双正交多码CDMA系统在衰落信道的性能分析

在直接序列扩频通信（ＤＳ／ＣＤＭＡ）系统中,为了有效地实现用户高数据率的传输,以适应宽带ＣＤＭＡ技术发展的要求,本文提出了一种双正交多码ＣＤＭＡ系统（称为ＢＭＣ－ＣＤＭＡ）。相似于多载波调制,传输的高数据泫首先进行串－并转换,然后对变换后的低数据流用双正交码进行扩频调制。不同于多载波调制,各支路扩频信号用同一载波进行调制。并对此系统在衰落信道性能进行了计算,还对数值结果进行了分析。     

多码多载波CDMA系统的性能分析

文中提出了一种新的多码多载波CDMA(MC-MC-CDMA)系统,并对此系统在频率选择性衰落信道的性能做了分析.相似于多载波调制,传输的高数据率数据首先进行串-并转换,再对变换后的低数据流用一组正交序列进行扩频调制,然后对各支路的扩频信号分别用L个正交的载波进行调制.MC-MC-CDMA系统中每个用户使用多个正交的码可以实现多数据率的传送并且在时域上进行扩时,满足下一代通信标准的要求.     

一种用于CDMA系统的正交序列调制方法

在宽带移动通信系统中，经常考虑采用通过ＦＦＴ实现的多载波调制，如ＯＦＤＭ。本文提出了一种利用ＦＨＴ实现的ＣＤＭＡ系统的正交序列调制方案。其基本思想为利用Ｗａｌｓｈ函数作为载波，将Ｗａｌｓｈ函数分组，从每组中选出一些作为载波，这样不同的载波组合方式本身将包含用户信息。这种方法实现简单，可提高传输效率，并容易与ＣＤＭＡ相结合，能有效地抑制多径干扰。仿真结果表明，该方案在多径衰落信道中能得到很好的性能。     

同步CDMA系统中一类新的扩频序列

码分多址（ＣＤＭＡ）技术已作为第三代数字移动通信及个人通信系统的无线接入技术进行广泛的研究和应用。而ＣＤＭＡ系统中扩频序列问题一直是ＣＤＭＡ技术中的关键问题。文献４给出了Ｓ－ＣＤＭＡ系统中的扩频序列实数加编码的新方法,但对构造具有纠错能力的扩序列至今尚未发现。本文给了了Ｓ－ＣＤＭＡ系统中具有纠错能力的一类新的扩频序列和它的译码算法。     

卷积编码正交序列扩频多码CDMA系统在Nakagami衰落信道的性能

本文提出了一种可以有效地实现用户数据率传输的卷积编码正交扩频多码ＣＤＭＡ系统，以适应未来移动通信业务发展的需求。     

WH-m/M相乘复合码扩频系统的互扰统计特性

本文建立了复合码ＤＳ－ＣＤＭＡ扩频系统的数学模型,推导了多址干扰的数学表示,定义了用户之间的互扰因子,并进行了计算,研究发现,在扩频比相同的上,若ＰＮ序列周期大小扩频比,且序列的伪随机性产好,则采用ＷＨ－ｍ／Ｍ复合序列与采用ｍ－Ｍ序列的扩频系统,其互扰因子均呈高斯分布,且数字特征相同,当ＰＮ序列周期等于扩频比时,互扰因子不具有高斯分布特性,该结论不要求扩频比足够大,而且对同步和异步ＤＳ－ＣＤＭＡ通     

频率分集扩展频谱码分多址系统

频率分集扩展频谱码分多址（ＦＤ／ＳＳＭＡ，ＦｒｅｑｕｅｎｃｙＤｉｖｅｒｓｉｔｙ／ＳｐｒｅａｄＳｐｅｃｔｒｕｍＭｕｌｔｉｐｌｅＡｃｃｅｓ）系统是一种新的扩频多址通信方案。它基于多载波传输理论，并与直接序列扩频多址（ＤＳ／ＳＳＭＡ）系统在时间域和频率域构...     

