Patent Publication Number: US-7711072-B2

Title: Receiving method and receiver

Description:
RELATED APPLICATIONS 
   This application is a divisional of application Ser. No. 10/716,495, filed Nov. 20, 2003 now U.S. Pat. No. 7,453,955, which claims priority to Japanese Application No. 2002-337307, filed Nov. 20, 2002, the contents of which are hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a receiving technology. It particularly relates to a receiving method and a receiving apparatus which controls a weighting coefficient for synthesizing radio signals received by a plurality of antennas. 
   2. Description of the Related Art 
   In wireless communication, it is in general desired to effectively use limited frequency resources. In order to use the frequency resources effectively, radio waves of same frequency are, for example, utilized as repeatedly as possible in short-range. In this case, however, communication quality degrades because of cochannel interference caused by a radio base station or mobile terminal closely located, which utilizes the same frequency. As one technology for preventing such communication quality degradation deriving from the cochannel interference, the adaptive array antenna technology can be named. 
   In the adaptive array antenna technology, signals received by a plurality of antennas are respectively weighted with different weighting coefficients and synthesized. The weighting coefficients are adaptively updated so that an error signal between a signal to be transmitted and the signal after the synthesis might be small. Here, the signal to be transmitted is determined based on the signal after synthesis. In order to update the weighting coefficients adaptively, the RLS (Recursive Least Squares) algorithm, the LMS (Least Mean Squares) algorithm or the like is utilized. The RLS algorithm generally converges at high speed. The RLS algorithm, however, requires a high speed or a huge arithmetic circuit since computation performed is very complicated. The LMS algorithm can be realized with a simpler arithmetic circuit than that of the RLS algorithm. However, the convergence speed thereof is low. 
   Related Art List 
   
