宽带CDMAWL系统的数字接收机的实现

无线本地环（WLL）是一种无线接入系统,它用无线的方式代替了传统的铜线连接用户到本地交换机。介绍了一种用于宽带CDMA WLL系统的数字接收机。叙述了WLL的系统组成、网络结构、反向链路信道结构和反向中继接收机设计规范,并论述了代码捕获和代码跟踪模块的功能。接收机的运行时钟频率可达65．536MHz。     

固定无线宽带接入技术

1无线接入网概述 无线接入网又称为无线本地环路(WLL),由无线基站和用户单位组成.无线基站包括基站收发信机、基站控制器,它提供一个面向程控交换机的标准网络接口V5接口和面向用户侧的空中接口,并完成无线接口的认证和保密、无线资源管理、用户单位登记、路由选择、计费维护以及协议转换、语言与数字的代码转换等功能.用户单元包括收发信机,并提供一个面向基站的无线接口和而向用户的传统接口.传统接口实现协议转换、代码转换、认证、本地供电等功能.交换机与基站之间用数字传输系统相连.基站把网络侧进来的复合网络标准的数字信号,转换成数字空中接口信号.用户单元接收机站送来的无线信号,并将其转换成为模拟信号或者标准数字信号,再用有线手段与用户设备相连.     

数字无线本地环路系统

无线技术使得发展中国家能快速地为适应21世纪的要求改进他们现有的电话网络。无线本地环路(WLL)系统使用无线技术提供可靠的、灵活的和经济的本地电话服务,以取代传统的铜钱环路。WLL有时被称为“固定蜂窝系统”。 从服务提供者的角度来看,WLL的最重要的好处是投资成本低,网络扩容十分迅速,以及较低的维护费用和丰厚的补偿。另外,在建立一个WLL系统的过程中不需要知道用户的精确位置,这样就为系统的规划和部署增加了灵活性。已经证明WLL网络有能力在灾     

无线本地环路的研究与应用

无线本地环路（WLL）技术发展迅猛。本文在介绍WLL系统结构的基础上，着重对其技术类型和业务应用进行了探讨，并就我国发展WLL技术的有关问题提出了建议。     

无线接入技术的应用

从电信部门的业务提供点（如交换机,CATV中心）到用户之间的网络称作用户接入网,而无线接入是完成用户接入网的一种重要的接入方式。无线接入技术也称无线接续技术,或称无线本地环路（WLL）,其主要功能是以无线技术为传输媒介向用户提供固定或移动终端的业务。无线本地环路为有线接入提供了一种应用形式灵活、系统经济可靠、实现方便、维护简单的通话方案。因此,无线接入技术受到各国电信业的高度重视。一、国内无线接入技术选用及频率使用应注意的问题1．设备选型上要因地制宜,适度超前无线接入采用的技术多种多样,应用形式五花…     

基于宽带CDMA技术无线本地环路系统设计

介绍了一种基于宽带码分多址(CDMA)技术的无线本地环路(WLL)系统的设计,重点分析讨论了这种基于宽带CDMA的WLL系统的空中接口协议和系统结构的组成、特点及功能。     

浅谈无线本地环路接入网技术及其应用

一、无线本地环路(WLL)接入网系统的组成 WLL又称无线微区蜂窝接入网,是采用个人手持电话系统PHS和DLC两种系统技术集成的本地接入网系统,这里强调的是“接入”,它是将遥远的用户接入到公用网,而不是交换机移到用户区来。     

无线本地环路技术

所谓无线本地环路(WLL）,就是采用无线技术,接入本地公众网,向用户提供电信业务,通过建立无线本地环路系统,可使已建立电信网的运营商利用现有的交换机资源,快速开展和经济地提供电信业务,避免与有线线路安装和维护有关的瓶颈;对新业务运营商来说,无线本地环路系统可使之能因电信政策变化获得更多的机会,在市场竞争中有立足之地。     

