Pseudo-random Code Research Articles

ДВОКВАДРАНТНЕ АНАЛОГО-ЦИФРОВЕ ПЕРЕТВОРЕННЯ МОНТЕ-КАРЛО

In the current conditions of technological development and under last year's circumstances, the use of mobile means of remote control and information transformation is justified by ease of use, reliability, safety of pilot operators and economic efficiency. An urgent task is the development and implementation of effective methods and means of analog-digital conversion. In control systems, a number of sources of information have the character of integral accumulation of instantaneous parameter values. It is substantiated that the method of Monte Carlo statistical research is effective for the transformation of such information. The application of this method was limited by the need to implement generators of pseudo-random code sequences with a uniform distribution. The development of the Monte Carlo analog-to-digital conversion method proposed in the article was based on the application of code orderings generated by reflectively mapped Rademacher functions. The conducted studies showed one of the best uniformity distribution indicators of the scanning signal of the analog-to-digital Monte Carlo converters. Based on the proposed method of generating pseudo-random code sequences with uniform distribution, digital generators-formers of reference signals as part of Monte Carlo analog-to-digital converters were developed for the first time. The circuit of the Monte Carlo analog-to-digital converter, which carries out two-quadrant analog-to-digital conversion separately of the "+" and "–" components of the converted signal, as well as its integral value, was developed and investigated. A Monte Carlo analog-to-digital conversion scheme has been developed. Oscillograms and time diagrams of the formation of numerical pulses as a result of the conversion are given. The proposed Monte Carlo analog-to-digital conversion method and device have the prospect of application in resource consumption accounting systems, in particular, accounting for electric energy, fuel, gas, water, and other media.

Estimation of Vertical Phase Center Offset and Phase Center Variations for BDS-3 B1CB2a Signals

The BeiDou Global Satellite Navigation System (BDS-3) broadcast newly developed B1C and B2a signals. To provide a better service for global users, the vertical phase center offset (PCO) and phase center variation (PCV) are estimated for the B1C/B2a ionospheric-free linear combination of the BDS-3 inclined geostationary orbit (IGSO) and medium earth orbit (MEO) satellites in this study. And considering the traditional PCC estimation method needs two Precise orbit determination (POD) processing, based on the correlation between PCO z-offset and PCV, the theoretical analysis and experimental comparison have been made to discuss whether the POD procedure for the PCO estimation can be omitted. The estimated z-offset time series revealed the inadequacy of the solar radiation pressure (SRP) model for the IGSO satellites and the MEO satellites with Pseudo Random Noise code (PRN) C45 and C46. The PCVraws estimated by the traditional method and the PCO estimation omitted method have the same characteristic. The final PCO z-offsets and PCVs calculated by the two schemes agreed very well with differences can be harmlessly ignored, which confirmed that the PCO estimation can be safely omitted to save computation time. The PCC model proposed in this study has been compared with the Test and Assessment Research Center of China Satellite Navigation Office (TARC/CSNO) released model, the qualities of the orbits and BDS-only precise point positioning (PPP) solutions of the new model both show improvements, except for the IGSO orbits. The analysis of the IGSO orbits further verifies the SRP model is not suitable for the IGSO satellites.

A New 2D Displacement Measurement Method Based on an Eddy Current Sensor and Absolute Encoding

A new method of two-dimensional (2D) plane displacement measurement based on an eddy current sensor is proposed in this paper. A series of grooves with different widths and depths are graved on the linear displacement table to form 2D absolute coding using the idea of pseudorandom coding. The eddy current sensor array is arranged above the groove to identify the coding. An artificial neural network is used to establish a measurement model which is the mapping relationship between the output of the eddy current sensor array and the 2D displacement of the workbench. A feasibility experiment showed that in the range of 20 × 20 mm, the root mean square error of measurement in the X- and Y-directions are 83 and 73 μm, respectively. The new method integrates eddy current sensor and artificial neural network modeling to realize 2D displacement measurement, which provides a new solution for displacement and angle measurement.

