Abstract:
A method of outputting a demodulation result for soft-decision decoding is provided, which is comprised of the steps of: (a) detecting a channel distortion of a received signal generated in a communication channel using a training signal contained in the received signal and a reference training signal, outputting a channel distortion data: (b) generating a distortion-based reliability data from the channel distortion data; (c) compensating the received signal using the channel distortion data, generating a compensated, received signal; (d) demodulating the compensated, received signal and deciding the received signal thus demodulated using a soft decision technique, outputting a decision result; and (e) outputting a demodulation result using the decision result and the distortion-based reliability data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and a device of receiving digital signals and a receiver and more particularly, to a method and a device of outputting the demodulation result in soft-decision decoding that enhances the decoding capability of error-correcting codes, which makes it possible to output necessary reliability information with high accuracy, and a receiver using the method or device. 
     2. Description of the Prior Art 
     The soft-decision decoding technique is a technique that estimates the original digital signal from a noise-containing digital signal that has been sent through transmission lines by deciding the level of the noise-containing digital signal as a multi-valued signal (not a two-valued signal) using a plurality of threshold values. In other words, this technique is one that estimates the two-valued (i.e., “0” and “1”), original information through the multi-valued decoding by deciding the level of the noise-containing digital signal using a plurality of threshold values. This technique has an advantage that the error correction rate is better than that of the hard-decision decoding technology that estimates the two-valued, original information through the two-valued decoding by deciding the level of the noise-containing digital signal using a single threshold value. 
     An example of the prior-art soft-decision decoding systems is shown in the Japanese Non-Examined Patent Publication No. 8-317006 published in November 1996. In this system, the level reliability information on the basis of the received signal level and the phase reliability information on the basis of the received signal phase are used as the reliability information necessary for soft decision decoding. This prior-art system is explained below with reference to FIG.  1 . 
     As shown in FIG. 1, the prior-art soft-decision decoding system comprises an input terminal  1000 , a demodulation circuit  1001 , a level detection circuit  1002 , a level normalization circuit  1003 , a soft-decision result calculation circuit  1004 , a phase-reliability detection circuit  1006 , and an output terminal  1005 . 
     A received signal RS inputted through the input terminal  1000  is applied to the demodulation circuit  1001 . The circuit  1001  demodulates the signal RS to generate a demodulated signal and then, decodes the demodulated signal using the soft-decision decoding technique. Thus, the circuit  1001  outputs a decision result, i.e., the demodulated data DD, to the level normalization circuit  1003 , the soft-decision result calculation circuit  1004 , and the phase-reliability detection circuit  1006 . 
     The received signal RS is further applied to the level detection circuit  1002  and the phase-reliability detection circuit  1006 . The level detection circuit  1002  detects the level of the signal RS thus applied and outputs a receiving level signal RSL to the level normalization circuit  1003 . The level normalization circuit  1003  normalizes the level of the receiving level signal RSL on the basis of the decision result or demodulated data DD, outputting a receiving level reliability data LR. The “receiving level reliability” means the reliability relating to the receiving level of the received signal RS. The normalization operation of the circuit  1003  is necessitated by the following reason. 
     Since the decision result or demodulated data DD is a multi-valued demodulated data having different levels, the receiving level reliability is unable to be correctly estimated or evaluated from the receiving level itself. In other words, the receiving level reliability needs to be normalized. 
     On the other hand, the phase-reliability detection circuit  1006  detects the phase difference between the received signal RS and the demodulated data or decision result DD, outputting the level-based reliability data PR to the soft-decision result calculation circuit  1004 . 
     The soft-decision result calculation circuit  1004  receives the demodulated data DD, the phase-based reliability data PR, and the level-based reliability data LR, outputting a demodulation data DR applicable to the subsequent decoding operation. 
     With the prior-art soft-decision decoding system shown in FIG. 1, normalization is essential for calculating the level-based reliability data LR on the basis of the decision result or demodulated data DD, which raises a problem that the circuit scale of the system becomes large. 
     Also, if the decision result or demodulated data DD is incorrect due to noise, there arises a problem that the reliability of the level-based reliability data LR, which is dependent upon the decision result DD, is lowered and as a result, the decoding capability of the error-correction codes degrades. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a method and a device of outputting a demodulation result in soft-decision decoding that make it possible to output necessary reliability information with high accuracy using a simple circuit configuration. 
