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Weak signal detection capability and real-time signal processing capability is significant for the underground space detection system. In this paper, an underground space detection system based on the channelization algorithm is designed. Through the channelization algorithm based on the weighted-overlap-add (WOLA) structure, the system can detect four weak signal energy values of different frequencies at one time. Simulation and experimental results show that compared with traditional detection methods, the system has a breakneck processing speed, and the weak signal detection ability can be improved.

GPS, as a widely used positioning tool, covers more aspects of people's daily life and people have been interested in the study of GPS signal acquisition algorithm for a long time. In this paper, a widely used signal acquisition algorithm with superior performance, PMF-FFT algorithm, is optimized. A fast GPS signal acquisition method based on fuzzy logic is proposed to solve the problem of signal acquisition failure caused by weak signal being ignored as noise under low SNR condition. Simulation results prove that the algorithm proposed in this paper can effectively capture signals and performs well under weak signals.

There is a growing need to continue operating the Global Navigation Satellite Systems (GNSS) receivers under increasingly challenging and stressful conditions, where signal experiences deep fading, blockage, or high platform dynamics. As the most fragile component of the GNSS receiver, the carrier tracking loop must achieve improved tracking capability. The subject of GNSS tracking loop design has been well studied. This thesis takes the control system design perspective, presents tracking loop design as a state feedback/state estimator framework, sheds insight on frequency domain analysis, derives optimal parameters for carrier tracking loop design, and proposes adaptive tracking solutions for challenging environment. Two generalized carrier tracking loops, namely, the generalized phase tracking loop and the generalized frequency tracking loop, are studied using this state space framework. For the generalized phase tracking loop design, three approaches, i.e., proportional integral filter (PIF), Wiener filter (WF), and Kalman filter (KF), are presented in an unified manner from the state feedback/state estimator framework. With the state space framework, analytical equations characterizing the carrier phase tracking loop performance are derived. These equations relate the phase tracking error variance and dynamic stress phase error to the filter design parameters, such as integration time and noise equivalent bandwidth, as well as other parameters, such as thermal noise, oscillator noise, and receiver platform dynamics. From these equations, filter design parameters are optimized under various operating scenarios, such as weak signal or high dynamics. More specifically, the tracking sensitivities of the generalized phase tracking loop with these designs are obtained. Building on this analysis, an adaptive phase tracking scheme with time-varying integration time or loop bandwidth is proposed. A similar approach is applied to frequency tracking loop design. The PIF design is mapped to the state space structure through the equivalent closed-loop transfer function. Traditional KF-based frequency tracking loop design assumes white Gaussian noise. However, the frequency error measurement noise is non-white and so analytical equations for the frequency tracking error variance and dynamic stress frequency error are derived, taking into account the non-white noise characteristic. Frequency tracking error variance is used to evaluate the frequency tracking loop performance under the effects of thermal noise, oscillator noise, and platform dynamics. Using these analytical equations, optimal loop parameters are obtained, and the frequency tracking sensitivity is characterized. Based on these theoretical analysis, an adaptive frequency tracking scheme with loop bandwidth is proposed. Simulation results demonstrate the effectiveness of the proposed adaptive generalized carrier phase/frequency tracking architecture and verify the theoretical prediction. Doctor of Philosophy (EEE)

In ordinary consciousness, noise is associated with the term “hindrance”; it is considered as a nuisance that can lead to communication or signal transmission failure or prevent the detection of a weak signal to be measured. However, under certain conditions the impact of noise can be counter-intuitively a resource. In nonlinear systems, noise can induce novel regimes leading to the formation of synchronized structures, coherence between the output and the input of resonators or even to the amplification of weak signals. In other words, noise can play a constructive role, with potential benefits for signal processing or measurement for instance. Single or coupled Nano-Opto-ElectroMechanical resonators whose design is based on suspended photonic crystal membrane could be used as a toy-system to pursue two main goals: stochastic amplification and chaos. As such noise-aided processes might have a strong impact in noise-assisted applications including signal processing or sensing.

