Abstract:
A method and apparatus for detecting paths of a received signal by analyzing a delay power profile of the received signal comprises a detection of peaks in the delay power profile by a peak detector having a threshold that is set based upon the noise environment. Peaks detected by the peak detector are passed to a data path detector having second threshold set at a power level higher than the threshold in the peak detector. In one embodiment, a third threshold is set within a filter to suppress secondary maxima created by the generation of the delay power profile. The detected paths may set in a rake type receiver.

Description:
This application claims the benefit of European Patent Authority; 03002483.0, filed Feb. 5, 2003. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of wireless transmission, and more particularly to the detection of transmitted signals. 
     BACKGROUND 
     CDMA data transmission systems, for example for use in a 3GPP-WCDMA-FDD device, usually have a “rake” receiver comprising various “fingers”, with each finger being assigned to a delayed path (data transmission path) [lacuna] received signal. 
     The number of active fingers and the delay in each “finger” in a rake receiver are assigned on the basis of a data transmission path searching unit. The operating parameters for the data transmission path searching unit are assigned by a “finger” management unit. 
     In wireless data stream transmission systems, signals pass via different data transmission paths to which different “fading” can be applied. 
     Since every data transmission path has a different length and the data stream signals propagate on the different paths at approximately the same data transmission speed, the data stream signal arrival times at the data stream receiver differ, in some cases substantially, for the different data transmission paths. 
     The data transmission path searching unit is now used to determine an arrival time for the data stream signals from the different data transmission paths. In line with the 3GPP standard (UMTS), the data stream is made up of frames and slots (data frames and data slots). A data frame has, by way of example, a duration of 10 milliseconds (ms) and contains 15 data slots. Each data slot has 2560 chips, which means that the chip frequency in this example is 3.84 MHz. 
     Since the bandwidth of a CDMA system is usually high, a chip period is very small, which means that delays on different data transmission paths are usually greater than one chip period. 
     These delayed arrival times for the various propagation paths result in data symbols transmitted at various times being superimposed at the receiver, an effect which is called intersymbol interference (ISI) and, without suitable countermeasures, has disadvantageous consequences for data reception. To compensate for ISI and to make advantageous use of the diversity of the various propagation paths, CDMA systems usually involve the use of a technique which is used to receive the data stream signals from all the relevant data transmission paths separately, and they are then combined. 
     On the basis of the prior art, this is done in a rake receiver, which is a data stream receiver which receives as many multipath data stream signals as possible. The rake receiver combines the signals from all these paths to produce a data stream signal which is as “interference free” as possible and which is stronger than the individual components. Individual paths are found by cross-correlating a reference pattern with the received signal. 
     The estimation of “power delay profiles” (PDPs) is fundamental to the operability of a rake receiver. The power delay profiles for different data transmission paths are estimated, by way of example, by a mobile UMTS receiver in order to determine the amplitude or a power and the delayed timing of the data transmission paths for data streams with regard to a receiver timing reference. 
     The power delay profile is determined by means of a correlation using a (primary or secondary) “pilot channel” (CPICH—Common Pilot Channel) which transmits a predetermined symbol sequence. In conventional manner, a complex correlation is provided between the incoming signal (r(i)), which is sampled at double the chip rate, and a known, complex conjugate pilot sequence signal p*(i), likewise sampled at double the chip frequency, in line with the general relationship, where N corr  is the correlation length. 
     
       
         
           
             
               
                 
