AU4602099A - Method and radio station for signal transmission in a radio communication system - Google Patents

Description

GR 98 P 1831 Description Method and radio station for signal transmission in a radio communications system 5 The invention relates to a method and a radio station for signal transmission in a radio communications system, in particular in a mobile radio system. 10 In radio communications systems, information such as voice, video information or other data is or are transmitted by means of electromagnetic waves via a radio interface between a transmitting and a receiving radio station, for example a base station and a mobile 15 station, respectively, in the case of a mobile radio system. The electromagnetic waves are in this case transmitted at carrier frequencies which are in the frequency band intended for the respective system. The carrier frequencies for the GSM mobile radio system 20 (Global System for Mobile Communication) are in the 900 MHz, 1 800 MHz and 1 900 MHz bands. Carrier frequencies in the band around 2 000 MHz are intended to be used for future mobile radio systems using CDMA and TD/CDMA transmission methods via the radio 25 interface, such as the UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems. The signals to be transmitted are produced in a transmitting devices in the radio station. The 30 transmission signals are supplied via cable links and various other devices such as preamplifiers etc. to an antenna device which, in the end, transmits the radio signals. The transmitted radio signals are received and evaluated by a receiving devices in the received radio 35 station.

GR 98 P 1831 - 2 In real operational conditions for radio communications systems, the radio signals are subject to widely differing types of interference and reach the receiving device on very different propagation paths. 5 Apart from a direct propagation path, the radio signals can also be reflected or refracted on obstructions such as mountains, trees, buildings and the like. The radio signals from the various propagation paths are super imposed in the receiving device. This leads to 10 cancellation effects which at times have a severe adverse effect on reception of the radio signals, in this context refer to J.D. Parsons, "The Mobile Radio Propagation Channel", Pentech Press Publishers, London, 1992, pages 108-113. 15 Various methods are known for overcoming these cancellation effects, which are also referred to as fading effects. These fading effects can be reduced by antenna diversity, that is to say by using a number of antennas for the transmitting and/or receiving device. 20 However, since the use of antenna diversity means an increase in the costs and complexity in the base station and in the mobile station of a mobile radio system, antenna diversity has so far been used only in the base stations. 25 Furthermore, it is known from the GSM mobile radio system for the reception conditions to be improved by using a frequency hopping method (FH), that is to say changing the transmission frequency for the radio signals (M. Mouly, M.B. Pautet, "The GSM System 30 for Mobile Communications", 1992, inter alia, pages 218-223). Furthermore, methods and devices are known from the prior art according to the documents DE 44 32 928, WO 93/20625 and WO 95/32558 which use a combination of a frequency hopping method and an 35 antenna diversity method. Apart from complex implementation, these methods have the disadvantage that they cannot be used for the broadband 3rd generation mobile radio systems, for which it is predicted GR 98 P 1831 - 3 that only one frequency band will in each case be available for the uplink and downlink direction for the FDD method (FDD - Frequency Division Duplex), and one frequency band for the uplink and downlink direction 5 for the TDD method (TDD - Time Division Duplex). A mobile radio system based on microcells is known from the article by Kondo, -Suwh "Linear Predictive Transmission Diversity for TDMA/'DD Personal Communication Systems", IEICE Trans. Commun., 10 Vol. E79-B, No. 10, October 1996, pages 1586-1591, in which the base station makes a linear prediction of the signal strength at the mobile station on the basis of the reciprocity between the uplink and the downlink direction. The base station receives a signal in the 15 uplink direction from the, mobile station using reception diversity by means of two antenna devices, and measures the signal strength of the received signal during the reception time. The base station uses these measurements to determine