Abstract:
In order to support the effective use of services in wireless telecommunications systems, radio devices are designed in such a way that they maintain at least two lists in which connection-relevant data of base stations are stored, separated according to the service which they support. In order to set up a connection, a base station is determined from the list according to the required service.

Description:
BACKGROUND OF THE INVENTION 
   In the terminal equipment domain of telecommunications, radio paths are becoming increasingly important. Cordless telephones, mobile radio terminals and the wireless connection technology “RLL” (Radio in the Local Loop) or “WLL” (Wireless Local Loop) are well-known examples of this. With the aim of defining a standard for a high-performance and universal air interface, an air interface known as “DECT” (Digital Enhanced (formerly: European) Cordless Telecommunication) was defined at the instigation of European companies. The DECT standard is described in the documents ETS (European Telecommunication Standard) 300 175-1, . . . , Oct. 9, 1992 of the ETSI (European Telecommunication Standards Institute) and is known therefrom. 
   A DECT system allows up to 120 simultaneous connections between base stations and mobile units, which are furthermore understood to include not only mobile terminals but also, as for example in the wireless connection technology “Radio in the Local Loop”, stationary system components which communicate with a base station via an air interface and which include the functional scope of a mobile unit. As such, up to 10 frequencies between 1.88 and 1.90 GHz are available and up to 12 simultaneous duplex voice connections (time slots, voice channels) can be implemented per frequency. 
   Furthermore, interworking between DECT and “ISDN” (Integrated Services Digital Network) is specified in the DECT standard. Along with the time slots (channels) at 32 kbit/s (“Full Slots”) and 8 kbit/s (“Half Slots”) required for voice connections, time slots with a transmission rate of 64 kbit/s provided to support ISDN are also specified. 
   Base stations and corresponding mobile units are generally known which, for faster data transmission of, for example, 64 kbit/s or to support DECT/ISDN interworking, support transmission rates of both 32 kbit/s “Full Slots” and 64 kbit/s “Double Slots.” That is to say up to 6 channels with a transmission rate of 64 kbit/s, i.e. a maximum of 2 complete ISDN connections having two base channels “B-channel”, each at 64 kbit/s, and one control channel “D-channel” at 16 kbit/s, are provided. 
   “Scanning” of local radio devices to determine free and occupied channels, which is carried out by all DECT devices at least every 30 seconds as a background process, is known from the DECT standard. The information determined in this way is stored in a list known as the RSSI (“Received Signal Strength Indication”) list, where free channels with little interference are identified by high values and occupied channels with substantial interference are identified by low values, for subsequent selection. If a radio cell is supplied with radio resources by two base stations, or if these base stations partially cover a common radio coverage area (overlapping of radio cells), whereby the first base station supports only “Full Slots” and the second base station both “Full Slots” and “Double Slots”, a mobile station which supports both “Full Slots” and “Double Slots” and which, for example, requires the voice transmission service, i.e. a transmission rate of 32 kbit/s (“Full Slots”), requires a facility to determine which base station provides this service. 
   In terms of a universal telecommunications system “Universal Mobile Telecommunication System” UMTS, it is also conceivable for two base stations to supply two different telecommunications systems, for example a first base station supplies a DECT radio area and a second base station supplies a “Global System for Mobile” GSM radio area, whereby the radio coverage areas totally or partially overlap each other for the implementation of the UMTS. Mobile units which support both systems, therefore, similarly require a facility to distinguish between these base stations. 
   An object to which the present invention is directed is to indicate a method for controlling the selection of base stations in a cellular radio telecommunications system, in which the radio transmission resources made available in the radio telecommunications system, in particular in an RLL or WLL system, are effectively used. 
   SUMMARY OF THE INVENTION 
   In the method according to the present invention, connection-relevant data are stored in at least one memory in at least one radio cell of a cellular radio telecommunications system by at least one radio device which supports at least one first service and one second service. Base stations signal which services they respectively support. Primary data records of base stations, which signal the support of the first service, are stored by the radio device in a first list, and secondary data records of base stations, which signal the support of the second service, are stored in the second list. The connection-relevant data are therefore stored in the lists and separated according to services. If the signaling changes, the lists are updated accordingly. 
   An advantage of the method according to the present invention is the storage, separated according to supported services, of the data of a number of base stations, which offer themselves as alternatives for the support of a specific service. 
   An advantage of a further development of the present invention is the guarantee that a connection is set up to the base station with the best transmission characteristics. 
   An advantage of another embodiment the present invention, in a further embodiment, a simplification of the method since the structuring of the list is carried out independently of measurements of the base stations. 
   An advantage of another embodiment is the simple and low-cost implementation of the method, since no additional measurements or data evaluation are required in order to determine the sequence of data records within a list. 
   An advantage of yet another embodiment of the present invention is the guarantee that a connection is set up. 
   Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  shows a radio telecommunications system with base stations, mobile stations and a network termination designed as a mobile station. 
