AR自编码扩频系统中扩频序列的特性研究

在扩展频谱通信中,扩频序列的性能与系统的抗多址干扰、抗多径衰落的能力,和信号的低截获率概率有密切关系,也关系到捕获与同步系统的实现。扩频序列的特性对扩频系统的性能有重要影响。在自编码扩频通信系统中,自编码扩频序列的特性对于自编码扩频系统的性能同样非常重要。该文详细分析了采用AR滤波方式产生的扩频序列的扩频特性。计算机仿真说明,用AR滤波提取自编码扩频序列完全满足自编码扩频通信的要求。     

软扩频通信系统的研究

文章介绍了软扩频通信系统的基本原理、编码和实现框图,分析了软扩频通信系统接收机的性能,并比较了软扩频系统同步接收的几种方案。结果表明,滑动相关捕获是一种有效的伪码捕获方法,软扩频通信系统能够进行可靠的通信。     

基于AR自编码扩频的卫星测控通信技术

文章介绍了卫星自编码扩频测控通信的原理和方案,提出了利用自回归滤波的方法从信源序列中提取扩频码的AR白编码扩频系统,并对该系统的误码性能进行了理论分析和仿真。分析与仿真结果表明,AR自编码扩频系统改善了普通自编码扩频系统的误码性能,降低了传输信号的截获率,为自编码扩频通信在卫星测控通信领域的应用提供了可选的方案。     

直序扩频系统中扩频码同步技术的研究

针对扩频通信中伪随机序列的快速捕获问题,文中提出了扩频信号快速捕获方法,来解决低信噪比条件下伪码序列的捕获问题.首先对直接扩频通信系统的基础理论做了探讨,而后重点研究了两种基带扩频信号同步捕获方案--序列相位搜索捕获法和不连续相位滑动相关法,序列相位搜索捕获法主要适用于m序列码周期较短的情况,而不连续滑动相关法则克服了...     

直接序列扩频通信中m序列的同步方案及其FPGA实现

文中介绍了直接序列扩频通信中m序列的两种主要同步捕获方法：滑动相关法和数字匹配滤波器法，并对其同步时间和抗噪声性能进行了理论分析和实验比较。结果表明，数字匹配滤波技术在直接序列扩频伪码同步捕获时，有其突出的特点，尤其在突发通信时，可以大大减少同步捕获时间。论文同时给出了其FPGA实现。     

扩频码捕获及其FPGA实现

介绍了直接序列扩频通信中m序列的构造及其滑动相关同步捕获方法,并对其同步时间和抗噪声性能进行了理论分析和实验比较。结果表明,滑动相关法在直接序列扩频码同步捕获中具有优越的抗噪性能。文章同时给出了MATLAB的抗噪声估计及其滑动相关法的FPGA实现方法。     

中频数字化直接序列扩频接收机的实现

给出了统一信道直接序列扩频通信系统的中频数字化接收机的实现方案。采用该方案所实现的直接序列扩频通信系统的载波与伪随机码的捕获分别采用了FFT辅助捕获技术,载波的跟踪采用了数字CPAFC环路牵引,数字COST-AS环路精确跟踪技术,伪码跟踪采用的是数字DLL环路实现。系统中I通道采用可编程GOLD扩频,Q通道采用截断m序列直扩,并置截断m序列与GOLD码具有相同速率、倍周期的关系,以简化系统伪码的同步电路设计。最后,讨论了该系统应用于扩频测距时,测量数据的"置中值"处理方法。     

数字匹配滤波与自适应门限检测技术在扩频中的应用

文中给出了数字匹配滤波技术和自适应门限检测技术的基本原理,并对其性能进行了分析。运用数字匹配 滤波结合自适应门限检测技术进行直接序列扩频伪码(周期为N)捕获,可以缩小捕获时间,增大捕获的动态范围和提高扩频 系统在快速变化信道中的误码性能,尤适于突发扩频通信。     

通信测距复合系统中的扩频码捕获研究

在通信测距复合系统中，长序列PN码的快速捕获是一个不可避免的问题。扩频码同步是扩频通信系统中的关键技术，针对传统的捕获方法的缺点，提出一种改进的序列估计的捕获方法，给出系统结构并说明了工作原理。     

高动态短时突发扩频信号的快速捕获

针对低信噪比和大多普勒频移环境下,短帧突发直接序列扩频通信系统要求在短时间内以很低虚警和漏警概率捕获信号这一难题,设计了仅使用独特码的短时突发扩频信号帧结构,在接收端将扩频码与独特码作为一个复合扩频码看待,提出了基于FFT的高动态突发信号捕获方法,可同时快速完成突发信号检测、扩频码捕获、频偏估计、帧同步检测和位定时捕获等任务。仿真结果表明:该算法能有效消除多普勒频移对短时突发扩频信号捕获性能的影响。     

自编码直接序列扩频通信原理样机的实现及测试

自编码直接序列扩频通信由于提高了通信信号的隐蔽性,且保持了直接序列扩频通信技术原有的抗干扰性能,对改善军事抗干扰通信具有积极意义。根据自编码直接序列扩频通信的特点,设计出了原理样机,并提出和实现了一种基于帧变化并发送同步头的初始同步方案,效果良好。经过测试,所有性能指标均已达到预期目标,并且与单用户下的理论分析结论相吻合。     

