Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2000-08-08
2004-07-13
Liu, Shuwang (Department: 2634)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S261000, C375S279000, C375S281000, C375S298000
Reexamination Certificate
active
06763072
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and an apparatus for modulation based on orthogonal frequency division multiplexing (OFDM). In addition, this invention relates to a method and an apparatus for demodulation concerning OFDM. Furthermore, this invention relates a method and an apparatus for digital quadrature modulation. Also, this invention relates to a method and an apparatus for digital quadrature demodulation.
2. Description of the Related Art
In orthogonal frequency division multiplexing (OFDM), digital in-phase (I) signals and digital quadrature (Q) signals resulting from a QAM-corresponding process or a QPSK-corresponding process are assigned to respective orthogonal frequencies for IDFT or IFFT. Here, QAM is short for quadrature amplitude modulation, and QPSK is short for quadrature phase shift keying. In addition, IDFT is short for inverse discrete Fourier transform, and IFFT is short for inverse fast Fourier transform. The IDFT or IFFT is executed while the I signals are set as real-part terms and the Q signals are set as imaginary-part terms. By the IDFT or IFFT, the I signals are converted and combined into a digital multiplexing-resultant I signal, and the Q signals are converted and combined into a digital multiplexing-resultant Q signal. The digital multiplexing-resultant I and Q signals are changed into analog forms. The analog I and Q signals are combined and converted into an RF multiple-carrier signal in a desired frequency band. The RF multiple-carrier signal is transmitted as a radio wave.
A prior-art apparatus for modulation based on OFDM requires a relatively-high sampling frequency. Therefore, the prior-art modulation apparatus uses parts which can accurately operate even at high frequencies. Such parts are expensive.
A prior-art apparatus for demodulation concerning OFDM requires a relatively-high sampling frequency. Therefore, the prior-art demodulation apparatus uses parts which can accurately operate even at high frequencies. Such parts are expensive.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide an improved method of modulation based on orthogonal frequency division multiplexing (OFDM).
It is a second object of this invention to provide an improved apparatus for modulation based on OFDM.
It is a third object of this invention to provide an improved method of demodulation concerning OFDM.
It is a fourth object of this invention to provide an improved apparatus for demodulation concerning OFDM.
It is a fifth object of this invention to provide an improved digital quadrature modulation apparatus.
It is a sixth object of this invention to provide an improved method of digital quadrature modulation.
It is a seventh object of this invention to provide an improved digital quadrature demodulation apparatus.
It is an eighth object of this invention to provide an improved method of digital quadrature demodulation.
It is a ninth object of this invention to provide an improved digital quadrature modulator.
A first aspect of this invention provides a method of modulation based on orthogonal frequency division multiplexing. The method comprises the steps of assigning data pieces representative of in-phase components and quadrature components of a digital-modulation-resultant signal to frequencies for inverse fast Fourier transform; executing the inverse fast Fourier transform at a predetermined sampling frequency Fs to convert the data pieces into a real-part signal and an imaginary-part signal; shifting phases of the real-part signal and the imaginary-part signal to convert the real-part signal and the imaginary-part signal into a phase-shifted real-part signal and a phase-shifted imaginary-part signal; dividing the phase-shifted real-part signal into a sequence of even-numbered samples and a sequence of odd-numbered samples; dividing the phase-shifted imaginary-part signal into a sequence of even-numbered samples and a sequence of odd-numbered samples; multiplying the sequence of the phase-shifted even-numbered samples of the real-part signal by “1” to generate a first multiplication-result signal I(2n); multiplying the sequence of the even-numbered samples of the phase-shifted imaginary-part signal by “−1” to generate a second multiplication-result signal −Q(2n); multiplying the sequence of the odd-numbered samples of the phase-shifted real-part signal by “−1” to generate a third multiplication-result signal −I(2n+1); multiplying the sequence of the odd-numbered samples of the phase-shifted imaginary-part signal by “1” to generate a fourth multiplication-result signal Q(2n+1); sequentially selecting the first multiplication-result signal I(2n), the second multiplication-result signal −Q(2n), the third multiplication-result signal −I(2n+1), and the fourth multiplication-result signal Q(2n+1) at a frequency equal to twice the predetermined sampling frequency Fs to generate a digital quadrature-modulation-resultant signal; and converting the digital quadrature-modulation-resultant signal into an analog quadrature-modulation-resultant signal at a frequency equal to twice the predetermined sampling frequency Fs.
A second aspect of this invention is based on the first aspect thereof, and provides a method wherein the sequentially selecting step comprises inputting the first multiplication-result signal I(2n), the second multiplication-result signal −Q(2n), the third multiplication-result signal −I(2n+1), and the fourth multiplication-result signal Q(2n+1) into shift registers respectively at a frequency equal to half the predetermined sampling frequency Fs; and sequentially selecting output signals from the shift registers at a frequency equal to twice the predetermined sampling frequency Fs to generate the digital quadrature-modulation-resultant signal.
A third aspect of this invention provides an apparatus for modulation based on orthogonal frequency division multiplexing. The apparatus comprises means for assigning data pieces representative of in-phase components and quadrature components of a digital-modulation-resultant signal to frequencies for inverse fast Fourier transform; means for executing the inverse fast Fourier transform at a predetermined sampling frequency Fs to convert the data pieces into a real-part signal and an imaginary-part signal; means for shifting phases of the real-part signal and the imaginary-part signal to convert the real-part signal and the imaginary-part signal into a phase-shifted real-part signal and a phase-shifted imaginary-part signal; means for dividing the phase-shifted real-part signal into a sequence of even-numbered samples and a sequence of odd-numbered samples; means for dividing the phase-shifted imaginary-part signal into a sequence of even-numbered samples and a sequence of odd-numbered samples; a multiplier for multiplying the sequence of the even-numbered samples of the phase-shifted real-part signal by “1” to generate a first multiplication-result signal I(2n); a multiplier for multiplying the sequence of the even-numbered samples of the phase-shifted imaginary-part signal by “−1” to generate a second multiplication-result signal −Q(2n); a multiplier for multiplying the sequence of the odd-numbered samples of the phase-shifted real-part signal by “−1” to generate a third multiplication-result signal −I(2n+1); a multiplier for multiplying the sequence of the odd-numbered samples of the phase-shifted imaginary-part signal by “1” to generate a fourth multiplication-result signal Q(2n+1); means for sequentially selecting the first multiplication-result signal I(2n), the second multiplication-result signal −Q(2n), the third multiplication-result signal −I(2n+1), and the fourth multiplication-result signal Q(2n+1) at a frequency equal to twice the predetermined sampling frequency Fs to generate a digital quadrature-modulation-resultant signal; and a D/A converter for converting the digital quadrature-modu
Kaneko Keiichi
Matsui Kazunari
Saiki Takaaki
Takaoka Katsumi
Liu Shuwang
Victor Company of Japan Ltd.
Woo Louis
LandOfFree
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