39 results about "Pulse-position modulation" patented technology

The invention discloses a chaos communication and perception integrated signal processing method and device and a communication system, and the method comprises the steps: segmenting an information bit sequence into a modulation bit sequence, an index bit sequence and a PPM bit sequence, and carrying out the processing of an initial signal vector through the combination of a pulse position modulation technology, according to the scheme, the frequency spectrum utilization rate is optimized through dual control of modulation bits and index bits, initial modulation signals are segmented according to PPM orders, signal vectors are generated, time domain offset is carried out on the signal vectors in combination with a shift matrix, the good self-correlation characteristic and the low cross-correlation characteristic of LFM signals are utilized, on the basis of an original DCSK-LFM modulation mode, the frequency spectrum utilization rate is improved, and the frequency spectrum utilization rate is improved. And in combination with pulse position modulation and index modulation, the same carrier can bear more information, so that the transmission rate when the method is applied to a JRC system and the overall performance of a communication system are improved.

The embodiment of the present application provides a laser communication modulation method and system thereof, which can solve the technical problem of poor sensitivity of free-space laser communication under extremely low signal-to-noise ratio conditions. The method includes performing polarization-selective modulation on a coding sequence to obtain multiple groups of linearly polarized light pulses. Each group of linearly polarized light pulses is sent to different photon detectors through different channels to obtain a first photon count and a second photon count. According to the first photon count and the second photon count of all groups of linearly polarized light pulses, a log-likelihood ratio is obtained through soft decision. Then, the original information prediction value is obtained through channel decoding. In this way, polarization-selective pulse position modulation and its corresponding demodulation method can obtain better communication sensitivity and stronger resistance to background noise compared to PPM‑PC. In addition, optical signals in different polarization states carry different data respectively, and are then transmitted in sequence, with a high transmission rate.

The invention discloses a high-robustness pulse position modulation signal receiver, and the receiver comprises a clock data recovery circuit which receives a PPM signal, carries out the continuous frequency division processing, and generates two clock signals CLKB and CLKJZ; the PPM decoding circuit is used for outputting demodulation data and feedback signals; the self-calibration current feedback circuit is used for receiving clock signals CLKB and CLKJZ and a feedback signal, selecting one of the CLKB and the CLKJZ to be output to the PPM decoding circuit based on judgment on the feedback signal, and outputting a control word ICTRL to the current digital-to-analog converter; and the current digital-to-analog converter is used for inputting a reference current IBG and the control word ICTRL from a band-gap reference and outputting a current ICP to the PPM decoding circuit. The decoding circuit has the advantages of being simple in structure, low in power consumption, high in robustness and the like, and data demodulation of PPM signals can be achieved more reliably.

The invention discloses a high-frequency injection type laser wireless energy transmission system which comprises a transmitting end, a receiving end and a mixed pulse position modulation module, the transmitting end is composed of a straight current source, a pulse current source and a semiconductor laser, and the receiving end comprises a photovoltaic cell, a Boost converter, a demodulation circuit and a load. In the system, a pulse signal is transmitted based on a complementary protocol of a data code and a check code; the straight current source provides stable power transmission, the improved pulse current source based on the LCL resonant converter realizes high-speed information modulation, and the problems of high switching loss and remarkable trailing effect in the traditional scheme are solved. According to the hybrid multi-pulse position modulation method provided by the invention, the coding efficiency is improved by dynamically distributing pulse position combinations, the power fluctuation is balanced by the complementary verification protocol, the problems of power and information restriction and energy and communication function interference of a traditional system are solved, the communication rate is improved, and the method is suitable for the fields of Internet of Things, industrial intelligent equipment and the like.

The invention discloses an efficient soft demodulation method and system suitable for pulse position modulation, and relates to the technical field of laser communication. Pulse position modulation signals and preset channel parameters are received, and time slot receiving signals are acquired based on the pulse position modulation signals, the preset channel parameters comprise the optical signal intensity and noise power of a Gaussian channel, the pulse optical signal electron number of a Poisson channel and the electron number of an ambient optical signal; inputting the time slot receiving signal and a preset channel parameter into a pre-established soft demodulation model based on a maximum posteriori and a maximum likelihood criterion, and outputting to obtain a log likelihood ratio LLR of a modulation bit; meanwhile, the index logarithm operation of the LLR is simplified by adopting a max-log method, and the calculation complexity is reduced; aI is adopted to optimize the scaling coefficient for the performance loss caused by soft demodulation calculation simplification to balance the performance loss and the implementation complexity, so that the transmission efficiency of PPM modulation is improved.

