应用空时编码的正交多载波直接序列扩频CDMA系统

本文把空时编码(STC)技术应用于正交多载波直接序列扩频CDMA(MC—DS—CDMA)系统，给出了空时编码MC—DS—CDMA系统的发射机和接收机方案。计算机仿真给出了应用空时编码的MC—DS—CDMA系统性能，和普通MC—DS—CDMA以及应用空时编码的多载波CDMA(MC—CDMA)系统的性能比较也由计算机仿真给出。     

汉明码在多载波CDMA系统中的应用

本文讨论了GMC-CDMA技术。GMC-CDMA提供了全数字、统一的结构，包含了单载波和多载波CDMA系统。然后，本文用信道编码对GMC-CDMA技术改进，采用在GMC-CDMA系统前先进行蝙码采确保低误码率。仿真结果会表明：经过编码后的系统能取得更低的误码率。图像在编码的GMC-CDMA和未编码的GMC—CDMA两个系统中的不同传输效果进一步验证了这一结论。     

基于不同载波干涉编码OFDM性能分析

在载波干涉编码正交频分复用（CI/OFDM）系统中采用了几种CDMA扩频序列作为载波干涉码。并比较了用不同载波干涉编码的正交频分复用（OFDM）系统性能。从理论分析和Matlab实验仿真得出CI/OFDM系统的比特误码率（BER）随着子载波数目增加而变低,BER与采用不同的载波干涉（CI）编码无关。并证明CI/OFDM系统的峰均比（PAPR）主要取决于子载波数的大小以及CI码的性质。     

一种天线分集的多载波CDMA上行链路方案

多载波系统能克服多径信道频率选择性的影响，而应用多天线发射和接收能获得分集增益。本文提出了一种两天线发、多天线收的多载波CDMA上行链路系统方案。在发射端，空时块码被用来进行发射分集。对于多载波CDMA上行链路系统，不同的用户的信号经历了不同的多径衰落，信号间的正交性不再能够保持。本文提出了一种接收机方案，并讨论了几种联合检测方法来恢复所有用户在两个编码时刻发送的信息符号，并给出计算机仿真结果。     

低峰值平均功率比的多载波CDMA

多载波CDMA技术是CDMA和正交频分复用(OFDM)技术的综合,具有抗干扰能力强、频谱效率高、数据传输速率高等优点,在未来个人通信业务(PCS)和第三代移动通信中具有良好的发展前景。但是,多载波CDMA信号峰平比比较高,影响到功放的功率效率,这已成为目前多载波CDMA系统实用化的一大障碍。本文利用格雷互补序列的特性有效降低多载波CDMA信号的峰平比,对于任意载波数的多载波CDMA信号,其峰平比上限为6dB。     

基于优化多带复小波的多载波CDMA及反向链路性能

在分析多载波码分多址的原理基础上,利用优化生成的多带复小波,提出了一种基于优化多带复小波的多载波CDMA系统反向链路模型,并采用基于多天线的空间分集合并(SDC)技术进一步完善所提系统.该系统可利用优化多带复小波的优良特性来避免通常多载波CDMA由于插入循环前缀所带来的频谱效率的下降,在此基础上我们研究了所提系统采用空间分集合并技术时在瑞利衰落信道下的反向链路性能;给出相应的误比特率分析.理论分析和仿真结果表明采用基于最大比合并的SDC技术可显著提高所提系统抗空间衰落和各种干扰的能力,而且基于SDC技术的所提系统要好于同样基于SDC技术的通常多载波CDMA系统和基于实小波包的多载波CDMA系统.     

多载波CDMA技术简介

CDMA技术能提供高容量、软切换,可望用于多媒体业务,但其性能受到多址干扰和符号间干扰的影响;正交频分复用对频率选择性衰落不敏感,可以用于无线环境中高速数据的传送,综合两者的优点,所形成的多载波CDMA具有很强的竞争力,可望用于第三代移动通信系统。本文介绍了三种多载波CDMA技术,即MC-CDMA、多载波DS-CDMA和多音CDMA,并简单介绍了它们的发射和接收技术。     

广义正交传输系统及其高效实现方法

基于子带变换理论构建的广义正交传输复用模型，不仅适用于TDMA、FDMA和CDMA多用户系统，也适用于像OFDM之类的多载波（MC）系统以及由OFDM与CDMA综合而成的MC-CDMA系统。该模型在结构上等效于均匀DFT滤波器组，可以采用FFT结合多相滤波器组的方式高效实现。本文实现的多载波系统具有子载波间隔可伸缩性特点，而复杂性与OFDM加窗处理相接近。在相同的仿真环境下得到的结果表明：基于软脉冲响应的多载波系统（MCSIS）误码率性能优于OFDM；对于相同衰落信道，MC-CDMA系统抗衰落特性明显优于OFDM。     

