721 results about "Pseudo-code" patented technology

The invention discloses a software FMEA (failure mode and effects analysis) method based on level dependency modeling. The method includes 1, understanding an object to be analyzed completely and deeply as required, and determining an analyzing target; 2, establishing a system-grade level dependency model by utilizing outline design as a reference; 3, selecting a module to be analyzed and determine a failure mode thereof, analyzing a failure influence propagation path and a failure reason tracing path to determine a failure reason and the failure influence and provide improvements according to system-grade level dependency model reachability node analysis; 4, selecting a detailed-grade FMEA analyzing object according to a system-grade FMEA result; 5 establishing a detailed-grade level dependency model on the basis of detailed design or a pseudo-code of the selected object to be analyzed; 6, selecting key variables to be analyzed according to the detailed-grade level dependency model; 7, determining a specific failure mode of the key variables to be analyzed, and analyzing producing reasons and failure influences of the variables and providing improvements according to detailed-grade level dependency model reachability node analysis.

The invention discloses a satellite signal vector tracking method based on SINS / GPS deep integration data fusion. In the method, compensation is carried out on inertia element errors through channel filter information fusion, SINS / GPS deep integration navigation data fusion and an SINS system based on an SINS / GPS deep integration navigation system; and position and speed parameters of a current computation period are corrected to obtain accurate navigation parameters and generate local inference signals as well as keep the tracking for all visual GPS satellite signals; and a loop formed by channel filters and a main filter is utilized to complete the vector tracking and integration navigation information processing to the GPS satellite signals. The invention has excellent noise inhibitioncapacity and dynamic tracking performance, can ensure the navigation accuracy and the reliability of an integration system during the temporary interruption of the GPS satellite signals, and can maintain better pseudo code phase and carrier frequency tracking property in an environment with low carrier-to-noise ratio.

The present invention discloses a radio altimeter based on PN code distance measurement which comprises of emitting module, receiving module and digital signal processing module, wherein, clock input signal of emitting module as intrinsic signal is transferred to modulator, after the intrinsic signal is modulated by modulating code input by digital signal processing module, variable RF signal is output as effect of power control signal, and radiated after amplified by power amplifier, the clock signal of receiving module as receiving intrinsic signal is mixed with receiving intrinsic, outputs intermediate frequency and transmitted to digital signal processing module after amplified of intermediate frequency amplifier as action of AGC control signal to produce PN code, clock, power control signal and AGC control signal, and capturing and tracking receiving signal to output measurement data. The present invention has merits of large height measurement range and high measurement precision, and is useful for measuring height of the flying load to ground.

The invention relates to a high dynamic satellite navigation signal rapid capture and tracking system and method. The method comprises the following implementation steps that S1, related parameters are set according to the capture requirements, and intermediate frequency signals are read to be mixed with local carrier; S2, windowing is performed on PMF and FFT modules based on the conventional PMF+FFT to implement capturing; S3, an adaptive threshold adjustment method is adopted on signal peak judgment after FFT operation so as to obtain the capture result; S4, the process enters the tracking stage, frequency mixing and pseudo code correlation are performed on the intermediate frequency data and the result after correlation is integrally cleared so as to obtain a coherent integral value; S5, dimension enlarged unscented Kalman filter is adopted for carrier tracking, and the state vector optimal estimation value is obtained according to the dynamic model and the measurement model of the system; and S6, the conventional code ring under carrier aiding is adopted in code tracking. According to the method, the problems of rapid capture and tracking of the high dynamic satellite navigation signals can be solved, and the dynamic performance can be 100g.

