OFDM communications methods and apparatus
First Claim
1. A method of processing a frequency division multiplexed signal representing a plurality of symbols and including a plurality of tones, a first subset of said plurality of tones being allocated to a first user, the method comprising the steps of:
- performing a time domain to frequency domain transform operation on the frequency division multiplexed signal to generate a frequency domain signal therefrom;
filtering the frequency domain signal to remove tones in said plurality of tones which are not included in said first subset of tones;
performing a frequency domain to time domain transform operation on the filtered frequency domain signal to generate a filtered time domain signal;
performing, after performing said frequency domain to time domain transform operation, a channel equalization operation on the filtered time domain signal; and
recovering symbols transmitted to the first user from the filtered time domain signal following equalization.
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Abstract
OFDM signal communication methods and apparatus are described. In accordance with the invention OFDM signals are generated in the time domain with symbols being mapped to specific points in time. Training symbols may be included in the transmitted OFDM signal to facilitate symbol recovery. An exemplary receiver of the invention receives the OFDM signal from the communications channel, converts it into the frequency domain, and then filters it in the frequency domain to eliminate tones corresponding to other users. The filtered signal free of MAC interference is then converted into the time domain where channel estimation and compensation operations are performed. After channel compensation symbol recovery is performed in the time domain.
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Citations
48 Claims
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1. A method of processing a frequency division multiplexed signal representing a plurality of symbols and including a plurality of tones, a first subset of said plurality of tones being allocated to a first user, the method comprising the steps of:
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performing a time domain to frequency domain transform operation on the frequency division multiplexed signal to generate a frequency domain signal therefrom; filtering the frequency domain signal to remove tones in said plurality of tones which are not included in said first subset of tones; performing a frequency domain to time domain transform operation on the filtered frequency domain signal to generate a filtered time domain signal; performing, after performing said frequency domain to time domain transform operation, a channel equalization operation on the filtered time domain signal; and recovering symbols transmitted to the first user from the filtered time domain signal following equalization. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. An apparatus for processing a frequency division multiplexed signal representing a plurality of symbols and including a plurality tones, a first subset of said plurality of tones being allocated to a first user, the apparatus comprising:
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a time to frequency domain transform module for generating a frequency domain signal from the frequency division multiplexed signal; a tone filter for filtering, from the frequency domain signal generated by the time to frequency domain transform module, tones other than those included in the first subset to thereby generate a filtered frequency domain signal; a frequency to time domain transform module for performing a frequency domain to time domain transform operation on the filtered frequency domain signal to thereby generate a time domain signal; a channel equalizer, located after said frequency to time domain transform module, for performing a channel equalization operation on the time domain signal produced by the frequency to time domain transform module; and a time instant to symbol mapping module coupled to the channel equalizer for mapping signal values at points in time to symbol values. - View Dependent Claims (22, 23, 24, 25, 26, 27)
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28. A method of processing a received orthogonal frequency division multiplexed signal to generate symbol values, the method comprising:
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performing a frequency domain to time domain transform operation to generate an OFDM time domain signal; performing, after performing said frequency domain to time domain transform operation, a channel equalization operation on the OFDM time domain signal in the time domain; and mapping values of the OFDM time domain signal, after channel equalization at instants in time used to transmit symbol values, to symbol values. - View Dependent Claims (29, 30)
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31. An orthogonal frequency division multiplexed (OFDM) signal receiver for receiving an OFDM signal, the receiver comprising:
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a frequency domain to time domain transform hardware module for performing a frequency domain to time domain transform operation to generate an OFOM time domain signal; a time domain channel equalization hardware module, located after said frequency domain to time domain transform module, for performing a channel equalization operation on the OFDM time domain signal generated by said frequency to time domain transform operation; and a time instant to symbol mapping hardware module for mapping values of the time domain signal after channel equalization at instants in time used to transmit symbol values to symbol values. - View Dependent Claims (32, 33)
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34. A communications system composing:
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an orthogonal frequency division multiplexed signal transmitter including; a symbol to time instant mapping module for trapping a plurality of symbols to be transmitted to uniformly spaced points in time within a time period corresponding to a symbol duration; and an orthogonal frequency division multiplexed signal receiver including; a frequency domain to time domain transform module for performing a frequency domain to time domain transform operation on a received OFDM signal to thereby generate a time domain signal; a time domain channel equalization module, located after said frequency domain to time domain transform module, for performing a channel equalization operation on the time domain signal; and a time instant to symbol mapping module for mapping signal values at points in time used to transmit symbols to symbol values. - View Dependent Claims (35, 36, 37)
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38. An apparatus comprising:
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a processor for processing a frequency division multiplexed signal representing a plurality of symbols and including a plurality of tones, a first subset of said plurality of tones being allocated to a first user, the processor being configured to; perform a time domain to frequency domain transform operation on the frequency division multiplexed signal to generate a frequency domain signal therefrom; filter the frequency domain signal to remove tones in said plurality of tones which are not included in said first subset of tones; perform a frequency domain to time domain transform operation on the filtered frequency domain signal to generate a filtered time domain signal; perform, after performing said frequency domain to time domain transform operation, a channel equalization operation on the filtered time domain signal; and recover symbols transmitted to the first user from the filtered time domain signal following equalization.
