Abstract:
A method for transmitting signaling is proposed which is simple and efficient without taking up significant transmission capacity. In the method, a transmission of the signaling takes place between a mobile station ( 12 ) and a base station ( 11 ) in a mobile radio network. The signaling is transmitted in at least one predetermined time slot ( 301 ), and a different signaling is assigned to each mobile station ( 12 ) disposed in a radio cell of the base station ( 11 ), so that signaling operations of various mobile stations, transmitted via the at least predetermined time slot, can be distinguished from one another in the base station ( 11 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention is based on a method for transmitting signaling. 
     Methods for transmitting signaling between a mobile station and a base station in a mobile radio network are already known, for instance from the publication entitled “Fast Uplink Signalling Mechanism for FDD and TDD systems”, Tdoc SMG2 UMTS-L1 227/98, Philips Research Laboratories, 1998. 
     SUMMARY OF THE INVENTION 
     The method according to the invention having the characteristics of the main claim has the advantage over the prior art that the signaling is transmitted in at least one predetermined time slot, and a different signaling is assigned to each mobile station disposed in a radio cell of the base station, so that signaling operations of various mobile stations transmitted via the at least one predetermined time slot can be distinguished from one another in the base station. In this way, an unambiguous signaling can be achieved. It is as a rule therefore unnecessary to repeat the transmission of the signaling. Hence the signaling leads to the desired outcome especially quickly. This assures that the least possible use will be made of transmission resources. Signaling of a plurality of mobile stations is possible by using only a single joint time slot. 
     By the provisions recited in the dependent claims, advantageous refinements of and improvements to the method defined by the main claim are possible. 
     It is advantageous that each of the mobile stations is assigned its own signaling in the form of a different code. Especially in a mobile radio network based on code division multiple access with orthogonal codes, this makes it possible to achieve an umambiguous signaling, using the available codes, in a simple and efficient way without significantly claiming additional transmission resources. 
     Another advantage is that signaling received in the base station is correlated with all the codes assigned to the mobile stations, in order to ascertain the mobile station associated with the signaling received. In this way, the base station can unambiguously determine the mobile station that has transmitted the signaling. 
     It is especially advantageous that the mobile stations are each assigned a time lag by which a predetermined signaling sequence is transmitted in delayed fashion in the at least one predetermined time slot. This provides an alternative possibility of unambiguous, efficient signaling, in which only one time slot and one predetermined signaling sequence are required. 
     Another advantage is that the predetermined signaling sequence is transmitted in spread form by means of a predetermined code. In this way, transmission of the signaling can be achieved while claiming minimal transmission capacity, especially whenever the predetermined code is taken from a set of orthogonal codes, for instance for use in a code division multiple access system. 
     It is also advantageous that in the base station, on the basis of the amplitude course over time of the received predetermined signaling sequence, the time lag employed is detected in order to ascertain the assigned mobile station. In this way, the base station can unambiguously determine which mobile station sent the signaling. 
     Another advantage is that the signaling operations are transmitting with a power that is substantially lower than the power for transmitting useful data. In this way, the additional interference caused by the signaling is minimized. 
     It is also advantageous that at least one of the signaling operations is transmitted together with another signaling or with useful data of an already existing connection in the at least one predetermined time slot. This economizes on transmission capacity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are shown in the drawing and explained in further detail in the ensuing description. 
         FIG. 1  shows a mobile radio network in simplified form; 
         FIG. 2  shows the layout of a burst for a transmission in a time division duplex operating mode; 
         FIG. 3  shows the layout of a transmission frame in the time division duplex operating mode; and 
         FIG. 4  shows a code tree for generating a code. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a mobile radio network  10 , which can for instance be embodied by the GSM standard (Global System for Mobile Communication) or the UMTS standard (Universal Mobile Telecommunications System), not only the useful data, which are present for instance in the form of speech signals, but also signaling data, for instance for hand-over procedures or for setting up new channels must be transmitted both in a downlink transmission direction  13  from a stationary base station  11  to a mobile station  12  as in  FIG. 1  but also in an uplink transmission direction  14  from the mobile station  12  to the base station  11 . The invention will be described below in terms of a mobile radio network, as an example on the basis of a mobile radio network  10  by the UMTS standard, which will hereinafter be called a UMTS mobile radio network  10 . 
     In the UMTS mobile radio network  10 , two modes for transmission by way of the air interface are provided: In an FDD mode (Frequency Division Duplex), two different frequencies exist for the uplink transmission direction  14  and the downlink transmission direction  13 . In a TDD mode (Time Division Duplex), only a single carrier frequency is used for both transmission directions, and by the allocation of time slots a separation between the downlink transmission direction  13  and the uplink transmission direction  14  is made. 
     The signals of various subscribers of the mobile radio network are separated from one another by spreading using orthogonal codes. In the TDD mode, the thus-spread signals of the various subscribers are transmitted within the same time slot. 