Many biological signals that reflect the human health are relatively weak, and high-resolution Analog-Digital Converters (ADCs) are required to measure them. The over-sampling technology is a method for increasing the accuracy, equal to the accuracy of high resolution ADCs, when an ADC has low resolution. For high resolution ADCs, their accuracy from the over-sampling technology would break its maximum limitation. During our signal collection, there are two items which affect our results: 1. measurement error; 2. non-linear characteristics at the end points. In over-sampling method of detecting weak signal of wearable devices by using the unidirectional saw-tooth shaped function, the magnitude of the shaped function is as close as possible to the integer multiple of the quantization step size to reduce the additional measurement error. To reduce the difficulty of the adding shaped function, which features nonlinearity of the starting point, a new method of detecting the weak signal by adding the bidirectional saw-tooth shaped function is proposed. The experimental results show this method is feasible for improving the ADC resolution.

A novel communication and navigation fusion system (CNFS) was developed to realized high accuracy positioning in constrained conditions. Communication and navigation fusion signal transmitted by base stations are in the same time and frequency band but are allocated different power levels. The positioning receiver of CNFS requires signal coverage of at least four base stations to realize positioning. The improvement of receiver sensitivity is an important way to expand signal coverage of base station. As an essential stage of signal processing in CNFS positioning receiver, signal acquisition requires a trade-off between improvement of acquisition frequency accuracy and reduction in computational load. A new acquisition algorithm called PMF-FC-BA-FFT method is proposed to acquire the carrier frequency accurately with lower computational load in a weak signal environment. The received signal is firstly filtered by partially matched filters (PMF) with local replica pseudorandom noise (PRN) sequences being coefficients to strip off the PRN code in the signal. Frequency compensation (FC) was performed to avoid the large attenuation in block accumulation (BA) and generate a series of signals with a small frequency offset step. Block accumulation was then executed. Finally, the acquisition detection was performed based on a series of fast Fourier transformation (FFT) outputs to obtain acquisition results with fine frequency estimation. Simulations and experimental tests results show that the proposed method can realize high accuracy frequency acquisition in a weak signal environment with fewer computational resources compared with existing acquisition methods.

Modern communication systems seek to increase capacities to allow users to access various applications. One of the proposed technologies that used to support the resources of systems is coordinated multipoint (CoMP) technology, this technology aims to increase the signal to noise ratio for the users of weak signal. This paper explains the influence of coordinated multipoint technology on the traffic of 802.16e system, which consists of seven cells in cases of different types of applications such as browsing and file transfer.

This study analyses the bit transition and integration over multiple code periods in weak global navigation satellite system signal acquisition. Bit transition must be considered in weak signal environments as it causes a correlation peak splitting reducing the correlation gain. In this study, a modified time parallel acquisition (MTPA) scheme is designed to solve the bit transition problem, and different accumulation schemes over multiple code periods are proposed to detect weak signals. Especially, a fast Fourier transform-based symbol combination for bit transition algorithm, which is suitable for the MTPA scheme, is presented in order to accelerate the coherent accumulation. Simulation results, along with the receiver operative characteristic curves, are presented to verify the performance of the MTPA and accumulation algorithms.

In ultralong fiber laser key distribution, two sides use standard optical equipment to create kilometer long fiber lasers in a communication link to establish a secret key. Its security rests on the assumption that any attacker would need much more sophisticated equipment and techniques than those of the legitimate user in order to discover the generated key. We present a challenge to that assumption with a hidden probe attack in which the eavesdropper hides a weak signal in the unavoidable noise floor that appears in the laser during amplification and probes with it the configuration of one or both communication parties. We comment how this attack can compromise different proposals for ultralong laser key distribution and propose possible countermeasures., 9 pages, 8 figures. Comments welcome

Weak signal acquisition attracts global attention in GNSS research. Coherent losses caused by bit flipping lead to acquisition difficulty for traditional methods. An optimized semi-bit frequency compensated differential post-correlation processing is proposed through analyzing problems of the conventional differential post-correlation processing in this paper. The impact of data flipping is eliminated by the semi-bit time control logic, and the processing loss of carrier estimation error is improved by the carrier frequency compensation circuit. Theoretical analysis and simulation results show that the improved differential coherent accumulation technology can significantly improve the environment of weak signal detection probability of GNSS signals.

