A METHOD AND EQUIPMENT FOR CARRYING OUT SPECIAL FUNCTIONS IN A CELLULAR RADIO SYSTEM

Abstract: A method and equipment implementing the method by which terminals and cells associated with special functions can be flexibly connected to a radio system. The radio system comprises means for defining priority cells and dividing radio subscribers into subscriber classes. A cell associated with a special function is defined to support the subscriber class or classes associated with said special function only, the cell also being defined as a priority cell. The terminal is arranged to update its subscriber class at least when registering into the system and when a possible change concerning the subscriber class is performed. At this point, new special function cells can be added to the system without having to collect the terminals for redefinition.

Description: A METHOD AND EQUIPEMENT FOR CARRYING OUT SPECIAL FUNCTIONS IN A CELLULAR RADIO SYSTEM BACKGROUND OF THE INVENTION The invention relates to a radio system and particularly to a method and equipment implementing the method for carrying out special functions in a cellular radio system where terminals are primarily arranged to be camped on cells defined as priority cells supporting at least one subscriber class associated with the terminal. The cells send information on the priority of the cell and the subscriber classes supported by the cell. Most recent radio systems are designed in such a manner that all subscribers of the radio system are able to operate with their terminals in the entire network area and to utilize the essential functions of the system. The radio system has to offer adequate services for organizations in different situations and environments. For a mobile subscriber it is very important to get in touch with his/her organization and also to be able to maintain the connec- tion when moving from one place to another. In order to obtain an extensive coverage, terminals and some parts of the network, particularly at the radio interface, are arranged to different functional conditions and environments in various ways, for example, regarding used transmission powers, directing antennas etc. Management of such elements has conventionally been imple- mented to a radio system by means of fixed equipment and unit-specific definitions causing unnecessary inflexibility to the configuration of the system. An example of such an implementation is the public safety and security network which must offer reliable services for organizations that may simultaneously operate in the air and on the ground. Radio terminals mounted in aircrafts, e.g. airplanes and helicopters, have to meet international and national norms, the precise regulations must thus also be fulfilled by the terminals meant to be used in the operative use of an organization. Below such a terminal to be mounted in an aircraft will be referred to as an air radio irrespective of whether the terminal is a simple transceiver unit or a subscriber unit capable of more intelligent operations. Special air cells are typically connected to the system in order to handle the traffic of air radios. The base stations of the air cells are mainly designed to be applicable to the needs of air radios by adjusting the transmission power, antenna direction, height of the antenna mast and other properties ac- cordingly. Since the number of subscribers using an air radio is typically small, 2 the air cells can be dimensioned to a fairly small number of channels. However, it is important that other radio equipment used in the system, which will be referred to as ground radios below, do not cause load to the air cells with, for example, unnecessary registration attempts. Since the air cells are gener- ally designed to serve radios moving in the air, their coverage ends close to the ground. An air radio has to move rapidly and flexibly from an air cell to a ground cell and vice versa so that the calls will not be disconnected when approaching the ground. In addition, the carrying capacity of a radio signal is significantly wider in the air than on the ground, the radio signal sent by an air radio therefore often reaches several ground cells. That is why it is important to make sure that the air radios do not cause interference to other cells, for example, the normal cells on the ground. The properties described above have conventionally been carried out in radio systems by terminal-specific definitions based on cell identifiers or radio frequencies. Typically, during initialization certain adjustments have been performed on the terminal, on the basis of which the operation of the terminal has been prevented or permitted only in cells having a particular cell identifier or at particular radio frequencies. By means of the definitions the terminal may have been arranged to prioritize certain cells having a particular cell identifier. The arrangement is fairly inflexible regardless of its many advantages, since the minor changes in the structure of the system cause a need to redefine the equipment. For example, in order to add a new air cell the operator has to collect all air radios from the field for adding the new cell identifier to their air cell register. BRIEF DESCRIPTION OF THE INVENTION An object of the invention is to provide a method and equipment implementing the method enabling a radio system to be designed and utilized in such a manner that terminals and cells associated with special functions can flexibly be connected to the radio system. The objects of the invention are achieved with a method and a system, characterized by what is