异步多相DS／CDMA系统模型分析

文章在文献「１」的基础上了以直接序列扩频为基础的正交多相位编码载波多相扩频ＣＤＭＡ系统模型,就扩频序列的相关性与多址干扰的关系进行了定量分析,修正了扩邓列的非周期相关函数的定义,给出了多址干扰与扩频序列的广义奇相关函数的数学关系式。文章还对文献「１」中的错误进行了分析。     

在多径衰落信道下FD/SSMA系统的性能分析

多载波频率分集扩展频谱码分多址系统（ＦＤ／ＳＳＭＡ）是一种基于多载波传输,与直接序列扩展频谱码分多址系统（ＤＳ／ＳＳＭＡ）存在时间－频率对偶关系的扩频多址通信方案。在多径传输信道下,基于ＦＤ／ＳＳＭＡ信号的锐自相关和低互相关特性,本文提出ＦＤ／ＳＳＭＡ系统可以采用路径分集接收的方案。分析和模拟计算表明,在多径衰落信道下,采用路径分集方案时ＦＤ／ＳＳＭＡ系统的性能将得到明显的改善。     

市区多径衰落信道中的TCM DS／SSMA系统性能分析

本文将网络编码调制（ＴＣＭ）应用于市区多径衰落信道下的直接序列扩频多址（ＤＳ／ＳＳＭＡ）系统中，应用ＤＳ条件下市区多径衰落信道的等效模型，提出了一种采用理论分析和数值模拟相结合分析ＴＣＭＤＳ／ＳＳＭＡ系统在该信道下性能的新方法，并将传统的Ｕｎｇｅｒｂｏｅｃｋ型ＴＣＭ才本文所构成的若干种低码率ＴＣＭＤＳ／ＳＳＭＡ系统的性能进行了比较。     

一种基于快跳频技术的多载波CDMA系统

为进一步提高多载波CDMA系统的频带效率与抗干扰能力,提出了一种跳频多址技术结合多载波调制的传输方案,利用跳频技术将部分子载波传输与随机交织引入到多载波传输系统中,给出了系统实现的模型,并对该传输方案的系统带宽和误码性能进行了分析。理论分析与仿真结果表明：与以往的多载波CDMA系统相比,所建议系统的结构简单,性能优异,消除了已有系统中峰均功率比高和远近效应等问题,具有较强的抗多址干扰与窄带干扰的能力,并能有效地抗信道中突发错误的能力。     

Performance analysis of Doppler shift effects on OFDM‐based and MC‐CDMA‐based cognitive radios

The present development of high data rate wireless applications has led to extra bandwidth demands. However, finding a new spectrum bandwidth to accommodate these applications and services is a challenging task because of the scarcity of spectrum resources. In fact, the spectrum is utilized inefficiently for conventional spectrum allocation, so Federal Communications Commission has proposed dynamic spectrum access mechanism in cognitive radio, where unlicensed users can opportunistically borrow unused licensed spectrum, which is a challenge to obtain contiguous frequency spectrum block. This also has a significant impact on multicarrier transmission systems such as orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC‐CDMA). As a solution, this paper develops non‐contiguous OFDM (NC‐OFDM) and non‐contiguous MC‐CDMA (NC‐MC‐CDMA) cognitive system. The implementation of NC‐OFDM and NC‐MC‐CDMA systems provides high data rate via a large number of non‐contiguous subcarriers without interfering with the existing transmissions. The system performance evaluates NC‐OFDM and NC‐MC‐CDMA for mobile scenario where each propagation path will experience Doppler frequency shift because of the relative motion between the transmitter and receiver. The simulation results of this paper proved that NC‐OFDM system is a superior candidate than NC‐MC‐CDMA system considering the mobility for cognitive users. Copyright © 2013 John Wiley & Sons, Ltd.     