Blind Estimation of GPS M-Code Signals under Noncooperative Conditions

In the process of Global Positioning System (GPS) modernization, M-code signals with better immunity to interference have been proposed and used in place of P(Y) signals as new authorization signals. A typical positioning, navigation, and timing (PNT) service is based on the local interrelation operation between the reference signal and the received signal. To obtain a PNT, the receiver should generate replicas of the pseudorandom code for acquisition and tracking. However, due to the use of an encryption algorithm, the receiver cannot use the M-code signal under noncooperative conditions. This paper presents an algorithm for estimating M-code sequences without prior knowledge. This algorithm adopts a waveform matching technique and a time domain filtering method to extract M-code from the in-phase channel and quadrature channel of the GPS L1 band. A high-gain antenna is used to receive GPS signals to keep the signal from being drowned out by noise. The experimental results show the feasibility of the method. Therefore, it is helpful for studying and evaluating the performance achieved without prior knowledge of the GPS signals.

1.8 m/0.5 s Resolution Coherent Doppler Wind Lidar Using Continuous Phase Modulation

A high-spatial-resolution coherent Doppler wind lidar (CDWL) with high modulation efficiency is reported. The pseudo-random phase coding (PRPC) links the spatial resolution to the modulation rate but suffers from the non-rectangular transition caused by the limited bandwidth. With the help of continuous phase modulation (CPM), the abrupt phase switching between successive bit intervals is avoided, thus significantly reducing the bandwidth requirement. By mapping the binary sequence into different transition states rather than phase levels, a 10-fold modulation efficiency improvement is realized. In experiments, the performance of the proposed lidar is compared with lidars in the PRPC method and conventional non-coding method. Continuous radial wind profile measurement of 800 m is demonstrated with spatial and temporal resolution of 1.8 m and 0.5 s, which is the highest spatial resolution realized by a pulsed CDWL to our best knowledge.

A Pseudo-Random Signal Generator for Offset Calibration Circuit

A pseudo-random signal generator based on 0.5μm CMOS technology is presented, and it is applied for an auto-zero operational amplifier. The generator circuit includes a linear feedback shift register for generating pseudo-random sequences, and a multi-level counter module for counting the system clock pulses. A group of pseudo-random codes generated by the linear feedback shift register are as the initial value of the counter. When the counter reaches the maximum value, the output of the counter will control the output signal to flip. At the same time, a new group of the pseudo-random code will reset the counter again, and finally generate a square wave signal whose frequency varies randomly. The generator circuit is simulated and verified. The simulation results show that the frequency of the output signal can vary from 2 kHz to 4 kHz with random characteristic. The generated pseudo-random signal can be used for the switching clock control of the auto-zero operational amplifier offset calibration circuit, so that the switching glitch of the auto-zero op-amp is random, which can significantly reduce the harmonics in the output signal of the op-amp.

Resolution Improvement in a High-Power Magnetic Resonance Imaging Gradient Power Amplifier

High-resolution gradient power amplifiers are required to generate high-fidelity gradient fields in magnetic resonance imaging (MRI) systems. Various aspects of gradient power amplifiers have been the subject of research in the past years, however, systematic analysis and design methods for its resolution improvement have not been sufficiently addressed. This article addresses this research gap with comprehensive analysis and design methods for resolution improvement. First, a method for systematic resolution characterization of the MRI gradient power amplifier with gradient coil is proposed. Second, noise modeling with respect to the critical aspects in the system resolution degradation is developed and discussed. Third, the resolution improvement methods of bandwidth optimization, pseudorandom code modulation, and utilizing silicon carbide (SiC) switching power devices are proposed and analyzed, achieving a resolution at the one part in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${10^6}$</tex-math></inline-formula> level. Finally, the resolution improvement methods are experimentally validated in a 1000 V/400 A SiC gradient power amplifier. The experimental results show a 3.6 times reduction in the peak spurious signals and resolution improvement at all current levels and pulse lengths, compared to a conventional insulated gate bipolar transistor GPA. These results prove the validity of the proposed methods for resolution improvement in a high-power MRI gradient power amplifier, enabling future high-power and high-resolution amplifier designs.

Method for 10 Gbps near-ground quasi-static free-space laser transmission by nutation mutual coupling

This study proposes a method to reduce link loss in near-ground space laser communication with fiber-nutation-based mutual coupling. We designed a transmit-receive coaxial laser terminal with a 50 mm aperture and implemented beam acquisition tracking and nutation coupling using a single-detector and single-actuator. Following an indoor experiment and a 1 km field test, the single-ended nutation coupling and the two-way nutation mutual coupling theories were compared and analyzed. In conclusion, the proposed method could significantly increase the reception efficiency by ∼8 dB. The bit error rate of 10 Gbps pseudo-random code transmission was 2.478E-9. We also demonstrated video transmission.