基于W-CDMA的WLL系统设计

文章介绍了一种基于W－CDMA（宽带码分多址）技术的WLL（无线本地环路）系统的设计。首先说明了无线本地环路的特点,并分析了选用W－CDMA方案可以很好地满足用户日益增长的业务需求并可以实现向第三代无线通信系统（IMT－2000）的平稳过渡。然后重点分析讨论了这种基于W－CDMA的WLL系统的空中接口协议和系统结构的组成、特点和功能。     

无线本地环路技术及其在电信普遍服务中的应用

文章对无线本地环路技术及CDMA450系统进行了简要说明,并对目前存在的几种WLL系统从性能上进行了对比。通过对系统容量的分析,提出了进一步改善CDMA450系统容量的方法。     

Reverse link performance of wireless local loop CDMA networks

We study the effect of directional subscriber antennas on the reverse link performance of a power-controlled code-division multiple access (CDMA) network in wireless local loop deployments. We investigate the capacity gain that is attained in wireless local loop (WLL) CDMA over mobile cellular systems and its variation as a function of the channel statistics. We also determine the overhead that soft handoff and directional subscriber antennas impose on the WLL system capacity     

The effect of narrowbeam antenna and multiple tiers on systemcapacity in CDMA wireless local loop

The wireless local loop (WLL) system is a local telephone system without wireline connection. It is believed to be a fast and cost-effective means to provide local phone service in rural areas and third world countries. WLL is a fixed radio communication system; narrowbeam antennas can be employed at both the base station and subscriber's side at high spots so that the propagation between base station and house is very close to free space propagation. This gives the WLL system many inherent advantages over the traditional cellular system, such as bigger coverage area, low power, reduced interference, higher capacity, no fast fading, and no handoff. In this article ideal multiple-tier hexagonal cells are used to derive the capacity of a CDMA WLL system. First, the reverse link interference from each tier to the center cell is calculated separately. Then, the interference ratio of reverse links in a WLL system is analytically derived as a function of total tier number. The result shows that interference from other cells is proportional to the beam width of the house antenna. The authors also found that tier number plays a vital role in system capacity in a free-space propagation (20 dB/dec) environment. At the extreme, the system capacity will drop to zero for an infinite-tier cell structure. A WLL simulator is also built to verify the authors' analytical solution     

A single-chip 2.4-GHz direct-conversion CMOS receiver for wirelesslocal loop using multiphase reduced frequency conversion technique

A single-chip direct-conversion CMOS receiver for 2.4-GHz wide-band code-division multiple-access wireless local loop (WLL) is described. The chip includes a low noise amplifier, a 12-phase downconverter, a variable gain amplifier, a g_m-C channel selection filter, a programmable phase-locked loop for seven channel frequencies, and a 4-bit flash analog-to-digital converter. The proposed multiphase reduced frequency conversion scheme combined with a multiphase sampling fractional-N prescaler, a cascaded dc-offset canceler and distributed automatic gain control loops offers solutions to problems of a direct-conversion receiver. Experimental results show -115-dBm sensitivity, 4.4-dB noise figure, and 95-dB dynamic range, which sufficiently meet commercial WLL specification     

A wireless local loop system based on wideband CDMA technology

This article describes a wireless local loop system based on wideband CDMA technology. The unique features of CDMA technology make it a formidable alternative for fixed wireless telephone applications. The W-CDMA technology used by this WLL system is selected to provide primarily ISDN-like services and data rates to subscribers. This technology also provides a smooth transition into the third generation wireless technology. The air interface used in this WLL system is an interim TTA standard, which specifies a CDMA-based protocol operating in the 2.30-2.40 GHz band. The standard allows two types of bandwidth (5 and 10 MHz). The WLL system described in this article includes the WLL gateway switch, the radio port controller and the radio interface unit. The gateway switch connects the radio system to the PSTN and ISDN. The RPC provides concentration and control functions to a number of base stations called RPs. The RIU is comprised of the fixed units attached to the residential or commercial buildings. Also included are the radio port operation and maintenance (RPOM) unit, which is responsible for maintaining and managing the radio network elements, and the interworking function unit, which is used as a gateway to data services such as the Internet and PSPDN     

