FI104684B - Method of selecting a home cell for a subscriber device - Google Patents

Description

104684

The present invention relates to a method for determining a home cell for a subscriber station in a cellular radio system.

The invention further relates to a cellular radio system including a mobile switching center, base stations comprising means for establishing communications with radio frequency signals to subscriber units located within their coverage area, means for controlling base stations between communication equipment between from optional base stations to establish communication connections.

The invention relates primarily to a WLL system 15 (Wireless Local Loop), that is, a system utilizing stationary subscriber equipment whose communication signals are transmitted on a radio path utilizing a cellular radio system, although the invention may also be applied in other contexts. Since the subscriber devices of WLL systems 20 are generally mounted in a fixed location, there is generally no need for such devices to provide mobility, i.e., the ability to establish a communication link through any system base station. Even if the WLL subscriber units are subscriber units of a: - 25 lock radio system which also has mobile subscriber units for which the system provides the above mentioned mobility, it is advantageous if the mobility could be removed or at least restricted to certain cells from the WLL subscriber units. In this case, the number of required location updates and handover operations can be reduced, which saves system re-. already dedicated. Thus, with WLL systems, there is a need to define a home cell for each UE.

104684 2

In prior art solutions, a home cell has been defined for a specific subscriber unit so that when a subscriber unit is added to the system, the operator has checked, for example, on the map, which radio cell 5 is presumably best covering the geographical area where the subscriber unit will be located. Thereafter, the radio cell has been defined by the operator as the home cell of the subscriber unit. The major disadvantage of this known solution is that the field strength of a given radio cell may vary greatly within a cell, particularly in an urban area where buildings interfere with signal propagation, whereby the home cell of a given subscriber device may fail if the cell is selected solely on the map. The fact that the 15 operators would send service personnel to the location of each subscriber unit to perform field strength measurements is, for practical reasons, not possible due to the large amount of work required.

The object of the present invention is to solve the problem described above and to provide a method for determining the home cell of a subscriber unit so that the most suitable home cell for each subscriber unit can be safely and easily selected. This object is achieved by the method according to the invention, which is characterized by:. - allowing the subscriber device to freely use any or a limited number of optional radio cells within the system to establish communications, when the subscriber device communicates via a specific radio cell, or when accessing a subscriber device through a specified radio cell, based on the information stored in said register, the radio cells most utilized by the subscriber unit 35 and defining the subscriber unit size as at least one of said most used radio cells.

The invention is based on the idea that, when a home cell 5 is being defined for a particular subscriber unit, the subscriber unit is initially allowed to freely use any or a limited number of optional radio cells within the system to establish communication connections. That is, the subscriber device in question is initially given either completely free movement 10 or at least free movement in certain predetermined cells. Thus, the subscriber unit may establish a connection through a radio cell belonging to the system of its choice, provided, of course, that a free channel is available in that cell. In the case of a subscriber station moving within a limited area or, alternatively, a stationary subscriber unit, such as a WLL subscriber unit, it is possible that the subscriber unit is stationary in a location that includes a plurality of optional radio cells. Thus, the subscriber unit = 20 tends to select the radio cell with the best reception. It is also possible that a radio cell will temporarily sound better or worse at a particular time, so that the subscriber device may not always select the same radio cell when establishing a communication connection. 25 I can. According to the invention, statistics are maintained on the radio cells used by the subscriber unit, whereupon, after a while, it is possible to determine which cell has been most utilized by the subscriber unit, i.e., what would be the best home cell for the subscriber unit. According to the invention, said statistics may be recorded in said statistics. information such as how long calls from the subscriber unit have been made through different cells, and. how many calls the UE has made through different cells ii. Further, data may be recorded 35 regarding the traffic situation of the cell being used (e.g., • 104684 4-hour / congestion), the traffic situation of the neighboring cell of the cell being used, and the strength measurements of the cell and neighbor cells being used.