which antenna produces the 20 greatest signal strength at the mobile station location, and the base station then transmits the signal in the downlink direction via the predicted antenna. The invention is based on the object of 25 specifying a method and a radio station which allow the cancellation effect in future radio communications systems to be reduced. This object is achieved by the method as claimed in the features of the independent patent claim 1, and by the radio station as claimed in 30 the features of the independent patent claim 17. Developments of the invention can be found in the dependent claims. According to the invention, in the method for signal transmission via a radio interface in a radio 35 communications system as claimed in the independent patent claim 1, which uses a GR 98 P 1831 - 4 subscriber separation method to distinguish between signals, in which a radio channel is defined at least by a frequency band and a connection-specific fine structure, at least one radio channel is assigned for 5 signal transmission between a first and a second radio station, and at least one signal is transmitted via at least two transmission paths. At least one characteristic value relating to the transmission conditions on the radio interface is' determined for 10 each transmission path. A control signal is derived from a comparison of the mutually corresponding characteristic values, by means of which control signal the transmission path is selected specifically for the radio channel for transmitting a subsequent signal. 15 This method advantageously offers the capability to determine a characteristic value for each transmission path, in order to carry out an assessment of the transmission conditions for this transmission path. The comparison of the respective characteristic 20 values determined for each transmission path is used to select the most suitable path, and one or more subsequent signals are transmitted on this path. The determination of the characteristic values is carried out separately and specifically for each radio channel, 25 since the transmission conditions may differ depending on the respectively used connection-specific fine structure. In consequence, the special feature of this system, which is that a number of radio channels within one frequency band are used for signal transmission, is 30 taken into account since the optimum transmission path is determined for each radio channel, as a result of which the transmission characteristics are advantageously optimized. According to a first development of the 35 invention, the signal is sent by the second radio station and is received via at least two antenna devices of the first radio station using GR 98 P 1831 - 5 diversity reception. The characteristic values are determined, and the control signal derived, from the signal received by the respective antenna device. The control signal actuates a switching device which 5 switches a subsequent signal specifically for the radio channel to one of the antenna devices of the first radio station. With this refinement, it is possible to determine in the first radio station the antenna device, that is to say the transmission path, via which 10 it is better to receive the signal sent by the second radio station. The result of the reception situation allows conclusions to be drawn on the transmission situation for the first radio station, and advantageously makes it possible to use the switching 15 device to select the antenna device which offers the better transmission quality. As an alternative to the first development, according to a second development of the invention, the signal is transmitted, separated in time, via in each 20 case one transmission path. Based on this feature, a further refinement of the invention means that the signal which is separated in time is sent by in each case one antenna device of the first radio station, and is received by the second radio station. The 25 characteristic values are determined from the respectively received signal, and the control signal is derived from their comparison. The control signal is used to actuate a switching device, which switches a subsequent signal specifically for the radio channel to 30 one of the antenna devices of the first radio station. This refinement advantageously allows the transmission conditions on the radio interface to be determined in the second radio station if the latter has only one antenna device, and allows the subsequent signals to be 35 switched to one of the antenna devices of the first radio station.

