CENTRALIZED CONTROL OF RADIO NETWORK IN A MOBILE COMMUNICATIONS SYSTEM BACKGROUND OF THE INVENTION Field of the invention The present invention relates generally to the field of mobile telecommunications and, particularly, to a method and apparatus for controlling radio network resources in a cellular communications system. Description of the Related Art Generally, the use of packet switching in mobile communication systems provides operators with a versatile platform for a wide variety of data applications. In fact, communications system developers anticipate that packet-switched communications will form a significant part of mobile telephony traffic in the future. Therefore, it is important to ensure that future packet switched systems will be able to operate effectively in a wide range of communication environments. It is also important to ensure that future packet switched systems will be developed with a high degree of network design flexibility. In existing mobile packet switched systems, control of the radio network (eg, air interface) is carried out through a control logic, (eg, programmatic algorithms) executed in processors located in the mobile stations. In contrast, a radio network control in most mobile systems switched by circuit is carried out through a control logic in the network, which sends dedicated control messages to specific mobile stations. The primary reason why the mobile station radio network control is a packet switched system is to avoid incurring a substantial signaling load resulting from the simultaneous signaling of the network to a large number of mobile stations in order to package waiting in a standby mode. On the other hand, a centralized radio network control (from the network side) provides an operator with a more comprehensive, more complete and more efficient control of the network. As such, more sophisticated control algorithms can be employed by the network control entity, and the control data can be processed in a much more efficient way than in the case of decentralized networks where mobile stations exercise control of the radio network. An important advantage of centralized control of the radio network is that higher quality traffic connections can be made, which in turn leads to higher network capacities. This benefit is the primary reason why a centralized radio network control is used in systems switched by circuits operating in the active mode. However, such a benefit can not currently be obtained from packet switched systems operating in active mode, because most packet switched data transfers occur for relatively short periods of time. Specifically, in contrast to circuit switched connection durations, packet data transmissions are generally too short to allow adequate time for optimization settings in the radio network (eg, individual transfers, power level adjustments, etc.) . If a packet switched system and a circuit switched system share a frequency band in the same geographical area, the growth of the population of mobile stations in each of the systems contributes to the increased interference of radio signals with the traffic of the another system. In a multi-service environment of this type, the packet switched system is typically an addition to an existing circuit-switched system that has a relatively broad subscriber base. Accordingly, the amount of packet switched traffic being transported is relatively small compared to the switched traffic. Therefore, it follows that a higher percentage of packet switched traffic than circuit switched traffic will be subject to signal interference. This interference occurs primarily because the edges of the cells for the packet switched traffic and the edges of the cells for the circuit switched traffic differ among themselves due to differences between the cell selection algorithms for the two types of traffic. In existing cellular communications systems, control of the radio network is carried out either by a network entity (or entities) or by mobile stations. In other words, no existing cellular system operator has the option to determine which of the two (network or mobile) will exercise overall control of the radio network. Specifically, the important functions of the radio network of cell selection and reselection, and power calculations of mobile stations are controlled either by the network entity or by the mobile stations involved. For example, in the Nordic Mobile Telephone System (NMT) (Nordic Mobile Telephony System), Total Access Communications System (TACS) (Total Access Communication System), Advanced Mobile Phone System (AMPS) (Advanced Mobile Telephony System) , Digital Advanced
Mobile Phone System (D-AMPS) (Mobile Telephony System
Avanzado Digital), Global System for Mobile Communications
(GSM) (Global System for Mobile Communications), Personal
Digital Cellular System (PDC) (Personal Digital Cellular System), and IS-95 Code Multiple Division Access System (CDMA) (Multiple Access System by IS-95 Code Division), one or more network entities exercise control over the radio network in active mode, while mobile stations exercise control over the radio network in idle mode. On the other hand, in the circuit switched system of Digital European Cordless Telephone (DECT)
(Digital European Wireless Telephone), and in packet switched systems Cellular Digital Packet Data (CDPD)