The major advantages of the method according to the invention 5 are that the home cell determination can take into account the actual cellular coverage of the subscriber's installation site, without requiring field strength measurements at the site, that a new home cell method can be defined for each subscriber device. in pre-existing systems, since the changes it requires to existing cellular radio systems can be made, for example, by modifying the software of the mobile telephone call center.

The method according to the invention can also be utilized continuously, i.e. the system can, for example, continuously monitor the cell through which the subscriber device has attempted to communicate, whereby the home cell or cells 20 of the subscriber device can be automatically renamed, e.g.

The method of the invention may also be applied to assigning more than one home cell to a particular subscriber unit. For example, if a subscriber uses the same 25 subscriber units in his summer cottage and in his city apartment, the subscriber unit can be assigned two home cells, which in this case are practically spaced apart. In accordance with the invention, subscriber units may also be designated to the subscriber unit, wherein each of the 30 sets includes a plurality of adjacent cells. Thus, the most appropriate radio cell from the home cell group can be provided to the subscriber unit.

The invention further relates to a cellular radio system in which the method according to the invention can be applied.

The system according to the invention is characterized in that • 104684 system includes register means for storing information necessary for identifying their base stations,. means for communicating or communicating with said specific subscriber station, and means for identifying the base stations most utilized by said subscriber station in its communications.

Preferred embodiments of the method and system of the invention are apparent from the attached dependent claims 2 to 4 and 6 to 9.

The invention will now be described in more detail with the aid of a few embodiments of the invention with reference to the accompanying figures, in which Figure 1 is a flow chart of a first preferred embodiment of the method of the invention.

Figure 2 is a block diagram of a first preferred embodiment of the system of the invention, Figure 3 is a block diagram of a second preferred embodiment of the system of the invention, and Figure 4 is a block diagram of a third preferred embodiment of the system of the invention.

Figure 1 shows a flow chart of a first preferred embodiment of the method according to the invention. In block A of FIG. 1, a specific subscriber unit for which it is desired to define a home cell is initially provided with free mobility in the system, i.e., the subscriber unit is free to use any base station in the system to establish a communication connection. Alternatively, the subscriber unit may be allowed to move freely within a predetermined number of cells 30 and. The subscriber unit may be a new subscriber unit that is, *, implemented, or alternatively the subscriber unit may have a predefined home cell, whereupon the operator, for example after a change in the network, wants to check whether the home cell of that subscriber unit should be changed.

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In block B, the system monitors the subscriber unit for detecting incoming or outgoing calls to the subscriber unit, respectively.

When a call to or from the subscriber unit 5 is detected, the system, in block C, registers the identifier needed to identify the cell / base station used in the predetermined register. At the same time, the connection time can be recorded in the register during or after the connection, i.e. how long the subscriber device has 10 connections through the cell / base station, traffic status information for that cell / base station (i.e. how much cell / base station capacity is currently available) traffic status information of the neighboring cell sites of the cell / base stations. The register 15 may further store information on how well the subscriber unit hears signals from different radio cells. For example, the subscriber unit of the GSM mobile communication system reports to the system the measurement data of the base station it uses and of the six strongest neighboring base stations it hears. According to the invention, this measurement data can also be stored in said register.

For example, the subscriber unit may be monitored for a predetermined time before the actual home cell of the subscriber unit is determined. Alternatively, the home cell may be. 25 determine when a predetermined number of events have been recorded for said subscriber unit in said register. In this case, the transition through block D to block E. The determination of the home cell may also be continuous, i.e. the subscriber station is continuously monitored, after which its home cell may be automatically renamed; for example, at predetermined intervals.

In block E, the entries in the register are used to determine the identities of the cells most used by the subscriber unit in establishing the connection.