                   
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     In the case of the transmission diversity which is possible in the UMTS standard, it is necessary to perform this correlation for the data transmission paths of an “antenna  1 ” and of an “antenna  2 ”. In this context, the expressions “antenna  1 ” and “antenna  2 ” denote two different transmission devices in a data stream transmitter, for example antennas, so that at least two different data transmission paths are produced. In this context, the correlation length N corr  is an even-numbered multiple of a pilot sequence symbol length, i.e. an even-numbered multiple of a CPICH symbol length of 256 chips. Although increasing the correlation length N corr  increases the signal-to-noise ratio for a power delay profile estimation in a desirable manner, on the other hand this power delay profile estimation then becomes more sensitive to any sampling clock error. For this reason, a power delay profile estimation needs to be averaged over time. 
     The operability of the rake receiver is based quite fundamentally on correct positioning of a particular number of rake fingers on multiple data transmission paths in order to be able to combine the power thereof and to obtain a diversity boost. 
     Conventional methods use a “PDP (Power Delay Profile) determination device” in order to determine those data transmission paths which have the highest power. The output of each PDP determination device is compared with a threshold value, and all peak values in the received signal above this threshold are processed further by a finger positioning block. 
     Disadvantageously, the setting of a threshold value is extremely critical with regard to the detection of incorrect data transmission paths. Particularly in environments with a low signal-to-noise ratio or a high level of noise, which can be brought about, in particular, by a moving, mobile data stream receiver on account of fading effects, the amplitude distributions of noise and amplitude distributions of data transmission paths can overlap such that exact setting of a threshold value is no longer possible. 
     In conventional manner, the PDP determination device is in the form of a correlation filter, for example, which has the further disadvantage that secondary maxima are produced which simulate invalid data transmission paths, i.e. shadow data transmission paths. 
     If the threshold value is set to be too low, then a power delay profile determination is severely disturbed by noise, and not all peak values which are linked to a correlation of received signal and pilot sequence signal correspond to actual, i.e. valid, data transmission paths. 
     Disadvantageously, the peak values of the useful signal and of the noise signal are subject to statistical processes, which means that a relation between data transmission paths and noise peak values in the case of power delay profile determination is a statistical process which is dependent on an existing noise scenario. 
     In particular, conventional methods have disadvantages to the effect that data transmission paths are not correctly identified if, as is unavoidable in the case of mobile systems, new data transmission paths appear and existing data transmission paths disappear, which means that uniform monitoring of the data transmission paths is necessary. 
     It is therefore an object of the present invention to provide an apparatus for receiving a data stream which can be transmitted via at least one data transmission path in which a level of accuracy for data transmission path detection is improved as compared with conventional methods, with noise peak values differing from data transmission path peak values, and shadow data transmission paths being able to be avoided. 
     SUMMARY 
     In accordance with the present invention, transmission path detection is accomplished using threshold settings within a peak value detection device, a data transmission path profile determination device and, in one embodiment, a shadow transmission path filter. The thresholds in the peak detection device and data transmission path profile determination device are adapted to the noise environment. The threshold in the filter is established to suppress secondary maxima resulting from a correlation filter used to generate a delay power profile. 
     The advantage of the invention is thus that different signal-to-noise scenarios can exist with which the inventive apparatus can align itself. 
     Expediently, this increases the detection probability for valid data transmission paths, whereas a probability of detection of invalid data transmission paths is reduced as compared with methods based on the prior art. 
     Another advantage is that the setting of a threshold value is no longer critical as compared with the prior art, since the threshold value is automatically aligned with a noise environment. 
     It is also advantageous that different threshold values are provided which permit peak value detection, data transmission path profile determination and shadow data transmission path filtering. 
     In particular, it is expedient that the threshold values can be adapted to different environment scenarios if information is available about the environment scenarios. 
     Advantageously, the inventive apparatus can be implemented in a CDMA modem. 
     In one embodiment of the invention, an apparatus for receiving a data stream which can be transmitted via at least one data transmission path essentially has:
         a) a data stream receiver for receiving the data stream;   b) a power delay profile determination unit for determining at least one power delay profile;   c) a peak value detection device for detecting at least one peak value in the power delay profile;   d) a data transmission path profile determination device for determining a data transmission path profile for the at least one data transmission path;   e) a filtering device for suppressing shadow path signals and for outputting a finger positioning signal; and   f) a setting device for setting data transmission paths, which are associated with a data transmission, on the basis of the finger positioning signal.       