多载波CDMA系统中的频域线性相位内插算法

多载波CDMA系统结合了正交频分复用（OFDM）技术和CDMA技术的优点,自1993年提出以来就受到广泛的重视。本文主要讨论了载波频偏对连续OFDM符号的影响,提出了一种新的频域线性相位内插算法来估计信道响应,以对抗载波频偏对连续OFDM符号引起的相位旋转。理论分析和仿真试验都证明我们提出的算法能有效减少载波频偏对系统性能的影响。这种新算法适用于使用导频信号块状分布的多载波CDMA系统或OFDM系统。     

多带正交频分复用系统抗窄带干扰技术

针对超宽带通信系统存在严重窄带干扰问题,基于传统的超宽带通信系统的解决方案,研究了一种基于窄带抑制正交频分复用的新的超宽带系统。新的系统充分利用一个子带内所有子载波的频率分集性,将子载波的编码数据流扩展到相应子带的所有子载波上,增强了多带正交频分复用系统的抗干扰能力。理论分析和仿真结果均表明,这种方法能进一步提高系统的抗干扰能力。     

Cyclic shifted orthogonal complementary codes for multicarrier CDMA systems

In this letter, we present a set of cyclic shifted orthogonal complementary (cyclic-OC) codes for multicarrier CDMA systems. The conventional OC codes are not adequate for the system because they are able to support only the limited number of users. By applying the proposed cyclic-OC codes for the inter-symbol interference (ISI)-free multicarrier systems, the number of users can be extended to the size of code length. We validate the effectiveness of the proposed scheme through simulations.     

Asynchronous multicarrier DS-CDMA using mutually orthogonalcomplementary sets of sequences

The use of sets of multiple spreading sequences per user in multicarrier code-division multiple-access (CDMA) is investigated. Each user is assumed to have a distinct set of spreading sequences, with a different spreading sequence for each carrier in each user's set. We show that when these sets of sequences are chosen to be the mutually orthogonal (MO) complementary sets of sequences, multiple-access interference is minimal on a nonfading channel. As a result of the autocorrelation sidelobe cancellation properties of the MO complementary sequences, it is possible to pack symbols more closely together on the nonfading channel, resulting in a higher data rate than in multicarrier CDMA using the same spreading sequence for each carrier. The resulting communication system scheme results in an easily parallelized receiver architecture that may be useful in nonfading coherent channels, such as the optical fiber channel or the Rician channel with a strong line-of-sight component. On the Rayleigh fading channel, the performance of the system is identical to that of multicarrier CDMA employing a single spreading sequence per user, with only a minimal increase in receiver complexity     

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     

正交序列扩频多码CDMA系统在AWGN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，本文提出了一种正交扩频多码ＣＤＭＡ系统（称为ＯＭＣ－ＣＤＭＡ）。相似于多载波调制，传输的高数据率首先进行串－并转换，然后对转换后的低数据流用正交序列进行扩频调制。不同于多载波调制，各支路扩频信号用同一载波进行调制。这里，我们对此系统在ＡＷＧＮ信道的性能进行了计算，并对数值结果进行了分析。     

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。     

Overview of multicarrier CDMA

The authors present an overview of new multiple access schemes based on a combination of code division and multicarrier techniques, such as multicarrier code-division multiple access (MC-CDMA), multicarrier direct sequence CDMA (multicarrier DS-CDMA), and multitone CDMA (MT-CDMA)     

Spectral overlay of multicarrier CDMA on existing CDMA mobilesystems

A spectral overlay of a narrow-band code division multiple access (CDMA) system and a wide-band multicarrier CDMA system is considered as a means for existing CDMA mobile networks to evolve into a future CDMA network. The achievable joint capacity of the overlaid system is provided and compared with that of another network evolution strategy of spectrally overlaying wide-band single-carrier CDMA to the existing CDMA systems     

Performance of a Modified Multicarrier Direct Sequence CDMA System

In this paper, we present an improved multicarrier direct sequence (DS) code division multiple access (CDMA) scheme by modifying the system originally proposed by Kondo and Milstein [13]. In this modified system, different spreading sequences multiplied by a data sequence modulate different carriers. This is to prevent the multiple access capability from reducing when the fading characteristics of different carrier frequencies are highly correlated. We have derived a formula which determines the mean values of the relative received signal strength in a single carrier DS CDMA rake system and in a multicarrier DS-CDMA system. We present results on the comparison of the bit error rate (BER) performance of the two systems including the effect of correlation between fading characteristics of different frequencies under various multipath fading conditions. The results indicate that with 50 users the modified multicarrier DS CDMA system can achieve an uncoded irreducible BER of 1.7 × 10^??3 with an average received signal-to-noise ratio per bit of 10 dB, which is better than 3.0 × 10^??3 achieved by the single carrier DS CDMA rake system, and also show that if multicarrier CDMA system is used with respect to single carrier CDMA system, the SNR gain is up to 4.5 dB for the uncode BER of 10^??3 being achieved.     

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.     

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.