31results about How to "Lower SNR Threshold" patented technology

A data-assisted satellite-borne AIS signal synchronization parameter estimation method comprises that an antenna receives a radio frequency signal emitted by an earth ship AIS system and sends the radio frequency signal to a receiver; the receiver demodulates the received radio frequency signal into a baseband signal and inputs the demodulated radio frequency signal into an FPGA (field programmable gate array) data acquisition module; the FPGA data acquisition module subjects the received baseband signal to analog-digital conversion to obtain a digital baseband signal and inputs the digital baseband signal into a signal processing module; the signal processing module processes the received digital baseband signal to obtain correct AIS ship information and to send the correct AIS ship information into a data storage module; and the data storage module stores the received AIS ship information. The data-assisted satellite-borne AIS signal synchronization parameter estimation method has the advantages that under signal downsampling and by introducing the self-correlation operation and the maximum likelihood operation, the performance of large estimation range and small estimation error of frequency offset of the satellite-borne AIS signal can be achieved; and through the accumulation argument operation and the accumulation module value operation, high-accuracy timing estimation, phase shift estimation and amplitude estimation are achieved.

The invention provides a maneuvering target detection method based on time-frequency analysis. The maneuvering target detection method based on time-frequency analysis comprises the following steps that radar echo signals of a sky wave radar in a first position range are obtained as first radar echo signals, wherein the radar echo signals comprise maneuvering target echoes; phase transformation is carried out on the first radar echo signals, and second radar echo signals are obtained; a joint domain based on time and instant frequency change rates is obtained by carrying out matching Fourier transformation related to the instant frequency change rates of a maneuvering target on the second radar echo signals at different moments respectively; in an established coordinate system with the time and the instant frequency change rates as coordinate axes, integration is carried out on the joint domain along a straight line which is parallel to the time coordinate axis and corresponds to different instant frequency change rates, and an energy function of the accumulated maneuvering target is obtained; whether the energy function is smaller than a preset energy threshold value or not is judged; when the energy function is larger than or equal to the energy threshold value, it is determined that the maneuvering target is within the first position range.

The invention relates to an adaptive turbo equalization method, an equalizer and an underwater acoustic communication system. The method comprises the following steps: calculating a primary symbol estimated value (the formula is as shown in the specification) according to a received symbol sequence r (i) and a priori symbol mean vector (the formula is as shown in the specification); calculating a symbol estimated value (the formula is as shown in the specification) fed back by a prior variance according to the primary symbol estimated value (the formula is as shown in the specification) and a prior symbol variance v (i); and calculating an output log likelihood ratio LLR of each symbol according to the symbol estimated value (the formula is as shown in the specification) fed back by the prior variance. The priori symbol information is mapped to obtain a priori symbol mean and a priori symbol variance. According to the adaptive turbo equalization method provided by the invention, the priori symbol information output by an SIOS decoder is better utilized, the communication performance under time-varying multipath is improved, and the signal to noise ratio threshold is reduced.

The invention discloses an underwater acoustic communication balanced decoding method based on a recursive chaotic code, and the method comprises: step 1, inputting an information source information sequence into a recursive chaos model by a coding sending end, carrying out the recursive chaotic coding, generating a symbol frame sequence, generating an information sub-frame, and sending the information sub-frame after signal modulation to a coding receiving end; step 2, the coding receiving end demodulating the received information subframes to generate a symbol sequence, and generating a joint equalization decoding tree according to the number of information fragments in the symbol sequence and the number of information fragments in the information source information sequence; and step 3,the coding receiving end calculating the Euclidean distance between the symbol sequence in each branch and the symbol sequence which is actually received, selecting the branch with the minimum Euclidean distance, and marking the branch as a decoding result. Through the technical scheme provided by the invention, the bit error rate performance of the underwater acoustic communication system is improved, the influence of strong inter-code crosstalk of the underwater acoustic channel and the complexity of a joint equalization decoding algorithm are reduced, and the transmission reliability of the underwater acoustic channel is improved.

The invention discloses a method and a device for estimating a frequency ramp and a frequency deviation in a satellite mobile communication system. The method comprises the following steps of: according to parameters of an actual communication system, obtaining a range of a normalized frequency ramp value aD and calculating a trial interval delta aD of the frequency ramp value; carrying out repeated test on the normalized frequency ramp value aD by utilizing a frequency deviation estimating method, wherein the test interval each time is delta aD, one or a plurality of (aD, fD) number pairs are obtained in each trial process, and a set is formed by all the (aD, fD) number pairs after all the test processes are completed; and substituting all the (aD, fD) number pairs in the set into a likelihood function G (aD, fD), searching the (aD, fD) number pair capable of ensuring the likelihood function to attain the maximum value and using the (aD, fD) number pair as estimation values of the frequency ramp and the frequency deviation. The method and the device have the advantages of low SNR (Signal to Noise Ratio) threshold, low computational complexity and high estimation accuracy. In the actual application, the existing module can be continuously used in the method for estimating the frequency deviation, the estimation on the frequency ramp can be realized without great improvement, and the method and the device are very convenient.

