79results about How to "Low probability of intercept" patented technology

A method and apparatus for determining the range, radial velocity, and bearing angles of scattering objects reflecting RF signals or for determining the range, radial velocity, and bearing angles of sources RF signals. An array of antenna elements is utilized, the array of antenna elements each having an associated two state modulator wherein transmitted and/or received energy is phase encoded according to a sequence of multibit codes, the bits of the multibit codes each preferably having two states with approximately a 50% probability for each of the two states occurring within each given multibit code in said sequence of multibit codes, thereby allowing the determination of range, radial velocity, and bearing angles through digital computation after the scattered signals have been received.

In one embodiment, the disclosure relates to a method for estimating and predicting a target emitter's kinematics, the method including the steps of: (a) passively sampling, at a first sampling rate, an emitter signal to obtain at least one passively measured signal attribute for estimating the target kinematics; (b) inputting the passively measured signal attribute to an estimator at a first sampling rate; (c) determining a radar duty cycle for active radar measurements as a multiple of the first sampling rate, the multiple defining a duration between radar transmissions; (d) directing a radar system to make active target measurements at the determined duty cycle; (e) inputting to the estimator the active target measurements at the determined duty cycle, while continuously inputting the passively measured signal attributes.

The invention discloses a method for guaranteeing secure transmission of wireless data based on fountain codes. The method comprises the following steps that each time slot sending end adopts a fountain code method to complete a check package encoding process; after the check package generated at the sending end is subjected to CRC (Cyclic Redundancy Check) coding of a data link layer and channel coding of a physical layer, the check package is sent to a legal user, and a tapping user taps current time slot transmission check package information; when packet loss does not occur in the channel, a legal receiving end completes a decoded operation of the received check package, and updates a set of serial numbers of decoded information packets and feeds the set back to the sending end after correct decoding, otherwise the set of the serial numbers of the decoded information packets is not updated; and the legal receiving end judges whether the number of the successfully decoded information packets is equal to the number of source information packets and decides whether to inform the sending end to stop sending the check package according to the information. According to the method, real-time adjustment of an encoding scheme for the sending end is carried out according to the decoding speed of the legal user, so that the intercept probability for the tapping user in a wireless data transmission process is remarkably reduced and the transmission efficiency of the sending end is improved.

The invention relates to a method for acquiring a wide-band frequency modulation stepped chaos radar signal, which comprises the following steps: acquiring an echo baseband signal rn(t) of each subpulse; then, correspondingly carrying out matched filtering or correlation processing on the baseband echo signal rn(t) of each subpulse and the respective baseband chaos sequence, thus obtaining a frequency domain signal Un(f) of each subpulse; carrying spectral migration on the frequency domain signal Un(f) of each subpulse, and then carrying out de-overlapping and phase compensation, wherein the frequency shift quantity of the spectral migration is equal to the frequency interval DELTAf of a local frequency source; and carrying out coherence stack on the subpulse signal subjected to de-overlapping and phase compensation, thus obtaining a synthesized large wide-band signal, wherein the band width of the synthesized wide-band signal is B+(N-1)DELTAf. The invention provides a new technical route for realizing a chaos radar signal having an ultra large band width. By combining the chaos signal and the frequency stepped signal, the advantages of the both are combined. The method provided by the invention is simple and clear, is easy to realize, is applicable to frequency linear/nonlinear stepping and has important practical meanings in an actual system.

The invention discloses a laser frequency hopping underwater acoustic-induced digital communication system and a laser frequency hopping underwater acoustic-induced digital communication method. The reliability and security of both parties of communication in information transmission are guaranteed according to the channel characteristics of a communication environment. According to the invention, atmospheric optical communication and underwater acoustic communication are combined, the laser frequency hopping technology is adopted, a laser emits laser light under the control of a code formed by loading information to different repeated-frequency frames, and laser energy is transmitted by atmosphere to the surface of water and then interacts with water medium through evaporation or breakdown. Thus, optical wave energy is converted into acoustic wave energy which is transmitted underwater in different directions and can be received by an underwater acoustic collector placed in any position within a certain range underwater, and thus, non-line-of-sight data communication from air to underwater can be completed. As long as both parties of communication abide by an agreed laser frequency hopping communication protocol, the information security and privacy of both parties of communication can be guaranteed to a certain extent. Thus, the communication method applicable to an open channel environment has more practical values.

