Patent Publication Number: US-2005141641-A1

Title: Receiving method and receiving apparatus with adaptive array signal processing

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to a receiving technology and, more particularly, to a receiving method and receiving apparatus in which signals received by a plurality of antennas are subject to adaptive array signal processing.  
      2. Description of the Related Art  
      In wireless communication, effective use of frequency resources, which are generally limited, is sought. One of the technologies available for effective use of frequency resources is an adaptive array antenna technology. In the adaptive array antenna technology, the amplitude and phase of signals transmitted and received by a plurality of antennas are controlled so that a directivity pattern of the antennas is formed. More specifically, in an apparatus provided with an adaptive array antenna, the amplitude and phase of signals received by a plurality of antennas are altered. The plurality of received signals thus altered are added to each other. The signal, to be received by the antennas of a directivity pattern according to the degree of alteration (hereinafter, referred to as “weight”) of the amplitude and phase, is received. Transmission of a signal is performed in a directivity pattern according to the weight.  
      In the adaptive array antenna technology, the weight may be calculated using, for example, a method based on the minimum mean square error (MMSE) method. In the MMSE method, a Wiener solution is known as a condition to give the most appropriate value of weight. Also, a recurrence formula requiring a smaller volume of calculation than determining the Weiner solution directly is known. For example, the recursive least squares (RLS) algorithm or the least mean square (LMS) algorithm are used as recurrence formulas.  
      For the purpose of increasing the data transmission rate and improving the transmission quality, data may be modulated using multiple carriers so that the resultant multicarrier signal is transmitted. When the multicarrier signal is applied to the adaptive array technology, it is necessary to calculate a weight corresponding to the multicarrier signal. A general practice for this purpose is to convert a received time-domain multicarrier signal into a frequency-domain multicarrier signal, which is then subject to a necessary process (See Reference (1) in the following Related Art List, for instance).  
      Related Art List  
      (1) Japanese Patent Application Laid-Open No. Hei10-210099.  
      When the adaptive algorithm is performed on the frequency-domain multicarrier signal and the weight is calculated for each subcarrier included in the multicarrier signal, the processing volume is increased as the number of subcarriers is increased. When the received signal may be a signal other than the multicarrier signal, i.e. when the received signal may be, for example, a spectrum spread signal, the adaptive algorithm process methods used should be switched from one to another so that both signals are properly processed. In circuit implementation, switching between adaptive algorithm process methods affects operation timings and handling of reference signals in relation to the frequency-domain signal and other signals. Therefore, there may be needed an extra circuit.  
     SUMMARY OF THE INVENTION  
      The present invention has been done in view of the aforementioned circumstances and its object is to provide a method and apparatus of receiving a multicarrier signal or a signal other than the multicarrier signal by a plurality of antennas and subjecting the received signal to adaptive array signal processing.  
      One mode of practicing the present invention is a receiver apparatus. The receiver apparatus comprises: an input unit receiving a plurality of signals; a calculating unit calculating a plurality of weight coefficients from the input plurality of signals; a synthesizing unit weighting the input plurality of signals with the plurality of weight coefficients calculated, and synthesizing the weighted signals; a determining unit determining whether the input plurality of signals are multicarrier signals or non-multicarrier signals; a first-demodulating unit performing demodulation by converting the synthesized signal from a time domain into a frequency domain, when the input plurality of signals are multicarrier signals; a second demodulating unit demodulating the synthesized signal, when the input plurality of signals are non-multicarrier signals. The calculating unit in this apparatus may calculate the plurality of weight coefficients, based on a time-domain multicarrier signal, when the input plurality of signals are multicarrier signals.  
      According to the aforementioned apparatus, a multicarrier signal is processed in a time domain for calculation of a plurality of weight coefficients, in a similar configuration as a non-multicarrier signal. Accordingly, an adaptive array process is executed regardless of whether the input signals are multicarrier signals or non-multicarrier signals.  
      Signals determined by said determining unit as being non-multicarrier signals may be spectrum spread signals, said calculating unit may store a time-domain multicarrier signal as a training signal to be used in adaptive algorithm for calculating the plurality of weight coefficients when the input plurality of signals are multicarrier signals, and also stores a spectrum spread signal to be used when the input plurality of signals are non-multicarrier signals, and said second demodulating unit may demodulate the synthesized signal by despreading.  