GR 98 P 1831 - 6 In this case, according to further alternative refinements, the characteristic values determined in the second radio station can be transmitted to the first radio station, which derives the control signal 5 from them and actuates the switching device, or the control signal is derived- in the second radio station from the specific characteristic values and this are transmitted to the first radio station, with the control signal actuating the switching device in the 10 first radio station. As a * consequence of a further development, the characteristic values and the control signal can advantageously be transmitted using in-band signaling since, in consequence, there is no disadvantageous effect on the transmission capacity of 15 the respective radio channel. According to a further development of the invention, when a number of radio channels are assigned for signal transmission between the first radio station and the second radio station, the control signal is 20 derived from a comparison of all the mutually corresponding characteristic values intended for the respective radio channels. The control signal is used to select a common transmission path for all the radio channels for the subsequent signals. This method, which 25 is referred to as channel pooling, is known inter alia from the article by J. Mayer, J. Schlee, T. Weber "Protocol and Signalling Aspects of Joint Detection CDMA", PIMRC'97, Helsinki, 1997, pages 867-871. The channel pooling method is used advantageously, for 30 example, in order to allow communications links to be provided with different data rates to and from radio stations, or to allow a number of services to be operated in parallel on one communications link. As a consequence of a further refinement of the 35 invention, the- connection-specific fine structure is formed by a CDMA code. The subscriber separation methods chosen for the third generation mobile radio system UMTS, according to which GR 98 P 1831 - 7 a distinction is drawn between subscribers on the basis of the respective CDMA code, advantageously allows a large number of radio channels in one broadband frequency band, and thus high utilization of scarce 5 radio resources. Based on this refinement, a further refinement uses a TD/CDMA method as the subscriber separation method. In this case; a radio channel is defined by a frequency band, a timeslot and a CDMA code. This subscriber separation method can be used 10 particularly advantageously if the signals are transmitted using a TDD method. In this case, the signals are transmitted from the first radio station to the second radio station, and from the second radio station to the first radio station, separated in time, 15 in one frequency band. The refinement according to the invention allows the most suitable transmission path to be determined specifically for each radio channel in a timeslot, and to be used for transmitting subsequent signals. 20 In addition to the selection of -a transmission path, further refinements of the invention allow at least two successive signals to be transmitted, using a TD/CDMA subscriber separation method, with the timeslot being changed and/or with the frequency band being 25 changed, and with the respectively used timeslot or the respectively used 'frequency band being changed periodically and in synchronism with the time protocol of the subscriber separation method. These refinements have the advantage \of increased transmission quality 30 since, in consequence, interference which occurs in specific timeslots or in a specific frequency band interferes - with only a small proportion of the transmitted signals, and thus has only a minor effect on reception, as a result of these changes.