     In line with one preferred development of the present invention, the peak value detection device has a comparison unit for comparing the power delay profile with a first threshold value. 
     In line with another preferred development of the present invention, a power delay profile determination unit for determining at least one power delay profile for the at least one data transmission path is provided. 
     In line with yet another preferred development of the present invention, a summation unit for summing the data streams transmitted by individual data transmission paths is provided. 
     In line with yet another preferred development of the present invention, the peak value detection device has a threshold value setting unit which can be used to set the first threshold value adaptively. 
     In line with yet another preferred development of the present invention, the data transmission path profile determination device has a data transmission path profile unit for summing weighted peak values and a data transmission path detection unit for detecting a valid data transmission path. 
     In line with yet another preferred development of the present invention, the power delay profile determination unit is provided together with a peak value sorting unit in a common matched hardware block. 
     In line with yet another preferred development of the present invention, a received signal strength determination unit for determining the received signal strength of the received signal is provided in a matched hardware block. 
     In accordance with one embodiment of the present invention, a method for receiving a data stream transmitted via at least one data transmission path comprises the following steps:
         a) receiving the data stream;   b) determining at least one power delay profile;   c) detecting at least one peak value in the determined power delay profile;   d) determining a data transmission path profile;   e) suppressing shadow transmission path signals; and   f) setting data transmission paths in a receiver.       

     The “shadow transmission path” to which reference is made in this context is a transmission path which is invalid, i.e. which does not contribute to data transmission of the data stream which is to be transmitted. A shadow transmission path can be simulated, by way of example, by secondary maxima from a correlation filter contained in a power delay profile determination unit. 
     In line with yet another preferred development of the present invention, a first threshold value is set on a variable basis in the peak value detection device. 
     Advantageously, a first threshold value may be set on the basis of a noise environment. 
     Another advantage is that a first threshold value may be set on the basis of a mean value, a variance and/or a standard deviation for noise peak values. 
     In line with yet another preferred development of the present invention, the first threshold value is matched to a noise environment such that a preselection of possible data transmission path positions is advantageously provided. 
     In line with yet another preferred development of the present invention, the power delay profile estimation and the peak value detection are performed periodically by the peak value detection device. 
     The present invention advantageously permits the power delay profile estimation and the peak value detection to be performed periodically by the peak value detection device at an interval of time which corresponds to a data frame or to a multiple of data frames. 
     In line with yet another preferred development of the present invention, a prescribable number of preceding periods in the data transmission path profile determination device is stored, with the detected peak values preferably being summed in the manner of an ongoing histogram. It is also expedient that the data transmission path profile determination device stores the prescribable number of preceding periods and weights the detected peak values before summation with a received signal strength. 
     In line with yet another preferred development of the present invention, the temporal summation points when the detected peak values are summed by the data transmission path profile determination device correspond to delay positions k=0, 1, . . . , L−1 of a correlation function. 
     In line with yet another preferred development of the present invention, those data transmission path positions which appear fewer than a predetermined number of times are set to 0. 
     In line with yet another preferred development of the present invention, a second threshold value is prescribed in the data transmission path profile determination device, and the peak values summed in the manner of an ongoing histogram are compared with it. 
     In line with yet another preferred development of the present invention, the second threshold value is set on the basis of an existing noise or an existing noise environment or an existing noise scenario. 
     In line with yet another preferred development of the present invention, the second threshold value is provided on the basis of the first threshold value, which is multiplied by a constant factor. 
     In line with yet another preferred development of the present invention, secondary maxima from a correlation filter are compared with a third threshold value in the filtering device for suppressing shadow transmission path signals. 
     In line with yet another preferred development of the present invention, the first, second and/or third threshold values are updated periodically. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the description below. In the drawings: 
         FIG. 1  shows a schematic block diagram of a data transmission system having multiple data transmission paths; 
         FIG. 2  shows a schematic structure for a pilot channel which can be used to transmit a pilot sequence signal having a prescribed symbol sequence; 
         FIG. 3  shows a block diagram of a rake receiver with devices for data transmission path detection and finger positioning; 
         FIG. 4  shows a graph showing peak values for the useful signal (data transmission signal) and for noise signals in relation to a threshold value which is set in order to determine power delay profiles; 
         FIG. 5  shows a block diagram of an exemplary embodiment of the inventive method; 
         FIG. 6  shows a preferred exemplary embodiment based on the present invention; 
         FIG. 7  shows another preferred exemplary embodiment based on the present invention; and 
         FIG. 8  shows yet another preferred exemplary embodiment based on the present invention. 
     