基于正交互补码的CMDA系统仿真

给出一种用于未来移动通信的CDMA系统,即基于正交全补码的多载波CDMA系统,其中的核心技术是使用正交全补码编码,叙述了CDMA系统结构和多载波技术,介绍了正交全补码编码原理,分析了正交全补码的多载波系统编码领域的最新CDMA系统特点,计算机仿真误码率结果表明：提出的基于正交全补码的CDMA比传统的CDMA具有更好的性能。     

Ricean衰落信道下一种正交多载波CDMA系统的性能

本文提出了一种新的多载波码分多址(MC-CDMA)系统.与传统系统相比,其主要区别是采用多个并行MC-CDMA分支,每一个分支用一组正交子载波进行调制.在每个分支上,使用相同扩频序列的不同码片调制子载波.这种系统能更有效地利用传输带宽,实现频率分集.由于该系统降低了每个子载波上的数据速率,扩频序列更容易同步.最后给出了系统在Ricean衰落信道下的性能分析.     

基于特征扩频的卫星转发器频谱资源聚合研究

针对CDMA卫星通信系统受到严重外部干扰,且可连续使用的频谱受限问题,提出3种基于特征扩频的卫星转发器频谱聚合方案,实现多个转发器频谱高效聚合的同时对抗系统受到的外部干扰。通过仿真表明,所提方案能够克服基于现有认知多载波CDMA方法进行卫星转发器频谱聚合的设计复杂度较高、频谱聚合效率低的缺点,并且所提整体特征扩频方案在性能和支持用户数方面均优于另外2种多载波特征扩频方案,提高了系统对多个转发器的非连续频谱利用率,进而提升系统容量。     

Application of Rate Compatible Punctured Turbo Coded Hybrid ARQ to MC‐CDMA Mobile Radio

MC‐CDMA, a multicarrier (MC) modulation scheme based on code division multiple access (CDMA), is the most likely candidate for the next generation of mobile radio communications. The rate compatible punctured turbo (RCPT) coded hybrid automatic repeat request (HARQ) has been found to give improved throughput performance in a direct sequence (DS) CDMA system. However, the extent to which the RCPT HARQ improves the throughput performance of an MC‐CDMA system has not been fully understood. In this paper, we apply the RCPT HARQ to MC‐CDMA and evaluate by computer simulations its performance in a frequency selective Rayleigh fading channel. We found that the performance of RCPT HARQ MC‐CDMA is almost insensitive to channel characteristics. The performance can be drastically improved with receive diversity combined with space‐time transmit diversity. In addition, the comparison of RCPT HARQ MC‐CDMA, orthogonal frequency division multiplexing, and DS‐CDMA shows that under similar conditions the throughput of MC‐CDMA is the best in a frequency selective fading channel.     

Multicarrier CDMA for future generation mobile communication

Future generations of wireless communication systems will be designed with the aim of making the best possible use of the limited radio spectrum in order to further increase throughput as well as user-capacity. In this paper, the application of multicarrier CDMA (code division multiple access) within mobile communication systems is discussed. An overview of the main types of multicarrier spread-spectrum systems is given. The multicarrier CDMA system is described in detail, including its relationship with OFDM (orthogonal frequency division multiplexing), its general performance in comparison with direct sequence CDMA and some specific implementation problems. The paper also presents some results comparing the performance of a selection of algorithms that can be used to isolate the individual signal of each user. Potential capacity increases achievable with adaptive loading in time and frequency slots is briefly demonstrated. By allocating users multiple codes, very high data rates can be achieved, and the paper gives a comparison of multicode, multicarrier CDMA with OFDM-based wireless LAN systems     

Residue number system-based multicarrier CDMA system for high-speedbroadband wireless access

This correspondence is concerned with a new method to enhance the bandwidth efficiency of a multicarrier CDMA system by using a residue number based representation for information symbols. The residues are mapped into a set of orthogonal sequences and are transmitted in parallel. A new modulation scheme is proposed to increase the data rate further by combining residue number representation, PSK/QAM modulation, orthogonal spreading and multicarrier modulation. The performance of the proposed system is evaluated in a frequency selective Rayleigh fading channel via extensive simulations. The present correspondence discusses the design issues associated with the system together with the performance results