CDMA2000中信号交织器的设计与仿真

为了提高低信噪比情况下系统的纠错能力,Turbo码作为通信传输系统中的一种新兴的信道纠错编码技术,逐渐成为了信息编码界的研究热点。交织器是Turbo码编、译码器的重要组成部件。本设计对CDMA2000中的Turbo交织器进行了介绍,设计了交织器模块,并通过MATLAB进一步对交织器的应用进行了仿真。     

全光CDMA编译码器

主要介绍了几种全光CDMA编译码器，即质数编译码器、梯形网络编译码器和光谱编译码器。着重讨论了它们的原理、特性和应用前景。     

数字集成电路讲座(8) 第五讲 编译码器

<正> 在数字电路系统中,编译码器的功能是将一种数码变换成另一种数码。编译码器的输出状态是其输入变量各种组合的结果。编译码器的输出既可操作或控制系统其它部分,也可驱动显示器,实现数字、符号的显示。 编译码器通常是一种组合电路,其工作状态的改变无需依赖时序脉冲。这里介绍的译码器分为数码译码器和显示译     

Logistic数字混沌序列性能分析

混沌作为一种非线性动态系统中的现象,受到了人们的重视,研究工作者纷纷探索他在通信中的可能应用。讨论了一种广泛研究的离散时间动态系统Logistic Map所产生的数字混沌序列,通过与m序列比较,分析了其白噪声统计特性,并用计算机进行仿真,做了相应的实验数据分析。结果表明数字混沌序列具有较理想的自相关和互相关特性,且数目极大,是CDMA系统中扩频码的优选码型。     

光通信系统中LDPC码的构造及其编译码算法分析

针对低密度奇偶校验（LDPC）码的相关理论和LDPC码自身特性以及光通信系统具有低噪声、高信噪比的传输特点进行分析后,提出了光通信系统中LDPC码型的构造方法,这为光通信系统中LDPC码型的构造和仿真分析奠定了基础。并对光通信系统中LDPC码的编译码算法进行了深入分析与研究,得到一些有利于降低其编译码算法复杂度的重要结论,这有助于降低其编译码器的设计与实现复杂度。     

一种基于混沌序列相关同步的DS-CDMA通信系统

本文介绍了一种基于混沌序列相关同步的DS－CDMA通信系统，其核心就是经混沌序列作为地址码，利用混沌序列优越的相关特性进行相关解调。文中推导出了多用户相关解调的表达式，表明在系统同步的前提下，系统性能取决于混沌序列的相关性。文中还讲述了系统构成方法以及相关同步检测和相关解调的原理，最后给出的计算机仿真结果证明了上述原理的正确性。     

DS─CDMA系统容量的分析

CDMA技术的开发应用是为了增加系统的通信容量。而CDMA系统的系统容量与系统的信噪比密切相关。本文主要根据信息理论对DS－CDMA系统的容量作了简要分析，得到了系统总容量的边界．并说明了系统信噪比与容量的关系。     

140Mb/s 64QAM系统中能纠一位Lee错误的纠错编、译码器的实现

随着近年中容量数字微波系统的发展,在近期我国基本上可以掌握64QAM数字微波系统的生产技术,而纠错编、译码器是数字微波系统中很重要的一部分。本文介绍的64QAM数字微波四次群的纠错编、译码器采用SLCE(81/84)码,由于该码具有透明性和低冗余度,因此实现起来具有明显的优点。     

第三代CDMA的扩频技术和差错控制技术

该文介绍了第三代CDMA的扩频技术和差错控制技术,分析了复QPSK扩频技术和Turbo编译码器构成的差错控制技术。这些技术将显著提高第三代CDMA的性能。     

MC—CDMA系统中的信道编码技术

将正交频分复用（OFDM）与码分多址（CDMA）相结合,构成MC-CDMA系统。在简单讲述卷积码和Turbo码的编译码器结构的基础上,将这两种编码方案应用于MC-CDMA系统的下行链路中,并进行了计算机模拟。     

多用户相干CSK数字通信系统的误码性能分析

基于离散混沌信号,提出一种在AWGN环境中双基函数相干CSK系统多用户噪声性能的分析方法。用Logistic映射作为混沌发生器,导出了用信噪比、用户数及比特序列长度表示的误码率(BER)表达式,理论计算与仿真结果相符。单用户情况下的BER和已提出的噪声性能上界是笔者所得结果的特例。     

FM解调的性能分析与测试方法

在无线通信中,调频调制（FM）方式因其抗噪性能好、实现简单被广泛应用。分析了FM解调的信噪比性能,给出了一种FM解调信噪比的测试方法。     

Application and standardization of turbo codes in third-generationhigh-speed wireless data services

This paper addresses the application of turbo codes for third-generation wireless services. It describes the specific characteristics of high-rate data applications in third-generation wide-band code-division multiple-access (CDMA) systems that make turbo codes superior to convolutional codes. In particular, it shows the positive effect of fast power control employed in these systems on the relative performance of turbo codes with respect to convolutional codes. It also shows how turbo and convolutional codes behave differently when the figure of merit is changed to frame error rate from bit error rate for high-speed data services. Furthermore, it describes in detail how and why the standardized turbo code has been selected in the presence of other candidates, which were also based on iterative decoding. Details of turbo interleaving and trellis termination as specified in the standards are explained. Performance of turbo codes under wide-band CDMA operating conditions are presented. The suitability of turbo codes for low-rate data applications is discussed. Finally it is shown that the performance loss as a result of internal decoder parameter quantization is negligible     

