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