The invention provides a pilot frequency information and satellite ephemeris joint Doppler frequency shift estimation and compensation method which includes the steps: a receiving pilot frequency signals from a low-orbit satellite by a ground terminal k; b acquiring satellite ephemeris data of the latest time tk, the frequency and the phase of carrier waves and the frequency and the phase of pseudo codes based on the pilot frequency signals by the ground terminal k; c calculating Doppler frequency shift between the ground terminal k and the low-orbit satellite based on satellite ephemeris information of the pilot frequency signals corresponding to the latest time tk, the frequency and the phase of the carrier waves and the frequency and the phase of the pseudo codes; d adjusting the frequency of the pseudo codes and the frequency of the carrier waves based on the Doppler frequency shift, and performing Doppler compensation when uplink signals are transmitted. The Doppler frequency shift is estimated and compensated by a high-precision pilot frequency method with small calculated amount, and the Doppler frequency shift is preferentially estimated and compensated by a high-precision orbit ephemeris method when the terminal suddenly cannot receive the pilot frequency signals due to reasons such as blocking of tall buildings.

The invention relates to a generation and capture system of an encrypted frame hopping spread spectrum signal of an air fleet link, belonging to the technical field of aeronautical data link and radio navigation. The invention discloses a system framework of an encrypted frame hopping spread spectrum signal generation and capture method which can be implemented on a digital signal processor (DSP)and a FPGA (field programmable gate array) of a circuit board, and provides a baseband signal generation algorithm of an encrypted frame hopping spread spectrum system to replace a traditional long periodic sequence spread spectrum code and a compound pseudo code by absorbing the advantages of the easy capture of the compound pseudo code and the difficult breaking of the long periodic sequence spread spectrum code; and meanwhile, the invention provides two advanced and high-performance encrypted frame hopping spread spectrum signal capture algorithms, i.e. a frequency domain parallel capture method of the encrypted frame hopping spread spectrum signal of based on a FFT (fast fourier transform algorithm) and a direct capture method of the encrypted frame hopping spread spectrum signal based on a matching filter and the FFT. The invention solves the problem of difficult capture of the traditional long periodic sequence spread spectrum code. The method can be widely applied to satellite navigation receivers, range measurement systems and communication systems based on a quiescent carrier modulation direct sequence spread spectrum system.

The invention relates to a two-way ranging and time comparison processing terminal which is characterized in that: the processing terminal comprises a frequency benchmark, a radio frequency front end, a noise source, a frequency synthesis, a transmitting channel, a receiving channel, a medium frequency signal processor, a machine case, a display and control system, a power source distributor and a LAN switching module, wherein the configuration of the entire processing terminal is a 4U machine case postnotal plate joint interconnecting structure fastened by a standard machine cabinet; the frequency benchmark, the transmitting channel, the receiving channel, the medium frequency signal processor and the power source distributor are arranged inside a standard 4U machine case; the display and control system, which is realized through the configuration of an external notebook computer and display and control software, is in interaction with the outside through the LAN switching module. The entire processing terminal has simple equipment and high integration level; communication, ranging and time comparison are completed inside a unified channel, thereby saving frequency band resource; a pseudo code ranging system is adopted to ensure high ranging precision; moreover, the processing terminal, which has the functions of simulating dynamic state and time delay inside the transmitting channel, is used to realize the quantitative detection of the performance of a receiving terminal.

The invention discloses a fully-digital direct sequence spread spectrum communication system and a rapid pseudo code capturing method thereof. A digital signal is processed by using an FPGA (Field Programmable Gate Array) which comprises a pseudo code capturing module, a sampling signal of an ADC (Analog To Digital Converter) is subjected to frequency mixing with a signal of a local carrier NCO (Numerically Controlled Oscillator) and filtered to obtain a baseband signal, residual carrier Doppler frequency is eliminated from the baseband signal by adopting a differential multiplying mode, thus the phase deviation of a receiving signal and a local pseudo code is further obtained through an FFT (Fast Fourier Transform) algorithm without scanning on a carrier frequency domain; and when the phase deviation of the pseudo code is obtained, a local pseudo code phase is modified and is subjected to correlation degree of dissociation with the receiving signal, and the carrier Doppler frequency is figured out by using the FFT algorithm, and is compensated to a carrier NCO and a pseudo code NCO, thus carrier frequency capturing and pseudo code capturing are realized.