(Data in Cellular Digital Packs) and Mobitex, mobile stations exercise control over the radio network in both active and inactive modes. In other words, it is the mobile stations that exert control over the radio network in the idle mode, in all the aforementioned systems. COMPENDIUM OF THE INVENTION A problem encountered in the systems of the prior art is that the control of the radio network in the inactive mode is always exercised by the mobile station. When considering the uplink transmission of a packet in a packet switched system, it would sometimes be desirable to allow the use of more advanced radio network control (eg, cell reselection algorithms) than is traditionally available. in a mobile station. Accordingly, it is an object of the present invention to provide a centralized radio network control to at least one first mobile station in a mobile communication system having at least one second mobile station not equipped with centralized radio network control. It is also an object of the present invention to optimize signal capacity and quality for all traffic in a mobile communication system that provides various bearer services. It is another object of the present invention to minimize the need for improved mobile terminals in a mobile communication system that provides various bearer services. It is another object of the present invention to minimize the interference of radio signals between packet switched traffic and circuit switched traffic in a cellular communication system. In accordance with the present invention the above objects as well as other objects are achieved through a method and apparatus for assigning radio network control in a mobile communication system that offers two or more types of bearer services. The mobile network issues an initial control message that instructs some mobile terminals to suspend the use of their normal radio network control protocols and after they accept radio network control decisions from the mobile network. Accordingly, the mobile network can use virtually the same control logic for all mobile terminals to which it provides service, regardless of the type of bearer service being carried. As a result, the radio signal interference between mobile terminals carrying the different bearer services can be minimized. BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the method and apparatus of the present invention can be obtained with reference to the following detailed description taken in conjunction with the accompanying drawings wherein: Figure 1 is a simplified schematic drawing of a cellular communication system that it carries both circuit switched traffic and packet switched traffic, in accordance with a preferred embodiment of the present invention; Figure 2 is a diagram illustrating a message format that can be used to implement the method and apparatus for controlling one or more radio networks, in accordance with the preferred embodiment of the present invention; Figure 3 is a simplified schematic drawing illustrating an application for the present invention; and Figure 4 is a simplified schematic drawing illustrating a second application for the present invention. Figure 5 is a schematic block diagram illustrating a mobile radio terminal that can be employed to implement the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE DRAWINGS The preferred embodiment of the present invention and its advantages are better understood with references to figures 1-5 of the drawings, where similar numbers are used for similar and corresponding parts of the various drawings. Figure 1 is a simplified schematic drawing of a cellular communication system carrying both circuit switched traffic and packet switched traffic, in accordance with a preferred embodiment of the present invention. For example, the General Packet Radio Service (GPRS) is a new packet data service that has been specified for use in switched digital GSM circuit. For a complete presentation of GSM, see The GSM System for Mobile Communications "(the GSM System for Mobile Communications) by M. Mouly and MB Pauter, Cell &Sys., Copyright 1992 (ISBN: 2-9507190-0- 7) The current GPRS standard is described in the GSM Technical Specification, GSM 04.60, Version 0.9.1, September 26, 1996. It is notable that even when the modality illustrated in Figure 1 is focused towards a system that can carry both packet data traffic and circuit data traffic (eg, GPRS and GSM), the scope of the present invention is not limited thereto, for example, the concept of the present invention can be applied. to any cellular communication system where radio network control functions are maintained and exercised by one or more network entities or by one or several populations of mobile stations In the case of the exemplary embodiment illustrated in figure 1, the system 10 i ncludes a Public Land Mobile Network (PLMN) 12. The network 12 may include a first base station / transceiver unit 14 for, in this example, sending and receiving circuit switched traffic (e.g., GSM) ), and a second base station / transceiver unit 16 for, in this example, sending and receiving packet switched traffic (eg GPRS). For purposes of clarity, only base station / transceiver units 14 and 16 are illustrated, but it will be understood that network 12 may also include other mobile network components, such as (eg, one or more mobile service switching centers MSCs). ), home location records (HLRs) or visitor location records (VLRs). In this embodiment, a mobile terminal (e.g., cellular telephone) 18 is connected through an air interface to a base station / transceiver unit 14. The mobile terminal 18 therefore functions to send and receive traffic switched on. circuit. A mobile terminal 18 may represent one or