IMT—2000CDMA宏小区蜂窝无线网络的仿真

ＩＭＴ－２０００ＣＤＭＡ宏小区蜂窝无线网络的仿真,是为评估当前在第三代移动通信系统中较具实力的Ｗ－ＣＤＭＡ和ｃｄｍａ２０００技术而开发的。仿真包括链路级和系统仿真两部分,主要分析研究、验证了评估了两种ＣＤＭＡ无线传输技术的性能以及ＣＤＭＡ无线网络的频谱效率／系统容量。     

第三代移动通信系统（下）

４３种主要的ＩＭＴ－２０００无线传输技术（ＲＴＴ）提案的比较目前国际上呼声最高的３种ＩＭＴ－２０００ＲＴＴ提案是Ｗ－ＣＤＭＡ、Ｗ－ＣＤＭＡＯｎｅ、ＴＤＭＡ／ＣＤＭＡ（ＴＤ－ＣＤＭＡ）,下面对其技术特点和主要技术参数作一比较。４１技术特点Ｗ－ＣＤＭＡ...     

码分多址（CDMA）移动通信系统的发展

本文简述了ＣＤＭＡ的技术优势，分别介绍了窄带码分多址（Ｎ－ＣＤＭＡ）移动通信系统和宽带码多址（Ｗ－ＣＤＭＡ）技术的发展情况，最后，提出应加强对Ｗ－ＣＤＭＡ技术上和研究并积极参与到第三代移动通信体制标准的制定工作中去     

宽带CDMA在IMT—2000中的应用技术

从第三代移动通信系统ＩＭＴ－ ２０００ 的无线传输技术要求出发,分析宽带ＣＤＭＡ的技术特点和Ｗ－ ＣＤＭＡ、ｃｄｍａ２０００ 等典型提案,探讨它在ＩＭＴ－ ２０００ 无线接入子系统中的应用方案和关键技术     

第三代移动通信系统的佼佼者—宽带CDMA

本文通过分析移动通信与个人通信的发展趋势,认为基于ＩＳ－９５标准的Ｗ－ＣＤＭＡ系统是第三供移动通信系统中前景看好的代表系统。文章阐述了Ｗ－ＣＤＭＡ的优势,有待解决的问题以及支持Ｗ－ＣＤＭＡ的新技术,本文工作得到了“８６３”高科技计划个人通信项目组的支持。     

同步CDMA系统中一类新的扩频序列

码分多址（ＣＤＭＡ）技术已作为第三代数字移动通信及个人通信系统的无线接入技术进行广泛的研究和应用。而ＣＤＭＡ系统中扩频序列问题一直是ＣＤＭＡ技术中的关键问题。文献４给出了Ｓ－ＣＤＭＡ系统中的扩频序列实数加编码的新方法,但对构造具有纠错能力的扩序列至今尚未发现。本文给了了Ｓ－ＣＤＭＡ系统中具有纠错能力的一类新的扩频序列和它的译码算法。     

威迪森进军W-CDMA无线接入芯片市场

深圳威迪森（ＷＩＲＥＬＥＳＳ　ＤＩＧＩＴＡＬ ＣＥＮＴＥＲ）通信技术有限公司,是国内专业从事无线扩频通信产品开发及生产的高科技公司、继推出“ＷＤＣ无线数字扩频平台”产品后,该公司又将研发第二代改良产品。从第一代的模块转向第二代的ＡＳＩＣ,并实现性能上升级。这片 ＡＳＩＣ现定位于Ｗ－ＣＤＭＡ,主要应用面向第三代移动通信Ｗ－ＣＤＭＡ无线 威迪森公司总经理董涛表示。威迪森是根据市场需求研发这片ＡＳＩＣ的,是公司现有“ＷＤＣ无线数字扩频平台”产品的改良和升级。另外,第三代移动通信的技术基础是扩频;而威迪森 …     

从cdmaOne到Cdma2000的无缝演进路径

在２０００年世界无线电大会上，第３代移动通信系统（３Ｇ）的地面系统被确定可使用５种无线传输技术，它们是ＣＤＭＡ－ＤＳ、ＣＤＭＡ－ＭＣ、ＣＤＭＡ－ＴＤＤ、ＴＤＭＡ－ＳＣ和ＴＤＭＡ－ＴＤＤ。其中前３种基于ＣＤＭＡ（码分多址）技术，后两种基于ＴＤＭＡ（时分多址）技术。可见，在３Ｇ标准中，ＣＤＭＡ是主流技术。ＣＤＭＡ（Ｃｏｄｅ Ｄｉｖｉｓｉｏｎ Ｍｕｌｔｉｐｌｅ Ａｃｃｅｓｓ）蜂窝系统由于采用了一种称之为扩频的通信技术，所以与采用ＴＤＭＡ和ＦＤＭＡ（频分多址）的ＧＳＭ蜂窝系统相比，具有抗干扰性好、系统容量…     