Satellite navigation system has been widely used in various fields, because of the signal which is received on the ground is weak and the low ratio of signal to interference, the signal is susceptible to be interfered. The adaptive antenna system using power inversion algorithm with information technology is very suitable for the weak signal and strong interference. The paper presents a detailed analysis on the principle with information technology. By building the hardware circuit in the QuartusII, the self-adapting anti-interference system of power inversion algorithm with information technology which based on Linearly Constraint Minimum Variance (LCMV) criterion can be achieved. The correctness of the theoretical analysis and correctness of the design are verified by experiment, the requirements of satellite navigation receiver on the side of anti-interference has been also proved.

In the field of detecting weak signals with large dynamic range, CMOS image sensor, as an optical sensor component, has the advantages of large dynamic range and wide spectral response range, and is often used to detect weak signals. The commercial CMOS image sensor system usually adopts the ADC with 16-bit accuracy, which can not satisfy the detection of weak signal in some cases. In this study, CMOS image sensor S10122 chip from Hammatsu company of Japan was used as the core device. ADI company’s 16-bit ADC chip LTC2182 and 16-bit DAC chip LTC1668 were used. The circuit was designed according to twice sampling principles to improve ADC accuracy. The results show that the accuracy of ADC can be improved from 16 to 18 bits under certain conditions.

Lock-in Amplifier is very useful in many weak signals processing systems. To lower down the system cost and to raise the speed of the system, a digital Lock-in Amplifier processor with nanosize electronic technology based on FPGA chip and the algorithm appropriate for hardware to implement was introduced. The frequency of the signal which can be lock-in amplified by the processor is up to 158 KHz, and the error in the experiment is less than 1.27. Also, the cost of the system is much lower than the system scheme based on DPS chips.

