Patent Publication Number: US-2006013290-A1

Title: Detection of synchronization timing in CDMA receiving apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a CDMA (Code Division Multiple Access) receiving apparatus, and a method of detecting a synchronization timing in the CDMA receiving apparatus.  
      2. Description of the Related Art  
      A CDMA receiving apparatus in accordance with the CDMA communication standard calculates a delay profile indicative of a relative power value distribution in a time direction based on a correlation value of a received signal to a known code sequence, selects a synchronization timing of the received signal by detecting a peak on the calculated delay profile as a path, and demodulates the received signal using the selected synchronization timing (see, for example, JP-A-10-336072 and JP-A-2003-78448 which are hereinafter called “Documents 1, 2” respectively).  
      In the following, the configuration of a conventional CDMA receiving apparatus of the type mentioned above will be described in detail with reference to  FIGS. 1 and 2 .  
      A CDMA receiving apparatus illustrated in  FIG. 1  is a CDMA receiving apparatus disclosed in Document 2. This CDMA receiving apparatus comprises antenna  300 , radio receiver unit  302 , correlated power calculation unit  304 , path detector unit  306 , path level thresholding unit  308 , finger-assigned path selector unit  310 , finger assignment unit  312 , and demodulation processing unit  314 .  
      Radio receiver unit  302  converts analog radio signal  301  received by antenna  300  to digital baseband signal  303 .  
      Correlated power calculator  304  calculates a correlated value of digital baseband signal  303 , and further calculates delay profile  305  by converting the correlated value to a power value.  
      Path detector unit  306  detects N peaks on delay profile  305  as paths, and generates timing/level information  307 - 1 - 307 -N indicative of a path timing and a path level associated with each of the N detected paths.  
      Path level thresholding unit  308  determines whether or not each of the N detected paths is equal to or higher than a path level threshold, selects M paths which are equal to or higher than the path level threshold, and generates M pieces of path timing /level information  309 - 1 - 309 -M.  
      Finger-assigned path selector unit  310  selects paths assigned to fingers (finger-assigned paths) from M candidate paths equal to or higher than the path level threshold starting in order from the path having the highest level, and excludes paths within the same-path detection time range previously set centered at each selected path, from candidates for finger-assigned paths, from the next selections onward. Also, finger-assigned path selector unit  310  generates K pieces of timing/level information  311 - 1 - 311 -K on K finger-assigned paths selected by the foregoing processing.  
      Finger assignment unit  312  assigns the path timings of the K finger-assigned paths to J fingers as synchronization timings, and generates J pieces of path timing information  313 - 1 - 313 -J.  
      Demodulation processing unit  314  performs demodulation processing such as despreading, RAKE combining, decoding and the like using the synchronization timings assigned to the J fingers by finger assignment unit  312 .  
      In the CDMA receiving apparatus illustrated in  FIG. 1 , path level thresholding unit  308  selects detected paths which have a level equal to or higher than the path level threshold on delay profile  305 , finger-assigned path selector unit  310  selects the detected paths equal to or higher than the path level threshold as finger-assigned paths, and demodulation processing unit  314  demodulates a received signal using path timings of the finger-assigned paths as synchronization timings. The same-path detection time range has been previously set in finger-assigned path selector unit  310 . Therefore, finger-assigned path selector unit  310  regards a path falling within the previously set same-path detection time range and having a level equal to or higher than the path level threshold as the same path as a previously selected finger-assigned path, and excludes such a path from candidates for finger-assigned paths from the next selection onward.  
      Communication signals in the CDMA communication standard are not correlated to each other if their path timings are spaced apart by 1 chip or more. For this reason, the same-path detection time range is generally set in a range of ±0.5 chips centered at the path timing of a detected path.  
      Accordingly, finger-assigned path selector  310  regards paths found within ±0.5 chips from a previously selected finger-assigned path as the same paths as the finger-assigned path, and excludes those paths from candidates for finger-assigned paths from the next selection onward irrespective of whatever path level they have. In this way, finger-assigned path selector unit  310  can be prevented from erroneously detecting a path found within ±0.5 chips centered at the path timing of a finger-assigned path as another finger-assigned path. On the other hand, however, if paths arrive in a concentrated manner at the same time, a large number of paths cannot be detected as finger-assigned paths.  
      An article “CDMA Path-search Method Using a Combined Delay Profile of Diversity Antennas” by Aoyama, Yoshida, and Ushirokawa (The Institute of Electronics, Information and Communication Engineers, Technical Report, RCS99-67, 1999) shows that many paths arrive in a concentrated manner in an interval of approximately two chips under radio wave propagation environments in urban areas. When the same-path detection time range is set to ±0.5 chips under in environments, a large number of paths cannot be detected.  
      Therefore, a uniquely set same-path detection time range can cause a lower path detectability factor depending on certain radio wave propagation environments, thus leading to a lower demodulation accuracy in the RAKE combining, and a degraded reception quality.  
      On the other hand, a CDMA receiving apparatus illustrated in  FIG. 2  employs an array antenna composed of a plurality of antenna elements. This CDMA receiving apparatus calculates not only a delay profile indicative of a correlated power level distribution in the time direction but also an angle profile indicative of a correlated power level distribution in an angle direction to set a same-path detection time range and a same-path detection angle range in the time direction and angle direction, respectively. This CDMA receiving apparatus comprises a plurality of antennas  400 - 1 - 400 D, radio receiver unit  402 , correlated value calculation unit  404 , beam former unit  406 , path detector unit  408 , path level thresholding unit  410 , finger-assigned path selector unit  412 , finger assignment unit  414 , and demodulation processing unit  416 .  
