Receiver and receiving method

[0002] The present invention relates to a receiver capable of adaptively taking phase synchronization with high accuracy for a modulated signal in which sub-carriers are multiplexed, such as an OFDM (Orthogonal Frequency Division Multiplexing) system.

[0003] One example of this kind of conventional receiver is described in JP-A-95174/1995. FIG. 13 is a block diagram of its apparatus for demodulating an OFDM signal. This apparatus detects a phase difference from a modulation result of an arbitrary carrier in order to conduct phase synchronization for a modulated signal in which sub-carriers are multiplexed.

[0004] In FIG. 13, 1000-1-1000-n are input terminals, 1001 is a fast Fourier transform (FFT) circuit of n points, 1002 is a parallel/serial transform circuit, 1003 is a selector, 1004 is a phase difference detector, and 1005 and 1006 are output terminals.

[0005] Serial/parallel transformed n received signals are input to the FFT circuit 1001 of n points through the input terminals 1000-1-1000-n. The FFT circuit 1001 applies Fourier transformation to the input signals and de-multiplexes sub-carriers therefrom, and inputs the sub-carriers to the parallel/serial transform circuit 1002.

[0006] The parallel/serial transform circuit 1002 applies parallel/serial transform to each of the input sub-carrier components and outputs it to the output terminal 1005, and also, outputs it to the selector 1004. Furthermore, the parallel/serial transform circuit 1002 outputs to the selector 1003 a pulse for indicating time when each subcarrier component is output.

[0007] The selector 1003 selects a sub-carrier component to be input, based on the input pulse, and outputs it to the phase difference detecting circuit 1004.

[0008] In the phase difference detecting circuit 1004, assuming that a phase of a symbol under ideal condition in which phase synchronization is established is a reference phase, a difference between the input sub-carrier component and the reference phase is detected as a phase error, and it is output to the output terminal 1006. The phase error output to the output terminal 1006 is integrated by a loop filter and so forth, and is fed back to a local oscillator.

[0009] However, in the above-mentioned conventional OFDM signal demodulating apparatus, there is a task that it becomes to be difficult to detect a correct phase difference when distortion occurs in the selected sub-carrier component due to disturbance such as a noise in a communication line.

[0010] Also, in JP-A-95174/1995, although it is suggested to adaptively select a sub-carrier based on a noise and distortion, a method and an arrangement therefor are not disclosed.

[0011] The present invention is made to solve the above-mentioned problems.

[0012] Moreover, the objective of the invention is to provide a receiver for receiving a modulated wave in which a plurality of sub-carriers are multiplexed, to provide the receiver for conducting phase tracking with high accuracy, and capable of obtaining high reception characteristic.

[0013] In a receiver for receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, the receiver of the first present invention has a sub-carrier demodulating circuit for receiving the above-described plurality of (k, 1≦k≦N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of the above-described sub-carrier components as a demodulation result of each of the above-described plurality of sub-carrier components, and for conducting determination based on the above-described demodulation result and outputting a determination result, and also, outputting a distortion correction coefficient for each of the above-described plurality of sub-carrier components, and a value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and a phase estimating circuit for receiving the determination result of each of the above-described plurality of sub-carrier components, the distortion correction coefficient for each of the above-described plurality of sub-carrier components, and the value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and for outputting a phase error.

[0014] For example, the phase estimating circuit of the first present invention has k phase comparison circuits for receiving the determination result of each of the above-described plurality of sub-carrier components and the value which is generated by correcting each of the above-described plurality of sub-carrier components based on the above-described distortion correction coefficient, and for detecting a phase difference between the above-described corresponding demodulation result and the value corrected based on the above-described distortion correction coefficient, and outputting it as a phase difference of each sub-carrier, k electric power detecting circuits for receiving the distortion correction coefficient for each of the above-described plurality of sub-carrier components, detecting electric power of the distortion correction coefficient for each of the above-described plurality of sub-carrier components, and outputting it as distortion correction coefficient electric power of each sub-carrier, k weight setting circuits for receiving each distortion correction coefficient electric power of the above-described each sub-carrier, and based on the distortion correction coefficient electric power of the above-described each sub-carrier, for obtaining a weight for the above-described each sub-carrier for weighting a phase difference of the above-described each sub-carrier and conducting synthesis thereof, and outputting the weight, and a weighting and synthesizing circuit for outputting a result of weighting and synthesizing a phase difference of the above-described each sub-carrier based on the weight for the above-described each sub-carrier as a phase error.

