Sakoda, Kazuyuki (Tokyo, JP)

09/783809

11/15/2001

02/15/2001

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375/267

(IPC1-7): H04B007/02; H04L001/02; H04K001/10; H04L027/28

Cooper & Dunham LLP (1185 Avenue of the Americas, New York, NY, 10036, US)

What is claimed is:

1. A signal component demultiplexing apparatus for demultiplexing a certain group of signals from among a group of multi-carrier modulated signals (group of symbols), comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit including: a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein: m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

2. A receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, comprising: a receiving means for receiving a group of signals; a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means; an orthogonal transforming means for orthogonally transforming the group of signals demultiplexed at said signal component demultiplexing apparatus; and a decoding means for decoding said orthogonally transformed information.

3. A communication apparatus having a transmitting apparatus and a receiving apparatus in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, wherein said transmitting apparatus has: an encoding means for independently encoding information of a plurality of channels, a signal point arranging means for arranging signal points by modulating said encoded information based on a predetermined modulation method, a signal multiplexing means for multiplexing said plurality of signal point-arranged signals cyclically on a time axis, an inverse orthogonal transforming means for inversely orthogonally transforming said multiplexed signal, and a transmitting means for transmitting said orthogonally transformed information and said receiving apparatus has: a receiving means for receiving said transmitted group of signals, a signal component demultiplexing means for selecting and demultiplexing said received group of signals, an orthogonal transforming means for orthogonally transforming said selected and demultiplexed signal, and a decoding means for decoding said orthogonally transformed information, wherein the signal component demultiplexing means is configured by branching circuits connected in stages and hierarchically by a branching method, each branching circuit including: a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

4. A communication apparatus as set forth in claim 3, wherein said signal multiplexing means in said transmitting apparatus multiplexes said plurality of signal point-arranged signals while shifting the frequency for every channel at predetermined subcarriers.

5. A communication apparatus as set forth in claim 3, wherein the modulation method in said signal point arranging means in said transmitting apparatus uses orthogonal frequency division multiplexing (OFDM).

6. A communication apparatus as set forth in claim 3, wherein said inverse orthogonal transform processing means in said transmitting apparatus performs inverse Fourier transform processing, and said orthogonal transform processing means in said receiver performs Fourier transform processing.

7. A receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, comprising a receiving means for receiving a group of signals, a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a signal selecting means for selecting and outputting at least one group of symbols of predetermined subcarriers from among the symbol strings demultiplexed at said signal component demultiplexing apparatus; a frequency offset compensating means for compensating for frequency offset of at least one group of symbols selected and output by said signal selecting means; two orthogonal transforming means for orthogonally transforming output signals of said frequency offset compensating means; and a decoding means for decoding said orthogonally transformed signal.

8. A receiving apparatus as set forth in claim 7, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

9. A communication apparatus having a transmitting apparatus and a receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, wherein said transmitting apparatus has: an encoding means for independently encoding information of a plurality of channels, a signal point arranging means for arranging signal points by modulating said encoded information based on a predetermined modulation method, a signal multiplexing means for multiplexing said plurality of signal point-arranged signals cyclically on a time axis, an inverse orthogonal transforming means for inversely orthogonally transforming said multiplexed signal, and a transmitting means for transmitting said orthogonally transformed group of signals and said receiving apparatus has: a receiving means for receiving said transmitted group of signals, a signal component demultiplexing apparatus for demultiplexing said received group of signals configured by branching circuits connected in stages and hierarchically by a branching method, each branching circuit including: a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a signal selecting means for selecting and outputting at least one group of symbols of predetermined subcarriers from among the symbol strings demultiplexed at said signal component demultiplexing apparatus; a frequency offset compensating means for compensating for frequency offset of at least one group of symbols selected and output by said signal selecting means; two orthogonal transforming means for orthogonally transforming output signals of said frequency offset compensating means; and a decoding means for decoding said orthogonally transformed signal.

10. A communication apparatus as set forth in claim 9, wherein said signal multiplexing means in said transmitting apparatus multiplexes said plurality of signal point-arranged signals while shifting the frequency for every channel at predetermined subcarriers.

11. A communication apparatus as set forth in claim 9, wherein the modulation method in said signal point arranging means in said transmitting apparatus uses orthogonal frequency division multiplexing (OFDM).

12. A communication apparatus as set forth in claim 9, wherein said inverse orthogonal transform processing means in said transmitting apparatus performs inverse Fourier transform processing, and said orthogonal transform processing means in said receiver performs Fourier transform processing.

13. A communication apparatus as set forth in claim 9, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

14. A receiving apparatus in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, including: a receiving means for receiving a group of signals, a signal component demultiplexing apparatus for demultiplexing said received group of signals configured by branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a frequency offset compensating means for compensating for frequency offset of at least one group of symbols selected and output by said signal selecting means; two orthogonal transforming means for orthogonally transforming output signals of said frequency offset compensating means; and a decoding means for decoding said orthogonally transformed signals.

15. A receiving apparatus as set forth in claim 14, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

16. A communication apparatus having a transmitting apparatus and receiving apparatus in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, wherein: said transmitting apparatus has an encoding means for independently encoding information of a plurality of channels, a signal point arranging means for arranging signal points by modulating said encoded information based on a predetermined modulation method, a signal multiplexing means for multiplexing said plurality of signal point-arranged signals cyclically on a time axis, an inverse orthogonal transforming means for inversely orthogonally transforming said multiplexed signal, and a transmitting means for transmitting said orthogonally transformed group of signals and said receiving apparatus has: a receiving means for receiving said transmitted group of signals, a signal component demultiplexing apparatus for demultiplexing said received group of signals configured by branching circuits connected in stages and hierarchically by a branching method, each branching circuit including: a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a frequency offset compensating means for compensating for frequency offset of at least one group of symbols demultiplexed by said signal component demultiplexing apparatus; two orthogonal transforming means for orthogonally transforming output signals of said frequency offset compensating means; and a decoding means for decoding said orthogonally transformed signals.

17. A communication apparatus as set forth in claim 16, wherein said signal multiplexing means in said transmitting apparatus multiplexes said plurality of signal point-arranged signals while shifting the frequency for every channel at predetermined subcarriers.

18. A communication apparatus as set forth in claim 9, wherein the modulation method in said signal point arranging means in said transmitting apparatus uses orthogonal frequency division multiplexing (OFDM).

19. A communication apparatus as set forth in claim 16, wherein said inverse orthogonal transform processing means in said transmitting apparatus performs inverse Fourier transform processing, and said orthogonal transform processing means in said receiver performs Fourier transform processing.

20. A communication apparatus as set forth in claim 16, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

21. A filter apparatus for extracting a specific signal from a group of multi-carrier modulated signals, provided with a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a signal selecting means for selecting and outputting a group of symbols of a specific subcarrier from among the symbol strings demultiplexed at said signal component demultiplexing apparatus; and a frequency offset compensating means for compensating for frequency offset of the group of symbols selected and output by said signal selecting means.

