67 results about "Conjugate symmetry" patented technology

Disclosed is a method, a computer program product and a device that includes a receiver for receiving a downlink signal transmitted into a cell. The receiver is operable to obtain time, carrier frequency and cell-specific preamble synchronization to the received signal and includes a plurality of synchronization units that include a first detector to detect a frame boundary using preamble delay correlation; a second detector to detect the frame boundary with greater precision using a conjugate symmetry property over a region identified by the first detector; a cyclic prefix correlator to resolve symbol boundary repetition; an estimator, using the cyclic prefix, to estimate and correct a fractional carrier frequency offset; an operator to perform a Fast Fourier Transform of an identified preamble symbol and a frequency domain cross-correlator to identify cell-specific preamble sequences and an integer frequency offset in sub-carrier spacing. The transmitted signal may be a downlink signal transmitted into the cell from a base station that is compatible with IEEE 802.16e (WiMAX).

A sequence generation method for allowing a reception end to effectively detect a sequence used for a specific channel of an OFDM communication system, and a signal transmission/reception method using the same are disclosed. During the sequence generation, an index is selected from among the index set having the conjugate symmetry property between indexes, and a specific part corresponding to the frequency “0” is omitted from a transmitted signal. In addition, a reception end can calculate a cross-correlation value between a received (Rx) signal and each sequence using only one cross-correlation calculation based on the conjugate symmetry property.

The invention discloses a wireless optical orthogonal multi-carrier communication method with a low peak to average power ratio. The wireless optical orthogonal multi-carrier communication method comprises the following steps that at a transmitting end, firstly, modulated frequency domain signals are converted into a semi-positive definite planning convex optimization problem by adopting a tone injection algorithm via a relaxation method, and solving is carried out through general convex optimization and randomized methods; secondly, the frequency domain signals are symmetrically mapped to subcarriers in a conjugate mode, and a cyclic prefix is added after reverse fast Fourier transformation; at last, time domain transmission signals are added into direct-current offset to drive a light-emitting diode to emit light. At a receiving end, photovoltaic conversion is achieved through a photodiode; signals are removed from the cyclic prefix and conjugate symmetry parts after amplification, filtering, analog-digital conversion and fast Fourier transformation; the signals are modulated to be recovered in an original planisphere; at last, receiving symbols are obtained through demodulation. According to the wireless optical orthogonal multi-carrier communication method, the peak to average power ratio of a wireless optical communication PFDM system can be effectively reduced, requirements of a power amplifier and an LED for linear degrees are reduced, non-linear distortion is reduced, and receiving performance is improved.

A synchronization method in OFDM broadband wireless access system includes such steps as utilizing NO.1 frame head as a delay related decision to realize rough synchronization, using the conjugate symmetry of No.2 frame head to realize accurate timing, the frame heads roughly and accurately estimate the decimal frequency deviation separately, the frequency field sequences of the two heads are used to estimate the integer frequency bias and finally synchronous tracing.

A sequence generation method for allowing a reception end to effectively detect a sequence used for a specific channel of an OFDM communication system, and a signal transmission/reception method using the same are disclosed. During the sequence generation, an index is selected from among the index set having the conjugate symmetry property between indexes, and a specific part corresponding to the frequency '0' is omitted from a transmitted signal. In addition, a reception end can calculate a cross-correlation value between a received (Rx) signal and each sequence using only one cross-correlation calculation based on the conjugate symmetry property.

The invention discloses a timing frequency synchronization method based on an improved Park frequency domain training sequence. The timing frequency synchronization method comprises the following steps: firstly sending a training sequence before an OFDM data symbol is sent, wherein all the sub carriers of the training sequence in the frequency domain respectively send a pseudorandom real number, and structure of a corresponding time domain training symbol is conjugate symmetric; performing timing synchronization by an FS-Park synchronization method firstly by using the time domain training symbol, then performing estimation on fractional part of frequency offset based on a cyclic prefix in the time domain and performing estimation on integral frequency offset by utilizing cross correlationof the training sequence in the frequency domain, obtaining the total frequency offset, namely the sum of the integral frequency offset and the fractional part of frequency offset, and completing synchronization. The timing frequency synchronization method disclosed by the invention designs a new training sequence, and then a more ideal time domain training symbol structure is obtained; and thenbased on the training sequence and the corresponding time domain training symbol thereof, the integral frequency offset and the fractional part of frequency offset are estimated respectively, and timing synchronization estimation is performed.