      Radio receiver unit  402  converts analog radio signals  401 - 1 - 401 -D received respectively by antennas  400 - 1 - 400 -D to digital baseband signals  403 - 1 - 403 -D, respectively.  
      Correlated value calculation unit  404  calculates correlated values for digital baseband signals  403 - 1 - 403 -D, and generates correlated values  405 - 1 - 405 -D.  
      Beam former unit  406  multiplies correlated values  405 - 1 - 405 -D by an antenna weight, calculates a sum of the products over antennas, and further converts the resulting sum to power values to calculate two-dimensional profile  407  which is a combination of the delay profile with the angle profile.  
      Path detector unit  408  detects N peaks on two-dimensional profile  407  as paths, and generates timing/direction of arrival/level information  409 - 1 - 409 -N indicative of a path timing, direction of arrival, and a path level of each of the N detected paths.  
      Path level thresholding unit  410  determines whether or not N detected paths are each equal to or higher than a path level threshold, selects M paths equal to or higher than the path level threshold, and generates M pieces of path timing/direction of arrival/level information  411 - 1 - 411 -M.  
      Finger-assigned path selector unit  412  selects finger-assigned paths, from M candidate paths equal to or higher than the path level threshold, starting in order from the path having the highest level, and excludes paths within a previously set same-path detection time range and same-path detection angle range centered at each selected path, from candidates for finger-assigned paths, from the next selection onward. Also, finger-assigned path selector unit  412  generates timing/direction of arrival/level information  413 - 1 - 413 -K on K finger-assigned paths selected by the foregoing processing.  
      Finger assignment unit  414  assigns the path timings and directions of arrival of the K finger-assigned paths to J fingers as synchronization timings and arrival directions, respectively, and generates J pieces of path timing/ direction of arrival information  415 - 1 - 415 -J.  
      Demodulation processing unit  416  performs demodulation processing on digital baseband signals  403 - 1 - 403 -D using the synchronization timings and directions of arrival assigned to the J fingers, including despreading, beam forming, RAKE combining, decoding, and the like.  
      In the CDMA receiving apparatus illustrated in  FIG. 2 , beam former unit  406  can generate an angle profile in the angle direction in addition to the delay profile in the time direction by multiplying correlated values  405 - 1 - 405 -D by antenna weights and calculates a sum of the products over antennas. Also, path detector unit  408  can estimate the arrival direction of the received signal in addition to the synchronization timing of the received signal by detecting paths from two-dimensional profile  407 .  
      However, since the same-path detection time range in the time direction is uniquely set on the delay profile, the demodulation accuracy becomes lower in the RAKE combining depending on some radio wave propagation environments, resulting in a degraded reception quality, as is the case with the CDMA receiving apparatus illustrated in  FIG. 1 . Also, the same-path detection angle range in the angle direction is uniquely set on the angle profile, causing a deterioration in path detection rate, a failure in accurately finding the direction of arrival of a received signal, and a degraded reception quality.  
      As described above, conventional CDMA receiving apparatuses experience the problem of degraded reception quality due to the same-path detection time range which is uniquely set irrespective of the radio wave propagation environment.  
     SUMMARY OF THE INVENTION  
      It is therefore an object of the present invention to provide a CDMA receiving apparatus which is capable of maintaining a reception quality irrespective of a radio wave propagation environment, and to provide a method of detecting synchronization timing in the CDMA receiving apparatus.  
      According to a first aspect of the present invention, a CDMA receiving apparatus includes an antenna, calculating means, path detecting means, path level thresholding means, delay spread calculating means, same-path detection time range calculating means, finger-assigned path selecting means, and demodulation processing means.  
      The calculating means calculates a delay spread indicative of a correlated power value distribution in a time direction of a signal received by the antenna. The path detecting means detects peaks on the delay profile as paths. The path level thresholding means determines whether or not each of the detected paths has a path level equal to or higher than a path level threshold.  
      The delay spread calculating means calculates a delay spread based on path timings and path levels of paths which are determined to have a path level equal to or higher than the path level threshold. The same-path detection time range calculating means calculates a same-path detection time range in accordance with the delay spread.  
      The finger-assigned path selecting means selects finger-assigned paths from those paths determined to have a path level equal to or higher than the path level threshold starting in order from the one having the highest level, and excludes paths within the same-path detection time range centered at each selected path, from candidates for finger-assigned paths, from the next selection onward.  
      The demodulation processing means demodulates the received signal using the path timings of the finger-assigned paths as synchronization timings.  
      According to the first aspect, a same-path detection time range is selected in accordance with a particular radio wave propagation environment by calculating a delay spread based on path timings and path levels of paths, and paths are selected for assignment to fingers using the same-path detection time range. It is therefore possible to improve the accuracy of detecting synchronization timings for a received signal and to improve the reception quality of the CDMA receiving apparatus.  
      According to a second aspect of the present invention, a CDMA receiving apparatus includes a plurality of antennas, calculating means, path detecting means, path level thresholding means, delay spread calculating means, same-path detection time range calculating means, angle spread calculating means, same-path detection angle range calculating means, finger-assigned path selecting means, and demodulation processing means.  
      The calculating means calculates a delay profile indicative of a correlated power value distribution in a time direction of the signals received by the plurality of antennas and an angle profile indicative of a correlated power value distribution in an angle direction of the received signals, and combines the delay profile with the angle profile to calculate a two-dimensional profile. The path detecting means detects peaks on the two-dimensional profile as paths. The path level thresholding means determines whether or not each of the detected paths has a path level equal to or higher than a path level threshold.  