[0015] For example, the above-described weight setting circuits of the first present invention make a weight for weighting to be large if the distortion correction coefficient electric power of the above-described each sub-carrier is small, and make a weight for weighting to be small if the distortion correction coefficient electric power of the above-described each sub-carrier is large.

[0016] For example, the above-described weight setting circuits of the first present invention set a weight to be 1 if the distortion correction coefficient electric power of the above-described each sub-carrier is smaller than a determined threshold value, and set a weight to be 0 if the distortion correction coefficient electric power of the above-described each sub-carrier is larger than a determined threshold value.

[0017] In a receiver for receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, the receiver of the second present invention has a sub-carrier demodulating circuit for receiving the above-described plurality of (k, 1≦k≦N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of the above-described sub-carrier components as a demodulation result of each of the above-described plurality of sub-carrier components, and for conducting determination based on the above-described demodulation result and outputting a determination result, and outputting a value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and a phase estimating circuit for receiving the determination result of each of the above-described plurality of sub-carrier components, the value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and the above-described plurality of sub-carrier components which are multiplexed and de-multiplexed, and for outputting a phase error.

[0018] For example, the phase estimating circuit of the second present invention has k phase comparison circuits for receiving the determination result of each of the above-described plurality of sub-carrier components and the value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, detecting the above-described corresponding demodulation result and the value which is obtained by correcting distortion generated in each of the above-described plurality of sub-carrier components, and outputting them as a phase difference of each sub-carrier, k electric power detecting circuits for receiving the above-described plurality of sub-carrier components which are multiplexed and de-multiplexed, detecting electric power of the above-described plurality of sub-carrier, components which are multiplexed and de-multiplexed, and outputting it as electric power of each sub-carrier component, k weight setting circuits for receiving each electric power of the above-described each sub-carrier component, and based on the electric power of the above-described each sub-carrier component, for obtaining a weight for the above-described each sub-carrier for weighting a phase difference of the above-described each sub-carrier and conducting synthesis thereof, and outputting the weight, and a weighting and synthesizing circuit for outputting a result of weighting and synthesizing a phase difference of the above-described each sub-carrier based on the weight for the above-described each sub-carrier as a phase error.

[0019] For example, the weight setting circuits of the second present invention make a weight for weighting to be small if the electric power of the above-described each sub-carrier component is small, and make a weight for weighting to be large if the electric power of the above-described each sub-carrier component is large.

[0020] For example, the weight setting circuits of the second present invention set a weight to be 0 if the electric power of the above-described each sub-carrier component is smaller than a determined threshold value, and set a weight to be 1 if the electric power of the above-described each sub-carrier component is larger than a determined threshold value.

[0021] In a receiving method of receiving a modulated wave for carrying a data in which N sub-carriers are multiplexed, said receiving method comprises the steps of:

[0022] receiving a plurality of (k, 1≦k≦N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of said sub-carrier components as a demodulation result of each of said plurality of sub-carrier components,

[0023] conducting determination based on said demodulation result and outputting a determination result, and outputting a distortion correction coefficient for each of said plurality of sub-carrier components, and a value which is generated by correcting each of said plurality of sub-carrier components based on said distortion correction coefficient; and

[0024] estimating a phase error based on said determination result of each of said plurality of sub-carrier components, said distortion correction coefficient for each of said plurality of sub-carrier components and said value which is generated by correcting each of said plurality of sub-carrier components based on said distortion correction coefficient.