The invention discloses a code phase identification based deception signal detection method of a satellite receiver. The method comprises the following steps that S1) when the satellite receiver recaptures and tracks signals, deception signal detection is carried out on the basis of code phase identification by utilizing peak value results related to pseudo code despreading in the baseband signal processing process of the satellite receiver; S2) if no deception signals are found via detection, a carrier movement state obtained by a track reckoning method and satellite movement state information obtained by ephemeris parameters are used to further carry out code phase identification on the recaptured and tracked signals, namely, the pseudo phase parameters despread by the satellite receiver are distinguished; and S3) if it is detected that the despreading demodulation signals of the satellite receiver include the deception signals, alarm is raised against the deception signals, the deception signals are isolated, and thus, capabilities of resisting cheating and interference of the satellite receiver are enhanced.

The invention discloses a method and a system for capturing a weak GNSS (Global Navigation Satellite System) signal under the condition of large-scale frequency deviation. The method comprises the following steps of: according to a pre-detection integration time, a carrier frequency and a sampling rate, determining a maximum carrier frequency searching step; dividing the whole frequency range to be searched into a plurality of carrier frequency units according to the maximum frequency searching step to realize rough search of the carrier frequency; mapping a received satellite signal onto each carrier frequency unit and regulating a local pseudo code rate according to the carrier frequency units so as to reduce the influence of code Doppler; calculating correlation in a flexible zero-padding mode through FFT (Fast Fourier Transform) / IFFT (Inverse Fast Fourier Transform) so as to realize code phase parallel search; and carrying out FFT operation on different correlation values corresponding to the same code phase so as to fulfill the aim of carrying out fine search on the carrier frequencies in the carrier frequency units. By the method and the system, a capturing speed and a capturing sensitivity of a receiver can be improved, so that the receiver completes the work of capturing a weak navigation signal pseudo code under the condition of the large-scale frequency deviation.

The invention discloses a burst direct sequence spread spectrum system and a pseudo code synchronization method of a burst direct sequence spread spectrum waveform thereof. By adoption of the burst direct sequence spread spectrum system disclosed by the invention, the capturing, tracking and convergence times of a burst direct sequence spread spectrum signal can be greatly shortened, and the frequency offset estimation precision is relatively high. The burst direct sequence spread spectrum system disclosed by the invention is realized by the following technical scheme: in a signal modulation system, a specific segment of lead data is added in front of user data after scrambling and channel encoding are carried out on the user data for accomplishing signal capture and synchronization; and in a signal demodulation system, pseudo code phase capture and carrier frequency offset capture are carried out on a digital baseband signal to accomplish signal capture, coarse pseudo code phase synchronization and coarse frequency offset compensation with a coarse synchronizer, precise signal synchronization of a coarse synchronization signal is separately accomplished by pseudo code phase and carrier phase synchronization loops, identification information and a starting position of a user data segment are determined from a precise synchronization signal by a frame synchronizer, and the user data are restored by channel decoding and descrambling.

The invention relates to a universal pseudocode synchronization system of comprehensive satellite baseband equipment, and the system comprises six parts, i.e. a digital lower variable frequency module (10), a tracking related module (20), a capture pre-processing module (30), a capture related module (40), a capture management module (50) and a tracking control module (60), and completes the pseudocode capture, carrier tracking, pseudocode tracking and bit synchronization functions of remote control or range finding data in a test to a satellite according to a preset process; and the six parts are realized in a field-programmable gate array (FPGA). According to the universal pseudocode synchronization system of the comprehensive satellite baseband equipment, the parameters of the capture module are configured flexibly according to the test needs of the actual satellite, so that the quick capture and tracking of various remote control signal or range finding signal pseudocodes are realized, and the system has better practical value and wide application prospect in the technical field of comprehensive satellite baseband testing.