       
       1. Japanese Patent Application Laid-open No. 2002-26788 
     
  
   In utilizing the adaptive array antenna for a radio mobile terminal, it is suitable to use the LMS algorithm for updating weighting coefficients, since it is desirable that an arithmetic circuit is small. However, the convergence speed of the LMS algorithm is low in general. Thus, if it is desired to delay received signals to be synthesized until the LMS algorithm converges, processing delay becomes large and therefore it is possibly impossible to use the adaptive array antenna in a real time application such as TV conference system where permissible delay time is limited. On the other hand, a response characteristic generally degrades if the weighting coefficients at the timing where the LMS algorithm has not converged yet in order to diminish the processing delay. 
   SUMMARY OF THE INVENTION 
   The inventor of the present invention has made the present invention in view of the foregoing circumstances and an object thereof is to provide a receiver having simple arithmetic circuits, of which the processing delay is small. It is also an object of the present invention to provide a receiver of which the response characteristic hardly degrades even in the case the weighting coefficients have not converged yet. Moreover, it is also an object of the present invention to provide a receiver which can switch a plural types of weighting coefficients. 
   A preferred embodiment according to the present invention relates to a receiver. This receiver includes: an input unit which inputs a plurality of signals on which a processing is to be performed; a switching unit which switches a plurality of weighting coefficients by which the plurality of inputted signals are multiplied between a plurality of first weighting coefficients to be temporarily utilized and a plurality of second weighting coefficients which have higher adaptabilities; a controller which instructs the switching unit to switch the weighting coefficients between the plurality of first weighting coefficients and the plurality of second weighting coefficients; and a synthesizer which synthesizes results of multiplications, where the multiplications are performed on the plurality of inputted signals and the plurality of weighting coefficients. 
   The plurality of weighting coefficients include (A, B, C, D) of which the number of terms is equal to that of the plurality of signals, where the results of multiplications between them and (X 1 , Y 1 ), (X 2 , Y 2 ) become (AX 1 , BY 1 ) and (CX 2 , DY 2 ). The plurality of weighting coefficients also include (A, B) of which the number of terms is different from that of the plurality of signals, where the results of multiplications become (AX 1 , BY 1 ) and (AX 2 , BY 2 ). 
   The receiver described above enables to acquire a response characteristic optimal in each timing by switching the weighting coefficients which have different characteristics. 
   Another preferred embodiment of the present invention also relates to a receiver. The receiver includes: an input unit which inputs a plurality of signals on which a processing is to be performed; a switching unit which switches a plurality of weighting coefficients by which the plurality of inputted signals are multiplied between a plurality of first weighting coefficients and a plurality of second weighting coefficients; a controller which instructs the switching unit to switch the weighting coefficients between the plurality of first weighting coefficients and the plurality of second weighting coefficients in a prescribed interval, where the plurality of signals are inputted in a sequential manner during the interval; and a synthesizer which synthesizes results of multiplications, where the multiplications are performed on the plurality of inputted signals and the plurality of weighting coefficients. 
   The “sequential manner” merely means that the known received signal is sequential. As long as the signals are inputted sequentially, the time length does not necessarily need to be long but may be short. Moreover, the sequential manner here may include a case where the signals are inputted in a discrete manner in accordance with a certain rule, if the apparatus recognizes the rule. That is, the “sequential manner” here includes every case where the receiver can recognize the manner of inputting the signals as “sequential” one. 
   The plurality of first weighting coefficients may be set in a manner that, as results of multiplications by the plurality of inputted signals, a multiplication result corresponding to one signal among the plurality of inputted signals becomes effective. The one signal among the plurality of inputted signals may be a signal having a largest value among the plurality of inputted signals. The plurality of first weighting coefficients may be set by utilizing the plurality of second weighting coefficients which have already been set. 
   The receiver may further include: a weighting coefficient updating unit which updates a plurality of third weighting coefficients adaptively based on the plurality of inputted signals; a gap estimator which estimates gaps between the plurality of first weighting coefficients and the plurality of third weighting coefficients by performing a correlation processing between at least one of the plurality of inputted signals and a known signal; and a gap compensator which generates the plurality of second weighting coefficients by compensating the plurality of third weighting coefficients based on the estimated gaps. 
   The signals inputted during the prescribed interval in the sequential manner may include signals having different characteristics and the controller may instruct to switch the weighting coefficients between the first weighting coefficients and the second weighting coefficients when it is detected a shift point where the characteristics of the signals change. The controller may input sequentially the plurality of third weighting coefficients updated in the weight coefficient updating unit and may instruct the switching unit to switch the weighting coefficients between the first weighting coefficients and the second weighting coefficients when fluctuation of the plurality of third weighting coefficients converges within a prescribed range. 
   The receiver described above enables to acquire a response characteristic optimal in each time by switching the weighting coefficients which have different characteristics during the interval. 
   Still, another preferred embodiment according to the present invention relates to a receiving method. This method includes: inputting a plurality of signals on which a processing is to be performed; switching a plurality of weighting coefficients by which the plurality of inputted signals are multiplied between a plurality of first weighting coefficients to be temporarily utilized and a plurality of a second weighting coefficients which have higher adaptabilities; giving an instruction of switching the weighting coefficients between the plurality of first weighting coefficients and the plurality of second weighting coefficients; and synthesizing results of multiplications, where the multiplications are performed on the plurality of inputted signals and the plurality of weighting coefficients. 
   Still another preferred embodiment according to the present invention relates to a receiving method. This method includes: inputting a plurality of signals on which a processing is to be performed; switching a plurality of weighting coefficients by which the plurality of inputted signals are multiplied between a plurality of first weighting coefficients and a plurality of second weighting coefficients; giving an instruction of switching the weighting coefficients between the plurality of first weighting coefficients and the plurality of second weighting coefficients in a prescribed interval, where the plurality of signals are inputted in a sequential manner during the interval; and synthesizing results of multiplications, where the multiplications are performed on the plurality of inputted signals and the plurality of weighting coefficients. 
   The plurality of first weighting coefficients may be set in a manner that, as results of multiplications by the plurality of inputted signals, a multiplication result corresponding to one signal among the plurality of inputted signals becomes effective. The one signal among the plurality of inputted signals may be a signal having a largest value among the plurality of inputted signals. The plurality of first weighting coefficients may be set by utilizing the plurality of second weighting coefficients which have already been set. 
   The receiving method may further include: updating a plurality of third weighting coefficients adaptively based on the plurality of inputted signals; estimating gaps between the plurality of first weighting coefficients and the plurality of third weighting coefficients by performing a correlation processing between at least one of the plurality of inputted signals and a known signal; and generating the plurality of second weighting coefficients by compensating the plurality of third weighting coefficients based on the estimated gaps. 