The embodiment of the invention provides a laser communication modulation method and system, which can solve the technical problem of poor free space laser communication sensitivity under the condition of extremely low signal-to-noise ratio. The method comprises the following steps: performing polarization selection modulation on a coding sequence to obtain multiple groups of linearly polarized light pulses; and sending each group of linearly polarized light pulses to different photon detectors through different channels to obtain a first photon count and a second photon count. And obtaining a log-likelihood ratio through soft decision according to the first photon count and the second photon count of all groups of linearly polarized light pulses. And an original information prediction value is obtained through channel decoding. Thus, compared with PPM-PC, better communication sensitivity and stronger background noise resistance can be obtained by performing polarization selection pulse position modulation and a corresponding demodulation mode. And the optical signals in different polarization states respectively bear different data, and then are respectively transmitted in sequence, so that the transmission rate is high.

The invention discloses a frame conversion DCSK system based on pulse position modulation and a communication method, the system comprises a modulator and a demodulator, and the modulator and the demodulator transmit signals through a channel; the modulator is used for generating a chaotic signal and applying dynamic frame transformation to the chaotic signal to construct a frame structure with time slot variability; and the demodulator is used for receiving the modulation signal sent by the modulator to obtain a received signal, and carrying out dynamic frame structure adjustment and multi-path delay alignment processing on the received signal. Compared with the prior art, the method has the advantages that a frame transformation mechanism and a pulse position modulation technology are introduced, so that the reconstruction of a chaos signal frame structure and the optimization of an information mapping mode are realized. Partial information bits are used for pulse position mapping, and only a single pulse is excited in a sparse vector, so that a modulation signal has stronger anti-interference capability, and the robustness of a system in a low signal-to-noise ratio environment is effectively improved.

The invention discloses a free space optical communication and sensing integrated system based on intensity modulation direct detection and time domain cross-correlation, and belongs to the field of optical communication, the system adopts an intensity modulation direct detection architecture, a transmitter uses a differential pulse position modulation signal, a DPIM signal is loaded to an optical carrier through a Mach-Zehnder modulator, and the DPIM signal is transmitted to the optical carrier through the Mach-Zehnder modulator; shaping the light beam and coupling the light beam into a free space; and the receiver couples the spatial optical signal into the optical fiber and demodulates the spatial optical signal after photoelectric conversion, so that a communication function is realized. And the transmitter receives the echo optical signal reflected by the receiver, performs analog-to-digital conversion on the echo optical signal, and then obtains the time delay of the echo signal compared with the transmitting signal by combining with a time domain cross-correlation algorithm, thereby obtaining the distance information of the two communication parties. According to the system, the radar ranging function is seamlessly integrated into a free space optical communication system, the communication and ranging functions can be simultaneously realized without additional hardware, the two functions can be simultaneously performed without mutual interference, and the system has the advantages of simple structure, low cost and high ranging precision.

An optical receiver implements a method to provide a digital output of a received on-off keyed optical signal. The method includes receiving an on-off keyed optical signal via a coherent optical front-end receiver utilizing a locally mixed laser LO for a reference signal to perform quadrature detection of the optical signal to generate an electrical signal, performing symbol / slot timing recovery on the electrical signal using a timing error detector, performing carrier frequency and phase recovery on a symbol / slot signal to generate a frequency and phase recovered signal, and demodulating the frequency and phase recovered signal via a demodulation circuit to provide a digital output representative of the received on-off keyed optical signal.

An anti-interference distance measurement device and method, the device comprising a pulse position modulator (1011) and a phase shift keying modulator (1012) connected to the pulse position modulator (1011); the pulse position modulator (1011) is used to generate a baseband signal according to a random number signal; each random number in the random number signal corresponds to a pulse position of the baseband signal; when there are multiple consecutive identical random numbers in the random number signal, there are M time intervals between the pulse positions corresponding to the multiple consecutive identical random numbers in the baseband signal; the phase of the random number signal and the baseband signal are synchronized; the phase shift keying modulator (1012) is used to modulate a carrier signal and a baseband signal to generate a first signal; the first signal is used to drive a light emitter (103) to generate a first pulse light to illuminate an object to be measured. The anti-interference distance measurement device and method can improve the anti-interference ability of the distance measurement signal.