The invention discloses a low-probability-of-intercept transmitted signal waveform design method based on FDA-OFDM. The invention solves the technical problem that a frequency diversity array transmitted signal is easy to intercept and interfere. The low-probability-of-intercept transmitted signal waveform design method comprises an implementation method of: constructing an array model of a frequency diversity array; designing an orthogonal transmitted signal; constructing an array oriented matrix A; defining a weighting moderate matrix W; and by the array oriented matrix A and the weighting moderate matrix W together, obtaining a frequency diversity array beam energy diagram so as to complete low-probability-of-intercept transmitted signal waveform design based on FDA-OFDM. According to the invention, the transmitted signal adopts orthogonal waveform design; each array element uses two orthogonal subcarriers; a transmitted signal beam pattern is changed from conventionality, complexity is improved, and the transmitted signal beam pattern is a result of overlaying two transmitted signals at an assumed target position. According to the invention, the probability of intercepting andidentifying the transmitted signals is reduced, interference resistance is promoted, and the low-probability-of-intercept transmitted signal waveform design method is beneficial for implementing low-probability-of-intercept performance of the signals. The low-probability-of-intercept transmitted signal waveform design method can be applied to a frequency diversity array MIMO radar, inhibition on distance correlation interference and spuriousness and low-probability-of-intercept electronic detection.

The invention belongs to a radar and communication integrated scheme based on a radar launching mode of a TDCS (Transform Domain Communication System), introduces the TDCS and is particularly applicable to a super-resolution radar and communication integrated system requiring self-adaptive frequency conversion and initiative anti-interference as well as low interception rate. According to a super-resolution radar and communication integrated method based on TDCS radar launching mode, a launching signal can self-adaptively adjust the launching frequency, signal interference is initiatively avoided while the spectrum efficiency is improved, and besides, the demand for low acquisition probability is also met because of CCSK (Cyclic Code Shift Keying) modulation.

The invention belongs to the technical field of coherent transferring type jamming inhibition techniques, and in particular relates to a coherent transferring type jamming inhibition method for airborne radar. The coherent transferring type jamming inhibition method specifically comprises the following steps: firstly, detecting and estimating the parameters of transferring type jamming through high repetition frequency pulse strings emitted from the radar, and optimizing a transmitting direction graph by using the estimated jamming parameters, thereby forming zero trap in a jamming reconnaissance direction, reducing the probability that a transmitting signal is intercepted, and achieving the purpose of reducing the interception rate in the direction of a jammer. Due to the active confrontation on the transferring type jamming, the burden of a receiving end in signal processing is effectively alleviated. Therefore, a self-adaptation transmitting method based on jamming inhibition has significant practical meanings.

An improved spread spectrum communications system is disclosed in which M-ary symbols are defined corresponding to each state of digital data to be transmitted and in which each of those M-ary symbols are represented by a plurality of tones selected from a set of N frequencies. A different plurality of tones out of the set N is established to represent each of the M-ary symbols during each successive timing interval, with selection of the tones comprising each such plurality of tones being determined in accordance with a known coding pattern. Phasing of the tones comprising each such plurality is also determined in accordance with a known coding sequence. After selection of the symbol corresponding to the data to be transmitted during a given timing interval, the frequency domain representation of the plurality of tones corresponding to that symbol is converted to the time domain for transmission. That time domain signal is converted back to the frequency domain by the receiver and the resultant signal processed by M-ary signal correlators synchronized with coding established by the transmitter to determine the transmitted symbol.

Devices and methods for transmitting and receiving communications are disclosed. These communications comprise using stealth assemblers and stealth interpreters to construct and interpret false start-of-frame delimiters, alternative preambles, and/or modified protocols in packets.

