TD-SCDMA系统所采用的技术(二)

３综合采用各种多址方式TD-SCDMA系统综合使用CDMA、TDMA、FDMA和SDMA四种多址方式，充分发挥码分、时分、频分和空分制式技术优势，最大限度地提高系统容量。TD-SCDMA多址技术原理如图1所示，其三维空间分别为CDMA码道、频率和时间。图1是典型的TD-SCDMA信道结构，三个载波带宽为1.6MHz，用TDMA方式将每个载波分为7个业务时隙（5个下行时隙DL和2个上行时隙UL）和1个DL/UL隔离时隙，采用CDMA技术将每个时隙扩频，最多可得16码道（即扩频系数为16），每个码道可传输一个用户信息。TD-SCDMA的基本信元（RU）由时…     

CDMA移动电话测试指标及维修

1 概述 CDMA通信体制与目前常用的FDMA和TDMA不同,它通过采用Hadama矩阵排列算法得到不同的扩频码来区分不同的用户（多址连接）。当发/收两端的扩频码不匹配时,在接收端收到的是噪声;当发/收两端的扩频码相匹配时,接收机通过相关接收可获得相关峰,然后就可以解调出有用的信息来。从理论上来说,全球的CDMA用户可以共享同一时间资源、同一频率资源。例如:中国联通的CDMA用户可以在同一时间共用CH283信道（前向信道即BS发的频率为:878.49MHz,反向信道即手机发的频率为:833.49MHz）。但实际上,由于互相关性足够好的扩频码数量有限,故在CDMA通信体制中还要用到其他的信道,例如CH384、CH777等等。CDMA通信的理论基础可以用非常著名的Shanon公式来说明:     

利用联合CDMA/TDMA多址协议实现多媒体信息传输

语音、数据和视频(该文限于可视电话、电视会议)等多种形式的信息传输是3G系统具备的重要特性。该文提出的联合CDMA/TDMA协议综合了两种多址方式的优点,采用动态分配码信道和时隙的方式,可以很好地满足不同业务信息的性能需要。文中给出该协议中信道模型以及各业务模型,并对系统的性能进行了分析。     

时隙多码CDMA和单码 CDMA多址接入技术研究

CDMA作为一种多址接入技术在无线网络中已广为应用.本文在多码CDMA和单码GDMA研究的基础上,构造了时隙多码CDMA和单码CDMA在无线分组数据网络中的随机多址接入模型,并且分析了两种系统的吞吐率特性和归一化时延特性.     

对多载波CDMA方案的分析

目前，第三代移动通信的主流标准(包括TD-SCDMA、WCDMA和cdma2000)都是采用扩频码分多址(CDMA)方式作为其空中接口的技术，由于CDMA技术可以提供比传统多址技术(例如：TDMA、FDMA)更大的系统容量，并且具有抗信道频率选择性衰落的良好特性，该技术就成为未来支持无线移动通信中高速数据多媒体业务的有力竞争者。     

CDMA多用户传输系统物理层仿真

为了研究CDMA系统抗多址干扰和多径干扰能力的目的,采用同一信道下比较调制对系统性能的影响,以及相同的调制方法下比较不同信道系统的性能的方法,做了对CDMA多用户传输系统的仿真实验,获得CDMA通信系统抗多址干扰和抗多径干扰能力与系统扩频码正交性能之间的关系,得到CDMA系统优化性能的结论,并通过仿真实例验证各种传输模型的特点。     

CDMA中几个值得注意的问题

一、CDMA蜂窝移动通信发展概要 数字蜂窝系统在多址方式上主要采用TDMA(如GSM;DAMPS;PDC)或CDMA(QCDMA;BCDMA;SCDMA)。 90年代初,美国提出了CDMA数字蜂窝移动通信系统,其发展速度惊人,1993年7月17日美国TIA正式公布了CDMA公共空中接口标准IS-95(QCDMA),使其成为与TDMA并驾齐驱的数字蜂窝移动通信系统。 IS-95公共空间接口是双模式(CDMA/AMPS)接口标准,俗称QCDMA,其接口标准如下:     