22. A filter apparatus as set forth in claim 21, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

23. A receiving apparatus in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, including a receiving means for receiving a group of multi-carrier modulated signals; a filter apparatus for extracting a specific signal from the group of multi-carrier modulated signals received at said receiving means; an orthogonal transforming means for orthogonally transforming the signal extracted at the filter apparatus, and a decoding means for decoding said orthogonally transformed signal, wherein said filter apparatus comprises a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a signal selecting means for selecting and outputting a group of symbols of a specific subcarrier from among the symbol strings demultiplexed at said signal component demultiplexing apparatus; and a frequency offset compensating means for compensating for frequency offset of the group of symbols selected and output by said signal selecting means.

24. A receiving apparatus as set forth in claim 23, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

25. A filter apparatus for extracting a specific signal from a group of multi-carrier modulated signals, comprising: a subcarrier selecting means for selecting a subcarrier, at least one signal selecting means for selecting and outputting a specific group of signals from among the input group of signals in accordance with said selected subcarrier, and a frequency offset compensating means for compensating the frequency offset of a signal selected by said signal selecting means.

26. A filter apparatus as set forth in claim 25, wherein said signal selecting means has: a phase offset adjusting means for shifting the phase of an input group of signals in accordance with the selected subcarrier; a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols; and an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string between symbol strings alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

27. A filter apparatus as set forth in claim 25, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

28. A receiving apparatus in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, comprising: a receiving means for receiving a group of multi-carrier modulated signals, a filter apparatus for extracting a specific signal from the group of multi-carrier modulated signals received at said receiving means, an orthogonal transforming means for orthogonally transforming the signal extracted at the filter apparatus, and a decoding means for decoding said orthogonally transformed signal, wherein said filter apparatus comprises: a subcarrier selecting means for selecting a subcarrier, at least one signal selecting means for selecting and outputting a specific group of signals from among the input group of signals in accordance with said selected subcarrier, and a frequency offset compensating means for compensating the frequency offset of a signal selected by said signal selecting means.

29. A receiving apparatus as set forth in claim 28, wherein said signal selecting means has: a phase offset adjusting means for shifting the phase of an input group of signals in accordance with the selected subcarrier; a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols; and an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string between symbol strings alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

30. A receiving apparatus as set forth in claim 28, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

31. A filter apparatus for extracting a specific signal from a group of multi-carrier modulated signals, comprising: a pass subcarrier selection signal outputting means for outputting a complex sine wave signal in accordance with a channel to be selected, a multiplying means for multiplying a complex sine wave signal output from said pass subcarrier selection signal outputting means and the input group of signals, at least one signal component demultiplexing means for selecting a specific group of signals from the results of multiplication in said multiplying means, and a symbol rearranging means for rearranging the output of said signal component demultiplexing apparatus on the frequency axis.

32. A filter apparatus as set forth in claim 31, wherein said signal component demultiplexing means comprises circuits connected in stages and hierarchically by a branching method, each circuit comprising: a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols and an adding means for adding an output signal of said symbol delaying means and an input group of signals to calculate one symbol string alternately positioned on a frequency axis, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

33. A receiving apparatus in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, comprising: a receiving means for receiving a group of multi-carrier modulated signals, a filter apparatus for extracting a specific signal from the group of multi-carrier modulated signals received at said receiving means, an orthogonal transforming means for orthogonally transforming the signal extracted at the filter apparatus, and a decoding means for decoding said orthogonally transformed signal, wherein said filter apparatus is provided with: a pass subcarrier selection signal outputting means for outputting a complex sine wave signal in accordance with a channel to be selected, a multiplying means for multiplying a complex sine wave signal output from said pass subcarrier selection signal outputting means and the input group of signals, at least one signal component demultiplexing means for selecting a specific group of signals from the results of multiplication in said multiplying means, and a symbol rearranging means for rearranging the output of said signal component demultiplexing apparatus on the frequency axis.

34. A receiving apparatus as set forth in claim 33, wherein said signal component demultiplexing means comprises circuits connected in stages and hierarchically by a branching method, each circuit comprising: a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols and an adding means for adding an output signal of said symbol delaying means and an input group of signals to calculate one symbol string alternately positioned on a frequency axis, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

35. A receiving apparatus as set forth in claim 33, wherein said frequency offset compensating means has: a frequency offset compensation signal generating means for outputting a complex sine wave signal for said frequency offset compensation, a multiplying means for multiplying said group of signals and the complex sine wave signal output from said frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

36. A receiving apparatus in multiplex communication based on multi-carrier modulation where a plurality of channels of subcarriers are cyclically arranged, comprising: a receiving means for receiving a group of multi-carrier modulated signals, a switching means for switching the input group of signals, a buffer means for holding the group of multi-carrier modulated signals received at said receiving means, a filter apparatus connected after said switching means and for selecting and outputting a specific group of signals from the input group of signals, an orthogonal transforming means for orthogonally transforming the signals extracted at said filter apparatus, and a decoding means for decoding said orthogonally transformed signals, wherein said switching means outputs one symbol's worth of the group of signals to said filter apparatus, and said buffer means holds the input one symbol's worth of the group of signals during that time and transmits the group of signals held at said buffer means via said switching means to said filter apparatus after the end of transmitting the signals to said filter apparatus and said filter apparatus selects and outputs only a designated subcarrier from the group of signals input via said switching means.

37. A receiving apparatus as set forth in claim 36, wherein said filter apparatus comprises: a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a signal selecting means for selecting and outputting a group of symbols of a specific subcarrier from among the symbol strings demultiplexed at said signal component demultiplexing apparatus; and a frequency offset compensating means for compensating for frequency offset of the group of symbols selected and output by said signal selecting means.

38. A receiving apparatus as set forth in claim 36, wherein said filter apparatus comprises: a subcarrier selecting means for selecting a subcarrier, at least one signal selecting means for selecting and outputting a specific group of signals from among the input group of signals in accordance with said selected subcarrier, and a frequency offset compensating means for compensating the frequency offset of a signal selected by said signal selecting means.

39. A receiving apparatus as set forth in claim 36, wherein said filter apparatus comprises: a pass subcarrier selection signal outputting means for outputting a complex sine wave signal in accordance with a channel to be selected, a multiplying means for multiplying a complex sine wave signal output from said pass subcarrier selection signal outputting means and the input group of signals, at least one signal component demultiplexing means for selecting a specific group of signals from the results of multiplication in said multiplying means, and a symbol rearranging means for rearranging the output of said signal component demultiplexing apparatus on the frequency axis.

40. A receiving apparatus in multiplex communication based on multi-carrier modulation where a plurality of channels of the subcarriers are cyclically arranged, comprising: a receiving means for receiving a group of multi-carrier modulated signals, a first filter apparatus for selecting and outputting a group of signals of even number carriers from a group of multi-carrier modulated signals received at said receiving means, a second filter apparatus for selecting and outputting a group of signals of odd number carriers from a group of multi-carrier modulated signals received at said receiving means, a buffer means for holding the output group of signals of said second filter apparatus, a switching means for switching the output group of signals of said first filter apparatus, an orthogonal transforming means connected after said switching means and orthogonally transforming the switched output signals, and a decoding means for decoding said orthogonally transformed signals, wherein said switching means transmits the output signals of said first filter apparatus to said orthogonal transforming means and transmits the group of signals held at said buffer means via said switching means to said orthogonal transforming means after the end of transmitting the signals to said orthogonal transforming means.