GR 98 P 1831 - 8 As a result of a further advantageous development of the invention, the transmitted signals are received in the first radio station and/or in the second radio station using a joint detection method. 5 This method, which is known inter alia from the article by J. Mayer et. al. already mentioned above, allows the reception quality to be increased advantageously since all the fine structures in use are used for detection of a signal which is coded by means of a connection 10 specific fine structure. According to a further refinement of the invention, the characteristic value can be related to a reception level, a bit error rate and/or a value proportional to the signal delay time between the first 15 radio station and the second radio station, and/or to a signal-to-noise ratio. Characteristic values which can be found particularly easily in radio communications systems are the reception level and the bit error rate (which are quoted as scaled values RXLEV, RXQUAL) 20 since, as a rule, they already exist in present-day implementations. The method according to the invention and the radio station according to the invention will now be explained in more detail with reference to 25 illustrations in the drawings, in which: Figure 1 shows a block diagram of a radio communications system, in particular of a mobile radio system, and a radio communications system-typical operational 30 environment which is characterized by multi path propagation, Figure 2 shows a schematic illustration of the frame structure of the radio interface, and of the construction of a radio block, 35 Figure 3 shows a block diagram of the radio station according to the invention as a base station and a mobile station in a mobile radio system, GR 98 P 1831 - 9 Figure 4 shows a flowchart of the method according to the invention for the radio communications system as shown in Figure 1, and Figure 5 shows an illustration with respect to time of 5 an example of signal transmission from the point of view of a base station in a mobile radio system. The radio communications system illustrated in Figure 1 and in the form of a" mobile radio system 10 comprises a large number of mobile switching centers MSC, which are networked to one another and produce access to a landline network PSTN. Furthermore, these mobile switching centers MSC are each connected to at least one device RNM for allocating radio resources. 15 Each of these devices RNM in turn allows a connection to be set up to at least one base station BS. Such a base station BS is a radio station which can set up links via a radio interface to other radio stations, for example to mobile stations MS or to stationary 20 terminals. At least one radio cell is formed by each base station BS, and radio stations located in the area of this radio cell are supplied with radio resources. In addition, a number of radio cells can be supplied by each base station BS if sectorization is used or if the 25 cell structures are hierarchical. In real operational conditions for radio communications systems, radio signals are subject to widely differing types of interference between the base station BS and the mobile station MS, which is 30 mentioned by way of example, and reach the receiving device in the mobile station MS on very different propagation paths. Apart from a direct propagation path, the radio signals can also be reflected or defracted on obstructions such as mountains, trees, 35 buildings or the like. The radio signals from the various propagation paths are superimposed in the receiving device, which leads to cancellation effects which can severely adversely affect reception of the radio signals. The GR 98 P 1831 - 10 functionality of the illustrated structure is used by the radio communications system according' to the invention. The frame structure of the radio interface, as 5 it is implemented in the third generation mobile radio' system UMTS, is shown in Figure 2. A broadband frequency band, for example with a bandwidth of B = 5 MHz, is split in accordance with a TDMA component into a number of timeslots ts, for example 16 timeslots 10 tsl to ts16. Each timeslot ts within the frequency band B forms a frequency channel fk. The successive timeslots ts within the frequency band B are broken down in accordance with a frame structure. Thus, for example, 16 timeslots tsl to ts16 are combined to form 15 a frame fr. When using a TDD transmission method, some of the timeslots tsl to ts16 are used for signal transmission in the uplink direction, and some of the timeslots tsl to ts16 are used for transmission in the 20 downlink direction, with the transmission in the uplink direction taking place, for example, at a time before the transmission in the downlink direction.. In-between, there is a switching point SP, by means of which it is possible to vary the number of timeslots which are used 25 for transmission in the uplink direction and the number of timeslots for the downlink direction in a flexible manner. A frequency channel fk for the uplink direction in this case corresponds to the frequency channel fk for the downlink direction. The other frequency 30 channels fk are structured in the same way. Within the frequency channels fk which are intended for user data transmission, information from a number of communications links is transmitted in radio blocks. These radio blocks for user data transmission 35 are composed of sections with data d, each of which has sections embedded in it containing training sequences tseql to tseqn which are known at the reception end. The GR 98 P 1831 - 11 data d are spread on a connection-specific basis using a fine structure, a spread code c (CDMA code) \ so that, for example, n links can be separated by this CDMA component at the reception end. 5 The spreading of individual symbols' of data d with Q chips means that subsections of duration tchip are transmitted within the symbol duration tsym. The Q chips in this case form the individu-al CDMA code c. A guard time gp is also provided within the timeslot ts, 10 to compensate for different signal -delay times on the links for successive timeslots ts. By way of example, Figure 3 shows two radio stations, which are in the form of a base station BS and a mobile station MS in a mobile radio system. There 15 is a radio link for signal transmission between the two radio