结合RS纠错编码和Walsh变换的软扩频技术

为了解决实际工程中信号被干扰的问题,增强纠检错能力,并提高保密性,提出了一种结合了RS纠错编码和Walsh变换的软扩频技术.通过对RS纠错编码产生和利用Walsh函数与复合码技术的Walsh变换方法的研究,以及和一般直扩频的比较,利用Matlab仿真阐述了软扩频技术的优势,并介绍了这种软扩频技术在实际工程中的应用.     

cdma2000系统中Walsh码的优化分配算法

Walsh码是码分多址系统中一种重要的正交扩频码。随着 3G系统的发展 ,高速率数据业务的引入 ,对有限Walsh码资源的需求日益增加 ,因此合理的管理和分配成为必然。本文以cdma2 0 0 0系统中Walsh码的使用为例 ,分析了Walsh码的工作原理和使用现状 ,提出了一种动态分配的优化算法。     

基于编码法降低MC-CDMA系统峰均比技术研究

分析了多载波码分多址（MC-CDMA）系统模型及扩频码序列性能,根据MC-CDMA系统特点,研究了采用GOLAY码、Gold码及Walsh码等不同扩频序列及不同序列长度对MC-CDMA系统峰均比的影响。仿真分析了序列长度为16、32及64位时MC-CDMA系统峰均比性能。     

LS码与、Walsh码的上行链路容量比较

该文首先分析了多径衰落信道下CDMA系统上行链路信道容量,文章对单用户接收机、多用户接收机两种情况下的信道容量分别作了讨论.对LS码和Walsh码的上行链路容量进行了比较.通过仿真可以看出在多用户检测条件下,两种扩频码提供的容量相差不大,而在单用户检测条件下,LS码则要大大优于Walsh码。     

m序列在双正交码扩频系统中的应用

m序列具有优良的伪随机特性,被广泛应用于双正交码扩频系统。文章介绍了扩频码字为m序列的双正交 码扩频调制原理、解扩译码算法,并基于m序列与Walsh序列的位置换关系,提出了一种通过快速Hadamard变换(FHT)实现m 序列相关分析的方法。     

JTIDS系统的低复杂度多进制扩频检测方法

传统多进制扩频调制使用多个相关器进行检测,每个相关器产生一个相关值,实现复杂.提出了一种使用FIR滤波器的基于扩频码段分路和延时相加的实用多进制扩频检测方法,通过FIR滤波即可产生所有相关值,实现结构简单,特别适合在使用周期移位伪随机序列的联合战术信息分发系统(JTIDS)中应用,可有效降低JTIDS系统中多进制扩频信号的检测复杂度和工程实现难度.仿真比较了优选扩频序列和Walsh正交码集的误比特率性能,获得了良好的性能结果.     

CDMA通信编码研究

扩频序列设计和选择是码分多址(CDMA)数字蜂窝移动通信的关键技术之一。扩频码序列的设计就是构造不同结构的具有良好特性的伪随机序列来满足CDMA系统的要求。目前研究最深入的和使用最多的是m序列和Gold序列及Walsh序列。文中从理论上和工程实用角度对扩频序列(m序列、Gold序列及Walsh序列等)的性能和特点进行了分析,同时给出了m序列、Gold序列及Walsh序列等的形成方法。     

多进制正交扩频系统的灵巧干扰

短波第三代自动链路建立(3G-ALE)系统中的突发波形采用多进制正交扩频调制,所使用的扩频码为Walsh码。经扩频处理的信号频谱被展宽,但能量在频谱上的分布仍相对集中于部分特定的频点。系统通过对扩频信号叠加扰码的方法将信号能量分散在整个信号带宽内。针对3G-ALE系统的这一特点,提出了解扩相关器输出干扰分量最大化的干扰准则,设计了基于扰码同步的灵巧干扰信号。仿真结果表明,灵巧干扰与常规干扰相比有更为卓越的干扰性能。     

一种基于RS码序列的软扩频系统及其Simulink仿真

介绍软扩频系统和里德-索罗门编码的基本原理，提出一种基于里德-索罗门码序列的软扩频系统，并且用Simulink仿真工具对该系统进行了建模。为了验证系统的抗干扰性能，对其进行了仿真分析，给出了这种软扩频系统和一般直扩频系统在单频干扰和宽带干扰下的误码率，仿真结果表明：这种基于里德．索罗门码序列的软扩频系统对单频信号干扰和宽带干扰有很好的抑制效果。     

扩频码PSO优化分配降低MC-CDMA信号峰均比

高峰均比(PAPR)是多载波码分多址(MC CDMA)技术应用中亟待解决的关键问题。对于采用Walsh Hadamard(WH)扩频码的系统来说,优化用户扩频码的分配方案可降低系统的PAPR,但最优扩频码分配方法运算复杂度太高。为此,采用具有优良迭代寻优能力的粒子群优化算法(PSO)来降低算法的复杂度。改进算法将最优分配方案的高维搜索问题转化为粒子群迭代寻优过程。分析比较和仿真结果表明,与最优算法相比,改进算法在降低PAPR性能方面有0.5～1.5 dB的性能损失,而复杂度远小于最优算法,是一种简单实用的峰均比降低方法。     