EU’s Galileo project is a market-based GNSS (Global Navigation Satellite System) that is under development. It is expected that Galileo will provide the positioning services based on new technologies in 2020s. Because Galileo E1 signal for OS (Open Service) shares the same center frequency with GPS L1 C/A signal, CBOC (Composite Binary Offset Carrier) modulation scheme is used in the E1 signal to guarantee interoperability between two systems. With E1 signal consisting of a data channel and a pilot channel at the same frequency band, there exist several options in designing signal acquisition for Assisted-Galileo receivers. Furthermore, compared to SNR worksheet of Assisted-GPS, some factors should be examined in Assisted-Galileo due to different correlation profile and code length of E1 signal. This paper presents SNR worksheets of Galileo E1 signals in E1-B and E1-C channel. Three implementation losses that are quite different from GPS are mainly analyzed in establishing SNR worksheets. In the worksheet, hybrid long integration of 1.5s is considered to acquire weak signal less than -150dBm. Simulation results show that the final SNR of E1-B signal with -150dBm is 19.4dB and that of E1-C signal is 25.2dB. Comparison of relative computation shows that E1-B channel is more profitable to acquire the strongest signal in weak signal environment. With information from the first satellite signal acquisition, fast acquisition of the weak signal around -155dBm can be performed with E1-C signal in the subsequent satellites. Keywords: Galileo, composite-BOC, implementation losses, SNR worksheet, signal acquisition I. 서론 유럽연합의 Galileo 계획은 군 주도의 GPS, GLONASS 등과 다르게 시장 기반의 독립적인 측위 시스템이다. 계획은 크게 IOV (In-Orbit Validation)와 FOC (Full Operational Capability)로 나뉠 수 있다. ESA (European Space Agency)는 두 대의 Galileo 테스트베드 위성에 대한 시험을 마쳤으며, 2011년 10월에 두 대의 IOV 위성을 발사하였고 2012년 10월에 남은 두 대의 IOV 위성을 발사하여 우주 및 지상국에 대한 성능 평가를 진행 중에 있다. IOV 단계가 종료되면 더 많은 위성을 발사하여 2020년대에는 FOC 단계에 도달할 예정이다[1]. Galileo는 E1, E5, E6의 세 개의 주파수 대역을 사용하며, 일반 사용자가 무료로 사용할 수 있는 OS (Open Service)는 E1과 E5 대역에서 제공한다. 이 중 E1 대역은 GPS L1 대역과 중심주파수를 공유하는 동시에 신호의 기본 주파수가 1.023MHz로 같기 때문에 GPS L1 및 Galileo E1 OS 신호를 동시에 사용할 수 있는 다중 GNSS (Global Navigation Satellite System) 수신기를 쉽게 설계, 구현할 수 있다. 두 시스템을 동시에 사용하게 되면 DOP (Dilution of Precision) 이 개선되며, 더 많은 위성으로부터의 거리정보를 이용하여 측위 성능을 향상시킬 수 있다[2]. 한편 Galileo E1과 같은 L1 대역의 GNSS 신호는 실내에서 약 20dB, 콘크리트 건물 안에서는 30dB 이상 감소하기 때문에[2] 실내에서는 낮은 SNR (Signal-to-Noise Ratio)과 원근 효과 (near-far effect)로 인하여 미약 신호를 검출하기 어렵다. 더욱이 다중 GNSS (Global Navigation Satellite System) 환경 하에서는 시스템 간 간섭에 의하여 약 신호에 대한 SNIR (Signal to Noise plus Interference Ratio)이 기존의 상황보다 현저히 저하되기 때문에 약 신호 획득이 더욱 어려워진다. 따라서 미래 GNSS 환경에서는 미약 신호 획득을 위한 민감도 향상 기법이 중요하다. A-GNSS (Assisted-GNSS) 기술은 무선 통신망을 이용하여 GNSS 수신기에 보조 정보를 제공하여 TTFF (Time To First Fix)를 줄이고 수신감도를 향상시킬 수 있는 기술로서 미래 GNSS 환경에서 GNSS 신호 음영지역 문제를 경감시켜 줄 것으로 예상된다[3]. A-GNSS 수신기는 일반적으로 동기 누적(coherent integration) 결과를 비동기 누적(non-coherent integration)하는 혼합 장기 중첩(hybrid long integration)을 통하여 수신감도를 개선하며, 이를 통하여 약 신호 환경에서도 의사거리 추정이 가능해진다[4]. 동기 누적 방식은 신호의 주기적 특성을 이용하여 일정 개수의 주기 신호를 누적하여 수신감도를 향상시키는 기법이나, 동기 누적 이득을 높이기 위하여 동기 누적 길이를Manuscript received August 9, 2012 / revised January 18, 2013 / accepted 길게 하면 주파수 부정합 오차가 증가한다[5]. 주파수 부정합 오차의 영향을 줄이기 위하여 주파수 탐색 간격을 줄이면 신호 획득에 필요한 계산량이 증가하는 단점이 있다[6]. 한편, 동기 누적 후 이득이 작으면 비동기 누적 시 제곱 손실이 크게 발생하여 혼합 장기 중첩의 전체 이득이 낮아지는

Based on the analysis of infrared detection technology and Lambert-Beer law a new kind of quad-channel non-dispersive infrared (NDIR) gas concentration analyzer is designed by applying the modulated IR light source and a quad thermopile sensor into automobile exhaust gases concentration detection. The emphasis is paid on the analysis of modulated light source, gas chamber, sensor and the acquisition and processing circuit of the signal. The result of simulation and analysis of the designed circuit proved the feasibility of the design.

In this paper, a new PRN code optimal design based on unequal-length code modulation is proposed. The better performance of code acquisition in weak signals will be achieved by using this method, because the cross- correlations between different signals have been sliding, thus suppressing multiple access interference effectively. Theoretical analysis and simulation show that this design has predictive power for compressing multi-access interference. Meanwhile, it does not need extra acquisition effort, thus it is convenient, feasible and effective.

Nowadays the weak signal detection technology is necessary in scientific research field, in which the phase-locked amplifying technology is widely used in the field of weak signal detection because it can meet the requirements of high speed and high accuracy. System Generator software is adopted as a tool since System Generator can make the design more conveniently and efficiently. The design of each module in orthogonal vector type digital phase-locked amplifier is introduced in this paper. The overall design was verified. The simulation results confirm that the design is feasible.

Cognitive radio (CR) is one of the most important challenges in contemporary communication. Because cognitive technologies are based on matching transmission parameters to the surrounding radio environment, several practical problems related to weak signal detection must be solved. These include, e.g., uncertainty of the noise variance value, the changes of this value in time and space, limited hardware resources or time of detection. All of these factors can seriously degrade system performance. The search for practically useful solutions of the encountered difficulties is therefore very important for the successful development and implementation of CR technology. This article provides an overview and comparison of chosen blind detection methods proposed for use in CR receivers. The comparison is based on simulation results, and the methods are compared in terms of detection efficiency, time complexity and robustness to changes in transmission parameters.

The method based on stochastic resonance is a newly developed signal processing technology. Different from other methods by restraining the noise, it takes full advantage of the noises to strengthen the weak signal to improve SNR of the system. Based on stochastic resonance theory, a heterodyne system is presented in the paper to detect the frequency of the weak periodic signal. The simulation results manifest that the method is effective and the system parameters have extensive influence for frequency measurement. The parameters of the system are investigated for optimizing system design and weak signal detection.

Stochastic resonance (SR) is a nonlinear phenomenon which can be used to detect weak signal. The theory of SR in a biased mono-stable system driven by multiplicative and additive white noise as well as a weak periodic signal is investigated. The virtual instrument (VI) for weak signal detecting based on this theory is designed with LabVIEW. This instrument can be used to detect weak periodic signals which meets the conditions given and can greatly improved the power spectrum of the weak signal. The results that related to different sets of parameters are given and the features of these results are in accordance with the theory of mono-stable SR. Thus, the application of this theory in the detecting of weak signal is proven to be valid.

In order to track the carrier phases of Global Navigation Satellite Systems (GNSS) signals in signal degraded environments, a dual antenna joint carrier tracking loop is proposed and evaluated. This proposed tracking loop processes inputs from two antennas, namely the master antenna and the slave antenna. The master antenna captures signals in open-sky environments, while the slave antenna capture signals in degraded environments. In this architecture, a Phase Lock Loop (PLL) is adopted as a master loop to track the carrier phase of the open-sky signals. The Doppler frequency estimated by this master loop is utilized to assist weak carrier tracking in the slave loop. As both antennas experience similar signal dynamics due to satellite motion and clock frequency variations, a much narrower loop bandwidth and possibly a longer coherent integration can be adopted to track the weak signals in slave channels, by utilizing the Doppler aid from master channels. PLL tracking performance is affected by the satellite/user dynamics, clock instability, and thermal noise. In this paper, their impacts on the proposed phase tracking loop are analyzed and verified by both simulation and field data. Theoretical analysis and experimental results show that the proposed loop structure can track degraded signals (i.e., 18 dB-Hz) with a very narrow loop bandwidth (i.e., 0.5 Hz) and a TCXO clock.

Stochastic resonance(SR) is one of the applications in weak signal detection. Many researchers used the combination of the traditional first-order bistable system and genetic algorithm(GA), but the output of first-order bistable system is not smoothly enough, genetic algorithm has the phenomenon of losting in locally value. Aimming at the drawbacks above, second-order and under-damped stochastic resonance based on quantum genetic algorithm(QGA) is proposed. The test in simulation data and vibreation signals show that the presented method can raise the SNR ratio effectively, which has advantages of simplicity and fast convergence speed.

In this paper, the carrier-to-noise power ratio estimation performances for commercial GPS receiver are shown by simulation and are analyzed under weak signal reception, high sensitivity signal reception, and the matched spectrum jamming signal reception environments.

