Atheros announced its 2010 family of three-stream, high-data-rate and rate-over-range chips: The AR9300 XSPAN line up has a three-stream, 3x3 format for up to 450 Mbps raw (300 Mbps TCP/IP) 802.11n traffic. But speed is critical only at close distances: the chips have been designed to keep data rates high as devices move further and further from an access point.
Pen Li, senior product marketing manager at Atheros, explained that the company's goal with what it's calling SST3 technology is to "maintain signal reliability across the entire link." To that end, it's employing four features.
At short ranges, maximum likelihood demodulation (MLD) employs a massive amount of calculation to figure out the best of a matrix of potential encoding systems to use. Li said this could effectively increase antenna gain by 6 dB over the current technique. "Up to this point, the industry has been using this sub-optimal scheme called zero forcing." That was because the necessary CPU cycles weren't available in earlier generations. Atheros says this extends higher rates (up to 200 Mbps of TCP/IP throughput) 100 percent further than current tech.
At medium distances, where maximum speeds can't be maintained, higher rates can still be ensured with transmit beamforming, a well-known technique of varying signal strength to steer a beam to a receiver based on its understood location. However, Li says Atheros takes this a step further by beamforming on each subcarrier of an OFDM signal. (OFDM breaks a channel into many subchannels each of which sends data much more slowly than a monolithic channel would. This allows better signal reconstruction, and allows subchannels to be interferred with without degrading other subchannels. It's fundamental to 802.11g, 802.11n, and, in a slightly modified form, WiMax.)
This transmit beamforming boost keeps rates higher--at around the 100 Mbps TCP/IP data rate--50 percent further.
For the longest distances, Atheros will use maximal ratio combining (MRC), which uses some magic to pull signals from different paths, relying on a certain amount of redundancy, to push range by 20 percent further than current systems. MRC in a more limited form was used in Atheros's SST technology. With a 3x3 antenna matrix, it can be used to greater advantage.
Across all three methods, Atheros will use low density parity check (LDPC), a binary forward error correction with very low overhead to reduce error rates. Forward error correction encodes additional data to allow a receiver to fix errant bits without asking for a packet retransmission.
Atheros is pusing this chip line-up as its flagship brand, with suggestions for applications for home and mobile computing (better range), media (set-top boxes, gaming, multiple HD streams), and business (better performance in dense environments or less expensive deployments with fewer APs).
The chips are slated to be sampled in the first quarter of 2010. Atheros didn't offer guidance about when its OEM partners would have products available based on the designs, but it's likely by the end of 2010 at least consumer devices would appear.
While three-stream devices are already on the market, there's only one piece of client hardware for laptops, meaning that only range and reliability can be improved with a three-stream device, not throughput.