      The apparatus may further comprise a control unit designating, for demodulation, a switch from the second demodulating unit to the first demodulating unit for a demodulation process, when the input plurality of signals change from non-multicarrier signals to multicarrier signals. The apparatus may further comprise a control unit designating, for demodulation, a switch from the first demodulating unit to the second demodulating unit for a demodulation process, when the input plurality of signals change from multicarrier signals to non-multicarrier signals.  
      Another mode of practicing the present invention is a receiving method. The method calculates a plurality of weight coefficients from an input plurality of signals, weights the input plurality of signals with the plurality of weight coefficients calculated, and synthesizes resultant signals, wherein the input plurality of signals are processed based on a time-domain signal, and the plurality of weight coefficients are calculated, regardless of whether the input plurality of signals are multicarrier signals or not.  
      Still another mode of practicing the present invention is a receiving method. The method comprises: receiving a plurality of signals; calculating a plurality of weight coefficients from the input plurality of signals; weighting the input plurality of signals with the plurality of weight coefficients calculated, and synthesizing the weighted signals; determining whether the input plurality of signals are multicarrier signals or non-multicarrier signals; performing demodulation by converting the synthesized signal from a time domain into a frequency domain, when the input plurality of signals are multi carrier signals; demodulating the synthesized signal, when the input plurality of signals are non-multicarrier signals. The calculating in this method may be based on a time-domain multicarrier signal, when the input plurality of signals are multicarrier signals.  
      Non-multicarrier signals determined as such in the determining may be spectrum spread signals, the calculating may store a time-domain multicarrier signal as a training signal to be used in adaptive algorithm for calculating the plurality of weight coefficients when the input plurality of signals are multicarrier signals, and also stores a spectrum spread signal to be used when the input plurality of signals are non-multicarrier signals, and the demodulating may demodulate the synthesized signal by despreading.  
      The receiving method may further comprise designating, for demodulation, a switch from the demodulating of the synthesized signal to the performing of demodulation by converting the synthesized signal from a time domain into a frequency domain, when the input plurality of signals change from non-multicarrier signals to multicarrier signals. The receiving method may further designating, for demodulation, a switch from the performing of demodulation by converting the synthesized signal from a time domain into a frequency domain to the demodulating of the synthesized signal, when the input plurality of signals change from multicarrier signals to non-multicarrier signals.  
      Yet another mode of practicing the present invention is a program. This program, executable by a computer, includes the functions of: receiving a plurality of signals via a wireless network; calculating a plurality of weight coefficients from the input plurality of signals and storing the weight coefficients in a memory; weighting the input plurality of signals with the plurality of weight coefficients stored in the memory, and synthesizing the weighted signals; determining whether the input plurality of signals are multicarrier signals or non-multicarrier signals; performing demodulation by converting the synthesized signal from a time domain into a frequency domain, when the input plurality of signals are multicarrier signals; demodulating the synthesized signal, when the input plurality of signals are non-multicarrier signals. The calculating in this program may be based on a time-domain multicarrier signal, when the input plurality of signals are multicarrier signals.  
      Non-multicarrier signals determined as such in the determining may be spectrum spread signals, the calculating and storing may store a time-domain multicarrier signal as a training signal to be used in adaptive algorithm for calculating the plurality of weight coefficients when the input plurality of signals are multicarrier signals, and also stores a spectrum spread signal to be used when the input plurality of signals are non-multicarrier signals, and the demodulating may demodulate the synthesized signal by despreading.  
      It is to be noted that any arbitrary combination of the above-described structural components and expressions changed among a method, an apparatus, a system, a recording medium, a computer program and so forth 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 communications system according to an example of the present invention.  
       FIG. 2  shows one of burst formats according to the example.  
       FIG. 3  shows another burst format according to the example.  
       FIG. 4  shows yet another burst format according to the example.  
       FIG. 5  shows a structure of a first radio unit of  FIG. 1 .  
       FIG. 6  shows a structure of a signal processing unit and a modem unit of  FIG. 1 .  
       FIG. 7  shows a structure of a receiving weight vector calculating unit.  
       FIG. 8  is a flowchart showing a procedure of a demodulation process in a signal processing unit and a modem unit. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The invention will now be described based on the following examples 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 examples are not necessarily essential to the invention.  