     Another object of the present invention is to provide a receiver having an enhanced decoding capability of error-correcting codes. 
     The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description. 
     According to a first aspect of the present invention, a method of outputting a demodulation result in soft-decision decoding is provided, which is comprised of the steps of: 
     (a) demodulating a received signal and deciding the received signal thus demodulated using a soft decision technique, outputting a decision result; 
     (b) estimating a distortion of the received signal generated in a communication channel, outputting a channel distortion data; and 
     (c) calculating a demodulation result on the basis of the decision result and the channel distortion data. 
     With the method of outputting a demodulation result in soft-decision decoding according to the first aspect, the distortion of the received signal generated in the communication channel is estimated to output the channel distortion data and then, the demodulation result is calculated on the basis of the decision result and the channel distortion data. This means that the channel distortion data (instead of the level of the received signal) is used as the level reliability information. Thus, the level reliability information can be obtained independent of the decision result, which simplifies the circuit configuration. 
     As a result, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration. 
     According to a second aspect of the present invention, another method of outputting a demodulation result in soft-decision decoding is provided, which is comprised of the steps of: 
     (a) detecting a channel distortion of a received signal generated in a communication channel using a training signal contained in the received signal and a reference training signal, outputting a channel distortion data; 
     (b) generating a distortion-based reliability data from the channel distortion data; 
     (c) compensating the received signal using the channel distortion data, generating a compensated, received signal; 
     (d) demodulating the compensated, received signal and deciding the received signal thus demodulated using a soft decision technique, outputting a decision result; and 
     (e) outputting a demodulation result using the decision result and the distortion-based reliability data. 
     With the method of outputting a demodulation result in soft-decision decoding according to the second aspect, the channel distortion of the received signal generated in the communication channel is detected using the training signal contained in the received signal and the reference training signal. Also, the distortion-based reliability data is generated from the channel distortion data of the received signal. The received signal is compensated using the channel distortion data to thereby generate the compensated, received signal. Using the compensated, received signal, the decision result is generated. Thus, the channel distortion data (instead of the level of the received signal) of the received signal is used as the level reliability information. 
     As a result, the level reliability information can be obtained independent of the decision result and therefore, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration. 
     According to a third aspect of the present invention, a device of outputting a demodulation result in soft-decision decoding is provided, which is comprised of: 
     (a) a demodulator means for demodulating a received signal and for deciding the received signal thus demodulated using a soft decision technique, outputting a decision result; 
     (b) a channel distortion estimator means for estimating a distortion of the received signal generated in a communication channel, outputting a channel distortion data to the demodulator means; and 
     (c) a demodulation result calculator means for calculating a demodulation result on the basis of the decision result from the demodulator means and the channel distortion data from the channel distortion estimator means. 
     With the device of outputting a demodulation result in soft-decision decoding according to the third aspect, because of the same reason as that of the method according to the first aspect, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration. 
     According to a fourth aspect of the present invention, another device of outputting a demodulation result in soft-decision decoding is provided, which is comprised of: 
     (a) a channel distortion detector means for detecting a channel distortion of a received signal generated in a communication channel using a training signal contained in the received signal and a reference training signal, outputting a channel distortion data; 
     (b) a distortion-based reliability data generator means for generating a distortion-based reliability data from the channel distortion data; 
     (c) a compensator means for compensating the received signal using the channel distortion data, generating a compensated, received signal; 
     (d) a demodulator means for demodulating the compensated, received signal and deciding the received signal thus demodulated using a soft decision technique, outputting a decision result; and 
     (e) a demodulation result output means for outputting a demodulation result using the decision result and the distortion-based reliability data. 
     With the device of outputting a demodulation result in soft-decision decoding according to the fourth aspect, because of the same reason as that of the method according to the second aspect, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration. 
