Design of cyclic shift interleavers for Turbo Codes

In this paper we consider cyclic shift interleavers for turbo coding. The properties of cyclic shift interleavers are discussed and compared with S-random interleavers. It is shown that the cyclic shift interleavers are equivalent or better than the S-random interleavers in the ability to break low weight input patterns. We estimated the performance of turbo codes with cyclic shift interleavers and compared it with the performance of S-random interleavers for varions interleaver sizes. The simulation results show that a turbo code with a cyclic shift interleaver can achieve a better performance than an S-random interleaver if the parameters of the cyclic shift interleaver are chosen properly. In addition, the cyclic interleavers have the advantages of lower design complexity and memory requirements.     

循环谱密度的两通道最大嫡谱估计

对周期平稳随机过程的循环谱密度的估计,过去主要采用时域平均周期图法和频域平滑周期图法,但当短数据时,上述方法的分辨率很低,方差很大。本文提出了循环谱密度的两通道最大熵谱估计,该方法不仅具有很高的分辨率,而且估计的方差也很小,具有较好的估计性能。     

一种对MIMO 雷达正交QPSK 信号的参数估计方法

针对多输入多输出雷达所采用的正交四相编码信号,提出了基于循环自相关函数的参数估计方法。文中首先对正交四相编码信号模型的循环自相关函数和循环谱密度函数进行了推导;然后,依据推导结果,通过对循环谱密度函数最大模值位置的搜索完成了对信号载频的估计;最后,对不同延时条件下循环自相关函数在相位修正后进行累积,实现了对码速率的估计。仿真表明,文中算法在信噪比优于1 dB 后,可以较好地完成对正交四相编码信号的调制参数估计。     

一种基于多循环频率的韧性时延与多普勒频移联合估计算法

本文提出了一种基于分数低阶循环模糊函数的多循环频率时延与多普勒频移联合估计算法.该方法将分数低阶矩与循环平稳特性相结合,能够在SαS(Symmetric α Stable)脉冲噪声条件下检测信号的循环平稳特性.算法充分利用了信号的循环频率信息,具备较强的抑制干扰能力.仿真结果表明,在脉冲噪声和干扰环境中本文提出的算法均...     

一种基于循环小波累积量的谐波恢复方法

循环统计量是乘性和加性噪声中谐波恢复问题的主要分析工具之一。本文在其基础上提出了一种新的理论与方法——基于循环小波累积量的谐波恢复方法。首先,提出了循环小波累积量的定义。然后,建立了基于一阶、二阶、三阶循环小波累积量的谐波分量的频率和相位的估计方法。在此基础上,采用了一种可调参数的小波,通过调节其参数来改善传统方法中频率分辨率低的缺陷。最后给出了模拟实验结果。     

形式幂级数环中的循环码

研究了形式幂级数环与有限链环上的循环码与负循环码,利用环同构与交换图技术得到这2类环上循环码与负循环码,以及Dougherty等得到的形式幂级数环上的循环码的投影码也是循环码的结果,给出了形式幂级数环上码为循环码的一个充要条件。借助这一条件,得到了含有形式幂级数环的中国积中循环码的投影码的循环性。     

乘性噪声背景下基于三阶循环矩的二维近场源定位方法

 本文提出一种基于三阶循环矩的近场源二维参数估计方法.该方法以均匀线阵为接收传感器阵列,通过构造三个三阶循环矩矩阵估计出近场源的方位角和距离参数,利用循环统计量去除加性噪声,通过预校准法消除乘性噪声,适用于乘性噪声或乘性噪声和加性噪声共存背景下的二维近场源定位.仿真实验验证了该方法的有效性.     