The invention discloses an LED array visible light communication system based on DFT-S OFDM and an LED array visible light communication method. An LED light source composed of a plurality of LED chips serves as the emitting end, and the LED chips are independently driven to form LED array emitting systems which do not disturb each other. The DFT-S OFDM modulation mode is adopted by each LED emitter, the LED emitters occupy different OFDM frequency band resources respectively, circumference conjugate symmetry is applied to OFDM frequency domain subcarriers to guarantee real number property of OFDM base band data, and a centralized DFT-S OFDM mode and a staggered DFT-S OFDM mode are applied to the visible light communication system. The DFT-S technology applied to the LED array visible light communication system based on DFT-S OFDM and the LED array visible light communication method can obviously restrain the peak-to-average power ratio of the visible light communication system, obvious frequency domain diversity gains are acquired in the aspect of bit error rate performance, and the LED array emitting structure protects system transmission ratio against effect.

The invention discloses an estimation algorithm for two-dimensional direction of arrival (DOA) of an L-shaped array by adopting time-frequency analysis. The estimation algorithm disclosed by the invention mainly aims at solving the problem of two-dimensional DOA estimation of time-frequency spectrum aliasing and spatial neighborhood information sources and is suitable for low signal to noise ratio and underdetermined conditions. The estimation algorithm is realized by the following steps: firstly, forming the L-shaped array on an xz plane by using two uniform linear arrays to construct total receiving data; secondly, transforming the total receiving data into a time-frequency domain by adopting STFT (Short Time Fourier Transform); thirdly, selecting single information source time-frequency points of all the information sources in a two-dimensional direction, and establishing a time-frequency receiving data matrix of single information sources; fourthly, constructing a time-frequency cross correlation matrix; fifthly, calculating a novel receiving matrix subjected to aperture expansion; sixthly, based on a propagation operator principle, defining a propagation operator subjected to the aperture expansion; seventhly, constructing an angle selection matrix, and calculating the two-dimensional DOA according to rotational invariance among sub-matrixes. According to the estimation algorithm disclosed by the invention, estimation precision of the time-frequency spectrum aliasing and spatial neighborhood information sources and the success rate are improved, high robustness of noises is realized, and required number of array elements can be reduced.

The invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) time synchronization algorithm based on a conjugate symmetric sequence. The OFDM time synchronization algorithm comprises the steps of constructing a sequence with conjugate symmetry; carrying out symmetric related calculation at a receiving end by using the conjugate symmetry of the sequence so as to obtain a related peak value of a timing measurement function; and determining a beginning position of an OFDM signal by using the position of the related peak value so as to finish time synchronization. By using the invention, the adverse effect on the time synchronization, caused by a cyclic prefix and the conjugate symmetry of the sequence, is overcome, and higher timing accuracy is obtained; and the OFDM time synchronization algorithm based on the conjugate symmetric sequence, provided by the invention, can be effectively used for the time synchronization of the OFDM system under a multipath channel.

The invention discloses a visible light OFDM system self-adaptive low peak ratio method based on subcarrier reservation. The method comprises the following steps: (1) at a transmitting end, allowing binary bit information flow generated by an information source to be subjected to adaptive orthogonal amplitude modulation to form a frequency domain data signal of the transmitting end; (2) determining the number of reserved subcarriers and corresponding positions in the visible light communication system; (3) performing conjugate symmetry processing on the frequency domain data signal on the OFDMsubcarrier; (4) calculating a reserved subcarrier frequency domain value; (5) performing IFFT operation on the OFDM frequency domain signal, and adding a cyclic prefix to obtain a time domain electric signal for driving the LED; (6) carrying out direct current bias or clipping on the electric signal, and then an LED is driven to emit an optical signal; (7) at a receiving end, converting the optical signal into an electric signal through a photodiode; (8) converting the obtained electric signal into a frequency domain signal; And (9) demodulating to obtain binary information flow. According to the invention, the requirement of the system on the linearity of the power amplifier and the LED lamp is reduced, and the nonlinear distortion is reduced.