       FIG. 2  shows a flow diagram of the method for selecting base stations in the radio telecommunications system according to  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a telecommunications system designed as a DECT system with radio cells PC 1  and PC 2  designed as picocells. Information is transmitted, in each case, via a DECT air interface designed according to the DECT standard, via which the “DECT radio channel” wireless transmission medium is accessed through a combination of FDMA, TDMA and TDD access methods (Frequency Division Multiple Access/Time Division Multiple Access/Time Division Duplex). Ten carrier frequencies, each with a channel spacing of 1.728 MHz, are available in the frequency range between 1880 MHz and 1900 MHz (FDMA), whereby the time frame defined for each carrier is divided up into 24 time slots or channels (TDMA). 
   For transmitting voice data, DECT fixed parts FP 11 , FP 21 , FP 22  use time slots with a transmission rate of 32 kbit/s (Full Slot), corresponding to a first service D 1 . Time slots with a transmission rate of 64 kbit/s, corresponding to the second service D 2  (Double Slot), are used by the DECT fixed part FP 22  above all for the transmission of packet data. A radio network termination RNT to which a telephone T is connected and a DECT mobile part PP can be connected in a wireless manner to the DECT fixed parts FP 11 , FP 21 , FP 22  via the DECT air interface. The DECT mobile part PP and the radio network termination RNT similarly support the first service D 1  of the DECT system and the second service D 2  of the DECT system. The DECT mobile part PP and the radio network termination RNT store connection-relevant data of the DECT fixed parts FP 11 , FP 12 , FP 21 , FP 22 , which use “Full Slots”, as primary data records in the form of a first list L 1  in a first memory SP 1  and connection-relevant data of the DECT fixed parts FP 11 , FP 12 , FP 21 , FP 22 , which use “Double Slots”, as secondary data records in the form of a second list L 2  in a second memory SP 2 . 
   Alternatively, it is also possible for the data records or lists L 1 , L 2  to be stored in a single memory. 
   An alternative embodiment of the radio telecommunications system from  FIG. 1  is provided if the first service D 1  is made available within a first radio cell which, for example, has a radio range according to the DECT standard, and the second service D 2  is made available within a second radio cell which, for example, has a radio range according to the GSM standard, whereby the DECT radio coverage area is partially or fully covered by the GSM radio coverage area in order to enable the implementation of a universal telecommunications system, for example UMTS. In this embodiment, the case may occur wherein the type of data in the first service D 1  and in the second service D 2  are the same, for example voice data, but differ in terms of the different radio ranges of the radio cells in which they are made available. The primary and secondary data records are then stored according to the radio ranges in the first list L 1  or the second list L 2 . 
   In the event that the types of data transmitted in the first service D 1  and in the second service D 2  differ from one another (e.g., first service D 1 : voice data, second service D 2 : packet data) and are made available in radio cells with different radio ranges, the primary and secondary data rates can be stored in the first list L 1  or second list L 2  according to the radio range or on the basis of the service D 1 , D 2  which is provided. 
   In  FIG. 2 , the method for selecting base stations is described with reference to a flow diagram, the method being carried out in an arrangement according to  FIG. 1  between the DECT fixed parts FP 11 , FP 21 , FP 22 , the DECT mobile part PP and the radio network termination RNT. 
   In the initial condition, first DECT fixed parts FP 21 , FP 22  signal to the DECT mobile part PP and the radio network termination RNT which service D 1 , D 2  they support. In addition, the radio network termination RNT receives the signaling of the supported service D 1 , D 2  from the second DECT fixed part FP 11 . In the DECT mobile part PP and the radio network termination RNT, a check is first carried out to ascertain whether signaling has taken place; i.e., whether an update of the relevant list(s) L 1 , L 2  is required. 
   If this is the case, the primary data records from the DECT fixed parts FP 11 , FP 21 , FP 22  signaling the support of the first service D 1  are stored in the form of the first list L 1  in the memory SP 1 , SP 2  and/or secondary data records from the DECT fixed parts FP 11 , FP 21 , FP 22  signaling the support of the second service D 2  are stored in the form of the second list L 2  in the memory SP 1 , SP 2 . The sequence of the data records stored, or to be stored, in the lists L 1 , L 2  is derived from the sequence in which the signaling is received. 
   Alternatively, the data records stored or to be stored can be arranged within the list L 1 , L 2 , according to transmission characteristics of the corresponding DECT fixed parts FP 11 , FP 21 , FP 22 , or according to ordering criteria based on the type of data records stored or to be stored; e.g., alphabetically or numerically. 
   If this is not the case, i.e. an update is not required, a connection request is expected. 
   If the DECT mobile part PP or the radio network termination RNT wishes to set up a telecommunications connection, a first data record of the primary or secondary data record is, in each case, read from the relevant list L 1 , L 2  in order to initiate the connection set-up according to the required service D 1 , D 2 . The associated DECT fixed part FP 11 , FP 21 , FP 22  is then determined from the data record and the connection to this DECT fixed part FP 11 , FP 21 , FP 22  is set up. If this connection is not established, a second (further) data record of the primary or secondary data records is read from the relevant list L 1 , L 2  and a connection initiation is started. If no further data record exists within the list L 1 , L 2 , the procedure restarts with the first data record of the list L 1 , L 2 . 
   Alternatively, if no further data record exists, following a predefined pause time, during which the telecommunications connection set-up is temporarily impossible (e.g., interruption of the telecommunications connection set-up), the procedure can restart with the first data record.