Next-Generation Cable System Architectures
October 5, 2013, IEEE Communications Society and Consumer Electronics Society, Santa Clara, CA—Michail Tsatsanis from Entropic talked about the silicon innovations that enable the next generation cable architecture. The cable systems are facing challenges due to the changes in their media mix.
Now the cable is not just for delivering video to the TV, but is the access network for the Web and a gateway for the home to many other services. The increases in Internet bandwidth are mostly driven by the increases in IP video, and the cable infrastructure has had to change from a coax base—head-end, trunk, tap, drop cable to the home—to a fiber infrastructure for digital traffic. The original designs called for the CATV to have an effective bandwidth of 350MHz for the 100MHz channel set. The channels were on 6 MHz spacing. The coax system changed to QAM (quadrature amplitude modulation) for better bandwidth use.
The digital infrastructure comprises a master head-end going to a regional hub. This hub feeds intermediate nodes to deliver content to the home. The cable system is in 132M homes in the US with 129M of those passed by basic cable and 124M by advanced data services.
One challenge is the legacy issues of the older cable systems. The narrow channels were designed for NTSC content and the 6MHz channels were designed to match the broadcast standards and channel spacing. Some of the newer video services need 200MHz bandwidth to support the 1Gb/s rates. The costs are the barriers to support this Gb bandwidth. DOCSIS 3.0 tries to solve this issue by adding channel bonding. Channel bonding requires a more complex MAC, so 3.1 and IEEE EPOC are trying to address this issue with greater overhead to reduce the complexity.
The change to a digital infrastructure calls for a change in modem architecture to a digital format. A broadband ADC reduces the number of tuners, so one tuner is used rather than the 24 narrow-band tuners needed for channel bonding. This change in architecture reduces costs and power in the receiver.
A Gb/s A-D converter is possible in two versions; a relaxed analog specification A-D with corrections in digital, or parallel streams and concatenation. Both allow increased functionality and ease the transition to digital infrastructure. The digital also allows for adaptive corrective training to compensate for drift and aging characteristics.
It is not only the cable infrastructure that is changing. MoCA is looking at home network changes and architectures. The gateway/DVR is also going to a digital IP structure resulting in a sTB without a tuner. The gateway aggregates all of the other functions.
As the architectures change, power management becomes an issue. In the older TVs, when you didn’t want to watch, you just turned off the TV. Now, the routers/gateways etc. with standby and other operating functions cannot turn off, since the gateway is also a media server for other platforms. To keep power low, new architectures are going into a low-power state that calls for a sleep-wake up cycle. In the latest MoCA spec, the standard calls for a wake up every 100ms to check for messages. The equipment is also set to use fast/slow responses with dynamic voltage controls for lower overall power.
The move to digital calls for high bandwidth, multi-channel receivers that use a broadband ADC as a digital tuner. This change in architecture results in lower overall costs and smaller bills of materials, but require a change in the MAC and PHY to support the newer low power operational modes.
The slides from the presentation can be found on the IEEE SCV Consumer Electronics web site at : http://ewh.ieee.org/r6/scv/ce/meetings/comsec-ces/index.html
