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 of a Multicarrier CDMA System with Rayleigh Fading Multipath Channels

This paper examines the performance of a multicarrier CDMA system in a Rayleigh fading channel without a RAKE receiver. Since the multicarrier technique is a diversity reception technique used in the frequency domain, the signal is transmitted at different frequency bands and undergoes different fading. The superimposed signal of the multipath components after going through the mobile channel will be processed by an Fourier Transform to enter the frequency domain, where the time delays in various paths are converted to the phase shifts in the compound signal. In this paper, we use sounding bits to extract the characteristics of the mobile channel and to partly remove the multipath effect. From the simulation, it is found that the multicarrier technique is simpler than the technique used in the single carrier system with a RAKE receiver while producing a better performance than that of the RAKE receiver.     

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。     

Performance of Multicarrier CDMA Rake System over Rayleigh Fading Channel

Based on the theory of multicarrier (MC) technique and the Rake receiver, a multicarrier DS-CDMA Rake system is proposed, where a data sequence multiplied by a spreading sequence modulates multiple carriers. The receiver provides a Rake for each subcarrier, and the outputs of the Rakes are combined by a maximal-ratio combiner. The average probability of error of the system is derived from an uncorrelated subcarrier and frequency-selective fading channel model. The system performances are evaluated over Rayleigh fading channel with an exponential multipath intensity profile(MIP) and with a rectangular MIP, respectively, when multipath interference is present. It is found that this kind of model has larger superiority in an exponential MIP than in a rectangular MIP.     

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.     

Performance of a Multiuser Detector with Multicarrier Transmission for a DS/CDMA System

In this paper, a new multiuser detector combining decorrelating detector and multicarrier transmission scheme is proposed and analyzed in a frequency selective Rayleigh fading channel. The bit error probability and asymptotic multiuser efficiency are derived as performance measures. From numerical results, it is shown that the proposed detector achieves better BER performance and lower computational complexity compared to a conventional decorrelating detector. It is also shown that the proposed detector is robust to partial narrowband interference, and alleviates near-far problem effectively. The results in this paper can be applied to design of a wideband CDMA system.     

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.     

A Multicarrier CDMA System for Joint Time-Frequency Diversity Using Divided Spreading Sequence

One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can provides another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity.     

多载波频率分集扩展频谱码分多址通信系统及性能分析

多载波频率分集扩展频谱码分多址通信（ＦＤ／ＳＳＭＡ）系统是一种基于多载波传输、利用与直接序列扩扩展频谱码分多址系统（ＤＳ／ＳＳＭＡ）的时间－频率对偶关系而提出的新的扩展频谱多址方案。本文给出了ＦＤ／ＳＳＭＡ系统的基本原理,分析了在加性高斯白噪声信道下ＦＤ／ＳＳＭＡ的多址性能和抗单频干扰能力,并通过高斯近似法和Ｍｏｎｔｅ－Ｃａｒｌｏ模拟方法得到了系统的平均误比特率。     

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。     

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。     

CDMA发射分集系统的多用户检测常模算法分析

空时分集技术的最大优点在于在不增加带宽的情况下可以提高系统的可靠性,是目前移动通信的研究热点.常模算法是一种性能优良的码分多址(CDMA)盲多用户检测技术,能确保判决信号与实际传送信号之间的差错较小,误码率性能良好.文中提出将标准线性受限常模算法(LCCMA)与空时分组码(STBC)相结合,设计出一种收敛快、能够改善系统性能的基于2-空时分组码的多用户接收机.     

CMA Performance in CDMA Transmit Diversity System

1IntroductionThe capacity and performance of CDMAare largelyaffected by disturbances ,and Multi-Access Interference( MAI) is the main disturbance factor whenthe numberof user is large . Blind adaptive Multi-User Detection(B-MUD)is aneffectivetechniquetoreduce MAI[1 ~2].In many advanced and convergence faster algorithms ,Constant Mode Algorithm ( CMA) is an efficient B-MUDand has better systemperformance .Refs .[3 ~6]depict the CMAin details .The channel of mobile communications p…     