      Before describing the present invention in detail, a summary of will be given. An example of the present invention relates to a base station apparatus performing an adaptive array signal process on a plurality of signals received by a plurality of antennas. The type of base station apparatus assumed as a target of application is a base station apparatus for wireless local area network (LAN). The wireless LAN processed in the base station apparatus are based on a system complying with IEEE802.11a, a system complying with IEEE802.11b and a system complying with IEEE02.11g. In other words, the base station apparatus is capable of using both 2.4 GHz and 5 GHz as a radio frequency. Both the spectrum spreading scheme and the orthogonal frequency division multiplexing (OFDM) scheme may be used as a secondary modulation scheme in a baseband.  
      A radio frequency for the base station apparatus is set up externally by, for example, a switch. That is, one of 2.4 GHz and 5 GHz is selected for communication. When the apparatus is set up for 5 GHz, the OFDM modulation scheme is used as a secondary modulation scheme. When the apparatus is set up for 2.4 GHz, one of the spectrum spreading scheme and the OFDM modulation scheme is used. In the base station apparatus according to this example, an adaptive algorithm is applied to signals in an adaptive array signal process in order to estimate a receiving weight vector. A training signal in an adaptive algorithm is stored as a time-domain signal even when the OFDM modulation scheme is employed. In the case of spectrum spreading communication, a spread spectrum signal is stored. That is, the adaptive algorithm is applied to a signal subjected to secondary modulation. For this reason, application of the adaptive algorithm according to this example does not depend on whether the secondary modulation is the spectrum spreading scheme or the OFDM modulation scheme. Further, after the training, the same adaptive algorithm process is applied only by changing the value of a determination signal which is to be referred to.  
       FIG. 1  shows a structure of a communications system  100  according to this example. The communications system  100  includes a terminal apparatus  10 , a base station apparatus  34  and a network  32 . The terminal apparatus  10  includes a baseband unit  26 , a modem unit  28 , a radio unit  30  and a terminal antenna  16 . The base station apparatus  34  includes a first base station antenna  14   a , a second base station antenna  14   b , an Nth base station antenna  14   n , generically referred to as a base station antenna  14 , a first radio unit  12   a , a second radio unit  12   b , an Nth radio unit  12   n , generically referred to as a radio unit  12 , a signal processing unit  18 , a modem unit  20 , a baseband unit  22  and a control unit  24 . The terminal apparatus  10  involves a first digital received signal  300   a , a second digital received signal  300   b , an Nth digital received signal  300   n , generically referred to as a digital received signal  300 , a first digital transmission-signal  302   a , a second digital transmission signal  302   b , an Nth digital transmission signal  302   n , generically referred to as a digital transmission signal  302 , a synthesized signal  304 , a pre-separation signal  308 , a signal processing unit control signal  310 , a radio unit control signal  318  and a modem control signal  332 .  
      The baseband unit  22  of the base station apparatus  34  is an interface with the network  32 . The baseband unit  26  of the terminal apparatus  10  is an interface for a PC connected to the terminal apparatus  10  or an application in the terminal apparatus  10 . The baseband units  22  and  26  are responsible for transmission and receiving, respectively, of information signals for transmission by communications system  100 . Error correction or automatic retransmission process may be included. However, a description of these is omitted.  
      The modem unit  20  of the base station apparatus  34  and the modem unit  28  of the terminal apparatus  10  generate a signal for transmission by modulating a carrier with an information signal and demodulates the received signal so as to reproduce the information signal. The modem unit  20  includes a spreading unit and a despreading unit adapted for the spectrum spreading scheme, and also includes an inverse fast Fourier transform (IFFT) unit and a fast Fourier transform (FFT) unit for the OFDM modulation scheme.  
      The signal processing unit  18  performs signal processing necessary for transmission and receiving by the adaptive array antennas. The radio unit  12  of the base station apparatus  34  and the radio unit  30  of the terminal apparatus  10  perform a frequency conversion processes between a baseband signal and a radio signal. The baseband signal is processed by the signal processing unit  18 , the modem unit  20 , the baseband unit  22 , the baseband unit  26  and the modem unit  28 . The radio unit also performs an amplitude process, and an AD or DA conversion process. Since it is assumed that the communications system  100  is adapted for wireless LAN according to IEEE802.11a, IEEE802.11b and IEEE802.11g, the radio unit  12  is adapted for the radio frequency of 2.4 GHz and 5 GHz. The value of radio frequency is set by a user using a switch (not shown).  
