多径衰落下多天线CDMA系统信道容量研究

该文对准静态Rayleigh衰落下MIMO-CDMA系统信道容量进行了研究,分析了扩频码为Walsh函数,基于多码检测的极大似然检测器(MLD)和解相关检测器的性能,并和MMSE多用户检测器(MUD)进行了比较;分析了对不同检测器在一定的信噪比下系统天线数目和信道容量的关系。仿真结果表明:在相同的情况下,基于Walsh码CDMA系统容量按MUD、干扰方差已知的MLD,干扰方差未知的MLD和解相关检测器递减,并且后面的3种检测器在大信噪比的时候均有渐进的平台效应;在信噪比较大且一定时,CDMA系统信道容量与天线数目呈线性关系。     

CDMA接入信道的容量分析

本文简要介绍了CDMA接入信道的特性,随后给出了接入信道容量的概念和计算方法,最后提出了优化接入信道容量的建议.     

同信道干扰对多载波CDMA蜂窝系统下行信道的影响

该文主要讨论多载波CDMA蜂窝系统在下行信道中的同信道干扰问题,理论分析了同信道干扰的解析表达式,并通过计算机仿真得出了在一定的传播损耗下多载波CDMA蜂窝系统下行信道的性能。通过仿真发现,即使在有小区间同信道干扰情况下,通过简单的小区布置,多载波CDMA蜂窝系统下行信道就可以有很大的信道容量。     

LS码与、Walsh码的上行链路容量比较

该文首先分析了多径衰落信道下CDMA系统上行链路信道容量,文章对单用户接收机、多用户接收机两种情况下的信道容量分别作了讨论.对LS码和Walsh码的上行链路容量进行了比较.通过仿真可以看出在多用户检测条件下,两种扩频码提供的容量相差不大,而在单用户检测条件下,LS码则要大大优于Walsh码。     

CDMA寻呼信道的容量分析

本文介绍了一种估算CDMA IS-95寻呼信道容量的方法,可用于指导无线网络的设计和规划.     

在宏分集接收技术下扩频信道的容量分析

研究的是在服从瑞利分布受阴影效应影响的衰减信道中。采用直接序列扩频方式的CDMA无线移动通信系统的信道容量。用到的模型是以多用户检测宏分集(MDM)接收技术为基础建立的，他的特点是在阴影衰落信道中．在误码率较低的条件下,取得较高的数据传输速率。其信道容量可由每个小区中的用户数量来确定。     

开展第四代(4G)移动通信基础研究——实现我国移动通信跨越式发展的途径

自从1880年马可尼建立第一个无线通信系统以来,移动通信历经了长足的变化和发展。特别是香农在其信息论中提出了信道容量的概念之后,围绕着如何逼近香农公式定义的信道容量,移动通信经历了第一代频分多址(FDMA)的模拟话音通信,第二代时分多址的数字话音通信(TDMA),发展到了今天的第三代码分多址(CDMA)的多媒体通信。它对人们的工作、学习和生活产生了巨大的影响。     

信道估计误差对Rayleigh衰落下多天线CDMA系统信道容量影响

目前对多天线信道容量的研究几乎都是集中在具有精确信道估计的假设上,但是它实现起来有一定的难度.在Walsh扩频地址码、多码检测和最大似然接收机的基础上,研究了Rayleigh衰落情况下信道估计误差对MIMO CDMA系统的影响.分析及仿真结果均表明:信道容量随着信道估计误差的增加迅速下降;对于N×N系统,在固定的信道估计误差和信噪比下容量和天线的数目呈线性关系,容量增加的斜率随信道估计误差的增大而减小.     

