130 results about "Inverse fft" patented technology

A system for efficiently filtering interfering signals in a front end of a GPS receiver is disclosed. Such interfering signals can emanate from friendly, as well as unfriendly, sources. One embodiment includes a GPS receiver with a space-time adaptive processing (STAP) filter. At least a portion of the interfering signals are removed by applying weights to the inputs. One embodiment adaptively calculates and applies the weights by Fourier Transform convolution and Fourier Transform correlation. The Fourier Transform can be computed via a Fast Fourier Transform (FFT). This approach advantageously reduces computational complexity to practical levels. Another embodiment utilizes redundancy in the covariance matrix to further reduce computational complexity. In another embodiment, an improved FFT and an improved Inverse FFT further reduce computational complexity and improve speed. Advantageously, embodiments can efficiently null a relatively large number of jammers at a relatively low cost and with relatively low operating power.

A multi-path equalization system for orthogonal frequency division multiplexing communication (OFDM) system includes a first estimator for estimating the channel characteristic using pilot signal. A divider is coupled to the estimator for dividing each sub-carrier with the channel characteristic to get the equalization to the data signal. A de-mapper uses the phase and amplitude correction of the channel estimate to recover the data signals. An improved channel estimation is provided by a repeat channel estimation feedback loop that includes the de-mapper a multiplier, an inverse fast Fourier transform (IFFT), a low pass filter and a fast Fourier transform (FFT). The improved channel estimation is obtained by multiplying at the multiplier the conjugate of the de-mapped data to the input sub-carriers and applying inverse FFT, low pass filtering and FFT to get the new channel estimate. Each sub-carrier is divided with new channel characteristic to get new equalization to the data signal. The channel estimation is repeated until there is convergence. The output is provided after the de-mapper. In the case of channel decoding to improve performance a Viterbi decoder and convolutional encoder is coupled in loop between the de-mapper and the multiplier.

Several techniques are disclosed for isolating either heart or breath rate data from a photoplethysmograph, which is a time domain signal such as from a pulse oximeter. The techniques involve the use of filtering in the frequency domain, after a Fast Fourier Transform (FFT) has been conducted on a given photoplethysmograph also references as a given set of discrete time-domain data. The filtering may be applied to an identified fundamental frequency and one or more harmonics for heart related parameters. The filter may be truncated to the frequency data set and further applied multiple times to improve roll off. After filtering, an Inverse FFT (IFFT) is used to reconstruct the time-domain signal, except with undesirable frequency content eliminated or reduced. Calculation or measurement of parameters is then conducted on this reconstructed time-domain signal.

A spectral notch modulation technique for encoding information in a signal involves transforming the signal into the frequency domain via a fast Fourier transform (FFT) of length N, such that the signal is represented by N frequency bins, selectively nulling M of the N frequency bins, where nulled combinations of M frequency bins respectively correspond to encoded information bits, transforming the selectively nulled signal to the time domain via an inverse FFT, and transmitting the selectively nulled signal. At the receiving end, the signal is demodulated to recover the encoded information by transforming the signal into the frequency domain via a fast Fourier transform (FFT) of length N, identifying the set of M nulled frequency bins among the N frequency bins, and converting the set of M nulled frequency bins to corresponding information bits.

The invention discloses a quantum secret key distribution privacy amplification method supporting large-scale dynamic changes. The method includes the steps of firstly, conducting initialization, wherein the optimal operation scale m of an FFT module is calculated according to the actual running parameters of a quantum secret key distribution system when the privacy amplification method is started, and the initialization scale is an FFT operation and inverse FFT operation module of m; secondly, normalizing data, wherein the final security secret key length r is calculated according to the detector counting rate Q mu of the quantum secret key distribution system, the quantum bit error rate E mu, the corrected weak security secret key length n and the security parameter s of the quantum secret key distribution system, and normalizing an initial secret key string and a Toeplitz matrix according to the parameter m, the parameter n and the parameter r; thirdly, conducting data operation, wherein the operation process of the Toeplitz matrix and the initial secret key string is operated through the FFT technology, the first r items of the calculation result are taken to form a result vector, namely, the final security secrete key. The method has the advantages of being high in flexibility, better in processing performance, and the like.

The invention provides a method for removing an accompaniment from a song. The method comprises the steps that an accompaniment audio signal and a song audio signal are obtained; FFT is carried out on the song audio signal and the accompaniment audio signal to obtain a song audio signal amplitude spectrum, an accompaniment audio signal amplitude spectrum and the phase of the song audio signal; the accompaniment audio signal amplitude spectrum is enhanced; the enhanced accompaniment audio signal amplitude spectrum is subtracted from the song audio signal amplitude spectrum to obtain a result, inverse FFT is carried out with the combination of the phase and the result, and therefore an audio signal without the accompaniment is obtained. The invention further provides a device for removing the accompaniment from the song. According to the method and device for removing the accompaniment from the song, the degree of purity of the song obtained after separation is accomplished can be improved, separation execution efficiency is high, and an algorithm is simple and easy to implement.

Method and system for tolerating impulsive burst noise in pilot based OFDM systems, especially using DVB-T standard. The method contains following steps: 1) recognition of the impulse position and possibly length in the time domain symbol, 2) blanking of those samples of the symbol where significant amount of impulse noise is present, 3) calculating the first estimate of the received signal from the blanked symbol, 4) using a prior information (guard band carriers, pilot carriers) an estimate of the blanked symbol is calculated using inverse FFT on the differences of the observed carrier values from the known values in the frequency domain, 5) correction values for the frequency domain carriers are derived taking the FFT of the restored time domain samples, 6) finally the corrected estimate of the received symbol is derived by summing the correction values of step 5 to the first estimate of carriers derived in step 3. The method allows correction of relatively long bursts of impulse noise with minor degradation. The method provides considerably reliable data reception in broadcast systems.

In accordance with the present invention, the system and method removes interfering signals from a communications signal and includes a Fast Fourier Transform (FFT) circuit for taking the FFT of a received signal and segmenting the signal into segments. A frequency shifting circuit can shift each segment in frequency to place an interfering signal within a single FFT band to be later substantially nulled. An inverse FFT circuit can place the segments of signals back within the time domain.

Several techniques are disclosed for isolating either heart or breath rate data from a photoplethysmograph, which is a time domain signal such as from a pulse oximeter. The techniques involve the use of filtering in the frequency domain, after a Fast Fourier Transform (FFT) has been conducted on a given photoplethysmograph also references as a given set of discrete time-domain data. The filtering may be applied to an identified fundamental frequency and one or more harmonics for heart related parameters. The filter may be truncated to the frequency data set and further applied multiple times to improve roll off. After filtering, an Inverse FFT (IFFT) is used to reconstruct the time-domain signal, except with undesirable frequency content eliminated or reduced. Calculation or measurement of parameters is then conducted on this reconstructed time-domain signal.

The invention relates to a 1553B digital communication device. In order to expand the communication capacity, expand the data-transfer capacity and enhance the communication properties such as property in resisting interference and the like in a 1553B bus, the invention provides the technical scheme: a receiving method for bandwidth expansion of a 1553B communication bus. The following method sub-modules: an analog front end (AFE), a frame detecting module, a symbol synchronizing module, an inverse FFT (fast Fourier transformation) module, a block floating point module, a channel balancing module, a frequency offset synchronizing module, a QAM (quadrature amplitude modulation) de-mapping module of a dynamic threshold and a base-band processing module are provided in the receiving method, wherein the AFE is used for performing signal amplification and AD (analog-to-digital) conversion, sampling an analog signal into a digital signal and transmitting; the frame detecting module is used for detecting the access situation of a frame; the IFFT module is used for processing a base-band signal. The method provided by the invention is mainly used for 1553B digital communication.

The invention provides a method for improving the frequency domain anti-interference performance of a direct-spread/frequency-hopping mixed spread frequency system and aims to solve the problems of influence on the anti-interference performance caused by discontinuous phase and poor suppression performance of a fast time-varying interference signal. The method is implemented by adopting the technical scheme that: a distance measurement and speed measurement receiver having a frequency domain anti-interference function consists of a de-hopping module, a band-pass filter, a frequency domain anti-interference module, a demodulation module, a de-spreading module and a distance measurement and speed measurement module, which are sequentially connected on the same line in series, a frequency-hopping tracking module which is bridged on the de-hopping module and the frequency domain anti-interference module in parallel, and a carrier and code tracking module which is bridged on the demodulation module and the de-spreading module in parallel; and the frequency domain anti-interference module is divided into a windowing sub-module which is in frequency-hopping synchronization with the frequency-hopping tracking module, a fast Fourier transformation (FFT) sub-module, an interference suppression processing sub-module and an inverse FFT (IFFT) sub-module. The method is applicable to suppression of a narrow-band interference signal.