41. A receiving apparatus as set forth in claim 41, wherein each of said first and second filter apparatuses comprises: said filter apparatus includes a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2^m) radians with a reference 0 Hz, an adding means for adding an output signal of said symbol delaying means and an output signal of said phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of said phase offset adjusting means from the output signal of said symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to said signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz; a signal selecting means for selecting and outputting a group of symbols of a specific subcarrier from among the symbol strings demultiplexed at said signal component demultiplexing apparatus; and a frequency offset compensating means for compensating for frequency offset of the group of symbols selected and output by said signal selecting means.

42. A receiving apparatus as set forth in claim 41, wherein each of said first and second filter apparatuses comprises: a subcarrier selecting means for selecting a subcarrier, at least one signal selecting means for selecting and outputting a specific group of signals from among the input group of signals in accordance with said selected subcarrier, and a frequency offset compensating means for compensating the frequency offset of a signal selected by said signal selecting means.

43. A receiving apparatus as set forth in claim 41, wherein each of said first and second filter apparatuses comprises: a pass subcarrier selection signal outputting means for outputting a complex sine wave signal in accordance with a channel to be selected, a multiplying means for multiplying a complex sine wave signal output from said pass subcarrier selection signal outputting means and the input group of signals, at least one signal component demultiplexing means for selecting a specific group of signals from the results of multiplication in said multiplying means, and a symbol rearranging means for rearranging the output of said signal component demultiplexing apparatus on the frequency axis.

44. A communication method comprising an encoding and transmitting step including the steps of independently encoding information of a plurality of channels, arranging signal points by modulating said encoded information based on a predetermined modulation method, multiplexing said plurality of signal point-arranged signals cyclically on a time axis, inversely orthogonally transforming said multiplexed signal, and transmitting said orthogonally transformed information and a receiving and decoding step including the steps of receiving said transmitted signal, selecting and outputting only the signal of an intended channel from among said received multiplexed signal after the orthogonal transformation, orthogonally transforming said selected and output signal, and decoding said orthogonally transformed information, wherein the signal selection processing in said receiving step comprises: giving a delay of N/2^(m+1) symbols, shifting the phase by exactly π(k/2^m) radians, and performing branched and in stages the procedure of adding said symbol delayed signal and said phase shifted signal to calculate one symbol string alternately located on the frequency axis in said input multiplexed signal or subtracting said phase shifted signal from said symbol delayed signal to calculate the other symbol string alternately located on the frequency axis in said input multiplexed signal, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a communication apparatus (communication system), transmitter and receiver, and communication method, more particularly relates to a digital communication apparatus (system) for multi-carrier modulation, a wireless transmitter (wireless transmitting apparatus) and a wireless receiver (wireless receiving apparatus) used in a digital communication apparatus (system), and a communication method of the same.

[0003] More specifically, the present invention relates to a signal component demultiplexing apparatus for demultiplexing a multi-carrier signal multiplexed by orthogonal frequency division multiplexing (OFDM) to a symbol series, a filter apparatus for extracting specific symbols from a multi-carrier signal, and a signal receiving apparatus having these signal component demultiplexing apparatus, filter apparatus, etc.

[0004] 2. Description of the Related Art

[0005] As an example of a signal modulated by OFDM, one of a digital audio broadcasting (DAB) system will be described.

[0006] The DAB system is known as a high quality digital audio terrestrial broadcasting method enabling mobile reception developed by the EUREKA 147 project. Progress is being made in commercialization of digital satellite audio broadcasting using the DAB system for the satellite broadcasting.

[0007] As the modulation method used in such a digital communication system (apparatus), OFDM has been proposed due to its tolerance to multi-path fading, ghosts, etc.

[0008] OFDM is a multi-carrier modulation method usually using tens to hundreds of orthogonal carriers. Each carrier is modulated by a modulation method such as quadrature amplitude modulation (QAM) or phase shift keying (PSK).

[0009] In the DAB system etc., digital audio signals of multiple channels are transmitted by multi-carrier communication.

[0010] FIGS. 21A and 21B are views of an example of the configuration of a digital wireless communication system used in a DAB system or the like using OFDM as the multi-carrier modulation method. FIGS. 21A and 21B illustrate parts of the DAB system in a simple form.

[0011] In the following explanation, the DAB system will be illustrated and the explanation made focusing on multiplexing.

[0012] A wireless transmitting apparatus 10 of an OFDM type wireless communication system illustrated in FIG. 21A has an encoder circuit 11 , a symbol mapping circuit 12 , a multiplexer (signal multiplexing circuit) 13 , a frequency interleave circuit 14 , an inverse fast Fourier transform (IFFT) circuit 15 , a wireless transmitter circuit 16 , and an antenna 17 .

[0013] An information bit stream is encoded, interleaved, and otherwise processed in the encoder circuit 11 , then its bits are mapped to transmission symbols in the symbol mapping circuit 12 . This work is separately carried out for every channel. In the example shown in FIG. 21 A, for example, 64 ksps (symbols/sec) of symbols are created per channel.

[0014] These symbol streams are simply connected in series in the multiplexer 13 to form a multiplexed symbol stream. For example, if 18 channels of 64 ksps per channel are multiplexed, the transmission rate of the multiplexed symbol stream becomes 1152 ksps (=18×64 ksps).

[0015] The symbols of the multiplexed symbol stream are rearranged by frequency interleaving in the frequency interleave circuit 14 . The symbols of each channel are dispersed by this work.

[0016] Next, the dispersed symbols of the symbol stream are arranged on the frequency axis, then the symbol expressions on the frequency axis are transformed to symbols on the time axis by the IFFT processing in the inverse fast Fourier transform (IFFT) circuit 15 , which are then sent from the transmitter circuit 16 via the antenna 17 into the air.

[0017] An example of the symbol string comprised of the six carriers formed into a multi-carrier signal output from the transmitting apparatus 10 is illustrated in FIG. 22 .

[0018] Up until now, specific symbols among a plurality of symbols (symbol series) formed into the above multi-carrier signal have not been solely extracted.

[0019] Therefore, we suppose the wireless signal receiver extracts the intended symbols or carrier components from the symbol series illustrated in FIG. 22 using an existing technique.

[0020] FIG. 23 is a view of a first method for demultiplexing a multi-carrier signal.

[0021] In this method, a plurality of band pass filters having frequency band characteristics of the corresponding carriers are provided. The corresponding symbols are extracted by these band pass filters. As such filters, use can be made of for example comb type filters.

[0022] However, such a method is unsuitable for demultiplexing symbols of a modulation method such as OFDM where the carriers are crammed together. Namely, with a modulation method using OFDM, a large number of carriers are crammed in a certain frequency band, therefore adjoining signal components cannot be sufficiently isolated. Accordingly, each band pass filter must have a sharp frequency characteristic in order to discriminate between carrier signals of adjoining frequencies.