A Generalized Analytical Framework for SMPT in a Multicode CDMA Wireless System

Simultaneous MAC Packet Transmission (SMPT) has recently been proposed for stabilizing the throughput over wireless links, which is one of the key challenges in providing high-quality wireless multimedia services. SMPT stabilizes the wireless link by transmitting multiple packets on multiple CDMA channels in parallel in response to packet drops due to wireless link errors. These parallel packet transmissions stabilize the link layer throughput, but they also increase the interference level in a given cell of a cellular network or cluster of an ad-hoc network, which in turn reduces the number of traffic flows that can be simultaneously supported in a cell/cluster. We have recently developed an analytical framework for the class of SMPT mechanisms for a simple Bernoulli packet generation process, which does not reflect the oftentimes bursty packet generation processes encountered in real networks. In this paper we develop a generalized analytical framework for SMPT, which accommodates bursty packet traffic (and also non-bursty Bernoulli traffic). This framework expresses the system dynamics in transition probabilities for a Markov chain and calculates the effects of the interference through an iterative approach. The numerical results from our analytical framework and verifying simulations indicate that SMPT provides a significant reduction in packet loss and buffer occupancies (and delay), especially for persistent traffic bursts, in exchange for a reduced number of supported flows. Our analytical framework quantifies these system trade-offs with good accuracy and can thus be employed for resource management.Manjunath Krishnam received the B.E. degree in Electronics and Communications from R.V. College of Engineering, Bangalore University, Bangalore, India, in 1996, the M.S. degree and Ph.D. degree in Electrical Engineering from Arizona State University, Tempe, AZ, in 1999 and 2004 respectively. His research interests are in the areas of network performance analysis, network and traffic modeling, and resource management in wireless networks. Mr. Krishnam is a member of IEEE.Martin Reisslein is an Assistant Professor in the Department of Electrical Engineering at Arizona State University, Tempe. He is affiliated with ASUs Wireless Integrated Nano Technologyy (WINTech) center. He received the Dipl.-Ing. (FH) degree from the Fachhochschule Dieburg, Germany, in 1994, and the M.S.E. degree from the University of Pennsylvania, Philadelphia, in 1996. Both in electrical engineering. He received his Ph.D. in systems engineering from the University of Pennsylvania in 1998. During the academic year 1994–1995 he visited the University of Pennsylvania as a Fulbright scholar. From July 1998 through October 2000 he was a scientist with the German National Research Center for Information Technology (GMD FOKUS), Berlin. While in Berlin he was teaching courses on performance evaluation and computer networking at the Technical University Berlin. He is editor–in–chief of the IEEE Communications Surveys and Tutorials and has served on the Technical Program Committees of IEEE Infocom, IEEE Globecom, and the IEEE International Symposium on Computer and Communications. He has organized sessions at the IEEE Computer Communications Workshop (CCW). He maintains an extensive library of video traces for network performance evaluation, including frame size traces of MPEG–4 and H.263 encoded video, at He is co–recipient of the Best Paper Award of the SPIE Photonics East 2000—Terabit Optical Networking conference. His research interests are in the areas of Internet Quality of Service, video traffic characterization, wireless networking, and optical networking.     

一种可以高速传输数据的MTCM正交序列多码CDMA系统

为了有效地实现用户高速数据的传输本文提出了一种ＭＴＣＭ正交序列多码ＣＤＭＡ系统。这对此系统在ＡＷＧＮ信道的性能进行了计算,并和未编码系统的数值结果进行了分析和比较。     

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。     

The Performance of Multicarrier CDMA for the Correlated Rayleigh Fading Channel

We present an new method for the analytical calculation of the error probability in a Rayleigh fading channel with correlated fading amplitudes. Even though the method can be applied for more general problems, we restrict ourselves on the investigation of a multicarrier CDMA transmission. The frequency correlation between the fading amplitudes of the carriers is given by the delay power spectrum of the channel. We generalize the well-known analytical expressions for the pairwise error probability of the uncorrelated Rayleigh channel to this case of correlated fading. This probability can be expressed in a closed form by an integral over a finite interval which can be easily evaluated numerically. We present some examples to show how much of the diversity of a code remains useful if the transmission channel does not provide an arbitrary degree of diversity.     

基于时空混沌码分多址系统性能分析

将时空混沌序列应用于DS—CDMA系统，给出了系统同步模型，并对系统性能进行了分析。结果表明：用混沌序列作为地址码的CDMA系统，可以有效地抑制干扰的影响，并能提高系统的传输效率，对CDMA系统性能的改善起到重要作用。     

码分多址通信的计算机仿真

随着通信技术的发展，通信系统的研究成为一项越来越复杂的工程，所以，对通信系统的仿真就日益成为一种重要的研究手段。本文介绍一种对CDMA码分多址通信系统进行计算机仿真的方法。该方法基于通信过程的基本特征，充分利用软件系统的技术特点，具有非常好的可扩展性和执行速度。通过把仿真结果同理论结论进行对比，证明该仿真方法非常有效。     

Multicode Sparse-Sequence CDMA: Approach to Optimum Performance by Linearly Complex WSLAS Detectors

This paper investigates the performance-complexity tradeoff of the wide-sense likelihood ascent search (WSLAS) detectors in large multicode sparse-sequence CDMA. It is illustrated that when each sequence has sparsely only 16 nonzero chips, in a channel load up to 1.05 bits/s/Hz and a broad SNR region, the linearly complex WSLAS detectors can achieve the benchmark optimum BER while the complexity is significantly reduced from 0.5 times bit number to a constant less than 30 additions per bit by the sequence sparsity. The evaluation result of multiuse efficiency also shows that the sparse sequences of 16 nonzero chips can already provide a sufficient degree of freedom.