日本和泰国共同实验第三代移动通信

日本ＮＥＣ１９９９年３月２日和ＴＯＴ（泰国电话公司）签署一项协议,决定共同实验第三代移动通信系统Ｗ－ＣＤＭＡ,预计１９９９年１１月前后开始现场试验。ＮＥＣ准备以此为契机扩展自己的Ｗ－ＣＤＭＡ在全球的势力。该实验将由日本ＮＥＣ提供无线基站设备、无线控制、交换模拟设备等一套Ｗ－ＣＤＭＡ系统和终端,同时还和ＮＴＴＤｏＣｏＭｏ一起对ＴＯＴ进行技术支持。自１９９８年３月ＮＴＴＤｏＣｏＭｏ和ＴＯＴ建立关于第三代移动通信系统的相关协作关系以来,ＮＴＴＤｏＣｏＭｏ和ＮＥＣ一直力图和ＴＯＴ进行Ｗ－ＣＤＭＡ系统的技…     

无线多媒体码分多址(CDMA)通信

随着多媒体业务的普遍应用和发展,必然要求无线通信能够提供语音、数据、图像等相关业务。由于多媒体业务中各业务的信息速率、业务质量（ＱｏＳ）及业务特性方面的差异,如何有效地利用有限的系统资源以满足多媒体通信的要求是无线多媒体通信系统的一个重要课题。码分多址（ＣＤＭＡ）技术以频谱利用率高、抗多径、抗干扰、软容量、软切换、宏分集等特点,被认为将是移动通信中最主要的多址接入手段,它为无线多媒体系统的实现提供了一个可行方案。本文分析了无线多媒体ＣＤＭＡ通信中的宽带ＣＤＭＡ技术、时分双工通信方式并简要介绍了其中的一些传输、控制技术。     

基于网络的视频通信系统的设计

随着移动通信和多媒体通信的飞速发展,构建于无线网络之上的多媒体服务已经被越来越多的用户所接受。2．5代移动通信CDMA的典型带宽为30～50kb／s,可以传输低速的视频,但是对多媒体应用来说,其质量还是未能达到要求。在现有技术条件下,如何在CDMA无线信道中保证视频流的质量以及如何扩大带宽提高视频质量,是值得研究的问题。文中提出了一种在多个CDMA通道中进行视频传输的框架,利用多个CDMA无线信道绑定的方法,提高了视频的帧率和分辨率。     

Capacity Analysis for Connection Admission Control in Indoor Multimedia CDMA Wireless Communications

In this paper, the capacity analysis for connection admission control is presented for the reverse-link transmission of a packetized indoor multimedia wireless communication system using direct sequence code division multiple access (DS/CDMA). Since CDMA is interference limited, the signal-to-interference-plus-noise ratio criterion is used to check if there is enough system resources (i.e., the CDMA channels and received signal power) for each new connection request. Taking into account the stochastical nature of multimedia traffic, the effective bit rate is used to characterize the resources required by each mobile user and a linear approximation is then used to find the total resources required by all the mobile users already admitted to the system and the new connection request. Transmission errors due to both base station buffer overflow and wireless channel impairments are considered. The capacity of multimedia traffic is determined in such a way that the utilization of the system resources is maximized and, at the same time, the required transmission bit error rate and transmission delay of all users admitted to the system are guaranteed. Computer simulation results are given to demonstrate the performance of the proposed method for capacity analysis.     

A complementary codes‐based CDMA architecture for wideband mobile internet with high spectral efficiency and exact rate matching

The future wireless communication systems ought to offer high spectral efficiency and flexibility to carry multimedia services with variable rate requirements. The data rate change should be made scalable, continuous and real‐time based to match exactly to what required in different content for conservation of precious bandwidth. The rate change in multiples of two, as implemented in the UMTS W‐CDMA standard, is clearly undesirable. In particular, the multiple access technique itself should support asymmetrical traffic in up‐ and down‐links to fit different connection modes of Internet‐based applications. This paper is to propose an innovative CDMA architecture based on complete complementary (CC) codes, which can address all above concerns. The architecture makes use of ‘offset‐stacked’ spreading modulation, based on which both high spectral efficiency and flexible rate matching are guaranteed. The proposed CC–CDMA system can support continuously alterable data rates, which can match exactly to the user demand without the need of complex ‘rate‐matching’ algorithms. Copyright © 2003 John Wiley & Sons, Ltd.     