    
    
     In the figures, identical reference symbols denote components or steps which are the same or have the same function. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic block diagram of a data transmission system in which different data transmission paths  101 , namely direct data transmission paths  101   a  and indirect data transmission paths  101   b ,  101   c , contribute to transmission of data stream  102 . 
     There are a direct data transmission path  101   a  and data transmission paths which proceed through reflections on buildings, elevations and other facilities etc., such as the data transmission paths  101   b  and  101   c . In this context, a data stream transmitter  200  typically has one or two transmission devices (antennas)  201  and  202 , while a data stream receiver  100  has a reception device  109 . 
     As can be seen from the block diagram in  FIG. 1 , the propagation times on the data transmission paths  101   a - 101   c  transmitting the data stream  102  are different. In a “worst case”, the delay time is typically 30 μs, which corresponds to a distance difference of 9 km. This “worst case” delay time has been specified by test cases in the 3GPP standard. To calculate a power delay profile, a number L of values which, for this “worst case”, has been set to L=240 is required. 
       FIG. 2  schematically shows the structure of a pilot channel with a prescribed pilot sequence. As shown, a data stream is made up of individual data frames  203   a  . . .  203   i  . . .  203 N. In the exemplary embodiment of the invention, each data frame has a duration of T f =10 ms (milliseconds). Each data frame is divided into individual slots  204   a  . . .  204   i  . . .  204   n.    
     In the exemplary embodiment of the invention, a data frame is divided into n=15 slots. Each slot transmits 10 symbols, which are denoted by A and −A in  FIG. 2 . The first symbols, indicated by the reference symbol  205  for a first antenna  1  or for a first transmission device  201 , and the second symbols, indicated by the reference symbol  206  for a second antenna  2  or for a second transmission device  202 , for a specific slot form a pilot sequence signal with a prescribable pilot sequence. 
     A symbol is made up of 256 chips in the exemplary embodiment, where a chip represents the smallest digital unit. This means that a time slot T slot  comprises 2560 chips, and when two bits are provided per symbol—for real and imaginary parts, i.e. (1+j)−20 bits are provided for each individual slot  204   a - 204   n.    
     With the indicated duration of a data frame  203  and the prescribed number of 15 slots which each contain ten symbols or 2560 chips, a chip rate of 3.84 Mchip/s is obtained. To form correlation functions, the data stream is now sampled at double the chip rate, i.e. at 7.68×10 6  sampling steps per second. 
     This makes it possible to determine a correlation function with a resolution of half a chip. Advantageously, a correlation length N corr  is set to a multiple of the symbol length (×1, ×2, ×4 . . . ). 
     The variable L indicated in the equation above thus denotes a maximum shift when forming the correlation functions, i.e. n proceeds from 0, 1, 2 . . . L−1. If L is set equal to 240, the result is a delay time of 31.25 μs, which is also sufficient for the “worst case”. 
     In line with the equation above, the result both for an antenna  1  and for an antenna  2 , i.e. transmission devices  201  and  202 , is different correlation functions as a function of n, with a total power delay profile being determined by forming the sum of the squares of the magnitudes of the individual correlation functions. 
     This results in a power delay profile PDP as a function of n as follows 
                         X   _     Ant1     ⁡     (   n   )       =       ∑     i   =   0       Ncorr   -   1       ⁢         r   _     ⁡     (     n   +     2   ⁢   i       )       ·         p   _     Ant1   *     ⁡     (     2   ⁢   i     )                   (   1   )                     X   _     Ant2     ⁡     (   n   )       =       ∑     i   =   0         N   corr     -   1       ⁢         r   _     ⁡     (     n   +     2   ⁢   i       )       ·         p   _     Ant2   -     ⁡     (     2   ⁢   i     )                   (   2   )                 PDP ( n )=|   X     Ant1 ( n )| 2   +| X     Ant2 ( n )| 2   (3) 
