172 results about "Negative frequency" patented technology

A reduction in a peak-to-mean envelope power ratio of a multicarrier signal, represented as a time domain signal, is achieved by applying (76) an offset, indicative of a difference (74) between a mean signal level and a midpoint level of the time domain signal, to the time domain signal. Alternatively, constellation values of positive and negative frequency components are modified by differing functions to produce a modified data set. Preferably, the negative frequency components are set to a predetermined value (namely zero (124)) to provide an alternate coding scheme Once the multicarrier signal has been converted into a time domain representation, real and imaginary parts (126-128) of the modified data set that consequently only contain positive frequency components and zeros are compared with one another to identify (130) which of the real and imaginary parts has a lower peak-to-average signal ratio (134) for the time domain representation. Then, based upon which of the peak-to-average signal ratios is lowest (136), either the real and imaginary part of the time domain signal is selected for subsequent transmission (138).

Apparatus, methods and systems for compensating for an I / Q imbalance may include compensating for an imbalance between a first component of a data signal and a second component of the data signal. The data signal may be modulated by a carrier signal having a frequency error. The first component may be characterized by at least one parameter. The method may include receiving the data and carrier signals; selecting a value for the parameter such that the frequency domain energy at negative frequencies is reduced; and modifying at least one of the components based on the value.

A downconverter and upconverter are provided which can obtain a satisfactory image rejection ratio in a low-Intermediate Frequency (IF) scheme while reducing power consumption, and can improve Error Vector Magnitude (EVM) in a zero-IF scheme. A complex-coefficient transversal filter rejects one side of a positive or negative frequency, and converts a Radio Frequency (RF) signal to a complex RF signal configured by real and imaginary parts. A local oscillator outputs a complex local signal in which a set frequency is set as a center frequency. A full-complex mixer, connected to the complex-coefficient transversal filter and the local oscillator, perform a frequency conversion process by multiplying a complex signal output from the complex-coefficient transversal filter and the complex local signal output from the local oscillator, and outputs a complex signal of a frequency separated by the set frequency from a frequency of the RF signal.

A method and apparatus are disclosed for frequency offset estimation and interleaver synchronization, using periodic signature sequences, such as Barker codes. The periodic signature sequence is used for interleaver synchronization or frequency offset estimation or both. The periodic signature sequence is transmitted over a certain number of bins in both the upper and lower sides of the DAB signal. Since the signature sequences are assigned to specific bins known to the receiver, any shift of the correlated peak from the expected location due to frequency offset errors can be estimated by the frequency offset algorithm. If the Barker sequence is placed, for example, in the last column of the DAB interleaver, the location of the Barker sequence upon correlation of the received digital signal identifies the beginning of an interleaver block. A Barker sequence is transmitted over a signature frame every L data frames on each side band, where L is generally the number of OFDM frames that can fill the interleaver memory. If the maximum frequency offset is M, then the frequency offset algorithm utilizes a search window of size n+2M (between bins N−M through N+n+M), and attempts to maintain the Barker sequence in the center of the search window. At the receiver, the Barker sequence is mapped to the OFDM signature bins that do not belong to uncertainty regions (the group of bins that can fall out of the receiver processing range for maximum positive and negative frequency offset values). Thus, the Barker sequence bins are processed by the disclosed receiver as long as the frequency offset does not exceed the specified maximum frequency offset.

A low-interception speed measurement method comprises the steps that 1, frequency modulated continuous waves are generated, echo signals of an object with measured speed are received through an antenna, frequency mixing is carried out on the echo signals and B-path signals, and baseband signals are obtained; 2, the baseband signals are converted into digital signals, sampling and zero filling are carried out, FFT is carried out on the rising part of trace frequency, FFT is carried out on the reduction part of return trace frequency after conjugate taking, and frequency spectrums corresponding to positive / negative frequency modulation slopes are obtained; 3, the frequency spectrums corresponding to the positive / negative frequency modulation slopes are subtracted after module taking, the difference value is changed into an absolute value, and an objective frequency spectrum is obtained; 4, whether an object to be detected exists or not is determined, and if the object to be detected exists, the frequency corresponding to two peak value points within the frequency spectrum normalization range is found out in the objective frequency spectrum, and the speed of the object to be detected is worked out. The invention further discloses a low-interception speed measurement radar. The low-interception speed measurement method and radar have the advantage that the probability that the lower-measurement-speed radar is intercepted by a radar detector can be effectively reduced due to the adoption of the frequency modulated continuous waves with low-interception-probability wave forms.