In recent years, the requirement for the accuracy, performance and stability of the gas sensors is increased in industrial production, home security, environmental monitoring and medical fields, so the research and development of gas sensors are also increasingly important. Many existing sensors such as electrochemical gas sensors have low accuracy and poor stability which can not satisfy the needs of the society. According to the deficiencies of the existing gas sensors, through designing the rational structure of the chamber and the technique of weak signal detection, this paper designed a CO 2 gas concentration sensor based on NDIR method with the advantages of good stability, high precision, fast response, simple and compact structure, etc.

Aiming at the application for High-Earth orbit spaceflight navigation, the paper is about the weak BDS signal acquisition on High-Earth orbit. First, this paper achieves the receiving power and Doppler-shift of the High-Earth orbit receiver by simulating the navigation signal characteristic which based on the STK (Satellite Tool Kit). In order to solve the problem of the secondary code witch modulated on BDS B1I and improve the acquisition sensibility, this paper analyses the autocorrelation characteristic of the data which modulated with the NH code, comes up with the resolution of using the alternate half-bit method by combining the coherent integration with the non-coherent integration. The result indicates that it can successfully acquire the −178 dBW BDS B1I signal under the mentioned method.

This paper considers discrete-time distributed detection of a constant, weak signal in dependent noise. A number of sensors transmit binary decisions to a central processor, which assimilates them to produce a "nal verdict. Asymptotic relative e$ciency (ARE) performance measure is used to compare the decentralized and centralized detection schemes. The precise de"nitions of ARE-robustness and asymptotic ARE-robustness are introduced, and utilized to understand better the trade-o!s involved in multiple-sensor detection in the presence of dependent noise. ( 1999 Elsevier Science

In this paper a new approach of ultra sensitive sensor based on coplanar waveguide is proposed. This sensor consists of two Wilkinson power dividers, makes use of the path difference of the two branches resulting in the opposite in phase, thus the weak signal changes emerge from the dramatically reduced background and the sensitivity is greatly improved.

A novel effective approach to weak continuous and digital signals processing in communication channels with high noise levels is proposed and investigated. The essence of proposed approach is illustrated by examples of various electronic devices. The conditions which allow obtaining the maximal gain in signal to noise ratio are found. This gain exceeds 50 dB for sensitive amplifier and approximately equals to 30 dB for detector of digital cosine video impulse. It is shown that the proposed approach ensures obtaining a lot more gain in signal to noise ratio compared to existing technical solutions. The considered advantages of the described devices allow employing the proposed approach to effective information processing in communication systems with low operating power. Статья посвящена решению проблемы обнаружения слабых аналоговых сигналов на фоне сильного шума с обеспечением гораздо большего выигрыша в отношении сигнал/шум в сравнении с уже существующими техническими решениями. В статье рассматривается устройство обработки сигналов, описывается сущность способа, условия достижения поставленной задачи получения максимального выигрыша в отношении сигнал/шум, превышающего 50 дБ, и преимущества рассмотренного устройства, которое является эффективным для систем обработки информации с малым уровнем мощности.

The recovery of signal under the presence of noise is utmost essential for proper communication. The signals corrupted due to noise can be recovered using various techniques. However the weak signals are more prone to noise and hence they can be easily degraded due to noise. In such cases, a digital lock-in amplifier becomes an essential device for recovery of such weak signals. Keeping the cost, speed and other considerations, we will present the implementation of digital lock-in amplifier and how it recovers the weak signal under extreme noisy conditions.

A brief introduction of the principle of correlation detection is present in this paper. As portable field-test equipment, an optical densitometer is designed with correlation detection technology to increase detection precision. In the process of designing, cross-correlation is applied to extract weak signal from strong noise. Simulation result with MATLAB shows that the correlation detection processed good performance in this application.