     It will be assumed as an example below that the UMTS mobile radio network  10 , shown in simplified form in  FIG. 1 , is embodied by the TDD mode.  FIG. 3  shows the layout of a transmission frame  30  used for the purpose. Each transmission frame, in this example, has a chronological length of 10 ms and comprises a total of fifteen time slots  301 ,  302 , . . . ,  315 . A first time slot  301  is to be reserved for transmission in the uplink transmission direction  14 , and a second time slot  303  is to be reserved for transmission in the downlink transmission direction  13 . Within each of the time slots  301 ,  302 , . . . ,  315 , precisely one so-called TDD burst  20  as in  FIG. 2  can be transmitted. This burst comprises two data blocks  21 ,  23  for data transmission, a midamble block  22  for channel estimation, and a protective spacing  24 . 
     Within each of the time slots  301 ,  302 , . . . ,  315 , useful data from a maximum of sixteen subscribers can be transmitted, on the principles of a CDMA system (Code Division Multiple Access). To achieve this, the useful data to be transmitted from the various subscribers must be spread in the applicable time slot before being transmitted. In  FIG. 4 , a code tree is shown, with the aid of which so-called OVSF (Orthogonal Variable Spreading Factor) codes are created for spreading the useful data to be transmitted. 
     Along with the useful data, signaling operations are also transmitted between the mobile station  12  and the base station  11 . These signaling operations can serve for instance to request a transmission channel, send a command for regulating the transmission power, or transmit a reference signal for a channel estimation. In all these cases named, a reaction to the signaling is to be brought about in the station that receives the signaling. This reaction, for the cases cited as examples, then comprises either the allocation of a transmission channel, the adjustment of the transmission power, or the estimation of the channel pulse response on the basis of the reference signal received, for instance for use for a predistortion by a JP (Joint Predistortion) process. Below, how such signaling operations are transmitted from the mobile station  12  to the base station  11  will be described, taking as an example signaling for requesting a transmission channel. 
     In a first exemplary embodiment, the signaling operations are generated from the OVSF codes described. The code tree shown in  FIG. 4  illustrates the generation of the OVSF codes up to a spread factor SF=8. In the TDD of the UMTS mobile radio network  10 , OVSF codes with spread factors SFε{1,2,4,8,16} are currently possible. With the aid of the OVSF codes, orthogonal code sequences can be generated, and an essential property is that codes of different length are also orthogonal to one another. 
     In this first exemplary embodiment, transmission of the signaling operations is meant to be possible only in the first time slot  301 . Within the first time slot  301 , all the signaling operations are generated from a certain, previously defined spreading code of length  16 , where the spread factor SF is thus 16. For instance, the last spreading code with the spread factor SF=16 selected, which in  FIG. 4 , where the code tree is shown up to the spread factor SF=8, would be located at the lowermost point if continued appropriately. This lowermost branch of the code tree with the spread factor SF=16 is now expanded up to the spread factor or length of  256 . Thus within the first time slot  301 , a total of sixteen codes are available for the signaling. In other words, sixteen codes with a spread factor of  256  of the OVSF codes are used for the signaling. 
     With these codes of length  256  for the signaling, only one signaling burst is now constructed, which has the same structure as the TDD burst  20  shown in  FIG. 2 . The code for the signaling is repeated within the data blocks  21 ,  23  until such time as these blocks are filled; the code for the signaling can be cut off at the last required repetition for filling up the data blocks  21 ,  23 . In the first time slot  301 , the midamble block  22  is also allocated to each such TDD burst  20  embodied as a signaling burst. 
     Among the codes described for signaling, the code that would be located at the very bottom in the code tree of  FIG. 4 , with the spread factor SF=256, is allocated or assigned to the mobile station  12 , for instance at the time of check-in into the radio cell of the base station  11 . It could additionally be agreed that the mobile station  12  has complete authority for signaling. Then mobile stations without authority for signaling are not allocated any codes for signaling. Each mobile station authorized for signaling is assigned a different code for signaling. If the mobile station  12  requires only one channel for useful data transmission in the uplink transmission direction  14 , hereinafter called the uplink channel, then in the first time slot  301 , it sends its allocated code for signaling in order to request such a channel, whereupon the base station  11  informs the mobile station  12  of the parameters for such an uplink channel in the second time slot  303 . The allocated uplink channel can also be located in the first time slot  301 , so that in the subsequent transmission frame  30  the mobile station  12  can likewise begin to transmit the useful data in the first time slot  301 . 
     The transmission power of the signaling burst  20  is substantially below the transmission power of a normal burst for transmitting useful data. Thus the additional interference in the uplink transmission direction  14 , caused by the use of the signaling burst  20 , is minimal. Detecting the signaling code, received in the base station  11 , and thus detecting the mobile station  12  assigned to this signaling, is done by correlation with the sixteen different predetermined codes for signaling. Alternatively, the signaling codes can be detected by a JD (Joint Detection) process. 
     In the event that the sixteen predetermined codes for signaling in the first time slot  301 , as the sole time slot used for signaling per transmission frame  30 , are too few, the transmission of the signaling could be expanded to additional time slots in the uplink transmission direction  14 . It would also be conceivable to increase the number of predetermined codes for signaling, by using even higher spread factors than 256 in the code tree for generating these signaling codes. For instance, if an expansion to the spread factor SF=1024 is accomplished, a total of sixty-four codes for signaling are available. 