A TFI-OFDM transmission system includes a data generator generating data having a speed corresponding to a transmission speed mode; a convolutional encoder convolutional-encoding the data, an interleaver bit-interleaving the encoded data, an OFDM modulator inputting a first data group into a positive frequency domain and a second data group into a negative frequency domain, executing an IFFT, and outputting OFDM symbols; a buffer temporarily storing the OFDM symbols in order to sequentially transmit the OFDM symbols in a time domain at least two times; and a frequency generator generating certain frequencies to transmit the OFDM symbols in a certain number of frequency bands corresponding to transmission channels.

The invention relates to the field of flow detection, and provides a Coriolis mass flow transmitter based on DSP, which comprises an amplifying filter circuit, an analog-to-digital converter 1, an analog-to-digital converter 2, a voltage reference source, a voltage follower, a current source, a difference amplifier, an analog-to-digital converter 3, a simulation driver module, a digital signal processor DSP minimum system, an expanding SRAM, an expanding EEPROM, a man-machine interface, 4-20mA current output and pulse output, a power module and a software. The simulation driver module stimulates a vibration exciter in the Coriolis mass flow transmitter so as to lead a flow tube to vibrate with natural frequency. Two magnetoelectric sensors positioned at two sides of the flow tube output two ways of sine-wave signals which are amplified and filtered by two ways of conditioning circuits with same parameter, then respectively and simultaneously sampled by two analog-to-digital converters with same model, and converted in digital value, and delivered to DSP by two multichannel buffered serial ports of the DSP. DSP adopts digital filter to eliminate the noise of the signals, is self-adaptive to a lattice notch filter to calculate the frequency, and then adopts the DTFT algorithm taking negative frequency into account to calculate to phase difference, thus obtaining the mass flow finally.

A downconverter and upconverter are provided which can obtain a sufficient image rejection ratio in a low-Intermediate Frequency (IF) scheme while reducing power consumption and can suppress Error Vector Magnitude (EVM)-related degradation in a zero-IF scheme. A complex-coefficient transversal filter rejects one side of a positive or negative frequency, and converts a Radio Frequency (RF) signal to a complex RF signal configured by real and imaginary parts. A local oscillator outputs a real local signal with a set frequency. A half-complex mixer, connected to the complex-coefficient transversal filter and the local oscillator, performs a frequency conversion process by multiplying the complex RF signal output from the complex-coefficient transversal filter and the real local signal output from the local oscillator, and outputs a complex signal of a frequency separated by the set frequency from a frequency of the RF signal.

The invention discloses a method for detecting a single channel synthetic aperture radar (SAR) ground motion target, which includes conducting clutter locking estimation on original echo data to obtain clutter Doppler center frequency, converting the original echo data into direction spectrum, dividing the direction spectrum into positive frequency spectrum and negative frequency spectrum with the clutter Doppler center frequency as a boundary, obtaining a first auxiliary look complex image and a second auxiliary look complex image respectively through the positive frequency spectrum and the negative frequency spectrum, conducting direction rectification on the first auxiliary look complex image and the second auxiliary look complex image, obtaining a first auxiliary look amplitude image and a second auxiliary look amplitude image through the first auxiliary look complex image and the second auxiliary look complex image which receives the direction rectification, conducting amplitude comparison on corresponding pixels of the first auxiliary look amplitude image and the second auxiliary look amplitude image. The pixel position corresponds to a movable target if the amplitude ratio is larger than the set detection threshold, otherwise, the pixel position corresponds to the clutter background, so that the movable target detection result can be obtained. The method can effectively restrain clutter and detect ground low speed motion targets.

An input signal is pre-distorted to reduce spurious emissions resulting from subsequent signal amplification. Frequency-dependent pre-distortion is preferably implemented in combination with frequency-independent pre-distortion, where the frequency-dependent pre-distortion corresponds to amplifier distortion that has a magnitude that is proportional to the frequency offset from the carrier frequency and a ±90° phase shift on either side of the carrier frequency. The frequency-dependent pre-distortion is generated by differentiating waveforms corresponding to two different sets of pre-distortion parameters with respect to time. In one embodiment, one of the differentiated waveforms is applied to a positive-frequency filter and the other to a negative-frequency filter to generate positive- and negative-frequency pre-distortion signals, respectively, to account for asymmetries in the amplifier characteristics. In another embodiment, only one of the differentiated waveforms is applied to an asymmetric filter (i.e., either a positive-frequency filter or a negative-frequency filter).