The invention discloses a measuring method for pseudo code delay of a spread spectrum signal with high dynamic range and low signal-to-noise ratio. A spread spectrum receiver is used for performing ADC (Analog to Digital Converter) sampling on an intermediate frequency analog signal; the intermediate frequency analog signal is subjected to digital downconversion to obtain a baseband complex signal r(k)=I(k)+jQ(k); the baseband complex signal is simultaneously outputted to a pseudo code capturing unit, a carrier and pseudo code closed-loop tracking unit and a pseudo code time delay open-loop estimation unit; the carrier and pseudo code closed-loop tracking unit is used for tracking carrier frequency and pseudo code phase according to the captured doppler frequency and pseudo code phase information; a pseudo code time delay measuring pulse is used for outputting the doppler frequency and the pseudo code phase information to the pseudo code time delay open-loop estimation unit and outputting the pseudo code phase information to a pseudo code time delay calculation unit; the pseudo code time delay calculation unit is used for correcting closed-loop tracking measurement data of the pseudo time delay by using the open-loop estimation result and realizing quick high-precision measurement of the pseudo time delay. By the adoption of the method, the quick high-precision measurement of the pseudo time delay in the complex environment can be realized.

A long baseline satellite formation GNSS relative positioning method based on ambiguity fixing is provided in order to improve the success rate of ambiguity fixing and the accuracy of relative positioning results. According to the technical scheme, the method comprises the following steps: first, collecting and pre-processing input data, and determining the absolute general orbit of a formation satellite; then, eliminating the geometric distance and clock error in differential observation data, estimating a single-difference phase ambiguity float solution and a single-difference ionosphere delay parameter, carrying out double-difference transform to get a double-difference wide-lane ambiguity float solution and a covariance matrix, and fixing the double-difference wide-lane integer ambiguity and the double-difference narrow-lane integer ambiguity; and finally, outputting the relative positioning result of ambiguity fixing. By adopting the method of the invention, the problem that ambiguity fixing strongly depends on a pseudo code with low observation precision due to equally-weighted pseudo code and phase processing in M-W combination in the traditional method is avoided, the success rate of long baseline satellite formation GNSS relative positioning ambiguity fixing and the accuracy of final relative positioning results are improved, calculation is stable, and the reliability of relative positioning results is improved.

The invention relates to a method for rapidly capturing a multi-mode high dynamic spread spectrum signal which is realized based on an FPGA. The method comprises the steps of: (1) performing double interpolation and down-conversion on an input intermediate frequency sampled data, performing down-conversion on an intermediate frequency digital signal in order to form a zero intermediate frequency and output I and Q two-path zero intermediate frequency signals, (2) generating a zero intermediate frequency signal having a two-times bit rate, (3) inputting the sampled I and Q two-path data to a matched filter, performing relative operation by utilizing a time division multiplex folding algorithm, and outputting the relative operated result of n sections of single points of the I and Q two paths, (4) serially capturing a judged sample value and (5) performing non-coherent accumulation treatment on the serially captured judged sample value according to a pseudo code length in a capturing mode parameter in order to find out a maximum judged sample value and judge whether the value is more than a captured judgment threshold for the purpose of realizing capture judgment. The method can adapt to rapidly capturing a multi-mode high dynamic spread spectrum signal having multi-information rate, multi-pseudo code rate and multi-pseudo code length.

The invention discloses a full coherence accumulation time-frequency domain parallel capturing method based on FFT, in order to quickly capture a burst direct sequence spread spectrum signal with low signal to noise ratio and large frequency offset. The full coherence accumulation time-frequency domain parallel capturing method disclosed by the invention comprises two realization parts: pseudo code correlation based on FFT and full coherence accumulation based on FFT. Two methods of symbol correlation and zero complement FFT are used for further reducing the sinc loss in a pseudo code correlation process and the scallop loss in an accumulation process. The parallel capturing method is used for reducing the consumption of processing resources by the buffer of a large amount of intermediate data information and a parallel processing architecture based on FFT, obtaining a very high signal to noise ratio of a correlation peak within a short time, precisely evaluating Doppler frequency offset in a parallel search process of a pseudo code phase and reducing the average capturing time.