stations BS and MS. The base station BS is equipped with two antenna devices Al and A2 and a transmitting/receiving device TRX, via which it can transmit and receive user and signaling information. An 20 evaluation device AW, which is also provided in the base station BS, is supplied with signals output from the respective reception path of the two antenna devices Al and A2, and characteristic values relating to the transmission conditions of the radio interface 25 are in each case determined from them. Such characteristic values, which may be obtained only after internal conversions in the evaluation device AW, are, for example, the reception lever RXLEV, a scaled variable relating to the bit error rate RXQUAL, a lead 30 time ta or a signal-to-noise ratio C/I. The characteristic values RXLEV, RXQUAL can be signaled, for example, by the mobile station MS as in the GSM mobile radio system, while the details relating to the signal delay time can be obtained in the form of the 35 lead time ta, and the details relating to the signal to-noise ratio C/I GR 98 P 1831 - 12 can be obtained from the received signals in the base station BS itself. The characteristic values determined for the respective reception path are supplied to a control 5 device SE' which is connected downstream of the evaluation device AW and carries out a comparison of respectively mutually corresponding characteristic values. The control device SE uses this comparison to derive a control signal stsig and thus actuates a 10 switching device UE which switches signals to be sent in radio channels downstream of the transmitting/receiving device TRX to one of the antenna devices Al or A2. In this cas-e, the signals can be switched independently for transmission and reception, 15 that is to say the signals sent by the mobile station MS are, for example, received via both antenna devices Al and A2 and are supplied to the transmitting/receiving device TRX. This is used advantageously according to the invention if the 20 reception of the radio channels in the base station BS takes place using a joint detection method. Various scenarios are feasible for determining the characteristic values and for deriving the control signal stsig. According to a first example, this can be 25 done by the mobile station MS sending a signal in an assigned radio channel, with this signal being received by the two antenna devices Al and A2 using a diversity principle. The evaluation device AW uses this received signal to determine the respective characteristic 30 values for the subsequent determination of which transmission path and which antenna device Al or A2 offers the better transmission conditions. This determination process related to reception allows the transmission situation to be deduced, since the 35 transmission conditions are generally identical for transmission and reception. The control device GR 98 P 1831 -13 SE in the base station BS selects that antenna device Al or A2 via which signals are then sent in the downlink direction in the same radio channel. A second example indicates a further option. In 5 this case, a signal is in each case transmitted in a radio channel to the mobile station MS, separated in time, by the base station BS. Time separation is required since the mobile station MS has only one antenna device A3 and is thus unable to receive two 10 signals in the same radio channel at the same time. The mobile station MS is in this case equipped with an evaluation device AW in which it can - determine characteristic values relating to the transmission conditions on the respective transmission path. These 15 characteristic values which have been determined are then sent by the mobile station MS, for example via in band signaling, to the base station BS, in which the values are supplied to the control device SE which uses them to derive the control signal stsig for actuating 20 the switching device UE. According to a third example, the mobile station MS may also be equipped with a control device SE, using which it derives a control signal stsig directly from the characteristic values determined in 25 the evaluation device AW, and transmits this control signal stsig to the base station BS, with the switching device UE being actuated by this control signal stsig. Furthermore, it is feasible for characteristic values relating to the transmission conditions for the 30 radio channel to be determined both in the base station BS and in the mobile station MS, and for these values to be supplied to the control device SE in the base station BS, which means that it is possible to make a more accurate estimate GR 98 P 1831 - 14 of the actual transmission conditions on the radio interface. The characteristic values should be determined separately for each radio channel in a timeslot in a 5 radio communications system having TD/CDMA subscriber separation, since the different CDMA spread codes c, as a result of which the radio channels in a timeslot ts differ, mean that different transmission conditions may also occur. In the situation where a number of radio 10 channels are assigned in one timeslot ts for signal transmission between the base station BS and the mobile station MS, for example using the channel pooling principle as has already been explained in the introduction to the description, characteristic values 15 are determined separately for each radio channel and signals which in each case have to be sent from the base station BS are sent via the antenna device Al or A2 which has the better transmission conditions. During the process of assigning radio channels in a timeslot 20 ts to a number of mobile stations MS, this refinement means that the best transmission path is selected for each radio channel. Depending on the selected antenna device Al, A2 via which subsequent signals will be sent in the respective radio channel, the transmission power 25 for each timeslot ts and CDMA code c can be controlled separately, as it were. The method according to the invention can also be applied, for example, in the same way to CDMA subscriber separation methods, in which a radio channel 30 is in each case defined by the frequency band B and a CDMA code c. In this case, characteristic values are in each case determined and a transmission path for the radio channel is selected, for example, at periodic time intervals.