The invention discloses an FPGA-based inter-channel amplitude and phase error characteristic frequency domain windowing estimation method. The problem of reduced inter-channel coherence, which is caused by inconsistent amplitude and phase characteristics of multiple channels of the existing radar system, is solved. The method comprises the steps that (1) channel data are input; (2) time-frequency conversion is carried out on channel signals; (3) spectrum alignment is carried out on the spectrums of the channel signals; (4) FFT conversion is carried out on a spectrum alignment result; (5) windowing is carried out on the FFT conversion result of spectrum alignment; (6) and inverse FFT operation is carried out the windowed data to acquire inter-channel amplitude and phase error characteristic estimation. According to the invention, fast and efficient functions of FFT time-frequency conversion and time sequence logic control of FPGA are fully used; a high-quality amplitude and phase error characteristic estimation result can be acquired under the condition of large spurious noise; the influence of spurious noise on the estimation result is reduced; and the method can be applied to a two-channel and/or multi-channel radar real-time signal processing system.

The invention relates to a method for generating a machine carried interference synthetic aperture radar (InSAR) original echo wave. The method comprises: step 1: implementing position method of Fourier transformation (FFT) on equivalent back scattering coefficientª†1ú¼2(xú¼ª†), and then multiplying a phase function with defocus item and reducing and enlarging factor P1ú¢exp{j(ªš2/alphaª†0ú®ª†ú½j[ª©1,2(ªš)/4B]ª†2}; stp2: implementing distance FFT on the result form step 1, then multiplying a phase function with reducing and enlarging factor P2ú¢exp{j(1-ª©1,2(ªš))/ª©1,2(ªš)BªÃ}; step 3: implementing distance inverse FFT on the result from the step 2, then multiplying a phase function with reducing and enlarging factor P3ú¢exp{-Jú¿1/4Bú®ª†2}; step 4: implementing distance inverse FFT on the result from the step 3, then multiplying a phase function with space constant exciting response function, distance horizontal shift factor and the reducing and enlarging factor P4ú¢Gú¿ªšú¼ªÃú¼ª†0ú®exp{-jªÃª†s1,2ú½j[ª©1,2(ªš)-1]BªÃ2}; step 5: implementing two dimensional inverse FFT on the result from step 4 and getting the needed original echo wave data h1ú¼2(xíõú¼ríõ).

The invention discloses an arrival direction estimation method based on minimum mutual entropy spectrum analysis. The method comprises steps that: a signal is emitted by an emission energy transducer; echo of an emitted sound signal is received by a reception hydrophone array; modeling of a plane wave model is carried out for the received echo signal, and processing is carried out by utilizing the minimum mutual entropy spectrum estimation method to acquired a space power spectrum estimation value; analysis on the space power spectrum estimation value is carried out, and a corresponding abscissa of the peak value is an estimation angle of the object. According to the arrival direction estimation method, through one-time data sampling employing the array with relatively a few array elements, a spectrum analysis result with high resolution can be acquired. A cepstrum method is further employed, a convergence speed of a minimum mutual entropy spectrum analysis algorithm can be improved through reverse FFT transformation. Compared with a routine space spectrum estimation method, the arrival direction estimation method provided by the invention has advantages of higher resolution and smaller operand, and real-time processing on the array signal can be carried out. The algorithm is independent of the pre-estimated source number, and relatively good tolerance, relatively high resolution and an extremely low sidelobe level are realized.

The invention relates to a voice noise reduction method and device based on signal autocorrelation. The method comprises steps that 1), a noise-containing simulation voice signal is acquired through avoice reception module; 2), the simulation signal is converted by an A/D conversion module into a digital signal; 3), the digital signal is enframed through a voice enframing module; 4), autocorrelation operation of the signals after enframing is carried out through an autocorrelation de-noising module; 5), FFT analysis on an autocorrelation function of each noise-containing signal in a time-delay domain is carried out through an FFT analysis module; 6), threshold de-noising processing for FFT transformation is carried out through a threshold noise reduction module; 7), re-sampling of a frequency domain autocorrelation signal is carried out through a re-sampling and phase matching module, and phase matching of the frequency domain autocorrelation signal and the noise-containing signals iscarried out; 8), inverse FFT transformation is carried out by an inverse FFT transformation module through utilizing a frequency domain amplitude after processing and the phase, and the signals are returned to the time domain; and 9), recombination of each signal after de-noising is carried out through a frame recombination module to acquire voice signals after de-noising. The method is advantaged in that language sharpness can be substantially improved under the -20dB signal to noise ratio strong noise environment.