The invention provides a method for determining satellite navigation signal quality evaluation parameters. The satellite navigation signal quality evaluation parameters comprise Gabor bandwidth, error vector magnitude (EVM), amplitude error, phase error, pseudo-code consistency, phase deviation, phase loss, S curve offset and delay stability. By changing an ideal pseudo-code generating mode, common spread spectrum signals such as binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) can be evaluated, various special navigation signals such as binary offset carrier (BOC), alternate binary offset carrier (AltBoc), time division alternate binary offset carrier (Td-AltBoc) and time multiplexed binary offset carrier (TMBOC) can be evaluated; and by the high-precision evaluation of pseudo-code phase and carrier phase, each evaluation item of the navigation signals can be highly precisely evaluated, and the requirement on navigation satellite effective load testing can be met.

The invention provides a method for realizing interference resistance and multipath restraint of a navigation receiver with an array antenna. According to the method, an interference resistance and multipath restraint two-stage treatment structure adopting a digital correlator as a boundary for division is provided according to the difference of the influence of interference and multipath signals to navigation receiver baseband processing; in the first-stage processing, before de-spreading, a space-time covariance matrix of array receiving data is estimated at first, and the interference resistance is realized by utilizing a subspace projection technique according to the characteristic that the interference signal power is far greater than navigation signal power and noise power; in the second-stage processing, before de-spreading, the spatial smooth de-correlation treatment is carried out at first, then, a generalized sidelobe cancellation technology based on Householder transformation is utilized to carry out beam formation to realize the multipath restraint. Theoretical analyses and simulation results show that the cascade treatment technology can effectively suppress strong interference, and remarkably reduce the influence of the multipath signals to navigation receiver pseudo code measurement.

The embodiment of the invention provides a rapid associated acquisition device, comprising an intermediate frequency carrier removing module, a code generator, a sampling module, a register module, a matching filter, a relevant result memorizer, a secondary code stripping module, a data processing module and a signal detection unit. On the other aspect, the embodiment of the invention provides a rapid associated acquisition method. In the technical scheme provided by the invention, rapid associated acquisition to the secondary code-containing GNSS (Global Navigation Satellite System) signal is provided through the matching filter technology and the FFT (Fast Fourier Transform) technology, thus, the aim of associated acquisition of satellite pseudo code primary position and secondary code primary position is realized; and the carrier frequency can be searched in parallel, the limit of the frequency offset sensitivity of the secondary code to the searching step size when performing pseudo code and secondary code associated acquisition is solved, the calculated quantity is reduced greatly, and the acquisition speed is improved, so that the device and the method provided by the invention are not only suitable for weak signal reacquisition with prior information, but also suitable for cold start high sensitivity acquisition.

Characters of the method are that carrying out folding operation for mapping same segment of received signal into different frequency cells to implement parallel searching frequency cells; next, using parallel searching method for multiple code phases to implement parallel searching multiple code phase units; when implementing, the method determines number of frequency unit to be searched based on frequency range and step length for searching frequency, and then carries out folding operation for same segment of received signal mapped to different frequency cells; afterwards, using FFT technique for implementing parallel correlation between the folded signals and local pseudo code so as to realize parallel searching multiple code phases. Under condition of not increasing complexity of algorithm and hardware markedly, realizing parallel searching carrier frequency unit and multiple code phase units, the method raises searching speed, and reduces time for capturing pseudo code.

The invention relates to the technical filed of information processing, in particular to an image formula Chinese document retrieval method based on content, which solves the problem that the existing retrieval method based on the OCR technology can not effectively process the image formula document with serious character degradation. The method comprises the following steps: firstly, carrying out the character division on the image formula document to obtain single character image; secondly, extracting a characteristic vector of the character image; thirdly, constructing a hash function based on the local sensitive hash transformation principle LSH, transforming each characteristic vector of each character image to be a pseudo code, and establishing a character index database; and fourthly, inputting a query keyword to obtain the pseudo code expression of the query keyword, then comparing the pseudo code of the query keyword and the pseudo code in the character index database on the character similarity to further obtain all similar words of the query keyword, outputting the similar words according to the sequence thereof in the document, and finishing the retrieval. The invention is applicable to the Chinese document retrieval of the image formula.