The invention discloses an LED visible light orthogonal multicarrier communication method with low peak average power ratio. The LED visible light orthogonal multicarrier communication method with low peak average power ratio comprises the steps of deducing and transforming a problem of optimizing a peak to average power ratio into a convex optimization problem based on a characteristic of OFDM subcarrier conjugate symmetry in visible light communication at a transmitting end; calculating a reserved subcarrier frequency threshold through a conventional convex optimization method; processing a signal in which the reserved subcarriers are inserted to obtain a time domain transmitting signal; and removing conjugate subcarriers from the signal at a receiving end, then filtering away the reserved subcarriers through a filtering module and finally demodulating to obtain a received signal. According to the LED visible light orthogonal multicarrier communication method with low peak average power ratio, a traditional subcarrier reservation method is applied to the visible light communication, the number and position of the reserved subcarriers are determined based on the channel characteristics in the visible light, deductive analysis is carried out based on the characteristic of the optical channel subcarrier conjugate symmetry, and the optimization problem of the peak average power ratio is accordingly solved. In addition, the LED visible light orthogonal multicarrier communication method with low peak average power ratio is applicable to a DCO-OFDM system and an ACO-OFDM system.

A frame synchronization detecting method in an orthogonal frequency division multiplex system comprises: conjugating correlation calculation to data signals in a fore and aft conjugate correlation window of data signal in a data signal sequence to obtain a correlation calculation accumulate result by accumulating; calculating an average energy of data signals in the fore and aft conjugate correlation window; taking a metric value of a data signal as a ratio between the correlation calculation accumulate result and the average energy, and in a detecting period, such as in a length of 1.5 frame, determining a frame starting time based on a data signal with a metric value maximal. The method, based on a character that predecessor using BPSK modulate conjugates symmetry, performs a frame synchronization detect, solves the synchronization problem in the orthogonal frequency division multiplex system.

The invention discloses a low-complexity peak-to-average ratio restraining method for an optical communication DCO-OFDM (direct current-biased optical-orthogonal frequency division multiplexing) system. The low-complexity peak-to-average ratio restraining method comprises the following steps of firstly, performing precoding DFT (discrete Fourier transform) on inputted digital modulation signs so as to reduce correlation between the signs; secondly, performing subblock division and conjugate symmetry on a precoded data sequence; and finally, selecting a suboptimal phase twiddle factor for each subblock so as to reduce a peak-to-average ratio. Because IFFT (inverse fast Fourier transform) and suboptimal iterative loop phase factor selection are carried out sequentially, the implementing complexity of the system can be reduced while the peak-to-average ratio is restrained.

A method is presented for accelerating magnetic resonance imaging. In 3D MRI, the k-space in the phase encoding plane is divided into two symmetric parts and three asymmetric parts. Different sampling densities are applied in different parts. Images are reconstructed by iteratively minimizing a cost function when random sampling is applied in each part. A phase constraint term is added into the cost function to improve the quality of the reconstruction by exploiting the conjugate symmetry of k-space.

The invention is applicable to the field of communication, and provides a method for searching a physical cell identifier, a computer readable storage medium and a small base station. The method comprises the following steps: determining a strongest PSS signal position by adopting a sliding autocorrelation method by adopting a PSS sequence time domain mirror image conjugate symmetry characteristic, and finally determining a strongest SSB beam position of a current cell according to the strongest PSS signal position; and adopting different PSS sequences for cyclic shift in a frequency domain. According to the invention, the error probability of searching the strongest SSB wave beam when the carrier frequency offset exists in the received signal is reduced, and the operand caused by directlyadopting three PSS local sequences and receiving wireless frame sliding correlation calculation in the time domain is reduced.

The embodiment of the invention discloses a cell detecting method and a cell detecting device for interference cancellation. The method comprises the following steps of: performing full system multipath scanning based on secondary synchronization signal center conjugate symmetry; picking a strongest path with highest power, and identifying the time delay position of the strongest path; comparing the power of the strongest path with a first power threshold, and if the power of the strongest path is greater than the first power threshold, cancelling interference caused by signals of the path from the received mixed signals; identifying a cell of the strongest path, and accumulating the channel measurement of the cell; repeating the interference cancellation process till the detected power of the strongest path is smaller than or equal to the first power threshold; and performing valid cell screening based on a second power threshold to acquire a valid cell set and an intensity measurement sequence thereof. According to the embodiment, a valid interference cancellation effect can be achieved, and complexity can be reduced.