[0025] In the receiving method, wherein said step of estimating a phase error comprises the steps of:

[0026] receiving the determination result of each of said plurality of sub-carrier components and the value which is generated by correcting each of said plurality of sub-carrier components based on said distortion correction coefficient, and for detecting a phase difference between said corresponding demodulation result and the value corrected based on said distortion correction coefficient, and outputting it as a phase difference of each sub-carrier;

[0027] receiving the distortion correction coefficient for each of said plurality of sub-carrier components, detecting electric power of the distortion correction coefficient for each of said plurality of sub-carrier components, and outputting it as distortion correction coefficient electric power of each sub-carrier;

[0028] receiving each distortion correction coefficient electric power of said each sub-carrier, and based on the distortion correction coefficient electric power of said each sub-carrier, for obtaining a weight for said each sub-carrier for weighting a phase difference of said each sub-carrier and conducting synthesis thereof, and outputting the weight; and

[0029] outputting a result of weighting and synthesizing a phase difference of said each sub-carrier based on the weight for said each sub-carrier as a phase error.

[0030] In the receiving method, wherein said step of obtaining a weight make a weight for weighting to be large if the distortion correction coefficient electric power of said each sub-carrier is small, and make a weight for weighting to be small if the distortion correction coefficient electric power of said each sub-carrier is large.

[0031] In the receiving method, wherein said step of obtaining a weight set a weight to be 1 if the distortion correction coefficient electric power of said each sub-carrier is smaller than a determined threshold value, and set a weight to be 0 if the distortion correction coefficient electric power of said each sub-carrier is larger than a determined threshold value.

[0032] In a receiving method of receiving a modulated wave for transmitting a data in which N sub-carriers are multiplexed, said receiving method comprises the steps of:

[0033] receiving a plurality of (k, 1≦k≦N) sub-carrier components which are multiplexed and de-multiplexed, and outputting a result of demodulating each of said sub-carrier components as a demodulation result of each of said plurality of sub-carrier components,

[0034] conducting determination based on said demodulation result and outputting a determination result, and outputting a value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components; and

[0035] estimating a phase error based on said demodulation result of each of said plurality of sub-carrier components, said value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components and said plurality of sub-carrier components which are multiplexed and de-multiplexed.

[0036] In the receiving method, wherein said step of estimating phase error comprises the steps of:

[0037] receiving the determination result of each of said plurality of sub-carrier components and the value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components, detecting said corresponding demodulation result and the value which is obtained by correcting distortion generated in each of said plurality of sub-carrier components, and outputting them as a phase difference of each sub-carrier;

[0038] receiving said plurality of sub-carrier components which are multiplexed and de-multiplexed, detecting electric power of said plurality of sub-carrier components which are multiplexed and de-multiplexed, and outputting it as electric power of each sub-carrier component;

[0039] receiving each electric power of said each sub-carrier component, and based on the electric power of said each sub-carrier component, for obtaining a weight for said each sub-carrier for weighting a phase difference of said each sub-carrier and conducting synthesis thereof, and outputting the weight; and

[0040] outputting a result of weighting and synthesizing a phase difference of said each sub-carrier based on the weight for said each sub-carrier as a phase error.

[0041] In the receiving method, wherein said step of obtaining a weight make a weight for weighting to be small if the electric power of said each sub-carrier component is small, and make a weight for weighting to be large if the electric power of said each sub-carrier component is large.

[0042] In the receiving method, wherein said step of obtaining a weight set a weight to be 0 if the electric power of said each sub-carrier component is smaller than a determined threshold value, and set a weight to be 1 if the electric power of said each sub-carrier component is larger than a determined threshold value.

[0043] In the present invention, weighting based on a coefficient for correcting distortion generated in each sub-carrier is conducted for a demodulation result of each sub-carrier and a phase error of determination signal points. For example, a distortion correction coefficient for a sub-carrier in which large attenuation distortion occurs in a communication line becomes to be a large value so as to correct the attenuation distortion. On the other hand, a correction coefficient for a sub-carrier component in which distortion does not occur in a communication line becomes to be a value close to 1.

