T
ech pundits argue that the new Wi-Fi standard 802.11ac will replace wired gigabit Ethernet networking. 802.11ac is a supercharged version of 802.11n, offering link speeds ranging from 433 Mbps, up to multiple gigabits per second.
To make 802.11ac dozens of times faster than 802.11n, the new standard works exclusively in the 5GHz band uses a huge chunk of bandwidth (80 or 160MHz), operates in up to eight spatial streams (MIMO), and a technology called beamforming.
At its core, 802.11ac is essentially an updated version of 802.11n, according to Sebastian Anthony the author of an ExtremeTech article “What is 802.11ac WiFi, and how much faster than 802.11n is it?” 802.11n was a huge performance increase over 802.11a and g. 802.11n introduced some key technologies that brought massive speed boosts. Where 802.11n had support for four spatial streams (4×4 MIMO) and a channel width of 40MHz, 802.11ac can use eight spatial streams and has channels up to 80MHz wide, which can be combined to make 160MHz channels. This means that 802.11ac has 8 x 160MHz of spectral bandwidth to play with, versus 4 x 40MHz – a huge difference that allows 802.11ac to send vast amounts of data across the airwaves.
What is new in Wi-Fi
802.11ac also introduces 256-QAM modulation (up from 64-QAM in 802.11n), which sends 256 different signals over the same frequency by shifting each signal to a slightly different phase. In theory, this quadruples the spectral efficiency of 802.11ac over 802.11n. Spectral efficiency is a measure of how well a given wireless protocol/modulation/multiplexing technique uses the bandwidth available to it.
802.11ac also introduces standardized beamforming Matthew Gast, Director of Product Management at AeroHive Networks published an article, “Investing in Beamforming: Is it worth it?” that explains beamforming.
Rather than transmitting a radio signal in all directions, beamforming figures out where the receiver is, and focus the energy towards the receiver. Instead of spraying radio energy all over the place, send packets as a “rifle shot” directly to the receiver’s antenna Mr.Gast explains.
Beamforming is a two-step process: First, figure out how to “aim” the transmission at the receiver, and second, send the transmission. With beamforming, a transmitter is betting that by paying the cost of the channel measurement process, the data transmission that follows will speed up enough to pay off the cost.
802.11n Beamforming was non-standardized, in 802.11ac, there is only one method of beamforming, called the Null Data Packet (NDP). (rb- Read the AeroHive article for a full description of NDP)
Aerohive’s Gast concludes that by steering the energy towards a receiver, beamforming enables you to take a step up to a higher data rate. Mr. Gast estimates that 802.11-based beamforming gives you a 3-5 dB gain.
In theory, at the 5GHz band with beamforming, 802.11ac should have the same or better range than 802.11n However, Mr. Anthony says the 5GHz band, has less penetration power so it doesn’t have the same range as 2.4GHz (802.11b/g). The ExtremeTech article concludes that’s an acceptable trade-off: there simply isn’t enough spectral bandwidth in the cluttered 2.4GHz band to allow for 802.11ac’s gigabit-level speeds.
ExtremeTech‘s Anthony calculates there are two answers to how fast is Wi-Fi 802.11ac, the theoretical max speed, and the practical max speed that mere mortals will get surrounded by lots of signal-attenuating obstacles.
He calculates the theoretical max speed of 802.11ac is eight 160MHz 256-QAM channels, each of which is capable of 866.7Mbps – a grand total of 6,933Mbps, or just shy of 7Gbps. That’s a transfer rate of 900 megabytes per second. Compare this with 802.11n’s max theoretical speed, which was 600Mbps. He then says in practice, the current max speed of 802.11ac devices is 1.7Gbps.
ExtremeTech points out there will be a second wave of 802.11ac devices – due in 2014 after the standard is finalized – before 160MHz channels and multi-gigabit speeds become a reality. The max speed over an 80MHz channel is 433.3Mbps, and there aren’t any 802.11ac chipsets that support up to eight streams.
Kevin Fitchard at GigaOM reports that recently the Wi-Fi Alliance kicked off its 802.11ac certification program. First to get the official Wi-Fi stamp of approval was the Samsung Mega 6.3, followed by two other Samsung models.
As with the 802.11n certification process, the Wi-Fi equipment makers are moving faster than the standards bodies. The IEEE is actually still putting the finishing touches on the 802.11ac standard, which is not due until 2014.
The Wi-Fi Alliance expects the first batch of ac devices will support speeds of 433 Mbps and progress into more advanced levels of the standard. The Alliance has pre-certified systems from companies like Broadcom (BRCM), Qualcomm (QCOM), Realtek, and Marvell (MRVL). Cisco (CSCO) was one of the first vendors to get an access point certified.
“AC is going into mobile and portable devices first…,” Wi-Fi Alliance Marketing and Program Management Director Kelly Davis-Felner said. ABI Research estimates that 40 percent of all ac devices shipped in 2013 will be handsets.
rb-
While tech pundits argue that the new 802.11ac Wi-Fi will replace wired gigabit Ethernet networking at home and in the office. While the consumerization of IT and BYOD are strong forces, the life-cycle of cabling infrastructure is 25 years, a cost not lightly abandoned in the walls. it is more likely to happen at home first. Who wants all the crappy wires running all over the house?
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Ralph Bach has been in IT long enough to know better and has blogged from his Bach Seat about IT, careers, and anything else that catches his attention since 2005. You can follow him on LinkedIn, Facebook, and Twitter. Email the Bach Seat here.
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