An automatic tuning scheme for two active band-pass filters where both filters operate on the signal while simultaneously being tuned using a reference signal. To allow that the amplitude of a reference signal is made small and since both filters demonstrate a good linearity the build-up of the inter-modulation distortion does not occur. The first band-pass filter is tuned with the reference falling into its pass-band. The second band-pass filter is also tuned with the reference placed into its pass-band. The reference is practically eliminated by the virtue of the complexity of the second band-pass filter. Assuming the filter passes the signal for positive frequencies if the reference is made a negative frequency by appropriate 90 degrees phase shifting it will be attenuated by at least 55 dB, which is a sufficient signal-to-reference ratio.

Disclosed is a method for estimating carrier frequency of a PSK (phase shift keying) signal in Alpha-stable distribution noise. The method includes: valuing a cyclic covariance function of the received PSK signal with the Alpha-stable distribution noise; valuing a cyclic covariance spectrum by subjecting the cyclic covariance function to Fourier transform; extracting a section with cyclic frequency being epsilon=0Hz according to the obtained cyclic covariance spectrum; searching peak values of a positive semi-axis and a negative semi-axis of the section respectively to find a positive frequency value and a negative frequency value corresponding to the peak values, and valuing a mean value as the estimated value of the carrier frequency after absolute values are valued. The method is capable of estimating the carrier frequency of the PSK signal in the Alpha-stable distribution noise and is good in estimating performance in an environment of low signal to noise ratio.

The present invention suppresses a harmonic component without impairing the phase orthogonality of a pair of complex signals. A polyphase filter is configured so that K pieces of filter circuits, each of which comprises a resistor and a capacitor, are connected and +360 / K degrees out of phase with a preceding one. Since counterclockwise rotation occurs when expression is given in terms of the complex plane, a notch occurs in a negative frequency region. A RC value is set so that a notch occurs in a specified frequency band to suppress a (4N+1)-order harmonic component. Since the polyphase filter has a symmetrical structure, an unbalanced component contained in an input signal is eliminated at a frequency that agrees with a pole determined by the RC value. This action improves the orthogonality.

The invention discloses a high-accuracy sinusoidal signal measuring device for removing frequency spectrum leakage, comprising an analog signal pre-processing unit, a data acquisition unit, a digital signal processing unit, a measuring result display unit, and a communication interface unit, wherein the analog signal pre-processing unit is connected with the data acquisition unit through multipath signal wires, and the digital signal processing unit is connected with the data acquisition unit, the measuring result display unit and the communication interface unit respectively through an SPI (Serial Peripheral Interface) bus. The measuring method comprises the steps of: 1, continuously sampling a signal to be measured to obtain sequences S1 and S2; 2, carrying out fast Fourier transform onthe S1, extracting a peak frequency spectrum and obtaining the peak frequency spectrum of the S2 through recursion; 3, calculating the frequency of the signal to be measured by applying the peak frequency spectrums of the S1 and the S2; 4, calculating the phase of the signal to be measured according to the phase angle information of the peak frequency spectrums of the S1 and S2; 5, solving an equation set relevant to positive and negative frequency spectrum amplitudes to obtain the measured value of the amplitude of the signal to be measured; and 6, removing the influence of the frequency spectrum leakage to obtain the accurate measured valve of a direct-current component.

The invention discloses a sinusoidal signal frequency estimation method based on interpolation DFT, being applicable to electric energy quality assessment of a power system. A real sinusoidal signal has a mirrored negative frequency component on spectrum, so that the directly use of DFT generates a relatively large estimation error due to the spectrum leakage of the negative frequency component under an incoherent condition. Aiming at the problem, a two-point IpDFT algorithm based on signal adjacent spectral lines is provided. The method comprises the steps of firstly performing discrete Fourier transformation on a time domain signal x(n), and acquiring an index value corresponding a peak spectral line through searching DFT amplitude spectrum, namely a rough estimated value k0 of frequency; then positioning a secondary spectral line of the amplitude through comparing the left and right spectral line amplitudes of the peak spectral line; and at last, constructing an interpolation proportion by the two maximum DFT spectral lines, computing a deviation [delta]0 of the rough estimated value of the frequency and thus acquiring the complete signal frequency. The method can effectively suppress the spectrum leakage and interference, has the relatively high estimation accuracy and anti-noise performance, and has more significant superiority in the scene with severe spectrum interference.