MISO CDMA transmission with simplified receiver for wirelesscommunication handsets

The next-generation wireless personal and mobile communication systems are expected to accommodate not only high-quality voice services, but also a broad range of other multirate services. Of the various multiaccess techniques, wide-band code-division multiple access (CDMA) has been regarded as an important part of the third-generation wireless communication systems because of its high frequency utilization efficiency and suitability for handling multimedia and multirate services. In this paper, we consider a system with a simplified receiver structure for direct-sequence CDMA (DS/CDMA) wireless communication handsets, in which improved performance is demonstrated when compared to a conventional DS/CDMA system with a RAKE receiver at the mobile station. We arrive at this system by finding the optimal solution to a general multiple-input single-output (MISO) DS/CDMA smart antenna system. We find that this solution reduces to a pre-RAKE with space transmit diversity system under the assumption that a simple one-finger matched filter is used at the receiver. This system combines the advantages of pre-RAKE diversity and transmit antenna diversity. It is shown that significant system performance and capacity improvements are possible. The numerical results also reveal that this system is not too sensitive to channel estimation errors     

Uplink channel assignment with balanced load for code division multiple access cellular systems

In a code division multiple access (CDMA) wireless communication system, each mobile handset must be power controlled such that the power received at the base station is roughly the same. Otherwise, the interferences between mobile handsets will degrade the performance and increase the error rate. When a mobile handset uses channels from the neighbouring cells, it will raise its power to meet the threshold of signal strength. This will also increase the interference in the home cell. Therefore, we do not want a mobile handset to use channels from other cells blindly. In this paper, we propose an uplink channel assignment method based on the directed retry concept for CDMA cellular systems. The purpose is to achieve load balancing between neighbouring cells and at the same time controlling the interference levels at the base stations such that it will not affect the performance. Furthermore, priorities are given to handoff calls when assigning channels. Copyright © 2002 John Wiley & Sons, Ltd.     

Power control for wireless multimedia CDMA systems

In a wireless multimedia communication system where different types of traffic such as speech, data, and video have different data rates, good power control for individual traffic can ensure quality of service (QoS) and achieve a better throughput at the same time. The authors propose a closed-form power control function based on a parameter called the traffic exponent that simplifies the power control processing and improves the overall CDMA system performance     

Scheduling with base station diversity and fairness analysis for the downlink of CDMA cellular networks

Efficient packet scheduling in CDMA cellular networks is a challenging problem due to the time variant and stochastic nature of the channel fading process. Selection diversity is one of the most effective techniques utilizing random and independent variations of diverse channels to improve the performance of communication over fading channels. In this paper, we propose two packet scheduling schemes exploiting base station selection diversity in the downlink of CDMA cellular networks. The proposed schemes rely on the limited instantaneous channel state information (CSI) to select the best user from the best serving base station at each time slot. This technique increases the system throughput by increasing multiuser diversity gain and reducing the effective interference among adjacent base stations. Results of Monte Carlo simulations are given to demonstrate the improvement of system throughput using the proposed scheduling schemes. In addition, we investigate fairness issue of wireless scheduling schemes. Due to different characteristics of wireless scheduling schemes, the existing fairness indexes may result in misleading comparison among different schemes. We propose a new fairness index to compare the overall satisfaction of the network users for different scheduling schemes. Copyright © 2006 John Wiley & Sons, Ltd.     

Perspectives for present and future CDMA-based communications systems

In this article the main boosters of future CDMA communication systems are presented and described in order to highlight the ways to cope with the more challenging requirements of future systems and services. Particular attention is devoted to the inherent weak points of CDMA systems and detection techniques that can be used to overcome their impairments. Moreover, high-data-rate transmissions in wireless channels require proper link adaptation techniques; these are thoroughly described as well. Finally, the last part of this article focuses on the design of suitable protocol strategies for new heterogeneous multimedia packet services characterized by strict QoS requirements     

Adaptive nonuniform phase-shift-key modulation for multimediatraffic in wireless networks

The characteristics of mobile wireless communication channels fluctuate for many reasons, including movement of the radios, changes in path attenuation, and variations in interference. Several adaptive signaling techniques have been proposed for use in wideband code-division multiple-access (CDMA) systems including adaptive data rates, adaptive spreading code rates, discontinuous transmission, and multicode CDMA. We introduce adaptive signaling techniques that use nonuniform phase-shift-key (PSK) modulation. These techniques have several advantages for use in CDMA communications, and they support multimedia transmission by simultaneously delivering different types of traffic, each with its own required quality of service. The signaling methods that we propose deliver a basic message at a specified error rate and simultaneously deliver an additional message by exploiting any extra capability that is available. We show that by adapting the location of the points in a PSK constellation, the throughput can be maximized for the additional message while maintaining an acceptable error rate for the basic message. Responses to larger changes in channel quality are accomplished by adapting the PSK constellation size, signaling rate, and error-correcting code. Examples of adaptive signaling schemes that employ nonuniform PSK constellations are presented, including an application to a cellular CDMA system