一种降低MC-CDMA信号峰值平均功率比的方法

多载波信号的峰值平均功率比远远大于单载波系统,而且峰平比随着子载波个数无限增长.本文采用格雷互补序列及它的一个子类S-R序列作为多载波CDMA（MC-CDMA）的扩频码,来降低它的输出峰值平均功率比,对于任意长度的扩频码其峰平比不超过6dB.对长度为32的S-R序列扩频、Hadamard扩频及长度为31的m序列扩频的MC-CDMA信号进行了比较,其峰平比分别为6dB,13.68dB和12dB.     

利用格雷互补序列降低OFDM信号峰平比及其DSP实现

正交频分复用(OFDM)系统具有有效抗码间串扰、频谱效率高、可以提供高速率数据传输等优点,在第三代移动通信系统(3G)中具有良好的发展前景.但是,OFDM信号峰平比比较高,影响到功放的效率,这已经成为正交频分复用系统实用化的一大障碍.本文提出了一种有效降低正交频分复用信号峰平比的方法.它基于将格雷互补序列应用于正交频分复用通信系统,以降低信号的峰平比,对于任意载波数OFDM多载波信号,其峰平比可降至不大于6dB.本文还提供了一种用DSP实现的方法.     

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。     

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。     

用多幅值CPM减小OFDM信号的PAPR

正交频分复用(OFDM)是一种多载波调制(MCM)技术,其具有良好的抗多径衰落的能力和非常高的信道利用率.但是OFDM有一个固有缺点就是存在较高的峰平功率比(PAPR),本文提出将多幅值的连续相位调制信号与部分响应序列相结合的方法来减少OFDM信号的PAPR.     

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。     

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。     

LTE-A系统上行信道降低PAPR技术的算法研究

SC-FDMA (Single Carrier Frequency Division Multiple Access)系统峰均功率比(Peak of Average Power Ratio,PARP)较低,但是频谱利用率也很低.LTE-A(LTE-Advanced)系统作为LTE的技术演进,其关键技术之一聚合载波技术,利用片段带宽,提高频谱利用率,但是多个成员载波的引入会造成峰均比增加的问题.文章介绍在LTE-A多载波系统中,利用上行参考信号传输边带信息、分量载波自然分块的特点,提出一种易于实现且复杂度较低的降低PAPR的改进部分选择序列(Partial Transmit Sequences,PTS)算法.     

MC-CDMA与DS-CDMA的性能比较研究

在分析传统DS-CDMA优缺点的基础上,介绍了一种新的具有高频谱效率和适合于高速数据传输的多载波CDMA(MC-CDMA)技术方案。阐明了MC-CDMA的结构和信号形式,进而对其优缺点作出了归纳。仿真结果显示,由于其内在的频率分集性能和克服多径时延的能力,MC-CDMA可以表现出比DS-CDMA更好的误码率性能。     

基于OFDM的码分多址技术及其性能仿真

给出了多载波CDMA系统构架。目前提出有3种方案,分别是:频域扩频(MC CDMA)、时域扩频(MC DSCDMA)和多音CDMA(MT CDMA)。以MC CDMA,MC DS CDMA为例,对两种模型在AWGN和Rayleigh信道的性能进行了仿真。仿真数据表明:多载波频率分集CDMA系统(MC CDMA)在无线宽带数据传输中性能大大优于时域扩频CDMA系统,具有良好的应用前景。     

Multi-carrier CDMA system using a code orthogonalising filter

Detection using a code orthogonalising filter in the reverse link of a multi-carrier code division multiple access (MC-CDMA) system is discussed. In addition, a scheme which can reduce hardware complexity is proposed. Simulation results show that the proposed MC-CDMA system has superiority in performance over an MC-CDMA system under a multi-user environment     

利用部分传输序列减小MCCDMA系统的峰均比

为了更好地利用部分传输序列(PTS)来降低多载波码分多址(MC-CDMA)系统的峰均功率比(PAR),该文提出了对多路传输的子载波信号采用非均匀相邻分割方法。即在子载波频段上适当地减小低频和高频子载波块的大小,增大中间频率子载波块的大小可以进一步减小PAR。当中间频段数据块的大小是最低(或高)频段数据块的2倍时PAR达到最小,比均匀分割法下降0.2dB。针对旋转矩阵最优解的求解空间太大,该文同时采用遗传算法来减小计算的复杂度,仿真表明经过60代的进化可以达到最优解。     

On the performance and capacity of an asynchronous space-time block-coded MC-CDMA system in the presence of carrier frequency offset

In this paper, the bit-error rate (BER) performance and capacity of asynchronous space-time block-coded (STBC) multicarrier code-division multiple-access (MC-CDMA) systems in the presence of carrier frequency offset (CFO) between the transmitter and receiver oscillators are analyzed. The exact BER expression when using equal gain combining (EGC) and the approximate BER expression when using maximum ratio combining (MRC) are derived. These BER expressions are verified through simulations. Using these derived expressions, the achievable system capacity satisfying a minimum BER requirement can be studied for the two cases when EGC and MRC are used and, hence, it is possible to compare the achievable capacity of STBC MC-CDMA systems with that of MC-CDMA systems. It is concluded that small CFO has an insignificant effect on the BER and capacity of STBC MC-CDMA systems and that this range of CFO is important in transceiver design. Besides, STBC MC-CDMA systems with multiple receive antennas can achieve higher capacity than that of the MC-CDMA systems; this amount can be obtained analytically using the theoretical BER expressions derived.     