An orthogonal mixer generates first I and Q signals by down-converting an RF signal. A complex filter has an asymmetrical frequency gain property between a positive frequency domain and a negative frequency domain, and generates second I and Q signals by suppressing image signals included in the first I and Q signals compared with desired signals. An orthogonal compensation circuit is located at a subsequent stage of the complex filter, and corrects the second I and Q signals to cancel a phase difference error and an amplitude error of the desired signals between the second I and Q signals. Further, a control circuit adjusts an element characteristic of the complex filter to cancel a phase difference error and an amplitude error of the image signals that appear in the second I and Q signals.

A BPF outputs a real RF signal by suppressing a band out of an RF signal frequency band in a received signal. A local oscillator outputs a complex local signal with a predetermined frequency. A half-complex mixer performs frequency conversion by multiplying the real RF signal by a real part of the local signal, performs frequency conversion by multiplying the real RF signal by an imaginary part of the local signal, and outputs a complex signal separated by the predetermined frequency from a frequency of the real RF signal. A complex-coefficient SAW filter performs a convolution integral on an impulse response generated by an even function for a real part of the complex signal, performs a convolution integral on an impulse response generated by an odd function for an imaginary part of the complex signal, and outputs a real signal by suppressing one side of a positive or negative frequency.

The instantaneous peak positive and negative frequencies of a Doppler spectral image are determined using the spectral column signal mask derived from the instantaneous peak frequency function of the ultrasound system. Using the determined peak frequencies, the audio wraparound frequency is adjusted so as to substantially avoid aliasing effects.

The invention provides a harmonic measurement method which aims at obtaining a high-accuracy harmonic measurement result. The method comprises the following steps: sampling a signal to be measured; carrying out DET or FFT treatment on the sampling result to obtain a discrete spectrum; and selecting a plurality of measurement errors caused by spectral line revising long-range spectrum leakage, short-range spectrum leakage, negative frequency point leakage and the like from the discrete spectrum to obtain the high-accuracy harmonic measurement result. The method of the invention can be applied to the field of accurate harmonic measurement.

A vestigial sideband VSB receiver includes a digital processing part for selecting a desired channel frequency via an antenna and converting the desired channel frequency to an intermediate frequency to digitize a predetermined band of the intermediate frequency, a carrier wave restoring part for extracting pilot components from a signal of the digitized pass band to restore carrier waves, and a demodulator for separating components I and Q from the signal of the digitized pass band and multiplying the components with a complex carrier wave, which is restored in the carrier wave restoring part. The carrier waves are restored by extracting the pilot signals from the pass band and detecting the symmetrical errors of the carrier wave frequency, so that the carrier wave may be stably obtained and pursued with relation to the both positive and negative frequency offsets.

A digital communication circuit can be implemented can be implemented in a CMOS, or other IC structure. The digital circuit can utilize negative frequency removers or image frequency removers in the digital domain. The circuit can include mixers, switches, a complex filter, a low noise amplifier and summers. The image frequency can be removed digitally.

The invention discloses a method for testing the response time constant of a main servomotor of a hydraulic turbine governor, comprising the following steps: setting the adjustment parameters of the governor under the condition that the hydraulic turbine is in a static state; applying an absolute-value gradually increased positive-negative frequency step disturbance signal of the governor under the condition that the governor is in an automatic state, starting or stopping the main servomotor of the governor at a certain constant speed, moving a main distributing valve to a certain position in the starting or stopping direction from the middle position, and recording the speed of the main servomotor and the displacement of the main distributing valve; and calculating the response time constant Ty of the main servomotor according to the data obtained in the steps. The testing process is simple, and only a series of positive-negative frequency step disturbance tests is carried out. The data used in the test, comprising the main servomotor stroke, the main distributing valve displacement and the adjustor output yPID, can be easily collected.

The invention relates to an IF polyphase filter for filtering received RF signals. The signals are downconverted into intermediate frequency signals before filtering them in the IF polyphase filter. The IF polyphase filter comprises means for defining a passband for the IF polyphase filter. The IF polyphase filter further comprises a passband adapting element for setting the passband of the IF polyphase filter in positive or in negative frequencies. The invention further relates to a receiver comprising the IF polyphase filter according to the invention. The invention further relates to a method for filtering received RF signals by using an IF polyphase filter. The method comprises downconverting the received RF signals into intermediate frequency signals before filtering them in the IF polyphase filter, and defining a passband for the IF polyphase filter. The passband of the IF polyphase filter is set in positive or in negative frequencies.