The invention discloses a laser acoustic cross-medium pulse position modulation method based on 8B / 10B coding, which is used for improving the transmission rate of laser acoustic cross-medium communication. The method comprises the steps that 8B / 10B coding is adopted to balance the number of 0 and 1 in data, eight different pulse positions are utilized, three-bit data are transmitted in each laser operation, and the specific relation between the pulse positions and the corresponding data is modulated, and adjacent pulse symmetric coding and idle code implementation are adopted. According to the method, the problem of transmission rate caused by pulse position modulation change under the condition that the position of the previous pulse moves backwards and the position of the next pulse moves forwards is solved, and the bit error rate caused by position misjudgment is reduced.

The application discloses a kind of multistage separation integrated processing method and device, for the process synergy of existing technology is poor, separation efficiency is low, and secondary emulsification is prone to occur and so on, the application is controlled by PLC system coordination, in turn, filtering, heating, coupling enhanced separation, chaotic electric field dehydration, vacuum circulation separation and multi-gradient fine filter processing are carried out.Coupling enhanced separation unit combines electric field pre-separation and cyclone centrifugal enhanced separation;Chaotic electric field dehydration unit uses pulse position modulation electric field to destroy emulsion interface;Vacuum circulation separation unit realizes depth purification under negative pressure environment.The scheme realizes the step-by-step efficient removal of different particle size impurities in industrial waste oil, and the quality of regenerated oil is significantly improved, and the energy consumption of the system is greatly reduced.The device adopts modular design, and each unit is intelligently coordinated, with high processing efficiency, strong adaptability, stable operation and other advantages, providing reliable technical support for industrial waste oil resource utilization.

The invention provides a flight control signal decoding method and an unmanned aerial vehicle flight attitude adjusting method thereof, and relates to the technical field of unmanned aerial vehicles. The decoding method comprises the following steps: acquiring a pulse position modulation signal of a plurality of flight control instructions containing multiple channels, wherein the pulse position modulation signal represents the relationship between the pulse time interval of each channel and the corresponding flight control instruction; the pulse position modulation signal is detected, under the condition that the rising edge of the pulse position modulation signal is detected and triggering is interrupted, the counting result of a preset timer at the current moment is obtained, and the rising edge represents the critical moment when the level of the pulse position modulation signal jumps from the low level state to the high level state; determining a pulse period of each channel in the pulse position modulation signal based on a counting result of the timer; and decoding the pulse position modulation signal according to the pulse period to obtain a plurality of flight control signals corresponding to the plurality of channels.

According to the high-speed multi-mode chaos spread spectrum communication method, a transmitting end obtains transmission efficiency higher than that of traditional chaos differential keying, a chaos shaping filter modulates a bit stream into a chaos signal and uses the chaos signal as a reference signal, the limitation that in traditional DCSK communication, the reference signal cannot transmit information is avoided, and the communication rate is increased; orthogonal signal groups generated by chaotic signals through Schmidt orthogonalization realize same-frequency-band undisturbed transmission of multiple groups of signals, and each group of orthogonal signals is subjected to chaotic differential keying modulation and pulse position modulation respectively, so that a communication rate far higher than that of DCSK is obtained under the same spread spectrum gain; a receiving end carries out matched filtering / downsampling and summation filtering on a received reference signal, so that the noise interference of the reference signal is effectively reduced. And information decoding is performed by using the reference chaotic signal reconstructed by the decoding symbol and the orthogonal signal group, so that noise interference caused by the reference signal passing through a wireless channel is further reduced, and low-bit-error-rate decoding of an information path is facilitated.

The invention discloses an absorption shift keying molecular communication system and method based on a genetic algorithm codebook. The system comprises a model construction module, a codebook generation module and a signal demodulation module. The model construction module is used for constructing a molecular communication model under an absorption frequency shift keying architecture, and a sending end adopts an absorption frequency shift keying combined pulse position modulation as a hybrid modulation scheme of the molecular communication model; the codebook generation module is used for establishing a fitness function taking decoding error probability minimization as a target, optimizing a codebook through a genetic algorithm, and dynamically generating a system codebook adaptive to molecular channel characteristics; the signal demodulation module optimizes a molecular communication model based on a system codebook in combination with a two-step detector, and performs signal demodulation at a receiving end by using the optimized molecular communication model. The method is superior to an existing coding scheme, and the reliability of a molecular communication system under the condition that absorption frequency shift keying is combined with pulse position modulation under the constraint of an actual molecular channel is obviously improved.

