纠错编码技术在水声跳频通信中的性能研究

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。     

跳频组网同频干扰消除方法研究

为提高跳频组网效率,提出一种基于碰撞跳频码已知的同频干扰消除方案。在分析跳频组网同频干扰对跳频通信影响的基础上,采用在碰撞跳频码调制空码元的方式,避免频点碰撞,消除同频干扰,并对该方案应用于快跳系统时,进行优化以降低信息传输时延。结果表明:该方案能够有效消除跳频码碰撞引起的同频干扰,降低信息误码率,并通过合理的参数设置,可以较好地平衡快跳系统信息传输的有效性和可靠性。     

瑞利衰落信道下差分跳频通信系统抗部分频带噪声干扰的性能分析

在瑞利衰落信道和部分频带噪声干扰共存的环境下,针对逐符号检测和按序列检测两种信号检测方法,分别就差分跳频通信系统的误符号性能进行了理论分析,同时做出相应的计算机仿真.结果证实,差分跳频通信技术和按序列检测方法的结合,使通信系统的抗部分频带噪声干扰的性能得到了比较显著的提升.     

浅析跳频通信的关键技术

超短波通信的工作频带较宽,可以传送30路以下的话路或者数据信号。在众多的业务类别中,应急通信领域一直是超短波通信最重要的应用范围。主要讨论跳频通信的关键技术中的跳频图案、频率合成器和同步技术等方面,以其为超短波通信技术发展起到一定作用。     

浅海远程水声Turbo编码跳频通信研究

结合Turbo编码和水声跳频通信技术,基于数字信号处理(DSP)成功地研制出了一种高效的抗多途、抗噪声浅海远程水声通信系统.该系统针对浅海远程水声信道的低信噪比、强多途及快速时变衰落特点,采用一种联合有限脉冲响应(FIR)数字窄带滤波和线性调频信号互相关检测的快速、精确的帧同步方法;利用快速频谱分析进行解调,使用复杂度...     

水声通信中的混沌跳频技术研究

为了提高水声通信的保密性能,提出了一种简洁的混沌跳频图案实现方法。研究了量化logistic混沌序列产生的跳频图案性能,给出了平衡性、相关性、跳频间隔的仿真结果,验证了近距离水声通信中采用混沌跳频技术的可行性。     

跳频技术在超短波无线通信中的应用

作为一种扩频通信技术,跳频技术拥有许多技术优点,非常适合应用于超短波无线通信。本文着重介绍了跳频技术在超短波无线通信中的应用,分析了这一应用的技术优点和所涉及的关键技术,最后阐述了这一技术的应用现状及未来的发展趋势。     

乘积合并接收的差分跳频通信系统在瑞利衰落信道上抗多音干扰的性能分析

在瑞利衰落信道上,在多音干扰和加性高斯白噪声共存的条件下,对采用乘积合并接收(PCR)方法的差分跳频(DFH)通信系统的误符号性能进行了理论分析.为验证理论分析的正确性,进行了相应的计算机仿真,将采用 PCR 方法的误符号性能与采用线性合并接收(LCR)方法的误符号性能作了比较.结果证实,在瑞利衰落信道上,DFH 通信系统采用乘积合并接收的方法要比采用 LCR 方法具有更好的抗多音干扰的性能.     

跳频通信频率测试中应用自动测试系统的设想

跳频通信试验是通信对抗试验中常见的试验项目,试验中,要用到跳频信号源进行跳频序列的生成,用到调制域脉冲分析仪进行测试频率的捕获与分析工作,,这两项任务都由人工操作完成。文中提出了将自动测试系统应用于跳频通信频率测试的一种设想方案,由跳频信号源自动化系统开发和调制域脉冲分析仪自动化系统开发两个模块组成,以提高跳频通信试验的工作效率。     

超短波跳频电台数字处理平台的设计

本文主要对超短波跳频电台数字处理平台的设计及其中用到的信号处理技术进行了研究。通过方案设计和论证,我们采用高速ADC和DAC来实现超短波中频数字化,用可编程的上下变频器实现信号的上下变频,并且完成了硬件电路的设计和调试。     