[0023] For example, it is difficult to prepare various types of high precision filters such as comb type filters which have such sharp frequency characteristics. Further, this becomes considerably expensive in terms of price. Therefore, it is difficult to realize this.

[0024] FIG. 24 is a view of a second method of demultiplexing a multi-carrier signal.

[0025] In FIG. 24, a Fast Fourier transform (FFT) is applied to a signal received at a receiver circuit 22 in a Fast Fourier transform (FFT) circuit 23 to create a received symbol series arranged on the frequency axis. The symbol series is demultiplexed to separate symbols in a demultiplexer (signal demultiplexing apparatus) 29 . Due to this, it is possible to select only specific symbols.

[0026] In this method, however, even when extracting specific symbols, the fast Fourier transform is applied to all symbols. Therefore, a complex FFT circuit 23 must be provided, so the hardware configuration becomes complex.

[0027] FIG. 25 is a schematic view of the configuration when extracting only carrier signal components at constant intervals. In FIG. 25, a plurality of band pass filters having a plurality of different band pass characteristics are provided. Signals limited in bands by the filters are added to each other at adder circuits 28 A and 28 B to obtain the intended signal. In this case as well, as the band pass filters, for example, comb type filters can be used.

[0028] However, in the same way as with the method of FIG. 23 , since it is a multi-carrier method, this method also suffers from the disadvantages that carriers are crammed together, so the signal components cannot be sufficiently isolated. Also, it becomes difficult to prepare high precision filters having sharp frequency characteristics from the cost perspective etc.

[0029] FIG. 21B is a schematic view of the configuration of a wireless signal receiver in the DAB system illustrated in FIG. 21A .

[0030] A wireless receiving apparatus 20 of an ODFM wireless communication system 1 of FIG. 21B has an antenna 21 , a receiver circuit 22 , a Fast Fourier transform (FFT) circuit 23 , a symbol selection circuit 24 , a bit extraction circuit 25 , and a decoding circuit 26 .

[0031] By transforming the frequency of the signal of the intended frequency band received at the antenna 21 in the receiver circuit 22 and extracting only the baseband signal component, a baseband signal is obtained. The thus obtained baseband signal is expressed on the time axis of the signal with the information arranged on the frequency axis. Therefore, FFT processing is carried out in the FFT circuit 23 to extract subcarriers arranged on the frequency axis.

[0032] At this time, the symbols output by the FFT processing consist of the group of subcarriers of the signal bands received as a whole (for example, in the present example, containing 1152 ksps worth of information).

[0033] The symbol selection circuit 24 extracts the symbols from the group of subcarriers from the positions of the symbols of the intended channel arranged by the frequency interleaving at the transmission side illustrated in FIG. 21A . By this, the 64 kbps of information of the intended channel is extracted.

[0034] The received bit stream is extracted from among the symbol stream of the intended channel obtained in this way in the bit extraction circuit 25 to obtain the encoded bit stream, then this is decoded at the decoding circuit 26 to obtain the information bit stream of the intended channel.

[0035] Summarizing the disadvantages to be solved by the invention, in this way, in OFDM, multiplexing is carried out by allocating symbols of different channels to different subcarriers, but this means that the wireless receiving apparatus 20 receives a multiplexed signal of all channels transmitted and, further, that the FFT circuit 23 extracts the symbols of all of the channels, then the symbol selection circuit 24 selects the channel. Therefore, the FFT circuit 23 performs FFT processing entailing computations far exceeding the amount required for the originally required one channel's worth of information.

[0036] Namely, this means that the FFT circuit 23 performs the FFT signal processing for even channels which the wireless receiving apparatus 20 does not desire, so there is a disadvantage in that the FFT circuit 23 becomes unnecessarily large in scale.

[0037] As a method of solving this disadvantage, the present inventors have proposed the invention disclosed in for example Japanese laid open patent No. 2000-332722 published on Nov. 30, 2000. In the invention disclosed in Japanese laid open patent No. 2000-332722, circuits for demultiplexing a symbol string for every alternate subcarrier from the symbol series are provided in multiple stages hierarchically by a branching method.

SUMMARY OF THE INVENTION

[0038] An object of the present invention is to overcome the disadvantage by a method different from that of the invention disclosed in Japanese laid open patent No. 2000-332722, and to further extract only one symbol with a high efficiency.

[0039] Another object of the present invention is to provide a signal component demultiplexing apparatus capable of demultiplexing a symbol series in a branching manner with a high efficiency.

[0040] Another object of the present invention is to provide a filter apparatus capable of extracting specific symbols from a symbol series with a high efficiency.

[0041] Still another object of the present invention is to provide a receiving apparatus having the signal component demultiplexing apparatus and/or filter circuit.

[0042] Still another object of the present invention is to provide a communication system having a receiving apparatus and a transmitting apparatus.

[0043] Still another object of the present invention is to provide a communication method for the receiving processing and the transmitting processing.

[0044] According to a first aspect of the present invention, there is provided a signal component demultiplexing apparatus for demultiplexing a certain group of signals from among a group of multi-carrier modulated signals (group of symbols), comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit including a symbol delaying means for delaying an input group of signals by N/2 ^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2 ^m ) radians with a reference 0 Hz, an adding means for adding an output signal of the symbol delaying means and an output signal of the phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of the phase offset adjusting means from the output signal of the symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to the signal selecting and outputting means, wherein m is a parameter indicating the position of a stage of the branching circuit, N is the number of symbols existing within one modulation time, and k is a parameter indicating that a group of signals having a frequency offset of a subcarrier is input with a reference 0 Hz.

[0045] According to a second aspect of the present invention, there is provided a receiving apparatus, used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, comprising the above signal component demultiplexing apparatus.

[0046] The receiving apparatus has a receiving means for receiving a group of signals; a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2 ^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2 ^m ) radians with a reference 0 Hz, an adding means for adding an output signal of the symbol delaying means and an output signal of the phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of the phase offset adjusting means from the output signal of the symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to the signal selecting and outputting means; an orthogonal transforming means for orthogonally transforming the group of signals demultiplexed at the signal component demultiplexing apparatus; and a decoding means for decoding the orthogonally transformed information.

[0047] According to a third aspect of the present invention, there is provided a communication apparatus having a transmitting apparatus and the above receiving apparatus in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged.

[0048] The transmitting apparatus of the communication apparatus has an encoding means for independently encoding information of a plurality of channels, a signal point arranging means for arranging signal points by modulating the encoded information based on a predetermined modulation method, a signal multiplexing means for multiplexing the plurality of signal point-arranged signals cyclically on a time axis, an inverse orthogonal transforming means for inversely orthogonally transforming the multiplexed signal, and a transmitting means for transmitting the orthogonally transformed information.

[0049] The receiving apparatus of the communication apparatus has the same components as the above receiving apparatus, that is, a receiving means for receiving the transmitted group of signals, a signal component demultiplexing means for selecting and demultiplexing the received group of signals, an orthogonal transforming means for orthogonally transforming the selected and demultiplexed signal, and a decoding means for decoding the orthogonally transformed information.

[0050] The signal component demultiplexing means has the above configuration.