      The delay spread calculating means calculates a delay spread based on path timings and path levels of paths which are determined to have a level equal to or higher than the path level threshold. The same-path detection time range calculating means calculates a same-path detection time range in accordance with the delay spread.  
      The angle spread calculating means calculates an angle spread based on directions of arrival and path levels of the paths determined to have a level equal to or higher than the path level threshold. The same-path detection angle range calculating means calculates a same-path detection angle range in accordance with the angle spread.  
      The finger-assigned path selecting means selects finger-assigned paths from paths determined to have a level equal to or higher than the path level threshold starting in order from the path having the highest level, and excludes paths within the same-path detection time range and the same-path detection angle range centered at each selected path, from candidates for finger-assigned paths, from the next selection onward.  
      The demodulation processing means demodulates the received signals by using the path timings of the finger-assigned paths as the synchronization timings, and by using the directions of arrival of the finger-assigned paths as directions of arrival of the received signals.  
      According to the second aspect, a delay spread is calculated based on path timings and path levels of paths, and an angle spread is calculated based on directions of arrival and path levels of the paths to select a same-path detection time range and a same-path detection angle range in accordance with a particular radio wave propagation environment, and paths are selected for assignment to fingers using the same-path detection time range and same-path detection angle range. It is therefore possible to improve the accuracy of detecting synchronization timings for received signals, to accurately find directions of arrival of the received signals, and to improve the reception quality of the CDMA receiving apparatus.  
      The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram illustrating an exemplary configuration of a conventional CDMA receiving apparatus;  
       FIG. 2  is a block diagram illustrating another exemplary configuration of a conventional CDMA receiving apparatus;  
       FIG. 3  is a block diagram illustrating the configuration of a CDMA receiving apparatus according to a first embodiment of the present invention;  
       FIG. 4  is a graph showing a first path detection example which is illustrative of paths detected by the CDMA receiving apparatus illustrated in  FIG. 3 ;  
       FIG. 5  is a graph showing a second path detection example which is illustrative of a path detected by the CDMA receiving apparatus illustrated in  FIG. 3 ;  
       FIG. 6  is a block diagram illustrating the configuration of a CDMA receiving apparatus according to a second embodiment of the present invention;  
       FIG. 7  is a graph showing a third path detection example which is illustrative of a path detected by the CDMA receiving apparatus illustrated in  FIG. 6 ; and  
       FIG. 8  is a graph showing a fourth path detection example which is illustrative of another example of a path detected by the CDMA receiving apparatus illustrated in  FIG. 6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      First Embodiment  
      Referring to  FIG. 3 , a CDMA receiving apparatus of a first embodiment comprises antenna  100 , radio receiver unit  102 , correlated power calculation unit  104 , path detector unit  106 , path level thresholding unit  108 , delay spread calculation unit  110 , same-path detection time range calculation unit  112 , finger-assigned path selector unit  114 , finger assignment unit  116 , and demodulation processing unit  118 .  
      Radio receiver unit  102  converts analog radio signal  101  received by antenna  100  to digital baseband signal  103 .  
      Correlated power calculation unit  104  calculates a correlated value of digital baseband signal  103 , and converts the correlated value to a power value to generate delay profile  105 .  
      Path detector unit  106  detects N peaks on delay profile  105  as paths, and generates timing/level information  107 - 1 - 107 -N each indicative of a path timing and a path level associated with each of the N detected paths.  
      Path level thresholding unit  108  determines whether or not each of the N detected paths is equal to or higher than a path level threshold, selects M paths equal to or higher than the path level threshold, and generates M pieces of path timing/level information  109 - 1 - 109 -M.  
      Delay spread calculation unit  110  calculates delay spread  111  based on the path timings and path levels of the M paths which are equal to or higher than the path level threshold.  
      Same-path detection time range calculation unit  112  calculates same-path detection time range  113  in accordance with delay spread  111 .  
      Finger-assigned path selector unit  114  selects finger-assigned paths from M candidate paths equal to or higher than the path level threshold starting in order from the path having the highest level, and simultaneously excludes paths within same-path detection time range  113  centered at each selected path, from candidates for finger-assigned paths, from the next selection onward. Also, finger-assigned path selector unit  114  generates K pieces of timing/level information  115 - 1 - 115 -K on K finger-assigned paths selected by the foregoing processing.  
      Finger assignment unit  116  assigns the path timings of the K finger-assigned paths to J fingers as synchronization timings, and generates J pieces of path timing information  117 - 1 - 117 -J.  
      Demodulation processing unit  118  demodulates digital baseband signal  103  by performing despreading, RAKE combining, decoding and the like using the synchronization timings assigned to the J fingers by finger assignment unit  116 .  
      Now, characteristic features of this embodiment will be described in detail.  
      Delay spread calculation unit  110  calculates delay spread  111  based on path timing/level information  109 - 1 - 109 -M on the M paths, whose path levels, as determined by path level thresholding unit  108 , are equal to or higher than the path level threshold. Delay spread  111  is an index indicative of a temporal dispersion of paths on delay profile  105  which is calculated based on the timing and level of each path, and is calculated by the following Equation 1:  
               σ   τ     =         1       ∑     i   =   1     N     ⁢     P   i         ·       ∑     i   =   1     N     ⁢         (       τ   i     -     τ   ave       )     2     ⁢     P   i                     (     Eq   .           ⁢   1     )             
 