      The base station antenna  14  of the base station apparatus  34  and the terminal antenna  16  of the terminal apparatus  10  transmit and receive radio frequency signals. The directivity of the antennas may be as desired. It is assumed that a total of N antennas constitute the base station antenna  14 .  
      The control unit  24  controls the timing of the radio unit  12 , the signal processing unit  18 , the modem unit  20  and the baseband unit  22 . The control unit  24  controls the channel allocation.  
       FIG. 2  shows one of burst formats according to the example. The burst format shown corresponds to Short PLCP of the IEEE802.11b standard. As shown, a burst signal includes a preamble, a header and data, which are spectrum spread. The preamble is transmitted at a transmission rate of 1 Mbps according to the DBPSK modulation scheme. The header is transmitted at a transmission rate of 2 Mbps according to the DQPSK modulation scheme. The data are transmitted at 11 Mbps according to the CCK modulation scheme. The preamble includes a 56-bit SYNC and a 16-bit SFD. The header includes an 8-bit SIGNAL, an 8-bit SERVICE, a 16-bit LENGTH and a 16-bit CRC. The length of PSDU, corresponding to the data, is variable.  
       FIG. 3  shows another burst format according to the example. The burst format corresponds to the speech channel of the IEEE802.11a standard. In the burst signal, the OFDM modulation scheme is used. In the OFDM modulation scheme, the size of Fourier transform and the number of symbols in a guard interval combined constitute a unit. The unit in this example will be defined as an OFDM symbol. A preamble, primarily used for timing synchronization and carrier recovery, occupies four OFDM symbols at the head of the burst. As in  FIG. 2 , the header and the data are provided subsequent to the preamble. The format of  FIG. 2  is also used in the IEEE802.11g. This format is referred to as a OFDM format.  
       FIG. 4  shows yet another burst format according to the example. This burst format corresponds to Short Preamble PDU format of the IEEE802.11g standard. Like the burst signal of  FIG. 2 , the burst signal of  FIG. 4  includes a preamble, a header and data. The preamble and the header are spectrum spread. The preamble is transmitted at a transmission rate of 1 Mbps by the DBPSK modulation scheme. The header is transmitted at a transmission rate of 2 Mbps by the DQPSK modulation scheme. The data are OFDM modulated. This format will be referred to as a mixed format in contrast to the OFDM format described before.  
       FIG. 5  shows a structure of the first radio unit  12   a . The first radio unit  12   a  includes a switch unit  40 , a receiving unit  42  and a transmission unit  44 . The receiving unit  42  includes a frequency conversion unit  46 , a automatic gain control (AGC)  48 , a quadrature detection unit  50  and an AD conversion unit  52 . The transmission unit  44  includes an amplification unit  54 , a frequency conversion unit  56 , a quadrature modulation unit  58  and a DA conversion unit  60 .  
      The switch unit  40  switches between the receiving unit  42  and the transmission unit  44  for signal input and output, in accordance with a radio unit control signal  318 . More specifically, the switch unit  40  selects a signal from the transmission unit  44  for transmission and selects a signal to the receiving unit  42  for receiving.  
      The frequency conversion unit  46  of the receiving unit  42  and the frequency conversion unit  56  of the transmission unit  44  subject a target signal to frequency conversion between a radio frequency of one of 5 GHz and 2.4 GHz, and an intermediate frequency. As mentioned before, selection of 5 GHz or 2.4 GHz is done by a user using a switch (not shown).  
      The AGC  48  automatically controls the gain so as to fit the amplitude of the received signal within a dynamic range of the AD conversion unit  52 .  
      The quadrature detection unit  50  generates a baseband analog signal by subjecting the signal at the intermediate frequency to quadrature detection. The quadrature modulation unit  58  subjects the baseband analog signal to quadrature modulation and generates a signal at the intermediate frequency.  
      The AD conversion unit  52  converts the baseband analog signal into a digital signal, and the DA conversion unit  60  converts the baseband digital signal to an analog signal.  
      The amplification unit  54  amplifies the radio frequency signal for transmission.  
