Abstract:
There are provided a path search apparatus and method and array antenna unit using them which receive signals of a DS-CDMA scheme from an array antenna unit including a plurality of antenna elements and detect multipath timings. In a signal receiving system having a plurality of array antenna units ( 141, 142 ), a delay profile is combined for each of antenna elements ( 11 - 16 ), and path detection is performed using the combined output, thereby allowing higher-precision and higher-speed path detection. In addition to a delay profile for each antenna element, delay profiles may be combined across array antenna units (diversity branches). When beams are to be formed in a searcher section ( 44 ), delay profiles are combined for respective beams facing in a single direction across the array antenna units.

Description:
[0001]     This application is based upon and claims priority under U.S.C. §119 from PCT Application No. PCT/JP03/06111, filed May 16, 2003, at least entire content are incorporated herein by reference, and Japanese Patent Application No. 2002-147077 filed May 22, 2002, at least entire content are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a path search apparatus and method and an array antenna receiving apparatus using them and, more particularly, to a path search system which receives signals of a DS-CDMA (Direct Spread-Code Division Multiple Access) scheme from an array antenna unit comprising a plurality of antenna elements and detects multipath timings.  
       BACKGROUND OF THE INVENTION  
       [0003]     A receiving apparatus of a mobile communication system using a DS-CDMA scheme now use a diversity antenna. In a diversity antenna unit, to decrease correlation between antenna elements, antennas are arranged such that antenna elements  1  and  2  have a large interval D 1 , as shown in  FIG. 1  (e.g., an interval of several λ; λ is a signal wavelength). Since the correlation is small, one antenna element can often receive signals at a high level even when the reception level of the other antenna element decreases due to fading. The probability of degradation in reception quality can be reduced more than a case wherein fading waves are received using one antenna. A reception scheme using a diversity antenna unit, however, is directly influenced by interference waves if present.  
         [0004]     As a technique for reducing degradation in quality due to interference waves, there is available a reception technique using an array antenna unit. In this array antenna unit, antennas are arranged such that a plurality of antenna elements  3  to  5  have a small interval D 2  (an interval of about λ/2), as shown in  FIG. 2 . By multiplying a signal received by each antenna element by amplitude and phase weights, the directivity pattern (beam) of each antenna can equivalently be formed. If an area is divided by a plurality of beams thus formed, the influence of interference waves in a direction different from that of a desired wave can be suppressed.  
         [0005]     Since the array antenna unit has the small element interval D 2 , as shown in  FIG. 2 , correlation between the antenna elements becomes extremely large. For this reason, a decrease in reception level due to fading influences all antenna elements constituting the array antenna unit, and degradation in reception quality cannot be compensated. If an interval between antenna elements is increased, no ideal beam can be formed, and the primary object, i.e., suppression of interference waves cannot be attained.  
         [0006]     As a scheme which covers up disadvantages and exploits advantages of a diversity antenna unit and array antenna unit, a technique that pertains to an antenna unit is disclosed in, e.g., WO 00/03456. The antenna unit has a plurality of array antenna units each comprising a plurality of antenna elements  3  to  5  or  6  to  8 , as shown in  FIG. 3 , and the plurality of array antenna units are separated from each other such that correlation between them can be neglected.  
         [0007]     However, in the description of a receiving apparatus of a DS-CDMA communication scheme which has a plurality of array antenna units each comprising the plurality of antenna elements  3  to  5  or  6  to  8 , as shown in  FIG. 3 , there is neither reference to nor implication of a path search scheme which detects multipath timings. Thus, high-precision and high-speed path search is demanded for a receiving apparatus having an antenna unit arrangement as shown in  FIG. 3 .  
         [0008]     An example of the arrangement of a receiving apparatus in a mobile communication system of a CDMA scheme using a conventional diversity antenna unit will be described with reference to  FIG. 4 .  
         [0009]     In searcher sections  401   a  and  401   b  of a conventional diversity antenna receiving apparatus in  FIG. 4 , detection of a synchronization chip timing (path detection) between a spreading code and a spread signal as a received signal is performed independently for each antenna. Path combining means  61   a  and  61   b  and an antenna combining (diversity combining) means  91  perform RAKE combination reception using the path timing information.  
         [0010]     The prior art will be described in detail with reference to  FIG. 4 . In  FIG. 4 , antennas  11   a  and  11   b  are equivalent to the diversity antennas  1  and  2  shown in  FIG. 1 . Signals received by the antennas  11   a  and  11   b  are frequency-converted into intermediate-frequency (IF band) signals in radio receivers  21   a  and  21   b  and are amplified. After the amplified signals are detected to I/Q channel baseband signals using quadrature detection, they are converted into digital signals by A/D converters. The outputs from the radio receivers  21   a  and  21   b  are sent out to finger sections  301   a  and  301   b  and searcher sections  401   a  and  401   b.    