Joint spatial-frequency blind multiuser detection based on LCCMA

Multicarrier code division multiple access (MC-CDMA) has the ability to combat with frequency selective fading and antenna array can enhance the performance of system. The paper proposes a novel joint spatial-frequency blind multiuser detection for antenna array MC-CDMA based on linear constraint constant modulation algorithm (LCCMA), which has robust performance and can ensue the weight vectors to converge to that of the desired user. Simulation indicates the proposed algorithm has better bit error ratio (BER) performance than that of the traditional beamforming-based two-step algorithm.     

Performance of Multiband Complex-Wavelet-Based MC-CDMA System with Space-Time Coding over Nakagami-m Fading Channels

Space-time coding technique and Multi-carrier CDMA (MC-CDMA) technique have received much interest due to their high frequency spectrum efficiency and high data rate transmission. On the basis of analyzing the two technique principle, utilizing the optimized multiband complex wavelet as multi-carrier basis function, we propose an MC-CDMA system based on multiband complex wavelet and space-time coding for downlink and investigate the system bit error rate (BER) performance over Nakagami-m fading channel. The system has much higher spectrum efficiency and data rate due to no need any cyclic prefix (CP) when compared to the conventional MC-CDMA system. Moreover, the application of space-time coding technique improves the ability against fading channel effectively and perfects the downlink performance further. Simulation results show that the proposed multiband complex-wavelet-based MC-CDMA (MBCW-MC-CDMA) system performs better than conventional MC-CDMA system and real wavelet-packet-based MC-CDMA system due to its superior ability against interferences. Especially, the space-time coded MBCW-MC-CDMA system has superior performance, and it outperforms single antenna MBCW-MC-CDMA and conventional MC-CDMA with space-time coding.     

Joint frequency-domain differential detection and equalization for DS-CDMA signal transmissions in a frequency-selective fading channel

It has been revealed that direct sequence code-division multiple access (DS-CDMA) can achieve a good bit-error rate (BER) performance, comparable to multicarrier CDMA (MC-CDMA), by using coherent frequency-domain equalization (FDE) instead of coherent Rake combining. However, coherent FDE requires accurate channel estimation. Pilot-assisted channel estimation is a practical solution, but its accuracy is sensitive to the Doppler spread. In this paper, a frequency-domain differential encoding and detection scheme is proposed for a DS-CDMA mobile radio. Joint frequency-domain differential detection and equalization (FDDDE) based on minimum mean-square error (MMSE) criterion is presented, where a simple decision feedback filter is used to provide a reliable reference signal for MMSE-FDDDE. Also presented is an approximate BER analysis. It is confirmed by both approximate BER analysis and computer simulation that MMSE-FDDDE provides good BER performance close to the coherent MMSE-FDE and shows high robustness against the Doppler spread; it outperforms coherent MMSE-FDE for large Doppler spreads. The proposed MMSE-FDDDE can also be applied to MC-CDMA. A performance comparison between uncoded DS- and MC-CDMA shows that DS-CDMA with MMSE-FDDDE achieves better BER performance than MC-CDMA with MMSE-FDDDE for small spreading factors.     

基于PN码相关性实现MC-CDMA帧同步的分析

由于多载波CDMA(MC-CDMA)技术自身的特点,其同步性能起着非常重要的作用。在基于PN码相关性实现MC-CDMA帧同步的算法的基础上,通过理论分析和仿真研究了虚假相关性峰值概率和循环自相关性对帧同步的影响,并提出用降低循环自相关性和自适应门限来解决影响的新方法。     

A MC-CDMA system based on orthogonal filter banks of wavelet transforms and partial combining

Multi Carrier Code Division Multiple Access (MC-CDMA) is an appropriate modulation technique for high data rates. In this modulation scheme, employing of combining techniques are unavoidable for restoring orthogonality between different user signals. In this paper, the combining techniques of a MC-CDMA based on wavelet transform are studied. The partial combining of the wavelet based MC-CDMA system is suggested and its performance is compared with the maximum ratio combining (MRC), equal gain combining (EGC), orthogonality restoring combining (ORC) and the minimum mean square error (MMSE) techniques. Orthogonal filter banks of the wavelet transforms provide orthogonality between the wavelets and scaling functions, subcarriers and spreading sequences. Therefore, they provide new dimensions in combatting multipath fading, inter carrier interference (ICI) and narrowband interference in MC-CDMA systems. Furthermore, analysis of partial combining shows that coefficients of this technique can be computed in a simple manner. Simulations results indicate that the bit error rate (BER) performance of the proposed scheme is almost comparable with the MMSE combining scheme and the proposed system has a proper performance in terms of BER versus the signal to noise ratio (SNR) in frequency selective fading channels.     

Multi-Rate Access Schemes for MC-CDMA

In order to accommodate different types of traffic in future wirelesscommunications, it is necessary to consider a system, which can operatesatisfactorily at multiple transmission rates. Due to its capability to copewith the hostile frequency selective fading, that limits transmission rate,and its suitability to handle multi-rate data, multi-carrier CDMA (MC-CDMA)has recently drawn considerable attention as a suitable candidate forsupporting multimedia services in wireless communications. Multi-rate accessschemes where users are able to transmit at different data rates on MC-CDMAsystems are presented in this paper. Four multi-rate access schemes: uncodedfixed spreading length (UFSL), coded fixed spreading length (CFSL), multi-codefixed spreading length (MFSL) and variable spreading length (VSL) schemes areproposed. With these schemes, different traffic such as voice, video and highrate data can be transmitted seamlessly through one MC-CDMA infrastructure.A chip-level minimum mean square error combining (MMSEC) technique is employedfor joint energy combining and interference cancellation purpose. Theperformance of these schemes with MMSEC is compared by both theoreticalderivations and simulation results under frequency selective Rayleigh fadingchannels.