多载波CDMA

本文中描述了三种多载波ＣＤＭＡ的基本原理和发射机结构,同时给出了三种多载波ＣＤＭＡ的性能比较。     

多载波CDMA及其技术简介

多载波CDMA具有更高的灵活性 ,更高的频谱效率 ,简单的检测技术 ,窄带干扰抑制能力等一系列优点 ,引起了研究者的广泛兴趣。文中介绍了三种多载波CDMA技术 ,即MC CDMA (多载波CDMA) ,多载波DS CD MA (直接序列CDMA)和多音CDMA并简单介绍了它们的发射和接收技术。最后还指出多载波CDMA技术所固有的缺陷。     

适用于下一代移动通信系统的多载波CDMA

峰均功率比过高一直是影响MC-CD-MA应用的一个重要因素,这已成为MC-CDMA技术实用化的最大障碍.从选择扩频码和选择映射两个不同的角度对降低峰均功率比进行研究,一方面,利用Zadoff-Chu序列作为MC-CDMA信号的扩频码,有效降低其峰均功率比;另一方面,在基本选择映射算法的基础上,提出了改进的选择映射算法,具有较好的实用价值.     

多载波CDMA系统

介绍了一种基于ＣＤＭＡ技术和ＯＦＤＭ的多载波ＣＤＭＡ系统,并对其三种类型进行了比较。     

对多载波CDMA方案的分析

目前，第三代移动通信的主流标准(包括TD-SCDMA、WCDMA和cdma2000)都是采用扩频码分多址(CDMA)方式作为其空中接口的技术，由于CDMA技术可以提供比传统多址技术(例如：TDMA、FDMA)更大的系统容量，并且具有抗信道频率选择性衰落的良好特性，该技术就成为未来支持无线移动通信中高速数据多媒体业务的有力竞争者。     

多载波CDMA在第三代移动通信中的应用

本文讨论了第三代移动通信系统中的一种新的CDMA体制，即将OFDM调制技术应用于CDMA的多载波CDMA（MC－CDMA），描述了它的系统结构，并分析了其检测技术、分集技术及信道估计方面的性能。     

基于OFDM的多载波CDMA系统的研究

MC—CDNA系统是将CDNA和OFDM技术的优点结合在一起的多址方案。首先介绍了OFDM的基本原理，并据此给出MC—CDNA系统的模型，通过对MC—CDNA和DS—CDNA的性能比较，MC—CDNA能提供更高的系统容量，结构更简单，抗干扰性更强，更适用于未来移动通信的需要。     

CDMA2000多载波交界规划研究

文章讨论了在CDMA2000系统中。手机在多载波交界区域由于无线规划不合理引起的瞬间脱网、被叫不良等常见的缺陷，并根据CDMA2000协议中相关空闲切换操作流程分析了原因，随后总结多载波交界建网的若干要求。最后提出了CDMA2000下多载波交界区域规划经验原则。     

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。     

未来宽带无线通信的多载波CDMA解决方案

通过对两种多载波CDMA方案与单载波DC-CDMA方案的比较，突出了利用时频联合扩展的多载波 发射分集的CDMA方案在宽带无线通信中特有的优势。该方案在使用较小数目的时频域正交的扩频码字集的情况下可以获得大的扩频增益，使得在高速通信条件下依然能够克服多种环境下的多径衰落，从而减少符号间干扰，且其处理复杂度较低；此外通过适当的选择参数可以使得该方案满足消除予载波间干扰的条件，并能够保持恒定的频率分集增益。     

A Low Complexity VCS Method for PAPR Reduction in Multicarrier Code Division Multiple Access

This paper investigates a peak to average power ratio (PAPR) reduction method in multicarrier code division multiple access (MC-CDMA) system. Variable code sets (VCS), a spreading codes selection scheme, can improve the PAPR property of the MC-CDMA signals, but this technique requires an exhaustive search over the combinations of spreading code sets. It is observed that when the number of active users increases, the search complexity will increase exponentially. Based on this fact, we propose a low complexity VCS (LC-VCS) method to reduce the computational complexity. The basic idea of LC-VCS is to derive new signals using the relationship between candidature signals. Simulation results show that the proposed approach can reduce PAPR with lower computational complexity. In addition, it can be blindly received without any side information.     

A Low Complexity VCS Method for PAPR Reduction in Multicarrier Code Division Multiple Access

This paper investigates a peak to average power ratio (PAPR) reduction method in multicarrier code division multiple access (MC-CDMA) system. Variable code sets (VCS), a spreading codes selection scheme, can improve the PAPR property of the MC-CDMA signals, but this technique requires an exhaustive search over the combinations of spreading code sets. It is observed that when the number of active users increases, the search complexity will increase exponentially. Based on this fact, we propose a low complexity VCS (LC-VCS) method to reduce the computational complexity. The basic idea of LC-VCS is to derive new signals using the relationship between candidature signals. Simulation results show that the proposed approach can reduce PAPR with lower computational complexity. In addition, it can be blindly received without any side information.     