       FIG. 6  shows a structure of the signal processing unit  18  and the modem unit  20 . The signal processing unit  18  includes a first multiplication unit  62   a , a second multiplication unit  62   b , an Nth multiplication unit  62   n , generically referred to as a multiplication unit  62 , an addition unit  64 , a receiving weight vector calculation unit  68 , a reference signal generation unit  70 , a first multiplication unit  74   a , a second multiplication unit  74   b , an Nth multiplication unit  74   n , generically referred to as a multiplication unit  74 , a transmission weight vector calculation unit  76 , a response vector calculation unit  80  and a correlation unit  200 . The modem unit  20  includes an FFT unit  202 , a despreading unit  204 , a demodulation unit  206 , an IFFT unit  208 , a spreading unit  210  and a modulation unit  212 . Signals involved are a weight reference signal  306 , a first receiving weight vector signal  312   a , a second receiving weight vector signal  312   b , an Nth receiving weight vector signal  312   n , generically referred to as a receiving weight vector signal  312 , a first transmission weight vector signal  314   a , a second transmission weight vector signal  314   b , an Nth transmission weight vector signal  314   n , generically referred to as a transmission weight vector signal  314 , a response reference signal  320  and a response vector signal  322 .  
      The correlation unit  200  calculates a correlation value from the digital received signal  300  and a predetermined signal. At least two signals are stored as predetermined signals. One of the predetermined signals is a pattern in which the entirety or a part of the preamble or the header of  FIGS. 2 and 4  are spectrum spread (hereinafter, such a pattern is referred to as a first pattern). The other predetermined signals is a pattern in which the entirety or a part of the preamble or the header of  FIG. 3  is translated into a time domain (hereinafter, such a pattern is referred to as a second pattern). When the frequency of the radio frequency signal received by the base station antenna  14  is 2.4 GHz, a correlation with the first pattern is higher than the other pattern, if the digital received signal  300  is an IEEE802.11b burst or of a mixed format according to IEEE802.11g. If the signal  300  is of an OFDM format according to IEEE802.11g, a correlation with the second pattern is higher than the other pattern. The system with which the received signal conforms is identified as described above. The identity of the system is output to the control unit  24  as the signal processing unit control signal  310 .  
      The receiving weight vector calculation unit  68  calculates, from the digital received signal  300 , the synthesized signal  304  and the weight reference signal  306 , the receiving weight vector signal  312  necessary to weight the digital received signal  300 , by the LMS algorithm. When the digital received signal  300  complies with the spectrum spreading scheme, the LMS algorithm is applied based on the spectrum spread signal. When the digital received signal  300  complies with the OFDM modulation scheme, the LMS algorithm is applied based on the time-domain signal. If the digital received signal  300  is of a mixed format defined in IEEE802.11g, the signal processing unit control signal  310  switches from the LMS algorithm process based on the spectrum spread signal to the LMS algorithm process based on the time-domain signal. A algorithm switch of a reverse pattern may be effected depending on the format of burst.  
      The multiplication unit  62  weights the digital received signal  300  by the receiving weight signal  312 , and the addition unit  64  adds the outputs of the multiplication unit  62  so as to output the synthesized signal  304 .  
      The reference signal generation unit  70  outputs a pre-stored training signal as the weight reference signal  306  and the response reference signal  320  during a training period. If the digital received signal  300  is an IEEE802.11b burst or of a mixed format of IEEE802.11b and IEEE802.11g, the spectrum spread preamble signal of  FIG. 2  or  FIG. 4  is stored as the training signal. If the digital received signal is of the OFDM format of IEEE802.11g, the time-domain preamble signal of  FIG. 3  is stored as the training signal. After the training period, the synthesized signal  304  is compared with a pre-defined threshold value for decision. The result of decision is output as the weight reference signal  306  and the response reference signal  320 . The decision may not necessarily be hard decision and may be soft decision.  
      The response vector calculation unit  80  calculates the response vector signal  322  indicating the receiving response characteristic defined as the characteristic of a received signal with respect to a transmitted signal, from the digital received signal  300  and the response reference signal  320 . The method of calculating the response vector signal  322  may be optional. For example, the response vector signal  322  may be calculated based on a correlating process. The digital received signal  300  and the response reference signal  320  may be input not only from the signal processing unit  18  but also from a signal processing unit corresponding to a terminal apparatus of a different user via a signal line (not shown). Indicating the digital received signal  300  corresponding to a first terminal apparatus by x1(t), the digital received signal  300  corresponding to a second terminal apparatus by x2(t), the response reference signal  320  corresponding to the first terminal apparatus by S1(t), and the response reference signal  320  corresponding to the second terminal apparatus by S2(t), x1(t) and x2(t) are given by the following equations.
