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Kafe 바로가기국가/구분 | United States(US) Patent 등록 |
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국제특허분류(IPC7판) |
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출원번호 | US-0931469 (2001-08-16) |
등록번호 | US-9130810 (2015-09-08) |
발명자 / 주소 |
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출원인 / 주소 |
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대리인 / 주소 |
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인용정보 | 피인용 횟수 : 12 인용 특허 : 365 |
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 exempl
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.
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 transf
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; andrecovering symbols transmitted to the first user from the filtered time domain signal following equalization. 2. The method of claim 1, wherein said frequency division multiplexed signal is an OFDM signal. 3. The method of claim 1, wherein recovering symbols further includes performing a channel estimation operation, said channel estimation operation including: identifying a training symbol in the filtered time domain signal; andgenerating at least one channel estimation as a function of the difference between the identified training symbol and a known training symbol value. 4. The method of claim 1, wherein the frequency division multiplexed signal corresponds to multiple symbol periods, the portion of the received signal corresponding to each symbol period including at least one training symbol; andwherein recovering symbols further includes performing a channel estimation operation, said channel estimation operation including, for each symbol period: identifying a training symbol in the filtered time domain signal; andgenerating at least one channel estimation as a function of the difference between the identified training symbol and a known training symbol value. 5. The method of claim 1, wherein the frequency division multiplexed signal corresponds to multiple dwells, each dwell being a period of time equal to multiple symbol periods, the first user being allocated the first subset of said plurality of tones for use throughout one of said dwells, the method further comprising: performing a channel estimation operation including, for each dwell: identifying a training symbol in the filtered time domain signal received during one symbol period within the dwell; andgenerating a channel estimation as a function of the difference between the identified training symbol and a known training symbol value. 6. The method of claim 5, wherein performing a channel equalization operation includes: using a channel estimation generated from a training symbol received during a dwell to perform a channel equalization operation on a portion of the filtered time domain signal corresponding to a symbol period in said dwell which does not include said identified training symbol. 7. The method of claim 5, wherein all of a plurality of symbols received during one of said symbol periods in each dwell include training symbols;wherein performing a channel estimation operation for each dwell further includes: generating a channel estimation for each of the training symbols received during said one of said symbol periods. 8. The method of claim 7, wherein performing a channel equalization operation includes: using the channel estimations generated from each of the received training symbols during said one of said symbol periods in each dwell, to perform separate channel equalization operations on each portion of the filtered time domain signal corresponding to a symbol in at least one other symbol period included in the same dwell in which the training symbols used to generate the channel estimations were received. 9. The method of claim 8, wherein the symbol period in which all received symbols are training symbols is located at the center of each dwell. 10. The method of claim 1, wherein the frequency division multiplexed signal is an orthogonal frequency division multiplexed signal; andwherein recovering symbols transmitted to the first user includes: mapping values of the filtered time domain signal at instants in time used to transmit symbol values to values in a set of symbol values. 11. The method of claim 10 wherein recovering symbols transmitted to the first user further includes: performing a symbol value to symbol value mapping operation to map symbol values generated by mapping values of the filtered time domain signal to values in another set of symbol values. 12. The method of claim 10, wherein performing a time domain to frequency domain transform operation includes performing one of a Fast Fourier Transform operation and a Discrete Fourier Transform operation; andwherein performing a frequency domain to time domain transform operation includes performing one of an Inverse Fast Fourier Transform operation and an Inverse Discrete Cosine Transform operation. 13. The method of claim 12, further comprising: receiving the frequency division multiplexed signal from a communications channel including frequency division multiplexed signals corresponding to users other than the first user. 14. The method of claim 1, wherein said step of recovering symbols transmitted to the first user from the filtered time domain signal is performed by performing a time domain signal to symbol value mapping operation in the time domain. 15. The method of claim 14, wherein performing the time domain signal to symbol value mapping operation in the time domain includes generating multiple symbol values for a portion of the filtered time domain signal corresponding to a symbol transmission time period, each symbol value being generated from a different part of the filtered time domain signal. 16. The method of claim 15, wherein the value of the filtered time domain signal at a single instant in time is used to generate one symbol value. 17. The method of claim 1, wherein recovering symbols from the filtered time domain signal includes recovering a plurality of symbol values from a portion of said filtered time domain signal corresponding to a single OFDM symbol transmission time period, each symbol value corresponding to a different point in time within the single OFDM symbol transmission time period. 18. The method of claim 17, where the different points in time within the symbol transmission time period from which individual symbol values are generated are uniformly spaced in time within the single OFDM symbol transmission tune period. 19. The method of claim 1, wherein said plurality of tones includes another subset of tones allocated to another user, said another user being different from said first user, said filtering of the frequency domain signal removing tones in said another subset of tones. 20. The method of claim 19, wherein said frequency division multiplexed signal is an OFDM signal, said first subset of tones and said another subset of tones corresponding to said OFDM signal. 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: 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; anda time instant to symbol mapping module coupled to the channel equalizer for mapping signal values at points in time to symbol values. 22. The apparatus of claim 21, wherein the frequency division multiplexed signal is an OFDM signal. 