     According to a fifth aspect of the present invention, a receiver is provided, which is comprised of: 
     (a) a demodulation circuit for outputting n decision results corresponding to n frequency-multiplexed sub-carriers of a received signal by demodulating the n sub-carriers and deciding then sub-carriers thus demodulated using a soft decision technique, where n is an integer greater than unity; 
     the n decision results being generated by using n channel-distortion coefficients corresponding to the n sub-carriers; 
     (b) a channel-distortion calculation circuit for calculating the n channel-distortion coefficients corresponding to the n sub-carriers; 
     (c) a reliability information calculation circuit for calculating reliability information for the n decision results corresponding to the n sub-carriers using the n channel-distortion coefficients; and 
     (d) a demodulation result output circuit for outputting a demodulation result using the n decision results corresponding to then sub-carriers and the reliability information corresponding to the n sub-carriers. 
     With the receiver according to the fifth aspect, because of substantially the same reason as that of the method according to the first aspect, an enhanced decoding capability of error-correcting codes can be realized. 
     In a preferred embodiment of the receiver according to the fifth aspect of the invention, the channel-distortion circuit comprises; 
     a training signal point memory for storing training signal points corresponding to n reference training signal points corresponding to the n sub-carriers; and 
     n division circuits for respectively dividing n training signal points of the n sub-carriers by the n reference training signal points to thereby output the n channel-distortion coefficients. 
     In another preferred embodiment of the receiver according to the fifth aspect of the invention, the reliability information calculator circuit comprises; 
     n level detection circuits for detecting the level of the n channel-distortion coefficients; 
     a threshold memory for storing threshold values for quantizing the reliability with respect to the level of the n channel-distortion coefficients; and 
     n quantization circuits for quantizing outputs of the n level detection circuits using the threshold values, thereby outputting reliability information corresponding to then decision results. 
     In still another preferred embodiment of the receiver according to the fifth aspect of the invention, the demodulation circuit outputs the n decision results corresponding to the n sub-carriers and n pieces of distance reliability information as reliability information for the n decision results. 
     In a further preferred embodiment of the receiver according to the fifth aspect of the invention, the demodulation circuit comprises; 
     n multiplier circuits for multiplying the n sub-carriers by the corresponding n channel-distortion coefficients; 
     n decision circuits for outputting the n decision results by demodulating the n sub-carriers and outputs of the n multiplier circuits; 
     n distance calculation circuits for calculating a distance between the n decision results and the outputs of the n multiplier circuits in a signal space; 
     a threshold memory for storing threshold values for quantizing the outputs of the n distance calculation circuits; and 
     n quantization circuits for quantizing the outputs of the n distance calculator circuits using the threshold values stored in the threshold memory and the outputs of then distance calculator circuits, thereby outputting distance reliability information as the reliability information for the n decision results. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawings. 
     FIG. 1 is a functional block diagram showing the configuration of a prior-art device of outputting a demodulation result in soft-decision decoding. 
     FIG. 2 is a functional block diagram showing the configuration of a device of outputting a demodulation result in soft-decision decoding according to a first embodiment of the invention. 
     FIG. 3 is a functional block diagram showing the configuration of the communication channel distortion detection circuit used in the device according to the first embodiment of FIG.  2 . 
     FIG. 4 is a functional block diagram showing the configuration of the soft-decision result operation circuit used in the device according to the first embodiment of FIG.  2 . 
     FIG. 5 is a functional block diagram showing the configuration of a receiver according to a second embodiment of the invention, in which the device of outputting a demodulation result in soft-decision decoding according to the first embodiment of FIG. 2 is used. 
     FIG. 6 is a functional block diagram showing the configuration of the communication channel distortion operation circuit used in the receiver according to the second embodiment of FIG.  5 . 
     FIG. 7 is a functional block diagram showing the configuration of the reliability data operation circuit used in the receiver according to the second embodiment of FIG.  5 . 
     FIG. 8 is a functional block diagram showing the configuration of the sub-carrier demodulation circuit used in the receiver according to the second embodiment of FIG.  5 . 
     FIG. 9 is a schematic view showing the format of packets having M data symbols, which is received by the receiver according to the second embodiment of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail below while referring to the drawings attached. 
     First Embodiment 
     A device of outputting a demodulation result in soft-decision decoding according to a first embodiment of the invention has the configuration as shown in FIG.  2 . 
     As shown in FIG. 2, the device according to the first embodiment comprises an input terminal  100 , a demodulation circuit  101 , a soft-decision result calculation circuit  102 , a channel distortion detection circuit  103 , and an output terminal  104 . 