The application discloses a kind of bionic concealed underwater acoustic communication detection integrated method.Existing method does not consider the concealment of communication and detection jointly.The method of the present application first extracts click sound signal and whistle signal, and carries out power and correlation screening;Then the original click sound signal is waveform encoded and pulse position modulated, and the original whistle signal is time-frequency shape encoded and waveform parameter modulated.Using the good detection performance of bionic modulated signal, generate bionic communication detection integrated signal.In echo signal receiving end, different echo signal processing method is used.In communication receiving end, combined demodulation method is used.The bionic whistle signal generated by the present application has high similarity with the original signal in time domain, and the time-frequency profile is continuous.The present application can improve the communication rate by sampling combined modulation, has good concealment, not only can realize the accurate estimation of target distance, speed and azimuth, but also has good communication performance.

The application discloses a torque sensor, comprising: a middle shaft; a shaft sleeve assembly fixed to the outer periphery of the middle shaft; the shaft sleeve assembly comprises a shaft sleeve body, a first control board and a first coil, the first control board and the first coil are both mounted on the shaft sleeve body; a disc claw assembly is sleeved on the periphery of the middle shaft and is in transmission connection with the middle shaft, the disc claw assembly comprises a strain gauge, a second control board and a second coil; wherein the second control board is configured to generate a pulse position modulation signal after digitally encoding the voltage signal output by the strain gauge; the duty cycle of each symbol in the pulse position modulation signal is not greater than 1 / 3; the first control board is configured to receive the pulse position modulation signal and output torque information after decoding. The torque sensor has low cost and high precision. In addition, the disc claw assembly and the shaft sleeve assembly can be arbitrarily matched, thereby improving the manufacturability and maintainability.

The invention discloses a semiconductor wafer factory carrying equipment communication method based on infrared light. The method comprises the following steps: establishing a non-contact communication link between process equipment and carrying equipment through an infrared light signal; mapping the IO signal into infrared pulse positions in different time slots by adopting pulse position modulation; non-contact communication link fault tolerance is realized through dual-channel redundancy; time sequence synchronization of the process equipment and the carrying equipment is realized by sending a timestamp synchronization frame; the communication quality is guaranteed through dynamic power adjustment and an error retransmission mechanism; and when the control instruction is transmitted, closed-loop confirmation is completed through safety interlocking logic. State interaction and control instruction transmission between the semiconductor equipment and the OHT are achieved by modulating infrared light signals, the problems of abrasion, pollution, high alignment precision requirement and the like existing in traditional physical contact type IO communication are solved, and the method is suitable for a semiconductor wafer factory automatic transportation system with high cleanliness and high reliability.

A WIRT system uses synchronizable PPM waveforms to convey information and power from an ET to a remote, far-field EH. In so doing, the solution presented herein reduces receiver complexity, optimizes power transfer, and meets information transfer requirements. The synchronizable PPM waveform comprises a plurality of pulsed-modulation symbols, each of which comprises one or more pulses position-modulated responsive to the information to be conveyed to the EH. The ET configures at least one pulse in each symbol of said synchronizable PPM waveform according to one or more synchronization constraints to enable symbol synchronization at the EH. The EH converts the RF power of the received synchronizable PPM waveform to a DC voltage, and synchronizes the received PPM waveform to extract the information in the PPM waveform.

The application discloses a kind of laser communication and laser imaging integrated system, including transmitting end and receiving end;The transmitting end includes the communication signal modulation unit, pulse laser source and transmitting optical path connected in sequence;The receiving end includes receiving optical path, photoelectric detector, amplification circuit, signal acquisition unit, communication signal demodulation unit and image reconstruction unit;The laser communication and laser correlation imaging mode based on pulse position modulation are used in the application, laser communication and laser imaging system can be realized in sharing hardware resources, function is relatively independent, not dependent on each other, and system performance is not sacrificed.At the same time, two systems can work independently also can work simultaneously to realize the effect of "visual communication".