Spatial Resolution Enhancement of Coherent Doppler Lidar by Pseudo-Random Phase Coding

A high spatial resolution coherent Doppler wind lidar (CDWL) incorporating pseudo-random phase coding (PRPC) is proposed and demonstrated. Random phase coding of the transmitted lightwave spreads the atmospheric backscattered spectrum and the spatial resolution can be enhanced as only the signal with specific time delay could be despread during decoding. The narrow peak of the despread spectrum provides higher wind velocity retrieval accuracy compared with conventional pulsed CDWL with the same spatial resolution. Spectrum difference is applied to reduce the interference between the spread and despread spectra. The new method's performance is verified in a comparison experiment with a non-coding CDWL. Continuous radial wind profile measurement over 800 m is demonstrated with spatial/temporal resolution of 4.5 m/1 s, at laser peak power of 250 W.

An Improved Sliding Matched Filter Method for Interrupted Sampling Repeater Jamming Suppression Based on Jamming Reconstruction

The development of the digital radio frequency memory (DRFM) has led to the interrupted sampling repeater jamming (ISRJ) becoming increasingly popular in electronic countermeasure (ECM). It is coherent with the emitted signal and extremely limits radar target detection which significantly obstructs radar electronic countercountermeasure (ECCM). In this paper, we study the ISRJ suppression for pseudo random code continuous wave (PRC-CW) radars. First, the relationship between the ISRJ and the radar waveform is obtained by analyzing the ISRJ principle. Second, the intermittent feature of the ISRJ with matched filter sliding is discussed and used to determine the retransmitted sampled slices (RSS). Third, the jamming signal is reconstructed using the minimum residual criterion and excluded from the echo signal. In the proposed method, we make the most of the information of the jamming signal for improving the anti-ISRJ performance in the low SNR regimes. This information pertains to the amplitude of the jamming signal being considerably higher than that of the real target signal. Fourth, utilizing this characteristic of the jamming signal, we propose an improved sliding matched filter method based on the RSS reconstruction. Last, numerical simulations illustrate the effectiveness of the proposed method and validation of the theoretical analysis.

Ultra-Low-Cost and Ultra-Low-Power, Miniature Acoustic Modems Using Multipath Tolerant Spread-Spectrum Techniques

To enable long-term, large-scale, dense underwater sensor networks or Internet of Underwater Things (IoUT) this research investigates new novel waveforms and experimental prototypes for robust communications on ultra-low-cost and ultra-low-power, miniature acoustic modems. Spread-spectrum M-ary orthogonal signalling (MOS) is used with symbols constructed from subsequences of long pseudorandom codes. This decorrelates multipath signals, even when the time-spread spans many symbols, so they present as random noise. A highly cost-engineered and miniaturised prototype acoustic modem implementation was created, for the 24 kHz–32 kHz band, with low receive power consumption (12.5 mW) and transmit power of &lt;1 W. Simulations show that the modulation scheme achieves 640 bit/s at −4.5 dB with AWGN or the equivalent level of multipath energy. Experimental validation of the hardware shows successful point-to-point communication at ranges of &gt;3 km in lakes and &gt;2 km in the sea including severe multipath. In lake testing of a 7-node, multi-hop, sensor network with TDA-MAC protocol, packet delivery was near 100% for all nodes. Trials of acoustic sensor nodes in the North Sea achieved 99.5% data delivery over a 3-month period and a wide range of sea conditions. Modulation and hardware have proven reliable in a variety of underwater environments. Competitive range and throughput with low cost and power are attractive for large-scale and long-term battery-operated networks. This research has delivered a viable and affordable communication technology for future IoUT applications.

A 120-target brain-computer interface based on code-modulated visual evoked potentials

BackgroundIn recent years, numerous studies on the brain-computer interface (BCI) have been published. However, the number of targets in most of the existing studies was not enough for many practical applications. New methodTo achieve highly efficient communications, this study proposed a 120-target BCI system based on code-modulated visual evoked potentials (c-VEPs). Four 31-bit pseudorandom codes were used, and each code generated 30 targets by cyclic shift with a lag of 1 bit. ResultsIn the online experiments, subjects could select one target in 1.04 s (0.52 s for stimulation and 0.52 s for gaze shifting) with an average information transfer rate (ITR) of 265.74 bits/min. Comparison with existing methodThe proposed system achieved more targets and higher ITR than other recent c-VEP based studies. which attributes to the optimal code combination and the 1-bit lag. ConclusionThe results illustrate that the proposed BCI system can achieve a high ITR with a short stimulation time. In addition, the c-VEP paradigm can shorten the training time, which ensures practicality in real applications.

