Electronic Design

Wi-Fi Chip Set Doubles Wireless Range Yet Saves Power

Transmission range for most standard Wi-Fi modems rarely extends beyond 100 meters in closed quarters or 300 meters in line-of-sight (LOS). However, in a recent LOS test, Atheros' fourth-generation 802.11 chip set with the company eXtended Range (XR) technology achieved a range of 790 meters. According to Sheung Li, Atheros product line manager, the XR technology can more than double the transmission range of typical 802.11a/b/g radios.

The range improvement is achieved in the MAC/baseband chip and not the RF chip. A combination of processing techniques are employed. These include using a new way to track, calibrate, and interpret the signals on the four pilot channels typical in orthogonal-frequency-division-multiplexing (OFDM) implementations. The chip also helps reduce the peak-to-average power ratio problem and improves the coding gain by backing off the data rate at long distances. Overall, the two-chip set gives a combined receive sensitivity of −105 dBm, which is more than −20 dBm better than the sensitivity required by the standard.

Another key improvement is reduced power consumption. Most WLAN radios are always on, even if data isn't being transmitted or received. With the new chip set, the power turns off when the unit is not in use. The overall power consumption is over 60% less than other competitive chip sets. That's even when the Atheros chips operate at the full 54-Mbit/s rate. The idle mode of the new power-management circuits reduces current consumption to just a trickle (4 mA).

One other feature is the Wake-on-Wireless and Wake-on-Theft provision. In this mode, the chips stay powered on even if the laptop, PDA, or other host device is off. The Wake-on-Theft capability alerts the network if a mobile device, such as a laptop or PDA, is removed from the facility without authorization, even if the device is powered off.

The AR5004X chip set covers the 802.11a/b/g applications, while the AR5004G covers only the 802.11b/g standards. Production is ramping up volume as you read this, and prices are expected to be just below the current price levels for equivalent chips, depending on volume, market, and application.

Atheros Communications Inc.
(408) 773-5344

See associated figure.

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