CDMA系统与GSM系统兼容性分析及计算

随着中国联通CDMA网络的开通，大量的CDMA基站及直放站被建设，系统覆盖日趋完善，其高效的频谱利用率及优良的语音通话质量，使CDMA迅速发展壮大起来。但是，CDMA系统与GSM系统的电磁环境兼容问题也日益突出，严重时导致系统无法工作。1 系统间干扰问题分析GSM、CDMA蜂窝通信系统不同的通信特点决定CDMA系统与GSM系统的电磁环境兼容问题主要是CDMA系统对GSM系统的干扰。CDMA是一种以扩频通信为基础的调制和多址连接技术。扩频通信技术在信号发端用一高速伪随机码与数字信号相乘，由于伪随机码的速率比数字信号的速率大…     

基于Fast-ICA的CDMA信号扩频序列盲估计及性能分析

DS-CDMA分为长码和短码扩频2种扩频方式,已有的扩频序列盲估计算法只适用于短码扩频信号,不能完成长码扩频信号的扩频序列估计。对长码扩频CDMA信号的数学模型进行分析,提出了一种的新的基于Fast-ICA的多用户扩频序列盲估计方法并推导了算法的理论性能。该方法不仅能适用于长码扩频CDMA信号,而且对同步短码扩频CDMA信号也同样适用。理论分析和仿真结果验证了该方法的有效性。     

平坦瑞利衰落环境下CDMA系统的多用户检测性能

在采用传统信号检测方式的CDMA无线通信网中,多址干扰限制了系统的容量和性能。多用户信号检测利用扩频码互相关信息在高斯信道中可以减小或消除多址干扰,缓解远近效应,增加系统容量。本文将多用户检测器直接用于平坦瑞利衰落的CDMA环境中,用分析与仿真相结合的方法讨论了典型多用户算法的误码性能。结果表明,平坦瑞利衰落信道中多用户检测算法的性能仍然优于传统检测算法。     

CDMA／SDMA系统性能分析

空分多址接入技术（SDMA）可以通过信号不同的空间传播路径来区分用户，从而提高了蜂窝移动通信系统容量．而此技术又可以和其他多址方式相互兼容，比如频分多址，时分多址，码分多址．CDMA／SDMA系统就是码分多址和空分多址两种接入技术相结合的系统．该系统可通过时空编码实现的．文中分析此种系统的性能，并与多用户环境下的CDMA系统进行了比较．     

Spreading Codes Generator for Wireless CDMA Networks

The prime characteristic of spread spectrum modulated signals is that their bandwidth is greater than the information rate. In this way a redundancy is introduced that allows the severe levels of inteference inherent in the transmission of digital information over radio and satellite links to be overcome. Current spread spectrum applications are primarily in military communications; nevertheless, there is growing interest in this technique for third generation mobile radio networks (UMTS, FPLTS, etc.) with open discussion regarding the practicality of using a multiple access system based on spread spectrum techniques (CDMA). However, in order to support as many users in the same bandwidth as other multiple access techniques such as TDMA or FDMA, it is important how to generate large families of sequences that present low cross-correlation. The aim of this paper is to describe a spreading codes generator that can produce a large number of PN sequences with good properties of auto- and cross-correlation. Moreover, the codes generated shows high unpredictability and good statistical behaviour. This also allows the implementation of some features that are common on military networks such as message privacy (increasingly important in commercial networks) without additional cost. The structure presented shows itself to be advantageous for high speed generation of codes at a low cost, low power consumption (allowing longer life for batteries), small size and simplicity of implementation, essential ingredients for commercial equipment. Another attractive feature is its structural parallelism, useful in VLSI implementations. All of these features render it potentially suitable for the implementation of channel bandwidth sharing systems in future wireless personal communications networks.     

码分多址系统的抗干扰分析

对于800MHz频段码分多址(CDMA)系统基站和直放站的杂散辐射对全球移动通信系统(GSM)900的干扰限制,信产部无(2002)65号文已作了明确规定。至于GSM900对CDMA的干扰,以及GSM1800和个人接入系统(PAS)等时分多址系统对第三代移动通信系统中宽带码分多址(WCDMA)系统的干扰影响有多大,文中以CDMA系统的抗干扰机理为基础,分析多系统共(站)址时这些干扰对CDMA系统容量的影响。工程实践中,通常采用滤波器来减少干扰对系统容量的影响,文中推导的公式可用来计算滤波器的衰减指标。     

A CDMA scheme based on perfect Gaussian integer sequences

Both m-sequences and Gold sequences have been applied as the pseudonoise (PN) code in the code division multiple access (CDMA) scheme to enable distinct users to simultaneously share the available capacity of a common channel, which is called direct sequence CDMA (DS-CDMA). However, this scheme does not provide the required ideal periodic cross-correlation function property among various members of sequences within the same set. This paper proposes a new perfect Gaussian integer sequence (PGIS)-based CDMA scheme called PGIS-CDMA; in this scheme, the PN code of DS-CDMA is replaced by a set of PGISs. The intrinsic orthogonal property of PGIS can be applied to a CDMA system to achieve perfect cochannel interference separability under the ideal synchronism; it can also be adapted at the receiver to obtain diversity gain and improve the carry-to-interference ratio. These two concepts are further developed to implement two PGIS-CDMA configurations, and they can outperform DS-CDMA on the basis of Gold sequences that possess a favorable cross-correlation property for the CDMA scheme.     