[0051] Preferably, the signal multiplexing means in the transmitting apparatus multiplexes the plurality of signal point-arranged signals while shifting the frequency for every channel at predetermined subcarriers.

[0052] More preferably, the modulation method in the signal point arranging means in the transmitting apparatus uses orthogonal frequency division multiplexing (OFDM).

[0053] Still more preferably, the inverse orthogonal transform processing means in the transmitting apparatus performs inverse Fourier transform processing, and the orthogonal transform processing means in the receiver performs Fourier transform processing.

[0054] According to a fourth aspect of the present invention, there is provided a communication apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, comprising a receiving means for receiving a group of signals; a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit provided with a symbol delaying means for delaying an input group of signals by N/2 ^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2 ^m ) radians with a reference 0 Hz, an adding means for adding an output signal of the symbol delaying means and an output signal of the phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of the phase offset adjusting means from the output signal of the symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to the signal selecting and outputting means; a signal selecting means for selecting and outputting at least one group of symbols of predetermined subcarriers from among the symbol strings demultiplexed at the signal component demultiplexing apparatus; a frequency offset compensating means for compensating for frequency offset of at least one group of symbols selected and output by the signal selecting means; two orthogonal transforming means for orthogonally transforming output signals of the frequency offset compensating means; and a decoding means for decoding the orthogonally transformed signal.

[0055] Preferably, the frequency offset compensating means has a frequency offset compensation signal generating means for outputting a complex sine wave signal for the frequency offset compensation, a multiplying means for multiplying the group of signals and the complex sine wave signal output from the frequency offset compensation signal generating means, and a rearranging means for rearranging symbols as the result of multiplication in the multiplying means along a frequency axis.

[0056] According to a fifth aspect of the present invention, there is provided a communication apparatus having a transmitting apparatus and a receiving apparatus of the fourth aspect of the invention used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged.

[0057] According to a sixth aspect of the present invention, there is provided a receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, provided with a receiving means for receiving a group of signals; a signal component demultiplexing apparatus for demultiplexing the received group of signals configured by branching circuits connected in stages and hierarchically by a branching method, each branching circuit including a symbol delaying means for delaying an input group of signals by N/2 ^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2 ^m ) radians, an adding means for adding an output signal of the symbol delaying means and an output signal of the phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of the phase offset adjusting means from the output signal of the symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to the signal selecting and outputting means; a frequency offset compensating means for compensating for frequency offset of at least one group of symbols selected and output by the signal selecting means; two orthogonal transforming means for orthogonally transforming output signals of the frequency offset compensating means; and a decoding means for decoding the orthogonally transformed signals.

[0058] According to a seventh aspect of the present invention, there is provided a communication apparatus and the above receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged.

[0059] According to an eighth aspect of the present invention, there is provided a filter apparatus for extracting a specific signal from a group of multi-carrier modulated signals, including a signal component demultiplexing apparatus comprising branching circuits connected in stages and hierarchically by a branching method, each branching circuit including a symbol delaying means for delaying an input group of signals by N/2 ^(m+1) symbols, a phase offset adjusting means for shifting the phase of the input group of signals by −π(k/2 ^m ) radians with a reference 0 Hz, an adding means for adding an output signal of the symbol delaying means and an output signal of the phase offset adjusting means to calculate one symbol string alternately positioned on a frequency axis in a multiplexed signal input to a signal selecting and outputting means, and a subtracting means for subtracting the output signal of the phase offset adjusting means from the output signal of the symbol delaying means to calculate the other symbol string alternately positioned on the frequency axis in the multiplexed signal input to the signal selecting and outputting means; a signal selecting means for selecting and outputting a group of symbols of a specific subcarrier from among the symbol strings demultiplexed at the signal component demultiplexing apparatus; and a frequency offset compensating means for compensating for frequency offset of the group of symbols selected and output by the signal selecting means.

[0060] According to a ninth aspect of the present invention, there is provided a receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, including a receiving means for receiving a group of multi-carrier modulated signals; the above filter apparatus for extracting a specific signal from the group of multi-carrier modulated signals received at the receiving means; an orthogonal transforming means for orthogonally transforming the signal extracted at the filter apparatus; and a decoding means for decoding the orthogonally transformed signal.

[0061] According to a 10th aspect of the present invention, there is provided a filter apparatus for extracting a specific signal from a group of multi-carrier modulated signals, provided with a subcarrier selecting means for selecting a subcarrier, at least one signal selecting means for selecting and outputting a specific group of signals from among the input group of signals in accordance with the selected subcarrier, and a frequency offset compensating means for compensating the frequency offset of a signal selected by the signal selecting means.

[0062] According to an 11th aspect of the present invention, there is provided a receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, provided with a receiving means for receiving a group of multi-carrier modulated signals, the above filter apparatus for extracting a specific signal from the group of multi-carrier modulated signals received at the receiving means, an orthogonal transforming means for orthogonally transforming the signal extracted at the filter apparatus, and a decoding means for decoding the orthogonally transformed signal.

[0063] According to a 12th aspect of the present invention, there is provided a filter apparatus for extracting a specific signal from a group of multi-carrier modulated signals, including a pass subcarrier selection signal outputting means for outputting a complex sine wave signal in accordance with a channel to be selected, a multiplying means for multiplying a complex sine wave signal output from the pass subcarrier selection signal outputting means and the input group of signals, at least one signal component demultiplexing means for selecting a specific group of signals from the results of multiplication in the multiplying means, and a symbol rearranging means for rearranging the output of the signal component demultiplexing apparatus on the frequency axis.

[0064] According to a 13th aspect of the present invention, there is provided a receiving apparatus used in multiplex communication based on multi-carrier modulation where subcarriers of a plurality of channels are cyclically arranged, including a receiving means for receiving a group of multi-carrier modulated signals, the above filter apparatus for extracting a specific signal from the group of multi-carrier modulated signals received at the receiving means, an orthogonal transforming means for orthogonally transforming the signal extracted at the filter apparatus, and a decoding means for decoding the orthogonally transformed signal.

[0065] According to a 14th aspect of the present invention, there is provided a receiving apparatus used in multiplex communication based on multi-carrier modulation where a plurality-of channels of subcarriers are cyclically arranged, provided with a receiving means for receiving a group of multi-carrier modulated signals; a switching means for switching the input group of signals; a buffer means for holding the group of multi-carrier modulated signals received at the receiving means; a filter apparatus connected after the switching means and for selecting and outputting a specific group of signals from the input group of signals; an orthogonal transforming means for orthogonally transforming the signals extracted at the filter apparatus; and a decoding means for decoding the orthogonally transformed signals, wherein the switching means outputs one symbol's worth of the group of signals to the filter apparatus, and the buffer means holds the input one symbol's worth of the group of signals during that time and transmits the group of signals held at the buffer means via the switching means to the filter apparatus after the end of transmitting the signals to the filter apparatus and the filter apparatus selects and outputs only a designated subcarrier from the group of signals input via the switching means.

[0066] As the filter apparatus, use can be made of the above various filter apparatuses.