      where i represents a path number; N the number of paths; P i  the path level of an i-th path; τ i  a path timing of the i-th path; and τ ave  an average path timing which is calculated by the following Equation 2:  
               τ   ave     =       1       ∑     i   =   1     N     ⁢     P   i         ·       ∑     i   =   1     N     ⁢       τ   i     ⁢     P   i                   (     Eq   .           ⁢   2     )             
 
      In this way, delay spread  111  calculated by delay spread calculation unit  110  is large when paths having similar levels are positioned apart from one another, and is small when paths having similar levels are concentrated.  
      Same-path detection time range calculation unit  112  determines same-path detection time range  113  corresponding to delay spread  111  calculated by delay spread calculation unit  110  based on a previously set reference table in which the delay spread corresponds to the same-path detection time range, and applies determined same-path detection time range  113  to finger-assigned path selector unit  114 . In this event, since paths are assumed to arrive in a dispersive manner when delay spread  111  is large, same-path detection time range calculation unit  112  selects large same-path detection time range  113 . In this way, the finger-assigned path selector unit  114  subsequently can be prevented from regarding a path close to a previously selected finger-assigned path as another path and erroneously detecting this path as another finger-assigned path. On the other hand, since paths are assumed to arrive concentrated together when delay spread  111  is small, same-path detection time range calculation unit  112  selects small same-path detection time range  113 . In this way, finger-assigned path selector unit  114  subsequently can be prevented from regarding a path close to a previously selected finger-assigned path as a same path and not detecting this path as another finger-assigned path.  
      Consider, for example, two examples of detected paths represented by delay profiles as shown in  FIGS. 4 and 5 , respectively. In the following, the example of detected paths shown in  FIG. 4  is called the “first path detection example,” and the example of detected paths shown in  FIG. 5  is called the “second path detection example.” A comparison of the two path detection examples reveals that a plurality of paths at similar levels arrive in a dispersive manner over time in the first path detection example, whereas a plurality of paths arrive largely concentrated together within the small time range in the second path detection example. Table 1 shows a path timing and a path level value of each path in the first path detection example, and Table 2 shows a path timing and a path level value of each path in the second path detection example.  
                           TABLE 1                       Path       Path Timing           Number   Path Name   (chip)   Path Level                  1   Path A   2.00   14        2   Path B   3.50   12        3   Path C   5.50   12        4   Path D   8.25   13        5   Path a   1.75   7       6   Path b   2.25   9       7   Path c   2.50   6       8   Path d   3.00   6       9   Path e   3.25   9       10    Path f   3.75   6       11    Path g   5.00   6       12    Path h   5.25   9       13    Path i   5.75   8       14    Path j   8.50   6                  
 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
               
               
                 Path 
                   
                 Path Timing 
                   
               
               
                 Number 
                 Path Name 
                 (chip) 
                 Path Level 
               
               
                   
               
             
            
               
                 1 
                 Path A 
                 3.50 
                  9 
               
               
                 2 
                 Path B 
                 4.25 
                 11 
               
               
                 3 
                 Path C 
                 5.00 
                 11 
               
               
                 4 
                 Path D 
                 5.75 
                 12 
               
               
                 5 
                 Path a 
                 3.25 
                  7 
               
               
                 6 
                 Path b 
                 3.75 
                  8 
               
               
                 7 
                 Path c 
                 4.00 
                 10 
               
               
                 8 
                 Path d 
                 4.50 
                 10 
               
               
                 9 
                 Path e 
                 4.75 
                 10 
               
               
                 10  
                 Path f 
                 5.25 
                  9 
               
               
                 11  
                 Path g 
                 5.50 
                 10 
               
               
                 12  
                 Path h 
                 6.00 
                 10 
               
               
                   
               
            
           
         
       
     