An assembly of simultaneously transmitted electrically generated signals, which contains a subset of binary spreading-code sequences that are members of a larger set of binary spreading-code sequences abailable to a particular node of a multi-node communication network. All sequences in the set of spreading-code sequences available to the particular node of the network can be generated by the same configuration of two linear-feedback binary shift registers, where feedback taps of the two linear-feedback binary sift registers correspond to primitive polynomials of the same degree over GF(2), the field of two elements.

The invention relates to a burst hybrid spread spectrum underwater sound covert communication method. The method is characterized by comprising the steps that step 1, information to be sent is divided into three groups, BPSK spread-spectrum modulation, CSK spread-spectrum modulation and MFSK spread-spectrum modulation are conducted on the three groups of information respectively, and three signals are mixed and modulated on frequency orthogonal carrier waves; step 2, the mixed and modulated signals are randomly sent in a pulsing mode; step 3, the signals are captured and tracked by a receiving end through a time-frequency two-dimensional search algorithm; step 4, the synchronized signals are demodulated, parallel-serial conversion is conducted on demodulated data, and therefore the sent information is obtained.

The invention relates to a mine communication system, in particular to a mine bi-directional speech direct-sequence spread-spectrum and through-the-earth communication system and method relating to the spread spectrum technique. A terrestrial television transceiver of the mine bi-directional speech direct-sequence spread-spectrum and through-the-earth communication system is communicated with a loop antenna and a handheld terminal, and the handheld terminal is communicated with a positioning device. A mine television transceiver is communicated with a mine loop antenna and a mine handheld terminal. A direct sequence spectrum communication system is arranged between the terrestrial loop antenna and the mine loop antenna. By adopting the proposal, the invention has the advantages of anti-interference, multi-path and low interception rate due to the direct-sequence spread-spectrum digital wireless communication system and can be used for bi-directional speech through earth communications. The mine bi-directional speech direct-sequence spread-spectrum and through-the-earth communication system and method apply to accident warning and rescue in mineral enterprises.

The invention discloses a radar communication waveform design method based on sparse frequency. The method includes the steps that step1, a radar Tag system receives scattering radar echoes, and a power spectral density matching method is adopted for designing sparse frequency radar waveforms for the scattering radar echoes; step2, eigen decomposition is performed on the sequence of the sparse frequency radar waveforms to obtain an eigenvector group, and part of the eigenvector group is used for designing communication waveforms; step3, the communication waveform obtained in the step2 are embedded into the obtained sparse frequency radar waveforms, and obtained hybrid waveforms are sent to a radar receiver. Compared with linear frequency modulation waveforms, the sparse frequency waveforms can widen the occupied space of a frequency band of communication signals, and therefore a higher communication rate can be obtained; meanwhile, communication signal samples are mutually orthogonal and related with the sparse frequency waveforms to some degree, and therefore it can be guaranteed that the error rate and interception rate of the communication signals are low.

The invention discloses a chaotic optical network physical layer protection method and system, a networking method and a network, related to the physical layer protection field of a chaotic optical network. The multi-dimensional physical layer protection method comprises the following steps: a transmitting end performs digital chaotic encryption after performing optical chaotic phase modulation, so as to control the speed of polarization change and the change amount of each time, and realize two-level hardware encryption in the physical layer of the chaotic optical network; and a receiving endfirst performs digital chaos decryption, and then performs optical chaotic phase demodulation, so as to realize two-level hardware decryption in the physical layer of the chaotic optical network. Theinvention encrypts in three dimensions of time, frequency and polarization; the chaotic signal and polarization disturbance obviously enhance the secrecy; and the speed of polarization change and thechange amount of each time are controlled; so that the intercept probability is significantly reduced.

The invention relates to a wideband frequency-modulation stepping noise radar signal processing method based on compressive sensing. The method comprises the following step of combining a noise signal, a frequency steeping signal and the compressive sensing, so that the method combines advantages of the noise signal, the frequency steeping signal and the compressive sensing, keeps the advantages of frequency stepping signal narrowband treatment, and also has the features of low intercept probability of the noise signal, interference resistance, and good electromagnetic compatibility; and meanwhile, the method also combines the compressive sensing to obtain a high-resolution image by utilizing a low data amount. According to the method disclosed by the invention, under the condition that an observation target is sparse, the requirements of (ultra) wideband signals on receiver A/D (Analogue to Digital) sampling, storage and transmission equipment are reduced and the method is easy to realize, so that the wideband frequency-modulation stepping noise radar signal processing method based on the compressive sensing has important real meaning to an actual system.

