HK1011497B - Location updating in a cellular radio network - Google Patents

Description

The present invention relates to a cellular radio network wherein each cell broadcasts one or more location area identifiers or identifiers adapted to be used as such, and which comprises mobile subscriber equipment capable of moving so that the location data of the mobile subscriber equipment is stored with an accuracy of a location area consisting of one or more cells in the cellular radio network. The invention also relates to subscriber equipment to be used in this type of cellular radio network and to a method for carrying out a location updating of the subscriber equipment in the network.

In a cellular radio network, base stations constantly broadcast information on themselves and on their neighborhood. This kind of information can include for instance a location area identifier, base station identifier, base station type identifier and so-called neighboring cell information. While being registered in a base station of a cell, a mobile radio station also monitors the quality of the transmission from the base stations indicated in the neighboring cell information broadcast from said base station, and switches to one of these base stations if the signal strength of the current base station weakens. The cellular radio network usually knows the location of a mobile radio station with an accuracy of a so-called location area, which includes a suitable number of predetermined cells with their respective base stations. The location area information broadcast from the base station indicates to the mobile radio station which location area the cell belongs to. When the mobile radio station changes cell within the same location area, no location updating to the cellular radio network is required. Instead, when the mobile radio station observes that the location area changes as it switches to a new base station, it initiates a location updating by transmitting a location updating request to the cellular radio network. As a result of this location updating request, the cellular radio network stores the new location of the mobile radio station in subscriber location registers.

EP-A-2-0505106 discloses a cellular telephone system having a microcell layer and a macrocell layer. The macrocell and microcell layers have different location area configurations. If the location of a mobile radio station is known with an accuracy of a location area only, it is necessary to page the mobile station via all the cells within the location area in order to set up a mobile-terminating call. This causes considerable signalling load especially on the radio path but also in the radio network between the exchange and the base stations. The amount of signalling due to subscriber paging is thus in direct proportion to the size of location areas. On the other hand, reducing the size of a location area in order to avoid the above-mentioned disadvantage will lead to a situation where a mobile station changes location area more often, whereby the rate of location updating and the signalling relating to it increase. Efforts are made today to increase the size of location areas in order to reduce location updating.

The mobility behaviour of individual users in a cellular radio network can vary very much. Some users frequently move across the typical location area boundaries while others stay normally within a very small part of the location area. Thus, instead of using the same location areas for all subscribers, it would be possible to optimize subscriber pagings and to better distribute the signalling relating to location updatings to different parts of the cellular network if location areas of different sizes were applied with regard to different users.

The object of the invention is to enable a flexible use of location areas of different sizes with regard to different users in a cellular radio network.

This is achieved with a cellular radio network according to claim 1.

Another aspect of the invention is subscriber equipment for a cellular radio network according to claim 4.

Yet another aspect of the invention is a method for carrying out a location updating in a cellular radio system according to claim 8.

The basic idea of the invention is that several coincident logical location area levels, that are hierarchical with respect to location area size, are used in the cellular radio network, or at least in part of it. Location area density is thus different at different location area levels; in other words, large location areas are used at some location area levels whereas small location areas are in use at others, correspondingly. Users/terminal equipments may either have a relatively fixed allocation to certain location area levels, or the terminal equipment may dynamically select the location area level appropriate at a given moment. As regards mobile-terminating calls, subscriber paging can be directed within an area of a suitable size, because the location of the terminal equipment is updated for the most accurate possible location area level applicable to a mobile station. For instance, stationary or low-mobility subscriber stations may use dense location area levels (small location areas), and fast-moving subscriber stations may use larger location area levels (large location areas). Since the invention offers the possibility of applying location areas of different sizes to different users/subscriber stations, and the location area boundaries of different location area levels are distributed in different ways, the amount of signalling in the cellular radio network radio due to simultaneous location updatings can be equalized, because location updatings are not carried out for all subscriber stations in the area of the same base stations. This is a significant property as the invention is compared to location updating in the present-day cellular networks, in which the entire network is divided into location areas existing at a single level. In this case, the location updating is carried out for all network users at the same location area boundaries, which causes significant signalling load. In some cases, it may be preferable to apply the several location area levels according to the invention only in part of the network, for instance in busy areas with a lot of signalling, and to apply one location area level in the normal manner in the rest of the network.

The invention will be described by means of illustrating embodiments with reference to the accompanying drawings, in which

• Figure 1 illustrates a cellular radio network according to the invention, and
• Figure 2 is a general block diagram of subscriber equipment according to the invention.

The present invention can be applied in connection with any cellular radio system, such as the digital GSM mobile phone system, NMT (Nordic Mobile Telephone), DCS1800, PCN (Personal Communication Network), UMC (Universal Mobile Communication), UMTS (Universal Mobile Telecommunication System), FPLMTS (Futute Public Land Mobile Telecommunication System), etc.