The invention discloses a Ka FMCW SAR moving object detection method and apparatus. The Ka FMCW SAR moving object detection method comprises the steps: 1) emitting triangular wave by an FMCW SAR, segmenting an echo signal, and obtaining a positive frequency modulation echo signal and a negative frequency modulation echo signal; 2) utilizing an RD algorithm to process the positive frequency modulation echo signal and the negative frequency modulation echo signal, and obtaining a positive frequency modulation image and a negative frequency modulation image; 3) compensating the time difference between the positive frequency modulation image and the negative frequency modulation image; and 4) performing subtraction processing on the two images after compensating the time difference. The scheme of the Ka FMCW SAR moving object detection method and apparatus can realize detection of a moving object based on an FMCW SAR.

The invention is a system and method for sharing components of a single-path receiver or transmitter system multiple antennas. Specifically, according to one embodiment of the present invention, multiple antennas simultaneously share an analog-to-digital converter unit. The signal from one antenna is downconverted to a positive frequency band while the signal from another antenna is downconverted to a negative frequency band, allowing the signals to be processed by the analog-to-digital converter unit with minimal interference between signals and without the need for time-periodic switching. According to another embodiment of the present invention, multiple antennas simultaneously share a digital-to-analog converter unit.

The invention discloses a space-borne synthetic aperture radar quadruplex-polarization method, which relates to the space-borne synthetic aperture radar technology and can simultaneously obtain synthetic aperture radar quadruplex-polarization echo data. On the basis of combination of polarization time division and linear frequency modulation signal positive and negative frequency modulation gradient codes, the space-borne synthetic aperture radar quadruplex-polarization method obtains a good range ambiguity performance under the condition without increasing complexity of system equipment. In addition, a principle of suppressing range ambiguity for the quadruplex-polarization method and a method for calculating space-borne synthetic aperture radar range ambiguity are provided.

The invention discloses a multi-band millimeter wave receiver and a multi-band millimeter wave receiving method. A plurality of processing circuits are used for performing orthogonal mixing frequency conversion on signals in different frequency bands to obtain a plurality of intermediate frequency signals at fixed center frequency, image signals serving as negative frequency components are removed by a plurality of band-pass filters to realize image rejection, the analogue intermediate frequency signals are simultaneously digitalized and down-converted according to a band-pass sampling theorem by an analogue-to-digital converter, and original signals of a transmitter are recovered by subsequent digital signal processing. According to the receiver and the method, image rejection performance can be improved, and system structure is simplified, and is easy to implement and integrate.

The invention discloses a fetal electrocardiogram instantaneous heart rate recognition method and system based on non-negative blind separation. The method comprises the following steps that electrocardiosignals obtained through being collected by a fetal electrocardiogram machine are preprocessed, after the wavelet denoising, a coherent averaging method is used for removing electrocardiogram components of a mother to obtain the fetal electrocardiosignals, the fetal electrocardiosignals are converted to the time-frequency domain to obtain a Choi-Williams spectrum and a Born-Jordan spectrum, and then, the spectrums are converted into a non-negative frequency spectrum; non-negative matrix factorization is used for blind separation to obtain non-negative time frequency components of the fetal electrocardiosignals; the instantaneous heart rate is calculated, the non-negative time frequency components of the obtained fetal electrocardiosignals are subjected to maximum value detection, and a threshold value is set; an interval traversing method is adopted for obtaining the maximum value of signal intervals, and all peak value points of a electrocardiogram curve are obtained; all peak value coordinates of the obtained electrocardiogram curve are converted, the forward difference is sequentially carried out, and the instantaneous heart rate of the fetus is obtained through an instantaneous heart rate formula. The method and the system provided by the invention have the advantages that the recognition is fast and simple, and the accuracy is high.

A downconverter and upconverter are provided which can obtain a sufficient image rejection ratio in a low-Intermediate Frequency (IF) scheme while reducing power consumption and can suppress Error Vector Magnitude (EVM)-related degradation in a zero-IF scheme. A complex-coefficient transversal filter rejects one side of a positive or negative frequency, and converts a Radio Frequency (RF) signal to a complex RF signal configured by real and imaginary parts. A local oscillator outputs a real local signal with a set frequency. A half-complex mixer, connected to the complex-coefficient transversal filter and the local oscillator, performs a frequency conversion process by multiplying the complex RF signal output from the complex-coefficient transversal filter and the real local signal output from the local oscillator, and outputs a complex signal of a frequency separated by the set frequency from a frequency of the RF signal.