         [0011]     In the searcher sections  401   a  and  401   b , correlation calculating means  101   a  and  101   b  calculate the code correlation values of desired wave signals contained in received signals at a plurality of chip timings. Correlation value averaging means  111   a  and  111   b  average correlation values output at a single chip timing from the correlation calculation means  101   a  and  101   b  for a predetermined period of time and output peak correlation values and delay profiles having undergone noise-level smoothing. The delay profiles generated by the correlation value averaging means  111   a  and  111   b  are input to path timing detecting means  131   a  and  131   b . The path timing detecting means  131   a  and  131   b  detect peaks from the combined delay profiles and notify the finger sections  301   a  and  301   b  of synchronization chip timings corresponding to the detected peaks.  
         [0012]     Each of the finger sections  301   a  and  301   b  has fingers corresponding in number to paths to be demodulated and has demodulating means  51   a  to  53   a  and  51   b  to  53   b  corresponding in number to the fingers. Each finger is allocated to one path (synchronization chip timing). The demodulators  51   a  to  53   a  and  51   b  to  53   b  demodulate signals at the synchronization chip timings and output the demodulated signals to the path combining means  61   a  and  61   b . The path combining means  61   a  and  61   b  combine the demodulation results for the respective paths into antenna outputs, which are supplied to and combined by a diversity combining means  91 . After that, the combination result is sent to a decoder (not shown).  
         [0013]     The example of a receiving apparatus in a mobile communication system of a CDMA scheme using a conventional diversity antenna has been described. High-precision and high-speed path search is demanded for this receiving apparatus.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention has been made in consideration of the above-mentioned circumstances, and has as its object to provide a path search apparatus and method which can perform high-precision and high-speed path search, and an array antenna receiving apparatus using them.  
         [0015]     To achieve the above-mentioned object, according to the present invention, there is provided a path search apparatus which receives a signal of a CDMA scheme by an array antenna unit including a plurality of antenna elements and detects a multipath timing, characterized by comprising a plurality of array antenna units, delay profile combining means for combining delay profiles for respective antenna elements in the plurality of array antenna units, and path timing detecting means for detecting path timings of respective outputs from the delay profile combining means.  
         [0016]     According to the present invention, the delay profile combining means is provided for each of the plurality of array antenna units and is arranged to combine the delay profiles for the antenna elements in the array antenna unit.  
         [0017]     According to the present invention, the delay profile combining means is arranged to collectively combine the delay profiles for the respective antenna elements in the plurality of array antenna units.  
         [0018]     According to the present invention, there is provided a path search apparatus further comprising beam forming means for forming a beam using as an input a signal received by each antenna element in each of the plurality of array antenna units, wherein the delay profile combining means is arranged to combine delay profiles for respective beams facing in a single direction across the plurality of array antenna units. The beam forming means in the path search apparatus has multiplying means for multiplying an output from each antenna element by a predetermined multiplication value.  
         [0019]     To achieve the above-mentioned object, according to the present invention, there is provided a path search method of receiving a signal of a CDMA scheme by a plurality of array antenna units each including a plurality of antenna elements and detecting a multipath timing, characterized by including the delay profile combining step of combining delay profiles for respective antenna elements in the plurality of array antenna units, and the path timing detecting step of detecting path timings of respective outputs in the delay profile combining step.  
         [0020]     According to the present invention, in the delay profile combining step, a delay profile for each antenna element is combined for each of the plurality of array antenna units.  
         [0021]     According to the present invention, in the delay profile combining step, the delay profiles for the respective antenna elements in the plurality of array antenna units are collectively combined.  
         [0022]     According to the present invention, there is provided a path search method characterized by further comprising the beam forming step of forming a beam using as an input a signal received by each antenna element in each of the plurality of array antenna units, wherein in the delay profile combining step, delay profiles are combined for respective beams facing in a single direction across the plurality of array antenna units. The beam forming step in the path search method comprises a multiplying step of multiplying an output from each antenna element by a predetermined multiplication value.  
         [0023]     To achieve the above-mentioned object, according to the present invention, there is provided an array antenna receiving apparatus characterized by comprising any one of the above-mentioned path search apparatuses, and demodulating means, provided for each of the plurality of array antenna units, for demodulating a signal received by each antenna element in the array antenna unit on the basis of a path timing detected by the path search apparatus.  
         [0024]     According to the present invention, there is provided an array antenna receiving apparatus characterized by further comprising weighting means, provided for each of the plurality of antenna units, for weighting demodulation outputs from the respective antenna elements by adaptive control, and combining means for RAKE-combining outputs from the weighting means.  