disclosed in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims. The idea of the invention is that a radio system comprises means for defining priority cells and for dividing radio subscribers into subscriber classes. The cells send information about the priority of the cell and the sub- 3 scriber classes supported by the cell, and provide, if needed, the corresponding information also concerning selected neighbour cells. A radio terminal in the area listens to the information sent by the cells and is mainly camped only on such a cell that supports the subscriber class associated with the radio terminal. If the cells supporting the subscriber class of the terminal include a priority cell, the radio is camped thereon. In the solution of the invention the subscribers are divided into different subscriber classes: those carrying out special functions and those not, when a particular special function is defined. A cell associated with a special function is defined to support a subscriber class or classes associated with said special function only and the cell is also defined as a priority cell. The terminal is arranged to update its subscriber class at least when registering into the system and in connection with a possible change in a subscriber class. The subscriber classes provide a possibility for the radio terminals as- sociated with special functions to operate both in the cells associated with special functions and also in other, so called normal cells. On account of the arrangement of the invention the cells associated with special functions are not loaded with unnecessary registration attempts, since based on the announced subscriber class information the terminals as- sociated with special functions mainly try to register only into the cells supporting the special function. Because of the priority of the cells associated with special functions the terminals associated with a special function always select a cell supporting that special function when it is possible on the basis of other criteria, although their subscriber class is supported also by other cells. How- ever, since the other cells support terminals associated with special functions too, the transfer from a special function cell to a normal cell is smooth. When a subscriber takes a terminal into use, his/her subscriber data is attached to the terminal data. The subscriber class of a terminal can be formed on the basis of a combination of said data, in which case the data can be arranged to be automatically updated to the system at registration. The subscriber class of the terminal can also be arranged to be defined in other ways, for example, on the basis of a message concerning the subscriber class provided through a user interface of a subscriber terminal. A subscriber class of the invention is preferably a dynamic property associated with the sub- scriber and/or the terminal. The subscriber class can also be a fixed operator 4 definition, in which case it is bound to the identifier and/or the terminal of the subscriber. The invention has the advantage that by defining cells associated with new special functions according to the invention, new special function cells can be added to the system without having to collect the terminals for redefinition. Correspondingly, a subscriber may, if needed, operate as an ordinary subscriber or as a special function subscriber, for example, by attaching his/her subscriber data to the property data of a similar terminal, for example, by means of a data message or a personal transferable subscriber identifier module. BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention will be described in greater detail in connection with the preferred embodiments with reference to the accompany- ing drawings, in which: Figure 1 illustrates the structure of a TETRA system, Figure 2 illustrates the cellular structure of a radio system, to which air cells supporting the function of air radios, radio terminals used in aircrafts, are connected, Figure 3 is a block diagram showing a terminal of the invention, Figure 4 shows an arrangement of the invention in a radio system. A DETAILED DESCRIPTION OF THE INVENTION The invention can be applied for arranging desired special functions in radio systems comprising means for providing the above definitions associated with the priority of a cell and the subscriber class of a terminal. In the following the invention will be described in connection with the digital TETRA system (Terrestrial Trunked Radio) using as an example the matching of elements needed to service units operating in the air and on the ground, without restricting the invention to said system or special function. As to the TETRA system, reference is made to publication ETS 300 392-2 "Radio Equipment and Systems (RES); Trans-European Trunked Radio (TETRA); Voiceplus Data (V+D); Part 2: Air Interface (Al)", March 1996. Figure 1 shows an exemplary structure of a TETRA system. A Mobile Station MS communicates with a Base Station BS over the radio path Air. The air interface is defined in the TETRA standard. Each base station BS 5 is connected by a circuit to a Digital Exchange DXT for TETRA of the fixed transmission network. The TETRA exchanges DXT are connected to other exchanges DXT and to a Digital Central Exchange DXTc for TETRA by a fixed circuit, the DXTc being an exchange to which other exchanges DXT and/or other central exchanges DXTc are connected so as to provide alternative paths for the traffic. The interface to another TETRA network is here arranged in the central exchange DXTc, but it can also be located in the other