[0044] In this manner, by conducting the weighting for a phase error of each sub-carrier, which is proportional to an inverse number of a distortion correction coefficient, influence of a noise is suppressed, and the present invention is equivalent to adaptively selecting a sub-carrier in which a noise component is less and to conducting phase synchronization.

[0045] This and other objects, features, and advantages of the present invention will become more apparent upon a reading of the following detailed description and drawings, in which:

[0046] FIG. 1 is a block diagram showing an embodiment of a receiver of the first present invention,

[0047] FIG. 2 is a block diagram showing an embodiment of the sub-carrier demodulating circuit 102 in FIG. 1,

[0048] FIG. 3 is a block diagram showing an embodiment of the distortion compensation coefficient setting circuit 208 in FIG. 1,

[0049] FIG. 4 is a block diagram showing an embodiment of the phase estimating circuit 103 in FIG. 1,

[0050] FIG. 5 is a view showing one example of input and output characteristic of a group of the weight setting circuits 305-1-305-k in FIG. 4,

[0051] FIG. 6 is a view showing another example of input and output characteristic of a group of the weight setting circuits 305-1-305-k in FIG. 4,

[0052] FIG. 7 is a view showing an example of a packet format that is input to the receiver of the present invention,

[0053] FIG. 8 is a block diagram showing an embodiment of a receiver of the second present invention,

[0054] FIG. 9 is a block diagram showing an embodiment of the sub-carrier demodulating circuit 602 in FIG. 8,

[0055] FIG. 10 is a block diagram showing an embodiment of the phase estimating circuit 603 in FIG. 8,

[0056] FIG. 11 is a view showing one example of input and output characteristic of a group of the weight setting circuits 705-1-705-k in FIG. 10,

[0057] FIG. 12 is a view showing another example of input and output characteristic of a group of the weight setting circuits 705-1-705-k in FIG. 10 and

[0058] FIG. 13 is a block diagram of a receiver having a conventional phase tracking function.

[0059] Embodiments of the present invention will be explained by referring to drawings.

[0060] FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to packet communication. In FIG. 1, 100-1-100-n are input terminals, 101 is a fast Fourier transform (FFT) circuit, 102 is a sub-carrier demodulating circuit circuit, 103 is a phase estimating circuit, and 104 and 105 are output terminals. Here, the FFT circuit 101 conducts n points Fourier transform.

[0061] Also, as an example of a transmission packet having M data symbols, an arrangement shown in FIG. 7 is used. As shown in FIG. 7, this transmission packet has a transmission start lamp signal 500 for indicating a transmission start, a training signal 501 for timing control, a training signal 502 for communication line distortion estimation, M data symbols 503-1-503-M, and a transmission end lamp signal 504 for indicating a transmission end.

[0062] The packet of FIG. 7, which is constructed of an OFDM modulated symbol in which N sub-carriers are multiplexed, is serial/parallel-transformed for every n (N≦n) samples after sampling, and is input to the FFT circuit 101 through the input terminals 100-1-100-n. In the FFT circuit 101, Fourier-transform is applied to an input signal, and k (1≦k≦N) sub-carrier components are output. The k sub-carrier components output from the FFT circuit 101 are output to the sub-carrier demodulating circuit 102.

[0063] The sub-carrier demodulating circuit 102 demodulates the k sub-carrier components and determines a demodulation result, and outputs a signal for any of determination signal points R(1)-R(k). Further, based on the determined determination signal points R(1)-R(k), serial/parallel transform is applied to a transmitted information bit, and it is output to the output terminal 104. Furthermore, the sub-carrier demodulating circuit 102 outputs distortion correction coefficients C(1)-C(k) that are used during demodulation of each sub-carrier, each of sub-carrier components S(1)-S(k) in which distortion is corrected, and the determination signal points R(1)-R(k) for each sub-carrier to the phase estimating circuit 103.

[0064] The phase estimating circuit 103 receives the distortion compensation coefficients C(1)-C(k) for each sub-carrier, the determination signal points R(1)-R(k), and each of the sub-carrier components S(1)-S(k) in which distortion is corrected, which are obtained from the sub-carrier demodulating circuit 102, and outputs a phase error signal to the output terminal 105.

[0065] The phase error signal output to the output terminal 105 is integrated by a loop filter and so forth, and is fed back to a local oscillator, and thereby, phase tracking is realized.

[0066] The sub-carrier demodulating circuit 102 can be constructed as FIG. 2, for example. In FIG. 2, 200-1-200-k are input terminals, 201-1-201-k are demodulating circuits, 202 is a parallel-serial transform circuit, 206-1-206-k are multipliers, 207-1-207-k are mapping circuits, 208 is a distortion compensation coefficient setting circuit, and 203, 204-1-204-k, 205-1-205-k and 209-1-209-k are output terminals. The k sub-carrier components output from the FFT circuit 101 are input to the input terminals 200-1-200-k.

[0067] Out of the packet of a format shown in FIG. 7, a part of the training signal 502 for communication line distortion estimation is input to the distortion compensation coefficient setting circuit 208, and the distortion compensation coefficients C(1)-C(k) for each sub-carrier are obtained. The distortion compensation coefficients C(1)-C(k) are output to a group of the multipliers 204-1-204-k. Further, by means of the group of the multipliers 206-1-206-k, the distortion compensation coefficients C(1)-C(k) are multiplied by each sub-carrier which forms each symbol of the data symbols 503-1-503-M received after the distortion compensation coefficients C(1)-C(k) are obtained, and distortion which occurs in a communication line is compensated.

[0068] An output from each of the multipliers 206-1-206-k is output to the output terminals 209-1-209-k as the corrected sub-carrier components S(1)-S(k). Further, outputs from the group of the multipliers 206-1-206-k are demodulated to any of the transmission signal points, respectively, by a group of the demodulating circuits 201-1-201-k.

[0069] The signal points R(1)-R(k) corresponding to each sub-carrier component, which are output from the demodulating circuits 201-1-201-k, are output to a group of the output terminals 205-1-205-k, and also, to a group of the mapping circuits 207-1-207-k. The group of the mapping circuits 207-1-207-k apply mapping to the respective input signal points along a bit line corresponding to the signal points, and output them to the parallel-serial transform circuit 202. In the parallel/serial transform circuit 202, parallel/serial transform is applied to the bit line from the mapping circuits 207-1-207-k, and it is output to the output terminal 203 as a demodulation result.

[0070] Also, the distortion correction coefficient setting circuit 208 can be constructed as FIG. 3, for example. In

[0071] FIG. 3, 220-1-220-k are input terminals, 221-1-221-k are division circuits, 222 is a training signal point memory, and 223-1-223-k are output terminals. The k sub-carrier components that form the training signal 502 for communication line distortion estimation are input to the input terminals 220-1-220-k. The division circuits 221-1-221-k divide the signal points of each sub-carrier that forms the training signal 502 for communication line distortion-estimation at a received signal point of each sub-carrier, which are stored in the corresponding training signal point memory 222, respectively. These division results become to be values for correcting communication line distortion for each sub-carrier component. These values are output to the output terminals 223-1-223-k as the distortion correction coefficients C(1)-C(k) for each sub-carrier component.

[0072] The phase estimating circuit 103 can be constructed as FIG. 4. In the figure, 300-1-300-k, 301-1-301-k and 307-1-307-k are input terminals, 302-1-302-k are phase comparison circuits, 303-1-303-k are electric power detecting circuits, 305-1-305-k are weight setting circuits, and 308 is an output terminal. Also, 307 is a weighting synthesis circuit, and it is constructed of multipliers 304-1-304-k and an addition circuit 306.