多相编码信号谱相关特征检测与参数估计

基于时域和频域2种循环谱密度估计方法,研究和总结了多相编码信号的循环谱特征及其与信号参数的关系。提出了一种没有先验知识条件下多相编码信号参数提取方法。首先介绍了多相编码信号的表示形式,然后使用循环谱密度函数估计方法分析了信号的循环谱特征,在此基础上提出了基于循环谱特征的信号参数提取方法。通过对6个典型多相编码信号参数提取相对误差的计算,验证了该算法的有效性。     

基于循环谱的直扩信号到达时差估计

以循环谱理论为基础,分析了直扩信号在平稳噪声及窄带干扰情况下的循环统计特性,研究了直扩信号的到达时差估计模型和提取方法。在单一循环频率的基础上,对算法进行改进,提出了全相干循环估计器的到达时差算法。通过计算机仿真,验证了改进算法不仅对信号具有选择能力,而且较单循环估计器和传统互相关方法具有更强的抑制噪声能力。最后通过仿真得到了估计性能曲线,验证了理论的正确性。     

时间重叠的循环谱估计

首次将时间重叠法和ssinc窗应用于循环谱估计中,提出了时间重叠的循环谱估计方法,使循环谱估计取得了突破性的进展(:1)循环谱的偏离误差减小,有效频率分辨率提高,能准确地分辨出循环频率方向和谱频率轴方向的谱峰;(2)计算量大大减少。通过时间的重叠过程,减少DFT要求的数据量,提高了循环谱估计的实时性。     

Combined Selective Mapping and Binary Cyclic Codes for PAPR Reduction in OFDM Systems

In this paper, we consider reduction of PAPR in OFDM systems with BPSK subcarriers by combining SLM and binary cyclic codes. This combining strategy can be used for both error correction and PAPR reduction. We decompose a binary cyclic code into direct sum of two cyclic subcodes: the correction subcode used for error correction and the scrambling subcode for PAPR reduction. The transmitted OFDM signal is selected that achieves minimum PAPR, from the set of binary cyclic codewords. The received signal can be easily decoded without the need of any side information. Simulations show that the proposed scheme with simplex code as scrambling subcode achieves good PAPR reduction.     

OFDM系统中基于改进阈值的DFT信道估计算法

在正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统中,传统的离散傅里叶变换(Discrete Fourier Transform,DFT)信道估计算法对循环前缀之内的噪声没有得到抑制,只是抑制了循环前缀之外的噪声.以循环前缀之外的噪声点的能量值来设置阈值对于循环前缀之内噪声的滤除不是很理想,为此本文通过将循环前缀内外的样本点分别排序,分别选取其中一部分样本能量值的平均值,并乘以适当系数,以两部分和作为一种新的时域阈值来抑制噪声.仿真结果表明,本文改进的算法能很好地抑制循环前缀之内的噪声,保留了有效的信号,误码率和均方误差均比得到进一步的降低.     

Optimized Dispersion Compensation Using Orthogonal Frequency-Division Multiplexing

Orthogonal frequency-division multiplexing (OFDM) can compensate for linear distortions, such as group-velocity dispersion (GVD) and polarization-mode dispersion (PMD), provided the cyclic prefix is sufficiently long. Typically, GVD is dominant, as it requires a longer cyclic prefix. Assuming coherent detection, we show how to analytically compute the minimum number of subcarriers and cyclic prefix length required to achieve a specified power penalty, trading off power penalties from the cyclic prefix and from residual inter-symbol interference (ISI) and inter-carrier interference (ICI). We derive an analytical expression for the power penalty from residual ISI and ICI.      

脉冲噪声环境下基于分数低阶循环相关的MUSIC算法

该文以稳定分布作为噪声模型,研究了脉冲噪声环境下循环平稳信号的波达方向估计问题。针对在脉冲噪声环境中基于传统2阶循环相关的算法效果显著退化的问题,该文提出了基于分数低阶循环相关的分数低阶循环MUSIC算法(FLOCC-MUSIC)。将分数低阶循环相关与MUSIC算法相结合,可以有效抑制脉冲噪声的同频带干扰。计算机仿真表明了此算法可有效完成高斯噪声和脉冲噪声条件下的波达方向估计,其性能优于传统的基于2阶循环相关的Cyclic-MUSIC。     

