Cable Media - March 2018 20_CABLE MEDIA 2018 | Page 16

Company contribution

Company contribution

Winning the race for speed

Mike Collins , product manager , CATV / Broadband Products and Nitish Khullar , product manager , HFC Monitoring Platform , share their advice on how to keep up with faster speeds and increasing bandwidths .

In the era of OTT video streaming and with file sharing and interactive gaming a part of our daily lives , there is a neverending demand for faster speeds and more bandwidth . Designed to support multiple Gbps of capacity , DOCSIS 3.1 technology enables cable operators to meet the needs of bandwidth hungry subscribers . In addition , DOCSIS 3.1 can be deployed on existing HFC infrastructures , reducing maintenance and deployment costs .

The Nuts and Bolts of DOCSIS 3.1 DOCSIS 3.1 technology supports speeds up to 10 Gbps downstream and up to 1 Gbps upstream . This is made possible with the combination of Orthogonal Frequency-Division Multiplexing ( OFDM ) transmission and Low- Density Parity Check ( LDPC ) line encoding .
OFDM is a modulation format that multiplexes multiple thousands of tightly spaced , very narrow subcarriers that are QAM modulated . In contrast , legacy DOCSIS bonds up to 32 channels , each with a fixed width of either 6 or 8 MHz . The OFDM transmission technique gives the network the ability to bond larger groups of the spectrum together much more efficiently . OFDM also provides precise control of each sub-carrier , resulting in superior noise mitigation .
Legacy DOCSIS versions use Reed-Solomon forward error correction ( FEC ). The immense processing capabilities in modern chipsets allow DOCSIS 3.1 to use LDPC , a more robust and efficient FEC technique . LDPC codes can be set very close to the noise floor , thus providing around a 6dB gain compared to Reed-Solomon . In effect , LDPC provides performance close to the Shannon Limit for channel capacity . The efficiencies LDPC provide save around 2 bps / Hz . This means for example , that a 6 MHz downstream channel can effectively transmit an additional 12 Mbps .
The combination of OFDM and LDPC improves the spectral efficiency of the HFC network , and increases capacity significantly , by enabling two fundamental enhancements from legacy DOCSIS : 1 ) Removes the 256- QAM limit of legacy DOCSIS 3.0 , and allows higher modulation orders , up to 4096-QAM . 2 ) Allows practical expansion of Spectrum usage , up to 204 MHz for the Upstream and 1.8 GHz for the Downstream .
More Robust Networks DOCSIS 3.1 equipment can use modulation profiles for OFDM . Operators are not required to choose a modulation profile that would provide service to all the cable modems in the plant , usually the ones with the lowest signalto-noise ratio . Since the standard now allows an outside plant to operate with multiple modulation profiles , some CMTSs allow up to 16 modulation profiles to be defined and optimised for different areas of the network .
A higher QAM profile would be used for cable modems on sections of the network that can support 4096-QAM . For cable modem clusters in areas where there are RF impairments , the cable modems can use modulation profiles made up of 1024 and 256-QAM modulations . By combining OFDM and multiple modulation profiles , the operator can optimise the CMTS configuration to the real-time subscribe demand and / or channel conditions .
The CMTS can be configured to shift down automatically if there is an unacceptable signalto-noise ratio . This adds an additional layer of robustness to the network when unexpected events cause a degradation in the signal to noise quality without operator intervention .
DOCSIS 3.1 Benefits When it comes to deployment , DOCSIS 3.1 is flexible and cost-efficient . Ideally , upgrading all equipment leverages the most advantages of DOCSIS 3.1 , but it is not necessary to reap some of the benefits . Recent field trials have shown that current DOCSIS 3.0 capable networks that support 256-QAM can support 1024-QAM modulation with an upgrade to a D3.1 CMTS and Cable Modem , without any plant changes . Hence , for initial deployments , DOCSIS 3.1 does not require any upgrades to the HFC network and it will capitalise on HFC network upgrades to increase network capacity when they are performed .
Since DOCSIS 3.1 is fully backward compatible to DOCSIS 3.0 , the large numbers of DOCSIS 3.0 cable modems already deployed will not need to be upgraded . New DOCSIS 3.1 cable modems are also backward compatible with legacy DOCSIS 3.0 CMTS .
16 Cable Media ADVANCED TELEVISION