共查询到19条相似文献,搜索用时 218 毫秒
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纠错编码技术在水声跳频通信中的性能研究 总被引:1,自引:0,他引:1
将水声跳频通信系统与纠错编码技术相结合进行了研究,针对复杂多变、强多途和起伏干扰的浅水水声信道,建立了基于BELLHOP射线模型的时变衰落水声信道模型,该信道模型建立起了信道特性与海洋环境参数之间的关系,在海洋环境参数给定的条件下可以精确仿真信道。在此基础上通过系统仿真的方法研究了卷积码、RS码和串行级联码三种纠错编码方案在水声跳频通信系统中的性能,给出了两种典型信道下的仿真结果并进行了对比分析,结果表明串行级联码具有更强的纠错能力,比较适合复杂多变的水声衰落信道。 相似文献
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水声信道是一个极其复杂的时变-空变-频变信道,因而进行水声通信,必须克服时变多途干扰等困难。将抗干扰能力强的跳频通信技术应用于水声通信领域,对于隐蔽性、保密性要求高的系统来说,该体制有着卓越的特性。在仿真环境下,对比研究了m序列和基于二维logistic映射的混沌序列的相关性、平衡性、功率谱特性、多址性等性能。构建了一种在低声能条件下的水声跳频通信系统,给出了系统编解码技术的实现方法。发射的帧信号由激活信号、同步信号、时延信号和三组(15,11)汉明码循环3次组成,采用了时间与频率的双分集技术进行纠错解码,从而增强了系统的保密性。通过外场试验,验证了利用m序列和混沌序列进行水声跳频通信的可行性,并对试验结果进行了对比研究。由于混沌序列的数量巨大且性能优异,非常适用于水声组网通信和保密性要求高的水声通信系统。因此,混沌序列在今后的水声跳频通信领域应有更广阔的应用前景。 相似文献
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跳频通信具有良好的抗干扰、低截获概率、灵活组网和抗衰落能力。本文详细介绍了数字通信中跳频发射机的工作原理、跳频发射机的基带功率、换频时间、跳频信号调制质量等参数的测试原理和测试方法。 相似文献
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针对正弦信号源捷变状态切换后的建立时间、开机后波形建立时间以及过载恢复时间等的精确测量问题,提出了一种基于局域波形四参数拟合的测量分析方法,然后将拟合模型参数拓展到全局,进而获得拟合回归波形与过渡过程波形的回归残差波形。该波形的收敛过程反映了正弦波建立过程中的残差收敛变化过程。以它为目标对象,加上主观设定的建立时间的条件判据,可以获得正弦建立时间的起始和终止两个时刻点,最终获得完整的正弦信号建立时间。在两组不同条件下的状态切换实验结果,验证了该方法的有效性和可行性。该方法也可以推广应用到脉冲调频、脉冲调幅、脉冲调相、捷变频信号的建立时间测量评价中。 相似文献
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研究了一种用多个不同频率的CW窄脉冲与帧同步脉冲的时延差携带信息的水声通信技术。该技术利用多个不同频率的CW矩形窄脉冲与帧同步CW矩形窄脉冲之间的时延值进行信息编码,在接收端采用时延估计和频率检测技术进行解码,从而使码元间距成为可携带信息的有用资源,将码元间距扩展到足够宽,既可有效地克服水声信号的多途影响、提高频带利用率,又可大大减少码元脉冲数量,达到节省能量并提高通信可靠性的目的。仿真结果表明,该水声通信编码体制数据传输速率适中,编码和解码简易,系统稳健。 相似文献
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The a.c. conductivity of ionic materials shows two regions of frequency-dependent conductivity over a wide range of frequencies.
Jonscher’s law of dielectric response for ionic conductors enables us to characterize the conductivities. The region of low
frequency dispersion approximates to a frequency-independent plateau enabling us to obtain the d.c. conductivity. In some
other conductors, the presence of low-frequency dispersion cannot be neglected while determining the effective d.c. conductivity.
We have used this method to extract the d.c. conductivity and hopping rate as well as to estimate concentrations of the mobile
ions (carriers) in some NASICON analogues. 相似文献
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The electrical properties of undoped SnO2 thin films prepared by the sol-gel technique were investigated by conductivity measurements in a temperature range of 50-200 K. Structural characterizations of the films were performed by atomic force microscopy and X-ray diffraction. Optical properties of the samples were also characterized by optical absorption spectroscopy. The different hopping models were used to investigate the characteristics of electrical conduction by hopping in employed temperature range. It was shown that three types of behavior can be expected, nearest-neighbour hopping at high temperatures, the Mott variable-range hopping at low temperatures and Efros-Shklovskii variable-range hopping at lower temperatures. The criteria for the observation of these three regions were established and the transitional behavior of the conductivity was determined. The experimentally determined critical transition temperatures were at the orders of magnitudes with what could be expected based on hopping conduction calculations. Under these analyses, the compensation ratio of the films was determined. 相似文献
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A. N. Patil M. G. Patil K. K. Patankar V. L. Mathe R. P. Mahajan S. A. Patil 《Bulletin of Materials Science》2000,23(5):447-452
The dielectric properties (dielectric constant and loss) for the system Cu
x
Fe3−x
O4 with x = 1.0, 0.8, 0.6, 0.4 and 0.2, were studied in the temperature range 300 ∼ 800 K and also in the frequency range 1
kHz ∼ 1 MHz. A.c. conductivity was derived from dielectric constant and loss tangent data. The conduction in this system is
interpreted as due to small polaron hopping. The dielectric relaxation was observed for the compositions with tetragonal structure
whereas normal behaviour was observed for cubic structure. 相似文献
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Polycrystalline ceramic samples of sodium bismuth titanate with simultaneous doping at A and B sites have been studied for
the influence of these dopants on the electrical conduction mechanism. A.C. conductivity measurements were done on the prepared
sample in a wide range of frequency and temperature. These studies revealed that the conduction in the sample arises due to
hopping of bound charges. Four-term power law is used to characterize the frequency dependence of a.c. conductivity. From
the temperature dependence of the exponents, the a.c. conduction in the samples is explained. 相似文献
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We have successfully synthesized the system Sr1 −x
La
x
Ti1 −x
M′
x
O3 where M′ = Cr, Ni and Co by using conventional solid state ceramic method. Powder X-ray diffraction patterns of the different
compositions show the formation of single phase materials. Measurement of AC conductivity as a function of frequency at different
temperatures in the range 300–550 K show that conduction in these compositions occurs due to hopping of charge carriers between
localized transition metal ion sites. 相似文献
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Li‐Hong Chen Jiang‐Bin Guo Xuan Wang Xin‐Wei Dong Hai‐Xia Zhao La‐Sheng Long Lan‐Sun Zheng 《Advanced materials (Deerfield Beach, Fla.)》2017,29(43)
A giant room‐temperature magnetodielectric (MD) response upon the application of a small magnetic field is of fundamental importance for the practical application of a new generation of devices. Here, the giant room‐temperature magnetodielectric response is demonstrated in the metal–organic framework (MOF) of [NH2(CH3)2]n [FeIIIFeII(1?x )NiIIx (HCOO)6]n (x ≈ 0.63–0.69) ( 1) with its MD coefficient remaining between ?20% and ?24% in the 300–410 K temperature range, even at 0.1 T. Because a room‐temperature magnetodielectric response has never been observed in MOFs, the present work not only provides a new type of magnetodielectric material but also takes a solid step toward the practical application of MOFs in a new generation of devices. 相似文献