The invention belongs to the technical field of radar signal detection and evaluation, and particularly relates to a QFM signal parameter evaluation method based on a four-order asymmetrical product type kernel function. The method includes the steps of firstly, calculating the initial signal energy, setting a circulation initial value and establishing a matrix used for storing all subsequent component parameter estimation values; secondly, multiplying the time delay function of the four-order asymmetrical product type kernel function with the conjugation time delay function of the four-order asymmetrical product type kernel function, and conducting phase matching and converting on phases of the four-order asymmetrical product type kernel function, wherein the estimation values of the second parameters of the signal components can be obtained in the positions of frequency domain peak values; thirdly, constructing a new four-order asymmetrical product type kernel function for signals with compensation conducted on the second parameter estimation values, and conducting fast Fourier transform to obtain a frequency-frequency change rate two-dimensional distribution diagram, wherein third parameter estimation values and third parameter estimation values of the signal components can be obtained from the positions of the peak values; fourthly, filtering the signal components, estimated in the steps, out of the signal; fifthly, resetting cyclic variables and a signal, and calculating the ratio of the total energy of the signal to the initial signal energy.

The invention provides a space maneuvering target ISAR imaging method, device and equipment and a storage medium, and the method comprises the steps: carrying out the pulse compression and motion compensation of an echo signal, obtaining an original signal, carrying out the order reduction of the original signal through a high-order fuzzy function, achieving the parameter estimation through a coherent accumulation cubic phase function, and reconstructing the original signal, thereby achieving the ISAR imaging. According to the scheme, the second-order parameter and the third-order parameter of the original signal can be estimated at the same time, the calculation efficiency is high, and the calculation complexity is reduced; and meanwhile, by increasing self-term energy, the signal-to-noise ratio threshold is reduced, and the robustness of parameter estimation under the low signal-to-noise ratio is improved.

The invention discloses a bidirectional frequency domain Turbo equalization method adopting expected propagation, and the method comprises the steps: S1, receiving a transmission signal of an underwater acoustic or wireless channel, and approximately deducing the posteriori distribution characteristics of symbol bits of a received signal through employing an EP soft mapping method; S2, processingthe received signal by adopting a bidirectional frequency domain soft equalization method to obtain equalization external information; S3, combining the bidirectional equalization external informationby using a covariance-assisted bidirectional combination method; S4, inputting the combined external information into a Log-MAP decoding judgment method to obtain decoded external information, inputting the decoded external information into an EP soft mapping method as priori, and repeating the steps S1-S4; S5, determining whether the number of iterations reaches a preset number of iterations ornot, and if not, continuing to execute the steps S1-S4; and if so, determining decoding by utilizing a Log-MAP decoding judgment method, and outputting a decoding code word.

The invention provides a GPS satellite M code signal demodulation method based on combination of short code dispreading and timing recovery. The mutual promotion relation of short code dispreading and timing recovery is utilized, the signal-to-noise ratio threshold of demodulation can be effectively reduced, the antenna aperture is equivalently reduced, and the construction cost is saved. Firstly, the carrier frequency and carrier phase of a GPS satellite navigation signal are obtained through a typical carrier estimation method, carrier recovery and IQ separation are conducted, and extraction of a GPS M code signal is further achieved through band-pass filtering; and short code decoding is performed on the GPS M code signal to obtain coding gain, timing synchronization is performed by adopting blind processing for the first time on the basis, M code streams including innovation of the M code signals is solved after judgment, and the innovation is fed back to a front end to perform timing synchronization operation on the signals again. The timing synchronization precision can be improved.

The present invention discloses one kind of bit interleaving method for digital TV ground transmission. The method performs bit interleaving treatment of data block TPC(M2XN2) obtained via coding TPC(M2, M1, N2, N1), and there are K data blocks TPC(M2XN2) after TPC coding in the bit interleaving of each time. In the first step, the bit data in the same position of the TPC blocks from 1 to K are output successively and the data in all TPC blocks are output in diagonal order; and in the second step, the bit flow is divided into L blocks of P bits each and the data in [L/2] or [L/2]+1 blocks have the adjacent bits exchanged while maintaining the other blocks unchanged. The present invention can further strengthen the burst error resisting ability of digital TV ground transmission system.