     In a second exemplary embodiment, the signaling can be performed in still another way. In the first exemplary embodiment, the OVSF codes are used directly as codes for signaling. In the second exemplary embodiment, although once again a specific OVSF code with the spread factor SF=16 is now to be reserved again for the signaling, for instance the lowermost code in the code tree having the spread factor SF=16. However, this code is used for spreading a signaling sequence that is predetermined for all the mobile stations in the radio cell of the base station  11  that are authorized for the signaling. This signaling sequence is a fixed symbol sequence, identical for all the mobile stations authorized for signaling in the radio cell of the base station  11 , with good autocorrelation properties. The signaling sequence is spread with the OVSF code predetermined or reserved for the purpose and is transmitted in the data blocks  21  and  23  of the signaling burst  20 . The signaling sequence should comprise enough symbols that, being spread with the spread factor SF=16, it lasts precisely as long as the two data blocks  21  and  23  together. Each mobile station that uses this signaling sequence is allocated a different time lag for starting the signaling sequence. The mobile station  12  begins with the start of the signaling sequence exactly at the time of the start of the signaling burst  20 , shown in  FIG. 2  and used for the signaling. A second mobile station, not shown, in the radio cell of the base station  11  begins with its start of the signaling sequence four symbols later, for instance. This is equivalent to a time lag of sixty-four chips. Since the signaling sequence however contains four symbols more than can be transmitted, beginning with the aforementioned time lag, in the data blocks  21 ,  23 , the remaining four symbols are transmitted at the beginning of the signaling burst  20 . The signaling sequence is accordingly transmitted, cyclically delayed, for different mobile stations, and each time lag unambiguously identifies the mobile station  12  associated with this time lag. The time lag for the various mobile stations comprises multiples of four symbols, that is, multiples of sixty-four chips after spreading by the spread factor SF=16. This value of four symbols is equivalent to a maximum incident length of the transmission channel of sixty-four chips. The result is thirty possible different time lags, or thirty different mobile stations, per time slot used for the signaling in the uplink transmission direction  14 . The cyclically delayed signaling sequence is then further spread with the predetermined OVSF code described, so that the orthogonality relative to the other signals transmitted in the same time slot will be assured. Once again, each signaling burst  20  is allocated its own midamble block  22 . 
     The transmission power of this signaling burst  20  is once again very low in comparison with useful data bursts. The detection of the signaling bursts  20  received in the base station  11  is effected after the unspreading, for instance by means of a matched filter with peak detection. Depending on the point in time in the amplitude course of the received and unspread signaling burst  20  when a maximum value occurs, a conclusion can be drawn as the fundamental time lag and the transmitting mobile station associated with it, and accordingly the construction of an uplink channel requested by the signaling can be initiated. The unspreading of the signaling burst can also be performed a JD process. 
     In both exemplary embodiments, the signaling can be detected especially quickly, if the transmission quality allows this: If the detection quality within the first data block  21  is already sufficient to make a reliable decision, then the evaluation of the second data block  23  can be dispensed with. 
     In a further embodiment, it can additionally be provided that the spread signaling sequence be transmitted in only one of the two data blocks  21 ,  23 . To that end, in comparison with the embodiment described above, the signaling sequence is divided in half in terms of its length. Thus the various mobile stations can additionally be distinguished from one another in the base station  11  according to which of the two data blocks  21 ,  23  the signaling sequence was transmitted in and was received in the base station  11 . 
     Because of the rigid dividing up of the time slots to the different transmission directions, namely the downlink transmission direction  13  or the uplink transmission direction  14 , the advantage of fast signaling, for instance in the uplink transmission direction  14 , can under some circumstances be limited, especially if only one time slot in the uplink transmission direction  14  per transmission frame  30  is allocated. 
     This can be counteracted by providing that the transmission of the signaling, in the first or second exemplary embodiment, in the uplink transmission direction  14  is also made possible by using a time slot in the downlink transmission direction  13 . In general, the signaling can be transmitted together with another signaling or with useful data of an already existing connection, within a joint time slot. 
     Because of the low transmission power provided for transmitting the signaling burst  20 , only slight additional interference need be expected. However, both in the first and the second exemplary embodiment, it must be assured that the spreading code reserved for transmitting the signaling, having the spread factor SF=16, not be used in the downlink transmission direction  13 . 
     The use of a joint time slot for signaling as described forms its own signaling channel, which is also known as a FAUSCH (Fast Uplink Signaling CHannel) for the uplink transmission direction  14 . Although with the FAUSCH a new channel is introduced in the uplink transmission direction  14 , still the required changes in the mobile station  12  and the base station  11  are only slight. 
     An advantage of the method of the invention is the capability of the mobile station  12 , in the TDD mode, of transmitting a 1-bit signaling, for instance, without a time lag in the intended or predetermined joint first time slot  301  to the base station  11 ; in the base station  11 , the signaling then leads to a previously defined reaction and at the same time does not represent any significant worsening of other channels.