     In equations (1) to (3), the received, complex signal (received signal) is respectively denoted by  r (n), while  p (i) denotes the complex pilot signal, where r(n) and p(i) are respectively sampled at double the chip rate. 
     In this case, the shift is indicated by n=0, 1, 2, . . . L−1. 
     The power delay profile PDP is thus obtained through the sum of the squares of the magnitudes in line with equation (3) and is denoted by PDP(n). The power delay profile determination now needs to be averaged over a plurality of blocks with a correlation length N corr . N avg  denotes a number of blocks over which averaging takes place, the magnitude N avg  being able to vary on the basis of the network conditions. 
     In line with the example of the invention, it is now possible to alter the correlation length N corr  and the number of averaging operations N avg  without the need to alter or align hardware designs. 
       FIG. 3  shows a rake receiver which is used as a data stream receiver for receiving a data stream  102  which can be transmitted via at least one data transmission path. The rake receiver comprises a power delay profile determination unit  303  which is used to determine a power delay profile  300  (PDP). 
     The rake receiver also has a data transmission path detection unit  304 , a setting device  305  and a processing device  308 . The fundamental components of the processing device  308  comprise a summation unit  310  which sums different rake fingers  309   a - 309   n  in order to stipulate data transmission paths  101 ,  101   a - 101   c  which are suitable for transmitting the data stream  102 . 
     The rake receiver receives the data transmitted using the data stream  102  in the form of a received signal  301 . 
     The received signal is then correlated with a pilot sequence signal in the power delay profile determination unit, as already described, the correlation function for determining a power delay profile as a function of (k), i.e. the variable pdp cst (k), having the following form: 
                             pdp   est     ⁡     (   k   )       =       ⁢       1     N   avg       ·     1     N   corr   2       ·                     ⁢       ∑     l   =   0         N   avg     -   1       ⁢              ∑     n   =       n   start     +     l   ·     N   corr                 n     start   +     (     l   +   1     )         ⁢     N   corr       -   1       ⁢       r   ⁡     (       2   ⁢   n     +   k     )       ·       p   *     ⁡     (     2   ⁢   n     )                2                       ⁢         where   ⁢           ⁢   k     =   0     ,   1   ,           ⁢   …   ⁢           ,     L   -   1     ,                   (   4   )               
the received signal  301  being denoted by r(n) and the pilot sequence signal being denoted by p(k) in this context, with the two signals representing complex variables and being prescribed on the basis of the following equations (5) and (6):
   r ( n )= r   s ( n )+ jr   Q ( n )  (5)   p ( n )= p   s ( n )+ jp   Q ( n )  (6) 
     N corr  thus denotes a (partial) correlation length and N avg  denotes a number of averaging operations over (partial) correlations. 
     Both signals, the received signal and the pilot sequence signal, are sampled at double the chip rate. The power delay profile pdp (k) determined in line with the above equation (4) is finally output from the power delay profile determination unit  303  and is supplied to the data transmission path detection unit  304 . 
     In line with the invention, a first threshold value  103   a  (explained below with reference to  FIG. 4 ) is now added at a low position in the power delay profile determination unit  303 , which means that although data transmission paths have been preselected, a high rate of invalid data transmission paths is obtained. 
     In the data transmission path detection unit, the peak values  401   a - 401   n  ( FIG. 4 ) of a received signal power  107  are summed, with values which belong to the same delay time (k) being added. In this context, it is possible to stipulate a number N occ  which indicates how often a peak value  401   a - 401   n  needs to have been above the settable first threshold value  103   a  in order for the position of this peak value to be identified as a data transmission path. 
     A corresponding data transmission path position signal  306  is then output from the data transmission path detection unit  304  and is supplied to the setting device  305 . The setting device  305  then selects those positions from the power delay profile which need to be received with the fingers of the rake receiver. 