FIR parity check codes

This paper describes a method for packet synchronization and error detection for use in a synchronous digital communications system. The method relies upon a class of linear block codes that have parity checks that are expressed in terms of a finite-impulse response (FIR) filter. This system is incorporated in the newly established ITU standard of digital cable television standard, J.83 appendix B, which is based on an MPEG 2 transport packet data stream. This technique is also the basis for cable modem downstream transmission defined in the IEEE 802.14 and MCNS standards. The parity check structure is based on a pseudonoise sequence generated by a (binary) primitive polynomial. This structure allows for a computationally efficient implementation of the parity check FIR filter, in a recursive manner, that is none the less self-synchronizing. The FIR parity check codes that are described are characterized as the dual of a CRC-type, shortened cyclic code. The theory and computational structure of these codes are presented here; the J.83R code is used as an example of the general theory     

Direct-sequence codes based blind synchronization algorithm for UWB systems

A new blind (non-data-aided) synchronization algorithm based on direct-sequence (DS) codes is proposed for ultra-wideband (UWB) systems. The proposed approach fully exploits prior knowledge of DS codes and bypasses channel estimation. The real-time acquisition is achieved using integrating-and-dumping (I&D) operation and DS codes matching filter. Because of pseudo randomicity and periodicity of DS codes, both the speed and the accuracy of synchronization are improved significantly. A lower bound on the acquisition probability of the proposed approach is also derived. Simulations confirm performance improvement of the proposed algorithm relative to existing alternatives in terms of acquisition probability, normalized mean square error (NMSE), and bit error rate (BER).     

基于特殊导频码的OFDM系统高效同步算法

设计了一类适用于OFDM系统具有良好理想相关性的前导码结构。基于此前导码,提出了一种适用于OFDM系统的基于匹配滤波结构的高效帧定时同步捕获方法,该算法具有非常高的效率并且能够准确估计出定时同步位置。计算机仿真结果表明该捕获方法在低信噪比下具有较高捕获同步概率,而且同步精度很高。     

Metric‐based node synchronization of the Viterbi decoder in satellite applications

Convolutional codes are used in digital communication systems to correct errors that occur during transmission. Their use is now commonplace, particularly in power‐limited satellite and deep space communication systems. Before the decoder can correctly decode the received continuous bit sequence, however, it must establish where codewords begin and end in this sequence. The process of determining codeword boundaries is called node synchronization. In this paper we develop a node synchronization algorithm based on metric difference values with the objectives of simple implementation and reliable performance. Focusing on satellite applications, we consider the constraint length 7, rate ½ convolutional code standardized by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA); the approach we develop can be extended to other convolutional coding systems. Through simulation, we investigate the statistics of the received sequence, and highlight correlation in the sequence of the decoder metric values. In the light of these observations, we propose a synchronization algorithm, and develop a first‐order analysis of this simple up/down counter framing technique. We recommend framing parameters based on both the analytical results and the expected response of the framing algorithm to correlated metric values. Development of a simple node synchronization algorithm that accommodates correlated metric values has not been reported previously in the literature. Simulation results confirm that reliable node synchronization is possible with this very simple approach. Copyright © 2000 John Wiley & Sons, Ltd.     

小波滤波与AR模型在脑电信号处理的应用

针对脑-计算机接口技术中的脑电信号处理、事件相关同步和事件相关去同步的特点,提出了一种基于离散小波滤波和AR模型来提取脑电信号特征向量的方法。利用Daubechies类小波函数对脑电信号进行4层分解,然后使用Burg算法提取脑电信号8阶AR模型系数,最后用BP神经网络进行分类和比较。得到最优的正确率为71.64%,小波滤波的效果要优于FIR滤波器。     

A programmable pipelined digital differential matched filter forDSSS receiver

A programmable pipelined digital differential matched filter (PDMF) implemented for a direct sequence spread spectrum receiver is proposed in this paper. To reduce the power consumption, the PDMF architecture is based on the synchronization combined PN code phase acquisition algorithm. Compared with the conventional PN code phase acquisition algorithm, the theoretical analysis result indicates that the PDMF acquires both power efficient and preferable detection. Depending on different applications, programmability allows the PDMF to implement 3-tap, 5-tap, or 11-tap Barker codes with the same hardware but different precisions for each tap coefficient. For short tap Baker codes, the architecture could adopt more precision on each tap coefficient to resist the channel noise. Simulation results also show that there are fewer errors of high sample precision with the same tape     

一种有效的MIMO-OFDM系统时频同步方法

为了检测不同天线的时延和频偏,提高多输入多输出正交频分复用（MIMO-OFDM）系统同步算法性能,给出了一种有效的MIMO-OFDM系统定时和频率同步算法。该算法构造了一种新颖的基于恒包络零自相关码（CAZAC）的良好正交特性的训练序列结构,利用该训练序列结构可以有效地完成各发射天线的迟延和载波频偏估计。仿真结果表明,所给方法具有高的定时估计精度和低的计算复杂度,适用于各发射天线信号到达时延不同情况的MIMO-OFDM系统,具有很好的实用价值。