         [0025]     The operation of the present invention will be described. In a signal receiving system having a plurality of array antenna units, delay profiles are combined for respective antenna elements, and path detection is performed using the combined output, thereby allowing higher-precision and higher-speed path detection than a conventional path search scheme. In a signal receiving system having a plurality of array antenna units, delay profiles are combined not only for respective antenna elements but also across array antenna units (diversity branches). Path detection is performed using the combined output, thereby allowing high-precision and high-speed path detection. In a signal receiving system having a plurality of array antenna units, when beams are to be formed by a searcher section, delay profiles are combined for respective beams facing in a single direction across array antenna units (diversity branches), and path detection is performed using the combined output, thereby allowing high-precision and high-speed path detection.  
         [0026]     As described above, according to the present invention, path search can be performed at high precision and high speed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a view showing an antenna layout example using a diversity antenna unit;  
         [0028]      FIG. 2  is a view showing an antenna layout example using an array antenna unit;  
         [0029]      FIG. 3  is a view showing an antenna layout example using a combination of a diversity antenna unit and an array antenna unit;  
         [0030]      FIG. 4  is a block diagram showing an example of a receiving apparatus of a CDMA scheme which uses conventional diversity antenna units;  
         [0031]      FIG. 5  is a block diagram of the first embodiment of a receiving apparatus according to the present invention;  
         [0032]      FIG. 6  is a block diagram of the second embodiment of a receiving apparatus according to the present invention; and  
         [0033]      FIG. 7  is a block diagram of the third embodiment of a receiving apparatus according to the present invention; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     Preferred embodiments will be described with reference to the accompanying drawings to explain the present invention in detail.  
         [0035]     The first embodiment of the present invention will be described with reference to  FIG. 5 .  
         [0036]      FIG. 5  shows, as an example, a receiving apparatus which has two array antenna units each consisting of three antenna elements. In the present invention, however, the number of antenna elements or array antennas is not limited to that shown in  FIG. 5 . The present invention is also effective for an arbitrary number of antenna elements or array antennas. The interval between antenna elements is about half the wavelength of carrier waves, and an interval D 1  between array antenna units is set to a distance (several λ) which allows to sufficiently reduce the correlation.  
         [0037]     The first embodiment has an array antenna unit  141  comprising antenna elements  11  to  13 , and an array antenna unit  142  comprising antenna elements  14  to  16 , as shown in  FIG. 5 . The first embodiment includes radio receivers  21  to  26  which convert RF signals from the antenna elements into digital baseband signals, searcher sections  41  and  42  which detect the path positions (synchronization chip timings) of the respective array antenna units (diversity branches), finger sections  31  and  32  which demodulate signals at the timings detected by the searcher sections, calculate weights using a known adaptive algorithm such as MMSE (Minimum-Mean-Squared-Error), and multiply the signals by the weights to form beams, path combining means  81  and  82  which combine the demodulation results from the fingers, and a diversity combining means  91  which combines the demodulation results from the branches.  
         [0038]     The searcher section  41  includes correlation calculating means  101  to  103  corresponding in number to the antenna elements, correlation value averaging means  111  to  113  for averaging correlation results of the antenna elements and generate delay profiles, a delay profile combining means  121  for adding and combining the delay profiles, and a path timing detecting means  131  for detecting a synchronization chip timing from the combined delay profile. The other searcher section  42  includes the same components.  
         [0039]     The finger section  31  has a plurality of fingers, each of which includes demodulating means  51  to  53  corresponding in number to the antenna elements, a weight multiplying means  61 , and an adaptive control means  71 . The other finger section  32  includes the same components.  
         [0040]     The operation of the first embodiment will be described next. Receivers connected to the array antenna unit  141  and those connected to the array antenna unit  142  have the same arrangement. Thus, the receivers connected to the array antenna unit  141  will be exemplified below.  
         [0041]     RF signals received by the antenna elements  11  to  13  are sent to the radio receivers  21  to  23 , respectively. After the RF signals are frequency-converted into intermdiate-frequency (IF band) signals in the radio receivers  21  to  23 , they are amplified by automatic gain amplifiers. The amplified signals are detected to I/Q channel baseband signals using quadrature detection and are converted into digital signals by A/D converters. The outputs from the radio receiver  21  to  23  are sent to the finger section  31  and searcher section  41 .  
         [0042]     In the searcher section  41 , the correlation calculating means  101  to  103  calculate the code correlation values of desired wave signals contained in received signals at a plurality of chip timings for the respective antenna elements. The correlation value averaging means  111  to  113  average correlation values output at a single chip timing from the correlation calculating means  101  to  103  for a predetermined period of time and output peak correlation values and delay profiles having undergone noise-level smoothing.  
