Simple and High Performance Timing Synchronization in OFDM System

One ML timing offset estimation method for orthogonal frequency-division multiplexing(OFDM) systems is presented.The performance of our timing offset estimator are compared to that of H.Minn's estimator in terms of estimator variance error in both AWGN channel and multipath fading channel. Because no performance floor exists under high SNR condition,the new estimator can get more accurate estimation result with low computational complexity even under multipath fading environment.     

Frequency offset tracking algorithm for orthogonal frequency divisionmultiplexing systems using a pilot sub carrier

To improve the estimation precision of the carrier frequency offset in a multi path fast fading environment, the performance of the frequency offset tracking algorithm using a pilot sub carrier was studied extensively. Comparing with the frequency offset tracking algorithm based on a cyclic prefix, a frequency offset tracking algorithm using a pilot sub carrier can not only derive better frequency offset tracking performance in the AWGN channel, but also obtain exact frequency offset estimation in multi path fast fading channels. The algorithm using a pilot sub carrier therefore is more suitable for frequency offset tracking in the multi path fast fading channels.     

An algorithm of symbol timing rapid acquisition and tracking for π/4 DQPSK signals

Methods of IF difference detection combined with rapid acquisition synchronization and tracking principle by parallel processing methods were proposed in order to quickly achieve synchronous digital capture and tracking in π/4 DQPSK demodulation.Field program grid array (FPGA) technology to achieve rapid detection of synchronous capture and symbol tracking was adopted by using the improved algorithm in parallel with signal acquisition and frequency offset acquisition. This adoption took into account the characteristics of π/4 DQPSK and was in accordance with the detection of rapid acquisition synchronization and the tracking principle. The experimental results show that clock synchronization signals can be restored stably in eight symbol bit, accurately realize bit timing, and possess strong anti interference capability without affecting frequency differences. This proposed algorithm is suited for frequency hopping communication systems with high transmission rates.     

Improved Cosine Window and Its Implementation with DSP

An improved cosine window is put forward, which can reduce the spectrum leakage and can be easily implemented. The center of the method is to apply an exponent-m-to the usual window function. A proper value can be chosen for the exponent in light of the particular emphasis on frequency resolution, amplitude precision or sidelobe suppression and we can modify the characteristic of the window function through altering the value of m. Cycle of different times is effect.Carried out to implement it in DSP with software. The result of the emluator makes it clear that it is a method with good effect.     

Novel channel estimation algorithm for OFDM/TDM over fast fading channels

For the shortage of tracking ability against fast fading channel of the existing pilot structures and channel estimation algorithms in OFDM combined with time division multiplexing (OFDM/TDM) system, an improved channel estimation algorithm is proposed. The channel transfer functions are obtained by estimating the channel properties with two adjacent time domain multiplexing (TDM) pilot sequences, while the channel state information of the OFDM/TDM symbols is obtained with interpolation Combined with frequency domain equalization based on minimum mean square error (MMSE-FDE), the proposed algorithm can significantly compensate the path loss over fast fading channels. Simulation results show that, compared with the existing channel estimation algorithms, the proposed algorithm can achieve better performance, which is not only capable of dealing with slow fading channels, but also has a better tracking ability against fast fading channels with the same data transmission efficiency.     

Analysis of model-following control for multi-axle steering vehicle

The dynamic model of multi-axle steering vehicle is improved by considering the impact of the front-axle mechanical steering on the vehicle steering performance and implying the front-axle wheel angle in control variables to reduce the difficulty of vehicle control. On the basis of modified dynamic model, the multi-axle vehicle is analyzed by combining model-following method with pole assignment process. The transient response and frequency domain characteristics of the yaw angle velocity and sideslip angle at different speeds are obtained. The results indicate that, using model-following method to control vehicle can obtain desired tracking effects. At high speed, the transient response has no overshoot, the response time is shortened, and the stability of vehicle is improved.     

Blind estimation of IQ imbalance withnull subcarriers for OFDM systems

Orthogonal frequency division multiplexing (OFDM) is sensitive to the in-phase and quadrature-phase (IQ) imbalance induced by the direct conversion architectures. A compensation scheme of IQ imbalance exploiting null subcarriers in OFDM symbols is presented. The proposed algorithm is with high bandwidth utilization because the training symbols are not required. The effect of IQ imbalance on OFDM systems is studied, and the mirror relationship between the FFT of a sequence and that of its conjugate is employed to estimate and compensate the IQ imbalance. This method can be applied to multiple input multiple output (MIMO) OFDM systems with space time block code (STBC). Performance analysis shows that the proposed algorithm is asymptotically unbiased. The variance is inversely proportional to the number of OFDM symbols, null subcarriers, the SNR and the channel frequency response, and proportional to the IQ imbalance. Simulation results demonstrate that this scheme can obtain almost the optimal bit error rate (BER).     