     A rake finger thus corresponds to a propagation path. The rake fingers are summed in the summation unit  310  of the processing device  308  in accordance with a finger position signal  307  which is output by the setting device  305  and are output as an output signal  311 . 
       FIG. 4  shows a graph with different peak values  401   a - 401   n , which correspond to data transmission paths  101   a - 101   n , and also noise peak values  402   a - 402   n . In addition, the right-hand graph in  FIG. 4  shows a function of a probability distribution  111  over a power  108 , with two maxima having been set by way of example. The maximum at low power  108  corresponds to a noise signal  104 , while the maximum at high signal power corresponds to the data transmission paths  101 . The distance between the two maxima can be referred to as a signal-to-noise ratio  105 . In conventional methods based exclusively on the setting of the first threshold value  103   a , one drawback is that if the threshold value  103   a  has been set to be too low, a false alarm rate rises inadmissibly, whereas if the threshold value  103   a  has been set to be too high, a detection rate for valid data transmission paths decreases. 
     In line with the invention, as will be explained below with reference to  FIG. 5 , the first threshold value  103   a  is set to be low, which means that numerous noise peak values  402   a - 402   n  are also detected. 
       FIG. 5  shows a block diagram relating to the performance of a method in line with a preferred exemplary embodiment of the invention. Besides a peak value detection device  501 , data analysis data processing is performed in a data transmission path profile determination device  502  and in a filtering device  503 . 
     The peak value detection device  501  is supplied with a power delay profile signal which is determined by the power delay profile  300 . This signal is compared with the set, first threshold value  103   a  in a comparison unit in the peak value detection device  501 . This first threshold value  103   a  is chosen to be low in comparison with methods based on the prior art, as a result of which a detection probability for invalid paths rises, but also a detection probability for valid paths increases overall. The value which is output -from the peak value detection device  501  and is supplied to the data transmission path profile determination device  502  thus also represents just one preselection of possible data transmission path positions. In this first step, power delay profile determination (or power delay profile estimation) and peak value detection are performed periodically, typically with an interval of time for the frame or multiple frames, i.e. at an interval of 10 ms, respectively 20 ms, . . . etc. 
     The signal which is output by the peak value detection device  501  is processed further in the data transmission path profile determination device  502 . In the data transmission path profile determination device, the detected peak values  401   a - 401   n , like the detected noise peak values  402   a - 402   n , are added for the last M periods for respectively identical delays (k) in line with the method of an ongoing histogram. The containers for this ongoing “histogram” correspond to all possible delay positions k(0 . . . L−1). All positions which do not appear at least N occ  times within this observation window of length M are set to 0 in order to suppress high noise peak values or unstable data transmission paths. 
     Since the number of detected peak values is typically low as compared with the power delay profile length (N peak &lt;&lt;L), this data transmission path profile histogram needs to be calculated only for the delay positions at which a path has appeared within the last M-PDP determination periods. 
     The result of this histogram is subsequently compared with a second threshold value  103   b . All positions which exceed this second threshold value  103   b  are processed further and are output from the data transmission path profile determination device  502 . 
     The second threshold value  103   b  is derived from an estimation of the noise environment. Since noise peak values are statistically independent events, they usually appear at different positions in successive PDP determination steps. The second threshold value can be chosen, by way of example, on the basis of
 
