System and method for communicating data using efficient fast fourier transform (FFT) for orthogonal frequency division multiplexing (OFDM) modulation
First Claim
Patent Images
1. A communications device comprising:
- at least one memory element for storing complex exponential functions as frequency approximations of sine and cosine basis waveforms; and
a logic circuit for adding and subtracting the complex exponential functions to generate an orthogonal frequency division multiplexed (OFDM) communications signal as a plurality of N data subcarriers that carry communications data wherein said logic circuit is operative for logically shifting and adding cosine (nkω
/N) and sine (nkω
/N) corresponding to the input digital constellation symbols.
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Abstract
A communications device includes at least one memory device for storing complex exponential functions as approximations of sine and cosine basis waveforms. A logic circuit adds and subtracts the complex exponential functions to generate an Orthogonal Frequency Division Multiplexed (OFDM) communications signal as a plurality of N data subcarriers that carry communications data. The logic circuit provides efficient and accurate implementation of the IFFT for use as an OFDM modulator using additions of stored complex exponentials and modulation of the integer-valued QAM data symbols using logic shifts and sign changes (2'"'"'s complement).
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Citations
20 Claims
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1. A communications device comprising:
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at least one memory element for storing complex exponential functions as frequency approximations of sine and cosine basis waveforms; and a logic circuit for adding and subtracting the complex exponential functions to generate an orthogonal frequency division multiplexed (OFDM) communications signal as a plurality of N data subcarriers that carry communications data wherein said logic circuit is operative for logically shifting and adding cosine (nkω
/N) and sine (nkω
/N) corresponding to the input digital constellation symbols. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A system for communicating, comprising:
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an encoder for encoding a signal with a forward error correction code; and a modulator configured to approximate the frequencies of sine and cosine basis waveforms using complex exponential functions and at least one memory element configured to store the complex exponential functions and a logic circuit configured to add and subtract the stored complex exponential functions corresponding to digital constellation symbols to generate an orthogonal frequency division multiplexed (OFDM) communications signal as a plurality of N data subcarriers that carry communications data wherein said logic circuit is operative for logically shifting and adding cosine (nkω
/N) and sine (nkw/N) corresponding to the input digital constellation symbols. - View Dependent Claims (12, 13, 14)
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15. A method of communicating data, comprising:
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approximating frequencies of sine and cosine basis waveforms using complex exponential functions; storing the complex exponential functions within at least one memory element; adding and subtracting the complex exponential functions to generate an orthogonal frequency division multiplexed (OFDM) communications signal as a plurality of N data subcarriers that carry communications data; and transmitting the OFDM communications signal wherein said logic circuit is operative for logically shifting and adding cosine (nkω
/N) and sine (nkω
/N) corresponding to the input digital constellation symbols. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification