【文章內(nèi)容簡介】 DENDUBOUTSIDEPLANTHOMEPage 28‘Dish Farm’Headend/ HubTX/ RX, Modulators, Processors, etc.PS Power SupplyHybridFiber Coax (HFC) ArchitectureHeadend/HubPage 29PS Power SupplyHybridFiber Coax (HFC) ArchitectureOutside Plant (OSP) / Distribution SystemPower SuppliesOptical NodesRF AmplifiersTaps/ PassivesPage 30PS Power SupplyHybridFiber Coax (HFC) ArchitectureTelephonyVideoDataPage 31Signal SecuritySignal Security is a special issue. Many security approaches are handled in a typical headend.Some signals are scrambled before being received at the headend. The headend must then descramble them for carriage on the system.The cable system may elect to secure some signals via scrambling or jamming carriers.Additionally, the controllers that authorize descramblers in the customers home are usually located in the headend.Page 32Cable Theory: The Headend182。 Television signals are collected at the CATV’s receive site. Numerous offtheair antennas and satellite dishes receive multiple signals.184。 The collected signals are processed at the CATV headend (This includes all stereo processing and scrambling).185。 The multitude of different channels (frequencies) are now bined into a single broadband feed.186。 This feed is inserted into the HFC distribution path and is now called the forward path or downstream path.Page 334 GHz1 GHzReceiverModulatorvideoaudioCarriers/ChannelsCombinerMHzHeadend Signal ModulationPage 34Cable Theory: Distribution? In a conventional cable plant, the broadband signal is then distributed to subscribers? As the signal travels down the HFC plant:? The signal strength starts to diminish. This effect is called: Attenuation? Amplifiers and line extenders are used to keep the signal level constant.? Unfortunately, amplifiers cause distortion of the signal, so there is a technical limit to the number of amplifiers that can be cascaded.Page 35Cable Theory: Distribution? Different types of amplifiers are used for various applications. ? Trunk amplifiers are very high quality amplifiers that introduces minimal distortion. ? The trunk system is used to transport signals over the greatest distance so minimal distortion is critical.? Line extenders are allowed to contribute more distortions because the distance covered is shorter.? Power supplies must be used to provide the voltage to run the amplifiers. Standby powering has been added in recent years to help assure reliability.Page 36Hybrid Fibercoax (HFC)? In an HFC cable plant, signals are sent out as RF energy and changed to light via optical transmitters. ? HFC:? Is a cable architecture having an optimized bination of fiber in the trunk and coaxial cable in the distribution plant.? Has made it possible to increase signal quality, bandwidth, and reliability in a costeffective manner.? Reduces maintenance costs by being easy to work with or “Craftfriendly.”Page 37Hybrid FiberCoax (HFC)RF (Radio Frequency)An electromagic signal above the audio frequency range (20 Hz to 20,000 Hz) and below the infrared frequency range.Page 38The Electromagic Radiation SpectrumPage 39Fiber Node Hybrid Fiber Coax (HFC)Page 40The HFC Approach? To minimize signal losses referred to earlier, the cable system is broken into many smaller cable systems with amplifier cascades limited to between four and six amplifiers.? Each of these small cable “systems” is fed with a fiber link to the headend.Page 41Fiber Node Trunk AmplifiersBridger AmplifiersLine ExtendersDrop cableFiber vs. long amplifier cascades ? Greater channel capacity? Higher reliability? Higher quality to subscribersHybrid Fiber Coax (HFC)Page 42Receive Antenna FarmSatellite Receiver RackScrambler andProcessors AdInsertionLocal OrgTAPTAPTAPCATV HeadendPage 43Fiber Node AmplifiersAdd the Power SuppliesPage 44Forward CombinerForwardSplitterReturn SplitterReturn CombinerDataPPVPOTSWWWWHeadend receiverHeadend receiverHeadend receiverHeadend receiverHeadend modulatorHeadend modulatorHeadend modulatorHeadend modulatorOpticalReturnReceiverHFC PlantPage 45Laser History / TheoryThe implementation of new services such as HighSpeed data and telephony requires the use of “twoway” transmission.Twoway transmission has been available for many years. Qube was an early service deployed by Warner in the early 1980’s to demonstrate the capabilities of twoway systems. The systems work, but their costliness has prevented widespread deployment.Today we find that cable subscribers are excited about highspeed access to the inter. Will this be the business that will provide the money to convert