 S   103b   =N   occ   ·S   103a   (7)
 
where S denotes the corresponding threshold values.
 
     Equations (8) and (9) below thus give probabilities of noise peak values  401  being identified which are increased as compared with the conventional method, which uses just a peak value detection device  501 . At the same time, the detection probability for valid data transmission paths (equation 9) has remained the same.
 
 P   502 =( P   501 ) N   occ  for 402  (8)
 
 P   502   =P   501  for 401  (9)
 
     On account of this effect, most noise peak values are suppressed at the stage of the data transmission path profile determination device  502 , while a detection probability for the peak value  401 ,  401   a - 401   n  for the useful data stream signal is maintained. 
     The output signal from the data transmission path profile determination device is finally also supplied to the filtering device  503 , which provides a further improvement in the signal-to-noise ratio. 
     In the filtering device  503 , a third threshold value  103   c  is provided which is used to suppress secondary maxima from a correlation filter device which is used in the power delay profile determination unit  303 . The filtering device  503  is necessary particularly in scenarios in which a high signal-to-noise ratio is maintained, in which case the amplitudes of the correlation secondary lobes are in the same range or higher than the noise peak values. 
     These secondary maxima are brought about by less than optimal orthogonality in sampling code sequences of length N corr , and typically have the same position in consecutive PDP determination steps, these being spaced apart from one another by exactly one frame or a multiple of frames. The secondary maxima can result in the detection of (invalid) “shadow data transmission paths”  101   s , which cannot be suppressed by the first two stages  501  and  502 . 
     Since the side lobes of a particular sampling code have a defined relationship with the primary peak value  401   a - 401   n , the third threshold value  103   a  can be determined from the amplitude of the position of the strongest data transmission path and can be set with a variable Δ 103c  in line with the formula below
 
 S   103c =Max{401a, . . . , 401n}/Δ 103c   (10)
 
     The parameter Δ 103c  depends on the settings of the PDP determination device N corr  and N avg  and can be derived in advance and stored in a table. As the result of this third stage, the filtering device  503  outputs a finger positioning signal  504  which outputs the detected data transmission paths (described by a position and accumulated in the power over M periods). The detected data transmission paths are supplied to the processing device  308  described in  FIG. 3  in the form of a finger position signal  307 , so that corresponding adjustments for the rake fingers and summation thereof can be performed. 
     To perform automatic data transmission path detection, the threshold values  103   a ,  103   b  and  103   c  are automatically set and aligned with the corresponding noise environment. The setting for the first and second threshold values  103   a  and  103   b  can be derived on the basis of an estimation of a mean value μ pdp  and of a variance σ 2   pdp  or of a standard deviation σ pdp  in the noise samples pdp cst . In this context, the mean value μ pdp , the variance σ 2   pdp  and the standard deviation σ pdp  are detected from a received signal strength which, as will be explained with reference to  FIG. 6 , is output from a received signal strength determination unit  606 . 
     In the formulae below, this variable for the received signal strength is denoted by RSSI (Received Signal Strength Indicator).
 
 S   103a   =a   1 ·μ pdp   +b   1 σ pdp   (11)
 
or
 
 S   103a   =a   1 μ pdp   +b   2 σ 2   pdp   (12)
 
     The variables μ pdp , σ pdp  and σ 2   pdp  are determined from the signal RSSI in line with the equations below 
     
       
         
           
             
               
                 
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                               ⁡ 
                               
                                 ( 
                                 n 
                                 ) 
                               
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
             
               
                 
                   
                     σ 
                     pdp 
                   
                   = 
                   
                     RSSI 
                     
                       
                         N 
                         corr 
                       
                       ⁢ 
                       
                         
                           N 
                           avg 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
             
               
                 
                   
                     σ 
                     pdp 
                     2 
                   
                   = 
                   
                     
                       RSSI 
                       2 
                     
                     
                       
                         N 
                         corr 
                         2 
                       
                       · 
                       
                         N 
                         avg 
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
             
               
                 
                   
                     μ 
                     pdp 
                   
                   = 
                   
                     RSSI 
                     
                       N 
                       corr 
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
     Since the variable RSSI can change over time, the threshold values need to be updated periodically. If a distribution of noise samples corresponds to a Gaussian distribution function, the false detection rate P 502  can be controlled exactly by the first threshold value  103   a  in line with equation (11). The second threshold value  103   b  can be chosen on the basis of the first threshold value  103   a , in line with
 
 S   103b   =c·S   103a   (17)
 