23. The apparatus of claim 21, further comprising: a channel estimation circuit coupled to said frequency to time domain transform module and to the channel equalizer for generating at least one channel estimate from the time domain signal and for supplying the channel estimate to the channel equalizer. 24. The apparatus of claim 23, further comprising: a symbol to symbol mapping module coupled to the time instant to symbol mapping module. 25. The apparatus of claim 23, further comprising: a cyclic prefix discarding circuit coupled to the time to frequency domain transform module for discarding portions of the frequency division multiplexed signal corresponding to cyclic prefixes. 26. The apparatus of claim 21, wherein the frequency division multiplexed signal is an orthogonal frequency division multiplexed signal;wherein the time to frequency domain transform module is a Fast Fourier Transform circuit; andwherein the frequency to time domain transform module is an inverse Fast Fourier Transform circuit. 27. The apparatus of claim 21, wherein said time instant to symbol mapping module is a time domain signal processing module which maps each one of multiple individual time instants within an OFDM symbol time period to corresponding individual symbol values according to a one to one relationship between time instants and symbol values. 28. A method of processing a received orthogonal frequency division multiplexed signal to generate symbol values, the method comprising: 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; andmapping values of the OFDM time domain signal, after channel equalization at instants in time used to transmit symbol values, to symbol values. 29. The method of claim 28, further comprising: filleting the OFDM signal in the frequency domain to remove undesired signal tones prior to performing said channel equalization operation on the received OFDM time domain signal in the time domain. 30. The method of claim 28, wherein said mapping of values of the OFDM time domain signal after channel equalization involves performing said mapping of values in the time domain, said mapping including mapping of a plurality of individual instants in time within an OFDM symbol period to generate a corresponding plurality of symbol values, each of the plurality of symbol values corresponding to a single time instant. 31. An orthogonal frequency division multiplexed (OFDM) signal receiver for receiving an OFDM signal, the receiver comprising: 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; anda 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. 32. The receiver of claim 31, further comprising: a time to frequency domain signal transform circuit for converting the received OFDM signal to the frequency domain; anda tone filter coupled to the time to frequency domain signal transform circuit for performing a filtering operation on the received OFDM signal in the frequency domain. 33. The receiver of claim 31, wherein said time instant to symbol mapping module performs said mapping in the time domain, said mapping including mapping of a plurality of individual instants in time within an OFDM symbol period to generate corresponding plurality of symbol values, each of the plurality of symbol values corresponding to a different point in time. 34. A communications system composing: 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; andan 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; anda time instant to symbol mapping module for mapping signal values at points in time used to transmit symbols to symbol values. 35. The system of claim 34, wherein the receiver further includes: a time domain to frequency domain transform circuit for converting a received signal from the time domain to the frequency domain; anda tone filter coupled to the time domain to frequency domain transform circuit for filtering tones, outside a set of tones used by the receiver, from the received signal in the frequency domain, an output of the tone filter supplying the input to the frequency domain to time domain transform circuit. 36. The system of claim 34, wherein the received OFDM signal includes a plurality of uniformly spaced OFDM tones. 37. The system of claim 34, wherein said time instant to symbol mapping module maps different points in time within a single OFDM symbol transmission tune period to determine individual symbol values corresponding to individual ones of said different points in time. 38. An apparatus comprising: 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; andrecover symbols transmitted to the first user from the filtered time domain signal following equalization. 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: 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; andtime instant to symbol mapping means, coupled to the channel equalizer means, for mapping signal values at points in time to symbol values. 40. The apparatus of claim 39, wherein the frequency division multiplexed signal is an OFDM signal. 41. The apparatus of claim 39, further comprising: channel estimation means coupled to said frequency to time domain transform means and to the channel equalizer means for generating at least one channel estimate from the time domain signal and for supplying the channel estimate to the channel equalizer means. 42. The apparatus of claim 41, further comprising: symbol to symbol mapping means for performing a symbol to symbol mapping operation, said symbol to symbol mapping means being coupled to the time instant to symbol mapping means. 43. An orthogonal frequency division multiplexed (OFDM) signal receiver for receiving an OFDM signal, the receiver comprising: 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; andtime 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. 44. The receiver of claim 43, further comprising: time to frequency domain signal transform means for converting the received OFDM signal to the frequency domain; andtone filter means, coupled to the time to frequency domain signal transform means, for performing a filtering operation on the received OFDM signal in the frequency domain. 45. A communications system comprising: 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; andorthogonal 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; andtime instant to symbol mapping means for mapping signal values at points in time used to transmit symbols to symbol values. 46. The system of claim 45, wherein the receiver means further includes: time domain to frequency domain transform means for converting a received signal from the time domain to the frequency domain; andtone filter means coupled to the time domain to frequency domain transform means for filtering tones, outside a set of tones used by the receiver means, from the received signal in the frequency domain, an output of the tone filter means supplying the input to the frequency domain to time domain transform means. 47. The system of claim 45, wherein the received OFDM signal includes a plurality of uniformly spaced OFDM tones. 48. A computer program product, comprising: 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; anda 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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