This is by John Cox from Network World.
http://www.networkworld.com/news/2010/060210-atheros-wifi-chipset.html?page=1
Chip maker Atheros Wednesday released samples of its powerful new 802.11n Wi-Fi chipset, which tops out with a maximum data rate of 450Mbps for access points and routers, and a signal that's more consistent and resilient.
The 11n standard uses several innovations to boost data rate and throughput, and to maintain those higher levels consistently over longer distances compared to 802.11abg radios.
Like earlier Atheros 11n silicon, the new AR938x and AR9390 chipsets also have three antennas, part of a technology called multiple input multiple output (MIMO). With multiple antennas tuned to the same channel, the radio uses spectrum more efficiently, increasing overall performance. In addition, with multiple antennas on both ends of the send-receive chain, MIMO systems can recombine reflected signals to enhance them (otherwise these multipath reflections typically disrupt the signal).
Another part of the 11n innovation is using what are called multiple spatial streams, or distinct, separately encoded signals within a single spectral channel. Think of it as sending data in parallel: a lot more data in a given time or a given amount of data in much less time. The impact of multiple antennas and spatial streams is also affected by other optional techniques the vendor may implement.
In the past, Atheros and most other Wi-Fi chip vendors have had at best a three-antenna configuration with two spatial streams, for a maximum data rate of 300Mbps. The new chips are Atheros' first to use three spatial streams, one for each antenna pair, boosting the rate to 400Mbps.
Atheros will offer the new 3x3 chipsets at a "similar price range" to the previous generation chipset, says Tony Hsu, senior director of product marketing for Atheros' networking business unit.
A couple of vendors are offering 4x4 MIMO radios. Quantenna Communications has such a product in trials with a dozen carriers, aiming at multi-media applications within a home. It's a development that emphatically makes sense, says Network World blogger Craig Mathias.
The new products also include a range of 802.11n options, including transmit beam forming, which can be thought of as narrowing and focusing the radio signal to increase its range and decrease the impact of interference. Other techniques are Low Density Parity Check for much more efficient error-correction coding, and Maximum Likelihood equalization algorithms to demodulate the received signal with much greater accuracy than other methods.
Adding these techniques to a three-spatial stream chipset results in 50% greater range or up to 66% higher effective bandwidth, depending on the specific operating conditions, according to Atheros.
Apart from the raw increase in data rate and range, these kinds of advances also mean an improved radio environment for video and other streaming media. According to Atheros, its new 11n silicon can slow down the top data rate to reduce packet loss and latency, thus improving the quality of the video transmission. Other algorithms search for unused radio channels for the video stream. Atheros says the chipsets can support three simultaneous high-definition video streams.
The chipsets are available in sample quantities with full production due to ramp up in the third quarter.