盲速率判决技术在OFDM系统中的应用

该文借助CDMA系统中的盲速率判决技术解决交织与相位旋转(IPR-OFDM)( IPR:Interleaving and Phase Rotation),系统中接收端恢复交织序号,对接收信号进行检测的问题。IPR-OFDM系统在发送端使用了V 个交织器,接收端为了恢复数据需要知道发送端使用的交织器序号进行解交织。一种解决方法是发送辅助信息(SI:Side Information),这需要占用信道容量;该文借助于CDMA系统中速率判决的思想提出一种在接收端进行盲判的方法,它通过检测CRC(循环冗余校验码)和反转误码率(SER)信息等来获得所需要的交织序号,这种方法相对于前者提高了信道利用率。     

MIMO-MC-CDMA系统及其关键技术

本文介绍了下一代移动通信系统中关键技术--正交频分复用(OFDM),它具有良好的抗多径干扰性能和高频谱利用率.然后给出多载波调制和CDMA结合的MC-CDMA系统,此系统可以支持高数据传输率和高用户容量.接着简述了可以充分利用空间资源,提高无线信道容量和信道可靠性的MIMO技术,并给出结合MIMO和MC-CDMA即MIMO-MC-CDMA系统模型,最后简要介绍了此系统中所涉及的同步及信道估计技术.     

Multiple-access capacity in mobile user satellite systems

The channel capacity of a satellite direct sequence CDMA system is analyzed including the effects of faded user interference, overlapping antenna beams, imperfect equalization of the antenna pattern across an antenna cell, and diversity reception. Simplified models are used to describe the impact of these effects on the channel capacity of single and multiple cofrequency CDMA systems. In a comparison of the uplink and downlink paths, the uplink of the CDMA system is shown to limit the channel capacity because the downlink can utilize code-orthogonality and coherent demodulation. In a multiple system comparison between band-shared CDMA and band-segmented FDMA/TDMA technologies, FDMA/TDMA is shown to provide about the same capacity for uniformly distributed traffic conditions over many cells and dramatically better capacity when traffic is concentrated in one cell. Due to the peak nature of telephony, this result supports the use of band-segmented systems in mobile user satellite systems     

Capacity evaluation of packet-switched CDMA system

In this letter, an extended definition for packet-switched CDMA system capacity based on the protocol stack characteristics is proposed. According to the extended definition, the capacity of the packet-switched CDMA system for different ARQ protocols and different channel models is investigated. The results show that, compared with the traditional definition, the extended definition is more appropriate for describing the packet-switched CDMA network capacity     

Capacity Comparison of CDMA and TDMA in Vector Broadcast Channel

1　Introduction　MultipleInputMultipleOutput (MIMO)havereceivedagreatdealofattentionasamethodtoachievelargecapacityandhighreliabilityoverwire lesslink .Accordingtovectorbroadcastchannel,thebasestationanduserinthissystembothhavemulti pleantennas.Costa[1 ] hadpointedoutthatifthein terferencesignalwasindependentoftransmitsignalanditwasknownatthetransmitterthenthechan nelcapacitywiththeinterferenceisthesameasiftheinterferencewasnotexist.　Thoughthepreconditionofcosta sresultisscalarchannel.The…     

Comparison of hybrid FDMA/CDMA systems in frequency selectiveRayleigh fading

A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signalling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal     

CDMA cellular engineering issues

The frequency reuse efficiency for the proposed code division multiple access (CDMA) cellular system is analytically derived, and it is shown that the cell capacity of a fully loaded multiple cell system is about 75% of what would be available for a single cell system. In addition, an engineering issue in transitioning from analog advanced mobile phone system (AMPS) to CDMA system is discussed. Calculating excessive interference power due to a CDMA channel, it is shown that when a CDMA channel is introduced in a cell, there should be at least one ring of buffer cells, in which the analog channels falling into the CDMA band are not reused     

Performance analysis of cellular CDMA networks overfrequency-selective fading channel