     A received signal RS in burst mode is inputted into the device through the input terminal  100 . The received signal RS is commonly supplied to the demodulation circuit  101  and the channel distortion detection circuit  103 . 
     The channel distortion detection circuit  103  detects the distortion occurring in the communication channels from the training signal contained in the received signal RS and a reference training signal, outputting a channel distortion data DCC to the demodulation circuit  101 . Also, on the basis of the channel distortion data DCC thus obtained, the circuit  103  generates a reliability data DLR and outputs it to the soft-decision result calculation circuit  102 . 
     The demodulation circuit  101  compensates the received signal RS using the channel distortion data DCC from the circuit  103  and then, generates a decision result DD from the received signal RS thus compensated using the soft-decision technique. Then, the circuit  101  outputs the decision result DD to the soft-decision result calculation circuit  102 . 
     The soft-decision result calculation circuit  102  receives the decision result DD from the demodulation circuit  101  and the channel distortion data DLR from the channel distortion detection circuit  103 , thereby outputting a demodulation result DR toward the output terminal  104  for the subsequent decoding operation. 
     FIG. 3 shows an example of the configuration of the channel distortion detection circuit  103  used in the device of FIG.  2 . 
     As shown in FIG. 3, the channel distortion detection circuit  103  comprises a correlation calculation circuit  111 , a level detection circuit  112 , a quantization circuit  113 , a training signal point memory  114 , and a threshold memory  115 . An input terminal  110  is connected to the input of the correlation calculation circuit  111 . An output terminal  116  is connected to the output of the quantization circuit  113 . Another output terminal  117  is connected to the output of the correlation calculation circuit  111 . 
     The output terminal  116  is further connected to the input of the soft-decision result operation circuit  102 . The output terminal  117  is further connected to the input of the demodulation circuit  101 . 
     The received signal RS is applied to the correlation calculation circuit  111  through the input terminal  110 . The circuit  111  calculates the correlation between the training signal contained in the received signal RS and a reference training signal that has been stored in the training signal memory  114  in advance, outputting a distortion-compensating coefficient DCC to the level detection circuit  112 . The distortion-compensating coefficient DCC is sent to the demodulation circuit  101  through the output terminal  117 . The distortion-compensating coefficient DCC means the distortion of the signal RS encountered in the communication channels. 
     The level detection circuit  112  detects the level of the applied distortion-compensating coefficient DCC. The smaller the channel distortion becomes, the higher the correlation between the previously-stored reference training signal and the reference signal in the received signal RS (and therefore, the reliability level) becomes also. 
     The correlation or reliability level DRL obtained in the level detection circuit  112  is quantized by the quantization circuit  113  using the threshold values TH stored in the threshold memory  115 . Thus, the circuit  113  outputs the reliability information DLR to the soft-decision result operation circuit  102  through the output terminal  116  on the basis of the channel distortion. 
     FIG. 4 shows an example of the configuration of the soft-decision result calculation circuit  102  used in the device of FIG.  2 . 
     As shown in FIG. 4, the soft-decision result calculation circuit  102  is formed by a parallel-serial conversion circuit  122 . An input terminal  120  is connected to the input of the demodulating circuit  110 . Another input terminal  121  is connected to the output of the channel-distortion detection circuit  103 . 
     The parallel-serial conversion circuit  122  is supplied with the decision result DD from the demodulation circuit  101  through the input terminal  120  and the reliability data DLR from the channel distortion detection circuit  103  through the input terminal  121 . Then, the circuit  122  outputs the demodulation result DR for the subsequent decoding operation to the output terminal  123  or  104 . The circuit  122  converts the two data DD and DLR supplied in parallel to a serial signal as the demodulation result DR. 
     With the device of outputting a demodulation result in soft-decision decoding according to the first embodiment of the invention, the distortion of the received signal RS generated in the communication channels is detected from the training signal contained in the received signal RS and the reference training signal stored in the training signal point memory  114 . Also, the distortion-based reliability data DLR is generated from the channel distortion of the received signal RS in the channel distortion detection circuit  103 . The signal RS is compensated using the channel distortion to thereby generate the compensated, received signal. The compensated, received signal is demodulated by the demodulation circuit  101  and soft-decided, generating the decision result DD. Thus, the channel distortion data DCC (instead of the level of the received signal RS) is used as the level reliability information. 
