subscriber in the subscriber database for that traffic area, the so-called visitor register, and at the same time deleted from the visitor register of the previous traffic area. In addition, the cellular radio network generally comprises at least one centralized subscriber database, the so-called home register, where the subscriber's data is stored permanently. When a new subscriber registers in one of the visitor registers, the subscriber information concerning this subscriber is requested from the home register and at the same time the subscriber's location information is updated in the home register, which is maintained with the accuracy of the visitor register. The visitor register is usually connected to a mobile switching center and may have several traffic areas under it.

Since the location of the MS is known only with the accuracy of the traffic area 15, it is necessary to retrieve the MS to establish an incoming call via all radio cells belonging to this traffic area. This causes a significant signaling load in the radio network between the mobile switching center and the base stations as well as on the radio path. On the other hand, reducing the size of the traffic area in order to avoid the above-mentioned disadvantage results in the MS changing the traffic area more often, whereby the location update frequency of the subscribers and the associated signaling signaling increase. In order to reduce location update, efforts are currently being made for larger-25 silicon traffic areas.

It is an object of the present invention to provide a cellular radio network in which the signaling load associated with subscriber paging is reduced.

This is achieved by a cellular radio network 30 of the type described in the introduction, which according to the invention is characterized in that the subscriber register also stores in radio cell accuracy a wide paging area in which the subscriber radio station most frequently moves, and radio stations in which the subscriber station is primarily called.

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3 ^ n18 2 search area not in the traffic area indicated by the location information provided by the subscriber register.

The basic idea of the invention is, in addition to the location update with the accuracy of the subscriber's traffic area, to determine, on the basis of the subscriber's mobility area, a subscriber-specific search area, which is the area of the radio network in which the subscriber more normally moves. At the beginning of the call, the subscriber is retrieved from an area that belongs to both the traffic area determined by the location information and the subscriber-specific search area-10, i.e. the intersection area of these areas where the subscriber can be expected to be most likely. As a result, the subscriber search does not have to be performed in all radio cells belonging to the traffic area, as in the previous solutions, whereby the inertial load of the radio network is reduced compared to the previous one. However, if the subscriber is not found in the intersection of the traffic area and the subscriber-specific search area, a new search is performed on the entire traffic area where the subscriber is located according to the location information. The broad search area used in the invention can be defined in different ways. It can be determined on the basis of information provided by the subscriber himself or automatically on the basis of information stored in the cellular radio network about the subscriber's movement.

The invention also makes it possible to increase the size of the traffic areas used by the network and thereby further reduce the signaling load, since the number of location updates performed by the subscriber is reduced, while the invention can keep the area from which the subscriber is sought relatively small.

The invention will now be described in more detail by means of exemplary embodiments with reference to the accompanying drawings, in which Figure 1 schematically illustrates a system according to the invention, Figure 2 is a signaling diagram illustrating a call set-up procedure, and Figure 3 illustrates the distribution of the radio network into traffic areas, radio cells and subscriber-specific paging areas.

In the following, the invention will be described in connection with a digital GSM mobile telephone system. However, the invention can be applied to any other cellular radio system of the same type, such as the planned UMS (Universal Mobile Te-10 telecommunication System).

The basic structure and basic functions of a GSM mobile telephone system are well known to those skilled in the art and are relatively well defined in the GSM system specifications. In the following, some basic concepts and elements of the GSM system that are relevant to the description of the invention will be defined with reference to Figure 1. The area where GSM mobile services are available is called the GSM network, which can cover several countries. The GSM network can be divided into national GSM networks, which means the areas of one operator providing GSM services. There may also be several GSM networks in one country and the areas they cover may geographically overlap. In the following presentation, a mobile telephone system refers primarily to such a "national-25" mobile telephone network, which may be connected to other national mobile telephone networks or other data transmission systems, such as the public telephone network.

The national GSM network may comprise one or more central areas, i.e. an area where 30 services are provided by one mobile switching center MSC. The GSM central area, in turn, can be divided into one or more traffic areas, which is an area covered by several radio cells. A cell is defined as the smallest geographical area of the system, comprising one or more fixed radio stations, i.e. the base station BTS, and using certain

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5 qn182 traffic channels. Figure 3 illustrates a part of a cellular radio system divided by thick solid lines into traffic areas A, B, C, D, E and F. Each traffic area A to F consists respectively of a number of radio cells 5 A1: A2 to A2g, B1 to B24, C1; - C28, D1 χ - D25, E1X - E27 and F11 'F26'

