Research Of Reducing The Noise Affect In HFC Network

With the progress of society and rapid development of technology, people's needs for broadband services, such as video-on-demand, videophone and internet, has been expanding. Thus broadband communications network becomes a necessity . Presently, the broadband access technology ,that is"the last kilometer"of information freeway , is growing rapidly. Among the numerous access technologies HFC(Hybrid Fiber/Coax) network has gained more and more attention for its uniquely broad bandwidth.However with its wide spreading , its weakness of low anti-jamming becomes obvious, which influences its further development. Therefore, it is really necessary to improve the anti-jamming ability of CMTS(Cable Modem Termination System) based on current DOCSIS protocol.This paper firstly investigates the topology, architecture, key devices and channel features of HFC network, then points out its inherent disadvantages of this kind of topology. Thereafter according to the analysis of variable network noises, the paper lists the damage degree of noise jam to the network. Meanwhile, on the basis of the network topology this paper detailedly states the formation of funneling effect and origin of funneling noise, and also demonstrates its huge damage to network. How to reduce its damage to network? This paper gives us too ways:one is to adopt a better modulation mechanism, S-CDMA, to bate noise jamming. The other way is to implement automatic frequency agility under strong noise, based on the ranging and burst configuration mechanism of current DOCSIS protocol, meanwhile, guaranteeing CMTS's normal operating. This paper comprehensively analyzes the anti-jamming mechanism of DOCSIS, then presents the specific implementation of the latter method. In the end the paper demonstrates the experimenting output under analogue noises , and also particularly describes its running situation.