 
 x   1 ( t )= h   11   S   1 ( t )+ h   21 S 2 ( t )
 
 x   2 ( t )= h   12   S   1 ( t )+ h   22   S   2 ( t )  (1)
 
 where hij indicates a response characteristic that occurs between an ith terminal apparatus and a jth base station antenna  14   j . Noise is neglected. A first correlation matrix R1 is given by the following equation, where E indicates an ensemble average.  
               R   1     =     [           E   ⁡     [       x   1     ⁢     S   1   *       ]             E   ⁡     [       x   2     ⁢     S   1   *       ]                 E   ⁡     [       x   1     ⁢     S   2   *       ]             E   ⁡     [       x   2     ⁢     S   2   *       ]             ]             (   2   )             
 
      A correlation matrix R2 between the response reference signals  320  is calculated by the following equation.  
               R   2     =     [           E   ⁡     [       S   1     ⁢     S   1   *       ]             E   ⁡     [       S   1   *     ⁢     S   2       ]                 E   ⁡     [       S   2     ⁢     S   1   *       ]             E   ⁡     [       S   2   *     ⁢     S   2       ]             ]             (   3   )             
 
      Finally, an inverse matrix of the second correlation matrix R2 and the first correlation matrix R1 are multiplied, and the response vector signal  322  given by the following equation is obtained.  
               [           h   11           h   12               h   21           h   22           ]     =       R   1     ⁢     R   2     -   1                 (   4   )             
 
      The transmission weight vector calculation unit  76  estimates the transmission weight vector signal  314  necessary to weight the pre-separation signal  308 , from the receiving vector signal  312  and the response vector signal  322  indicating the receiving response characteristic. The method for estimating the transmission vector signal  314  maybe as desired. The simplest method may be to use the receiving weight vector signal  312  and the response vector signal  322  as they are. Alternatively, the receiving weight vector signal  312  and the response vector signal  322  may be corrected by the related-art technology in consideration of Doppler frequency variation occurring in the propagation environment between the timing of the receiving process and the timing of the transmission process. It is assumed here that the response vector signal  322  is used as the transmission weight vector signal  314 .  
      The FFT unit  202  calculates a fast Fourier transform of the synthesized signal  304  and outputs a frequency-domain signal. The despreading unit  204  despreads the synthesized signal  304  and outputs a despread signal. In the case of mixed format of IEEE802.11g, the modem unit control signal  332  switches from the process in the despreading unit  204  to the process in the FFT unit  202 . Switching may occur in a reverse pattern depending on the format of burst. The demodulation unit  206  demodulates the signal output from the FFT unit  202  or the despreading unit  204 .  
      The modulation unit  212  modulates information for transmission. The IFFT unit  208  calculates an inverse Fourier transform of the modulated information so as to output a time-domain signal. The spreading unit  210  spreads the modulated information so as to output the spread signal. The time-domain signal output from the IFFT unit  208  and the spread signal output from the spreading unit  210  are indicated as pre-separation signal  308 .  
      The multiplication unit  74  weights the pre-separation signal  308  by the transmission weight vector signal  314  so as to output the digital transmission signal  302 . The aforementioned operation is timed in accordance with the signal processing unit control signal  310 .  
      In terms of hardware the above-described structure can be realized by a CPU, a memory and other LSIs of an arbitrary computer. In terms of software, it is realized by memory-loaded programs which have a reserved management function or the like, but drawn and described herein are function blocks that are realized in cooperation with those. Thus, it is understood by those skilled in the art that these function blocks can be realized in a variety of forms such as by hardware only, software only or the combination thereof.  
       FIG. 7  shows a structure of the receiving weight vector calculation unit  68 . The receiving weight vector calculation unit  68  is a generic reference to a first receiving weight vector calculation unit  68   a , a second receiving weight vector calculation unit  68   b  and an Nth receiving weight vector calculation unit  68   n . The receiving weight vector calculation unit  68  includes an addition unit  140 , a complex conjugate unit  142 , a multiplication unit  148 , a step size parameter storage unit  150 , a multiplication unit  152 , an addition unit  154  and a delay unit  156 .  
      The addition unit  140  calculates a difference between the synthesized signal  304  and the weight reference signal  306  so as to output an error signal, i.e., an error vector. The error signal is subject to complex conjugate transformation by the complex conjugate unit  142 .  
      The multiplication unit  148  multiplies the error signal subjected to complex conjugate transformation with the first digital received signal  300   a  so as to generate a first multiplication result.  
      The multiplication unit  152  multiplies the first multiplication result with a step size parameter stored in the step size parameter storage unit  150  so as to generate a second multiplication result. The second multiplication result is fed back by the delay unit  156  and the addition unit  154  and added to the new second multiplication result. The addition result updated one after another by the LMS algorithm is output as the receiving weight vector signal  312 . While the digital received signal  300  may be spectrum spread or OFDM modulated in the above-described structure, the only difference is the value of the weight reference signal  306 , the other aspects of the structure being the same in both cases.  
       FIG. 8  is a flowchart showing a procedure of the demodulation process in the signal processing unit  18  and the modem unit  20 . The correlation unit  200  calculates a correlation value from the digital received signal  300  (S 10 ). If it is determined from the correlation value that the received signal is an OFDM signal (Y in S 12 ), the receiving weight vector calculation unit  68  calculates the receiving weight vector signal  312  for the digital received signal  300 , which is the OFDM signal in the time domain (S 14 ). The multiplication unit  62  and the addition unit  64  subjects the digital received signal  300  to a synthesis process based on the receiving weight vector signal  312  so as to output the synthesized signal  304  (S 16 ). The FFT unit  202  calculates a fast Fourier transform of the synthesized signal  304  (S 18 ). If it is determined from the correlation value that the received signal is not an OFDM signal (N in S 12 ), the receiving weight vector calculation unit  68  calculates the receiving weight vector signal  312  for the digital received signal  300 , which is the spectrum spread signal (S 20 ). The multiplication unit  62  and the addition unit  64  subjects the digital received signal  300  to a synthesis process based on the receiving weight vector signal  312  so as to output the synthesized signal  304  (S 22 ). The despreading unit  204  despreads the synthesized signal  304  (S 24 ). The demodulation unit  206  demodulates the output signal from the FFT unit  202  or the despreading unit  204  (S 26 ).  
      Since the adaptive algorithm is executed in a time domain according to the example of the present invention, a signal other than a multicarrier signal is processed only by switching between reference signals. More specifically, the spectrum spread signal is processed properly. Operations to process the multicarrier signal and spectrum spread signal are nearly identical in timing. Therefore, the circuit is implemented merely by a simple correction. An increase in the number of sub-carriers only produces a small increase in the processing volume.  
      The present invention has been described based on the examples which are only exemplary. It is understood by those skilled in the art that there exist other various modifications to the combination of each component and process described above and that such modifications are encompassed by the scope of the present invention.  
      In the example of the present invention, the radio frequency used in the radio unit  12  is switched from one to the other using a switch (not shown) so that the circuit is set up for only one radio frequency. Alternatively, a plurality of radio units  12  adapted for respective radio frequencies may be provided so that the circuit may be used for the radio frequencies of 5 GHz and 2.4 GHz at the same time. In this case, the wireless LAN standard is identified based on the radio frequency detected by the radio unit  12  and the correlation value determined by the correlation unit  200 . According to this variation, the invention may be adapted for a plurality of wireless LAN standards regardless of the radio frequency. A single receiving weight vector calculation unit  68  may be applied to the plurality of wireless LAN standards by changing the reference signal.  
      In this example of the present invention, the correlation unit  200  discriminates between 1) the burst of IEEE802.11b or the mixed format of IEEE802.11g, and 2) the OFDM format of IEEE802.11g, based on the correlation value. Alternatively, the correlation unit  200  may only be adapted for the burst of IEEE802.11b or the mixed format of IEEE802.11g. That is, the correlation unit  200  may only be adapted for a case in which the head of a burst is spectrum spread. According to this variation, the process is simplified. This variation serves the purpose of configuring a single receiving weight vector calculation unit  68  to be adapted for a plurality of wireless LAN standards.  
      Although the present invention has been described by way of exemplary embodiments and modified examples as above, it should be understood that many changes and substitutions may still further be made by those skilled in the art without departing from the scope of the present invention which is defined by the appended claims.