The national GSM network usually contains a single home location register HLR, which is a database in which mobile telephone information, such as location information, is permanently stored. 10 The system further includes a plurality of visitor registers VLRs, one or more for a single central area. The visitor location register VLR is a database in which the information of a mobile phone is stored for the time that the mobile phone visits the area of the VLR. The VLR knows the location of the mobile phone MS si-15 with the accuracy of one traffic area. The HLR, in turn, knows in which VLR the mobile station MS is visiting and provides the mobile station MS with routing information for the terminating calls to the telephone network. The HLR, in turn, receives the necessary routing information from the VLR. The HLR and VLR have only 20 signaling connections to other components of the mobile network. In the cellular radio system shown by way of example in Figure 1, each central area has its own visitor location register VLR, which is connected to the mobile switching center MSC of that central area. Figure 1 illustrates two central areas, one with a mobile switching center MSC1 and a visitor location register VLR1 and the other with a mobile switching center MSC2 and a visitor location register VLR2. Below each central area there are one or more traffic areas, and in each traffic area the traffic is controlled by the base station driver BSC, which controls several fixed radio stations, i.e. base stations BTS. Each of the above radio cells has one base station BTS and one base station controller BTS serves several cells. The mobile telephone MS in a cell establishes a two-way radio connection with the base station 35 BTS of that cell. There is both a signaling connection and voice channels between the base station controller BSC and the mobile switching center 6 o π 1 e 2 MSC.

In Figure 1, the unit MSC1 controls the base station controller BSC1, which in turn controls the base stations BTS1 and BTS2. Correspondingly, the second central area under the MSC2 has 5 traffic areas with a base station controller BSC2 and base stations BTS3 and BTS4.

Figure 2 shows a signaling diagram in which the establishment of an incoming call is performed according to the GSM recommendation. The mobile switching center, in this case the transit exchange 10, the GMSC receives from the second network the international telephone number (international ISDN number) of the mobile telephone MS, and forwards it to the home location register HLR of the mobile telephone network, requesting routing information from it. The HLR, in turn, checks in its file in which VLR the mobile telephone MS with the ISDN number 15 is currently located and requests the VLR from that VLR to send it the IMSI of the international mobile telephone number used within the mobile telephone network. In Figure 2, the VLR assigns a roaming number (MSRN) to the mobile station MS for this call and sends it to the HLR. The HLR forwards this roaming number MSRN as routing information to the transit center GMSC (or other requesting MSC), which routes the call using this routing information to the mobile switching center MSC associated with that VLR. (Location Area Identification) should be located by transmitting the IMSI of the mobile phone through the BTS of all radio cell-30 base stations in that traffic area. Upon receiving the paging signal, the mobile station MS acknowledges receipt. Thereafter, according to the GSM specification, an authentication procedure, an encryption procedure, etc., any procedures related to the B-subscriber are performed, and a call is established between the A-subscriber 35 and the mobile telephone MS.

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As previously stated, performing a paging of a mobile telephone MS through all radio cells in the traffic area indicated by the LAI identifier causes a significant signaling load on the radio network. Therefore, in addition to the LAI identifier, the invention 5 determines, on the basis of the subscriber's mobility area, each subscriber has its own search area, which is the area of the radio network in which the subscriber usually moves. Since the subscriber-specific search area is determined by the subscriber's mobility area, it can be arbitrarily located in the area of one or more traffic areas or consist of several smaller search areas, for example the workplace and the home with its surroundings. In Fig. 3, the shaded area 31 shows a subscriber-specific paging area of one subscriber, comprising radio cells ~ A29 from traffic area 3A and radio cells B1g and B22 from traffic area B. The shaded area 32 is another subscriber-specific search area consisting of cells E20 and E27 in traffic area E and of the cells F- ^ g - and FgQ - Fgg in the traffic area F. In the invention, the mobile phone MS is retrieved at the beginning of the call from an area 20 belonging to both the traffic area determined by the LAI identifier and the subscriber-specific search area, i.e. the intersection area of these areas. If no subscriber is found in this area or there is no common area, the search is performed in the entire location area where the subscriber according to the LAI identifier is located.

For example, if the subscriber-specific paging area of the subscriber is the shaded area 31 of Figure 3 and the LAI identifier indicates traffic area A as the location area of the mobile MS, the cellular network searches the mobile area MS through common radio cell base stations A and the shaded area 31, i.e. Agg through which area the mobile phone MS is most likely to be located. In this way, the number of base stations participating in the paging and thus the sig-35 nalization load in the network can be reduced. However, if the mobile telephone MS does not answer in the area of the radio cells, the network performs a search of the mobile telephone MS in the entire traffic area A.