GR 98 P 1831 - 15 The method according to the invention can be simplified in that, for example, a number of radio channels which have been assigned to a single communications link between the base station B& and a 5 mobile station MS on the channel pooling principle are each sent via only one antenna device Al or A2 of the base station BS if the differences in the transmission conditions on the basis of the different CDMA code c are not significant. This likewise simplifies the 10 process of controlling the transmission power for transmission to the individual mobile stations MS. If it is found during the process of determining the characteristic values for the reception paths that the -difference between the respectively 15 determined characteristic values for the two reception paths of the antenna device Al, A2 is not greater than a predetermined threshold value, that is to say the transmission conditions for both paths are, for example, virtually identical, protected signal 20 transmission can be achieved by periodically changing between the antenna device Al, A2 when the base station BS is transmitting. This results in successive, decorrelated signals at the mobile station MS location, thus advantageously improving the transmission quality 25 when interference is present on the radio interface. For additional decorrelation of successive signals, it is also possible, for example, to change the timeslot ts while maintaining the assigned CDMA code c if transmission problems occur repeatedly in 30 specific timeslots ts. A further option, in the situation where a number of frequency bands B are available to the radio communications system, is to change between the frequency bands B using a type of frequency hopping method.

GR 98 P 1831 - 16 Figure 4 shows an example of a flowchart for one refinement of the method according 'to the invention. 8y way of example, in the flowchart block identified by the number 1, a signal is sent via the 5 radio interface between from the mobile station MS to the 'base station BS. The transmitted signal is transmitted, for example, in an assigned radio channel. The block identified by 2 represents reception of the transmitted signal in the base station BS via two 10 antenna devices Al and A2 using diversity reception. According to the blocks 3 and 4, the signal received via the respective antenna device Al and A2 is used to determine characteristic values relating to the transmission conditions on the radio interface for the 15 respective transmission paths. The characteristic values which are determined and correspond to one another are compared with one another in the block 5, and this can be done, for Iexample, in an evaluation device AW in the base station BS. The decision 20 resulting in the selection of the better transmission conditions is made in the decision block 6 depending on the type of characteristic values. If the transmission conditions for the transmission path via the first antenna device Al are better than the transmission 25 conditions via the second antenna device A2, then, in the block 7, the signals to be sent subsequently are switched in the radio channel via the first antenna device' Al to the mobile station MS. If, on the other hand, the transmission conditions via the second 30 antenna device A2 are better, then, as shown in block 8, signals to be sent subsequently by the base station BS are sent via the second antenna device A2. In addition to the procedure shown in Figure 4, the sequence can be supplemented, for example, by 35 checking the difference between the specific characteristic values of the GR 98 P 1831 - 17 reception paths. Provided this difference is not greater than a predetermined threshold value, then signals to be sent subsequently are alternately switched to in each case one antenna device Al or A2 5 using an antenna hopping method, thus advantageously decorrelating the transmitted signals. The evaluation of the signals sent by the mobile station MS can in this case be controlled by a timer, which is matched to the subscriber separation method and/or is synchronized 10 with it. Figure 5 shows a three-dimensional diagram in which, by way of example, signal transmission ac-cording to the invention is carried out in a radio communications system having TD/CDMA subscriber 15 separation and in which the uplink and downlink directions are separated using a TDD method. Firstly, the time t is plotted in the horizontal plane and is split into frames fri to fr4 using the TDMA subscriber separation method. Each frame frl to fr4 is subdivided 20 into, for example, 16 timeslots tsl to tsl6. As has already been explained with reference to Figure 2, the uplink and downlink directions are separated by a switching point SP, so that transmission takes place in both the uplink direction and the downlink direction 25 within one frame fr. Furthermore, a distinction on the basis of the CDMA code c is made in the horizontal plane. By way of example, four possible CDMA codes cl to c4 are shown, which allow separation into four radio channels within one timeslot ts when using a frequency 30 band b. In the vertical direction, two antenna devices Al and A2 are shown, by way of example, via which the signals can be sent from the base station BS. The example shown in Figure 5 is based on two radio channels being assigned to a communications link 35 between a base station BS, which has two antenna devices Al and A2, and a mobile station MS, using the channel pooling GR 98 P 1831 - 18 principle. The diagram in this case shows the processes of reception and transmission from the point of view of the base station BS. This configuration, which is illustrated by way of example, corresponds to Figure 3. 5 In the initial situation, the allocated radio channels are defined in the first frame frl by the timeslot ts4 for the uplink direction and by the timeslot ts12 for the downlink direction, and by the CDMA codes cl and c3 as well. Accordingly, in the first, frame frl, the 10 mobile station MS sends signals in the uplink direction in the timeslot ts4, using the CDMA'codes cl and c3, to the base station BS. The/ transmitted signals are received via the antenna devices Al and A2 in the base station BS, and characteristic values relating to the 15 respective transmission conditions on the radio interface are determined for each reception path and radio channel. Depending on the result of the evaluation in the evaluation device AW in the base station BS, the signals to be sent in the downlink 20 direction are switched to a respective one of the antenna devices Al or A2. For example, in the timeslot ts12 intended for the- downlink direction in the first frame frl, the base station BS sends signals via the first antenna unit Al in the radio channel identified 25 by the first CDMA code c1, if it has been found that the transmission characteristics for the first antenna device Al are better (shaded areas) . For example, the characteristic values can be determined in each frame fri to fr4. In this case, the antenna device Al is 30 used for transmission in each frame fr1 to fr4 for this radio channel in the example. For the ,radio channel identified by the third CDMA code c3, characteristic values are determined for both reception paths, whose difference does not exceed 35 a predetermined threshold value. In order to exploit this situation to obtain advantageous decorrelation of signals in two successive frames frl, fr2, the signals in the GR 98 P 1831 - 19 radio channel are each switched alternately to the second antenna device A2 and to the first antenna device Al, as is illustrated in the diagram. In addition, the diagram shows a sequence of changing the 5 timeslots ts between the individual frames fri to fr4, which can also be referred to as a timeslot hopping method. In this case, the timeslot ts respectively used for the uplink direction sand downlink direction is changed in accordance with a predetermined algorithm or 10 time sequence while retaining the CDMA code c, thug reducing the effect on the reception quality of interference which in each case occurs only in specific timeslots ts.