[0073] The carrier components S(I)-S(k) in which distortion is corrected are input to the input terminals 300-1-300-k, the signal points R(1)-R(k) corresponding to each of the sub-carrier components S(1)-S(k) are input to the input terminals 301-1-301-k, and the distortion correction coefficients C(1)-C(k) for each of the sub-carrier components S(1)-S(k) are input to the input terminals 307-1-307-k. The i-th (1≦i≦k)) phase comparison circuit 302-i receives the signal point R(i) obtained by demodulating the i-th sub-carrier component S(i), and the i-th carrier component S(i) in which distortion is corrected, and outputs a phase difference therebetween. Also, the i-th electric power detecting circuit 303-i obtains electric power of the distortion correction coefficient C(i) for the i-th sub-carrier, and outputs it to the weight setting circuit 305-i. A group of the weight setting circuits 305-1-305-k obtain weights based on the distortion correction coefficient C(i) for the input i-th sub-carrier component S(i), respectively, and output them.

[0074] With regard to input and output characteristic of the weight setting circuits, characteristic in FIG. 5 is used, for example. In other words, since reception electric power of a sub-carrier component in which an electric power value of a distortion correction coefficient is large is small, the reception electric power of the sub-carrier component is small, and a signal to noise ratio is also small. Accordingly, since there is a possibility that a noise largely affects a phase difference obtained from such a sub-carrier component, a weight is made to be small.

[0075] Also, with regard to the input and output characteristic of the weight setting circuits, as shown in FIG. 6, by setting a threshold value, and conducting non-linear operation in which a weight is 0 in case that the threshold value is exceeded, and the weight is 1 in case that the threshold value is not exceeded, it is possible to reduce influence of a noise.

[0076] A weight coefficient for each carrier component, which is obtained in this manner, is multiplied by a phase difference obtained from each carrier component in the multipliers 304-1-304-k, and weighting synthesis is conducted by adding a result of the multiplication in the addition circuit 306, and a result thereof is output to the output terminal 308 as a phase error.

[0077] Although the above embodiment is shown as for a case in which all k sub-carriers are modulated by a transmission data, the present invention can be easily applied to a case in which a sub-carrier for a pilot signal, which is modulated at a predetermined signal point, is included. In other words, assuming that a sub-carrier for a pilot signal is the j-th sub-carrier, a predetermined signal point can be input, instead of a signal point R(j) obtained by demodulating the j-th sub-carrier component that is input from the input terminal 301-j.

[0078] Furthermore, although this embodiment shows a case in which the k sub-carriers are used, it is also possible to obtain a phase error from sub-carriers, of which number is arbitrary and less than or equal to k.

[0079] Another embodiment of a receiver of the present invention will be explained using a block diagram of FIG. 8. In FIG. 8, 100-1-100-n are input terminals, 101 is a fast Fourier transform (FFT) circuit, 602 is a sub-carrier demodulating circuit circuit, 603 is a phase estimating circuit, and 104 and 105 are output terminals. Here, the input terminals 100-1-100-k, the FFT circuit 101, and the output terminals 104 and 105 are the same as those in FIG. 8. The k sub-carrier components output from the FFT circuit 101 are output to the sub-carrier demodulating circuit 602 and the phase estimating circuit 603. The sub-carrier demodulating circuit 602 demodulates the k sub-carrier components, and parallel/serial transform is applied to a transmitted information bit, and it is output to the output terminal 104.

[0080] Furthermore, the sub-carrier demodulating circuit 602 outputs determination signal points R(1)-R(k) for each sub-carrier and each of sub-carrier components S(1)-S(k) in which distortion is corrected to the phase estimating circuit 603. The phase estimating circuit 603 receives the determination signal points R(1)-R(k), and each of the sub-carrier components S(1)-S(k) in which distortion is corrected, which are obtained from the sub-carrier demodulating circuit 102, and receives the k sub-carrier components from the FFT circuit 101, and outputs a phase error signal to the output terminal 105. The phase error signal output to the output terminal 105 is integrated by a loop filter and so forth, and is fed back to a local oscillator, and thereby, phase tracking is realized.

