【作者】 李杰；

【导师】 童明俶；

【作者基本信息】 重庆大学 ， 控制理论与控制工程， 2003， 硕士

【摘要】 随着传统有线电视网络及其设备双向改造的完成， HFC（Hybrid fiber coax），即光纤同轴混合网已成为向用户提供双向宽带综合业务的重要途径。为了兼容传统的有线电视传输模式，HFC网络带宽首先被频分为若干个8 MHZ的频道，这些频道被统一划分为下行和上行信道。上行频带位于5-65MHZ之间，这一频带为高频（HF）和甚高频（VHF）的一部分，此频带易受噪声干扰；此外，由于从光节点到用户端为树型分支结构，同一光节点的多个用户共享同一信道，形成了漏斗效应。因此，上行信道具有频带窄，噪声大的特征，这一特征对上行信道的数据传输具有极大的影响。HFC网络下行信道采用一点对多点的广播方式，用户共享下行资源实现比较简单。上行信道是一个多点对一点的媒体共享信道。所以，目前局域网使用的媒体接入控制MAC协议如：CSMA/CD、令牌等，不适用于HFC网。因此，解决上行信道的噪声问题和上行资源共享是HFC网络能否成为一个多媒体业务通信平台的关键技术之一。目前，很多国际化组织已经针对HFC网络接入双向业务制定了一系列规范。其中最有影响的是IEEE802.14工作组制定的IEEE802.14标准和MCNS提出的DOCSIS规范。前者侧重于ATM信元的传输，提供了完善的QOS支持；后者侧重于变长IP数据包的传输，在DOCSIS V1.1中提出了QOS的概念。无论是IEEE802.14还是DOCSIS两者MAC层协议的设计重点都放在上行信道上，即上行信道的分配，服务调度以及冲突解决等。本文结合当前HFC网络中主要MAC层协议的设计思想从本质上分析了影响协议性能的关键因素，结合上行信道的利用率和数据传输延时这两方面的性能从理论上分析了 HFC网络上行信道的传输机制，并对分析结果进行了仿真。在此基础上提出基于ALOHA与S-CDMA的HFC网络上行资源共享技术，并在理论上对其①抗干扰能力、②上行信道利用率、③传输延时等方面作了详细的分析。证明了新型的基于ALOHA与S-CDMA上行资源共享技术的HFC网络的性能要优于传统的基于TDMA技术的HFC网络。更多还原

【Abstract】 With the development of conventional CATV system and the completion of its equipment’s tow-direction upgrading， HFC（Hybrid Fiber Coax）has become an important way to provide the two-direction integrating broadband service to users. To make itself compatible the transmission mode of the conventional CATV system, the bandwidth of HFC system is divided into many 8MHz channels, which include downstream and upstream channels. Upstream channels cover in 5～65MHz, which is a part of the bandwidth of high frequency（HF）and very high frequency（VHF）. It is liable to incur noises ingress onto the band. Since HFC system has the tree-and-branch topology between the fiber-node and subscriber units, subscriber units belonging to one fiber-node share the same upstream channel , forming the "noise funneling" effect. So the upstream channel has the character of narrower bandwidth and bigger noise. This character has a big influence on data transmission on the upstream channels. The downstream channel is a point-to-multipoint broadcasting channel with a wider bandwidth, while the upstream one is a multipoint-to-point share medium with a narrow bandwidth. So these popular medium access control protocols as CSMA/CD, Token-ring etc. are not suitable for HFC system. Therefore to solve the noises in the upstream channel and to share the sources of the upstream channels becomes one of the key technologies for HFC system to become a multimedia communication platform. Up to now, many international organizations have formed some specification to access the tow-direction services of HFC system. What is important is that the IEEE802.14 specification laid down by IEEE802.14 working group and DOCSIS made by MCNS (multimedia cable network system). The former one is related to the transmission of the ATM cell and to offer the perfection QOS(quality of service); the latter is related to the transmission of the length-variable IP data pack. The concept of the QOS appears in the DOCSIS v1.1 . Both IEEE802.14 and DOCSIS, focus in MAC protocol design on the upstream channels, i.e. sharing the upstream channels , dealing the services and resolving the contention.This dissertation gives theoretical analysis of the main factors that affect these performances of a MAC protocol, based on most popular designs. This dissertation presents a new technology that based on ALOHA and S-CDMA and theoretically analyzed the character of HFC system which use the new technology, such as the<WP=6>capacity of interference resisting, improving the bandwidth utility and lowering the access time delay. finally this dissertation gives demonstration that HFC system which use the new technology, is better than that using the conventional TDMA technology.更多还原