more of a plurality of circuit switched mobile terminals. A second mobile terminal 20 is connected through an air interface to a base station / transceiver unit 16. A mobile terminal 20 therefore functions to send and receive packet switched traffic. A mobile terminal 20 may represent one or more of a plurality of mobile terminals capable of handling packet switched traffic. In this example, transmissions from the base station / transceiver unit 14 define a circuit switched coverage area (e.g., a cell) 22, and transmissions from the base station / transceiver unit 16 define an area of packet switched coverage (or cells) 24. As shown in Figure 1, the circuit switched coverage area 22 splices the switched coverage area into packets 24 in region 26. Notably, circuit switched traffic and packet switched traffic may share the same frequency bands of radio network bearer, therefore, mobile terminals 18 or 20 moving in or near coverage area 26 may be operating in the same set of radio network bearer frequencies, while sending and receiving their circuit switched traffic or switched traffic in respective packet. Essentially, in accordance with the present invention, the network (12) issues an initial control message (through one or more base station / transceiver units 14 and 16) that commands the mobile terminals switched in packets or switched in circuit and combined in packets 20 that suspend their normal cell control protocols (GPRS) and then accept a certain decision to control the radio network coming from the network (12). When said mobile station is switched or is in an unknown geographical location and has access to a terrestrial system, it is necessary (from a logical perspective) that the mobile station employ internal algorithms for the initial selection of a base station for contact. But after this initial contact, the reselection of a cell (ie, when the mobile station remains in an inactive mode but has been moving), can be controlled from autonomous algorithms in the mobile station as achieved in conventional systems , or by a combination of algorithms in the mobile and in the network according to the present invention. Therefore, the network can use the same control logic (or virtually the same control logic) (for example, control algorithms) for both packet-switched mobile terminals and circuit-switched mobile terminals, which causes packet switched traffic behaves (from a control perspective) in virtually the same way as circuit switched traffic. Accordingly, in accordance with the present invention, a signal interference between mobile packet switched terminals and mobile circuit switched terminals can be minimized. For example, the network 12 may issue a control message on a general broadcast channel (e.g. Packet Broadcast Control Channel or PBCCH on the GPRS) which commands that all capable mobile terminals 20 to handle packet switched traffic suspends its normal activities (for example, standardized mobile internal GPRS) from radio network cell reselection and power order calculation, and instead uses the results of calculations made by network control algorithms of own radio of the network, in part, new algorithms replacing the existing norm, like for example, the norm GSM. The precise amount of radio network control that will be abandoned by the packet switching terminals in favor of the network (12) may vary in accordance with the overall system requirements (performance, capacity, etc.). In accordance with what has been described above, the initial control command from the network can be universally issued to a population of mobile terminals (e.g., packet switching terminals) in a cell or in a group of cells. The network can thus send one of the following exemplary control orders to the mobiles, giving instructions for: (1) sending signal measurement reports to the network; (2) accept specific cell identity information for the next cell reselection (the exact time of the transfer can be determined by the individual mobiles); (3) accepting cell identity information for immediate cell reselection (mobiles may later revert to their normal cell reselection protocols); (4) suspend the performance of their cell reselection calculations and accept cell identity information from the network for a reselection; (5) accept a single power level order sent from the network; or (6) suspend its own power order calculations and use power orders sent from the network. In addition, the network (12) can send additional control information to the mobile terminals (packet switched) in dedicated signaling messages or in packet transmissions (for example, through a Packet Data Traffie Channel). Data in Packages) or PDTCH in GPRS). This additional control information may include, for example, detailed information as to which measurement measurement frequencies to use, measurement report start and end times, priority information, identity information or performance characteristics. of certain cells or groups of cells, or control information that causes specific groups of mobile terminals to behave (from a control perspective) in a specific manner. In response, each mobile station (20) can send its measurement reports to the network (12) in dedicated signaling messages or in packet transmissions (for example, through the PDTCH in GPRS). Cell identity and power order information, which mobiles receive orders to accept, can be sent as individual transmissions from the network to each mobile in a dedicated signaling message or packet transmission. Figure 2 is a diagram illustrating a frame