   The signals inputted during the prescribed interval in the sequential manner may include signals having different characteristics. In giving the instruction of switching the weighting coefficients between the first weighting coefficients and the second weighting coefficients, the instruction may be given when it is detected a shift point where the characteristics of the signals change. The plurality of third weighting coefficients updated may be inputted sequentially in giving the instruction of switching the weighting coefficients between the first weighting coefficients and the second weighting coefficients, and the instruction may be given when fluctuation of the plurality of third weighting coefficients converges within a prescribed range. 
   Yet another preferred embodiment of the present invention relates to a program. The program includes: inputting a plurality of signals on which a processing is to be performed; switching a plurality of weighting coefficients by which the plurality of inputted signals are multiplied between a plurality of first weighting coefficients to be temporarily utilized and a plurality of a second weighting coefficients which have higher adaptabilities; giving an instruction of switching the weighting coefficients between the plurality of first weighting coefficients and the plurality of second weighting coefficients; and synthesizing results of multiplications, where the multiplications are performed on the plurality of inputted signals and the plurality of weighting coefficients. 
   Still another preferred embodiment according to the present invention relates to a program method. This program includes: inputting a plurality of signals on which a processing is to be performed; switching a plurality of weighting coefficients by which the plurality of inputted signals are multiplied between a plurality of first weighting coefficients and a plurality of second weighting coefficients; giving an instruction of switching the weighting coefficients between the plurality of first weighting coefficients and the plurality of second weighting coefficients in a prescribed interval, where the plurality of signals are inputted in a sequential manner during the interval; and synthesizing results of multiplications, where the multiplications are performed on the plurality of inputted signals and the plurality of weighting coefficients. 
   The plurality of first weighting coefficients may be set in a manner that, as results of multiplications by the plurality of inputted signals, a multiplication result corresponding to one signal among the plurality of inputted signals becomes effective. The one signal among the plurality of inputted signals may be a signal having a largest value among the plurality of inputted signals. The plurality of first weighting coefficients may be set by utilizing the plurality of second weighting coefficients which have already been set. 
   The receiving method may further include: updating a plurality of third weighting coefficients adaptively based on the plurality of inputted signals; estimating gaps between the plurality of first weighting coefficients and the plurality of third weighting coefficients by performing a correlation processing between at least one of the plurality of inputted signals and a known signal; and generating the plurality of second weighting coefficients by compensating the plurality of third weighting coefficients based on the estimated gaps. 
   The signals inputted during the prescribed interval in the sequential manner may include signals having different characteristics. In giving the instruction of switching the weighting coefficients between the first weighting coefficients and the second weighting coefficients, the instruction may be given when it is detected a shift point where the characteristics of the signals change. The plurality of third weighting coefficients updated may be inputted sequentially in giving the instruction of switching the weighting coefficients between the first weighting coefficients and the second weighting coefficients, and the instruction may be given when fluctuation of the plurality of third weighting coefficients converges within a prescribed range. 
   It is to be noted that any arbitrary replacement or substitution of the above-described structural components and the steps, expressions replaced or substituted in part or whole between a method and an apparatus as well as addition thereof, and expressions changed to a computer program, recording medium or the like are all effective as and encompassed by the present embodiments. 
   Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be sub-combination of these described features. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a structure of a communication system according to a first embodiment of the present invention. 
       FIG. 2  shows a burst format according to the first embodiment of the present invention. 
       FIG. 3  shows a burst format according to the first embodiment of the present invention. 
       FIG. 4  shows a structure of a receiver according to the first embodiment of the present invention. 
       FIG. 5  shows a structure of a first pre-processing unit shown in  FIG. 4 . 
       FIG. 6  shows a structure of the first pre-processing unit shown in  FIG. 4 . 
       FIG. 7  shows a structure of the first pre-processing unit shown in  FIG. 4 . 
       FIG. 8  shows a structure of a timing detection unit shown in  FIGS. 5 ,  6  and  7 . 
       FIG. 9  shows a structure of a rising edge detection unit shown in  FIG. 4 . 
       FIG. 10  shows an operation procedure of the rising edge detection unit shown in  FIG. 9 . 
       FIG. 11  shows a structure of an antenna determination unit shown in  FIG. 4 . 
       FIG. 12  shows a structure of a first weight computation unit shown in  FIG. 4 . 
       FIG. 13  shows a structure of a gap measuring unit shown in  FIG. 4 . 
       FIG. 14  shows a structure of a gap compensating unit shown in  FIG. 4 . 
       FIG. 15  shows a structure of a synthesizing unit shown in  FIG. 4 . 
       FIG. 16  shows a structure of a receiver according to a second embodiment of the present invention. 
       FIG. 17  shows a structure of an antenna determination unit shown in  FIG. 16 . 
       FIG. 18  shows a structure of a gap measuring unit shown in  FIG. 16 . 
       FIG. 19  shows a structure of a frequency error estimation unit shown in  FIG. 18 . 
       FIG. 20  shows a structure of a gap measuring unit shown in  FIG. 16 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention will now be described based on the preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention. 
   First Embodiment 
   The first embodiment of the present invention relates to a receiver provided with an adaptive array antenna which receives radio signals with a plurality of antennas as burst signals and synthesizes the received signals with weighting them respectively by different weighting coefficients. The burst signal is composed of a known training signal which is disposed in the head part thereof and a data signal. The receiver, in order to reduce processing delay, synthesizes the received signals by weighting them with the weighting coefficients without scarcely delaying them. The weighting coefficients are updated by the LMS algorithm one after another. As the weighting coefficients in the training signal interval, however, precedently prepared weighting coefficients of an omni antenna pattern are utilized since it is often the case that the weighting coefficients have not converged yet in the initial period of the training signal interval. Weighting coefficients of adaptive array antenna pattern, which are updated by the LMS algorithm, are utilized as the weighting coefficients in the interval of the data signal. 
     FIG. 1  shows a communication system including a transmitter  100  and a receiver  106  according to the first embodiment of the present invention. The transmitter  100  includes a modulator  102 , a RF unit  104 , and an antenna  132 . The receiver  106  includes a first antenna  134   a , a second antenna  134   b , a n-th antenna  134   n , a RF unit  108 , a signal processing unit  110 , and a demodulator  112 . Here the first antenna  134   a , the second antenna  134   b  and the n-th antenna  134   n  are generically named antennas  134 . 