The invention discloses a method for radar waveform designing and optimization, wherein the method belongs to the field of radar communication technology. The invention aims to provide the method for waveform designing and optimization, wherein the waveform has characteristics of relatively good thumbtack ambiguity function, low interception probability, relatively high interference resistance, good orthogonality, relatively low peak value power ratio, controllable spectral shape, controllable signal sparsity, controllable signal reconfigurability, etc. According to the method, a related dictionary is optimized according to the requirement for spectrum controllability and low peak mean value power ration in radar waveform design. Furthermore a signal generating system is formed by a signal synthesizing part, an observation matrix part and a sparsity coefficient control part in a closed-loop manner. In signal synthesizing, an output signal is generated according to the dictionary and the sparsity coefficient; a compressed signal is obtained from an output signal through an observation matrix; and the sparsity coefficient required for signal synthesizing at next time is directly obtained from the compression signal through a sparsity coefficient control system. Then in a signal reconstruction system, a reconstructed signal is synthesized from the compressed signal according to the information of the dictionary through the sparisity coefficient control system. The method for radar waveform designing and optimization realizes relatively good application characteristic of the designed radar waveform.

The invention discloses and relates to a radar waveform amplitude and phase modulation method based on mixed sequences and belongs to the field of radar transmitted waveform design. The method comprises steps of 1: obtaining to-be-modulated signals, judging periods requiring the signals, identifying numbers N of sub-pulse in one period where signals should be modulated, and mixing the tent sequence and the logistic sequence in proportion of 1:1 to obtain a mixed sequence with code length of N; using the mixed sequence in the step 2 to modulate phase positions of all pulse in the obtained periods; using the mixed sequence in the step 2 to modulate amplitude of the obtained modulated signals; and outputting modulation results. Combining advantages of amplitude modulation and phase modulation, signal amplitude and phase positions change along with chaotic signals, so complexity is increased and interception probability is reduced.

The invention belongs to the field of radar systems and particularly relates to a novel radar imaging method based on phase encoding orthogonal frequency division multiplexing (OFDM) signals. According to the specific technical scheme, a radar transmitting terminal transmits complementary phase encoding OFDM signal pulse pairs, a radar receiving terminal conducts pulse compression and overlaying on two pulse echoes, a one-dimensional range profile of a target is obtained, and signals complementary to the original phase encoding OFDM signals are worked out by means of a self-adaptive clone selection algorithm. The algorithm takes original phase encoding matrixes as antigens and complementary phase encoding matrixes as antibodies, and the optimal antibody with the maximum fitness function is sought as a solution through the superiority-inferiority degree of a fitness function measurement solution. The distance sidelobe of the phase encoding OFDM signals at the pulse repetition time is lowered, so that the resolution of radar imaging is improved, the intercept probability of radar signals is lowered, and anti-interference, anti-fading, multipath suppression, clutter interference and other properties are improved.

The invention relates to physical layer encryption in the technical field of wireless communication safety, and in particular relates to a method and device for encrypting MMSE (minimum mean square error) pre-equalization wireless channel based on multipath redundancy. In the method, under a TDD (time division duplex) working pattern, 1) firstly, a receiver sends channel detection signals by utilizing an upstream channel, wherein the channel detection signals are used for detecting a multipath channel; 2) the receiver estimates wireless channel multipath information between the receiver and atransmitter according the received channel detection signals sent by the upstream channel; 3) the wireless channel multipath information is subjected to turnover treatment; 4) a pre-equalization factor is obtained on the basis of a power constraint condition according to the wireless channel multipath information; and 5) signals to be sent are pretreated by utilizing a pre-equalization factor anda pre-treatment factor. According to the invention, based on the multipath redundant property of the wireless channel and time diversity concept, the environment adaptivity is introduced in a wireless wide band communication system by utilizing a time-reversal technology, the channel is encrypted by utilizing time reversal, and the safety issue brought by broadcast property of the wireless channel is solved.