A whole bit acquisition method for GPS weak signals relates to the acquisition treatment of a receiver in GNSS, and solves the problems that the prior software receiver can not forecast the information bit reversal, thereby easily causing the failure of the acquisition, and the better acquisition effect is difficult to achieve by adopting the differential coherent cumulative method. 20 sequences which are compressed into 4096 sampling points are acquired after satellite signals are subjected to the treatments related to frequency mixing, sampling, quantifying and time-domain averaging; the IFFT calculation is carried out after multiplying the 20 sequences with the sequences which are conjugated with the local stored pseudo-code FFT sequences through the FFT calculation; the maximum value which is obtained by the extraction after the mod squaring of the 20 two-dimensional pseudo-code auto-correlation value matrix is compared with a threshold value sigma 1, if the maximum value is larger than the sigma 1, the acquisition is successful; if the maximum value is smaller than the sigma 1, the whole bit algorithm is utilized to seek a peak value of the extracted related values by carrying out the coherent accumulation and the non-coherent accumulation of the 20 two-dimensional pseudo-code auto-correlation value matrix after the information bit reversal, the peak value is compared with the threshold value sigma 2, if the peak value is larger than the sigma 2, the acquisition is successful; and if the peak value is smaller than the sigma 2, the re-acquisition is carried out.

An IVR system designer receives design specification data (which may be either state definition data or IVR system document data) and stores it in a database. A design specification report can be generated based on the stored design specification data. The report may correspond to a chosen period of time or it may correspond to chosen version of the IVR system. It may provide one or more of the following: a summary of a state within the IVR system, a listing of the previous states that lead to the current state, prompts for the state, inputs for the state, a listing of decision outcomes, key performance indicator triggers for the state, global commands that are active in the state, business units for which the state is applicable, a sample dialogues listing, test scripts listing for testing the IVR system, a change history listing for the system, a design flow diagram for the system, or pseudo-code listing for a portion of the system.

The invention discloses a vector tracking-based GNSS / SINS deep integrated navigation method. The method includes the following steps that: after in-phase orthogonal signals outputted by a correlator are calculated by a phase discrimination function, an obtained phase discrimination result is adopted as measurement information of a pre-filter, so that a pre-filter model can be constructed to estimate tracking error information, and therefore, the pseudo-range and pseudo-range rate of a GNSS tracking channel can be obtained; an integrated navigation main filter performs processing according to the pseudo-ranges and pseudo-range rates outputted by the GNSS tracking channel and an SINS, so that pseudo-range deviation and range rate deviation can be obtained and are adopted as measurement variables quantity, and the measurement quantity is used for updating navigation error state variables, and updated navigation error parameters are fed back to the SINS, so that the navigation parameters of the SINS can be calibrated; and an integrated navigation system infers the signal tracking parameters of a GNSS according to the calibrated SINS navigation parameters and ephemeris information so as to control the local pseudo codes of a receiver and a carrier digital-controlled oscillator, and therefore, tracking for input signals can be maintained. The method of the invention has excellent anti-jamming performance and dynamic tracking ability, and has a bright application prospect.

The invention relates to the field of satellite communication and discloses a quick Beidou satellite signal capturing method and system based on a circulation mode. The method includes the steps that a Beidou satellite signal is received, and the satellite signal is processed so that a medium-frequency digital signal is obtained; a base-band signal is obtained according to the medium-frequency digital signal, and a complex signal of the base-band signal is obtained after further processing; numerical treatment is carried out on the complex signal and a signal output by a local pseudo-code generator, threshold judgment is carried out on a result, if a peak value larger than a threshold value occurs, the position corresponding to the peak value is determined to be a pseudo-code phase position, and a frequency value of a local carrier is captured as carrier frequency of the signal; if no peak value larger than the threshold value occurs, the searching range of Doppler frequency shift is adjusted, and circulatory capturing is carried out. According to the quick Beidou satellite signal capturing method and system, calculation in the capturing process of satellite signals is effectively reduced, complexity of the system is reduced, the capturing speed is high, capturing time is short, precision is high and the method and system are easy to use.