      In the first path detection example, paths A-D and paths a-j have levels equal to or higher than the path level threshold. Thus, delay spread calculation unit  110  calculates delay spread  111  using the path timings and path levels of these paths. Specifically, delay spread calculation unit  110  substitutes the values in Table 1 for the values in Equation 1 to calculate delay spread  111  of the first path detection example to be 2.13 chips. In the second path detection example, on the other hand, paths A-D and paths a-h have levels equal to or higher than the path level threshold. Thus, delay spread calculation unit  110  calculates delay spread  111  using the path timings and path levels of these paths. Specifically, delay spread calculating unit  110  substitutes the values in Table 2 for the values in Equation 1 to calculate delay spread  111  of the second path detection example to be 0.84 chips.  
      Same-path detection time range calculation unit  112  employs a reference table which selects 0.75 chips for same-path detection time range  113 , for example, when delay spread  111  is equal to or more than one chip, and selects 0.25 chips for same-path detection time range  113  when delay spread  111  is less than one chip. When such a reference table is used, same-path detection time range calculation unit  112  selects 0.75 chips as same-path detection time range  113  for the first path detection example, and selects 0.25 chips as same-path detection time range  113  for the second path detection example.  
      Therefore, in the first path detection example, subsequent finger-assigned path selector unit  114  regards paths outside of a range of ±0.75 chips centered at a path timing of a previously selected finger-assigned path as other paths. In the second path detection example, in turn, subsequent finger-assigned path selector unit  114  regards paths outside of a range of ±0.25 chips centered at a path timing of a previously selected finger-assigned path, as other paths.  
      Finger-assigned path selector unit  114  selects finger-assigned paths from those paths equal to or higher than the path level threshold starting in order from the one having the highest level, and simultaneously excludes all paths within same-path detection time range  113  centered at each selected path, from candidates for finger-assigned paths, from the next selection onward. In this event, when there are paths at the same level, finger-assigned path selector unit  114  preferentially selects the one which is earlier in path timing.  
      Specifically, in the first path detection example, finger-assigned path selector unit  114  first selects path A as a finger-assigned path, and simultaneously excludes paths found within a range of ±0.75 chips centered at path A, from candidates for finger-assigned paths, from the next selection onward, so that paths a-c will never be selected, from the next time onward. Then, finger-assigned path selector unit  114  performs similar processing on path D. By repeating the foregoing sequence, finger-assigned path selector unit  114  selects a total of four paths A-D. In the second path detection example, in turn, finger-assigned path selector unit  114  first selects path D as a finger-assigned path, and simultaneously excludes paths found within a range of ±0.25 chips centered at path D, from candidates for finger-assigned paths, from the next selection onward, so that paths g-h will never be selected from the next time onward. Then, finger-assigned path selector unit  114  performs similar processing on path B. By repeating the foregoing sequence, finger-assigned path selector unit  114  selects a total of four paths A-D.  
      Correspondingly, in a conventional CDMA receiving apparatus, in which the path detection time range is uniquely set, for example, to 0.25 chips when paths A-D have actually arrived in the first path detection example, path c close to path A, path d close to path B, and path g close to path C are erroneously selected as other finger-assigned paths. On the other hand, in a conventional CDMA receiving apparatus, in which path detection time range is uniquely set, for example, to 0.75 chips when paths A-D have actually arrived in the second path detection example, only paths B, D are selected as other finger-assigned paths.  
      In the first embodiment as described above, same-path detection time range  113  is adaptively determined with delay spread  111 , and paths are selected for assignment to fingers using this same-path detection time range  113 . In this way, accuracy is increased in the detection of the synchronization timing for a received signal so that the reception quality can be improved for the CDMA receiving apparatus.  
      In the following, the operation of the CDMA receiving apparatus according to the first embodiment will be described with reference to  FIG. 3 .  
      Analog radio signal  101  received by antenna  100  is converted to digital baseband signal  103  by radio receiver unit  102 , and digital baseband signal  103  is delivered to correlated power calculation unit  104  and demodulation processing unit  118 .  
      Correlated power calculation unit  104  multiplies digital baseband signal  103  by a known code sequence to calculate a correlated value, and further converts the correlated value to a power value to calculate delay profile  105 .  
      Path detector unit  106  detects N peaks on delay profile  105  starting in order from the one having the highest level, and delivers timing/level information  107 - 1 - 107 -N indicative of a path timing and a path level of each of the detected paths to path level thresholding unit  108 .  
      Path level thresholding unit  108  selects M paths having levels equal to or higher than a previously set path level threshold from the N paths detected by path detector unit  106 . The path level threshold in this event may be calculated by multiplying an average value of delay profile  105  by a previously set coefficient or by multiplying a maximum path level by a previously set coefficient equal to or less than one, but it does not herein particularly matter how the path level threshold is set.  
      M pieces of timing/level information  109 - 1 - 109 -M on the M paths having levels equal to or higher than the path level threshold are delivered from path level thresholding unit  108  to delay spread calculation unit  110  and finger-assigned path selector unit  114 .  
      Delay spread calculation unit  110  substitutes the path timings and path level values of the M paths selected by path level thresholding unit  108  for the values in Equation 1 based on timing/level information  109 - 1 - 109 -M to calculate delay spread  111  which is then delivered to same-path detection time range calculation unit  112 .  
      Same-path detection time range calculation unit  112  selects same-path detection time range  113  in accordance with delay spread  111  using a previously set reference table, and delivers selected same-path detection time range  113  to finger-assigned path selector unit  114 .  
      Finger-assigned path selector unit  114  selects finger-assigned paths from the M paths selected by path level thresholding unit  108  starting in order from the one having the highest level based on timing/level information  109 - 1 - 109 -M and same-path detection time range  113 , and simultaneously regards those paths found within same-path detection time range  113  of the selected path as the same path to exclude the paths from candidates for finger-assigned paths from the next selection onward. By repeating the foregoing sequence, finger-assigned path selector unit  114  selects K paths as finger-assigned paths. Then, finger-assigned path selector unit  114  delivers K pieces of timing/level information  115 - 1 - 115 -K on the K paths to finger assignment unit  116 .  