format that can be used to implement the method and apparatus for controlling one or more of the radio networks, in accordance with the preferred embodiment of the present invention. As described above, in order to initiate a network control in the radio network for the packet switched mobile terminals in Figure 1, the network 12 sends a broadcast message received by the mobile terminals switched in packets located in a network. cell or group of cells. For example, the message issued may be a system information message that includes a network control information element. With reference to Figure 2, for example, a radio network control information element is displayed, in a field position 4 in an exemplary GSM information message. Notably, even when a complete control message can be issued to packet switched signals, since such a message can be quite long, it is preferable to employ a single bit like? "control" arc in the initial control message This unique radio network control bit can be set to either * l "or" 0. "In this mode a * 1" at bit position 4 indicates that the mobile receivers must listen and decode a subsequent system information message. This subsequent information message may include additional control information. An N 0"at bit position 4 indicates that the mobile receiving terminals can follow normal operations and use their own radio network control protocols, more broadly, one element (preferably 1 bit) of network control information" it can be initially sent in a signaling message issued from the network (for example, on a Broadcast Control Channel or BCCH). In accordance with what has been described above, if the network control bit is set to '1' then the mobile receivers are alerted to listen for additional control instructions., for example, the Network Control bit is set to * 0"), the mobile receivers are alerted that no additional control instruction will follow and can continue to use their own control protocols.These additional instructions can be provided in a message of additional system information, such as Network_Control_Order (Cell control command) (Cell_Re-selection_Order (cell reselection order), Reporting_Period (reporting period), ... etc) An information element from ttCell_Re-selection_Order " (Cell reselection order), which preferably has one bit of length, can be set to "0" or * 1. "If this bit is" 0", then the mobile receivers must accept cell identity information at From the network to an immediate cell reselection, in this case, mobile receiving terminals can send measurement reports to the network, in accordance with other additional information. l provided in the control message. Each receiving mobile terminal can continue to use its normal cell reselection protocol until it receives new cell identity information from the network. The mobile then selects the new cell. On the other hand, if the Cell_Re-selection_Order bit (cell reselection order) is set to wl ", then the mobile receivers may suspend their own cell reselection calculations and accept new cell identity information for cell reselection, In this case, each mobile terminal sends measurement reports to the network, in accordance with requests for information provided in the control message No receiving mobile terminal performs cell reselection evaluation alone, but it selects the next cell based on the cell identity information received from the network.The Cell_Re-selection_Order bit (cell reselection order) can also be * 0", if the network intends that the mobile phones send only reports measurement. In this case, the network may stop sending cell identity information or power level order information to the mobile terminals involved. The Network_Control (network control) message sent from the network may also contain an information element "Reporting_Period." As an example, the Reporting_Period element may have a length of 3 bits. binary of the Reporting_Period field (report period) can be coded, for example, proportionally from 0.48 seconds (binary 0) to 3.84 seconds (binary 7), or as a geometric series from 0.24 seconds (binary 0) to 30.72 seconds (7 binary), or as any other appropriate code In the preferred mode, the control of the network will be maintained to the extent that the Network Control bit is issued with the value "L." The bit Network_Control (network control) can be reset to O "manually with an Operation and Maintenance message (O &; M) to the base station controller (BSC) if, for example, the system operator determines that network control is no longer necessary or desired. This bit can also be reset to 0"automatically through a device in the network When the bit of Network_Control is issued with the value" 0"the mobile terminals immediately resume control Measurement reports sent from the mobile terminals to the network are directed to the appropriate network entity (for example, a BSC in GSM) These measurement reports can include the following exemplary information: rxlev (signal strength to receive) and a quality measurement for the cell currently serving the mobile, number of valid neighbor cells, rxlev and carrier frequency issued for up to a defined number of valid neighbors, absolute output power (of the mobile transmitter) and amount of time advance employed, and additional measurements of neighbor signal strength Quality measurements sent to the network may include: an interference level measured as a function of signal strength for non-useful time segments A measurement of Bit Error Rate (BER) that is obtained from the downlink signaling related