     As a result, the level reliability information can be obtained independent of the decision result DD and therefore, the necessary reliability information can be outputted with high accuracy using a simple circuit configuration. 
     Second Embodiment 
     FIG. 5 shows a receiver designed for the Orthogonal Frequency Division Multiplexing (OFDM) system according to a second embodiment of the invention, in which the device of outputting a demodulation result in soft-decision decoding according to the first embodiment is used. In this receiver, a received signal RS contains n multiplexed sub-carriers. 
     As shown in FIG. 5, the OFDM type receiver is comprised of an input terminal  200 , a timing control circuit  201 , a serial-parallel conversion circuit  202 , a Fast Fourier Transformation (FFT) circuit  203 , n switches  204 - 1  to  204 -n, a channel distortion operation circuit  205 , a sub-carrier demodulation circuit  206 , a reliability data calculation circuit  207 , n parallel-serial conversion circuit  210 - 1  to  210 -n, a multiplexing circuit  211 , and an output terminal  212 , where n is an integer greater then unity (i.e., n≧2). 
     The received signal RS has a format of packets as shown in FIG.  9 . This format includes M data symbols  503 - 1  to  503 -M, where M is an integer greater then unity (i.e., M≧2). This format further includes a ramp signal  500  for indicating the transmission start, a training signal  501  for timing control, a training signal  502  for estimating the channel distortion, and a ramp signal  504  for indicating transmission end. 
     When the receiver of FIG. 5 receives the signal RS with the packet format shown in FIG. 9, the signal RS is supplied to the timing control circuit  201  and the serial-parallel conversion circuit  202 . The circuit  202  converts the serial data containing sample values forming the respective data symbols  503 - 1  to  503 -M to parallel data signals PS′ to the FFT circuit  203 . 
     The FFT circuit  203  performs the Fourier transformation with respect to the parallel data signals PS′ while using the pulse DSP for starting the channel-distortion detection sent from the timing control circuit  201  as a trigger signal. Thus, the circuit  203  separates the n sub-carriers contained in the parallel data signals PS′ and outputs them to the switches  204 - 1  to  204 -n, respectively. 
     The timing control circuit  201  has in advance a reference signal whose content corresponds to that of the training signal  501  in the signal RS (see FIG.  9 ). Then, the circuit  201  compares the content of the training signal  501  in the signal RS with that of the training signal stored previously, generating the correlation data. The circuit  201  defines the timing at which the value of the correlation data exceeds the previously-determined threshold value as the receiving time of the training signal  501 . 
     Then, the timing control circuit  201  calculates the timing at which the receipt of the training signal  502  for channel-distortion estimation, thereby outputting pulses DSP for starting the channel-distortion detection to the FFT circuit  203  according to the timing thus calculated. Moreover, the circuit  201  calculates the timing at which the first data symbol  503 - 1  is received, thereby outputting pulses DRP for receiving the data symbols to the switches  204 - 1  to  204 -n according to the timing thus calculated. 
     The initial states of the switches  204 - 1  to  204 -n are set in such a way that their input signals are sent to the channel distortion calculation circuit  205 . Thus, the training signal components TS- 1  to TS-n for channel distortion estimation of the sub-carriers SC- 1  to SC-n are supplied to the circuit  205 . 
     When the pulses for receiving the data symbols are supplied to the switches  204 - 1  to  204 -n, the destination of their input signals are switched to the sub-carrier demodulation circuit  206 . Thus, the data symbol components DS- 1  to DS-n of the sub-carriers SC- 1  to SC-n are supplied to the circuit  206 . 
     The channel distortion calculation circuit  205  calculates the channel distortion occurring in the individual sub-carriers SC- 1  to SC-n from the training signal components TS- 1  to TS-n of the sub-carriers SC- 1  to SC-n. Then, the circuit  206  outputs the compensation coefficients (i.e., the sub-carrier compensation coefficients) to the sub-carrier demodulation circuit  206  and the reliability data calculation circuit  207 . 