      Finger assignment unit  116  assigns the K finger-assigned paths to J fingers using the path timings of the K finger-assigned paths as synchronization timings based on timing/level information  115 - 1 - 115 -K. In this event, the fingers may be assigned by the following methods. A first method selects paths starting in order from the one having the highest level for assignment when J is less than K due to limitations and the like on the capacity of hardware associated with the CDMA receiving apparatus. A second method makes (J-K) fingers invalid such that they are not used in RAKE combining when K is less than J. A third method preferentially assigns those paths, found in a certain range of the path timing of a path that have been assigned to a finger in the preceding time, to the same finger as the preceding one. Assume however that it does not particularly matter how fingers are assigned. Then, finger assignment unit  116  delivers timing information  117 - 1 - 117 -J on paths assigned to J fingers to demodulation processing unit  118  as synchronization timings of the received signal.  
      Demodulation processing unit  118  demodulates digital baseband signal  103  of the received signal by performing despreading, RAKE combining, decoding and the like using timing information  117 - 1 - 117 -J assigned to the J fingers as synchronization timings.  
      Second Embodiment  
      A CDMA receiving apparatus of a second embodiment employs array antennas compose of a plurality of antenna elements. The CDMA receiving apparatus of this embodiment calculates not only a delay profile indicative of a correlated power value distribution in the time direction but also an angle profile indicative of a correlated power value distribution in an angle direction, and calculates a same-path detection time range and a same-path detection angle range in the time and angle directions, respectively. In this way, the CDMA receiving apparatus can accurately detect a synchronization timing and an arrival direction of a received signal.  
      Referring to  FIG. 6 , the CDMA receiving apparatus of this embodiment comprises antennas  200 - 1 - 200 -D composed of antenna elements, radio receiver unit  202 , correlated value calculation unit  204 , beam former unit  206 , path detector unit  208 , path level thresholding unit  210 , delay spread calculation unit  212 , same-path detection time range calculation unit  214 , angle spread calculation unit  216 , same-path detection angle range calculation unit  218 , finger-assigned path selector unit  220 , finger assignment unit  222 , and demodulation processing unit  224 .  
      Radio receiver  202  converts analog radio signals  201 - 1 - 201 -D respectively received by antennas  200 - 1 - 200 -D to digital baseband signals  203 - 1 - 203 -D, respectively.  
      Correlated value calculation unit  204  calculates correlated values  205 - 1 - 205 -D for digital baseband signals  203 - 1 - 203 -D, and delivers correlated values  205 - 1 - 205 -D.  
      Beam former unit  206  multiplies each of correlated values  205 - 1 - 205 -D by antenna weights, calculates a sum of the products over antennas, and further converts the resulting sum to a power value to calculate two-dimensional profile  207  which is a combination of the delay profile and the angle profile.  
      Path detector unit  208  detects N peaks on two-dimensional profile  207  as paths and generates N pieces of timing/direction of arrival/level information  209 - 1 - 209 -N each indicative of a path timing, a direction of arrival, and a path level of each of the N detected paths.  
      Path level thresholding unit  210  determines whether or not the N detected paths are equal to or higher than a path level threshold, selects M paths which are equal to or higher than the path level threshold, and generates M pieces of timing/direction of arrival/level information  211 - 1 - 211 -M on the M paths.  
      Delay spread calculation unit  212  calculates delay spread  213  based on the path timings and path levels of the M paths which are equal to or higher than the path level threshold.  
      Same-path detection time range calculation unit  214  calculates same-path detection time range  215  in accordance with delay spread  213 .  
      Angle spread calculation unit  216  calculates angle spread  217  based on the directions of arrival and path levels of the M paths which are equal to or higher than the path level threshold.  
      Same-path detection angle range calculation unit  218  calculates same-path detection angle range  219  in accordance with angle spread  217 .  
      Finger-assigned path selector unit  220  selects finger-assigned paths, from the M paths equal to or higher than the path level threshold, starting in order from the one having the highest path, and simultaneously excludes those paths found within same-path detection time range  215  and same-path detection angle range  219  centered at each selected path, from candidates for finger-assigned paths, from the next selection onward. Then, finger-assigned path selector unit  220  generates K pieces of timing/direction of arrival/level information  221 - 1 - 221 -K on the K finger-assigned paths selected through the foregoing processing.  
      Finger assignment unit  222  assigns the path timings and directions of arrival of the K finger-assigned paths to J fingers, respectively, as synchronization timings and arrival directions, and generates J pieces of timing/direction of arrival information  223 - 1 - 223 -J on the J paths.  
      Demodulation processing unit  224  demodulates digital baseband signals  203 - 1 - 203 -D by performing despreading, beam forming, RAKE combining, decoding and the like using the synchronization timing and arrival directions assigned to the J fingers by finger assignment unit  222 .  
      Specifically, the second embodiment differs from the first embodiment illustrated in  FIG. 3  in that the former additionally includes beam former unit  206  and angle spread calculation unit  216 , that the former additionally includes same-path detection angle range calculation unit  218 , that antennas  200 - 1 - 200 -D are composed of a plurality of antenna elements, and that correlated power calculation unit  104  is replaced with correlation calculation unit  204 .  
      Now, characteristic features of the second embodiment will be described in detail. The following description will be mainly focused on the configuration associated with the calculation of same-path detection angle range  219 .  
      Angle spread calculation unit  216  calculates angle spread  217  based on path timing/direction of arrival/level information  211 - 1 - 211 -M of the M paths, whose path levels, as determined by path level thresholding unit  210 , are equal to or higher than the path level threshold. Angle spread  217  is an index indicative of a spatial dispersion of paths on the angle profile that is calculated based on the direction of arrival and path level of each path, and is calculated by the following Equation 3:  
               σ   θ     =         1       ∑     i   =   1     N     ⁢     P   i         ·       ∑     i   =   1     N     ⁢         (       θ   i     -     θ   ave       )     2     ⁢     P   i                     (     Eq   .           ⁢   3     )             
 