to a packet transfer; and a BER measurement obtained from paging messages sent in the broadcast channel. The cell identity information that mobile receivers must accept may include, for example, a Global Cell Identity (CGI), and a "xdesyntable" value that are intended to prevent mobile terminals from reselecting the original cells (for example, example, if the Cell_Re-selection_Order bit (cell reselection order) is set to 0". Preferably, for the GPRS the cell identity information is sent from the network to the individual mobile terminals in a packet transmission in the PDTCH An exemplary application for the present invention is the collection of performance statistics for use by the network, for example, in the GPRS, by ordering packet switched mobile terminals to send measurement reports to In the network, an operator can collect performance statistics in terms of downlink conditions in the network. to be used for several other applications, such as network tuning, fault location, error determination, positioning services, as well as automatic or semi-automatic assignment of frequencies. For these measurement reporting applications, the selected reporting periods may be relatively long. Accordingly, the load on the packet channel can be maintained continuously and therefore kept under control, even in the case of systems carrying a relatively high amount of packet data traffic. Figure 3 is a simplified schematic drawing illustrating an application for the present invention. If a packet switched service is introduced to an existing circuit switched system (for example, GPRS added to GSM), and the packet switched system has to operate with the same carrier frequencies as the circuit switched system, with the system Package-switched using virtually the same radio network control logic as the circuit-switched system ensures that radio interference between the two systems will be minimal. Otherwise, the quality of the signal and the capacity of the circuit switched system would be diminished by the new packet switched traffic, and the quality of the packet switched service would be low. For example, with reference to the illustrative example of Figure 3, a mobile communication system 30 includes a base station / transceiver unit 32 that transmits and receives both circuit switched data and packet switched data. A mobile terminal 34 is configured to send and receive packet switched data to a base station / transceiver unit 32 or from a base station / transceiver unit 32. The terminal 34 may represent one or more mobile switched terminals by packages. The system 30 also includes a second base station / transceiver unit 36, which transmits and receives data switched by circuit. A mobile terminal 38 is configured to transmit circuit-switched data to a base station / transceiver unit 36 or from said base station / transceiver unit 36. As shown, transceivers 32 and 36 share carrier frequencies. of radio network. The dotted arrow indicated by the number '40 'indicates a co-channel interference that may have existed between the circuit-switched system and the packet-switched system, had it not been for the use of a centralized radio network control in accordance with The present invention In other words, the co-channel interference (40) is minimized because the circuit-switched and packet-switched systems employ the same radio network control logic (or at least virtually the same logic) thus causing the edges of cells 35 and 37 coincide instead of being different as shown in Fig. 3. Fig. 4 is a simplified schematic drawing illustrating another application for the present invention In the near future, what is known as ? microcells "for shipping services. An important type of data service package. In a microcell environment of this type, the desired cell boundaries can not always be provided by the "best server" which corresponds to the highest downlink signal strength received by a mobile station. The concept of * hierarchical functionality "has been used to manage cell selection in cell structures in layers of this type, an approach that has been used to try to connect mobile phones to a cell in a '' 'lower layer" of a hierarchy of layers, even if the "lower layer" cell is not defined by the "best server", thus making use of the available traffic capacity in the "lower layer". Referring now to Figure 4, a mobile communication system 50 includes a base station / transceiver unit 52 that transmits and receives power in a pattern defined as what is known as "macro cells." A second transceiver unit 54 transmits and receives energy that defines a microcell A third transceiver unit 56 transmits and receives energy defining a second microcell Transceiver unit 56 carries packet switched traffic and circuit switched traffic A hierarchical functionality scheme is used to define the micro-cells illustrated, for circuit-switched traffic, whereas the circuit-switched system and the packet-switched system illustrated in Figure 4 share radio network bearer frequencies within the same geographical area, if the packet switched system it does not support the use of a hierarchical functionality but if the circuit-switched system does Thus, in accordance with the present invention, the network administrator in the system 50 can direct the packet switched system to use the same control logic as the circuit switched system (thus causing, for example, that the limit of cells 57 is replaced by the limit of cell 58 for packet-switched traffic). This action will ensure that both the circuit-switched system and the packet-switched system will both have an adequate quality of service and will not cause interference between them, as explained in the previous exemplary application. Figure 5 is a schematic block diagram illustrating a mobile radio terminal that can be employed to implement the preferred embodiment of the present invention. The mobile radio terminal 300 includes a transmit / receive antenna 310. A transmitter section 320