exchanges DXT. The external interfaces, defined by the standard, to the Public Switched Telephone Network PSTN, the Integrated Services Digital Network ISDN, the Private Automatic Branch Exchange PABX and the Packet Data Network PDN are here located in one exchange DXT, but they can also be arranged in every exchange. The TETRA transmission network also comprises other interfaces and peripheral units, which are not shown in the Figure. They include, for example, network management systems and dispatcher systems. The radio system users also include organizations that operate in various conditions, like under ground, on the ground, in the air or at sea. In order to provide essential services for all organizations as extensively as possible, terminals and network elements arranged mainly to perform certain special functions are typically connected to the system. The solutions added to the system in order to provide services for the subscribers operating in the air can be mentioned as an example of such a procedure. Figure 2 illustrates the cellular structure of a radio system, to which air cells, for radio terminals used in aircrafts, supporting the operation of air radios are also connected. It should be noted that the present solution does not substantially examine the radios that the aircraft needs to maintain contact with air traffic control, but terminals operating through a radio interface in aircrafts and utilized in the operative function of a subscriber or subscribers. The properties and the use of all radios used in the air are strictly restricted by virtue of national and international regulations. These regulations also concern the terminals of the invention. The base stations of air cells are substantially planned in such a manner that the cell coverage is directed high into the air space, and that the coverage conceivably ends in the vicinity of the ground. Owing to the few air subscribers the number of radio channels in the air cell is generally small. 6 Here, it is assumed that the location of the base station is fixed, however, without restricting the invention to merely fixed base stations. Through a broadcast control channel each base station provides information about its operation and, if needed, also information about selected neighbour cells. The terminal listens to the broadcast control channel information available in the area and based thereon decides whether to camp on the cell. In the TETRA system, for example, a data unit D-MLE-SYSINFO PDU comprising a Subscriber class element is transmitted as a base station broadcast. This element is typically a bit map comprising 16 characters by which the terminal population can correspondingly be divided to belong to 16 subscriber classes at the most. The same data unit also comprises a BS service details element comprising the data in one bit indicating whether the cell is a priority cell or not. Subscriber class data associated with the division of terminals can be attached to an Individual TETRA Subscriber Identity ITSI. Based on the subscriber class data the system can in the first preferred embodiment control the local operation of the terminal used by said subscriber. In the first preferred embodiment the system decides upon the subscriber class data of each subscriber using the data transmitted by the terminal. The subscriber class data may be tightly tied to the subscriber identity ITSI or to the terminal, or it may change dynamically on the basis of the data provided for the system by the terminal or the subscriber. When the terminal registers into the system in the first preferred embodiment, the system informs the terminal to which subscriber class it belongs. In a second preferred embodiment the terminal identifies its subscriber class on the basis of some said data. If the terminal itself identifies its subscriber class, it does not necessarily have to inform the system about the subscriber class, since based on the data of the invention provided by the system the terminal is capable of identifying, for example, whether the cell supports the subscriber class of the terminal. When the terminal moving in the network area detects, based on the broadcast, that the cell does not support the subscriber class of the terminal, it does not try to register into the cell, if another cell supporting the subscriber class of the terminal is available. If a cell supporting said subscriber class is not found, the terminal may also register into a cell that does not support said subscriber class, but then only operations associated with certain cases, typically emergencies, are possible. Hence, the terminal always tends 7 to search for a cell that supports the subscriber class of the terminal and tries to register thereto. In the TETRA system the subscriber class can in accordance with the invention be arranged to be updated, for example, when a subscriber is being connected to the system or when a terminal is registered into a cell. In a preferred embodiment of the present invention the subscriber class of the terminal is defined on the basis of a combination of terminal type and subscriber data of a subscriber using the terminal. The subscriber data is included in a subscriber identification unit, a SIM card, which is detachably connected to the terminal. Subscriber data, from which the subscriber class can be concluded, may include, for example, the subscriber identity of a subscriber and naturally the subscriber class or the data indicating the subscriber class stored in the memory of an identification unit. Figure 3 is a block diagram showing the terminal of the invention