   The modulator  102  modulates an information signal to be transmitted and generates the transmission signal (hereinafter one signal included in the transmission signal is also called as a “symbol”). Any arbitrary modulation scheme may be utilized, such as QPSK (Quadri Phase Shift Keying), 16 QAM (16 Quadrature Amplitude Modulation), GMSK (Gaussian filtered Minimum Shift Keying). In the following embodiments, examples are described where the QPSK is utilized. Moreover, in a case of a multi carrier communication, the transmitter  100  is provided with the plurality of modulators  102  or inverse Fourier transform units. In a case of a spectrum spreading communication, the modulator  102  is provided with a spreading unit. 
   The RF unit  104  transforms the transmission signal into radio frequency signal. A frequency transformation unit, a power amplifier, a frequency oscillator and so forth are included therein. 
   The antenna  132  of the transmitter  100  transmits the radio frequency signals. The antenna may have arbitrary directivity and the number of the antennas may also be arbitrary. 
   The antennas  134  of the receiver  106  receive the radio frequency signals. In this embodiment, the number of the antennas  134  is n. When it is described in this embodiment that the receiver has a n-th component thereof, it means that the number of the components provided to the receiver  106  is same as the number of the antennas  134 , where the first, second, . . . n-th component basically performs same operation in parallel. 
   The RF unit  108  transforms the radio frequency signals into baseband received signals  300 . A frequency oscillator and so forth are provided to the RF unit  108 . In a case of the multi carrier communication, the RF unit  108  is provided with a Fourier transform unit. In a case of the spectrum spreading communication, the RF unit  108  is provided with a despreading unit. 
   The signal processing unit  110  synthesizes the baseband received signals  330  with respectively weighting by the weighting coefficients and controls each weighting coefficient adaptively. 
   The demodulator  112  demodulates the synthesized signals and performs decision on the transmitted information signal. The demodulator  112  may also be provided with a delay detection circuit or a carrier recovery circuit for coherent detection. 
     FIG. 2  and  FIG. 3  show other burst formats respectively utilized in different communication systems corresponding to the communication system shown in  FIG. 1 . Training signals and data signals included in the burst signals are also shown in those figures.  FIG. 2  shows a burst format utilized in a traffic channel of the Personal Handyphone System. A preamble is placed in initial 4 symbols of the burst, which is utilized for timing synchronization. The signals of the preamble and a unique word can serve as a known signal for the signal processing unit  110 , therefore the signal processing unit  110  can utilize the preamble and the unique word as the training signal. Data and CRC both following after the preamble and the unique word are unknown for the signal processing unit  110  and correspond to the data signal. 
     FIG. 3  shows a burst format utilized in a traffic channel of the IEEE 802.11a, which is one type of wireless LAN (Local Area Network). The IEEE 802.11a employs OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme. In the OFDM modulation scheme, the size of the Fourier transform and the number of the symbols of the guard interval are summated and the summation forms a unit. It is to be noted that this one unit is described as an OFDM symbol in this embodiment. A preamble is placed in initial 4 OFDM symbols of the burst, which is mainly utilized for timing synchronization and carrier recovery. The signals of the preamble can serve as a known signal for the signal processing unit  110 , therefore the signal processing unit  110  can utilize the preamble as the training signal. Header and Data both following after the preamble are unknown for the signal processing unit  110  and correspond to the data signal. 
     FIG. 4  shows a structure of the receiver  106  shown in  FIG. 1 . The RF unit  108  includes a first pre-processing unit  114   a , a second pre-processing unit  114   b , . . . and a n-th pre-processing unit  114   n , which are generically named pre-processing units  114 . The signal processing unit  110  includes: a first BB input unit  116   a , a second BB input unit  116   b , . . . and a n-th BB input unit  116   n  which are generically named BB input units  116 ; a synthesizing unit  118 ; a first weight computation unit  120   a , a second weight computation unit  120   b , . . . and a n-th weight computation unit  120   n  which are generically named weight computation units  120 ; a rising edge detection unit  122 ; a control unit  124 ; a training signal memory  126 ; an antenna determination unit  10 ; an initial weight data setting unit  12 ; a gap measuring unit  14 , a gap compensating unit  16 ; a weight switching unit  18 . The demodulator  112  includes a synchronous detection unit  20 , a decision unit  128  and a summing unit  130 . 
   Moreover the signals utilized in the receiver  106  include: a first baseband received signal  300   a , a second baseband received signal  300   b , . . . and n-th baseband received signal  300   n  which are generically named the baseband received signals  300 ; a training signal  302 ; a control signal  306 ; an error signal  308 ; a first control weighting coefficient  310   a , a second control weighting coefficient  310   b , . . . and a n-th control weighting coefficient  310   n  which are generically named control weighting coefficients  310 ; an antenna selection signal  314 ; a gap error signal  316 ; a first updated weighting coefficient  318   a , a second updated weighting coefficient  318   b , . . . and a n-th updated weighting coefficient  318   n  which are generically named updated weighting coefficients  318 ; a first initial weighting coefficient  320   a , a second initial weighting coefficient  320   b , . . . and a n-th initial weighting coefficient  320   n  which are generically named initial weighting coefficients  320 ; and a first weighting coefficient  322   a , a second weighting coefficient  322   b , . . . and a n-th weighting coefficient  322   n  which are generically named weighting coefficients  322 . 
   The pre-processing units  114  translates the radio frequency signals into the baseband received signals  300 . 
   The rising edge detection unit  122  detects the starts of the burst signals which serve as a trigger of the operation of the signal processing unit  110  from the baseband received signals  300 . The timings of the detected starts of the burst signals are informed to the control unit  124 . The control unit  124  computes timings when the interval of the training signal  302  ends, based on the timings of the starts of the burst signals. These timings are notified to each unit as control signals  306  in accordance with necessity. 
   The antenna determination unit  10  measures the electric power of each baseband received signal  300  after the interval of the training signal  302  is started in order to select one antenna  134  to be made effective in the interval of the training signal  302  and then determines the one baseband received signal  300  of which the electric power becomes is largest. Moreover, the antenna determination unit  10  outputs this information as the antenna selection signal  314 . 
   The initial weight data setting unit  12  sets the weighting coefficients  322  utilized in the interval of the training signal  302  as the initial weighting coefficients  320 . The initial weight data setting unit  12  makes only one initial weighting coefficient  302  effective by setting the value of the one initial weighting coefficient  320  as 1 and by setting the values of the other weighting coefficients  320  as 0. The one initial weighting coefficient  320  to be made effective is decided according to the antenna selection signal  314 . 
   The training signal memory  126  stores the training signal  302  and outputs the training signal in accordance with necessity. 
   The weight computation unit  120  updates the control weighting coefficients  310  based on the baseband received signals  300  and after-mentioned error signal  308  by the LMS algorithm. 
   The gap measuring unit  14 , based on the baseband received signals  300  and the training signal  302 , estimates the gap between the results of a synthesis processing performed in the after-mentioned synthesizing unit  118 , wherein one result is acquired by performing the synthesizing processing on the initial weighting coefficients  320  and baseband received signals  300  and the other is acquired by performing the synthesizing processing on the control weighting coefficients  310  and the baseband received signals  300 . The synthesis result acquired by utilizing the initial weighting coefficients  320  is the baseband received signal  300  as it is, which is corresponding to one antenna  134 . Therefore following expression (1) can be acquired. Here, it is presumed that the one antenna  134  is an i-th antenna  134 .
 
