Broadcom touts lower power draw of 802.11n WLAN chip

New 11n chip for access points touted to lower power demands, price tags
  • (Network World)
  • — 28 April, 2008 08:01

Broadcom this week has unveiled its latest 802.11n chip for wireless LAN access points, with advances that promise lower power demands and lower prices for enterprise-class products that could be available by year-end.

The new chip is a major advance for the chipmaker, which is squarely targeting the enterprise WLAN market for the first time. The company refashioned its previous two-chip device, which targeted consumer and small-home/small-office WLANs, into one chip. The decrease makes the chip easier and less expensive to use in products, reduces costs by reducing individual components, and -- perhaps most importantly -- slashes the power drawn by a device by as much as 50 per cent compared to its predecessor.

The lower power draw means an access point using Broadcom's new BCM4342 chip can run 11n radios in the 2.4GHz and 5GHz bands at the same time with existing 803.2af Power-over-Ethernet (PoE) products. Until now, nearly all 11n access points could use existing PoE only by using two PoE switch ports for each access point or by making a series of tradeoffs that typically somewhat reduced the 11n range or made the signal less robust. A third option would be upgrade to emerging higher-wattage PoE products that anticipate the IEEE 802.3at standard, expected to be ratified in late 2008 or early 2009.

Most of the advances in the Broadcom device were made by using a smaller chip geometry, 65 nanometers compared to 90 nanometers and 130 nanometers for rival products. The vendor's previous two-chip product used 130-nanometer and 180-nanometer processes.

As do nearly all other such chips, for each frequency band the new Broadcom device divides a transmit data stream into what are called two spatial streams, with a maximum data rate of 300Mbps in each band. Unusually, Broadcom does so by using what's called a 2x2 antenna configuration -- two antennas transmitting and two receiving. A 3x3 arrangement is more typical, giving the chip a selection of antenna options to improve signal quality and reliability on both the transmit and receive sides.

Marvell so far is the only chipmaker with an announced 11n chip that supports three spatial streams. But Broadcom executives say the company previously developed a nonlinear signal equalizer for 11n, a much more complicated process than a linear equalizer but one that performs much better in improving the bit-error rate, by suppressing a specific kind of interference that can occur under certain channel conditions. The result, they say, is that Broadcom's new chip delivers equal or better performance in a 2x2 arrangement compared to its 3x3 competitors, but with lower power demand, fewer components and a lower overall access-point cost. The new chip uses a third antenna for receiving, with the chip selecting the two-antenna combination that yields the best signal quality on a packet-by-packet basis. It's part of a continuing process of innovations by 11n chipmakers to "improve" the IEEE's Draft 2 11n standard.

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John Cox

Network World
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