An effect of multipath fading on the performance of a cellular code-division multiple-access (CDMA) system is analyzed in this paper. A wide-sense stationary uncorrelated scattering (WSSUS) channel model and the coherent binary phase-shift keying (BPSK) with asynchronous direct-sequence (DS) spreading signal are assumed in the analysis. The average error probability for both the forward link and reverse link of a cellular CDMA system over a frequency-selective fading channel using a conventional correlation-type receiver and RAKE receiver are derived. The impact of imperfect power control and channel capacity of a cellular CDMA system is also investigated. The closed forms of average error probability derived in the paper can save a lot of computation time to analyze the performance and channel capacity of a cellular CDMA system. The analytical results show that the performance and maximum transmission rate of cellular CDMA systems degrade with an increase in the number of simultaneous users and the number of interfering cells. The signal-to-interface ratio (SIR) for the reverse link derived in this paper can directly describe the interrelationships among a number of paths, number of users, number of interfering cells, fading factors, and maximum variation of a received unfaded signal     

The performance evaluation of spatial–temporal algorithms in W‐CDMA systems

Differing from FDMA, TDMA, and CDMA, space division multiple access (SDMA) uses space resources to improve communication system performance. Utilizing the smart antenna system is an approach to realize the SDMA technique. Smart antenna systems using the beamforming technique can reduce the co‐channel interference and multipath fading to increase the channel capacity and communication quality. In this study the smart antenna system and rake receiver are integrated. The performance of spatial–temporal structure applied to the W‐CDMA system is evaluated. From the cumulative distribution function simulation results, W‐CDMA system with spatial–temporal algorithm can exactly provide SINR gain to improve the system performance and capacity. Copyright © 2005 John Wiley & Sons, Ltd.     

Forward-link capacity of a DS/CDMA system with mixed multiratesources

Some studies have been done on capacity of a code division multiple access (CDMA) system with mixed multirate sources. However, a vast majority of these studies have concentrated on the reverse-link. This trend comes from the fact that the capacity of a CDMA system is reverse-link limited. However, the forward-link can be a limiting link because emerging data services are likely to require higher data rates in the forward-link than in the reverse-link. In this paper, we analyze and simulate the forward-link capacity of a CDMA system with mixed multirate sources in a multipath fading channel. The outage probability of the forward-link is derived for a CDMA system with mixed multirate sources. By introducing a forward-link power factor, the forward-link Erlang capacity is obtained in a closed form. The forward-link capacity is analyzed in terms of the number of multipaths, the number of RAKE fingers in a mobile station, closed-loop power control, and impact of soft handoff. The results in this paper can be applied to overall system design of a CDMA system with multimedia services in future mobile communication systems     

Optimum power control for CDMA with deterministic sequences in fading channels

We specify the capacity region for a power-controlled, fading code-division multiple-access (CDMA) channel. We investigate the properties of the optimum power allocation policy that maximizes the information-theoretic ergodic sum capacity of a CDMA system where the users are assigned arbitrary signature sequences in a frequency flat-fading environment. We provide an iterative waterfilling algorithm to obtain the powers of all users at all channel fade levels, and prove its convergence. Under certain mild conditions on the signature sequences, the optimum power allocation dictates that more than one user transmit simultaneously in some nonzero probability region of the space of all channel states. We identify these conditions, and provide an upper bound on the maximum number of users that can transmit simultaneously at any given time. Using these properties of the sum capacity maximizing power control policy, we also show that the capacity region of the fading CDMA channel is not in general strictly convex.     

Multi-Channel Assignment Schemes and Handoff Study in CDMA Cellular Systems

The CDMA system promisingly provides more capacity than AMPS. However, providing multi-channels for a CDMA system is requisite for satisfying the demand of capacity. In this paper, three schemes of multi-channel assignment are proposed. Based on computer simulation, performance measures, e.g. blocking probabilities, the overall capacity, the capacity of each channel, and the number of re-accesses, are obtained. Since the same frequency channel may be assigned to two adjacent cells, the effect of soft handoff is also considered. Numerical results demonstrate that scheme 3 (i.e., the random re-selection scheme) performs the best of the proposed three schemes because it provides the highest system capacity while keeping the cost of accessing channels (i.e., in terms of number of channel accesses) to a minimum.