[0067] According to a 15th aspect of the present invention, there is provided a receiving apparatus used in multiplex communication based on multi-carrier modulation where a plurality of channels of the subcarriers are cyclically arranged, provided with a receiving means for receiving a group of multi-carrier modulated signals; a first filter apparatus for selecting and outputting a group of signals of even number carriers from a group of multi-carrier modulated signals received at the receiving means; a second filter apparatus for selecting and outputting a group of signals of odd number carriers from a group of multi-carrier modulated signals received at the receiving means; a buffer means for holding the output group of signals of the second filter apparatus; a switching means for switching the output group of signals of the first filter apparatus; an orthogonal transforming means connected after the switching means and orthogonally transforming the switched output signals; and a decoding means for decoding the orthogonally transformed signals, wherein the switching means transmits the output signals of the first filter apparatus to the orthogonal transforming means and transmits the group of signals held at the buffer means via the switching means to the orthogonal transforming means after the end of transmitting the signals to the orthogonal transforming means.

[0068] As the filter apparatus, use can be made of the above various filter apparatuses.

[0069] According to a 16th aspect of the present invention, there is provided a communication method comprising an encoding and transmitting step of independently encoding information of a plurality of channels, arranging signal points by modulating the encoded information based on a predetermined modulation method, multiplexing the plurality of signal point-arranged signals cyclically on a time axis, inversely orthogonally transforming the multiplexed signal, and transmitting the orthogonally transformed information and a receiving and decoding step of receiving the transmitted signal, selecting and outputting only the signal of an intended channel from among the received multiplexed signal after the orthogonal transformation, orthogonally transforming the selected and output signal, and decoding the orthogonally transformed information, wherein the signal selection processing in the receiving step comprises giving a delay of N/2 ^(m+1) symbols, shifting the phase by exactly π(k/2 ^m ) radians, and performing branched and in stages the procedure of adding the symbol delayed signal and the phase shifted signal to calculate one symbol string alternately located on the frequency axis in the input multiplexed signal or subtracting the phase shifted signal from the symbol delayed signal to calculate the other symbol string alternately located on the frequency axis in the input multiplexed signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The above objects and features of the present invention will be more apparent from the following description of the preferred embodiments given with reference to the accompanying drawings, in which:

[0071] FIGS. 1A and 1B are views of the configuration of a communication system, a transmitting apparatus, and a receiving apparatus of the present invention and a digital wireless communication system used for example for a DAB system using OFDM as a multi-carrier modulation method according to an embodiment of a communication method, in which

[0072] FIG. 1A is a view of the configuration of the transmitting apparatus of an OFDM wireless communication system and

[0073] FIG. 1B is a view of the configuration of the receiving apparatus of an OFDM wireless communication system;

[0074] FIGS. 2A to 2 C are graphs showing processing of the transmitting apparatus illustrated in FIG. 1 A, in which,

[0075] FIG. 2A shows symbol streams independent for each channel,

[0076] FIG. 2B is a schematic view of the configuration of a multiplexer illustrated in FIG. 1 A, and

[0077] FIG. 2C is a graph showing a multi-carrier modulated signal;

[0078] FIG. 3 is a graph showing an arrangement of subcarriers of a plurality of channels modulated by the transmitting apparatus of FIG. 1A ;

[0079] FIG. 4 is a view of the configuration of a signal component demultiplexing apparatus illustrated in FIG. 1B ;

[0080] FIG. 5 is a view of the configuration of a branching circuit configuring part of the signal component demultiplexing apparatus illustrated in FIG. 4 ;

[0081] FIG. 6 is a view of an aspect of a symbol delay circuit illustrated in FIG. 5 ;

[0082] FIG. 7 is a view of an embodiment of a phase offset adjustment circuit illustrated in FIG. 5 ;

[0083] FIG. 8 is a view of the configuration of a receiving apparatus according to a second embodiment of the present invention;

[0084] FIG. 9 is a view of the configuration of a frequency offset compensation and/or elimination circuit illustrated in FIG. 8 ;

[0085] FIG. 10 is a view of the configuration of a receiving apparatus according to a third embodiment of the present invention.

[0086] FIG. 11 is a schematic view of the configuration of a receiving apparatus according to a fourth embodiment of the present invention;

[0087] FIG. 12 is a view of the configuration of a first embodiment of a filter apparatus shown in FIG. 11 ;

[0088] FIG. 13 is a view of the configuration of a second embodiment of the filter apparatus of FIG. 11 ;

[0089] FIG. 14 is a view of the configuration of a filter and decimation circuit illustrated in FIG. 13 ;

[0090] FIG. 15 is a view of the configuration of a third embodiment of the filter apparatus illustrated in FIG. 11 ;

[0091] FIG. 16 is a view of the configuration of a fourth embodiment of the filter apparatus illustrated in FIG. 11 ;

[0092] FIG. 17 is a view of the configuration of the filter and decimation circuit illustrated in FIG. 16 ;

[0093] FIG. 18 is a view of the configuration of a fifth embodiment of the filter apparatus illustrated in FIG. 11 ;

[0094] FIG. 19 is a view of the configuration of the receiving apparatus of a fifth embodiment of the present invention;

[0095] FIG. 20 is a view of the configuration of the receiving apparatus of a sixth embodiment of the present invention;

[0096] FIGS. 21A and 21B are views of examples of the configuration of the digital wireless communication system using OFDM applied to the DAB system or the like as the multi-carrier modulation method, in which,

[0097] FIG. 21A is a view of the configuration of the transmitting apparatus and

[0098] FIG. 21B is a view of the configuration of the receiving apparatus;

[0099] FIG. 22 is a graph showing an example of symbol strings formed into a multi-carrier signal output from the transmitting apparatus of FIG. 21A ;

[0100] FIG. 23 is a graph showing a first method for demultiplexing a multi-carrier signal of the related art;

[0101] FIG. 24 is a view of the configuration of a receiving apparatus showing a second method for demultiplexing a multi-carrier signal of the related art; and

[0102] FIG. 25 is a graph showing extraction of carriers of a fixed period of the related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] Preferred embodiments of the communication apparatus (communication system), transmitting apparatus (transmitter) and receiving apparatus (receiver), and communication method of the present invention will be explained by referring to the attached drawings.

[0104] In the following embodiments, a wireless communication system will be described as the communication system, but the present invention is not limited to a wireless communication system and can also be applied to a wired communication system. However, in the following embodiments, the communication system will be illustrated using an orthogonal frequency division multiplexing (OFDM) method suitable for a wireless communication system, for example, the DAB system.

[0105] First Embodiment of Communication Apparatus

[0106] A first embodiment of the communication system, transmitting apparatus, receiving apparatus, and communication method of the present invention will be explained next by referring to FIGS. 1A and 1B , FIGS. 2A to 2 C, and FIG. 3 .

[0107] FIGS. 1A and 1B are views of the configuration of a digital wireless communication system using OFDM as the multi-carrier modulation method as a first embodiment of the communication system, transmitting apparatus, receiving apparatus, and communication method of the present invention, in which FIG. 1A is a view of the configuration of a transmitting apparatus 30 of an OFDM wireless communication system, and FIG. 1B is a view of the configuration of a receiving apparatus 40 of the OFDM wireless communication system.