     Further preferred exemplary embodiments of the present invention will be described below. 
     In the subsequent figures, a reference symbol  601  denotes a processor device which has a multipurpose processor in software. This multipurpose processor can be implemented, by way of example, in a digital signal processor or a microcontroller. 
     A reference symbol  602  distinguishes a matched hardware block which needs to be designed specifically for the corresponding exemplary embodiment. The matched hardware block  602  and the processor device  601  are connected by means of a processor bus  603 . 
     In line with the exemplary embodiment shown in  FIG. 6 , the matched hardware block  602  a has a power delay profile determination unit  303 , a peak value detection device  501  and a received signal strength determination unit  606 . In addition, the matched hardware block  602   a  can comprise a threshold value determination unit  605 , which can also be provided in the form of a software module on the processor, however. The received signal  301  is supplied both to the power delay profile determination unit  303  and to the received signal strength determination unit  606 . 
     From the received signal strength determination unit  606 , an RSSI signal is derived in order to supply it to the peak value determination unit  605 . To detect peak values in the peak value detection device  501 , the first threshold value  103   a  is first determined in the threshold value determination unit  605  and is supplied to the peak value detection device. 
     It will be pointed out that an optimized first threshold value  103   a  can change for each power delay profile determination step, which means that it may be necessary to update this parameter for each individual determination operation in order to obtain an optimum operating response. 
     For these reasons, it is advantageous to set the first threshold value  103   a  on the basis of the RSSI signal, which has been derived on the basis of equation (14) above. The peak values  401   a - 401   n  detected using the set first threshold value  103   a  are stored in an output buffer store (not shown) and are then supplied to the processor device  601  via the processor bus  603 . 
     In the case of hardware calculation of the first threshold value  103   a , it is also necessary to supply the first threshold value to the processor device  601 , since calculation of the second threshold value  103   b  is based on the first threshold value  103   a , cf. equation (17) above. 
     The processor device  601   a  has a data transmission path profile unit  502   a , a data transmission path detection unit  502   b  and a filtering device  503 . As described above with reference to  FIG. 5 , in this way the second and third threshold values  103   b  and  103   c  are used to produce a finger positioning signal  504  and to output it to a downstream processing device  308 . 
     One advantage of the exemplary embodiment described with reference to  FIG. 6  is that implementing the first stage, i.e. peak value detection device  501 , in the matched hardware block  602   a  significantly reduces the volume of data which need to be transferred from the matched hardware block  602   a  to the processor device  601   a  via the processor bus. 
       FIG. 7  shows a further preferred exemplary embodiment of the present invention. A processor device  601   b  is connected to a matched hardware block  602   b  by means of processor bus  603 . The matched hardware block  602   b  in the exemplary embodiment in  FIG. 7  has, besides the power delay profile determination unit, a peak value sorting unit, with the received signal  301  respectively being supplied to the power delay profile determination unit  303  first of all. 
     The output signal from the power delay profile determination unit  303  is supplied to the peak value sorting unit  701 , which provides sorting of the peak values  401   a - 401   n  in terms of a received signal power  107 . 
     In the exemplary embodiment shown in  FIG. 7 , peak value detection is performed in a peak value detection device  501  provided in the processor device  601   b . In the exemplary embodiment shown in  FIG. 7 , the first threshold value  103   a  now does not need to be provided in advance, in contrast to the exemplary embodiment shown in  FIG. 6 , but rather is set by a threshold value setting unit  702 . A permanently set number of detected peak values which are sorted in terms of their magnitude by the peak value sorting unit  701  ensures that it is always the peak values  401   a - 401   n  with the highest received signal power  107  which are processed. 
     The first threshold value  103   a , provided by the threshold value setting unit, is also supplied to the data transmission path detection unit  502   b , in which the second threshold value  103   b  is set on the basis of the first threshold value  103   a . The remaining blocks in the processor device  601   b  correspond, in terms of their manner of operation, to the blocks shown in  FIG. 6  and are not described further at this point. 
       FIG. 8  shows a third preferred exemplary embodiment of the present invention. In  FIG. 8 , a matched hardware block  602   c  contains no function blocks other than the power delay profile determination unit  303 . All other functions are performed in the processor device  601   c  in order to provide the correct finger positioning signal  504 . 
     The exemplary embodiment shown in  FIG. 8  opens up the highest level of flexibility for a threshold value calculation, but requires a relatively large output buffer store (not shown) for the matched hardware block  602   c  as a power delay profile determination unit  303 . 
     Although the present invention has been described above with reference to preferred exemplary embodiments, it is not limited thereto but rather can be modified in diverse ways. 
     The invention is also not limited to said application options.