# US 9,438,460 B2 · Partial discrete fourier transform-spread in an orthogonal frequency division multiplexing system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,438,460 B2 - Document ID: US9438460B2 - Status: Granted - Kind: B2 - Application number: 14/885,264 - Filed: 2015-10-16 - Published: 2016-04-21 - Granted: 2016-09-06 - Earliest claimed: 2014-10-17 - Assignees: Finisar Corporation - Applicants: Finisar Corporation - Inventors: William Ling; Ilya Lyubomirsky - Web page: https://patentgrep.com/patent/US9438460B2 ## CPC - H04L 27/2633: {using partial FFTs} - H04B 10/50: Transmitters - H04B 10/541: {Digital intensity or amplitude modulation} - H04B 10/612: {for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK} - H04B 10/616: {Details of the electronic signal processing in coherent optical receivers} - H04L 27/2636: {with FFT or DFT modulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] transmitter or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]} - H04L 27/3411: {reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set} - H04L 27/362: {Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated (H04L27/366 takes precedence)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04B: TRANSMISSION ## Abstract A method of transmitting data may include converting a stream of serial data bits into a set of parallel quadrature amplitude modulation (QAM) symbols. The method may additionally include applying a partial discrete Fourier transform-spread technique to transform a block of low-frequency subcarriers into a single-carrier QAM signal. The single-carrier QAM signal may bear information of a first subset of QAM symbols from the set of parallel QAM symbols. The method may additionally include transforming one or more remaining QAM symbols to form one or more subcarriers. Each of the one or more subcarriers may bear information of a corresponding QAM symbol from the one or more remaining QAM symbols. The method may additionally include generating a hybrid signal that includes the single-carrier QAM signal and the one or more subcarriers. The method may additionally include transmitting the hybrid signal. ## Claims ### Claim 1 A method comprising: converting a first stream of serial data bits into a set of parallel quadrature amplitude modulation (QAM) symbols; applying a partial discrete Fourier transform-spread (DFT-S) technique to transform a first subset of QAM symbols from the set of parallel QAM symbols into a single carrier QAM signal; transforming one or more remaining QAM symbols from the set of parallel QAM symbols to form one or more high-frequency subcarrier signals, wherein each of the one or more high frequency subcarrier signals bears information of a corresponding QAM symbol from the one or more remaining QAM symbols; generating a hybrid signal that includes the single-carrier QAM signal and the one or more high frequency subcarrier signals; and transmitting the hybrid signal. ### Claim 2 (depends on 1) The method of claim 1, wherein applying the partial DFT-S technique to transform the first subset of QAM symbols into the single-carrier QAM signal comprises: performing a discrete Fourier transform (DFT) on the first subset of QAM symbols to generate a DFT output; pre-equalizing the DFT output to generate a pre-equalized output; and performing an inverse discrete Fourier transform on the pre-equalized output to generate the single-carrier QAM signal. ### Claim 3 (depends on 2) The method of claim 2, wherein pre-equalizing the DFT output to generate the pre-equalized output comprises multiplying the DFT output with real numbers that correspond to a pre-equalization transfer function. ### Claim 4 (depends on 1) The method of claim 1, wherein transforming the one or more remaining QAM symbols to form the one or more high-frequency subcarrier signals comprises performing an inverse discrete Fourier transform on the one or more remaining QAM symbols to generate the one or more high-frequency subcarrier signals. ### Claim 5 (depends on 1) The method of claim 1, wherein transmitting the hybrid signal comprises: converting the hybrid signal to a second stream of serial data bits; adding a cyclic prefix to the second stream of serial data bits; converting the second stream of serial data bits to an analog signal; and generating, based on the analog signal, a transmit laser beam configured to transmit through an optical channel. ### Claim 6 (depends on 1) The method of claim 1, wherein: the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and each of the one or more high-frequency subcarrier signals has a corresponding frequency higher than a frequency of any of the low-frequency subcarrier signals. ### Claim 7 (depends on 1) The method of claim 1, wherein the single-carrier QAM signal is orthogonal to each of the one or more high-frequency subcarrier signals. ### Claim 8 (depends on 1) The method of claim 1, wherein: the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and the single-carrier QAM signal occupies a frequency bandwidth associated with the low-frequency subcarrier signals. ### Claim 9 (depends on 1) The method of claim 1, wherein converting the first stream of serial data bits into the set of parallel QAM symbols comprises: converting the first stream of serial data bits into parallel streams of data bits; and converting corresponding data bits in each parallel stream to a corresponding QAM symbol based on a corresponding QAM constellation. ### Claim 10 (depends on 1) The method of claim 1, wherein: the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and the low-frequency subcarrier signals and the one or more high frequency subcarrier signals include discrete multitone subcarrier signals. ### Claim 11 A system comprising: a serial-to-parallel quadrature amplitude modulation (QAM) module configured to receive a first stream of serial data bits and to convert the first stream of serial data bits into a set of parallel QAM symbols; and a partial discrete Fourier transform-spread (DFT-S) module communicatively coupled to the serial-to-parallel QAM module, the partial DFT-S module configured to apply a partial DFT-S technique to transform a first subset of QAM symbols from the set of parallel QAM symbols into a single-carrier QAM signal, wherein: the partial DFT-S module includes a discrete Fourier transform (DFT) module and an inverse discrete Fourier transform (IDFT) module; the IDFT module is configured to transform one or more remaining QAM symbols from the set of parallel QAM symbols to form one or more high-frequency subcarrier signals, wherein each of the one or more high-frequency subcarrier signals bears information of a corresponding QAM symbol from the one or more remaining QAM symbols; and the IDFT module is configured to generate a hybrid signal that includes the single-carrier QAM signal and the one or more high-frequency subcarrier signals, wherein the hybrid signal is configured to transmit to a receiver. ### Claim 12 (depends on 11) The system of claim 11, wherein: the partial DFT-S module further includes a pre-equalizer; the DFT module is configured to perform a discrete Fourier transform on the first subset of QAM symbols to generate a DFT output; the pre-equalizer is configured to pre-equalize the DFT output to generate a pre-equalized output; and the IDFT module is configured to perform an inverse discrete Fourier transform on the pre-equalized output to generate the single-carrier QAM signal. ### Claim 13 (depends on 12) The system of claim 12, wherein the pre-equalizer is configured to pre-equalize the DFT output to generate the pre-equalized output by multiplying the DFT output with real numbers that correspond to a pre-equalization transfer function. ### Claim 14 (depends on 11) The system of claim 11, wherein the IDFT module is configured to transform the one or more remaining QAM symbols to form the one or more high-frequency subcarrier signals by performing an inverse discrete Fourier transform on the one or more remaining QAM symbols to generate the one or more high-frequency subcarrier signals. ### Claim 15 (depends on 11) The system of claim 11, further comprising: a parallel-to-serial module configured to convert the hybrid signal to a second stream of serial data bits and to add a cyclic prefix to the second stream of serial data bits; and a digital-to-analog converter configured to convert the second stream of serial data bits to an analog signal, wherein the analog signal is used to generate a transmit laser beam configured to transmit through an optical channel. ### Claim 16 (depends on 11) The system of claim 11, wherein: the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and each of the one or more high-frequency subcarrier signals has a corresponding frequency higher than a frequency of any of the low-frequency subcarrier signals. ### Claim 17 (depends on 11) The system of claim 11, wherein the single-carrier QAM signal is orthogonal to each of the one or more high-frequency subcarrier signals. ### Claim 18 (depends on 11) The system of claim 11, wherein: the first subset of QAM symbols would become low-frequency subcarrier signals absent application of the partial DFT-S technique to the first subset of QAM symbols; and the single-carrier QAM signal occupies a frequency bandwidth associated with the low-frequency subcarrier signals. ### Claim 19 (depends on 11) The system of claim 11, wherein the serial-to-parallel QAM module is configured to convert the first stream of serial data bits into the set of parallel QAM symbols by: converting the first stream of serial data bits into parallel streams of data bits; and converting corresponding data bits in each parallel stream to a corresponding QAM symbol based on a corresponding QAM constellation. ### Claim 20 A method comprising: receiving a first set of parallel pulse amplitude modulation (PAM) symbols or quadrature amplitude modulation (QAM) symbols to be transmitted in a low frequency band of a composite channel that includes a digital-to-analog converter (DAC), a driver amplifier, an electro-optical converter, an opto-electrical converter, and an analog-to-digital converter (ADC); receiving a second set of parallel QAM symbols to be transmitted in a high frequency band of the composite channel; transforming the first set of parallel PAM or QAM symbols into a single-carrier PAM or QAM signal that occupies the low frequency band, wherein the single-carrier PAM or QAM signal bears information of the first set of parallel PAM or QAM symbols; transforming the second set of parallel QAM symbols into a discrete multitone (DMT) signal that occupies the high frequency band, wherein the DMT signal bears information of the second set of parallel QAM symbols; generating a hybrid signal that includes the single-carrier PAM or QAM signal and the DMT signal; and transmitting the hybrid signal. ### Claim 21 (depends on 20) The method of claim 20, wherein: the first set of parallel PAM or QAM symbols comprises parallel PAM symbols; the single-carrier PAM or QAM signal comprises the single-carrier PAM signal; transforming the first set of parallel PAM symbols into the single-carrier PAM signal comprises: performing a fast Fourier transform (FFT) on the first set of parallel PAM symbols to generate an FFT output; pre-equalizing and power-scaling the FFT output to generate a pre-equalized output; and performing an inverse FFT (IFFT) on the pre-equalized and power-scaled output to generate the single-carrier PAM signal; and transforming the second set of parallel QAM symbols into the DMT signal comprises performing an IFFT on the second set of parallel QAM symbols to generate one or more subcarrier signals that make up the DMT signal. ### Claim 22 (depends on 21) The method of claim 21, wherein the single-carrier PAM signal is orthogonal to each of the one or more subcarrier signals. ### Claim 23 (depends on 21) The method of claim 21, wherein the low frequency band and the high frequency band of the composite channel partially overlap.