基于DSP的DTMF编解码技术的实现

DTMF信令广泛应用于各种交互控制应用领域,很多基于DSP的系统中都需要正确地处理DTMF信号,因此将DTMF编解码集成于DSP系统之中具有重要的工程实用价值。DTMF的编码过程基于两个二阶数字正弦波振荡器;DTMF的解码过程基于改进的Goertzel算法。本文详细论述了DTMF编解码算法的原理及其在TMS320C6000系列DSP上的实现技术方法。最后根据给出的试验测试结果可以看出,该算法非常适合在各种基于DSP的系统中应用。     

拉曼光谱方法研究1,1,3,3-四甲基脲的溶剂效应

测量了1,1,3,3-四甲基脲(TMU)在20种不同溶剂中的拉曼光谱,研究了TMU与溶剂之间的相互作用.将TMU羰基的拉曼频移分别与Kirkwood-Bauer-Magat(KBM)参数(ε-1)/(2ε+1)、溶剂受体数(acceptor number,AN)和线性溶剂自由能关系(linear solvation energy relationships,LSER)进行相关分析.结果表明,TMU的C=O键振动频移与KBM参数没有很好的线性关系,和受体数之间存在比较好的相关性,与LSER参数的线性关系最好.按受体数把溶剂分为质子性溶剂和非质子性溶剂,分别和羰基频移有好的相关性.通过对LSER参数的分析,可以很好地解释溶质和溶剂间的相互作用.     

Controlled Growth Morphology of Porous Nanocrystal Iron Oxide by Electrodeposition

Fe(II) was deposited into the bottom of the mesopores of highly ordered large caged cubic mesoporous silica by electrodeposition. And the deposited Fe mesoporous silica thin film was treated by 1%―4% HF to remove the SiO2 template and then calcined. It was found that nanowire bundles, dendritic plates of porous iron oxide, dense parallel backbones of porous iron oxide were obtained at 1.4―-1.6 V and 0.08―0.1 mol/L electrolyte concentration after calcinations; the dendritic pattern of porous iron oxide film ...     

STRUCTURAL EVOLUTION AND COMPOSITION CHANGE IN THE SURFACE REGION OF POLYPROPYLENE/CLAY NANOCOMPOSITES ANNEALED AT HIGH TEMPERATURES

A model experiment was done to clear the formation mechanism of protective layers during combustion of polypropylene(PP)/organically modified montmorillonite(OMMT) nanocomposites.The investigation was focused on the effects of annealing temperature on the structural changes and protective layer formation.The decomposition of OMMT and degradation of PP/OMMT nanocomposites were characterized by means of thermogravimetric analysis(TGA).The structural evolution and composition change in the surface region of...     

一种新型的基于相位域处理的基带DSSS信号接收方法

In this paper, the phase characteristic disturbance model for baseband direct sequence spread spectrum (DSSS) signal in additive white Gaussian noise (AWGN) environment is established, and the probability density function (PDF) of phase characteristic disturbance is obtained. Then a novel receiver model for baseband DSSS signal based on maximum likelihood (ML) criterion is proposed. The simulation results show that, comparing with correlation scheme, the performance of the proposed method for baseband DSSS signal is 1dB worse in AWGN environment. However, if there is narrow interference in the AWGN environment, the proposed method will show better performance up to 2.5dB, and it has good adaptive resistance to narrowband interference located in different frequency points. This method could be used as an alterative communication scheme for military circumstance when existing strong narrowband interference of various frequencies.     

Experimental investigation of a seven-element hexagonal fiber coherent array

The phase noises of a 10-m polarization-maintaining （PM） fiber and a 10-W PM fiber amplifier are experimentally measured. The results indicate that the 10-m PM fiber with similar phase noise could be used to investigate the architecture of master oscillator power amplifier coherent combination. A seven-element hexagonal fiber coherent array is developed to investigate the far-field distribution and phase controlling technique of a coherently combining fiber laser array. A hexagonal prism is designed as the combining and splitting component to achieve a fill factor of 0.66. The hill climbing method is employed to detect and lock the element phase.     

Suppressing the multimodal size distribution of InAs/GaAs quantum dots through flattening the surface fluctuation

A method of suppressing the multimodal size distribution of InAs/GaAs quantum dots(QDs) using molecular beam epitaxy through flattening the substrate surface is reported in this work.It is found that the surface roughness plays an important role in the growth of QDs through continuous surface evolution(SEQDs).SEQDs are the main components of small QD ensemble in QDs with multimodal size distribution.It is suggested that most of the SEQDs are very likely to nucleate during the growth interruption rather than...     

Analysis of Doppler-effect on satellite constellations with wavelength division multiplexing architectures

With the development of optical space communications, a global space-based optical backbone network is currently proposed by using broadband laser inter-satellite links （ISLs） which enable routing traffic through the space. Satellite optical networking techniques based on wavelength division multiplexing （WDM） ISLs can transit significantly high data rates signals. In this letter, a new function of wavelength excursion due to Doppler-effect is developed for the ISLs, considering the conception of pointing ahead mechanism. The characteristic of wavelength excursion induced by Doppler-effect is examined in one of low earth orbit （LEO） satellite constellation networks named the next-generation LEO system （NeLS） with WDM ISLs assumed, and the influence on its communications caused by wavelength excursion is analyzed.     

Evolution Handoff Strategy for Real-Time Video Transmission over Practical Cognitive Radio Networks

The transmission delay of realtime video packet mainly depends on the sensing time delay(short-term factor) and the entire frame transmission delay(long-term factor).Therefore,the optimization problem in the spectrum handoff process should be formulated as the combination of microscopic optimization and macroscopic optimization.In this paper,we focus on the issue of combining these two optimization models,and propose a novel Evolution Spectrum Handoff(ESH)strategy to minimize the expected transmission delay of real-time video packet.In the microoptimized model,considering the tradeoff between Primary User’s(PU’s) allowable collision percentage of each channel and transmission delay of video packet,we propose a mixed integer non-linear programming scheme.The scheme is able to achieve the minimum sensing time which is termed as an optimal stopping time.In the macro-optimized model,using the optimal stopping time as reward function within the partially observable Markov decision process framework,the EHS strategy is designed to search an optimal target channel set and minimize the expected delay of packet in the long-term real-time video transmission.Meanwhile,the minimum expected transmission delay is obtained under practical cognitive radio networks’ conditions,i.e.,secondary user’s mobility,PU’s random access,imperfect sensing information,etc..Theoretical analysis and simulation results show that the ESH strategy can effectively reduce the transmission delay of video packet in spectrum handoff process.     

A Transductive Scheme Based Inference Techniques for Network Forensic Analysis

Network forensics is a security infrastructure,and becomes the research focus of forensic investigation.However many challenges still exist in conducting network forensics:network has produced large amounts of data;the comprehensibility of evidence extracting from collected data;the efficiency of evidence analysis methods,etc.To solve these problems,in this paper we develop a network intrusion forensics system based on transductive scheme that can detect and analyze efficiently computer crime in networked environments,and extract digital evidence automatically.At the end of the paper,we evaluate our method on a series of experiments on KDD Cup 1999 dataset.The results demonstrate that our methods are actually effective for real-time network forensics,and can provide comprehensible aid for a forensic expert.