 x   i ( t )= h   i   S ( t )exp( jΔωt )+ n   i   t   (1)
 
   Here, hi is the response characteristic of the radio interval, S(t) is the transmission signal, Δω is the frequency offset between the frequency oscillators of the transmitter  100  and the receiver  106 , and ni(t) is a noise. On the other hand, a control weighting coefficient  310   wi  updated from the head region of the burst signal is given by:
 
Σh i w   i =1  (2)
 
   Here, it is presumed assumed that the control weighting coefficients have already converged sufficiently. 
   By performing the synthesis processing based on the ground of the above-described expression (2), following result of the synthesis processing can be acquired.
 
 y ( t )= S ( t )exp( jΔωt )+ n ( t )  (3)
 
   By comparing the synthesis results shown in (1) and (3), a gap error signal  316 C is given by:
 
C=h i   (4)
 
   The gap compensating unit  16  compensates the control weighting coefficients  310  with the gap error signal  316  and outputs the result of the compensation as the updated weighting coefficients  318 . 
   The weight switching unit- 18 , based on the instruction of the control signal  306 , selects the initial weighting coefficients  320  in the interval of the training signal  302  and selects the updated weighting coefficients  318  in the interval of the data signal. Then, the weight switching unit  18  outputs them as the weighting coefficients  322 . 
   The synthesizing unit  118  weights the baseband received signals  300  with the weighting coefficients  322  and then sums them up. 
   The synchronous detection unit  20  performs synchronous detection on the synthesized signals and also performs a carrier recovery necessary for the synchronous detection. 
   The decision unit  128  decides the transmitted information signal by comparing the signal acquired by the summation to a pre-determined threshold value. The decision may be either hard or soft. 
   The summing unit  130  generates the error signal  308  based on the difference value between the synchronous detected signal and the decided signal, which is to be utilized in the LMS algorithm in the weight computation units  120 . In an ideal situation, the error signal becomes zero since the LMS algorithm controls the weighting coefficients  310  so that the error signal  308  might become small. 
     FIG. 5  to  FIG. 7  show various structures of the first pre-processing unit  114   a . The first pre-processing unit  114   a  in the receiver  106  can accept and treat various signals in different communication systems such as shown in  FIG. 2  or  FIG. 3 , therefore the signal processing unit  110  following thereafter can operate ignoring the difference of the communication systems. The first pre-processing unit  114   a  in  FIG. 5  is for the single carrier communication system shown in  FIG. 2  such as Personal Handyphone System, cellular phone system or the like. The first pre-processing unit  114   a  in  FIG. 5  includes a frequency translation unit  136 , a quasi synchronous detector  138 , an AGC (Automatic Gain Control)  140 , an AD conversion unit  142 , and a timing detection unit  144 . The first pre-processing unit  114   a  shown in  FIG. 6  is for the spectrum spreading communication system such as the W-CDMA (Wideband-Code Division Multiple Access) or the wireless LAN implemented in relation to the IEEE 802.11b. In addition to the first pre-processing unit  114   a  shown in  FIG. 5 , that shown in  FIG. 6  further includes a despreading unit  172 . The first pre-processing unit  114   a  is for the multi carrier communication system shown in FIG.  3  such as the IEEE 802.11a or the Hiper LAN/2. In addition to the first pre-processing unit  114   a  shown in  FIG. 6 , that shown in  FIG. 7  further includes a Fourier transform unit  174 . 
   The frequency translation unit  136  translates the radio frequency signal into one intermediate frequency signal, a plurality of intermediate frequency signals or other signals. The quasi synchronous detector  138  performs quadrature detection on the intermediate frequency signal utilizing a frequency oscillator and generates a baseband analog signal. Since the frequency oscillator included in the quasi synchronous detector  138  operates independently from the frequency oscillator provided to the transmitter  100 , the frequencies between the two oscillators differ from each other. 
   The AGC  140  automatically controls gains so that the amplitude of the baseband analog signal might become an amplitude within the dynamic range of the AD conversion unit  142 . 
   The AD conversion unit  142  converts the baseband analog signal into a digital signal. Sampling interval for converting the baseband analog signal to the digital signal is generally set to be shorter than symbol interval in order to constrict the degradation of the signal. Here, the sampling interval is set to the half of the symbol interval (Hereinafter, the signal digitalized with this sampling interval is referred to as a “high speed digital signal”). 
   The timing detection unit  144  selects a baseband received signal  300  of an optimal sampling timing from the high speed digital signals. Alternatively, the timing detection unit  144  generates the baseband received signal  300  having the optimal sampling timing by performing a synthesis processing or the like on the high speed digital signals. 
   The despreading unit  172  shown in  FIG. 6  performs correlation processing on the baseband received signal  300  based on a predetermined code series. The Fourier transform unit  174  in  FIG. 7  performs the Fourier transform on the baseband received signal  300 . 
     FIG. 8  shows the structure of the timing detection unit  144 . The timing detection unit  144  includes: a first delay unit  146   a , a second delay unit  146   b , . . . and a (n−1)-th delay unit  146   n− 1 which are generically named delay units  146 ; a first multiplication unit  150   a , a second multiplication unit  150   b , a (n−1)-th multiplication unit  150   n− 1, . . . and a n-th multiplication unit  150   n  which are generically named multiplication units  150 ; a first data memory  152   a , a second data memory  152   b , a (n−1)-th data memory  152   n− 1, . . . a n-th data memory  152   n  which are generically named data memories  152 ; a summing unit  154 ; a decision unit  156 ; a main signal delay unit  158 ; and a selecting unit  160 . 
   The delay units  146  delay the inputted high speed digital signal for the correlation processing. The sampling interval of the high speed digital signal is set to half of the symbol interval. However the delay quantity of the delay units  146  is set to the symbol interval, therefore the high speed digital signal  150  is outputted from every other delay unit  146  to the multiplication units  150 . 
   The data memories  152  store 1 symbol of each preamble signal for the timing synchronism. 
   The multiplication units  150  perform multiplications on the high speed digital signals and the preamble signals, and the results thereof are summed up by the summing unit  154 . 
   The decision unit  156  selects an optimal sampling timing based on the result of the summation. The sampling interval of the high speed digital signal is half of the symbol signal and the interval of the high speed digital signal utilized for the summation is equal to the symbol interval, therefore there are two types of the summation results for every other high speed digital signal corresponding to each shifted sampling timing. The decision unit  156  compares the two types of the summation results and decides a timing corresponding to larger summation result as the optimal sampling timing. This decision should not necessarily be made by comparing the two types of the summation results once, but may be made by comparing them for several times. 
   The main signal delay unit  158  delays the high speed digital signal until the optimal sampling timing is determined by the decision unit  156 . 
   The selecting unit  160  selects a baseband received signal  300  corresponding to the optimal sampling timing from the high speed digital signals. Here one high speed digital signal is selected sequentially from the two successive high digital speed signals. 
     FIG. 9  shows the structure of the rising edge detection unit  122  included in the signal processing unit  110 . The rising edge detection unit  122  includes a power computation unit  162  and a decision unit  164 . The power computation unit  162  computes the received power of each baseband received signal  300  and then sums up the received power of each baseband received signal to acquire the whole power of the signals which are received by all the antennas  134 . 
   The decision unit  164  compares the whole received power of the signals with a predetermined condition and decides that the start of the burst signal is detected when the condition is satisfied. 
     FIG. 10  shows the operation of the rising edge detection unit  122 . The decision unit  164  sets an internal counter T to zero (S 10 ). The power computation unit  162  computes the received power from the baseband received signals  300  (S 12 ). The determination unit  164  compares the received power with a threshold value. When the received power is larger than the threshold value (Y in S 14 ), the decision unit  164  adds 1 to the T (S 16 ). When the T becomes larger than a predetermined value τ (Y in S 18 ), it is decided that the start of the burst signal is detected. The processing described-above is repeated until the start of the burst signal is detected (N in S 14 , N in S 18 ). 
     FIG. 11  shows the structure of the antenna determination unit  10 . The antenna determination unit  10  includes: a first level measuring unit  22   a , a second level measuring unit  22   b , . . . and a n-th level measuring unit  22   n  which are generically called level measuring units  22 ; and a selecting unit  24 . 
   The level measuring units  22  detect the start timing of the burst signal based on the control signal  306  and measure the electric power of each baseband received signal  300  during prescribed interval from the start timing. 
   The selecting unit  24  selects the baseband received signal  300  which has the largest electric power by comparing the electric power of each baseband received signal  300  and then outputs a result as the antenna selection signal  314 . 
     FIG. 12  shows the structure of the first weight computation unit  120   a . The first weight computation unit  120   a  includes a switching unit  48 , a complex conjugate unit  50 , a main signal delay unit  52 , a multiplication unit  54 , a step size parameter memory  56 , a multiplication unit  58 , a summing unit  60 , and a delay unit  62 . 
