共查询到19条相似文献,搜索用时 171 毫秒
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多载波CDMA的三种方案及其特性比较 总被引:3,自引:0,他引:3
多载波扩频码分多址系统是一种消除符号间干扰的有效技术。它结合了OFDM和CDMA的优点,在高速数据传输时,其抗符号间干扰的性能明显优于传统的单载波CDMA系统。本文首先分析了三种多载波CDMA方案的基本原理,然后对它们的系统特性进行了比较。 相似文献
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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。 相似文献
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针对多载波共频谱传输应急卫星通信系统,各干扰载波互不相关,且干扰载波的功率远大于扩频信号的功率,干扰载波对扩频信号存在严重的干扰,因此对于扩频信号的恢复,载波重构与干扰消除处理是必须的。对于多载波干扰消除其实现方式可分为串行干扰消除和并行干扰消除2种,为此分析和比较了2种典型实现方式,提出了基于数字重采样的改进方案。分析结果表明,基于数字重采样的串行干扰方式更适合多载波共频谱传输应急系统卫星通信系统的应用。 相似文献
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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. 相似文献
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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。 相似文献
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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。 相似文献
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在卫星通信网络中,要提供高质量的多媒体业务意味着所传输的视频和音频信号将占用大量的卫星转发器带宽。作为一种先进的多址技术,CDMA可以动态地管理系统资源。将CDMA技术应用于地球同步(GEO)卫星通信网络,可以最大限度地节约卫星转发器带宽。这里介绍了如何将基于DSP的DS/CDMA技术应用于卫星调制解调器,以实现卫星通信网络中的宽带多媒体业务。 相似文献
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Sanjay Dhar Roy Sumit Kundu Gianluigi Ferrari Riccardo Raheli 《International Journal of Communication Systems》2014,27(10):1582-1600
In this paper, the performance of cognitive radio (CR) code division multiple access (CDMA) systems is analyzed. More precisely, CR users belong to a cognitive radio network (CRN), which coexists with a primary radio network (PRN). Both CRN and PRN are CDMA‐based, with colocated base stations. Soft hand off and power control are considered in both the CRN and the PRN. Upon the development of an accurate simulator for a representative three‐cell cellular scenario, we evaluate the performance of the proposed CR system in terms of outage probability, blocking probability and average data rate of secondary users. Three different spectrum sensing techniques are. Two new schemes, based on interference limit, are proposed and compared with an existing adaptive spectrum sensing scheme. Spectrum activity measurements and spectrum sharing decisions have been considered for evaluating the performance of the three schemes. The paper proposes a new CR‐CDMA networking model and a simulation testbed for evaluating performances of secondary users and primary users in terms of outage, blocking, BER and average data rate in the presence of soft hand‐off and power control. For comparison purposes, the analysis in the absence of spectrum sensing is also investigated.Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Lanke Lakshmi Prasanna Kumar Kamavaram Ellore Srinivasa Murthy Mahendhra Nanjappa Giri Prasad 《International Journal of Communication Systems》2020,33(13)
From the past decade, the multicarrier code division multiple access (MC‐CDMA) transmission schemes have placed major role in wireless communications. It is providing a secured wireless communication to the users with guaranteed performance. In many situations, the performance of the MC‐CDMA is restricted due to the interference caused by multiple access interference (MAI), which also influences the frameworks of CDMA. To overcome this issue, we concentrated on developing the efficient technique for data transmission with interference cancellation for downlink MC‐CDMA. In the proposed method, the interference cancellation procedure is done by using the regeneration and subtraction of MAI from the signal. The simulation results are evaluated using the MC‐CDMA system with different decision functions. Results proved that the proposed system is efficient in reducing the MAI along with an improved bit error rate (BER). 相似文献
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Overview of multicarrier CDMA 总被引:43,自引:0,他引:43
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) 相似文献
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Three multirate access schemes, multicode, variable spreading gain (VSG), and spectral overlaid multiple‐symbol‐rate (MSR), for asynchronous space‐time block coded (STBC) multicarrier code division multiple access (MC‐CDMA) systems are proposed. The three possible spectral overlaid configurations for MSR systems are also investigated. The expressions to evaluate the multiple access interferences, bit error rate (BER) performances, and system capacities of a antenna STBC MC‐CDMA using the three multirate access schemes are obtained. Transmit power allocation is adjusted according to the service rates and the number of active users in each service class to maintain the link quality and to improve the system capacity. Our numerical results show that systems with multicode access scheme using orthogonal Gold spreading codes and with VSG access scheme have similar system performance and capacity, and both perform in general better than systems with MSR access scheme of any spectrum configurations. In case when non‐orthogonal Gold codes are used, multicode access scheme shows degradation in the system capacity as compared to VSG, due to the presence of larger self‐interference (SI) among the codes used by each user. The achievable capacities for the three spectral overlaid configurations of MSR multirate systems are also compared. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Potential increase in capacity along with the need to provide multimedia services and cope with multiuser interference (MUI) and intersymbol interference (ISI) arising due to wireless multipath propagation, motivate well multirate wideband code-division multiple-access (CDMA) systems. Unlike most existing continuous-time symbol-periodic and multipath-free studies, the present paper develops an all-digital block-precoded filter-bank framework capable of encompassing single- or multirate transceivers for asynchronous or quasi-synchronous CDMA transmissions through multipath channels. Thanks to symbol blocking and through appropriate design of user codes, the resulting generalized multicarrier (GMC) CDMA system not only subsumes known multicarrier CDMA variants, but also equips them with flexible multirate capabilities. It is computationally simple, and guarantees symbol recovery regardless of the (possibly unknown) FIR multipath channels in both downlink and uplink setups. Simulations corroborate that the novel GMC-CDMA system outperforms existing multirate alternatives in the presence of asynchronism and multipath, and illustrate the feasibility of recovering blindly multirate transmissions received through unknown frequency-selective channels in the uplink. The performance of GMC-CDMA system in UMTS channels is also simulated and compared with existing multirate schemes 相似文献
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While multicarrier CDMA techniques are used to reduce interference and improve the performance of the system in fading channel, carrier frequency offset and multiple access interference remain major obstacles for a multicarrier CDMA system's performance. In this article we propose a novel joint detection method called modified maximum likelihood multistage parallel interference canceller (M-ML-MPIC) to eliminate the frequency offset and MAI simultaneously. The main idea of our approach is to combine PIC multiuser detection and frequency offset estimation based on a maximum likelihood function with guard interval. We discuss our scheme and report on its performance using a set of simulation experiments. 相似文献
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Performance analysis of Doppler shift effects on OFDM‐based and MC‐CDMA‐based cognitive radios 下载免费PDF全文
Salem Bindhaiq Sharifah Kamilah Syed‐Yusof Haleh Hosseini 《International Journal of Communication Systems》2014,27(11):2658-2669
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. 相似文献
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This paper suggests that multicarrier modulation reduces the complexity and the delay caused by the multiuser interference cancellation process utilizing convolutional codes. For spread spectrum multiple access, multiuser interference (interference due to signals from other users) limits the performance of the communication link. To remove this interference, a multiuser interference cancellation technique which utilizes orthogonal convolutional codes has been proposed for the uplink (mobiles to a base station) of the cellular code-division multiple-access (CDMA) systems. However, this technique requires large interleavers and huge memory, or artificial multipath diversity and a RAKE system to achieve sufficient coding gain if it is applied to wireless indoor communications and fading is slow compared to the data rate. To reduce the complexity of the canceller, multicarrier modulation is employed as it provides frequency diversity gain and coding gain without the interleavers or a RAKE system. This paper shows that multicarrier modulation reduces the complexity of the canceller and still provides sufficient coding gain in order to cancel the multiuser interference. A canceller with decoding in the initial decision and multicarrier modulation improves the capacity by a factor of 1.4 as compared with a canceller without decoding 相似文献