The present invention provides a method, device and equipment for reducing noise of a pulse position modulation signal based on signal suppression. The noise reduction method comprises: S1, bandpass filtering the received electromagnetic logging signal to remove out-of-band interference and noise, and obtain a signal to be processed x(n); S2, constructing a signal suppression reference signal xr(n) according to the characteristics of the wireless electromagnetic logging signal; S3, using the wireless electromagnetic logging signal and the reference signal as input, using a recursive least squares adaptive filter to suppress the signal, and outputting a filter-synthesized cancellation signal xj(n); S4, low-pass filtering the cancellation signal xj(n) to obtain a useful signal s'(n) after noise reduction. The present invention improves the signal-to-noise ratio of the processed signal on the basis of traditional filtering technology, thereby improving the reliability and practicability of the logging signal transmission. The method is novel, has a small amount of calculation, and has strong universality. It has a good development prospect in the field of electromagnetic signal detection such as oil logging.

This invention discloses a bidirectional communication ranging method based on a room-temperature single-photon detector, belonging to the field of laser communication and ranging technology. The method employs a serial concatenated pulse position modulation coding and bidirectional asynchronous response ranging mechanism, designing a dedicated frame structure including a frame synchronization header, time information, and communication data. The proportion of ranging frames is controlled within the communication bandwidth, achieving integrated communication and ranging functions. At the receiving end, a coarse-fine concatenated time slot synchronization method is used: first, coarse synchronization is achieved by recovering the time slot clock through matched filtering; then, fine synchronization is achieved by compensating for residual time slot offsets based on a maximum likelihood estimation algorithm, significantly improving time slot synchronization accuracy. This invention, operating under room-temperature single-photon detector conditions, eliminates the need for cryogenic cooling equipment, effectively solving the problem of balancing communication rate and ranging accuracy. It significantly improves ranging accuracy and system stability, and is suitable for scenarios sensitive to size and power consumption, such as inter-satellite links and underwater communication.

The present invention provides an impulse fuze modulation method and system, belonging to the field of radio fuze technology. The method uses direct digital frequency synthesis technology to achieve pulse position modulation. The phase control word of the direct digital frequency synthesis technology can flexibly adjust the pulse position. At the same time, the phase control word is a true random signal sequence. The system includes: a random number generator, a crystal oscillator, an FPGA chip, an amplification and filtering circuit, and a signal judgment module. This solves the problem that the pseudo-random code modulation method used in existing impulse fuzes has the risk of being intercepted and the risk of adjacent fuzes winding around each other. It can fundamentally limit digital radio frequency storage technology, making forwarding deception interference completely ineffective.

This invention discloses a laser-induced acoustic underwater communication method and apparatus based on discrete linear frequency modulated pulse intervals, belonging to the field of cross-medium communication technology. The invention first maps the binary data to be transmitted into a pulse time interval pattern, where logic "0" and "1" correspond to pulse sequences with pulse intervals that decrease or increase linearly with time, respectively, and inserts a silence protection interval. A laser is controlled to emit pulses towards the water surface at non-uniform intervals, utilizing the photoacoustic effect to excite a train of acoustic pulses with discrete linear frequency modulated characteristics in the water. After acquiring the acoustic signal, the receiving end uses a local reference signal matching the transmitting end's pattern to perform dual-channel cross-correlation demodulation, achieving data decision-making and self-synchronization based on the amplitude and position of the correlation peaks. This invention combines the cross-medium advantages of laser-induced acoustics with the high processing gain characteristics of linear frequency modulated signals, solving the problem of poor multipath resistance in traditional pulse position modulation and significantly improving communication reliability in complex underwater acoustic channels.

The invention discloses a signal demodulation method, circuit and device, a storage medium and electronic equipment. Relates to the field of signal processing, and the method comprises the steps: obtaining a to-be-demodulated input signal, the input signal employing pulse position modulation; performing comparison processing on the input signal and the delay signal of the input signal through a first comparator to obtain a pulse position modulation signal; comparing the input signal with a reference level through a second comparator to obtain a signal triggering moment level; and under the condition that the level meets the triggering condition at the signal triggering moment, the pulse position modulation signal is demodulated through the single chip microcomputer. According to the invention, the problem that the signal demodulation cost is high when preprocessing of signal demodulation is carried out based on an FPGA chip in the prior art is solved.