In block F, the home cell of the base station is defined as one of the • 104684 7 most used cells. The selection can be based on either the number of applications or the cumulative total. teysaikoihin. In this case, the cell most used by the UE may not be automatically selected as the home cell, but other factors may also be taken into account. For example, if the cell most used by the subscriber unit has, on average, significantly more traffic than the next most used cell, then the next 10 most used cells can be defined as the home cell (of course provided the overlapping neighboring cells cover almost the same area). The naming of a home cell may thus utilize the traffic situation and measurement data described in block C, for example, selecting a home cell which has generally not been significantly more congested than neighboring cells when utilized by a subscriber unit. According to the invention, instead of a single home cell, several subscriber cells or groups of home cells may be assigned to a subscriber unit on the basis of information obtained in connection with the subscriber unit monitoring.

Figure 2 illustrates a block diagram of a first preferred embodiment of a cellular radio system according to the invention. The cellular radio system of Figure 2. 25 may be, for example, a GSM system (Groupe Special

Mobile) section. The system of Figure 2 is utilized for transmitting communications to both mobile MSs and WLL subscriber units 1 for fixed installation.

The system shown in Fig. 2 includes a mobile switching center MSC which, through two base station controllers BSC1 and BSC2 and three base stations BTS1 to BTS3, serves subscriber units MS and 1 located in the coverage area of the system.

The WLL subscriber unit 1 of FIG. 2, consisting of a terminal 104684 8 including a radio part and a telecommunication adapter and a terminal interface connected to the terminal, i.e. a fixed network telephone, is located where it can utilize either base station BTS2-BTS3 for its telecommunication connections. If the system operator wants to define a home cell for the subscriber unit 1, this is done according to the invention by initially providing the subscriber unit with free movement in the system or, alternatively, free movement in a particular part of the system. Thus, the subscriber unit (assumed to be permanently installed in the location shown in Figure 2) is free to use either of the base stations BTS2 and BTS3. During said training period, the mobile services switching center MSC monitors 15 subscriber units 1, whereby it registers in the register 2 with which base station / radio cell the subscriber unit 1 is connected, in each communication connection. The register 2 may be, for example, associated with the Home Location Register (HLR) register hh-20.

When the aforementioned training period ends, the information stored in the register 2 becomes clear which base station has been used the most by the UE. The cell maintained by the most used base station would naturally be the primary; - 25 instead, define that subscriber unit as the home cell, unless there are other reasons for selecting another cell. Once the WLL subscriber unit has a home cell defined, the mobile switching center stores the home cell information in register 2. The mobile switching center may then prevent that subscriber unit from utilizing other cells, thereby reducing the number of position updates' and handoff operations required in the system. However, even if the subscriber unit 1 requests a traffic channel from a cell other than its home cell, the mat-35 PBX MSC, via the base station controller BSC1 104684 9, only provides the traffic subscriber station with traffic channels from its home cell. In addition, the situation where. a subscriber station stationary in the boundary zone of two neighboring cells during a continuous connection would make channel switching operations with the solution according to the invention.

Of course, in the system of Figure 2, a home cell or multiple home cells may also be defined for a mobile station MS in a manner similar to that described above, whereby, for example, the operator may provide discounts to that mobile station when establishing a connection from one of its home cells.

Figure 3 illustrates another preferred embodiment of the system of the invention. The embodiment of FIG. 3 is otherwise similar to the case of FIG. 2, but in the embodiment of FIG. 3, a register 3 maintaining information about the access points used by the subscriber device MS during the training period (defining a home base station) is provided with the base station controller BSC3 and not with the PBX 20. Thus, during the training period, the register 3 records only the number of times the BTS4 and BTS5 cells have been used by the subscriber station MS. Correspondingly, when the training session is completed and a home cell is defined for the subscriber unit, the home cell information is stored in the base station controller register 3, where it can be retrieved when the subscriber unit MS is established.

The embodiment of Figure 3 also allows the system to take into account the home cell information of the ti-30 Widescreen MS stored in the register 3 only *; long as the subscriber unit is within the coverage area of base stations BTS4 to BTS5 controlled by base station controller BSC3. Thus, if the subscriber device is temporarily located, for example, in a cell of a base station BTS6 or another cell independent of the base station controller BSC3, the system itä 104684 10 does not care about what is registered in the register 3 of the base station controller BSC3.