The invention can also be used to effectively limit the desired cellular radio network services to subscriber-specific paging areas. This is done in such a way that if, in the example above, the mobile phone does not respond to the search performed in the cutting area or in the radio cells ^ 26 ~ A29, the network will not continue the search in a wider area. Correspondingly, if there are no common radio cells in the traffic area A, B, C, D, E TaiF and the subscriber-specific search area 31 or 32 indicated by the location information provided by the subscriber register VLR, the mobile phone search is not performed completely. In this way, regionally limited services can be provided to subscribers, to which lower prices can be applied if desired.

In GSM-type systems, information about subscriber-specific paging areas can be permanently stored in the HLR together with other subscriber information. When the mobile station MS registers with the mobile switching center MS for the first time, the VLR associated with this mobile switching center requests subscriber information from the HLR in the normal way and receives both subscriber information and subscriber-specific paging area information from the HLR in response. As the mobile station MS moves from one traffic area of the VLR to another, the VLR updates the location area identifier LAI it flies tal-25.

Alternatively, depending on the system structures, the paging area information may be stored in any suitable subscriber information register where it is readily available to the mobile switching center for mobile paging. In general, the present invention is applicable to all cellular radio systems in which the location update takes place with the accuracy of location areas comprising several radio cells.

The subscriber-specific search area can be defined in 35 different ways. It may, for example, be based on information provided by the subscriber.

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9 ° Π1P2 to work from their own movement. Alternatively, the cellular radio network can, on the basis of the stored information on the movement of the mobile telephone, statistically determine, for example, the typical location areas of the mobile telephone and thereby 5 subscriber-specific search areas.

The figures and the related description are only intended to illustrate the present invention. The details of the cellular radio network according to the invention may vary within the scope of the appended claims.

Claims (9)

1. Cellular radio network comprising mobile subscriber radio stations (MS), fixed radio stations (BTS1 Cellular radio telephone system according to claim 25, characterized in that the network comprises a plurality of exchanges (MSC1, MSC2) with subscriber registers (VLR1, VLR2) and central areas as well as at least one main subscriber register (HLR), where all subscriber information is constantly kept. in the network, location information 30 with the accuracy of a central area and said subscriber-specific search area information, whereby each central area's subscriber register (VL, R1, VLR2) temporarily preserves location information about the subscriber stations in the central area at the relevant time and the search area information as the main area information as received connection with II 13. nip 2 subscriber station's first registration. Cellular radio network according to claim 1 or 2, characterized in that if the traffic area (A, B, C, D, E, F) as the location information of the subscriber register (VLR1, VLR2) is specified and the subscriber-specific search area (31, 32) does not have common radio radios, the subscriber station is searched across the entire traffic area. Cellular radio network according to claim 1 or 2, characterized in that if the subscriber station is not found among the radio cells that are searched primarily and belonging to both the subscriber-specific search area (31, 32) and the traffic area (A, B, C, D, E, F) as the location information of the subscriber register is specified, the subscriber station is searched for the entire traffic area. Cellular radio network according to any of the preceding claims, characterized in that if the traffic area (A, B, C, D, E, F) as the location information of the subscriber register (VLR1, VLR2) is specified and the subscriber-specific search range (31, 32) having no common radio cells, no subscriber station search is performed. BTS4), at least one central (MSC1, MSC2) and a subscriber register associated therewith (VLR1, VLR2), the central area in which said at least one central area is distributed in traffic areas (A, B, C, D, E, F), each of which is, for its part, distributed into several radio cells, each of which comprises at least one fixed radio station (BTS1-BTS4), which can form a radio connection with the active subscriber existing in the radio cell at the time. stations, and wherein said subscriber register (VLR1, VLR2) maintains location information about each subscriber with the accuracy of a traffic area, characterized in that, in the subscriber register (VLR1, VLR2), a subscriber-specific (31 , 32), on which the subscriber radio station (MS) is most moving, and that the radio cells, where the subscriber radio station is primarily sought to make an incoming call, belong to the subscriber type ifikä search area (31, 32) and to the traffic area (A, B, C, D, E, F) as the location information of the subscriber register specified. Cellular radio network according to any of the preceding claims, characterized in that if the subscriber station is not found among the radio cells searched primarily and belonging to both the subscriber-specific search area (31, 32) and the traffic area (A, B, C , D, E, F) as the location information of the subscriber register indicated, the search is not continued in a wider area. Cellular radio network according to any of the preceding claims, characterized in that the subscriber-specific search area (31, 32) is determined by the subscriber himself. Cellular radio network according to any of the preceding claims, characterized in that the subscriber-specific search range (31, 32) is automatically determined due to the subscriber's mobility.