449 results about "Inverse discrete fourier transform" patented technology

Techniques for calculating the system characteristic of the adaptive filtering used for equalization and echo-suppression in a digital communications receiver, such as one used for receiving over-the-air broadcast digital television signal, are described. In these techniques, the system characteristic of the adaptive filtering is calculated from the discrete Fourier transform of successive portions of the input signal supplied to the adaptive filtering and from the discrete Fourier transform of corresponding portions of the transmitted signal, as estimated in the receiver. Receivers for implementing these techniques in various ways are also disclosed.

The invention discloses a large-scale MIMO channel state information feedback method based on FCFNN, and mainly aims to solve the problems of overlarge technical feedback overhead and poor channel feedback quality in the prior art. According to the scheme, the method comprises the following steps: on a user side, performing two-dimensional discrete Fourier transform and truncation processing on adownlink channel matrix of a space-frequency domain to obtain a channel matrix H; building a channel feedback model including an encoder and a decoder, and training the channel feedback model; placingthe trained encoder and decoder on the user side and a base station side respectively; inputting the channel matrix H into the encoder to obtain a compressed vector h on the user side, and feeding back the compressed vector to a base station; inputting the h into the decoder to obtain a rebuilt channel matrix by the base station; and performing zero-padding and two-dimension inverse discrete Fourier transform on the rebuilt channel matrix to obtain an original space-frequency domain channel matrix. Through adoption of the large-scale MIMO channel state information feedback method, feedback overhead of the channel state information is lowered, and the channel rebuilding quality is improved remarkably. The large-scale MIMO channel state information feedback method can be applied to a large-scale multi-input and multi-output communication system under a frequency division duplex mode.

Disclosed is a coded orthogonal frequency-division multiplexing (OFDM) system and method for reducing a peak-to-average power ratio (PAPR). The system and method include a modulator configured to modulate (e.g., using quadrature amplitude modulation (QAM)) coded bits into symbols. The system and method also include an inverse discrete fourier transform (IDFT) module to perform an IDFT on the symbols to produce an OFDM signal. The system and method measure the PAPR of the OFDM signal and transmit the signal to a receiver if the PAPR of the signal is less than a threshold PAPR.

Disclosed are a method and a system for in frequency domain optical coherent tomography imaging. The method employs sine phase modulation to recreate complex amplitude of the coherent frequency interference signal; and then performs inverse Fourier transform to the complex amplitude to get the tomographic images of the tested objects and eliminate the complex conjugate image, direct current background and self-coherent noise three spurious images, which enlarges the imaging depth of frequency domain optical coherent tomography imaging is two times larger than the original depth and realizes full depth finding of frequency domain optical coherent tomography imaging.

A method and apparatus in a wireless communication system comprising at least one transmitter provided with at least two antennas and at least one receiving unit provided with at least one antenna and wherein training sequences are transmitted from the at least two antennas of the at least one transmitter to the at least one antenna of the at least one receiving unit. Characterized in that first, prior to the transmission, a training sequence P(k) is Inverse Discrete Fourier Transformed to a sequence p(n). Second, for each antenna branch the Inverse Discrete Fourier Transformed sequence p(n) is cyclically rotated by a predetermined step, said predetermined step being p(n) is cyclically rotated by a predetermined step, said predetermined step being different for each antenna branch to generate cyclically rotated training sequences p(n−n1), p(n−n2). Third, the cyclically rotated training sequences p(n−n1), p(n−n2) are transmitted concurrently from said at least two antennas to the receiving unit. Fourth, at the receiving unit receiving the cyclically rotated training sequences, the received sequences being a superposition of transmitted training sequences, each individually affected by the propagation medium, are used to provide channel impulse response estimates for the transmission from respective antenna.

The taps of an equalizer are used as inputs to a discrete Fourier transform (DFT). Certain spectral components are extracted from the DFT and used to estimate the frequency difference. The frequency difference estimate is filtered using a phase locked loop and used to adjust one clock to synchronize the transmit and receive clocks.

The invention provides a phase difference measuring method based on improved windowing discrete Fourier transform. The phase difference measuring method includes the first step of collecting two periodic signals to be measured, the second step of analyzing the collected periodic signals to digital signals, the third step of carrying out windowing processing on the digital signals by constructing a 4-step Blackman-Harris window, and carrying out FFT spectral analysis on the signals subjected to windowing processing to obtain signal frequency spectrums, extracting fundamental wave parameters and respectively calculating initial phase angles of the periodic signals to be measured, and the fourth step of correcting phase positions of useful frequency spectrums according to a discrete spectrum correction method so as to calculate the phase differences of the periodic signals to be measured. The phase difference measuring method can effectively solve the problems that a time domain of a DFT algorithm is cut off, the introduced spectrums are revealed, and spectral analysis has bigger errors caused by the picket fence effect, overcomes the defects of spectrum leakage and lower frequency resolution in an interpolation method, improves the frequency resolution, and finally achieves the high-precision measurement of the phase differences.

