Electronic Design

Broadband Modem Chip Set Brings 1 Gbit/s To Cable

Cable TV modems are already the most common high-speed Internet access method for consumers and small businesses. Rates of several Mbits/s are common on existing cable systems, easily beating conventional modems and most DSL lines. But stand by for an even greater boost in speed from cable systems.

Narad Networks Inc., Westford, Mass., has announced its Ultra Broadband Modem (UBM) chip set. With it, cable TV companies can carry full-duplex Gigabit Ethernet transmissions on the coax cable portion of the existing hybrid fiber coax (HFC) network. The end result is an affordable 100-Mbit/s home/small business modem that can handle not only super-fast Internet access, but also voice-over-IP (VoIP) and services like video on demand.

Key to the UBM is its leveraging of the previously unused spectrum in HFC cable systems between 860 MHz and 2 GHz (see the figure). Traditional legacy services with over 140 6-MHz channels for TV and data services occupy the lower 860 MHz of bandwidth. Most HFC systems also support signals up to 1 GHz, but up to 2 GHz can be accommodated with special equipment.

The UBM takes advantage of the open area in the lower 1-GHz range and the range up to 2 GHz. It contains two full-duplex modems. One provides 100-Mbit/s capability, and the other permits 1-Gbit/s rates. Both use 16QAM full analog circuitry instead of DSP. The chips are made on a bipolar silicon-germanium (SiGe) process and form the heart of Narad's forthcoming product line.

The company will offer an optical network distribution switch (ONDS) that is installed at the cable headend and multiplexes the existing cable services along with 1-Gbit Ethernet (1GE) sources on the fiber trunk. Subscriber access switches (SAS) and related signal-conditioning equipment will allow the full 2-GHz bandwidth to be carried over the fiber portion of the network. Cable drops to the subscriber will carry switched Ethernet at 100 Mbits/s.

Narad will conduct field trials with a number of cable companies during the fourth quarter of this year. Equipment availability is expected late in the first quarter of 2002. For details, go to www.naradnetworks.com or call (978) 970-3009.

TAGS: Digital ICs
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