         [0043]     The delay profiles for the respective antenna elements generated by the correlation value averaging means  111  to  113  are combined at a single chip timing by the delay profile combining means  121  into a combined delay profile. The path timing detecting means  131  detects a plurality of peaks from the combined delay profile and notifies the finger section  31  of synchronization chip timings corresponding to the detected peaks.  
         [0044]     The finger section  31  has fingers corresponding in number to paths to be demodulated. One of them has the demodulating means  51  to  53  corresponding in number to the antenna elements. Each finger is allocated to one path (synchronization chip timing). The demodulating means  51  to  53  demodulate signals at the synchronization chip timings and output the demodulated signals to the weight multiplying means  61 . The weight multiplying means  61  multiplies the demodulation results by weights calculated by the adaptive control means  71  and supplies the multiplication results to the path combining means  81 .  
         [0045]     The path combining means  81  combines the demodulation results for the respective paths into one output from the array antenna unit  141  and outputs it to the diversity combining means  91 .  
         [0046]     The diversity combining means  91  combines an output result from the array antenna unit  141  and an output result similarly obtained from the array antenna unit  142  and sends the combination result to a decoder (not shown).  
         [0047]     According to the first embodiment, the level of noise contained in a delay profile is averaged and reduced, and peaks become prominent. Synchronization chip timings can be detected at high precision. The implementation of peak detection precision of the same level as that of a conventional scheme makes it possible to shorten the averaging time in each of the correlation value averaging means  111  to  116 . In other words, synchronization chip timings can be detected at high speed, and the capability of following up any variation in synchronization chip timing of a multipath wave generated upon movement of a terminal can be improved.  
         [0048]     Generally, the peak level of a correlation value varies independently under the conditions for antenna diversity in which the intervals between antenna units are much longer than the wavelength of carrier waves. The synchronization chip timings are considered to be substantially equal to each other. Under the circumstances, the second embodiment of the present invention will propose a receiver which also combines delay profiles across two array antenna units constituting branches.  
         [0049]      FIG. 6  shows an example of the arrangement of a receiver indicative of the second embodiment of the present invention. The same reference numerals in  FIG. 6  denote the same parts as those in  FIG. 5 .  
         [0050]     In  FIG. 6 , a delay profile combining means  123  does not output a result for each diversity branch and collectively combines the delay profiles for all the antenna elements in both the branches to output the combination result to a path timing detecting means  131 . The path timing detecting means  131  detects a plurality of peaks from the combined delay profile and notifies finger sections  31  and  32  in the branches of synchronization chip timings for the respective detected peaks. The remaining arrangement is the same as that in  FIG. 5 , and a description thereof will be omitted. Note that reference numeral  43  denotes a searcher section in  FIG. 6 .  
         [0051]     According to the second embodiment, synchronization chip timings can be detected more precisely than the first embodiment shown in  FIG. 5 . If peak detection precision only needs to be the same level as that of a conventional scheme, the second embodiment can detect synchronization chip timings at higher speed than the first embodiment.  
         [0052]     The present invention is also effective in forming beams by a searcher section. For an example,  FIG. 7  shows, as the third embodiment, the arrangement of a receiving apparatus which forms a multibeam of three beams for each diversity branch by a searcher section.  
         [0053]     A multibeam can suppress interference waves from a direction different from that of a desired wave by dividing a cover area for a plurality of beams using fixed weights. The details of this multibeam are disclosed in Japanese Unexamined Patent Publication No. 2001-345747, and a description thereof will be omitted.  
         [0054]     In  FIG. 7 , the same reference numerals denote the same parts as those in  FIGS. 5 and 6 . Referring to  FIG. 7 , weight multiplying means  63  and  64  are added to a searcher section  44 . Correlation calculating means  101  to  103  and  104  to  106  calculate correlation values for respective antenna elements. Weight multiplying means  63  and  64  of the respective array antenna units multiply the correlation values by predetermined fixed amplitude weights and phase weights. The correlation values for the antenna elements are converted into correlation values for beams.  
         [0055]     Correlation value averaging means  111  to  113  and  114  to  116  average the correlation values for the beams so as to output delay profiles for the respective beams. Delay profile combining means  124  to  126  combine beams facing in a single direction across the diversity branches at a single chip timing and generate respective combined delay profiles for three beams. A path timing detecting means  132  detects a plurality of peaks from the combined delay profile for the three beams and notifies finger sections  31  and  32  in both the diversity branches of synchronization chip timings for the beams detected.  
         [0056]     According to the third embodiment, when a searcher section is to form beams, synchronization chip timings can be detected at high precision and high speed. Note that the number of multibeams is not limited to a specific one.