Improvements in W-CDMA: principles and experimental results

This article first reviews the channel structure and spreading code assignment for the physical layer and transport channel multiplexing along with a sophisticated rate-matching scheme that accommodates composite transport channels with various levels of quality of service (QoS) on one physical channel. Then, the key technologies of wideband ds-cdma (w-cdma) wireless access are presented and the results of experiments pertaining to these technologies are evaluated. Flexible system deployment is possible by employing inter-cell asynchronous operation with a three-step fast cell search method. The signal-to-interference power ratio (sir) measurement based fast transmit power control (tpc) guarantees the minimum transmit power according to the channel load and the changes in the link conditions due to fading. Furthermore, various diversity technologies are described such as pilot symbol-assisted (psa) coherent Rake combining, antenna diversity, site diversity (soft/softer handover), and transmit diversity in the forward link that are effective in decreasing the required transmit power, which results in increases system capacity. This article also presents link-capacity enhancing techniques such as using an interference canceller (IC) and adaptive antenna array diversity (AMD) receiver/transmitter. Experimental results are presented for an actual multipath fading channel that indicate the potential of the IC and aaad transceiver to decrease the mobile transmit power in the reverse link and interference from high rate users with high transmit power in the forward link.     

Digital wireless local loop system

The digital access technologies for the wireless local loop (WLL) or fixed wireless system are discussed. WLL is an important means of providing telephone services more cheaply and quickly in the developing countries than through a wireline system. Capacities of a WLL system based on the IS-54 (now IS-136) TDMA, IS-95A CDMA, and ETSI GSM technologies are developed and compared     

一种新型室内无线光通信系统结构

在几种基本的室内无线光通信结构基础上,设计了一种新型系统结构,重点对其光学系统构造和模块实现进行详尽描述,使得该系统能在直射式视距链接通信和非直射式链接通信之间互相转换,既能在链路无障碍时高速率通信,又能在链路有障碍时保持连接的持续连通性。     

对利用PHS技术实现微小区无线接入系统的探讨

本文介绍了无线本地环路（ＷＬＬ）的发展，并着重分析了一种典型的微小区无线本地环路系统－美国ＵＴＳｔａｒｃｏｍ的ＡＩＲＳＴＡＲ－ＷＬＬ的结构、功能特点及应用。     

Adaptive interference cancellation for DS-CDMA systems using neuralnetwork techniques

The objective of this study is to apply and investigate a neural network-based decision feedback scheme for interference suppression in direct sequence code division multiple access (DS-CDMA) wireless networks. It is demonstrated that a decision feedback functional link equalizer (DFFLE) in combination with an eigenvector network can closely approximate a Bayesian receiver with significant advantages, such as improved bit-error ratio (BER) performance, adaptive operation, and single-user detection in a multiuser environment. It is assumed that the spreading codes of the interfering users will be unknown to the receiver. This detector configuration is appropriate for downlink communication between a base station and a mobile user in a digital wireless network. The BER performance in the presence of interfering users is evaluated. The improved performance of such a DFFLE receiver for CDMA is attributed to the nonlinear decision boundary it evaluates for the desired user. The receiver structure is also capable of rapid adaptation in a dynamic communications scenario for which there is entry/exit of users and imperfect power control. The convergence performance and error propagation of the DFFLE receiver are also considered and exhibit reasonable promise for third generation wireless DS-CDMA networks     

A Novel Detection Algorithm Efficient for Turbo Coded CDMA Signals in Detect and Forward Cooperative Channels

In this paper, a new detection algorithm is proposed for turbo coded Code Division Multiple Access (CDMA) signals in detect and forward cooperative channels. Use of user cooperation makes much improvement in the performance of CDMA systems. Due to the special structure of CDMA systems, cooperative schemes increase the sum and cutoff capacities of CDMA based wireless systems and improve the quality of user-partner link which enhances the overall performance of the system. In this paper, a new combining scheme is proposed that makes the receiver more robust against the decision errors in the partner link. This structure is simulated for punctured 1/2 rate 4 states turbo code in a channel with first order Markov time variation and different Rice factor variances. Through various simulations, it is shown when the channel estimates are available in the partner and receiver, the cooperation between users provides much diversity gain especially while using the new proposed combining algorithm.