The invention relates to the field of satellite navigation and radio positioning, and discloses a ground-based high-precision regional positioning navigation system and a ground-based high-precision regional positioning navigation method. The ground-based high-precision regional positioning navigation system comprises a plurality of distributed navigation base stations, a datum station and a monitoring station, wherein each navigation base station has a navigation signal broadcasting function, is equipped with transmitting and receiving antennas, and adopts a broadband variable-frequency channel design; 2) the navigation base stations and the datum station adopt a bidirectional time synchronization method to achieve time synchronization among the navigation base stations, and the datum station has a GNSS time reference function; the monitoring station has a navigation signal quality monitoring, evaluation and calibration function, and the monitoring station and the datum station can beco-locational. The invention further discloses a high-precision positioning method, which determines initial position coordinates of a receiver based on a single-difference pseudo code phase measurement value, and assists in completion of carrier ambiguity resolution and high-precision positioning. The ground-based high-precision regional positioning navigation system has the advantages of high environment adaptability, high positioning precision, high anti-interference performance, easy deployment, low cost, scalability and GNSS system cooperative work capability.

The invention discloses a direct sequence spread spectrum (DSSS) communication pseudo code capture method used in a wireless sensor network (WSN). The method comprises the following steps: step 1. carrying out differential treatment to an input signal and a local pseudo code, using a circumferential related characteristic of FFT to perform parallel search pseudo code phase to the input signal and the local pseudo code after the differential treatment, adjusting the local pseudo code phase so that the local pseudo code phase is synchronized with the input signal pseudo code and completing the pseudo code phase capture; step 2. using the FFT to perform parallel search carrier frequency offset to the input signal and the local pseudo code after the pseudo code synchronization and completing frequency offset correction. By using the pseudo code capture method of the invention, search time can be shortened and a search speed can be increased. The capture time can not be increased as a length of the pseudo code is longer and carrier wave frequency offset is larger. A correlator does not needed during a capture process. Resource consumption is low. The method can be flexibly modified according to a requirement of a system to a signal to noise ratio.

The invention provides a long distance and high accuracy oriented compound laser range finding method and system. According to the range finding method, the transmitting terminal uses two independent light sources with different wavelengths to generate two channels of range finding signals for performing range finding through a pulse coding method and a phase method respectively. The pulse coding method is a combination of a low order pseudo code signal with an impulse method. The range finding system includes two continuous lasers, an m-sequence signal modulation unit, a phase modulation unit, a pair of optical antennas, two photoelectric detectors, a pulse code processing module, a phase processing module and a range finding result calculation unit. According to the range finding system, two channels of range finding signals can be independently measured, free of interference by a pulse coding method and a phase method respectively; and the range finding results from these two methods are compounded for higher range finding accuracy. Also in the invention, the accuracy advantage of the pseudo-code range finding method is introduced into a conventional impulse method, which increases the measuring accuracy. Compared to the conventional impulse method, the method of the invention can better cope with interference. It takes a shorter pseudo-code acquisition matching time than the pseudo-code range finding method.

The invention provides a GPS (Global Positioning System) pseudo-random code tracking loop for preventing multi-path interference and a method for preventing the multi-path interference thereof. The loop comprises a mixer, a correlator, an integration accumulator, a small wave phase detector, a loop filter and a local pseudo-random code generator. In the invention, the GPS pseudo-random code tracking loop adopts the small wave phase detector to detect a discontinuity point wherein the self-correlation function curve slope changes into a positive value from a zero value, is more accurate in the phase detection result, is free from the influence of the number of multi-path signals, and does not need to estimate the multi-path signals. In the invention, the pseudo code tracking accurate of the GPS pseudo-random code tracking loop is higher than the tracking accuracy of the typical sooner-later pseudo code delay locking loop so that the measurement accuracy of the pseudo range is improved; therefore, the invention is beneficial to positioning accurately.