Direct synthesis of time domain pseudo-random 3D electromagnetic response with a band-limited source

Methods based on pseudo-random coded emission technology can effectively suppress the noise in electromagnetic exploration and improve the depth and resolution of the detection. Additionally, the synthesis of electromagnetic response signals excited by pseudo-random code sources can provide not only theoretical data for data processing but also intermediate results for evaluations of field data. Currently, pseudo-random signal simulations ignore the presence of source effects generated by band-limited sources in the Earth's impulse response. Furthermore, the simulation methods are mainly completed based on one-dimensional and two-dimensional formats and thus cannot accurately reflect the pseudo-random response of three-dimensional geoelectric structures. In this paper, 3D pseudo-random electromagnetic signals with a band-limited source were synthesized according to the propagating routine of the electromagnetic field. First, Maxwell's Equations were solved using a three-dimensional time-domain finite volume method. To avoid the singularity of the source and incorporate source effect response, the Gaussian function was introduced to simulate the band-limited impulse sources. The Earth's impulse response was obtained, which contained source effects under three-dimensional geoelectric structures. Then, ideal pseudo-random electromagnetic signals could be composed by convoluting the Earth's impulse response with a pseudo-random source waveform. Since the transmitter and receiver instruments were band-limited, a low-pass filter with a Blackman window was introduced to simulate the instrument's system response. The simulated pseudo-random signals were obtained by adding noise and the ideal pseudo-random electromagnetic signals were filtered using a low-pass filter. By comparison with signals acquired in the field, the correctness of the pseudo-random signal synthesis with source effects was successfully verified.

A 22-bit image encoder with optoelectronic integrated chip

This study aims to design an optoelectronic integrated chip to read absolute code information. A detector array matching the code disk was designed to better realize high-speed low-light detection. For the pseudo-random code channel, the readout circuit adopted a linear array CMOS image sensor architecture, where each pixel corresponded to an independent readout unit, making the readout signal more advantageous in terms of both reading speed and noise. For the incremental code channel, the readout circuit followed a distributed arrangement design, and a two-stage pipelined amplifier architecture was adopted to eliminate the influence of even harmonics and ensure the quality of the read signal. Finally, a high-precision angular displacement sensor test platform based on an optical continuous closed-loop was built to test the encoder prototype equipped with the chip. The results show that an angular resolution of 22 bits and a subdivision accuracy of 5.64″ have been achieved.

A new method for measuring 3D rotation angle of spherical joint

A new method for measuring 3D rotation angle of precision spherical joint based on eddy current sensors is proposed in this study. A pseudorandom code is used to generate a 2D plane absolute code and then mapped to the sphere. The 3D absolute code is formed on the ball head through precision cutting, and an eddy current sensor array is arranged in the ball socket to identify the code. The experimental tests were conducted on the parameter-optimized prototype, and the experimental results showed that the mean squared error of the 3D rotation angle measurement was approximately 25′ in the range. The proposed new measurement principle provides a new approach to the precision measurement of spherical rotary motion, which is expected to produce a breakthrough in the theory and technology of spherical-angle sensor measurement. The proposed new principle also provides a theoretical basis and technical experience for the integration and development of intelligent devices.

PN Code Acquisition in DS-CDMA Wireless Systems Using Smart Antenna and S-CFAR Processor

Code division multiple access (CDMA) is a class of techniques allowing multiple users to transmit simultaneously to meet the demand of the recently unprecedented revolution in wireless services. In CDMA systems, a unique pseudo-random (PN) code is assigned to each user to spread the signal at the transmitter side and facilitate signal&#x2019;s recovery at the receiver side. In particular, a CDMA receiver initially seeks synchronization or acquisition of PN code. This paper focuses on the development and analysis of a new adaptive serial search acquisition method for direct sequence (DS)-CDMA systems in Rayleigh slowly fading channels. The proposed method makes use of smart antenna and switched constant false alarm (S-CFAR) processor for PN code acquisition. The smart antenna and S-CFAR processor are employed to improve the PN acquisition performance by adjusting a decision threshold according to the environment. The performance of proposed acquisition system has been evaluated in terms of probability of false alarm, probability of detection, and mean acquisition time. Closed form expressions for the probability of false alarm and probability of detection have been derived. Further, numerical and simulation results have been presented to show the performance of proposed PN acquisition system in comparison with other existing CFAR-based PN acquisition schemes.

