Edge QAM Modulators Approach 100 Channels

The density of edge QAM (quadrature amplitude modulation) modulators is a delicate balance between what technology is capable of, what future applications will require and what operators are asking for and implementing now. So said the experts on the show floor at last week’s Cable-Tec Expo in Denver.

Operators are in a period of add-on expansion, where they might need to increase their existing number of QAM channels per service group from 2-4 to 4-16 QAMs, Chris Brown, senior product manager, digital video headend products, Motorola, said. “They are not going to throw away their existing equipment.”

Vendors, therefore, have to account for the network of today, tomorrow and the day after, Charles Cheevers, vice president product management, CTO Europe, ARRIS said. Timing is critical. “(We) are still somewhat conservative with 100-channel device,” Cheevers said. “We don’t feel the MSOs are ready to use it.”

ARRIS’ roadmap includes taking MSOs to 24 or 32 channel output tomorrow and then evolving using the same hardware to 100 channels. “It’s not a big bang approach…I can’t see the cable operator going straight to 100…(They) would need a lot more unicast services or all-digital simulcast into the same output as unicast,” Cheevers said.

While a few years ago folks were talking eight QAM channels per service group, today companies are lighting up 32, said Tony Pierson, vice president business development, LiquidXStream, which currently offers 36 QAM channels per RF port. “It’s exciting for the U.S. market, which has moved pretty (quickly) to much higher utilization in unicast, multicast-type services.”

Now the question is whether more than 100 QAM channels will be necessary. “With 64 QAMs on an RF port, if you have a small service group size, that means multiple streams per home for unicast,” Pierson said.

Enabling more

Harmonic first talked about a product in January 2008 that could deliver 100 QAM channels over a single RF port.  In Denver, Harmonic was demonstrating 72 live QAM channels through its HectoQAM edge processor, which is still in development.

Various technologies are enabling these kinds of efficiency gains.

Fast digital to analog conversion (Fast DAC) chipsets, for instance, eliminate the intermediate frequency step for QAM synthesis, which happens at a higher frequency instead. The component eliminated as a result is the upconvertor. Flexibility is another gain.

Whereas conventional block upconversion forced operators to find a contiguous chunk of spectrum, a Fast DAC scenario allows QAM channels to be spread across the spectrum.

“(The) Fast-DAC technology (chipset) generates QAM in the direct target frequency,” said Yoav Derazon, Harmonic senior manager, cable solution and strategy. Harmonic’s HectoQAM, slated for release in mid-2010, will provide four to four-and-a-half times the density the company offers today.

LiquidXStream’s Pierson said that because his company used its own chip from the beginning, it has been able to put QAM channels anywhere with no contiguous block constraint. “(However,) how many QAMs you can get in there and how wide the window can be enhanced (by an) improved DAC.”

Functionality

In addition to increasing density, edge QAM modulators also are supporting more applications. The concept of a universal EdgeQAM has expanded into playing a role for DOCSIS 3.0. As part of BigBand Networks’ vIP Pass, the company’s edge QAM puts a DOCSIS wrapper around the video and sends it to the DOCSIS 3.0 modem.

“The benefit is more efficient use of bandwidth and more efficient solution for video delivery over IP,” John Holobinko, BigBand vice president, marketing, said.

BigBand’s BEQ6200, scheduled to be released within three months, boasts twice the capacity of it’s the BEQ 6000, or up to 96 QAM channels in the 1.5 RU universal edge QAM modulator platform.

For its part, Cisco was talking QAM channels per single 13-RU chassis. Its RF Gateway 10 universal edge QAM offers up to 480 channels, using the DS-48 line cards. One benefit of such density is lower power consumption—a hot and “green” topic at Expo this year.

Cisco claims that whereas the typical edge QAM modulators consume 8–10 watts per channel, the RF Gateway 10 is twice as green, at 5 watts per channel.

Early mover, transmitter leap

One company so deep into QAM technology that it might be overlooked, Vecima Networks, also demonstrated its wares in Denver. Vecima not only got into the dense QAM modulator game early but also announced a deal earlier this year to supply DOCSIS 3.0 modules to a “leading” CMTS vendor.

Vecima’s new Terrace MDU Gateway probably drew more attention, but its HyperQAM, an edgeQAM device introduced in June 2007 that offers up to 128 QAM channel outputs in a 2RU platform, is another product that fits today’s cry for more channels and denser platforms.

Another company with component level expertise, Aurora Networks introduced at Cable-Tec Expo a QAM transmitter designed to help operators extend and evolve their narrowcast services. Incorporating a pre-amplifier, the AT3535G is designed to support 80-plus QAM channels, a leap from the 48 QAM channels supported by the AT3520G model.

—Monta Monaco Hernon (Ed note: Final section added 11/11/09)