As is well known, the geographical area covered by the network in cellular radio networks is divided into smaller separate radio areas, i.e. cells, in such a manner that while in cell C, a mobile radio station MS communicates with the network via a fixed radio station located in the cell, i.e. a base station BS, as illustrated in Figure 1. Mobile radio stations MS included in the system can freely move within the system area from a cell to another. The cellular radio network must, however, know the location of the mobile radio station MS in order to be able to route mobile-terminating calls to the MS or to page it for some other reason. Typically, the cellular radio network knows the location of the MS with an accuracy of an area consisting of one or more cells, this area being generally called a location area.

The base stations of the cellular network constantly broadcast information on themselves or their neighborhood, such as location area identifier LAI, base station identifier BSI, base station type identifier BSTI and so-called neighboring cell information. On the basis of neighboring cell information broadcast by said base station BS, the MS registered in a cell recognizes those neighboring cells the base-station transmission of which the MS should monitor. When the signal strength of the current base station BS weakens, the MS registers into the best of these monitored neighboring base stations. The location area identifier of the base station indicates to the MS which location area the base station BS belongs to. If the MS observes that the location area identifier LAI changes as the base station BS is changed, i.e. that the location area changes, the MS initiates a location updating by transmitting a location updating request to the cellular radio network. If the location area does not change when the base station changes, no location updating is carried out by the MS.

The location updating initiates the subscriber data updating of the subscriber concerned in the subscriber location register(s) of the cellular network. For instance in the GSM system, the cellular radio network comprises at least a home location register HLR, visitor location registers VLR, mobile exchanges MSC and base station controllers BSC, which are connected to the base stations BS of the network, as illustrated in Figure 1. The location area data of the subscriber is stored in the visitor location register VLR, of which there are typically one for each mobile exchange MSC, whereas the HLR knows the VLR within the area of which the subscriber is located. The structure and operation of the GSM system are further described in GSM specifications and in "The GSM system for Mobile Communications", M. Mouly & M-B. Pautet, Palaiseau, France, ISBN: 2-9507190-0-7.

In the cellular radio system shown as an example in Figure 1, each service area has its own visitor location register VLR, which is connected to the mobile exchange MSC of the service area concerned. Figure 1 illustrates two service areas, one of which comprises a mobile exchange MSC1 and a visitor location register VLR1 and the other of which comprises a mobile exchange MSC2 and a visitor location register VLR2. Under both exchanges MSC, one or more base station controllers BSC are provided, controlling several base stations BS. In Figure 1, the MSC1 controls the base station controller BSC1, which in turn controls the base stations BS of cells C1, C2, C3, C4, C5 and C6. Each base station BS communicates by means of a bidirectional radio link with the mobile stations MS in the corresponding cell. For clarity's sake, Figure 1 shows only one mobile station MS, located in the cell C3.

In present-day cellular radio networks, the entire network is divided into location areas LA existing at the same level, i.e. each cell is fixedly allocated to only one location area. This will cause many problems related to location updating and subscriber paging, which have been referred to earlier in the description.

According to the present invention, the cellular radio network is divided into several coincident location area levels, which are hierarchical with respect to location area size. Figure 1 illustrates three location area levels I, II and III, but the number of location area levels can vary if need be. Each of the cells C1, C2, C3, C4, C5 and C6 belongs to one location area at each location area level I, II and III. In the example of Figure 1, all six cells C1-C6 constitute one location area LA1 (L1). At the location area level II, the location area structure is denser and the location area size smaller in such a manner that the cells C1, C2 and C3 constitute a location area LA1 (L2), and the cells C4, C5 and C6 constitute another location area LA2 (L2). Correspondingly, at the location area level III the location area structure is even denser and the location area size smaller in such a manner that the cells C1 and C2 constitute a location area LA1 (LA3), the cells C3 and C4 constitute another location area LA2 (L3), and the cells C5 and C6 constitute a third location area LA3 (L3). In the example, the location area configuration becomes thus more accurate in switching from the location area level I to the level II and further to the level III. The location area levels are thus hierarchical with respect to location area size. It is preferable to assume that the location area level I be a so-called primary level with the largest possible location areas. The primary level is preferably for instance the location area configuration used in present-day networks, and the location area configuration becomes denser in switching to lower levels. This is a recommendable solution, because the operation according to the invention is thus independent of the number of location area levels.

With reference to Figure 1, the cell C3 for instance belongs simultaneously to the location area LA1 (L1) at the level I, to the location area LA1 (L2) at the level II, and to the location area LA2 (L3) at the level III. The base station of the cell C3 thus simultaneously broadcasts the location area identifiers LA1 (L1), LA1 (L2) and LA2 (L3) related to all the levels I, II and III. The mobile station MS located in the cell C3 receives constantly location area information on all the logical location area levels I

Claims (12)

1. A cellular radio network wherein each cell (C1-C6) broadcasts one or more location area identifiers or identifiers adapted to be used as such, and which comprises mobile subscriber equipment (MS) capable of moving so that the location data of the mobile subscriber equipment is stored with an accuracy of a location area (LA1,LA2,LA3) consisting of one or more cells in the cellular radio network, characterized in that

   at least part of the cellular radio network comprises at least two hierarchically arranged location area levels (L1,L2,L3) for each cell (C1-C6) , the size of location areas (LA1-LA5) being different at different location area levels (L1-L3).