   The switching unit  48  selects the training signal  302  in the interval of the training signals  302  by detecting the start timing of the burst signal and the end timing of interval of the training signal  302  based on the control signal  306  and then selects the error signal  308  in the interval of the data signal. 
   The main signal delay unit  52  delays the first baseband received signal  300   a  so that the first baseband received signal  300   a  might synchronize with the timing detected by the rising edge detection unit  122 . 
   The multiplication unit  54  generates a first multiplication result by multiplying the phase error  308  after complex conjugate transform in the complex conjugate unit  50  by the first baseband received signal  300   a  which is delayed by the main signal delay unit  52 . 
   The multiplication unit  58  generates a second multiplication result by multiplying the first multiplication result by a step size parameter stored in the step size parameter memory  56 . The second multiplication result is fed back by the delay unit  62  and the summing unit  60  and added to a new second multiplication result. The result of the summation is then sequentially updated by the LMS algorithm. This summation result is outputted as the first weighting coefficient  310   a.    
     FIG. 13  shows the structure of the gap measuring unit  14 . The gap measuring unit  14  includes a complex conjugate unit  44 , a selecting unit  64 , a buffer unit  66  and a multiplication unit  68 . 
   The selecting unit  64 , based on the antenna selection signal  314 , selects the baseband received signal  300  corresponding to the one initial weighting coefficient  320  which has been made effective in the interval of the training signal  302 . 
   The buffer unit  66  detects the start timing of the burst signal based on the control signal  306  and outputs the baseband received signal  300  at the start timing. 
   The multiplication unit  68  multiplies the training signal  302  after the complex conjugate processing in the complex conjugate unit  44  by the one baseband received signal  300  outputted from the buffer unit  66  and then outputs the gap error signal  316 . Here, it is presumed that both the training signal  302  and baseband received signal  300  are the head signal of the burst signal. 
     FIG. 14  shows the structure of the gap compensating unit  16 . The gap compensating unit  16  includes a first multiplication unit  70   a , a second multiplication unit  70   b , . . . and a n-th multiplication unit  70   n  which are generically named multiplication units  70 . 
   The multiplication units  70  detect the end timing of the interval of the training signal  302  based on the control signal  306 . Then the multiplication units  70  multiply the control weighting coefficients  310  by the gap error signal  316  and outputs the updated weighting coefficients  318 . 
     FIG. 15  shows the structure of the synthesizing unit  118  which is included in the signal processing unit  110 . The synthesizing unit  118  includes: a first delay unit  166   a , a second delay unit  166   b , . . . and a n-th delay unit  166   n  which are generically named delay units  166 ; a first multiplication unit  168   a , a second multiplication unit  168   b , . . . and a n-th multiplication unit  168   n  which are generically named multiplication units  168 ; and a summing unit  170 . 
   Since the delay time of the delay units  166  is from the detection of the head of the burst signal by the rising edge detection unit  122  until setting the weighting coefficients  322  by the initial weight data setting unit  12  via the weight switching unit  18 , the processing delay of the delay units  166  can be ignored in general. Therefore, synthesizing processing with less processing delay can be realized. 
   The multiplication units  168  multiply the baseband received signals  300  which are delayed by the delay units  166  by the weighting coefficients  322 . The summing unit  170  sums up the whole results of the multiplications by the multiplications units  168 . 
   Hereunder will be described the operation of the receiver  106  having the structure described above. The signals received by the plurality of antennas  134  are translated to the baseband received signals  300  by the quadrature detection and so forth. When the rising edge detection unit  122  detects the starts of the burst signals from the baseband received signals  300 , the interval of the training signal  302  is started. At the start timing of the interval of the training signal  302 , the antenna determination unit  10  selects the one baseband received signal  300 . Then the initial weight data setting unit  12  sets the initial weighting coefficients  320 , where the only initial weighting coefficient  320  corresponding to the selected baseband received signal  300  is made effective. 
   In the interval of the training signal  302 , the weight switching unit  18  outputs the initial weighting coefficients  320  as the weighting coefficients  322  and the synthesizing unit  118  sums up the baseband received signals  300  weighting them with the weighting coefficients  322 . Meanwhile, the weight computation units  120  update the control weighting coefficients  310  by the LMS algorithm. In the interval of the data signal, the gap compensating unit  16  compensates the control weighting coefficients  310  with the gap error signal  316  computed in the gap measuring unit  14  and then outputs them as the updated weighting coefficients  318 . Moreover, the weight switching unit  18  outputs the updated weighting coefficients  318  as the weighting coefficients  322  and the synthesizing unit  118  weights the baseband received signals  300  with the weighting coefficients  322  and sums them up. 
   According to the first embodiment, the processing delay can be reduced since the synthesizing processing is performed even in the interval of the training signal regardless of the convergence of the weighting coefficients. Moreover, communications with surrounding radio stations located in the vicinity can be realized since the omni antenna pattern is utilized for the weighting coefficients in the interval of the training signal. The weighting coefficients can be smoothly switched between the omni antenna pattern and the adaptive array antenna pattern. 
   Second Embodiment 
   In the second embodiment, same as the first embodiment, received signals are weighted with weighting coefficients and synthesized. The processing delay hardly occurs since the switching is performed between the omni antenna pattern which is precedently prepared and the adaptive array pattern updated by the LMS algorithm. In the first embodiment, the switching of the weighting coefficients between two types is performed in an undifferentiated manner at the timing where the training signal included in the burst signal ends. On the other hand, in the second embodiment, the switching of weighting coefficients between two types is performed adaptively at the timing where the LMS algorithm converges within a predetermined range. 
     FIG. 16  shows the structure of the receiver  106  according to the second embodiment. The structure thereof is almost same as the structure of the receiver  106  shown in  FIG. 4 . However, the receiver  106  shown in  FIG. 16  includes a first convergence information  324   a , a second convergence information  324   b , . . . and a n-th convergence information  324   n  which are generically named convergence information  324 . 
   The weight switching unit  18  shown in  FIG. 4  performs the switching operation in a manner that the initial weighting coefficient  320  is selected in the interval of the training signal  302  and the updated weighting coefficient is selected in the interval of the data signal, wherein the end timing of the interval of the initial weighting coefficients  320  severs as a trigger for the weight switching unit  18 . On the other hand, the weight switching unit  18  utilizes the timing where the control weighting coefficients  310  converge in the weight computation units  120  (hereinafter this timing is referred to as a “convergence timing”). The convergence timing is generated by the control unit  124  when the fluctuation of the control weighting coefficients  310  caused by updating them converges within in a range, wherein the range is determined precedently. Alternatively, the convergence timing may be generated by the control unit  124  when the updated error signal  308  becomes within a range, wherein the range is predetermined for the error signal  308 . 
   The control unit  124  notifies the convergence timing to each unit in accordance with the necessity, and each unit performs its assigned processing according to the convergence timing. 
     FIG. 17  shows the structure of the antenna determination unit  10 . The antenna determination unit  10  includes a switching unit  72 , a level measuring unit  74 , a storage  76  and a selecting unit  24 . 
   The switching unit  72  switches the plurality of baseband received signals  300  at a prescribed timing and outputs one baseband received signal  300 . The switching may be performed on the plurality of burst signals. 
   The level measuring unit  74  measures the electric power of the baseband received signal  300  selected by the switching unit  72 . Being different from the antenna determination unit  10  shown in  FIG. 11 , the electric power of the plurality of baseband received signals  300  is not measured at a time but measured for every baseband received signal  300  one by one, therefore the size of an arithmetic circuit for the level measuring unit  74  can be diminished. 
   The storage  76  stores the computed electric power of the baseband received signal  300 . 
     FIG. 18  shows the structure of the gap measuring unit  14 . The gap measuring unit  14  shown in  FIG. 18  is structured by adding a frequency error estimation unit  78 , an interval measuring unit  80 , a multiplication unit  82 , a complex number transformation unit  84 , a complex conjugate unit  86  and a multiplication unit  88  to the gap measuring unit  14  shown in  FIG. 13 . 
   In the second embodiment, being different from the first embodiment, the timing where the weight computation units  120  start updating the control weight coefficients  310  is the head of the long preamble of the burst format shown in  FIG. 3 . The control weighting coefficient  310   wi  updated from the head of the long preamble is given by the expression (5) below. Here, it is presumed that the control weighting coefficients  310  have converged sufficiently.
 
