A Study On The Improvement Methods Of The Technology Of Upstream Channel Sharing Of Hybrid Fiber Coax Network

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 thecapacity 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.