   each cell (C1-C6) being arranged to broadcast identifiers of those location areas (LA1-LA3) which the cell belongs to on said at least two location area levels (L1-L3).
2. A cellular radio network according to claim 1, characterized in that the mobile subscriber equipment (MS) has a fixed or a default-value based allocation to a certain location area level. (L1-L3)
3. A cellular radio network according to claim 1, characterized in that the mobile subscriber equipment (MS) is arranged to dynamically select the location area level (L1-L3) that it will use.
4. Subscriber equipment for a cellular radio network, in which cellular radio network each cell (C1-C6) broadcasts one or more location area identifiers or identifiers adapted to be used as such, and which comprises mobile subscriber equipment (MS) capable of moving so that the location data of the mobile subscriber equipment (MS) is stored with an accuracy of a location area (LA1-LA3) consisting of one or more cells in the cellular radio network, characterized in that the subscriber equipment comprises

   means (21,22) for receiving location area information from a cell (C1-C6), this location area information including, the location area identifiers of those location areas which the cell belongs to on at least two hierarchically arranged location area levels (L1-L3).

   means (22) for selecting the location area level, and

   means (21, 22) for carrying out a location updating when the subscriber equipment moves from one location area into another at the selected location area level.
5. Subscriber equipment according to claim 4, characterized in that said-selection means (22) are adapted to select a certain location area level fixedly or on a default-value basis.
6. Subscriber equipment according to claim 4, characterized in that said selection means comprise means (30,31,32) for measuring the period the subscriber equipment has been in the same cell or in the same location area, and for activating said location level selection means (22) to carry out a location updating to another location area level with a smaller location area size, in response to reaching a threshold time.
7. Subscriber equipment according to claim 4 or 6, characterized in that said selection means comprise means (31, 32) for monitoring the changes of location area, cell and/or location area level performed by the subscriber equipment, and for preventing the subscriber equipment (43) from changing to another location area level with a smaller location area size if the number of changes within the monitoring period exceeds a threshold value.
8. A method for carrying out a location updating in a cellular radio system, comprising the steps of

   storing the location data of a mobile subscriber equipment (MS) with an accuracy of a location area (LA1-LA3) consisting of one or more cells (C1-C6),

   broadcasting within each cell (C1-C6) one or more location area identifiers or identifiers adapted to be used as such,

   carrying out a location updating by updating said location data of the subscriber equipment (MS) at least when the subscriber equipment moves into a cell (C1-C6) which broadcasts a location area identifier not belonging to

   the location area (LA1-LA3) determined by the location data currently stored in the subscriber equipment (MS),    characterized by

   using at least two hierarchically arranged location area levels (L1-L3) for a single cell (C1-C6), the size of location areas (LA1-LA3) being different at different location area levels (L1-L3), in at least part of the cellular network,

   transmitting to the mobile subscriber equipment (MS) the identifiers of those location areas (LA1-LA2) which the current cell of the subscriber equipment (MS) belongs to on said at least two location area levels (L1-L3),

   selecting a location area level (L1-L3) for the mobile subscriber equipment (MS),

   carrying out the location updating of the mobile station (MS) when the subscriber equipment moves from a location area into another at the selected location area level (L1-L3).
9. A method according to claim 8, characterized by

   measuring the period the subscriber equipment (MS) has spent in the same cell (C1-C6) or in the same location area (LA1-LA3), and

   selecting another location area level (L1-L3) with a smaller location area size, in response to reaching a threshold value,

   carrying out a location updating at the selected location area level (L1-L3).
10. A method according to claim 8 or 9,    characterized by

    monitoring the changes of location area (LA1-LA3) cell (C1-C6) and/or location area level (L1-L3) performed by the subscriber equipment (MS), and

    comparing the number of changes with a threshold value,

    selecting a location area level (L1-L3) with a smaller location area size if the number of changes within a monitoring period falls below said threshold value,

    staying at the current location area level (L1-L3) if the number of changes within the monitoring period exceeds said threshold value.
11. A method according to claim 8 or 9,    characterized by

    monitoring the changes of location area, (LA1-LA3) cell (C1-C6) and/or location area level (L1-L3) performed by the subscriber equipment (MS), and

    comparing the number of changes with a threshold value,

    selecting a location area level (L1-L3) with a larger location area size if the number of changes within a monitoring period exceeds said threshold value,

    staying at the current location area level (L1-L3) if the number of changes within the monitoring period falls below said threshold value.
12. A method according to claim 8 or 9,    characterized by

    monitoring the changes of location area (LA1-LA3), cell (C1-C6) and/or location area level (L1-L3) performed by the subscriber equipment (MS), and

    comparing the number of changes with a first and a second threshold value, the second threshold value being higher than the first one,

    selecting a location area level (L1-L3) with a larger location area size if the number of changes within a monitoring period exceeds said second threshold value,

    selecting a location area level (L1-L3) with a smaller location area size if the number of changes within'the monitoring period falls below said first threshold value,

    staying at the current location area level (L1-L3) if the number of changes within the monitoring period is between said first and second threshold values.