in- eluding an actual terminal and a subscriber identification unit SIM detachably connected thereto. A SIM card (Subscriber Identity Module) used as the subscriber identification unit is a smart card to be located in the actual terminal. The smart card includes, for example, data for identifying the subscriber, such as the ITSI number individualizing the mobile station subscriber, and a certain amount of memory M2. The actual terminal comprises a transceiver Tx/Rx including antennas, a user interface Ul, a controller CP and more memory M1. When a subscriber starts using a terminal, he/she connects his/her personal SIM card thereto. In the first preferred embodiment the terminal is arranged to connect the subscriber identity obtained from the SIM card and the radio type included in the terminal and to provide the system with the data at registration. When accepting the registration the system confirms the subscriber class of the terminal. When the subscriber starts using another terminal he/she may transfer his/her SIM card to the new terminal, in which case the subscriber class of the terminal is correspondingly redefined at registration based on the subscriber data and terminal type. In the first preferred embodiment the subscriber may himself/herself provide information on the subscriber class through the user interface. In the second preferred embodiment the controller CP of the terminal is arranged to identify the subscriber class from the data stored in the memory M1 of the terminal and/or from the data obtained from the SIM card and possibly from the data provided by the subscriber received through the user interface Ul. 8 Figure 4 illustrates the arrangement of the first preferred embodiment of the invention. The Figure shows a radio system, to which air cells A, B, C and ground cells X, Y, Z are defined. In the air radio case the subscribers are divided into two categories: air subscribers and other subscribers. Radio terminals intended to be used by air subscribers are arranged to register their users as air subscribers, i.e. to support an air subscriber class AIR. The other radio terminals are arranged to register their subscribers into a ground subscriber class GROUND. The subscriber class element of the air cells A, B and C included in the cell broadcasting indicates that the cells do not support the subscriber class GROUND but do support the subscriber class AIR. In addition, the BS service details element of the air cells included in the cell broadcasting indicates that the cell is a priority cell. Ground cells correspondingly indicate that they support both the subscriber class AIR and the subscriber class GROUND, but indicate that the cells are not priority cells. Furthermore, all cells send information about their neighbour cells, which may be either air cells or ground cells, information about the subscriber classes supported by the cells and whether a neighbour cell is a priority cell or not. In the case shown in Figure 4 the air cell A, for example, sends information about its air neighbours B and C and its ground neighbours X, Y and Z below. Correspondingly the ground cell X, for example, provides information on the ground neighbours Y and Z and on the air cell A above. A ground cell may have only one air neighbour, since the air cells are generally significantly larger than the ground cells. Subscribers MM and NN register into the network through the ground cell X located at the airport. The subscriber MM enters the aircraft and starts using the radio mounted to the aircraft. When the MM places the SIM card into an air radio IR, it initiates the updating function of the radio terminal informing the system that the MM is now using an air radio. The system updates the data of subscriber MM, such as location, and informs the radio IR that it now belongs to the subscriber class AIR. Correspondingly the subscriber NN places his/her SIM card into a ground radio MR, in which case the system is informed about the NN using the ground radio MR. Correspondingly the system informs the ground radio that it now belongs the subscriber class GROUND. The ground cell X supports the subscriber classes AIR and GROUND, both radios thus registering at first into cell X. Simultaneously both 9 radios listen to the broadcasts of the neighbour cells and tend to register into a more appropriate cell. The ground radio MR observes the air cell A above, but since the air cells do not support the subscriber class GROUND, the ground radio does not try to register into the air cell. The air radio also observes the air cell A above, and detects that it supports the subscriber class AIR and is a priority cell. On this account, as soon as the air cell A can be received well enough, the air radio IR tends to register thereto. When the air radio IR travels in the air and has already registered into an air cell, both the current radio cell and the neighbour cell are priority cells, which is why the definition concerning priority between air cells does not substantially affect the cell change decisions. If the air radio moves into an environment, where none of the air cells is received well enough, it is then temporarily registered into a ground cell. However, as soon as one of the air cells is received well enough, the air radio IR tends to register into an air cell due to the priority of the air cell. A radio signal is carried higher and a much longer distance in the air than near the ground. A terminal travelling in the air space may thus cause significant interference for the operation of the ground cells. In the arrangement of the invention