Signal from Tunable diode laser absorption is weak and not easy to acquire. Methods of autocorrelation detection and crosscorrelation detection are used to collect the signal from strong noise on LabVIEW platform. The simulation results indicated that with the same amplitude and same SNR, all the detection error is less than 0.70%. This method is used to a poisonous gas monitor system based on LabVIEW and it is confirmed that the method is effective to obtain the fact signal from lower SNR signal. Remarkably the method is designed by LabVIEW, it is easy to modify, upgrade and used as a subVI in other LabVIEW control system.

By applying specified time-delayed correlation matrices, an algorithm for extracting desired echo in passive coherent location (PCL) system is proposed. Some experiment results are presented to verify the effectiveness of the proposed method.

In this paper, a comprehensive model is developed for the scientific CCD camera readout noise. The readout noise can significantly reduce the ability of weak signal detection and ultimately affects the performance of an image processing approach to some extent. The different readout noise sources in scientific CCD camera are well documented, however, there has been little paper on the development of an all-sided readout noise model about the scientific CCD camera. Based on the proposed model, this paper presents a new test method that is present for choosing the standard section by defining criteria of optimality. The proposed method can get the more accurate readout noise than the test method used by experiment and analysis. Besides, the proposed method is fast and simple and therefore can be fitted in the analysis of data and post-image processing, which have very important application in analysis of the CCD camera other performance indicators.

Showing a using by description of possibility of use EH-sensors as magnetometric sensors for weak signal reception.

In the paper, it analyses circular correlation and accumulation algorithm and further proposes a new algorithm that combines circular correlation with half bit and presents the detailed acquisition steps. The feasibility and effectiveness of the algorithm are verified by the simulation under MATLAB. The results show that the new algorithm can improve acquisition efficiency and sensitivity.

In order to obtain new ways of weak signal detection, we analyze the motion of Duffing oscillator in the case of different input state by solving the Duffing equation firstly, and then elaborate the basic principles of weak signal detection based on Duffing oscillator phase-change characteristics. Further illustrate the experiment that shows how to achieve the weak signal detection with Duffing oscillator based on virtual instrument technology, then discuss the impact on signal detection coming from Gaussian white noise and how to implement weak signal detection with noises. The results show that, Duffing oscillator not only can be effective on detection of weak signal in the background of strong noises, but also has high cost performance to achieve it with virtual instrument technology. Compared with existing methods, it can greatly improve the detection results and has broad application.

We derive the optimum and suboptimum selective rake receivers (SRRs) for fading environment exhibiting impulsive nature. Simulation results confirm that, when the noise is impulsive, the SRRs designed for impulsive noise offer performance improvement over those optimized for Gaussian environment. The suboptimum SRR is observed to exhibit almost the same performance as the optimum SRR.

A frequency selective limiter operating over more than 2 octaves bandwidth has been developed. The design uses single crystal ephaxial YIG films. Limiting threshold and leakage are about 1 milliwatt. Dynamic range approaches 20 dB. Selectivhy bandwidth for 3 dB weak signal compression is about +- 20 MHz at 100 mW input. An analytical method gives accurate predictions of limiting behavior when linear loss terms are included.

The operation of a pulsed solid‐state Maser consists essentially of alternate periods of spin inversion and stimulated spin emission. Inversion can be accomplished by a short driving pulse or an adiabatic rapid passage. In the emission phase a weak signal field causes the spin system to spiral back coherently and radiate. The emissive phase can be treated by equations which for finite relaxation times can not be solved in closed form, but which are amenable to machine computation. Such numerical solutions giving the transverse moment, output field, output power, and power gain as a function of time were computed for various relaxation times, input fields, and values of the oscillation parameter. The results are interpreted with respect to applications of both regenerative and superregenerative modes of operation.

Chaotic systems are sensitive to certain signals and immune to noise at the same time, the properties of which make it potential application in signal detection and equipment fault diagnosis. In this paper, some Virtual Instruments (VIs) are designed to implement the Duffing oscillator which is used for weak signal detection. The basic design idea of the VIs is presented and the diagrams of some VIs are shown in the paper. At last, some detection results of the simulated signals and the real signals are given. It is shown that to use VI for the detection in the field is advantageous.