Hybrid Fiber- Coaxial Networks: Technology and Challenges in Deploying Mul?- Gigabit Access Services. Kevin A. Noll

Transcription

1 Hybrid Fiber- Coaxial Networks: Technology and Challenges in Deploying Mul?- Gigabit Access Services Kevin A. Noll

2 Network Structure Most networks are constructed as a 4- level hierarchy Backbone Regional Metro Access Hub Hub Hub Hub Hub Hub Na#onal Backbone Hub Hub Regional Network Metro Area Network Hub Access Network

3 Access Network The largest component of the network in terms of Physical/Geographic Size Monetary Investment TWC Hybrid Fiber Coax (HFC) Access Network 125,000 Fiber Route Miles 344,000 Coax Plant Miles Hub Fiber Node Coax Amplifier Coax 1,130 Hubs 95,600 Fiber 1.9M RF 30 M Coax Nodes Amplifiers Connectors 3

4 HFC Network Components and Topology QAMs Hub Fiber Optic Cable <20 km Aerial Coax Feeder Cable Card TX FP CMTS Card TX Node Amplifier Spli\er Underground Coax Feeder Cable Tap ~ 800 [ Drop Cable ~100 [ Stereo TV #2 Set-top TV #1 4

5 Hub Node Tap 5

6 Func?ons in the Hub Recep?on of Video Signals from Content Networks/Programmers IP Connec?vity to Metro/Regional Networks Modula?on of Downstream Signals as QAM (digital) or VSB+DSB+SSB+FM (Analog) Pre- Condi?oning of Downstream Signals to combat impairments in the op?cal and RF network Decoding of Upstream QAM/QPSK Signals Conversion of RF Signals to/from Intensity Modulated Op?cal Signals for long- distance transmission 6

7 Func?ons of a Node and Amplifier HFC Node performs OE conversion of RF signals to/from hub can be located 50km or more from the hub Trunk/Distribu?on Amplifier performs amplifica?on of the RF signal a[er being degraded during transmission over coaxial cable May be cascaded 5- deep past the node (node+n architecture) 7

8 Func?ons of the Tap and Drop Tap A mul?port RF device that passes a specified amount of RF energy to a TAP port and passes the majority of RF energy from the INPUT to the THRU port Used to create a branch from the trunk coaxial cable to a subscriber s premises Drop The coaxial cable that a\aches the subscriber s premises to the tap port 8

9 HFC Powering FP Power Inserter Node Amplifier The HFC Node and Amplifiers are electronic devices that require electrical power. Power Supplies placed at regular intervals along the coaxial network provide power to the node and amplifiers Power Inser?on devices are used to couple AC and/or DC power to the same conductors carrying the RF signal The Coaxial Network is ALSO a power distribu?on network 9

10 Capabili?es of a Typical HFC Network Downstream MHz 116 x 6 MHz Channels = 256 SC- QAM (single carrier) ~ 6 bits/hz Upstream 5-42 MHz ~ 4 x 6 MHz Channels usable = 100 Mbps 64 SC- QAM ~ 2 bits/hz Typical 750 MHz System Upstream Downstream 5 MHz 42 MHz 54 MHz 750 MHz O H P Analog Services SD x Digital Services HSD E 65 slots 46 5 N 6 MHz = 1 slot 10

11 Increasing Capacity and Throughput Three basic components influence network capacity Load The Pipe Serving Group Size Load = The amount of data requested and sent by users on the network Pipe = Throughput and Capacity available in the network Serving Group Size = the # of users sharing the Pipe 11

12 Increasing Capacity and Throughput 1) Expand the Pipe Plant Upgrade (e.g. 750 MHz to 1 GHz) Analog Reclama#on Plant Hardening 2) Reduce # of users sharing the Pipe (smaller serving groups) Segmenta#on / Node Splits 3) Reduce the Load (Use the pipe more efficiently) MPEG- 4 / Next Genera#on Encoding DOCSIS

13 Reducing Serving Group Size BEFORE QAMs Card CMTS Card Fiber Optic Cable <20 km TX TX FP Node Node Split Reduces Serving Group Size by adding HFC Nodes and CMTS ports to serve the same number of users AFTER QAMs Card CMTS Card Fiber Optic Cable <20 km TX TX FP Node FP Node Increases Capacity ONLY Does NOT Increase Peak/Offered Speed 13

14 Expand the Pipe Reclaim Spectrum Legacy Analog Signals are inefficient users of spectrum 5% efficiency compared to MPEG- 4 Typically can occupy 50% of the available spectrum Replace Analog with Digital Signals that are more efficient MPEG- encoded Video on QAM can carry 2-20x more content than an analog channel Contractual Concerns must be sa?sfied Franchise Agreements, Market Recogni?on, Must- Carry Agreements may be impacted by conversion of analog to digital Deploy DTA to all subscribers who do not have Set- Top- Boxes (CAPEX $$, OPEX $$) 14

15 Expand the Pipe Use the Unusable Some operators avoid using sensi?ve frequencies MHz Aeronau?cal Mobile and Aeronau?cal Radio Naviga?on MHz Aeronau?cal Glideslope frequencies Requires Plant Hardening to ensure no leakage of signals from the coax plant 15

16 Expand the Pipe More Spectrum Expand the Available Spectrum Move the upper limit to 1GHz or higher Move the US/DS split Moniker Upstream Frequency Descrip#on Sub- Split 5-43 MHz Most used today Mid- Split 5-85 MHz Reasonable op?on High- Split MHz Difficult and Expensive Top- Split >1 GHz Much higher CPE cost Requires heavy- duty network upgrades 16

17 Expand the Pipe More Spectrum Nodes, Amplifiers, Filters All operate with a specific frequency- split All must be re- configured or replaced if not compa?ble with the new split Sample Amplifier Specification Sample Node Specification 17

18 Use the Pipe More Efficiently Be\er Compression Algorithms Reduces RAW load on the network Higher- Order Modula?on and FEC Modula#on Efficiency (bits/symbol) Bit Rate per 6 MHz (Mbps) Required SNR (db) 64 QAM >5 ~27 > QAM >7 ~40 > QAM >9 ~50 >30 OFDM w/ 4096 QAM ~65 Adapted from Chapman, Emmendorfer, Howald, Shulman, Mission is Possible: An Evolutionary Approach to Gigabit-Class DOCSIS, NCTA, May

19 Use the Pipe More Efficiently How to Achieve Be\er SNR? Plant Hardening Headend TX Hi Leaky gaskets, damaged housing Upstream RF level management issues Strand Corrosion Broken lashing wire Corrosion of Housing Power supply Noise & Hum Aging transistors, capacitors, integrated circuits Squirrel and rodent damage Reflective optical splice TX Laser clipping Optical reflections Dirty connectors Misalignment FP Lasers Lo Cracked or deformed coax Corrosion of coax Signal leakage Poor or nonexistent grounding Poor splices, no weather seal Radial cracks due to improperly formed expansion loop Unterminated taps, loose terminations Corroded or loose connectors resulting in Common path distortion Ingress: Ham & Shortwave, CB, paging systems 19

20 Plant Hardening 20

21 These tac?cs have enabled us to grow our max HSD speeds by ~300 over the last ~15 years (1 Mbps to 300 Mbps) Max Downstream Speeds (Mbps)

22 How long can we keep it up? Max Downstream Speeds (Mbps)

23 Q&A 23