0 Using FPGA-Based Channel Bonding for HDTV Over DSL

On an almost daily basis, new video or voice applications push the bandwidth requirements for DSL networks, while telecom carriers in the U.S. and worldwide are targeting delivery of digital and high-definition television (HDTV) to consumers. To achieve delivery of such services without deploying new fiber everywhere, carriers must leverage existing copper deployments already in the ground.

Most DSL lines offer enough capacity for delivering standard-definition television (SDTV). Most programs are available from streaming servers at bitrates of about 750 kbps, with some programs providing a 1.5 Mbps bitrate. However, to allow high-quality HDTV streaming and multiple channels simultaneously, a home must have a bandwidth of at least 16 Mbps. Although newer DSL generations of ADSL2 and VDSL can offer these speeds, they cannot offer high speed over a sufficiently longer distance on a typical DSL line. Therefore, HDTV programs can be delivered only to households close to the DSLAM. Those located further away can only receive lower quality SDTV programming.

To ensure that DSL remains the preferred choice for end users, service providers are looking for new ways to improve the performance of DSL networks. While VDSL and ADSL2 provide better performance, the distance limitations are difficult to overcome. Another scenario is to bring the DSLAMs closer to the end users, but the costs involved with installing new equipment in the network are often prohibitive.

Channel Bonding in DSLAMs and DSL Modems
DSL channel bonding provides the ideal mix of features: higher bandwidth to all users and the ability to extend the distance that can be reached at a certain bandwidth. Instead of using a single copper pair, DSL bonding distributes traffic over a bundle of copper pairs. To achieve an effective bandwidth of 12 Mbps, three DSL lines of 4 Mbps are bundled, with a channel bonding processor at each end of the lines. In most copper networks, subscribers are already connected via several wires, so no new cables need be installed to provide channel bonding service, as shown in Figure 1.

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