The application discloses a chaotic communication and sensing integrated signal processing method and device and a communication system. The scheme provided by the application divides an information bit sequence into a modulation bit sequence, an index bit sequence and a PPM bit sequence, processes an initial signal vector by combining a pulse position modulation technology, optimizes spectral utilization by double control of the modulation bit and the index bit, segments the initial modulation signal according to PPM orders and generates a signal vector, and offsets the signal vector in the time domain by combining a shift matrix. The scheme utilizes the good autocorrelation characteristics and the low cross-correlation characteristics of an LFM signal, and on the basis of the original DCSK-LFM modulation mode, combines pulse position modulation and index modulation, so that the same carrier can carry more information, thereby improving the transmission rate when applied to a JRC system and the overall performance of the communication system.

The invention relates to the technical field of motor control, and particularly discloses a double-random PWM motor noise suppression method based on a Mersen rotation algorithm. Comprising the following steps that S01, double random modulation is established, the double random modulation comprises random pulse position modulation and random switching period modulation, the random pulse position modulation is used for conducting controllable random offset on the geometric center position of a carrier signal, and the random switching period modulation is used for conducting random offset on the geometric center position of the carrier signal; the random switching period modulation changes the frequency fs of the triangular carrier wave to realize randomization of the random switching period Tn of the system; and S02, generating a pulse position offset coefficient required by random pulse position modulation and a periodic random number required by random switching period modulation by adopting a Meisson rotation algorithm, and dispersing PWM harmonic energy to other frequency intervals so as to suppress a switching frequency sub-harmonic amplitude and a switching frequency sub-second harmonic amplitude.

The invention discloses a pulse modulation system and method based on a neural network, and the method comprises the steps: firstly processing an input symbol bit stream through a pulse position modulation module, extracting a position-related symbol bit through an MLP, converting the position-related symbol bit into a normalized current value, and transmitting the normalized current value into a pulse neural network; controlling the occurrence time of a pulse time domain and outputting a pulse position vector by utilizing a membrane potential accumulation characteristic and a time-varying discharge threshold value of linear decline in a symbol period; extracting phase correlation symbol bits through a pulse phase modulation module, distributing the phase correlation symbol bits to positive and negative parallel channels, adjusting the phase based on a pulse position vector, and generating a pulse vector with position and phase characteristics; and finally, expanding the discrete vector into a continuous time domain pulse signal by a transposed convolutional layer. According to the invention, the limitation of hardware adaptability and expansibility of a traditional pulse modulation system is overcome, and an efficient and flexible scheme compatible with various pulse modulation variants is provided for the field of Internet of Things and wireless communication.

The invention discloses an underwater wireless optical communication system based on a pulse position modulation technology, and a transmitting module of the underwater wireless optical communication system comprises a transmitting end FPGA used for modulating target data into digital pulse signals; the driving modulation circuit is used for converting the digital pulse signal into a modulation current signal for controlling a light source; the light source module is used for generating a light signal based on the modulation current signal; the receiving module comprises an optical module used for performing power attenuation and stray light filtering on an optical signal; the photoelectric detector is used for performing photoelectric conversion and amplification on the optical signal to obtain an analog electric signal; the analog-to-digital conversion and pulse shaping circuit is used for performing analog-to-digital conversion and pulse shaping on the analog electric signal to obtain a digital signal; and the receiving end FPGA is used for performing bit synchronization, frame synchronization and demodulation on the digital signal to obtain demodulation data. By adopting the pulse position modulation technology, the FPGA design and the compact modular structure, the purposes of low power consumption, miniaturization and real-time information transmission are achieved.

The invention concerns a TOF vision camera and proposes an electronic control circuit comprising a modulation circuit MOD for modulating the carrier clock signal, applying a camera-specific pulse position modulation function k(t) in order to output a modulation clock signal fe which is applied in the camera as a camera light source modulation signal S-LED, in order to control the emission of a series of light pulses SE and in order to synchronously control the N capture phases ST0, ST1, ST2, ST3 of the matrix image sensor CI of the camera. This modulation clock signal fe is such that the clock pulses fe have a constant pulse duration Tp, fixed by the carrier frequency fp, where Tp=½fp, and with a variable time interval Toff between two successive pulses, modulated by said modulation function k(t), said time interval being at least equal to the pulse duration, defining a modulation clock cycle ratio fe that is variable but less than or equal to 50%.