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Hybrid Fiber-‐Coaxial Networks: Technology and Challenges in Deploying Mul?-‐Gigabit Access Services
Kevin A. Noll
Network Structure • Most networks are constructed as a 4-‐level hierarchy
– Backbone – Regional – Metro – Access
Na#onal Backbone
Regional Network
Metro Area Network Access Network
Hub
Hub
Hub
Hub
Hub
Hub Hub
Hub
Hub
Access Network • The largest component of the network in terms of
– Physical/Geographic Size – Monetary Investment
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TWC Hybrid Fiber Coax (HFC) Access Network
125,000 Fiber Route Miles
Hub Node
Fiber Amplifier
Coax Coax
95,600 Fiber Nodes
1.9M RF Amplifiers
344,000 Coax Plant Miles
1,130 Hubs 30 M Coax Connectors
HFC Network Components and Topology
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Stereo TV #2
Aerial Coax Feeder Cable
Underground Coax Feeder Cable
~ 800 [ Tap
Amplifier
Fiber Optic Cable <20 km
Node
Drop Cable ~100 [
CMTS
Set-top TV #1
Spli\er
H L
H L
TX RX
QAMs
TX RX
Card
Card
Hub
RX FP
H L
H L
H L
H L
H L
H L
H L
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Hub
Tap
Node
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
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Func?ons of a Node and Amplifier
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• 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)
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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
HFC Powering
• 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
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Amplifier Node
H L
H L
RX FP
H L
Power Inserter
Capabili?es of a Typical HFC Network • Downstream 54-‐750 MHz
– 116 x 6 MHz Channels = 4.3Gbps @ 256 SC-‐QAM (single carrier) – ~ 6 bits/Hz
• Upstream 5-‐42 MHz – ~ 4 x 6 MHz Channels usable = 100 Mbps throughput @ 64 SC-‐QAM – ~ 2 bits/Hz
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O PEN
HSD
Analog Services 65 slots
5 MHz 42 MHz 54 MHz 750 MHz
HSD 5
Digital Services 46
Upstream Downstream
x6 MHz = 1 slot
Typical 750 MHz System
Increasing Capacity and Throughput
• 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
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The Pipe Serving Group Size Load
Three basic components influence network capacity
Increasing Capacity and Throughput
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1) Expand the Pipe
2) Reduce # of users sharing the Pipe (smaller serving groups)
3) Reduce the Load (Use the pipe more efficiently)
Plant Upgrade (e.g. 750 MHz to 1 GHz)
Analog Reclama#on
Plant Hardening
MPEG-‐4 / Next Genera#on Encoding
DOCSIS 3.1
Segmenta#on / Node Splits
Reducing Serving Group Size • Node Split
– Reduces Serving Group Size by adding HFC Nodes and CMTS ports to serve the same number of users
• Increases Capacity ONLY • Does NOT Increase Peak/Offered Speed
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Fiber Optic Cable <20 km
Node
CMTS
TX RX
QAMs
TX RX
Card
Card
RX FP
H L
Fiber Optic Cable <20 km
Node CMTS
TX RX
QAMs
TX RX
Card
Card
RX FP
H L
Node
RX FP
H L
BEFORE
AFTER
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 $$, OPEX $$)
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Expand the Pipe – Use the Unusable • Some operators avoid using sensi?ve frequencies
– 108-‐137 MHz – Aeronau?cal Mobile and Aeronau?cal Radio Naviga?on – 328-‐355 MHz – Aeronau?cal Glideslope frequencies
• Requires Plant Hardening to ensure no leakage of signals from the coax plant
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Expand the Pipe – More Spectrum • Expand the Available Spectrum
– Move the upper limit to 1GHz or higher – Move the US/DS split
– Requires heavy-‐duty network upgrades
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Moniker Upstream Frequency Descrip#on
Sub-‐Split 5-‐43 MHz Most used today
Mid-‐Split 5-‐85 MHz Reasonable op?on
High-‐Split 5-‐200 MHz Difficult and Expensive
Top-‐Split >1 GHz Much higher CPE cost
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
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Sample Amplifier Specification
Sample Node Specification
Use the Pipe More Efficiently • Be\er Compression Algorithms
– Reduces RAW load on the network
• Higher-‐Order Modula?on and FEC
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Modula#on Efficiency (bits/symbol)
Bit Rate per 6 MHz (Mbps)
Required SNR (dB)
64 QAM >5 ~27 >18
256 QAM >7 ~40 >24
1024 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 2012
Use the Pipe More Efficiently • How to Achieve Be\er SNR? – Plant “Hardening”
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TX
RX TX
RX Hi
Lo
Headend
Cracked or deformed coax
Corrosion of coax
“Signal leakage”
Poor or non-existent
grounding
Leaky gaskets, damaged housing
Upstream RF level management issues
Poor splices, no weather seal
Radial cracks due to improperly formed expansion loop
Corroded or loose connectors
resulting in Common path distortion
Power supply Noise & Hum
Unterminated taps, loose terminations
Ingress: Ham & Shortwave, CB, paging systems
Reflective optical splice
Strand Corrosion Broken lashing wire
Corrosion of Housing
Laser clipping Optical reflections Dirty connectors Misalignment FP Lasers
Aging transistors, capacitors, integrated
circuits
Squirrel and rodent damage
Plant Hardening
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100 100
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0
50
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1996 2001 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Max Downstream Speeds (Mbps)
These tac?cs have enabled us to grow our max HSD speeds by ~300 over the last ~15 years (1 Mbps to 300 Mbps)
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100 100
300 300
0
50
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Max Downstream Speeds (Mbps)
How long can we keep it up?
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Q&A
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