Analysis and Research on VVT System Control Strategy for Motorcycle Engine

An original variable valve timing mechanism with two-mode intake timing parameters is developed according to the structural characteristics of small-medium displacement motorcycle engine. Based on cycle simulation, a cycle simulation model of VVT mechanism for motorcycle engine is created. The control strategy of variable valve timing and lifting running-model are carried out at idle speed low negative load, middle negative load, low speed high negative load and high speed high negative load. It has been proved that the performance of JH125 motorcycle engine can be effectively improved by loading the new type VVT system.     

Simulation Analysis on Decreasing Vibration of Motorcycle Engine Suspension System

With the development of high-speed and high-power, the motorcycle vibration from engine become one of the major factors affecting the performances of motorcycle. Elastic suspension structure is adopted between the engine and frame for the vibration during the process of designing a certain type of motorcycle with 200 cc engine in some enterprise.Through optimization of the suspension system performance parameters, inherent frequency of suspension system keeping away from the activated frequency of engine in common use is essential. Isolation performance is improved and the vibration is solved. As a result, the comfort is improved.     

Accuracy analysis for frequency estimation of amplitude ratio method

Aiming at the spectrum leakage that exists in fast Fourier transform (FFT),several ratio frequency estimation algorithms that widely used by engineering signal processing are deeply studied.Firstly,the principles and features of these algorithms are introduced,and the influences of three parameters on frequency estimation accuracy are concretely analyzed.These parameters are signal to noise (SNR),cycles covered in record and the distance from the DFT output peak to the true frequency in bin widths.Then,related simulations are carried out to analyze and compare the performance of these frequency correction methods.The simulation results show that the frequency estimation accuracy has lower limit.When the number of the waves in the tone is small,the accuracy of these methods is poor,but can be improved observably by increasing the waves for the most methods.When the number of the waves in the tone is large,most methods have high and stable accuracy.The performance of the Rife-Jane’s method and Vetterling’s method can be improved by using Hanning-tapered data.Finally,considering specific engineering environment,some rules and principles about how to choose appropriate algorithm are provided.     

One-cycle Technique Based Adjustable Ac Source

By using one-cycle control theory, a novel voltage source inverter is proposed. The conventional one-cycle control technique needs that the integrator is reset instantaneously. But it is very difficult to realize with hardware due to the finite time constant of the reset circuitry. Therefore, based on the one-cycle technique, the paper gives a new control scheme to resolve the problem with dual switched integrator, and the performance of the integrators is close to ideal. The paper also uses the dc offset to implement the voltage measurement. Furthermore, the amplitude and frequency of the output voltage are effectively adjustable. The one-cycle control technique not only provides fast dynamic response, but also can admirably suppress the perturbation yielded by dc source and abate the undesired harmonic contents. Simulation studies were performed to prove the proposed scheme. The results show that the one-cycle control based voltage source inverter makes good use of dc source that is 92.8% and THD is only O. 255 9%.     

Calculation on Natural Frequency and Main Vibration Mode of Double-lined Type Mounting System

The vibration characteristic of engine mounting system is analyzed, the vibration model of engine mounting system is established, and calculation method of natural frequency and main vibration mode of mounting system is put forward. Then an engine mounting system with double - lined type isolator is presented. Isolation performance of engine mounting system is improved greatly by selecting elastic coefficient of isolator reasonably.     

Performance Analysis of Anti-CW Interference in MC-CDMA Systems

The multicarrier-code division multiple access (MC-CDMA),which is the combination of direct sequence CDMA (DS-CDMA) and orthogonal frequency division multiplexing (OFDM) techniques, offers various advantages over single-carrier CDMA system. Some of the advantages are that MC-CDMA systems possess can remove the intersymbol interference (ISI) and enhance narrow-band interference suppression capabilities. So the MC-CDMA technique becomes a focus in the field of mobile communication. The authors introduce the typical MC-CDMA system model, discuss the decision statisticalvariable in Rayleigh fading channel included the CW interference, and give the expressions of probability of error in uplink. An approach is proposed with Modified Equal Gain Combining (MEGC) to decrease the effect of CW interference. Theoretical analysis and numerical results show that the anti-CW interference performance of MC-CDMA system can be improved used the MEGC approach.     

Application of frequency shifting in truncating substructure low order normal modes

A method to cutoff substructure low order normal modes in component mode synthesis is proposed. Frequency shifting technique is introduced in substructure free vibration differential equation. Quasi-static constraint mode is taken into coordinate transformation and the contribution of substructure low order normal modes to system middle frequency modes is reduced,thus substructure low order normal modes truncation is achieved. This technique is used to compute dynamic characteristics of a body-in-white FEM mode in the frequency band of 160~190 Hz. The results show that compared with traditional component mode synthesis,which keeps 1 836 normal modes,this method only needs 297 normal modes and saves 27.7% calculation time. It means frequency shifting technique can improve the computational efficiency for middle frequency band dynamic characteristics of complex structure.     