[0108] The transmitting apparatus 30 and the receiving apparatus 40 configure an OFDM wireless communication system.

[0109] Transmitting Apparatus (Transmitter) 30

[0110] The transmitting apparatus (transmitter) 30 will be explained first.

[0111] The transmitting apparatus 30 of the OFDM wireless communication system illustrated in FIG. 1A has a first channel encoder circuit 31 ₁ and a first channel symbol mapping circuit 32 ₁ , a second channel encoder circuit 31 ₂ and a second channel symbol mapping circuit 32 ₂ , . . . , and an Mth channel encoder circuit 31 _M and an Mth channel symbol mapping circuit 32 _M . This example shows the case where information bit streams of M number of channels are encoded.

[0112] The transmitting apparatus 30 further has a multiplexer (signal multiplexing circuit) 34 , a scrambling, IFFT, guard time adding, and window processing circuit 36 , a transmitter circuit 38 , and an antenna 39 .

[0113] The transmitting apparatus 30 has one set of the multiplexer 34 , scrambling, IFFT, guard time adding, and window processing circuit 36 , and transmitter circuit 38 with respect to the plurality of encoder circuits 31 ₁ to 31 _M and the plurality of symbol mapping circuits 32 ₁ to 32 _M . The same number of encoder circuits 31 and symbol mapping circuits 32 are provided as the number of channels.

[0114] The encoding, interleaving, and other processing are independently carried out in the encoder circuits 31 ₁ to 31 _M for the independent information bit streams of channel 1 to channel M.

[0115] A concrete example of the encoding in the encoder circuits 31 ₁ to 31 _M will be explained next. Where an OFDM wireless communication system is applied to the transmission of an audio signal of for example the DAB system, since the bit signals of the information bit streams are audio signals, the encoder circuits 31 ₁ to 31 _M encode audio signals. The encoder circuits 31 ₁ to 31 _M also interleave the signals according to need.

[0116] The encoded bit signals of the channels created at the encoder circuits 31 ₁ to 31 _M are mapped to transmission symbols in the symbol mapping circuits 32 ₁ to 32 _M , whereby the symbol streams are created.

[0117] The symbol mapping circuits 32 ₁ to 32 _M can apply various types of modulation methods used for OFDM. As such modulation methods, multi-value QAM, PSK, various other types of modulation methods can be applied.

[0118] In this way, the symbol mapping circuits 32 ₁ to 32 _M , as illustrated in FIG. 2 A, create independent symbol streams for each channel.

[0119] The symbol streams for the plurality of channels are multiplexed at the multiplexer 34 to create a multiplexed symbol stream. The multiplexer 34 has the switch circuit illustrated in FIG. 2B . Due to the multiplexing of the multiplexer 34 , the symbols of the plurality of channels illustrated in FIG. 2A become the multiplexed symbol stream comprised of the symbols of the plurality of channels arranged on the frequency axis as illustrated in FIG. 2C .

[0120] The multiplexed symbol stream multiplexed at the multiplexer 34 is scrambled by random phase shifting (RPS), random orthogonal transform (ROT), etc. in the scrambling, IFFT, guard time adding, and window processing circuit 36 .

[0121] The scrambling, IFFT, guard time adding, and window processing circuit 36 transforms the frequency domain multiplexed symbol stream to a multiplexed symbol stream of the time domain by an inverse Fourier fast transform (IFFT).

[0122] Further, the addition of the guard time and the window processing are applied to it in the scrambling, IFFT, guard time adding, and window processing circuit 36 .

[0123] The scrambling, IFFT, guard time adding, and window processing circuit 36 is shown as a single means for scrambling, inverse Fast Fourier transform (IFFT), guard time processing, window processing, etc. explained later. This processing may also be processed separately by individual circuits or individual means.

[0124] The scrambling, guard time processing and the window processing in the scrambling, IFFT, guard time adding, and window processing circuit 36 are not indispensable to the present invention. However, if the signal is scrambled, the privacy (secrecy) of the communication is raised.

[0125] As a representative example of the orthogonal transformation, IFFT was illustrated, but it is also possible to apply other orthogonal transforms, for example, inverse discrete cosine transform (IDCT), in place of IFFT in the scrambling, IFFT, guard time adding, and window processing circuit 36 .

[0126] From the above description, the scrambling, IFFT, guard time adding, and window processing circuit 36 is a circuit or means for applying an orthogonal transform.

[0127] The output symbols of the scrambling, IFFT, guard time adding, and window processing circuit 36 are convoluted with the high frequency signal in the transmitter circuit 38 and to be transformed to the intended frequency band, then transmitted into the air via the antenna 39 .

[0128] Next, an explanation will be made of the configuration of an internal portion of the multiplexer 34 and the arrangement of the symbols of the channels created by this multiplexing method by referring to FIGS. 2A to 2 C.

[0129] FIGS. 2A to 2 C are views showing a basic concept of the multiplexed transmission in the multiplexer 34 illustrated in FIG. 1 .

[0130] The multiplexer 34 illustrated in FIG. 1A is basically configured as the switching circuit illustrated in FIG. 2B .

[0131] FIG. 2A shows the symbol streams of channels multiplexed at the multiplexer 34 . Here, four channels from channel 1 (CH 1 ) to channel 4 (CH 4 ) are illustrated. The symbol streams of the channels are individually inserted in the multiplexer 34 .

[0132] FIG. 2B is a view showing the concept of the processing in the multiplexer 34 . The input symbol streams of the channels are cyclically switched and the symbols arranged so that the symbols of each channel cyclically appear. The multiplexed symbol stream is shown in FIG. 2C .

[0133] In this example, the case of multiplexing a maximum of four channels is taken as an example, so the symbols of each channel appear at a cycle of 4, but the maximum number of channels multiplexed is not limited to this. It is also possible to set the number at 2 ⁿ (n=1, 2, 3, 4, . . . ) for any whole number n. The cycle at which the symbols of each channel appear in this case becomes 2 ⁿ or the same as the maximum number of channels multiplexed.

[0134] When the multiplexing in the multiplexer 34 is the processing of 2 ² channels, when the number of the channels actually used for communication is smaller than the maximum number of channels multiplexed, a null symbol having an amplitude of “0 (zero)” is inserted as a symbol of an unused channel for the cyclic multiplexing in the multiplexer 34 .

[0135] FIG. 3 is a view of the arrangement of the subcarriers of a plurality of channels.

[0136] In the example illustrated in FIG. 3 , the case where there are four channels and performing OFDM processing with a subcarrier interval of 4 kHz for every channel, that is, the case of the 250 μs={fraction (1/4)} kHz for modulation of one symbol, is illustrated. While the interval between subcarriers of the multiplexed signal is 4 kHz, the channel 1 to channel 4 cyclically appear on the frequency axis in units of subcarriers, therefore the subcarrier of each channel appears at intervals of 16 kHz=4×4 kHz.

[0137] The symbol f _c in FIG. 3 indicates a carrier (carrier) frequency (center frequency of a band signal).