基于KHM聚类算法的跳频信号分选

针对跳频信号分选,主要研究了聚类算法及利用直方图来预估计聚类数目及初始中心的方法.首先对直方图方法进行改进,得到了对跳频信号参数估计值误差不敏感的方法,其次对初始化中心不敏感的KHM聚类算法进行改进并聚类,最后提出了通过定义类内距类间距的方法来确定最佳聚类数的算法.通过改进的KHM算法和估计聚类个数方法,利用跳频信号参...     

Evaluation codes at singular points of algebraic differential equations

We use the special geometry of singular points of algebraic differential equations on the affine plane over finite fields to study the main features and parameters of error correcting codes giving by evaluating functions at sets of singular points. In particular, one gets new methods to construct codes with designed minimum distance. This work was partially supported by MCyT BFM2001-2251.     

Performance of line codes in optical direct detection continuous phase frequency shift keying transmission system impaired by polarization mode dispersion

Small deviations from perfect circular symmetry in the core region of single mode fiber (SMF) cause optical pulses to become broadened as they propagate. This phenomenon is referred to as polarization mode dispersion (PMD), which leads to intersymbol interference and becomes a major impediment for the high speed long-haul fiber-optic links. We present here the theoretical complement for evaluating the performance of a line-coded continuous phase frequency shift keying (CPFSK) optical transmission system with a direct detection receiver. The analysis is carried out for two different line-coding schemes, i.e. alternate mark inversion (AMI) and order-1 coding, to investigate the effectiveness of the line coding in counteracting the effect of PMD in a CPFSK direct detection transmission system in the presence of group velocity dispersion (GVD) and receiver noise in a single mode fiber. The average bit error rate (BER) performances are evaluated without and compared to that of line codes at a bit rate of 10 Gb s^?1 considering Maxwellian distribution for the mean differential group delay (DGD). We found that the amount of power penalty improvement of line-coded systems is within 0.65 to 2.25 dB with respect to NRZ data at a BER of 10^?9.     

Dual codes of systematic group codes over abelian groups

For systematic codes over finite fields the following result is well known: If [I∣P] is the generator matrix then the generator matrix of its dual code is The main result is a generalization of this for systematic group codes over finite abelian groups. It is shown that given the endomorphisms which characterize a group code over an abelian group, the endomorphisms which characterize its dual code are identified easily. The self-dual codes are also characterized. It is shown that there are self-dual and MDS group codes over elementary abelian groups which can not be obtained as linear codes over finite fields. Received March 7, 1995; revised version April 3, 1996     

基于喷泉码的放大转发协作通信系统的性能

为了实现在发送端未知信道状态信息(CSI)条件下的高效协作通信,研究了基于喷泉码的协作通信系统的性能.研究表明,在放大转发协作中目的端接收到的喷泉码符号的差错率比译码转发协作低.同时为了更充分地利用协作分集增益,提出了将基于喷泉码的放大转发协作通信与自适应解调技术相结合的方案,该方案使协作分集更有效地作用于喷泉码译码,并实现在发送端未知CSI条件下的自适应传输.仿真结果表明,该方案与采用喷泉码的直传通信和译码转发协作通信相比,能够降低误比特率,加快译码速度.     

Ionic conductivity and hopping rate data for some NASICON analogues

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.     

Linear codes with balanced weight distribution

In this paper, we study particular linear codes defined overF _q , with an astonishing property, their weight distribution is balanced, i.e. there is the same number of codewords for each nonzero weight of the code. We call these codesBWD-codes. We first study BWD-codes by means of the Pless identities and we completely characterize the two-weight projective case. We study the class of codes defined under subgroups of the multiplicative group ofF _q ^s , using the Gauss sums. Then, given a primep and an integerN dividingp – 1, we construct all theN-weight BWD-codes of that class. We conclude this paper by some tables of BWD-codes and an open problem.