Σ h   i   w   i exp( jΔωsT )=1  (5)
 
   Here, sT is the time length of a short preamble interval. By performing the synthesizing processing based on the expression (5), the synthesis result is given by:
 
 y ( t )= S ( t )exp( jΔωt )exp(− jΔωsT )+ n ( t )  (6)
 
   By comparing these expressions, the gap error signal  316 C can be expressed as follows.
 
 C=h   i exp(− jΔωsT )  (7)
 
   The frequency error estimation unit  78  estimates a frequency error Δω based on the baseband received signals  300 . The interval measuring unit  80  measures the time sT of the short preamble interval based on the training signal  302 . 
   The multiplication unit  82  multiplies the frequency error by the time of the short preamble interval and acquires the phase error in the interval of the short preamble. This phase error is transformed to a complex number by the complex number transformation unit  84  and a complex conjugate processing is performed thereon by the complex conjugate unit  86 . 
   The multiplication unit  88  multiplies, by the above-described phase error, the result of the multiplication processing on the one baseband received signal  300  and the complex conjugated training signal  302 , and then generates the gap error signal  316 . 
     FIG. 19  shows the structure of the frequency error estimation unit  78 . The frequency error estimation unit  78  includes: a first main signal delay unit  26   a , a second main signal delay unit  26   b , . . . and a n-th main signal delay unit  26   n  which are generically named main signal delay units  26 ; a first multiplication unit  28   a , a second multiplication unit  28   b , . . . and a n-th multiplication unit  28   n  which are generically named multiplication units  28 ; a first delay unit  30   a , a second delay unit  30   b , . . . and a n-th delay unit  30   n  which are generically named delay units  30 ; a first complex conjugate unit  32   a , a second complex conjugate unit  32   b , . . . and a n-th complex conjugate unit  32   n  which are generically named complex conjugate units  32 ; a first multiplication unit  34   a , a second multiplication unit  34   b , . . . and a n-th multiplication unit  34   n  which are generically named multiplication units  34 ; an averaging unit  36 ; a phase transformation unit  38 ; and a training signal memory  42 . 
   The multiplication units  28  acquires a received signal Zi(t) which does not include transmission signal component by multiplying the baseband received signals  300  delayed in the main signal delay units  26  by the training signal  302  after the complex conjugate transform. The received signal Zi(t) is given by: 
   
     
       
         
           
             
               
                 
                   
                     
                       
                         
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   Here, it is assumed that a noise is sufficiently small and therefore the noise is ignored. 
   The delay units  30  and the complex conjugate units  32  delay the Zi(t) and then transform the Zi(t) to the complex conjugate. The Zi(t) transformed to the complex conjugate is multiplied by the original Zi(t) in the multiplication units  34 . The result Ai of the multiplication is given by: 
   
     
       
         
           
             
               
                 
                   
                     
                       
                         
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   Here, the delay time of the delay units  30  is set to the symbol interval T. 
   The averaging unit  36  averages the multiplication results corresponding to each antenna. The multiplication results of which the time is shifted may also be utilized. 
   The phase transformation unit  38  transforms the averaged multiplication result A to a phase signal B by utilizing an arc tangent ROM.
 