air cells are defined as priority cells. Therefore the terminals, whose subscriber class the air cells support, are primarily camped on an air cell if there are both ground cells and air cells to choose from. Since the air cells do not support the subscriber class of other terminals, the other terminals do not tend to register into air cells despite the priority of the air cells, and do not unnecessarily load the limited channel capacity of the air cells. The air radios, whose subscriber class the air cells support, tend to leave the ground cell as soon as one of the air cells can be heard well enough. The use of air cells thus becomes more effective and interference caused by air radios to ground cells is minimized. Since the decision to camp on air cells or ground cells is based on the subscriber class and the priority of the cell, and not as previously on the location area identifiers of the cell, adding a new air cell to the system does not cause reparameterization to the terminals used. Arranging the air cell parameters as described above, the terminals can be automatically directed to the desired cells as desired. Since the roaming between air cells and ground cells is flexible, when moving from ground channels available close to the ground to air channels available higher up in the air or when returning back to the ground, the 10 ongoing calls can continue without interruptions unlike before. In prior art solutions the transition between air cells and ground cells causes interruptions in use. The above embodiment describes how special function cells are ar- ranged in order to arrange the terminals used in aircrafts to the system. However, this is not the only way to apply the invention, which can also be applied to arrange other special functions to the radio system. Correspondingly, for example, special cells mainly intended for emergency and rescue operations can be arranged to the radio system. The operative area of the system typi- cally includes several areas, the extensive coverage of which is not economically justified. In order to maintain a certain rescue ability it should, however, be possible to arrange cells with a limited channel capacity to such destinations. The use of such cells would be restricted to certain central rescue resources and only to emergencies for ordinary subscribers. As the invention suggests, the subscribers are divided into rescue subscribers and other subscribers, the special cells into priority cells and to support the rescue subscriber class only. The other cells also support the rescue subscriber class. Sufficient resources are thus provided to support special functions, and the transition from a special cell to a normal operative environment is smooth. Adding resources does not cause any actions concerning reprogramming of terminals, such cells can thus be very rapidly added to the destination area. However, normal radios do not waste the limited resources of the cell with unnecessary radio traffic. By arranging the definition of the terminal subscriber class to be given in accordance with the invention at least when the subscriber starts to use a particular terminal, the subscriber is provided with an easy chance to act according to situation using his/her subscriber identification as a special subscriber (e.g. an air subscriber) or as an ordinary subscriber. In the above embodiment the subscriber class of the terminal is defined on the basis of the subscriber data in the SIM card and the terminal type. This is, however, only one preferable alternative for defining the subscriber class. The message can be implemented manually, in which case the subscriber informs the system through a terminal user interface Ul whether he/she operates as an air subscriber or as another subscriber. The message can be, for example, a short data message, and the system can be arranged to automatically update the subscriber class information. If the system uses a manned operator centre, the 11 definition can be arranged to be provided from the operator on the basis of the information the subscriber has given, for example, as a voice call or as a data message. However, it is essential, particularly when a dynamic subscriber class definition is used, that the terminal and the system are arranged to up- date the terminal subscriber class in connection with terminal registration or a change concerning the subscriber class. An example of such a change is a subscriber who starts using another terminal. If said special function is such that the same terminal is applicable to be used in normal and special function environments, the subscriber may select an appropriate moment for carrying out the selection of the subscriber class, for example, as described above. Another embodiment of the invention providing the same effect is an arrangement where both the air subscriber class AIR and ground subscriber class GROUND are allocated to the air subscriber MM. The air cells A, B, C are defined as priority cells and they support the air subscriber class AIR only, and the ground cells support the ground subscriber class GROUND only. Then, the ground subscribers do not tend to register into the air cells, but the air subscribers can register into both air and ground cells. Since the air cells are priority cells, air radios primarily register into the air cells. It is obvious for those skilled in the art that as technology advances the basic idea of the invention can be implemented in various ways. The invention and its embodiments are thus not restricted to the above examples but can be modified within the scope of the claims.

