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1、Using DS-CDMA to Realize Bi-direction Communications in CATV Network直接使用码分多址序列实现双方向通信有线电视网络 Abstract：In this paper， a new scheme using DS-CDMA to realize BiDirection communications in CATV network is addressed As a colusion，we can find that this is an economical realization of access network，having

2、good performances compared with some other schemes文摘:在这篇文章中,一个新的计划在有线电视使用码分多址实现双向通信网络解决。作为一个解决方案,我们可以发现这是一个经济的实现访问网络,与其他方案相比具有良好的性能。1 Introduction 1.介绍With the development of modern communications, the access network technology is showing its great importance day by day.随着现代通信的发展,接入网技术正显示出其重视。The ac

3、cess network technology can be divided into four categories：advanced cotton cable technology， FITL system，CATV network and WLL system接入网技术可分为四类:先进的棉花电缆技术,光纤环路系统、有线电视网络和系统广泛分布有线电视网络。The popularly distributed CATV network，for its relatively low price and good broad band transport characteristics， may

4、be the most prospective media to realize multi-service communications including voice， data and moving picture因其相对较低的价格和良好的宽带运输特点,可能是最准媒体实现多业务通信包括语音,数据和移动图像。In this paper，a new scheme using DSCDMA to realize Bi-Direction communications in CATV network is addressed在本文使用码分多址的新方案在有线电视网络实现双向通信地址。As a co

5、lusion，we can find that this is economical and with good performances compared with some other schemes作为一个解决方案,我们可以发现这是经济和与其他方案相比具有良好的性能。2Existing CATV Network2.现有的有线电视网络 The CATV network is a hierarchical and single-directionsystem，as we can see from Fig1， composed of three parts：front end part，tra

6、nsportation part and user distribution part. In the tranportation lines，there are many equipments such as amplifiers， branches and distributors有线电视网络层次和发展性系统,从图1中我们可以看到,由三部分组成:前端部分,运输和用户分配部分。交通运输线路,有很多设备如放大器、分支机构和分销商。3.Bi-direction System Design3.双向系统设计 In order to make Bidirection communication ava

7、ilable， we divide the whole bandwidth into twos：050 MHz as theupward passway and 50-400 MHz as the downward passway It is also needed to change the existing single direction equipmentsin transportation lines into Bi- direction equipments， JustAs Fig2 为了提供双向的沟通,我们将整个带宽分为两个:0-50 MHz的上行通道和50 - 400 MHz下

8、行通道。它也需要改变现有的单一方向的设备在运输到Bi -方向行设备,如图2所示。4 Features of Spread Spectrum Communication 4. 特性的扩频通信In the spread spectrum communication systems，the data is applied to a narrow-band modulator and the resulting narrow-band signal is widely spread using the spreading code (always the PN code) at the transim

9、ter在扩频通信系统中,数据是应用于窄带调制和由此产生的窄带信号被广泛传播使用传播代码(总是PN码)晶体管。The transmitted spread signal with interferring signals and noise is despread by the same spreading code and the resulting narrow-band signal is demodulated at the receiver传播信号干涉信号和噪声是由相同的传播代码解扩和由此产生的窄带信号在接收机解调处理。Because the spread signal can be

10、demodulated even in the presence of noise and interferring signals with higher spectrum densisties than the signal，it means that the spread signal has resistance to interferring signals and interception因为可以解调的信号传播甚至在噪声的存在和干涉信号频谱密度高于信号,这意味着传播信号抗干涉信号并拦截。By using PN codes to spread the narrow-band sign

11、al，it can support simutaneous digital communication among a large community of relatively uncoordinated users 利用PN码传播窄带信号,它可以支持同步数字通信的一个大型社区间的不协调用户。This is called code division multiple access(CDMA) which has been widely used in satelite communications and mobile communications这叫做码访问(码分多址)已广泛应用于卫星通信

12、和移动通信。5Physical Layer Design5.物理层设计 First we divide the 50 MHz bandwidth into 5 FDM channels for each FDM channel is 10 MHz首先我们将50 MHz带宽划分为5的频分复用渠道，每个频分复用通道10 MHz.To fulfill the need of data Communication and voice communication together， we make the signal data rates as 38.4k bps满足需要的数据一起交流和语音通信,我们

13、做的信号数据率为38.4 k个基点。 Considering the PN code length as 256，the spread spectrum signal chip rate is 98304 chips考虑到PN码长度为256,扩频信号芯片率是9830.4chips。 If we choose QPSK as the modulation way and use aBPF,we can limit the spread spectrum signal in 10 MHz我们选择芯片，如果选择四相相移键控调制方式和使用瘘,我们可以限制在10 MHz扩频信号。 Theoretical

14、ly，if the PN code were orthogonal and the signals were coordinated，there would be 256 CDMA channels available per FDM channel从理论上讲,如果PN码是正交的信号协调,会有256 码分多址信道可用码分多址通道.But in fact，considering the noise and the uncoordination of the signals， there are less channels availableThe exact number of CDMA cha

15、nnels available depends on the environment noise，the correlation performances of the used PN codes and the bit error rate(BER) needed by the communications但是事实上,考虑到噪声和信号的不协调,有更少的渠道他确切的码分多址信道的数量可用取决于环境噪音,相关性表演用PN码和比特误码率(BER)所需的通信。 In traditional way，the spread spectrum systems were realized by analog

16、 circuits or SAW devices. The resulting systems tended to be large and expensive在传统的方式中,扩频系统实现了模拟电路或设备。由此导致的系统往往是大型和昂贵的。With the development of digital signal processing and VLSI technologies,now we can develop a signal processing ASIC for an all digital spread spectrum Modem for this system.The blo

17、ck diagram of the system is in Fig随着数字信号处理和集成电路技术的发展,现在我们可以开发一个信号处理专用集成电路的这个系统的所有数字扩频调制解调器。 In traditional way，the spread spectrum systems were realized by analog circuits or SAW devices. The resulting systems tended to be large and expensiveWith the development of digital signal processing and VLSI

18、 technologies,now we can develop a signal processing ASIC for an all digital spread spectrum Modem for this system.The block diagram of the system is in Fig.3在传统的方式中,扩频系统实现了模拟电路或设备。由此导致的系统往往是大型和昂贵的。随着数字信号处理和集成电路技术的发展,现在我们可以开发一个信号处理专用集成电路的这个系统的所有数字扩频调制解调器。系统的框图如图3。6 Data Link Layer Design 6.数据链路层设计 O

19、ne CDMA channel of each FDM channel is used as paging channel and the left are used as traffic channels in the downward direction一个码分多址信道的频分复用通道作为分页通道和左作为交通通道向下的方向。 In the same way，one CDMA channel of each FDM channel is used as applying channel and the left are a1so used as traffic channels in the

20、upward direction.All the traffic channels are distributed on need，so the efficiency of the channels utilities is very high and the system can support a great number of users同样的,一个码分多址信道的频分复用通道作为申请通道,左边是用作交通通道向上的方向。需要所有的交通渠道分布,所以渠道实用程序的效率非常高,系统能够支持大量的用户。7Comparison With Other Schemes7.与其他方案的比较 Some tries to use other schemes in CATV network has beenmade， such as using CSMACD to implement a LAN or using FDMA to settle the telephone communicationsIn these schemes，compared with using CDMA, many difficult prob