[0138] In the embodiment of the present invention, in multiplexed communication by multi-carrier modulation, subcarriers of a plurality of channels are cyclically arranged. This is to facilitate the modulation of a large number of symbols and further to facilitate channel demultiplexing in a channel selection circuit 43 in the receiving apparatus 40 explained later.

[0139] First Embodiment of Receiving Apparatus

[0140] The receiving apparatus 40 of the OFDM wireless communication system illustrated in FIG. 1B will be explained next.

[0141] In this embodiment, similar to the transmitting apparatus 30 , the case where there are four multiplexed channels and performing OFDM processing with a subcarrier interval of 4 kHz for every channel, that is, the case of the 250 μs={fraction (1/4)} kHz for modulation of one symbol, is illustrated. Further, for convenience of the explanation, a case where the signal band of the multiplexed signal is 1024 kHz and there are 256 subcarriers is illustrated. This corresponds to the case where there are 64 (=256/4) subcarriers per channel.

[0142] The receiving apparatus 40 has a receiving antenna 41 , a high frequency receiver circuit 42 , a signal component demultiplexing apparatus (demultiplexer or channel selection circuit) 43 , an FFT and/or descrambling means 44 , a bit extraction circuit 45 , and a decoding circuit 46 .

[0143] The signal transmitted from the transmitting apparatus 30 of the OFDM wireless communication system is received at the receiving antenna 41 and down converted to the baseband area in the high frequency receiver circuit 42 . Further, it is converted to a digital signal at a not illustrated A/D converter and input from a connection line 202 to the signal component demultiplexing apparatus 43 .

[0144] The signal component demultiplexing apparatus 43 receives as input signals of channel 1 to channel 4 arranged on the frequency axis in terms of expression on the time axis.

[0145] The signal component demultiplexing apparatus 43 demultiplexes a signal for every plurality of channels inverse to the processing of the demultiplexer 34 in the transmitting apparatus 30 .

[0146] The detailed circuit configuration and processing method of this signal component demultiplexing apparatus 43 will be explained later by referring to FIG. 4 to FIG. 7 .

[0147] The number of symbols input from the high frequency receiver circuit 42 to the signal component demultiplexing apparatus 43 is 256 per modulation time (an over sample is not considered here for simplification), but the number of he subcarriers of the intended channel is {fraction (1/4)}, therefore the channel selection circuit 43 performs decimation on the frequency axis and outputs 64 (=256/4) symbols. Due to this, the number of symbols of the FFT processing in the FFT and/or descrambling means 44 is decreased to {fraction (1/4)}.

[0148] The output symbols of the signal component demultiplexing apparatus 43 are input via a signal line 204 to the FFT and/or descrambling means 44 .

[0149] The FFT and/or descrambling means 44 applies a fast Fourier transform (FFT) inverse to the IFFT (inverse fast Fourier transform) in the scrambling, IFFT, guard time adding, and window processing circuit 36 in the transmitting apparatus 30 to extract the symbol strings arranged on the frequency axis.

[0150] The signal component demultiplexing apparatus 43 selects and extracts the symbols of intended channel and applies them to the FFT and/or descrambling means 44 . Therefore, the symbols extracted by the FFT processing do not include the symbols of channels other than the intended channel. Namely, the processing in the processing means 44 need only be the FFT processing having the minimum number of points required for receiving the intended channel. As a result, the FFT processing circuit in the FFT and/or descrambling means 44 becomes small in scale.

[0151] The symbol stream of the intended channel extracted in this way is subjected to processing corresponding to the random phase shifting, random orthogonal transform processing, and other processing in the scrambling, IFFT, guard time adding, and window processing circuit 36 , descrambled in the transmitting apparatus 30 , and then input through the signal line 206 to the bit extraction circuit 45 .

[0152] The bit extraction circuit 45 extracts the bits in accordance with the modulation method by which the symbols were modulated and applies the encoded bit stream to the decoding circuit 46 . As such a modulation method, various modulation methods such as the QPSK, 8PSK, and 16QAM applied in OFDM can be applied.

[0153] The decoding circuit 46 extracts the information bit stream by deinterleaving and decoding reverse to the encoding and the interleaving carried out in the encoder circuits to 31 ₁ to 31 _M of the plurality of channels in the transmitting apparatus.

[0154] By providing the signal component demultiplexing apparatus 43 in a receiving apparatus 40 receiving signals of the symbol strings of a large number of subcarriers, it becomes possible to perform the processing after lowering (decimating) the sample rates in the FFT and descrambling means 44 , bit extraction circuit 45 , and decoding circuit 46 to that of the intended channel and it becomes possible to greatly reduce amounts of processing of the circuits 45 to 46 after the FFT and descrambling means 44 to for example (1/number of multiplexed channels).

[0155] Particularly, since the signal component demultiplexing apparatus 43 is provided in front of the FFT and descrambling means 44 and the amount of data of the FFT processing in the FFT and descrambling means 44 is decreased, the memory capacity for the FFT processing becomes small. This contributes a large degree to the reduction of scale of the receiving apparatus 40 . Further, the FFT processing time in the FFT and/or descrambling means 44 can be shortened.

[0156] The subcarrier of each channel is arranged over the entire frequency band of the system. Therefore when the present embodiment is applied to a wireless communication system with a large number of multiplexed channels like the DAB system, a large frequency diversity effect can be expected. By this, it becomes possible to suppress deterioration of the quality of service due to fading.

[0157] Signal Component Demultiplexing Apparatus 43

[0158] An embodiment of the signal component demultiplexing apparatus 43 shown in FIG. 1B will be explained next by referring to FIG. 4 to FIG. 7 .

[0159] FIG. 4 is a view of the configuration of the signal component demultiplexing apparatus 43 .

[0160] FIG. 5 is a circuit diagram of a branching circuit forming part of the signal component demultiplexing apparatus 43 illustrated in FIG. 4 .

[0161] FIG. 6 is a view of an example of a symbol delay circuit 43 a illustrated in FIG. 5 .

[0162] FIG. 7 is a view of an example of a phase offset adjustment circuit 43 b illustrated in FIG. 5 .

[0163] In the present embodiment, a case where there are subcarriers of 2 ³ channels=8 channels C0 to C7 will be explained.

[0164] The signal component demultiplexing apparatus 43 illustrated in FIG. 4 has one first stage branching circuit 431 , two second stage branching circuits 432 ₁ and 432 ₂ , and four third stage branching circuits 433 ₁ to 433 ₄ . The circuit configuration of the signal component demultiplexing apparatus 43 is designed so that the branching circuits 431 : 432 ₁ , 432 ₂ : 433 ₁ to 433 ₄ for sequentially branching the symbols fan out in the form of a power of 2 (or hierarchically like a hierarchy (pyramid) in the form of a power of 2).

[0165] The branching circuit is significant in the extraction of the symbol strings alternately branched to two systems for every subcarrier when the symbol strings are input.

[0166] It is possible to configure the signal component demultiplexing apparatus 43 by combining individual branching circuits 431 , 432 ₁ , 432 ₂ , and 433 ₁ to 433 ₄ as illustrated in FIG. 4 . It is also possible to configure these branching circuits by one d