Claims (19)

1. A method for signal transmission via a radio interface in a radio communications system, which 5 - uses a subscriber separation method to distinguish between signals, with a radio channel being defined at least by a frequency band (B) and a connection-specific fine structure (c), in which 10 - at least one radio channel is assigned for signal transmission between a first radio station (BS) and a second radio station (MS), - at least one signal is transmitted via at least two transmission paths, 15 - at least one characteristic value (RXLEV, RXQUAL, ta, C/I) relating to the transmission conditions on the radio interface is determined for each transmission path, - a control signal (stsig) is derived from a 20 comparison of the mutually corresponding characteristic values (RXLEV, RXQUAL, ta, C/I), by means of which control signal (stsig) the transmission path is selected specifically for the radio channel for transmitting a subsequent 25 signal.

2. The method as claimed in claim 1, in which - the signal is sent by the second radio station (MS) and is received via at least two antenna devices (Al, A2) of the first radio station (BS) 30 using diversity reception, - the characteristic values (RXLEV, RXQUAL, ta, C/I) are determined from the signal received by the respective antenna device (Al, A2), and - the control signal (stsig) which is derived from 35 the comparison of the mutually corresponding characteristic values (RXLEV, RXQUAL, ta, C/I) is used to actuate a switching device (UE) GR 98 P 1831 - 21 which switches a subsequent signal specifically for the radio channel to one of the antenna devices (Al, A2) of the first radio station (BS).

3. The method as claimed in claim 1, in which 5 the signal is transmitted, separated in, time, via, in each case one transmission path.

4. The method as claimed in claim 3, in which - the signal which is separated in time is sent by in each case one antenna device (Al, A2) of the 10 first radio station (BS) and is received by the second radio station (MS), - the characteristic values (RXLEV, RXQUAL, ta, C/I) are determined from the respectively received signal, and 15 - the control signal (stsig) is derived from the comparison of the mutually corresponding characteristic values (RXLEV, RXQUAL, ta, C/I) and is used to actuate a switching device (UE) which switches a subsequent signal specifically for the 20 radio channel to one of the antenna devices (Al, A2) of the first radio station (BS).