一种降低多载波信号峰均比的技术

多载波信号峰均比的降低在现代功率放大器研究和设计中具有重要意义。文章基于多载波信号的包络特征,提出了一种全新的峰均比降低技术。理论分析和计算机仿真结果表明:文章所提出的技术可以较大程度的改变信号的包络分布,进而大幅度降低多载波信号的峰均比。从实验结果也可以看出,采用了这种新型多载波信号峰均比降低技术的功率放大器,线性与现有功率放大器相比得到大幅度改善。     

基于Chebyshev混沌扩谱序列的MC-CDMA系统的峰均功率比研究

峰均功率比(PAPR)是多载波码分多址 (MC-CDMA)系统的一个重要指标, OFDM多载波调制技术虽然可以提高MC-CDMA系统的数据传输率和抗干扰能力, 但是在系统的峰均功率比方面则存在着亟待解决的问题。本文利用Chebyshev混沌扩谱序列的伪随机、非周期、数量大和良好的相关特性,作为MC-CDMA系统上行信道的扩谱序列,以改善输出信号的峰均功率比。分析和仿真结果表明在保持较低多址接入干扰的同时,还可以大大降低发射信号的峰均功率比。     

M-Sequence for Reducing Peak-to-Average Power Ratio in PTS-OFDM Systems

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峰均功率比约束下扩展目标波形优化

针对包络约束条件下扩展目标最优检测波形设计,提出了峰均功率比约束条件下最优检测波形优化方法。首先,建立了扩展目标信号模型;然后,通过将恒定包括约束转换成峰均功率比约束,推导出该约束下扩展目标最优检测波形优化模型;并将该非凸模型转换成易于求解的凸优化模型,由此获得了恒定包络和低起伏包络条件下的最优检测波形;最后,以某典型扩展目标为例,仿真对比了不同约束参数下波形的检测性能,验证了优化所得恒定包络、低起伏包络波形相比于传统Barker 码波形具有更好的检测性能。     

MIMO—OFDM系统中降低峰均功率比技术的研究

多输入多输出正交频分复用（MIMO-OFDM）系统已成为第四代无线通信的关键技术之一，而系统所产生的高峰均功率比（PAPR）信号是限制MIMO-OFDM技术实用化的主要障碍。针对此，对MIMO-OFDM系统中现有的几种降低PAPR的传统及改进算法进行了详细介绍，并描述了改进算法相对于传统算法的主要优点。     

OFDM系统中基于部分传输序列圆周移位最优和的降低峰值平均功率比的算法

本文针对正交频分复用（ＯＦＤＭ）系统提出了一种新的非常有效的降低其峰值平均功率比的方法．它基于求解ＯＦＤＭ系统部分传输序列圆周移位的最优和,同以前的基于部分传输序列最优组合的方法相比,在同样的条件下针对不同的ＯＦＤＭ系统,新算法的性能均有不同程度的提高,在实际应用中可以完全取代老的算法．     

Peak‐to‐Average Power Ratio Reduction Using N‐tuple Selective Mapping Method for MC‐CDMA

The multi‐carrier transmission signal in Multi‐Carrier Code Division Multiple Access (MC‐CDMA) has a high peak‐to‐average power ratio (PAPR), which results in nonlinear distortion and deteriorative system performance. An n‐tuple selective mapping method is proposed to reduce the PAPR, in this paper. This method generates 2ⁿ sequences of an original data sequence by adding n‐tuple of n PAPR control bits to it followed by an interleaver and error‐control code (ECC) to reduce its PAPR. The convolutional, Golay, and Hamming codes are used as ECCs in the proposed scheme. The proposed method uses different numbers of the n PAPR control bits to accomplish a noteworthy PAPR reduction and also avoids the need for a side‐information transmission. The simulation results authenticate the effectiveness of the proposed method.     

Influence of Discontinuous Transmission and Power Control on the Average SIR and the Outage Probability of the Uplink of CDMA Systems

In this paper the impact of the voice activity detection process and the powercontrolsystem on the average signal-to-interference ratio (SIR) is investigatedconcerningthe uplink of a single cell code division multiple access (CDMA) based mobilecommunication system. In the literature lower bounds on the average SIR areoftenemployed. Here we show the applicability of such bounds. For this purpose theresultsobtained from these bounds are compared with results obtained fromsimulations.Especially, for a few number of subscribers the differences between the lowerboundand the exact values are significant. Furthermore, the variance of the SIR isinvestigated for different parameters. We found out that significantvariations occurwhich affect the outage probability. But, many authors often employ only theaverageSIR, e.g. for their capacity estimations. However, the variance of the SIR hasto betaken into consideration too.