The current invention provides a DSP which accommodates multiple current X-DSL protocols and is further configurable to support future protocols. The DSP is implemented with shared and dedicated hardware components on both the transmit and receive paths. The DSP implements both the discrete Fourier transform (DFT) and inverse discrete Fourier transform (IDFT) portions across a wide range of sample sizes and X-DSL protocols. Multiple channels, each with varying ones of the X-DSL protocols can be handled in the same session. The DSP offers the speed associated with hardware implementation of the transforms and the flexibility of a software only implementation. Traffic flow is regulated in the chip using a packet based schema in which each packet is associated with a specific channel of upstream and downstream data. Header and control information in each packet is used to govern the processing of each packet as it moves along either the transmit path or receive path. The DSP of the current invention may advantageously be utilized in fields other than communications, such as: medical and other imaging, seismic analysis, radar and other military applications, pattern recognition, signal processing etc. The present invention provides a signal processing architecture that supports scalability of CO/DLC/ONU resources, and allows a significantly more flexible hardware response to the evolving X-DSL standards without over committing of hardware resources. As standards evolve hardware may be reconfigured to support the new standards.

The invention discloses a generation method for preamble symbols in a physical frame. The generation method comprises the steps of: carrying out inverse discrete Fourier transform on a frequency domain OFDM symbol with a preset length to obtain a time domain OFDM symbol; determining a cyclic prefix length; intercepting a time domain OFDM symbol with the cyclic prefix length from the time domain OFDM symbol to serve as a cyclic prefix; generating a modulation signal based on the intercepted time domain OFDM symbol with the cyclic prefix length; and generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol and the modulation signal. The technical scheme provided by the invention solves the problems of the current DVB_T2 standard and other standards that a DVB_T2 time domain structure has no cyclic prefix and is not suitable for coherent detection, and the failure probability of the preamble symbol detected by adopting a low complexity receiving algorithm in a complex frequency selectivity fading channel is high.

The invention discloses a method and equipment for generating a preamble sequence. The method comprises the following steps of: generating a frequency domain ZC sequence; determining a format and a time domain sampling point number of a target preamble sequence; performing inverse discrete Fourier transform of a corresponding preset small point number on the frequency domain ZC sequence according to the time domain sampling point number of the target preamble sequence to obtain a time domain sequence; performing interpolation on the time domain sequence, and converting the length of the time domain sequence into a length corresponding to the time domain sampling point number of the target preamble sequence; acquiring a phase rotation angle according to an initial position of the preset frequency domain resource; multiplying the time domain sequence with the converted length and the phase rotation angle, and performing phase conversion; performing corresponding subsequent processing on the time domain sequence with the converted phase according to the format of the target preamble sequence; and adding a cyclic prefix to the subsequent processed time domain sequence. The preamble sequence generating method disclosed by the embodiment of the invention avoids the occurrence of Fourier transform of a large point number so as to improve the operation speed, reduce the calculation quantity, improve the generating speed and reduce the power consumption and the circuit area at the same time.

The invention provides an adaptive modulation-demodulation method base on fractional order Fourier transform, aiming at reducing influence caused by feedback time delay specific to an MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) adaptive modulation system which has feedback time delay, and enabling the system to have better performance in a fast time-varying channel. The method has the technical scheme that inverse discrete fractional order Fourier transform is used to replace inverse discrete Fourier transform for carrying out subcarrier modulation at a transmitting terminal, discrete fractional order Fourier transform is used to replace discrete Fourier transform for carrying out subcarrier demodulation at a receiving terminal, the optimal fractional order Fourier transform order selection is carried out by channel estimation information fed back to the transmitting terminal by the receiving terminal, the deviation between the current channel state information and the feedback channel state information is reduced and the performance of the system having time delay is enhanced.

The invention relates to a method for modulating sub-carrier symbols to an intermediate-frequency OFDM signal having even and odd samples, including following steps:

• • transforming a number N of the sub-carrier symbols to pre-processed sub-carrier symbols;
  • performing a complex inverse discrete Fourier transformation (IDFT) on the pre-processed sub-carrier symbols to generate complex output symbols; and
  • transforming the complex output symbols to the intermediate-frequency OFDM signal,

wherein the sub-carrier symbols are transformed so that the even and odd samples of the intermediate-frequency OFDM signal are given by real and imaginary parts of the complex output symbols.