Figure 4 is a block diagram of a third preferred embodiment of the system of the invention.

Figure 4 illustrates a situation in which two subscriber cell groups are defined for subscriber station MS. The first home cell group is composed of three adjacent neighboring cells A and the second home cell group is composed of four adjacent 10 cells B, respectively. Figure 4 shows that the first and second home cell groups are spaced apart.

In the system of Figure 4, the operator may have defined that the mobile station MS may only make calls from the home cells A and B that have been assigned to it, but that the system may still transfer the handover of that subscriber unit during the connection, e.g. to a cell that is not defined as a home cell for the subscriber station MS.

It is to be understood that the foregoing description and the accompanying drawings are merely intended to illustrate the present invention. Various variations and modifications of the invention will be apparent to the artisan without departing from the scope and spirit of the invention set forth in the appended claims.

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Claims (9)

A method of determining home cell for a subscriber apparatus in a cellular radio system, characterized in that 1 subscriber apparatus is freely allowed to use any hoist or certain limited group of several optional radio cells belonging to the system for establishing telecommunication connections; at least the identification characteristic of the radio cell used when the subscriber apparatus establishes a connection via a particular radio cell or until the subscriber apparatus establishes a connection via a certain radio cell is stored in a predetermined register, the radio cells which have been used most by the subscriber apparatus are identified on the base unit. in said register, and as a home cell for the subscriber apparatus, at least one cell is determined among the most widely used radio cells. 20 2. A method according to claim 1, characterized in that several home cells are determined for the subscriber apparatus. 3. A method according to claim 1, characterized in that for the subscriber apparatus 25 home cell groups are spaced apart from each other, each home cell group being a group located next to each other. Method according to any of claims 1 to 3, characterized in that one or more home cells have been established for the subscriber device: the subscriber device is prevented from utilizing cells other than its home cells in its telecommunications connections by allocating the subscriber device only traffic channels from its home cells. 35 1S 104684 5. Cellular radio system comprising a mobile telephone exchange (MSC); • base stations (BTS1 - BTS6) which include means for providing telecommunications connections with 5 radio frequency signals to subscriber devices (MS, 1) located in their coverage area, organs (BSC1 - BSC4) for controlling the base stations for transmitting telecommunication signals between the subscriber apparatus and the mobile exchange, and a subscriber apparatus (1, MS) capable of utilizing any of several optional base stations for establishing the telecommunications connections, characterized in that the system comprises registering means (2, 3) necessary for identifying the base stations (BTS2, BTS3, BTS4, BTS5) through which said subscriber apparatus (1, MS) establishes a telecommunications connection or via which to said particular subscriber apparatus a connection is established, and means (MSC, BSC3) for identification of the base stations which n said subscriber apparatus has made the most use in its telecommunications connections. System according to claim 5, characterized in that the system comprises control means (MSC, BSC3) for determining at least one home base station for the subscriber apparatus among the base stations (BTS2, BTS3, BTS4, BTS5) as the subscriber apparatus on the base of the recording means ( 2, 3) have been most utilized, the control means (MSC, BSC3) being arranged to prevent the establishment of a telecommunication connection between the subscriber apparatus (1: MS) and some other base station than the home base station. 7. A system according to claim 5, characterized in that the system comprises control means for assigning several home base stations for the subscriber apparatus among the 35 base stations (BTS2, BTS3, BTS4, BTS5) which the subscriber apparatus on the base of the recording means has most utilized. System according to claim 6 or 7, characterized in that the control means (MSC, BSC3) have been arranged to prevent the establishment of a telecommunication connection between the subscriber apparatus and any other base station at a home base station by the subscriber apparatus ( 1, MS) is assigned a traffic channel at its home base station in response to a call conveyed from the subscriber apparatus 10 regardless of via which base station the call has been conveyed from the subscriber apparatus. System according to any one of claims 5 to 8, characterized in that said cellular radio system is a GSM system. • «1. t I Λ