Iterative multiuser interference reduction: turbo CDMA

We view the asynchronous random code division multiple-access (CDMA) channel as a time-varying convolutional code. We study the case where the users encode their data, and, therefore, the single user transmitters and the CDMA channel appear as the concatenation of two coding systems. At the receiver we employ serial turbo decoding strategies. Unlike conventional turbo codes where both the inner and outer code may be selected, in our case, the inner code is due to the CDMA channel which we assume to be random. Nevertheless, the decoding system resembles the decoder of a serial turbo code and single-user performance is obtained even for numbers of users approaching the spreading code length     

Generator of optical chaotic sequences

Because of their good properties of correlation and security, chaotic sequences have aroused considerable interest in radio CDMA systems. How to generate chaotic sequences and apply them to optical CDMA systems is an interesting and new research topic. A chaotic sequence generator has been designed using Mach-Zehnder interferometers the arm lengths of which are some special values. This generator can generate analogue chaotic sequences which satisfy the Chebyshev map. It can also be used as an encoder of optical CDMA systems to enhance security.     

A Two-Stage Capacity-Achieving Demodulation/Decoding Method for Random Matrix Channels

Iterative processing for linear matrix channels, aka turbo equalization, turbo demodulation, or turbo code-division multiple access (CDMA), has traditionally been addressed as the concatenation of conventional error control codes with the linear (matrix) channel. However, in several situations, such as CDMA, multiple-input–multiple-output (MIMO) channels, orthogonal frequency-division multiplexing (OFDM), and intersymbol–interference (ISI) channels, the channel itself either contains inherent signal redundancy or such redundancy can readily be introduced at the transmitter. For such systems, iterative demodulation of the linear channel exploiting this redundancy using simple iterative cancellation demodulators, followed by conventional feedforward error control decoding, provides a low-complexity, but extremely efficient decoding alternative. This two-stage demodulator/decoder outperforms more complex turbo CDMA methods for equal power modes (users). Furthermore, it is shown that arbitrary numbers of modes can be supported if an unequal power distribution is adopted. These power distributions are nested, which means that additional modes can be added without disturbing an existing mode population. The main result shows that these nested power distributions enable the two-stage receiver to approach the Shannon capacity of the channel to within less than one bit for any signal-to-noise ratio (SNR).      

A Novel Detection Algorithm Efficient for Turbo Coded CDMA Signals in Detect and Forward Cooperative Channels

In this paper, a new detection algorithm is proposed for turbo coded Code Division Multiple Access (CDMA) signals in detect and forward cooperative channels. Use of user cooperation makes much improvement in the performance of CDMA systems. Due to the special structure of CDMA systems, cooperative schemes increase the sum and cutoff capacities of CDMA based wireless systems and improve the quality of user-partner link which enhances the overall performance of the system. In this paper, a new combining scheme is proposed that makes the receiver more robust against the decision errors in the partner link. This structure is simulated for punctured 1/2 rate 4 states turbo code in a channel with first order Markov time variation and different Rice factor variances. Through various simulations, it is shown when the channel estimates are available in the partner and receiver, the cooperation between users provides much diversity gain especially while using the new proposed combining algorithm.     

Very Low-Complexity Hardware Interleaver for Turbo Decoding

This brief presents a very low complexity hardware interleaver implementation for turbo code in wideband CDMA (W-CDMA) systems. Algorithmic transformations are extensively exploited to reduce the computation complexity and latency. Novel VLSI architectures are developed. The hardware implementation results show that an entire turbo interleave pattern generation unit consumes only 4 k gates, which is an order of magnitude smaller than conventional designs.     

Performance of a turbo coded multicarrier DS/CDMA system withnonuniform repetition coding

This paper presents a turbo coded multicarrier direct sequence code division multiple access (DS/CDMA) system, where the outputs of a turbo encoder are repetition coded at multiple rates and transmitted in parallel over a number of subchannels. A performance bound useful in the so-called error floor region is obtained for Rayleigh fading channels when different diversity orders are given to each turbo code symbol. Simulation results are also provided for the low signal-to-noise ratio (SNR) region where the bound is not applicable. It is observed that the error floor can be lowered, with some performance loss in the low SNR region, by applying nonuniform repetition coding to the turbo code symbols     

Turbo multiuser detection with unknown interferers

We consider the problem of turbo multiuser detection for synchronous and asynchronous code-division multiple-access (CDMA) in the presence of unknown users. Turbo multiuser detectors, as previously developed, typically require knowledge of the signature waveforms of all of the users in the system and ignore users whose signature sequences are unknown, e.g., users outside the cell. We develop turbo multiuser detection for CDMA uplink systems and other environments in which the receiver has knowledge of the signature waveforms of only K˘⩽ K users. Subspace techniques are used to estimate the interference from the unknown-users and the interference estimate is subtracted from the received signal. We see that the new receiver significantly outperforms the conventional turbo multiuser receiver for moderate and high signal-to-noise ratios. It is also seen that the traditional turbo receiver provides little gain through iteration when unknown users are present