The invention discloses an OFDM channel estimation method for de-noising which is based on wavelet unbiased risk threshold value, which relates to the technical field of communication, the purpose of the invention is that the problem that an LS method is easy to be influenced by noise under the condition without channel information is effectively solved. The realizing process of the method comprises first, obtaining channel frequency response which contains noise according to the LS channel estimation method which is on the basis of an OFDM system which is based on pilot frequency, second, doing inverse discrete Fourier transform for the channel frequency response which is obtained and to get channel time-domain impulse response which contains noise, third, de-noising the channel time-domain impulse response the method for de-noising which is based on wavelet unbiased risk threshold value, and getting channel time-domain impulse response after de-noising, fourth, doing inverse discrete Fourier transform for the channel time-domain impulse response after de-noising, and getting frequency domain response of channel, and compensating the received signals by the channel time-domain impulse response after de-noising. The method can be used in OFDM channel estimation techniques under various multi-path channels.

The invention discloses a fast calculation method of discrete Fourier transformation (DFT)/inverse discrete Fourier transform (IDFT). The rapid calculation method comprises the following steps of: carrying out zero fill on a bit sequence to be transformed to enable the sequence length after the zero fill to accord with the processing range of a fast Fourier transform (FFT)/inverse fast Fourier transform (IFFT) processor; carrying out FFT/IFFT calculation on the sequence after zero fill by utilizing the FFT/IFFT processor, and resampling time domain/frequency domain of an FFT/IFFT calculation result sequence according to a sampling position determined by the sequence lengths before and after the zero fill; and outputting the resampling result as a DFT/ IDFT result sequence. The invention also discloses a fast calculation device of DFT/IDFT. By adopting the invention, the calculation complexity of DFT/IDFT can be reduced, and the calculation speed can be improved.

A Discrete Fourier Transform watermark for use with digital images/video. A Y component of a Y, U(Cb), V(Cr) digital data stream representing color components of digital video is extracted as the digital data for embedding the watermark. The digital data is then scaled to a standard size. A Discrete Fourier Transform (DFT) is performed on the digital data, and a magnitude domain of the Discrete Fourier Transform is computed. The watermark is embedded into selected frequency bands of the computed magnitude domain of the Discrete Fourier Transform, thereby creating a watermarked magnitude domain. The selected frequency bands comprise one or more middle frequency bands, and the middle frequency bands comprise a band of circular rings of the magnitude domain. An inverse Discrete Fourier Transform is performed on the watermarked magnitude domain to reconstruct the digital data with the embedded watermark.

The invention provides a constant envelope orthogonal frequency division multiplexing modulation method which is based on sine/cosine mapping and which is applied in the field of broadband wireless communication. During signal modulation, the method includes performing inverse discrete Fourier transform (IDFT) for a group of complex signals; arraying transformed data to be two groups of sequences of real numbers and performing linear amplitude-limited mapping; after being subjected to linear amplitude limiting, mapping sequences of the real numbers into sine or cosine values of unit circle signals, and allowing a signal receiving end to recover to send messages through linear calculation of two groups of discrete Fourier transform (DFT). During signal demodulation, the method includes performing two groups of discrete Fourier transform, combining two groups of data processed through discrete Fourier transform, and obtaining complex signals for bit demodulation. According to the constant envelope orthogonal frequency division multiplexing modulation method, transmitting power of an amplifier can be utilized completely against frequency selective fading influence of broadband transmission channels, and the problem of the need to reduce system complexity in broadband communication is solved.

The invention discloses a CHIRP-OFDM (orthogonal frequency division multiplexing) system frequency domain diversity receiving method which comprises the following steps; at an emitting end, modulating data after serial-parallel conversion to a frequency spectrum, carrying out inverse discrete Fourier transform so as to obtain a group of time domain signals, carrying out spread spectrum modulation on the time domain signals by taking chirp signals as carrier waves, and determining a frequency modulation slope; at a receiving end, removing cyclic prefixes of received serial signals, carrying out despread modulation on the signals, and conjugating the frequency modulation slope and the emitting end in a same way of taking determined chirp signals as carrier waves; carrying out the inverse discrete Fourier transform to obtain a frequency domain frequency spectrum, carrying out phase compensation on each spectrum line of multi-path signals, and overlying with each direct signal spectrum line, so as to enable all spectrum lines to be added in a same-phase way, and realize diversity reception and further recover signal sending; and carrying out digital demodulation so as to obtain data output. The method can effectively overcome frequency selective fading in channels and improves the system performance.