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39. An apparatus for processing a frequency division multiplexed signal representing a plurality of symbols and including a plurality tones, a first subset of said plurality of tones being allocated to a first user, the apparatus comprising:
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time to frequency domain transform means for generating a frequency domain signal from the frequency division multiplexed signal; tone filter means for filtering, from the frequency domain signal generated by the time to frequency domain transform means, tones other than those included in the first subset to thereby generate a filtered frequency domain signal; a frequency to time domain transform means for performing a frequency domain to time domain transform operation on the filtered frequency domain signal to thereby generate a time domain signal; channel equalizer means, located after said frequency to time domain transform means, for performing a channel equalization operation on the time domain signal produced by the frequency to time domain transform means; and time instant to symbol mapping means, coupled to the channel equalizer means, for mapping signal values at points in time to symbol values. - View Dependent Claims (40, 41, 42)
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43. An orthogonal frequency division multiplexed (OFDM) signal receiver for receiving an OFDM signal, the receiver comprising:
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frequency domain to time domain transform means for performing a frequency domain to time domain transform operation to generate an OFDM time domain signal; time domain channel equalization means, located after said frequency domain to time domain transform means, for performing a channel equalization operation on the OFDM time domain signal generated by said frequency to time domain transform means; and time instant to symbol mapping means for mapping values of the time domain signal after channel equalization at instants in time used to transmit symbol values to symbol values. - View Dependent Claims (44)
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45. A communications system comprising:
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orthogonal frequency division multiplexed signal transmitter means for generating and transmitting an orthogonal frequency division multiplexed signal, said orthogonal frequency division multiplexed signal transmitter means including; symbol to time instant mapping means for mapping a plurality of symbols to be transmitted to uniformly spaced points in time within a time period corresponding to a symbol duration; and orthogonal frequency division multiplexed signal receiver means for receiving and processing said orthogonal frequency division multiplexed signal, said orthogonal frequency division multiplexed signal receiver means including; frequency domain to time domain transform means for performing a frequency domain to time domain transform operation on said received orthogonal frequency division multiplexed signal to thereby generate a time domain signal; time domain channel equalization means, located alter said frequency domain to time domain transform means, for performing a channel equalization operation on the time domain signal; and time instant to symbol mapping means for mapping signal values at points in time used to transmit symbols to symbol values. - View Dependent Claims (46, 47)
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48. A computer program product, comprising:
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a non-transitory computer-readable medium comprising; a first set of codes for causing a computer to execute a time domain to frequency domain transform operation on the frequency division multiplexed signal to generate a frequency domain signal therefrom; a second set of codes for causing a computer to filter the frequency domain signal to remove tones in said plurality of tones which are not included in said first subset of tones; a third set of codes for causing a computer to execute a frequency domain to time domain transform operation on the filtered frequency domain signal to generate a filtered time domain signal; a fourth set of codes for causing a computer to execute, after performing said frequency domain to time domain transform operation, a channel equalization operation on the filtered time domain signal; and a fifth set of codes for causing a computer to acquire symbols transmitted to the first user from the filtered time domain signal following equalization.
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Specification