     FIG. 6 shows an example of the configuration of the channel distortion calculation circuit  205  used in the receiver of FIG.  5 . 
     The channel distortion calculation circuit  205  comprises n input terminals  220 -( 1 ) to  220 -(n), n division circuits  221 -( 1 ) to  221 -(n), a training signal point memory  222 , and n output terminals  223 -( 1 ) to  223 -(n). 
     The known signal points TSP- 1  to TSP-n corresponding respectively to then sub-carriers SC- 1  to SC-n have been previously stored in the training signal point memory  222 . The division circuits  221 -( 1 ) to  221 -(n) divide the known signal points TSP- 1  to TSP-n by the signal points of the training signal components TS- 1  to TS-n of the sub-carriers SC- 1  to SC-n, respectively, outputting n division results. The n division results represent the compensation values for compensating the channel distortion of the respective sub-carriers SC 1  to SC-n, which are outputted to the output terminals  223 -( 1 ) to  223 -(n). 
     Returning to FIG. 4, the sub-carrier demodulation circuit  206  receives the data symbol components DS- 1  to DS-n of the sub-carriers SC 1  to SC-n from the switches  204 - 1  to  204 -n and the sub-carrier compensation coefficients DCC- 1  to DCC-n from the channel distortion calculation circuit  205 . Then, the circuit  206  outputs the decision result DD- 1  to DD-n for the respective sub-carriers SC- 1  to SC-n and the distance-based reliability data SPR- 1  to SPR-n to the parallel-serial conversion circuit  210 - 1  to  210 -n, respectively. 
     FIG. 8 shows an example of the configuration of the sub-carrier demodulation circuit  206  used in the receiver of FIG.  5 . 
     As shown in FIG. 8, the circuit  206  comprises n input terminals  300 -( 1 ) to  300 -(n), n input terminals  307 -( 1 ) to  307 -(n), n decision circuits  302 -( 1 ) to  302 -(n), n distance calculation circuits  301 -( 1 ) to  301 -(n), n quantization circuits  303 -( 1 ) to  303 -(n), a distance threshold memory  304 , n multiplier circuits  308 -( 1 ) to  308 -(n), n output terminals  305 -( 1 ) to  305 -(n), and n output terminals  306 -( 1 ) to  306 -(n). 
     The components DS- 1  to DS-n of the n sub-carriers SC- 1  to SC-n are supplied to the multiplier circuits  308 -( 1 ) to  308 -(n) through the input terminals  300 -( 1 ) to  300 -(n), respectively. The sub-carrier compensation coefficients DCC- 1  to DCC-n for the n sub-carriers SC- 1  to SC-n are supplied to the multiplier circuits  308 -( 1 ) to  308 -(n) through the input terminals  307 -( 1 ) to  307 -(n), respectively. Then, the circuits  308 -( 1 ) to  308 -(n) multiply the components DS- 1  to DS-n by the sub-carrier compensation coefficients DCC- 1  to DCC-n, generating the output signals DS- 1 ′ to DS-n′, respectively. Thus, the channel distortion in the sub-carriers SC- 1  to SC-n is compensated. 
     The output signals DS- 1 ′ to DS-n′ of the multiplier circuits  308 -( 1 ) to  308 -(n) are supplied to the decision circuits  302 -( 1 ) to  302 -(n) and the distance calculation circuits  301 -( 1 ) to  301 -(n), respectively. The decision circuits  302 -( 1 ) to  302 -(n) make decision about the applied output signals DS- 1 ′ to DS-n′ of the multiplier circuits  308 -( 1 ) to  308 -(n) using the soft-decision technique, there by outputting the decision data DD- 1  to DD-n to the distance calculation circuits  301 -( 1 ) to  301 -(n) and the output terminals  306 -( 1 ) to  306 -(n), respectively. 
     The distance calculation circuits  301 -( 1 ) to  301 -(n) perform the mapping operation of the decision data DD- 1  to DD-n of the decision circuits  302 -( 1 ) to  302 -(n). Then, the circuits  301 -( 1 ) to  301 -(n) calculate the distances SPD- 1  to SPD-n between the signal points thus mapped and the output signals DS- 1 ′ to DS-n′ of the multiplier circuits  308 -( 1 ) to  308 -(n), thereby supplying the distances SPD- 1  to SPD-n to the quantization circuits  303 -( 1 ) to  303 -(n), respectively. 
