Philip Hunter /
06.27.2011
Originally featured on BroadcastEngineering.com
Full Band Capture could hasten IP migration for cable operators

The recent announcement by silicon maker Broadcom that it has cracked the problem of capturing and digitising the entire cable TV spectrum in a single chip could lead to reduced costs for cable TV operators and accelerate their migration to all-IP delivery. It will eliminate the need for multiple tuners to serve several channels at once within the home and will also halve power consumption, according to Broadcom. Another advantage, which would apply equally to any subsequent deployment of Full Band Capture by any other vendor, is deployment flexibility, in that the demodulator can tune to any frequency whenever it wants without being restricted.

For consumers, the main advantage of FBC, apart perhaps from lower cost gateways and other home distribution products, lies in faster channel change. Currently it can take 2 seconds or more to change channels on digital cable services, because of the delay while tuners retune to a different frequency and start to demodulate the data. FBC makes this almost instantaneous because the whole band is constantly being digitised on the fly and is fully ready for display.

Currently, tuners home in on the frequency band for a specified channel, which is 8MHz wide in Europe, and then demodulate the signals to extract the digital video stream. Alternatively, a DOCSIS gateway would extract IP packets from multiple bonded channels.

With FBC, the full demodulated digitised stream spanning the whole cable spectrum is presented to the STB or some gateway, which can then select the desired data or IP packets. Tuning then becomes an in-chip function, performed at lightning speed in a single SOC. At a stroke it solves the tuner proliferation problem, which has threatened to hike costs as homes with several TVs and other devices can require up to 5 or 6 of them. With FBC, devices such as tablets and mobile phones can access digital TV services without requiring some STB-based tuner function.

There is also an advantage for DOCSIS 3.0 services, which with channel bonding requires access to up to eight channels simultaneously. This has been addressed by wideband tuners that allow a single analog tuner to access and then demodulate up to eight channels within a 100MHz range. But while this reduces the number of analog tuners required, it places tight limitations on the frequency allocation of the DOCSIS 3.0 services. Furthermore it cannot be used for broadcast video services, because these can be located anywhere within the 1GHz cable spectrum. A wideband system with broadcast video would therefore still need four independent wideband tuners to access four channels located anywhere in spectrum.

It is also worth noting that the cable spectrum of up to 1GHz is not a clean slate, but is already usually cluttered, with various limitations over allocation of bandwidth, such as legacy analog broadcasts, and legacy boxes that cannot access all frequency ranges. These limitations curtail usable frequencies for new value-added services such as broadband, VOD and additional digital broadcast channels. Operators prefer to be able to position DOCSIS and broadcast services anywhere in their spectrum without constraints over adjacent channels, so that they can load balance various services and provide consumers with the maximum choices. With FBC, the whole spectrum then becomes immediately available in a flexible way, with no constraint at all over access. The whole spectrum becomes a stream of digital data that can be accessed randomly.

Indeed, implementing FBC is a digital to analogue conversion exercise, and only became possible with the advent of the latest 40nm chip technology, according to Broadcom. By compressing the geometry, signals have less far to travel within the chip, reducing latency and making it possible to pack all the signal processing operations required for FBC in a single SoC.

Broadcom's FBC is now available in three SoC systems, its 40nm 8-QAM BCM3128 and 4-QAM BCM3124 cable multireceiver SoCs, and the 400 Mbps BCM3383 Euro/DOCSIS 3.0 cable gateways.



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