(including modulation and equalization equipment) is connected to an antenna 310 and also to a first signal processor unit 340. The first signal processor unit 340 operates to control functions related to switched calls per output circuit (transmitted) . The transmitter section 320 is also connected to a second signal processor unit 352, which operates to control outgoing messages related to packet switched functions (e.g., GPRS messages). Similarly, the mobile radio terminal 300 includes a receiving station 330 (including demodulation and equalization equipment), which is also connected to an antenna 310 and a first signal processing unit 340 and a second signal processing unit 352, respectively, the first signal processing unit 340 operates to control functions related to switched calls per input circuit (received) and the second signal processing unit 352 operates to control input messages related to packet switched functions (e.g. GPRS input). In addition, the first signal processing unit 340 is capable of encoding and decoding channels, as well as processing speech signals in both the output and input directions. The first signal processing unit 340 is also connected to a microphone and a telephone receiver 341, and a logic control unit 350. A second signal processing unit 352 is also connected to a logic control unit 350, and can encode and decode channels, as well as process signals of packet switched messages (eg GPRS) in both the input address and the output address. The primary reason for the use of separate signal processing units (340, 352) for voice and packet switched services (eg GPRS), respectively, is that the protocols for these two applications differ considerably. Also, from a manufacturing and cost perspective, it is advantageous to produce only one type of circuit board for voice only mobile radios and for radio terminals additionally equipped for packet switched services (eg GPRS). As such, mobile terminals capable of voice only would not be simply equipped with the additional components required for mobile radio terminals capable of packet switching. Furthermore, as an alternative embodiment of the present invention, it is possible to combine signal processing units 340 and 352 into a single more powerful signal processor which, for example, could be replaced by a signal processing unit 340 and thus eliminate the unit signal processor 352 in FIG. 5. Control logic unit 350 operates, inter alia, to provide a higher level of control to signal processing units 340 and 352. Algorithms for controlling cell reselection for traffic of GPRS, for example, are implemented in control logic unit 350. In fact, the term "cell reselection" is associated with GPRS and corresponds to the term "transfer" associated with circuit switched GSM services. In operation, when controlled through an algorithm implemented on the network side, both the transfer operation and the cell reselection operation send measurement reports in the uplink, and orders in the downlink. For example, GPRS uplink control messages (e.g., measurement reports from the control logic unit 350 to the network) are connected from the control logic unit 350 through a second signal processing unit 352. and to the transmitter unit 320 and antenna 310. The GPRS downlink control messages (e.g., cell reselection information from the network to the control logic unit 350) are connected from the antenna 310 through the the receiving unit 330 and the second signal processing unit 352 and the logic control unit 350. For this exemplary embodiment, the control message formats and measurement report message can be based on the standard GPRS protocol. Further, even when GPRS communications use a protocol that is different from the voice protocol, the present invention can be easily implemented based on the description given above for a mobile radio terminal capable of offering a voice service and a switched service in packages (for example GPRS) combined, and the description provided in the GSM technical specification (currently GSM 01.60, 02.60, 03.60, 04.60) for the General Packet Radio Service (GPRS) (General Radio Package Service) published by the European Telecommunications Standard Institute (ETSI) (European Institute on Telecommunications Standards). The control logic unit 350 is also connected to an input / output (I / O) control unit 353, which adapts the signals to the interface between the keyboard and the display unit 360. In addition, the control unit input / output 353 is connected to a plug 361, which allows connection to a personal computer or PC (not explicitly illustrated). Preferably, for this mode, the PC is a portable PC that can be used to send and receive GPRS messages. Even though a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying drawings and described in the above detailed description, it will be understood that the invention is not limited to the embodiments presented but can be carried out with various arrangements, modifications and substitutions without departing from the spirit of the invention in accordance with what is presented and defined in the following claims