B=ΔωT  (10)
 
     FIG. 20  shows the structure of a gap measuring unit  14  which is different from the gap measuring unit  14  shown in  FIG. 18 . The gap measuring unit  14  shown in  FIG. 20  is structured by adding a counter unit  90 , a multiplication unit  92 , a complex number transformation unit  94 , a summing unit  96 , a summing unit  98  and a division unit  40  to the gap measuring unit  14  shown in  FIG. 18 . In the gap measuring unit  14  shown in  FIG. 18 , the multiplication of the baseband received signals  300  by the training signal  302  is performed only on the head signal of the burst signal. On the other hand, in the gap measuring unit  14  shown in  FIG. 20 , the multiplications are performed during prescribed time and the results thereof are averaged. 
   The summing unit  98  sums up the results of the multiplications by the multiplications unit  96  during prescribed time interval (hereinafter referred to as “averaging time”) in order to average the results of the multiplications of the baseband received signals  300  by the training signal  302 . 
   The counter unit  90  counts up the symbol intervals in order to acquire the phase error corresponding to the averaging time based on the frequency error outputted from the frequency error estimation unit  78 . The multiplication unit  92  acquires the phase error corresponding to each counter value by respectively multiplying each counter value by the frequency error. The phase errors are transformed to complex numbers in the complex number transformation unit  94  and are summed up in the summing unit  96  within the averaging time. 
   The division unit  40  divides the results of the multiplications summed up by the summing unit  98  with the phase errors summed up by the summing unit  96 . The succeeding processings are same as those of the gap measuring unit  14  shown in  FIG. 18 . 
   Hereunder will be described the operation of the receiver  106  having the structure described above. The signals received by the plurality of antennas  134  are transformed to the baseband received signals  300  by the quadrature detection and so forth. When the rising edge detection unit  122  detects the start timings of the burst signals from the baseband received signals  300 , the interval of the training signal  302  is started. At the start timing of the interval of the training signal  302 , the antenna determination unit  10  selects the one baseband received signal  300  and the initial weight data setting unit  12  sets the initial weighting coefficients  320  among which only the one initial weighting coefficient  320  corresponding to the selected baseband received signal  300  is made effective. Thereafter, the weight switching unit  18  outputs the initial weighting coefficients  320  as the weighting coefficients  322  and the synthesizing unit  118  weights the baseband received signals  300  with the weighting coefficients  322  and sums them up. 
   Meanwhile, the weight computation units  120  update the control weighting coefficients  310  by the LMS algorithm. When the control weighting coefficients  310  converge within the prescribed range, the gap compensating unit  16  compensates the control weighting coefficients  310  with the gap error signal  316  computed in the gap measuring unit  14  according to the instruction from the control unit  124  and then outputs them as the updated weighting coefficients  318 . Moreover, weight switching unit  18  outputs the updated weighting coefficients  318  as the weighting coefficients  322  and the synthesizing unit  118  weights the baseband received signals  300  with the weighting coefficients  322  and sums them up. 
   According to the second embodiment, the synthesis processing is performed regardless of the convergence of the weighting coefficients even in the interval of the training signal. Therefore, the processing delay can be reduced. Moreover, in the case that the adaptive algorithm converges during the training signal interval, the response characteristic can be improved by reflecting it to the weighting coefficients. This is because the switching of the weighting coefficients between two types is performed based on the convergence timing of the adaptive algorithm. 
   Although the present invention has been described by way of exemplary embodiments, it should be understood that many changes and substitutions may be made by those skilled in the art without departing from the scope of the present invention which is defined by the appended claims. 
   In the embodiments, the initial weight data setting unit  12  sets the effective value for the initial weighting coefficient  320  for the one baseband received signal  300  selected by the antenna determination unit  10 , which has the largest electric power, and the unit  12  sets the value which is not effective for the other initial weighting coefficients  320 . The initial weighting coefficients  320 , however, do not necessarily need to be set based on the electric power. For example, one fixed initial weighting coefficient  320  may be set to the effective value and the other initial weighting coefficients  320  may be set to the value that is not effective. In that case, the antenna determination unit  10  becomes unnecessary. 
   In the embodiments, the initial weight data setting unit  12  sets the effective value for the initial weighting coefficient  320  for the one baseband received signal  300  selected by the antenna determination unit  10 , which has the largest electric power, and the unit  12  sets the value which is not effective for the other initial weighting coefficients  320 . It is, however, not necessarily required to set the weighting of the omni antenna pattern for the initial weighting coefficients  320 . For example, the setting may be performed on the updated weighting coefficients  318  or the control weighting coefficients  310  which are utilized in the already received burst signal. When the fluctuation of the radio transmission environment is small, it is estimated that this setting will not cause a serious degradation of the response characteristic. 
   In the embodiments, the weight computation units  120  utilize the LMS algorithm as the adaptive algorithm. However, another algorithm such as the RLS algorithm may be utilized. Moreover, the weighting coefficients may not be updated. That is, it is sufficient if the adaptive algorithm is selected in accordance with the estimated radio transmission environment, the size of arithmetic circuits or the like. 
   In the first embodiment, the rising edge detection unit  122  computes the electric power of the baseband received signals  300  and detects the rising edge of the burst signal based on the computation result. The rising edge of the burst signal may be, however, detected by implementing another structure. For example, the rising edge may be detected by a matched filter which is shown as the structure of the timing detection unit  144 . That is, it is sufficient if the rising edge of the burst signal is detected accurately. 
   In the first embodiment, the training signal interval is the time where the initial weighting coefficients  320  are changed into the weighting coefficients  322 . However, the time does not need to be limited to the interval of the training signal. For example, the time may be shorter than the interval of the training signal. That is, the time can be set according to the length of the interval of the training signal and to the required estimation accuracy. 
   In the second embodiment, the delay time of the delay units  30  which are included in the frequency error estimating unit  78  is set to 1 symbol. The delay time, however, is not limited to 1 symbol. For example, the delay time may be 2 symbols or may be symbols in the interval between the start and end of the training signal. That is, it is sufficient if an optimum delay time of the delay units  30  is decided in accordance with the stability of the frequency oscillator and with the required accuracy of the frequency offset estimation.