5. The method as claimed in claim 4, in which the specific characteristic values (RXLEV, RXQUAL, ta, C/I) [lacuna] transmitted to the first radio station 25 (BS) , and the control signal (stsig) is derived from them.

6. The method as claimed in claim 4, in which the control signal (stsig) is derived in the second radio station (MS) and is transmitted to the first 30 radio station (BS).

7. The method as claimed in claim 5 or 6, in which the characteristic values (RXLEV, RXQUAL, ta, C/I) and the control signal (stsig) are transmitted using in band signaling. GR 98 P 1831 - 22

8. The method as claimed in one of the preceding claims, in which - when a number of radio channels are assigned for signal transmission between the first radio 5 station (BS) and the second radio station (MS) , the control signal (stsig) is derived from a comparison of all the respectively specific and mutually corresponding characteristic values (RXLEV, RXQUAL, ta, C/I), and 10 - the control signal (stsig) is used to select a common transmission path for all the radio channels for transmission of subsequent signals.

9. The method as claimed in one of the preceding claims, in which 15 in the situation where any difference between the specific and mutually corresponding characteristic values (RXLEV, RXQUAL, ta, C/I) does not exceed a predetermined threshold value, a transmission path is in each case selected on a periodically changing basis, 20 so that at least two successive, decorrelated signals are transmitted via different transmission paths.

10. The method as claimed in one of the preceding claims, in which the connection-specific fine structure is formed by a 25 CDMA code (c).

11. The method as claimed in claim 10, in which a TD/CDMA method is used as the subscriber separation method, with a radio channel being defined by a frequency band (B), a timeslot (ts) and a CDMA code. 30

12. The method as claimed in one of claims 11, in which the signals are transmitted using a TDD method, in which the signals are transmitted from the first radio station (BS) to the second radio station (MS) and from 35 the second radio station GR 98 P 1831 - 23 (MS) to the first radio station (BS), separated in time, in one frequency band (B).

13. The method as claimed in claim 11 or 12, in which 5 at least two successive signals are transmitted with the timeslot (ts) being changed, with the timeslot (ts) which is used for transmission being changed periodically and in synchronism with the time protocol of the subscriber separation method. 10

14. The method as claimed in one of the preceding claims, in which at least two successive signals are transmitted with the frequency band (B) being changed, with the frequency band (B) which is used for transmission being 15 changed periodically and in synchronism with the time protocol of the subscriber separation method.

15. The method as claimed in one of the preceding claims, in which the transmitted signals are received in the first radio 20 station (BS) and/or in the second radio station (MS) using a joint detection method.

16. The method as claimed in one of the preceding claims, in which a reception level, a bit error rate and/or a value proportional to the signal delay time 25 (ta) between the first radio station (BS) and the second radio station (MS), and/or a signal-to-noise ratio is defined as the characteristic value (RXLEV, RXQUAL, ta, C/I) .

17. A radio station (BS, MS) for signal 30 transmission via a radio interface in a radio communications system, which - uses a subscriber separation method to distinguish between signals, in which a radio channel is defined at least by a GR 98 P 1831 - 24 'frequency band (B) and a connection-specific fine structure (c), having - at least one antenna device (Al, A2) for receiving 5 and/or sending at least one signal which -is transmitted via at least two transmission paths, - an evaluation device (AW) for determining at least one characteristic value (RXLEV, RXQUAL, ta, C/I) relating to the transmission conditions on the 10 radio interface for each transmission path, - a control device (SE) for deriving a control signal (stsig) from a comparison of the mutually corresponding characteristic values (RXLEV, RXQUAL, ta, C/I), and 15 - a switching device (UE) which is actuated by the control signal (sig) and selects the transmission path specifically for the radio channel for transmitting a subsequent signal.

18. The radio station (BS, MS) as claimed in 20 claim 17, which is designed as a base station in a mobile radio system.

19. The radio station (BS, MS) as claimed in claim 17, 25 which is designed as a mobile station in a mobile radio system.