      where i represents a path number; N the number of paths; P i  the path level of an i-th path; θ i  a direction of arrival of the i-th path; and θ ave  an average direction of arrival of paths which is calculated by the following Equation 4:  
               θ   ave     =       1       ∑     i   =   1     N     ⁢     P   i         ·       ∑     i   =   1     N     ⁢       θ   i     ⁢     P   i                   (     Eq   .           ⁢   4     )             
 
      In this way, angle spread  217  calculated by angle spread calculation unit  216  is large when paths having similar levels arrive spatially apart from one another, and is small when paths arrive in a concentrated together at similar angles.  
      Same-path detection angle range calculation unit  218  determines same-path detection angle range  219  corresponding to angle spread  217  calculated by angle spread calculation unit  216  based on a previously set reference table in which the angle spread corresponds to the same-path detection angle range, and applies determined same-path detection angle range  219  to finger-assigned path selector unit  220 . In this event, since paths are assumed to arrive spatially in a dispersive manner when angle spread  217  is large, same-path detection angle range calculation unit  218  selects large same-path detection angle range  219 . In this way, finger-assigned path selector unit  220  subsequently can be prevented from regarding a path close to a previously selected finger-assigned path as another path and erroneously detecting this path as another finger-assigned path. On the other hand, since paths are assumed to arrive in concentration substantially at the same angle when angle spread  217  is small, same-path detection angle range calculation unit  218  selects small same-path detection angle range  219 . In this way, subsequent finger-assigned path selector unit  220  can be prevented from regarding a path close to a previously selected finger-assigned path as a same path and not detecting this path as another finger-assigned path.  
      Consider, for example, two examples of detected paths represented by delay profiles as shown in  FIGS. 7 and 8 . In the following, the example of detected paths shown in  FIG. 7  is called the “third path detection example,” and the example of detected paths shown in  FIG. 8  is called the “fourth path detection example.” A comparison of the two path detection examples reveals that a plurality of paths at similar levels arrive spatially in a dispersive manner in the third path detection example, whereas a plurality of paths arrive substantially concentrated together within the small angular range in the fourth path detection example. Table 3 shows a direction of arrival and a path level value of each path in the third path detection example, and Table 2 shows a direction of arrival and a path level value of each path in the fourth path detection example.  
                           TABLE 3                       Path       Direction of Arrival           Number   Path Name   (deg)   Path Level                                                1   Path A   −24   13.5       2   Path B   −10   11       3   Path C   10   11.5       4   Path D   32   13       5   Path a   −26   8       6   Path b   −22   9       7   Path c   −20   6       8   Path d   −12   6       9   Path e   −8   7       10    Path f   8   7       11    Path g   12   8       12    Path h   30   8.5       13    Path i   34   7                  
 