The invention belongs to the technical field of signal processing, and discloses a sending signal synchronous processing method and system, a storage medium, a program and a terminal. The method comprises the steps: obtaining a conjugate symmetry training sequence composed of three parts through a generated ZC sequence; loading the training sequence to the front of an FBMC/OQAM system symbol of atransmitting end for transmission, performing timing synchronization processing by utilizing the strong autocorrelation of an improved local sequence and a part of sequences of a receiving end, and detecting and finding the position of a synchronization frame header through peak search; and performing frequency offset estimation operation by utilizing the training sequence, and compensating frequency offset of data by utilizing the estimated angle value through solving an average frequency offset difference value between the two sections of sequences. According to the method, the precision ofsynchronous operation is improved, the receiver can accurately extract effective signals from the received signals under the condition that the communication channel environment is severe, and phase and frequency deflection generated by data symbols, reaching the receiver through wireless transmission, of the transmitted signals is successfully compensated.

The invention relates to a high-resolution minimum variance ultrasonic imaging method based on frequency domain segmentation and belongs to the acoustic imaging field. The method comprises the following steps of firstly, carrying out delay processing on a sampling signal received by an array element to obtain echo data required by ultrasonic focusing; secondly, selecting a frequency domain segmentation optimal window function according to a maximum concentration measurement criterion of an adaptive window function in STFT; converting an ultrasonic echo signal into a narrow-band sub-signal by using STFT; carrying out conjugate symmetry processing on a first half of narrow-band sub-signal to generate the other half of narrow-band signal by using conjugate symmetry; successively dividing a receiving array into sub-arrays with overlapped array elements, and carrying out forward and backward smoothing and diagonal loading processing on a frequency domain signal to obtain a sample covariancematrix; and finally, processing a frequency domain segmented minimum variance beam forming weight by using inverse fast Fourier transform to obtain a final time domain adaptive beam forming signal. By using the method, an ultrasonic imaging resolution can be remarkably improved, a contrast ratio is increased, and ultrasonic imaging quality can be integrally improved.

The invention discloses an array antenna optimization method for effectively controlling a dynamic range of excitation amplitude. Wave beams of different radiation requirements are realized in a relatively small excitation dynamic range; unit excitation corresponding to a directional graph meeting radiation performance requirements is obtained by using an improved iterative Fourier algorithm; units of a maximum part and a minimum part of the excitation amplitude are determined; an excitation complex value of the unit of the minimum part of the excitation amplitude is subjected to phase preservation and amplitude direct assignment processing; the obtained excitation complex value serves as a part of a final complex excitation vector of an antenna; and a complex excitation value of the unitof the residual part is searched for by utilizing an improved convex optimization algorithm to meet the radiation performance index requirements of the directional graph. The relatively small dynamicchange range of the complex excitation amplitude of the antenna can effectively simplify a feed network to reduce the feeder line cost, and the mutual coupling between the units can be well controlled; and the application range of the method is not limited to special preconditions such as excitation complex value conjugate symmetry, array element central symmetry layout, array element equal interval or the like.

The invention discloses an efficient transmission method of wireless light based on optimal amplitude modulation. The efficient transmission method is carried out according to the following steps that: a system generates a frequency domain symbol, which needs to be transmitted, on a transmitting end; a frequency domain signal generates a base band time domain transmitting signal in an actual value; optimal amplitude modulation coefficients are figured up, zoom amplitude modulation is carried out on the frequency domain signal on each sub-carrier and DC bias is added into an amplitude limiting time domain transmitting signal to drive a light emitting diode to transmit; a received optical signal is converted to an electric signal by a photoelectric diode, and a time domain receiving signal is obtained after processing, such as filtration and amplification, at a receiving end; fast Fourier transform is carried out on the time domain receiving signal, so that a frequency domain receiving signal is obtained and a conjugate symmetry part is removed; and lastly, a final receiving symbol is obtained through constellation demodulation. The efficient transmission method has the advantages of simple implementation and capabilities of reducing a peak-to-average power ratio of a wireless light communication OFDM (Orthogonal Frequency Division Multiplexing) system, reducing requirements of the transmitting end on linearity of a power amplifier and an LED (Light Emitting Diode) lamp and improving an error rate of an AC signal transmitting power reducing system.

The magnetic resonance imaging apparatus of an embodiment is provided with a data-collecting unit and an image-generating unit. From the subject, the data-collecting unit collects multiple magnetic resonance signals corresponding to a sampling region that is asymmetric in the wavenumber direction in the k-space with a data collection sequence having a first regularity and a data collection sequence having a second regularity that differs from the first regularity. The image-generating unit generates magnetic resonance image data by data-processing that comprises signal filling into the non-sampling region using k-space phase conjugate symmetry and image reconstruction processing based on the multiple magnetic resonance signals.