A time-varying signal processing method for Coriolis mass flowmeter

The mass flowrate of Coriolis mass flowmeter in practical application has slow changes with time. To solve the problem, an improved time-varying signal model whose frequency, amplitude and phase are time-varying based on the random walk model is established firstly. A new algorithm of adaptive notch filter with the capability of tracking frequency variation is applied to filter the sensor output signal of Coriolis mass flowmeter and its frequency is calculated next. An adaptive line enhancer based on the mentioned notch filter extracts fundamental frequency signal from noisy data. Then, by short window intercepting, the revised sliding DTFT recursive algorithm is introduced to calculate the real-time phase difference between two enhanced signals. With the frequency and phase difference obtained, the time interval between the two signals is calculated and then the mass flowrate is derived. The simulations and field test results show that the proposed method can not only track the change of frequency and phase, but also ensure the calculation accuracy when measuring small phase difference. The computational load of the algorithm is simple so that it can be applied to real-time signal processing for Coriolis mass flowmeter.     

Musical Note Recognition with DWT and FFT

The sole note is a regular cyclical signal. The best frequency domain resolution can be gotten with FFT. However, the harmonic components of the note are extremely rich, so FFT is unable to examine the fundamental frequency accurately. DWT can decompose the signal to low pass rapidly,and has a smooth low frequency approximation. This article brings forward DWT and FFT union musical note recognition method, which realizes the precise frequency recognition of the musical note and is an expected method.     

Realization of Flash Stimulation with PWM in the Extraction of Visual Evoked Potential

Evoked EEG signal can be obtained by flash stimulation in the extraction of flash visual evoked potential(FVEP).Experiments show that the width,frequency and flash times of flash pulses will play key role for extracting FVEP.Aims at the feature of VEP extraction and its correlation factors,the flash stimulation method with pulse width modulation(PWM) technology has been discussed,and the realization methods based on hardware and software are studied,then the output of precise PWM with special integrated circuit is realized.So the parameters of flash stimulation can be adjusted based on the material conditions of FVEP extraction,then VEP can be extracted effectively.Experiments show that it is of better effectiveness for FVEP extraction by using the method based on the output of precise PWM to control the flashing stimulation.     

Functional source separation to finger tappingrelated magnetoencephalography signal

It has been verified that the ICA can isolate sources from multi channel magnetoencephalography (MEG) signals. Based on the route of constrained ICA (cICA), this paper achieves a new solution of MEG inverse problem called functional source separation (FSS) by adding a functional constraint to the cost function of a basic ICA model. Source activity is obtained by applying this method to one MEG signal dataset under a self paced finger tapping task. The result is proved effective by calculating correlation coefficients between the weight vectors of function source separation method and the spatial filter coefficients of SAM method. It is found that finger tapping related functional source was localized in motor cortex of precentral gyrus. At the same time, the temporal and frequency information provided by FSS method could be a basis of exploring cortical control timing mechanisms associated with finger movements and extracting time frequency characteristics of the functional source.     

Harmonic wavelet demodulation for gearbox fault diagnosis

On the basis of partial decomposition in frequency domain with harmonic wavelet package method and Hilbert demodulation, the demodulation based on harmonic wavelet package transform is introduced. The Fourier spectra analysis is carried out after preprocessing, and the depth of decomposition and frequency band are determined by the analysis of frequency band distribution and the theoretic computation of gear box characteristic frequency. Then with FFT and IFFT the corresponding meshing component is extracted. Finally, the modulation information is extracted via Hilbert envelop analysis approach. With the proposed method, wear and notch faulty gearbox are tested and analyzed by experiment, respectively. The results prove that this method can locate gearbox fault precisely and provide corresponding basis for judging fault cause and degree.     

A Non-linear Circuit Model of A Self Scanned Photodiode Array Image Sensor

A non-linear circuit model of photodiode built according to the working principle of self-scanned photodiode array image sensor is presented for improving the property of the sensor. Through the analysis of the non_linear circuit model,we get the state equations, and the equations are resolved with Runge_Kutta algorithm. The Runge_Kutta algorithm is realized in C language, and the numeric result of the circuit is obtained. The analysis of the numeric result of the model shows that the non_linear performance of the sensor can be improved by reducing the capcitor of the PN junction and the dynamic performance of the image sensor can be enhanced by paralleling capacitor C M , and all the analysis is consistent with the real measurement results of the sensor. The circuit model of photodiode is improved over previous model.