Claims: 12 CLAIMS 1. A method for carrying out special functions in a cellular radio system where terminals are primarily arranged to be camped on cells defined as priority cells supporting at least one subscriber class associated with the terminal, the method sending information in the cell on the priority of the cell and the subscriber classes supported by the cell for controlling which terminals are camped on the cell, and being characterized by dividing the subscribers into special function subscribers and other subscribers, defining the cells associated with a selected special function as priority cells, defining that the cells in which the terminals associated with special functions are desired to operate, support the subscriber class associated with said special function, and defining that the cells associated with special functions support only certain subscriber classes associated with special functions. 2. A method as claimed in claim 1, characte rized by de- fining the cells intended to be used mainly by air radios as priority cells and to support the radio terminals belonging to an air subscriber class, and by also defining at least the normal cells of the system to support the air radios. 3. A method as claimed in claim 1, characte rized by defining the cells allocated mainly for emergencies as priority cells and to support the radio terminals belonging to a subscriber class associated with emergencies, and by also defining at least the normal cells of the system to support said radio terminals belonging to the subscriber class associated with emergencies. 4. A method as claimed in claim 3, characte rized by de- fining all the cells in the system to support said radio terminals belonging to the subscriber class associated with emergencies. 5. A cellular radio system, where parameters are used to group subscribers into subscriber classes, and said parameters can be used to define the supported subscriber classes for the cells, and where selected cells can be defined as priority cells, on which the terminals having an appropriate subscriber class are primarily camped, and where base stations are arranged 13 to send information in the cell on the priority of the cell and the subscriber classes supported by the cell for controlling which terminals are camped on the cell, characterized in that the cells associated with a selected special function are defined as priority cells and to support the subscriber class associated with said special function, and at least a part of the other cells that are not defined as priority cells is also arranged to support the subscriber class associated with said special function. 6. A radio system as claimed in claim 5, characterized by defining the cells intended to be used mainly by air radios as priority cells and to support the radio terminals belonging to the air subscriber class, and by also defining at least the normal cells in the system to support the air radios. 7. A radio system as claimed in claim 5, characterized by defining the cells allocated mainly for emergencies as priority cells and to support said radio terminals belonging to the subscriber class associated with emergencies, and by also defining at least the normal cells in the system to support said radios belonging to the subscriber class associated with emer- gencies. 8. A radio system as claimed in claim 7, characterized by defining all cells in the system to support said radio terminals belonging to the subscriber class associated with emergencies. 9. A radio system as claimed in claim 5, characterized in that, when a terminal is taken into use in a particular subscriber class, the terminal is arranged to update the subscriber class, and the information concerning the subscriber class of the terminal is transferred to be available for selected parts of the system. 10. A radio system as claimed in claim 9, characterized in that the terminal is arranged to identify its subscriber class based on data stored in the terminal. 11. A radio system as claimed in claim 9, characterized in that the terminal is arranged to identify the subscriber class of the terminal based on terminal and/or subscriber data obtained from the terminal. 12. A radio system as claimed in claim 9, 10 or 11, characterized in that the subscriber may provide information on the subscriber 14 class used through a user interface of the terminal. 13. A radio system as claimed in claim 11 or 12, characterized in that the system is arranged to inform the terminal about the subscriber class. 14. A radio system base station mainly intended for carrying out special functions, where parameters are used to define subscriber classes supported by a cell, the base station being arranged to send information in the cell on the priority of the cell and the subscriber classes supported by the cell for controlling which terminals are camped on the cell, characterized in that said cell is defined as a priority cell and to support the subscriber class associated with said special function. 15. A base station as claimed in claim 14, characterized in that the base station is arranged to support terminals associated with the air subscriber class. 16. A base station as claimed in claim 14, c h a ra cte ri zed in that the base station is arranged to support radio terminals belonging to the subscriber class associated with emergencies. 17. A terminal operating in a cellular radio system arranged to be camped on radio cells supporting the subscriber class of a subscriber using the terminal and to be camped on primarily selected priority cells, characterized in that the terminal is arranged to update the subscriber class, in response to the fact that the terminal is taken into use in a particular subscriber class, the information about the terminal subscriber class then being transferred to be available for selected parts of the system. 18. A terminal as claimed in claim 17, characterized in that the terminal is arranged to identify its subscriber class based on data stored in the terminal and/or the subscriber data of the terminal user. 19. A terminal as claimed in claim 17, characterized in that the terminal is arranged to receive information about its subscriber class from the system. 20. A terminal as claimed in claim 17, characterized in that the terminal is arranged to identify its subscriber class based on data provided through a user interface of the terminal of the subscriber.

Inventors: EEVA PENTTI, LAAKSONEN PIRKKO, EEVA, PENTTI, LAAKSONEN, PIRKKO
Applicants: EEVA PENTTI, LAAKSONEN PIRKKO, NOKIA TELECOMMUNICATIONS OY, EEVA, PENTTI, LAAKSONEN, PIRKKO
Application year: 1999
Main classification: H04Q7
IPC codes: H04W4, H04W84