High precision ranging lidar based on pseudorandom code modulation

High precision ranging lidar based on pseudorandom code modulation

Multi-channel pseudo-random coding single-photon ranging and imaging

We demonstrate a multi-channel pseudo-random coding single-photon ranging system. A pseudo-random multiplexing technique is proposed, which realizes multi-channel pseudo-random ranging only by using one single-photon detector and processing circuit. Compared with the time division multiplexing technique, it will not reduce the maximum unambiguous range while increasing the number of the ranging channel. Eight-channel pseudo-random coding single-photon ranging was realized with the ranging accuracy better than 2 cm. Moreover, photon counting imaging was realized through scanning the laser beams of the eight-channel pseudo-random ranging system. There is no crosstalk between channels, which is suitable for multi-beam long-distance single-photon Lidar.

Multi-Valued Automatic Cab Signalling System Based on the CDMA Technology

Purpose. The work is aimed at the development of principles for the construction of multi-valued automatic cab signalling system (ACS) using the wide-band pseudorandom signals. Methodology. An analysis of existing ACS systems and modern telecommunication technologies has been performed to achieve the stated purpose. The multi-valued automatic cab signalling system CDMA-ACS has been proposed. The mentioned system utilizes wide-band pseudo-noise signals to transmit commands. System parameters: frequency band – 155...395 Hz, pseudorandom codes – 16-bit Walsh codes, spectrum spreading factor – 16, source signal bandwidth – 15 Hz, carrier modulation – DBPSK (differential binary phase-shift keying), information rate – 15 bit/sec, code combination length – 4 bits, maximum amount of commands – 256, the duration of single command transmission – 0.27 sec. Functional diagrams of generator and receiver of the multi-valued automatic cab signalling system have been designed. It has been suggested to apply the correlation method to receive the ACS signals. Findings. To investigate the proposed CDMA-ACS system the simulation modelling has been accomplished in MATLAB in two stages: at the first stage, the CDMA-ACS system was investigated as disturbance-free; at the second stage – under the influence of powerful narrow-band disturbances (traction current harmonics). It has been found that the system shows high immunity to narrow-band harmonic disturbances. The most significant harmonics of the traction current related to the system are 250 Hz and 300 Hz, since they are the closest to the carrier frequency of 275 Hz. It has been determined that errors in decoding the ACS commands occur if the signal-to-noise ratio becomes lower than -8 dB. To reduce the influence of 250 Hz and 300 Hz, harmonics the application of additional band-reject filters was proposed. Originality. For the first time, the authors of this work carried out research on the multi-valued automatic cab signalling system with the use of wide-band pseudo-random Walsh codes. Practical value. Implementation of solutions being proposed allows improving the informativeness and interference immunity for the automatic cab signalling system, reducing the duration of command transmission from the railway track to the cab.

A Novel Measurement Scheme for Crossly-Polarized Channel Based on the Pseudorandom Codes of Analyzing the Fuzzy Function

With the rapid development of 5G communication, crossly-polarized transmitting and receiving scalable channels have received wide attention. We conduct an in-depth analysis of the 5.8 GHz horizontal and vertical crossly-polarized electromagnetic (EM) wave propagation and propose a novel test scheme for the feature of the particular EM wave propagation. The scheme acquires the channel characteristics and the interchannel coupling interference strength by transmitting and receiving pseudorandom codes and analyzing the fuzzy function of the corresponding noise-like signals. We then optimize the pseudorandom codes with parallel pseudorandom sequence generation method based on Hash function, greatly reducing calculation time. The transceiver’s mode adopts time division duplexing and chooses the pseudorandom codes as the system transceiver’s pseudorandom codes. The fuzzy function analysis and processing are performed by a MATLAB code and we can clearly obtain pin-shaped fuzzy images and coupling interference between crossly-polarized channels.