     
       
         
           
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
               
               
                 Path 
                   
                 Direction of Arrival 
                   
               
               
                 Number 
                 Path Name 
                 (deg) 
                 Path Level 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 Path A 
                 −6 
                 14  
               
               
                 2 
                 Path B 
                 0 
                 12  
               
               
                 3 
                 Path C 
                 6 
                 12  
               
               
                 4 
                 Path D 
                 12 
                 13  
               
               
                 5 
                 Path E 
                 18 
                 7 
               
               
                 6 
                 Path a 
                 −4 
                 9 
               
               
                 7 
                 Path b 
                 −2 
                 6 
               
               
                 8 
                 Path c 
                 2 
                 6 
               
               
                 9 
                 Path d 
                 4 
                 9 
               
               
                 10  
                 Path e 
                 8 
                 6 
               
               
                 11  
                 Path f 
                 10 
                 6 
               
               
                 12  
                 Path g 
                 14 
                 9 
               
               
                 13  
                 Path h 
                 16 
                 8 
               
               
                 14  
                 Path i 
                 20 
                 6 
               
               
                   
               
            
           
         
       
     
      In the third path detection example, paths A-D and paths a-i have levels equal to or higher than the path level threshold. Thus, angle spread calculation unit  216  calculates angle spread  217  using the directions of arrival and path levels of these paths. Specifically, angle spread calculation unit  216  substitutes the values in Table 3 for the values in Equation 3 to calculate angle spread  217  of the third path detection example to be 21.64 deg. In the fourth path detection example, on the other hand, paths A-E and paths a-i have levels equal to or higher than the path level threshold. Thus, angle spread calculation unit  216  calculates angle spread  217  using the directions of arrival and path levels of these paths. Specifically, angle spread calculating unit  216  substitutes the values in Table 4 for the values in Equation 3 to calculate angle spread  217  of the fourth path detection example to be 8.07 deg.  
      Same-path detection angle range calculation unit  218  employs a reference table which selects, for example, 6 deg for same-path detection angle range  219  when angle spread  217  is equal to or more than 10 deg, and selects 2 deg for same-path detection angle range  219  when angle spread  217  is less than 10 deg. When such a reference table is used, same-path detection angle range calculation unit  218  selects 6 deg as same-path detection angle range  219  for the third path detection example, and selects 2 deg as same-path detection angle range  219  for the fourth path detection example.  
      Therefore, in the third path detection example, finger-assigned path selector unit  220  subsequently regards paths outside of a range of ±6 deg centered at a direction of arrival of a previously selected finger-assigned path as other paths. In the fourth path detection example, in turn, finger-assigned path selector unit  220  subsequently regards paths outside of a range of ±2 deg centered at a direction of arrival of a previously selected finger-assigned path as other paths.  
      Finger-assigned path selector unit  220  selects finger-assigned paths, from paths equal to or higher than the path level threshold, starting in order from the one having the highest level, and simultaneously excludes all paths within same-path detection angle range  219  centered at each selected path, from candidates for finger-assigned paths, from the next selection onward. In this event, when there are paths at the same level, finger-assigned path selector unit  220  preferentially selects the one which has a smaller direction of arrival.  
      Specifically, in the third path detection example, finger-assigned path selector unit  220  first selects path A as a finger-assigned path, and simultaneously excludes paths found within a range of ±6 deg centered at path A, from candidates for finger-assigned paths, from the next selection onward, so that paths a-c will never be selected, from the next time onward. Then, finger-assigned path selector unit  220  performs similar processing on path D. By repeating the foregoing sequence, finger-assigned path selector unit  220  selects a total of four paths A-D. In the fourth path detection example, in turn, finger-assigned path selector unit  220  first selects path B as a finger-assigned path, and simultaneously excludes paths found within a range of ±2 deg centered at path B from candidates for finger-assigned paths, from the next selection onward, so that paths b-c will never be selected, from the next time onward. Then, finger-assigned path selector unit  220  performs similar processing on path C. By repeating the foregoing sequence, finger-assigned path selector unit  114  selects a total of five paths A-E.  
      Correspondingly, in a conventional CDMA receiving apparatus, in which the path detection angle range is uniquely set, for example, to 2 deg when paths A-D have actually arrived in the third path detection example, path c close to path A is erroneously selected as other finger-assigned path. On the other hand, in a conventional CDMA receiving apparatus, in which the path detection angle range is uniquely set, for example, to 6 deg when paths A-E have actually arrived in the fourth path detection example, only paths B, D, and i are selected as other finger-assigned paths because paths A, C, a-d are regarded as the same path as path B, and because paths E, e-h are regarded as the same path as path D, while path i is erroneously selected.  
      In the second embodiment as described above, same-path detection angle range  219  is adaptively determined with angle spread  217 , and paths are selected for assignment to fingers using this same-path detection angle range  219 , thereby making it possible to increase the accuracy in the detection of the arrival direction of a received signal and therefore to improve the reception quality of the CDMA receiving apparatus.  
      In the following, the operation of the CDMA receiving apparatus according to the second embodiment will be described with reference to  FIG. 6 .  
      Analog radio signals  201 - 1 - 201 -D received by antennas  200 - 1 - 200 -D are converted to digital baseband signals  203 - 1 - 203 -D respectively by radio receiver  202 , and digital baseband signals  203 - 1 - 203 -D are delivered to correlated value calculation unit  204  and demodulation processing unit  224 .  
      Correlated value calculation unit  204  multiplies digital baseband signals  203 - 1 - 203 -D by a known code sequence to calculate correlated values  205 - 1 - 205 -D which are delivered to beam former unit  206 . The processing up to this stage is performed independently for each of the antenna elements.  
      Beam former unit  206  multiplies correlated value  205 - 1 - 205 -D of each antenna element by antenna weights, calculates a sum of the products over antennas, and further converts the resulting sum to power values to calculate two-dimensional profile  207 . Two-dimensional profile  207  may be calculated by multiplying antenna weights corresponding to a direction of arrival for each angle resolution by the correlated value to form multiple beams to calculate two-dimensional profile  207 , but it does not particularly matter how two-dimensional profile  207  is calculated. Also, a calibration loop may be added to compensate a received signal for variations in phase and amplitude in the receiving apparatus so as to find a calibration coefficient in order to correct the antenna weights, but the calibration processing is not herein particularly taken into consideration.  
      Path detector unit  208  selects N peaks on two-dimensional profile  207  from the one having the highest level for detection as paths. Path detector unit  208  further delivers N pieces of timing/direction of arrival/level information  209 - 1 - 209 -N each indicative of a path timing, a direction of arrival, and a path level of each of the N detected paths to path level thresholding unit  210 .  
      Path level thresholding unit  210  selects paths having levels equal to or higher than a previously set path level threshold from the N paths detected by path detector unit  208  based on timing/direction of arrival/level information  209 - 1 - 209 -N. The path level threshold in this event may be calculated by multiplying an average value of the two-dimensional profile by a previously set coefficient or by multiplying a maximum path level by a previously set coefficient equal to or less than one, but it does not particularly matter how the path level threshold is set herein.  
      M pieces of timing/direction of arrival/level information  211 - 1 - 211 -M on the M paths having levels equal to or higher than the path level threshold are delivered from path level thresholding unit  210  to delay spread calculation unit  212  and finger-assigned path selector unit  220 .  
      Delay spread calculation unit  212  substitutes the path timings and path level values of the M paths selected by path level thresholding unit  210  for the values in Equation 1 based on timing/direction of arrival/level information  211 - 1 - 211 -N to calculate delay spread  213  which is then delivered to same-path detection time range calculation unit  214 .  
      Same-path detection time range calculation unit  214  selects same-path detection time range  215  in accordance with delay spread  213  using a previously set reference table, and delivers selected same-path detection time range  215  to finger-assigned path selector unit  220 .  
      Angle spread calculation unit  216  substitutes the direction of arrival and path level value of each of M paths selected by path level thresholding unit  210  for the values in Equation 3 based on timing/direction of arrival/level information  211 - 1 - 211 -M to calculate angle spread  217  which is then delivered to same-path detection angle range calculation unit  218 .  
      Same-path detection angle range calculation unit  218  selects same-path detection angle range  219  in accordance with angle spread  217  using a previously set reference table, and delivers selected same-path detection angle range  219  to finger-assigned path selector unit  220 .  
      Finger-assigned path selector unit  220  selects finger-assigned paths, from the M paths selected by path level thresholding unit  210 , starting in order from the one having the highest level based on timing/direction of arrival/level information  211 - 1 - 211 -M, same-path detection time range  215 , and same-path detection angle range  219 , and simultaneously regards those paths found within same-path detection time range  215  and same-path detection angle range  219  of each selected path as the same paths to exclude these paths from candidates for finger-assigned paths, from the next selection onward. By repeating the foregoing sequence, finger-assigned path selector unit  220  selects K paths as finger-assigned paths. Then, finger-assigned path selector unit  220  delivers K pieces of timing/direction of arrival/level information  221 - 1 - 221 -K on the K paths to finger assignment unit  222 . While it is assumed herein that same-path detection time range  215  and same-path detection angle range  219  are individually applied to the finger-assigned path selection, the same-path detection time range and same-path detection angle range may be two-dimensionally determined using both kinds of information.  
      Finger assignment unit  222  assigns the path timings and directions of arrival of the K finger-assigned paths to J fingers as synchronization timings and arrival directions based on timing/direction of arrival/level information  221 - 1 - 221 -K. In this event, the fingers may be assigned by the following methods. A first method selects paths starting in order from the one having the highest level for assignment when J is less than K due to limitations on the capacity of hardware and the like of the CDMA receiving apparatus. A second method makes (J-K) fingers invalid such that they are not used in RAKE combining when K is less than J. A third method preferentially assigns those paths found in certain ranges of the path timing and direction of arrival of a path assigned to a finger at the preceding time to the same finger as the preceding one. Assume, however, that it does not particularly matter how fingers are assigned. Then, finger assignment unit  222  delivers timing/direction of arrival information  223 - 1 - 223 -J indicative of the path timings and directions of arrival of the paths assigned to the J fingers to demodulation processing unit  224  as synchronization timings and arrival directions of the received signal.  
      Demodulation processing unit  224  demodulates digital baseband signals  203 - 1 - 203 -D of the received signals associated with the respective antenna elements by performing despreading, beam forming which involves multiplication of the despreaded signals by antenna weights corresponding to directions of arrival and antenna summation, RAKE combining, decoding and the like using timing/direction of arrival information  223 - 1 - 223 -J assigned to the J fingers as synchronization timings and directions of arrival.  
      While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.