BER Performance of Walsh–Hadamard Like Kronecker Product Codes in a DS-CDMA and Cognitive Underlay System

Walsh–Hadamard transform, a discrete unitary transform is widely used in many applications such as signature codes in the current wireless standards IS-95 CDMA, WCDMA, CDMA2000 and image transform applications. It is simple to implement this transform since they can be generated by a single Kronecker product recursion formula. In this paper, a new set of binary code families similar to Walsh codes are obtained based on the concept of code concatenation and permutation. It is shown that these codes can be generated by reconfiguring the Walsh–Hadamard code generator. Hence it can be utilized in reconfigurable radios such as underlay cognitive radio (UCR). Theoretical results showing the BER performance due to MAI between primary users and secondary users in an UCR is also obtained. Simulation results showing the BER performance of these codes in a direct sequence spread spectrum system and UCR system with quadrature multiplexing operating in the individual decoding mode under AWGN plus flat fading Rayleigh channel conditions is also obtained.     

LS码在水声扩频中的应用及估计

水声多径干扰限制了水声直接扩频通信系统的进一步应用,选取性能更好的扩频序列可以提高水声扩频系统的抗干扰性能。在讨论了LS码特性的基础上,提出了将LS码应用于水声直接扩频通信中,并分析了LS码应用的优势。通过多径瑞利水声信道模型仿真,验证了LS码水声扩频通信的良好性能。利用了二次谱和奇异值分解的方法对LS码水声直扩信号的扩频序列进行了估计。仿真结果表明,该方法在信噪比为-11dB时还能准确的估计出LS码。     

纠错码在M元扩频通信系统中的应用

研究了一种将M元扩频和纠错码相结合的通信方案。由于采用了M元扩频,在带限信道中获得了较高的数据传输速率;同时采用纠错编码,增强了系统的可靠性。两者的结合,较好地解决了通信系统有效性与可靠性两大问题。仿真结果表明该系统具有很好的性能。     

并元序列研究

对并元码偶作出进一步研究,首先提出了一类新的区组设计——并元加集偶的概念,研究了并元加集偶的一些特性。然后给出了并元加集偶与并元码偶的等价关系,应用这一等价关系给出了并元码偶存在的必要条件,也为并元加集偶的构造提供了理论依据。最后还研究了并元码偶的Walsh谱特性和重量分布特性。通过这些问题的研究,展示了Walsh变换新的应用。这些存在条件在这类码的理论研究和计算机搜索中有重要的作用。     

BER Performance of Walsh Hadamard Like Codes Based on Complementary Sequence Sets in a CDMA and Cognitive Underlay System

In this paper, a method of constructing a sequence set similar to Walsh Hadamard (WH) codes is described. In general, two complementary sequence set of length 2 is used as a basic kernel to construct WH codes. In this work, four complementary sequence set of length 3 is used as a basic kernel. The proposed code set have a nearly non linear phase sequences with a more evenly spread frequency spectrum when compared with WH codes. It is shown that the proposed spreading codes perform comparable to WH in a Direct Sequence code division multiple access (DS-CDMA) system in an Additive White Gaussian Noise and Rayleigh channel at a reduced code length. In this work, bit error rate performance of the Underlay Cognitive Radio system implemented using DS-CDMA system is simulated. Primary and Secondary Users are distinguished by assigning spreading codes from different families and it is assumed that the channel information is known by both the Primary and Secondary User receivers. This new code set offers good performance in a Cognitive Radio Underlay system.     

多进制正交扩频加卷积编码体制性能分析

介绍了多进制正交扩频加卷积编码体制的发射端和接收端的原理,给出了多进制正交扩频系统的理论误比特率性能,针对接收端需要对多路匹配滤波器输出信号进行最大值判决,以利于后级的信道译码,从对数似然比(LLR)出发,提出了一种适用于多进制正交扩频系统的次最优的软信息提取方法。对在AWGN信道中多进制正交扩频系统性能进行了MATLAB仿真。结果表明,多进制正交扩频加卷积编码体制不但能有效地解决带宽与处理增益之间的矛盾,还可以获得比直扩系统加卷积编码更高的增益。     

OCDD/CDMA: a new DS/CDMA with orthonormal code diversity detection

The paper presents a new spread spectrum communication system called orthonormal code diversity detection (OCDD)/CDMA system based on the novel concept of orthonormal-basis diversity which is a generalization of the existing spread spectrum diversity concepts such as path diversity and frequency diversity. The OCDD/CDMA system is similar to the conventional DS/CDMA system in the transmitter structure, but is different in the receiver structure as it employs the extended orthonormal basis-function set which is the union of the Walsh basis-functions multiplied by the PN sequences and, optionally, their delayed replicas. The received signal is matched to the extended basis functions, and the matched signal components are combined together after individual channel compensation. The proposed OCDD/CDMA system exhibits the bit error performance which is much improved over the conventional DS/CDMA system using maximal ratio combing. In addition, it is robust to the chip timing error, which becomes more crucial in the future DS/CDMA systems having a higher data rate and smaller chip interval. From the simulation results, we confirm that the OCDD/CDMA system is a unique spread spectrum communication technique that can effectively increase the diversity utilization in the slowly fading channel, overcoming the inherent problems in the DS/CDMA and OFDM/CDMA systems