The present invention relates to a system, method and program for speech recognition. In an embodiment of the invention a method for processing a speech signal consists of receiving a power spectrum of a speech signal and generating a log power spectrum signal of the power spectrum. The method further consists of performing discrete cosine transformation on the log power spectrum signal and cutting off cepstrum upper and lower terms of the discrete cosine transformed signal. The method further consists of performing inverse discrete cosine transformation on the signal from which the cepstrum upper and lower terms are cut off. The method further consists of converting the inverse discrete cosine transformed signal so as to bring the signal back to a power spectrum domain and filtering the power spectrum of the speech signal by using, as a filter, the signal which is brought back to the power spectrum domain.

A method of transmitting data in a multi-carrier communication system is disclosed. More specifically, the method includes mapping at least one data symbol to at least one subcarrier of a first frequency domain and at least one data symbol to at least one subcarrier of a second frequency domain, wherein the first frequency domain and the second frequency domain are mutually exclusive and the at least one data symbol mapped to the at least one subcarrier of the second frequency domain is multiplied by a spreading code, transforming the at least one data symbol mapped to the first frequency domain and the at least one data symbol mapped to the second frequency domain by an inverse discrete Fourier transform (IDFT) module, and transmitting the transformed data symbols to a receiving end.

A Fourier transform processor utilizing discrete circuits each of which is configurable for processing a wide range of sample sizes. A single pipeline supports multiplexed bi-directional transformations between for example the time and frequency domains. In an embodiment of the invention the Fourier Transform processor may be implemented as part of a digital signal processor (DSP). In this embodiment the DSP may implement both the discrete Fourier transform (DFT) and inverse discrete Fourier transform (IDFT) across a wide range of sample sizes and X-DSL protocols. Multiple channels, each with varying ones of the X-DSL protocols can be handled in the same session.

The invention relates to an upstream channel estimation method and an upstream channel estimation system suitable for an LTE (Long Term Evolution)-Advanced system. The upstream channel estimation method comprises the steps of extracting pilot frequency subcarrier information on a receiving antenna, and carrying out conjugate multiplying on the pilot frequency subcarrier information and a local pilot frequency of a first layer to obtain a frequency domain channel coefficient of all transport layers subjected to aliasing; according to the length of a subcarrier, adding a virtual subcarrier with a corresponding length at the tail of a primary channel coefficient; carrying out IDFT (Inverse Discrete Fourier Transform) calculation, and transforming to a time domain; adding a window in the time domain, because dislocation of a time domain impulse response of each transport layer occurs on the time domain, separating time domain impulse responses of different transport layers, and carrying out time domain cyclic shift to obtain a time domain impulse response corresponding to each transport layer; and carrying out DFT (Discrete Fourier Transformation) calculation on the time domain impulse response of each transport layer, transforming to the frequency domain, and removing the virtual subcarrier at the tail to obtain a frequency domain equivalent channel estimation matrix of each transport layer corresponding to the receiving antenna. With the adoption of the upstream channel estimation method and the upstream channel estimation system, the channel estimation problem after MIMO (Multiple Input Multiple Output) is introduced into the LTE-A upstream can be effectively solved, and the channel estimation accuracy is also improved; and the method is also suitable for an LTE system.

The invention relates to the field of optical fiber communication, discloses a three-dimensional orthogonal frequency-division multiplexing data modulation method and a data demodulation method, and aims to solve the technical problem of incapability of lowering signal PAPR (Peak to Average Power Ratio) under the condition of not influencing other performances of a system in the prior art. The method comprises the following specific steps: performing three-dimensional data constellation points mapping on a bit sequence to be transmitted to obtain an orthogonal frequency-division multiplexing (OFDM) signal based on three-dimensional mapping; performing three-path overlapping on the real parts and imaginary parts of a plurality of time domain signals obtained after performing three-dimensional inverse discrete Fourier transform (3D-IDFT) on a three-dimensional OFDM symbol respectively through a three-dimensional CAP orthogonal filter, and combining to obtain final transmission time domain data; acquiring data to be transmitted through the time domain signal of a 3D-CAP-OFDM system and transmitting the data to be transmitted. By adopting the methods, the technical effect of effectively lowering the signal PAPR under the condition of no influencing the other performance of the communication system is achieved.