     The quantization circuits  303 -( 1 ) to  303 -(n) quantize the distances SPD- 1  to SPD-n using the threshold values DTH stored in the threshold memory  304 , outputting the distance-based reliability data SPR- 1  to SPR-n about the decision results DD of the respective sub-carriers SC- 1  to SC-n toward the output terminals  305 -( 1 ) to  305 -(n), respectively. As seen from FIG. 5, the distance-based reliability data SPR- 1  to SPR-n thus outputted are supplied to the parallel-serial conversion circuit  210 - 1  to  210 -n, respectively. 
     The shorter the distances SPD- 1  to SPD-n become, the higher the reliability becomes. 
     Returning to FIG. 5, the reliability data calculation circuit  207  receives the sub-carrier compensation coefficients DCC- 1  to DCC-n from the channel distortion calculation circuit  205 , outputting the level-based reliability data DLR- 1  to DLR-n. 
     FIG. 7 shows an example of the configuration of the reliability data calculation circuit  207  used in the receiver of FIG.  5 . 
     As shown in FIG. 7, the circuit  207  comprises n input terminals  230 -( 1 ) to  230 -(n), n level detection circuits  231 -( 1 ) to  231 -(n), n quantization circuits  232 -( 1 ) to  232 -(n), a threshold memory  233 , and n output terminals  234 -( 1 ) to  234 -(n). 
     The sub-carrier compensation coefficients DCC- 1  to DCC-n, which are sent from the channel distortion calculation circuit  205 , are supplied to the level detection circuits  231 -( 1 ) to  231 -(n) through the input terminals  230 -( 1 ) to  230 -(n), respectively. Thus, the circuits  231 -( 1 ) to  231 -(n) detect the level of the sub-carrier compensation coefficients DCC- 1  to DCC-n, outputting the level data DRL- 1  to DRL-n, respectively. The level data DRL- 1  to DRL-n thus detected are sent to the quantization circuits  232 -( 1 ) to  232 -(n) and then, quantized according to the threshold values LTH stored in the threshold memory  233 , respectively. The quantized level data DLR- 1  to DLR-n thus obtained are outputted through the output terminals  234 -( 1 ) to  234 -(n) to the parallel-serial conversion circuits  210 - 1  to  210 -n as the level-based reliability information, respectively. 
     The lower the levels of the compensation coefficients DCC- 1  to DCC-n of the sub-carriers SC- 1  to SC-n become, the higher the reliability of the decision results DD- 1  to DD-n becomes. 
     Returning to FIG. 5, the parallel-serial conversion circuits  210 - 1  to  210 -n are supplied with the decision results DD- 1  to DD-n, the distance-based reliability information SPR- 1  to SPR-n from the sub-carrier demodulation circuit  206 , and the level-based reliability information DLR- 1  to DLR-n from the reliability data calculation circuit  207 . Then, the circuits  210 - 1  to  210 -n convert these data DD- 1  to DD-n, SPR- 1  to SPR-n, and DLR- 1  to DLR-n sent in parallel to n serial data DR- 1  to DR-n, respectively. As a result, the demodulation results DR- 1  to DR-n for the sub-carriers SC- 1  to SC-n, which are applicable to the subsequent decoding operation, are supplied to the multiplexing circuit  211 . 
     The multiplexing circuit  211  multiplexes the demodulation results DR- 1  to DR-n for the sub-carriers SC- 1  to SC-n and outputs a multiplexed demodulation result MDR containing the results DR- 1  to DR-n to the output terminal  212 . 
     With the receiver according to the second embodiment, as described above, the device of outputting a demodulation result in soft-decision decoding according to the first embodiment of FIG. 2 is used. Thus, an enhanced decoding capability of error-correcting codes can be realized. 
     In the above-explained second embodiment, the distance-based reliability data SPR- 1  to SPR-n are outputted, as shown in FIG.  8 . However, the invention is not limited thereto. The invention is applicable to any configuration outputting no distance-based reliability information or data. 
     While the preferred forms of the present invention have been described, it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention. The scope of the present invention, therefore, is to be determined solely by the following claims.