无线局域网中的预约CDMA接入技术

在传统的无线ＭＡＣ接入协议（如ＡＬＯＨＡ,ＣＳＭＡ／ＣＡ,ＴＤＭＡ和ＣＤＭＡ）的基础上,重点探讨了基于码分多址的预约ＣＤＭＡ无线多址接入协议。该协议的在无线局域网接入时,无论在时间延迟还是吞吐量特性方面均比传统的无线接入协议有很大的改善。     

A Cyclodespreader Architecture for Detecting Multiple Downlink Aperiodic CDMA Signals

Although a code-division multiple-access (CDMA) system is spectrally efficient and has some immunity against intentional reception, its capacity and performance are generally limited by multiple access interference (MAI) caused by other users. For an aperiodic CDMA system, the spreading sequences span multiple symbol intervals, and the cross-correlations between these sequences, which are a measure of the MAI, are periodic over multiple symbols. In this paper, we present a receiver with a parallel architecture that converts an aperiodic CDMA sequence into a piecewise periodic sequence in each arm. We refer to this receiver as a cyclodespreader because the despreader exploits the cyclostationary property of an aperiodic signal. As a result, the transmitted data can be detected separately in each arm of the receiver using low-complexity conventional algorithms proposed for periodic CDMA systems. The goal of the receiver is to decode several signals received from different cochannel base stations. The performance of the system is evaluated using real aperiodic CDMA signals, and it is compared to that of a conventional matched filter (MF) receiver using the number of correctly decoded messages as the performance measure.     

莱斯衰落信道中混合FDMA/CDMA性能分析

分析混合频分多址／码分多址系统在莱斯多径衰落信道的性能,并与占据相同带宽的宽带ＣＤＭＡ系统进行比较。系统采用二进制ＤＰＳＫ调制和瑞克接收机。结果表明,直达 径分量较强或信噪比较大时,混合系统的性能优于宽带ＣＤＭＡ系统,否则,宽带ＣＤＭＡ系统最优。     

OFDM-CDMA及其检测技术

传统的CDMA技术在无线通信方面有着FDMA和TDMA所无法比拟的突出性能,但在抗码间串扰和多址干扰方面存在的问题使其总体性能受到限制。随着DSP技术的发展,采用并行传输的OFDM技术正日趋成熟。本文介绍了一种新的无线通信技术OFDM-CDMA,对其发送和接收系统模型进行了完整的描述并分析了接收机中使用的几种检测技术,在频谱利用率、抗多径和多址干扰等方面,OFDM-CDMA等优于传统的CDMA技术。     

GSM和QUALCOMM CDMA系统信号设计方案的分析和比较

ＴＤＭＡ和ＣＤＭＡ方式是当前数字移动通信中的两大主注，本文以其各自的典型系统（即泛欧的数字蜂窝移动通信系统ＧＳＭ和Ｑｕａｌｃｏｍｍ公司的ＣＤＭＡ系统）为例，分别对它们的信号设计方案进行了分析和比较，并从中反映出了两个系统各自的特点和共同之处。     

Throughput analysis for interference limited TDMA and TDMA/CDMA wireless ad hoc networks

The node throughput, which is defined as the total rate received at each node, is evaluated for the interference limited TDMA and TDMA/CDMA wireless ad hoc networks. In the TDMA wireless ad hoc network, there is only one transmission link connected to each node in the same time slot, whereas in the TDMA/CDMA wireless ad hoc network there are multiple transmission links connected to each node in the same time slot. We first derive the node throughput for these two wireless ad hoc networks and then make a comparison of the node throughput between them. The theoretical results and simulation results both reveal that the TDMA wireless ad hoc network outperforms the TDMA/CDMA wireless ad hoc network in the node throughput. Copyright © 2008 John Wiley & Sons, Ltd.