[0081] The sub-carrier demodulating circuit 602 can be constructed as FIG. 9, for example. In FIG. 9, 650-1-650-k are input terminals, 651-1-651-k are demodulating circuits, 652 is a parallel-serial transform circuit, 656-1-656-k are multipliers, 657-1-657-k are mapping circuits, 208 is a distortion compensation coefficient setting circuit, and 653, and 655-1-655-k are output terminals. The k sub-carrier components output from the FFT circuit 101 are input to the input terminals 650-1-650-k.

[0082] Out of the packet of a format shown in FIG. 7, a part of the training signal 502 for communication line distortion estimation is input to the distortion compensation coefficient setting circuit 208, and the distortion compensation coefficients C(1)-C(k) for each sub-carrier are obtained. The same as that in FIG. 3 is used for the distortion compensation coefficient setting circuit 208. By means of the group of the multipliers 206-1-206-k, the distortion compensation coefficients C(1)-C(k) are multiplied by each sub-carrier which forms each symbol of the data symbols 503-1-503-M received after the distortion compensation coefficients C(1)-C(k) are obtained, and thereafter, the distortion compensation coefficients C(1)-C(k) are demodulated to any of the transmission signal points by a group of the demodulating circuits 651-1-651-k.

[0083] The signal points R(1)-R(k) corresponding to each sub-carrier component, which are output from the demodulating circuits 651-1-651-k, are output to a group of the output terminals 655-1-655-k, and also, to a group of the mapping circuits 657-1-657-k. The group of the mapping circuits 657-1-657-k apply mapping to the respective input signal points along a bit line corresponding to the signal points, and output them to the parallel-serial transform circuit 652. In the parallel/serial transform circuit 652, parallel/serial transform is applied to the bit line from the mapping circuits 657-1-657-k, and it is output to the output terminal 653 as a demodulation result.

[0084] The phase estimating circuit 603 in this embodiment can be constructed as FIG. 10. Points different from FIG. 4 are that an input to the electric power detecting circuits 303-1-303-k is not the distortion correction coefficients C(1)-C(k) for each sub-carrier, but the sub-carrier component obtained from the FFT circuit 101, and input and output characteristic of the weight setting circuits 705-1-705-k. Characteristic in FIG. 11 is desirable for the input and output characteristic of the weight setting circuits 705-1-705-k. In other words, since, when electric power of a sub-carrier component output from the FFT circuit 101 becomes to be smaller, influence due to a noise becomes to be larger, a weight of a phase difference obtained from the sub-carrier is made to be small, and since, when electric power of a sub-carrier component becomes to be larger, reliability becomes to be higher, the weight is made to be large.

[0085] Also, with regard to the input and output characteristic of the weight setting circuits, as shown in FIG. 12, by setting a threshold value, and conducting non-linear operation in which a weight is 1 in case that the threshold value is exceeded, and the weight is 0 in case that the threshold value is not exceeded, it is possible to reduce influence of a noise.

[0086] Although the above embodiment is shown as for a case in which all k sub-carriers are modulated by a transmission data, the present invention can be easily applied to a case in which a sub-carrier for a pilot signal, which is modulated at a predetermined signal point, is included. In other words, assuming that a sub-carrier for a pilot signal is the j-th sub-carrier, the present invention can be applied by inputting a predetermined signal point, instead of a signal point R(j) obtained by demodulating the j-th sub-carrier component that is input from the input terminal 301-j.

[0087] Furthermore, although this embodiment shows a case in which the k sub-carriers are used, it is also possible to obtain a phase error from sub-carriers, of which number is arbitrary and less than or equal to k.

[0088] According to the present invention, in the receiver for receiving a signal such as an OFDM signal, in which a plurality of sub-carriers are multiplexed and which is transmitted, it becomes to be possible to conduct phase tracking with high accuracy.