On repeated-root cyclic codes

A parity-check matrix for a q-ary repeated-root cyclic code is derived using the Hasse derivative. Then the minimum distance of a q-ary repeated-root cyclic code is expressed in terms of the minimum distance of a certain simple-root cyclic code. With the help of this result, several binary repeated-root cyclic codes of lengths up to n=62 are shown to contain the largest known number of codewords for their given length and minimum distance. The relative minimum distance d_min/n of q-ary repeated-root cyclic codes of rate r⩾R is proven to tend to zero as the largest multiplicity of a root of the generator g(x) increases to infinity. It is further shown that repeated-root cycle codes cannot be asymptotically better than simple-root cyclic codes     

单通道混合信号的幅度估计算法

针对非协作通信场合中同调制参数的MSK单通道混合信号的幅度估计问题进行研究。在MSK混合信号的循环谱推导的基础上,通过搜索零频率处循环频率轴上的大强度谱线进行混合信号的幅度估计,利用循环谱算法中的泄漏谱包络辅助来消除谱线选择时存在的模糊问题,并通过大强度谱线位置的泄漏谱包络值来修正相应位置的循环谱幅度,以提高估计精度。仿真结果表明在信噪比大于?15dB时,该方法对功率差异不大的混合信号幅度具有较高的估计精度。该算法无需任何先验信息,适用于低信噪比环境,具有实用价值。     

A 2-adic approach to the analysis of cyclic codes

This paper describes how 2-adic numbers can be used to analyze the structure of binary cyclic codes and of cyclic codes defined over Z _2(a), a⩾2, the ring of integers modulo 2^a. It provides a 2-adic proof of a theorem of McEliece that characterizes the possible Hamming weights that can appear in a binary cyclic code. A generalization of this theorem is derived that applies to cyclic codes over Z_2(a) that are obtained from binary cyclic codes by a sequence of Hensel lifts. This generalization characterizes the number of times a residue modulo 2^a appears as a component of an arbitrary codeword in the cyclic code. The limit of the sequence of Hensel lifts is a universal code defined over the 2-adic integers. This code was first introduced by Calderbank and Sloane (1995), and is the main subject of this paper. Binary cyclic codes and cyclic codes over Z_2(a) are obtained from these universal codes by reduction modulo some power of 2. A special case of particular interest is cyclic codes over Z₄ that are obtained from binary cyclic codes by means of a single Hensel lift. The binary images of such codes under the Gray isometry include the Kerdock, Preparata, and Delsart-Goethals codes. These are nonlinear binary codes that contain more codewords than any linear code presently known. Fundamental understanding of the composition of codewords in cyclic codes over Z₄ is central to the search for more families of optimal codes. This paper also constructs even unimodular lattices from the Hensel lift of extended binary cyclic codes that are self-dual with all Hamming weights divisible by 4. The Leech lattice arises in this way as do extremal lattices in dimensions 32 through 48     

Multiple-bases belief-propagation decoding of high-density cyclic codes

We introduce a new method for decoding short and moderate-length linear block codes with dense paritycheck matrix representations of cyclic form. This approach is termed multiple-bases belief-propagation. The proposed iterative scheme makes use of the fact that a code has many structurally diverse parity-check matrices, capable of detecting different error patterns. We show that this inherent code property leads to decoding algorithms with significantly better performance when compared to standard belief-propagation decoding. Furthermore, we describe how to choose sets of parity-check matrices of cyclic form amenable for multiple-bases decoding, based on analytical studies performed for the binary erasure channel. For several cyclic and extended cyclic codes, the multiple-bases belief propagation decoding performance can be shown to closely follow that of the maximum-likelihood decoder.     

循环码编译码方法研究

对循环码的编译码方法及其检错和纠错能力进行了深入的分析和探讨,结合(24,16)循环码进行编码器和译码器的设计,针对所设计的(24,16)循环码进行了BSC信道下的纠错性能仿真分析。     

On the minimum distance of cyclic codes

The main result is a new lower bound for the minimum distance of cyclic codes that includes earlier bounds (i.e., BCH bound, HT bound, Roos bound). This bound is related to a second method for bounding the minimum distance of a cyclic code, which we call shifting. This method can be even stronger than the first one. For all binary cyclic codes of length< 63(with two exceptions), we show that our methods yield the true minimum distance. The two exceptions at the end of our list are a code and its even-weight subcode. We treat several examples of cyclic codes of lengthgeq 63.