The good, bad and ugly of 802.11ac
Will wireless LAN technology allowing the simultaneous delivery of high-bandwidth data be available soon?
By Jay Botelho | Network World US | Published: 15:50, 14 February 2012
Imagine a world where family members can stream their favorite HD content to different rooms, all while your teenage son uploads his latest HD video "project" to YouTube. Well, with new wireless LAN technology based on 802.11ac quickly approaching - possibly in one or two years - this digital home network paradise could become a reality.
802.11ac leverages and learns from the advances offered with 802.11n, providing even greater throughput, simultaneous delivery of high-bandwidth data to multiple users, and better interoperability in the presence of existing commercial wireless devices and neighboring WLANs.
Compare that with what we have today with 11n, and we are looking at yet another major capability leap, both in terms of functionality and overall data delivery. Data rates will jump from the 600Mbps maximum with 11n to single client data rates up to 3.47Gbps with 11ac and total aggregate capacity of 6.93Gbps. Yes, we're talking wireless!
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WLAN equipment manufacturers are learning a great deal from 802.11n, and these lessons are clearly getting folded into 11ac. Two key features from 11n, MIMO (multiple-input, multiple-output) and channel bonding, form the foundation for 11ac enhancements, with a few more complex optional features.
The first really good thing about 11ac is that it is specifically designed for the 5GHz band. This frequency band provides greater flexibility for one of the key data rate enhancing features, channel bonding, which often goes unused in today's 11n equipment, since so much of that equipment is designed for the 2.4GHz band where channel bonding can cause serious interoperability issues. The 5GHz band offers more channels with wider spacing, and is far less sensitive to interference from other consumer devices, like baby monitors, wireless surveillance video cameras and microwave ovens. [Also see: "Wi-Fi devices crowd 2.4GHz band; IT looks to 5 GHz"]
Additional protocol enhancements are also being specified to make channel bonding less likely to cause interoperability issues. This includes things like the ability for devices to assess whether neighboring channels are clear and available for channel bonding, and for devices to reserve wider bandwidths in advance of data transmissions. This allows channel bonding to increase from 40MHz in 11n to 80 and even 160MHz under certain conditions in 11ac. Making channel bonding less invasive, and therefore used by default by wireless devices, is key to achieving the increased data rates in 11ac.
The second good thing about 11ac is that even though data rates are increasing significantly, power consumption is likely to decrease as compared to similar 11n capability, and this is a huge win.
802.11n is really starting to push the power limits, especially for mobile/portable devices, to the point where most portable devices cannot come close to taking full advantage of 11n capabilities. Through the use of more efficient data encoding mechanisms, 11ac allows devices to use fewer multiple transmissions paths while still achieving higher data rates, and it's the additional RF transmission chains that really eat up power.
Also, given that one primary use case of 11ac is video distribution within the home, power issues can be further mitigated since many of the devices will not be mobile - like your 52-inch LCD TV - meaning AC power is readily available. And video delivery is typically "one way," meaning a PC or DVR will be transmitting the video, requiring more power, while the TV or iPad will mostly be receiving the high bandwidth signal, which requires less power.
Lastly, 11ac introduces an optional capability where one transmitting device can send data, like streaming video, to multiple receiving devices simultaneously. Today, 802.11 traffic is essentially point-to-point. If the same video stream needs to be sent to three clients, it requires three times the bandwidth. With 11ac, the bandwidth is utilised much more efficiently.
As with many technological advances, 11ac is very complex, and this is certainly bad, especially for technologies that are targeted at the general consumer market. So far manufacturers, along with industry associations like the Wi-Fi Alliance, have done a great job in hiding complexity from end users, so there's some hope here. However, 11ac increases the number of configuration and operational options between transmitters and receivers, so clearly setting user expectations regarding the capabilities of each of their devices may be a significant challenge.
We just characterised power as being one of the good things, but it also remains a significant challenge in 11ac, especially for devices that are expected to be the source of high bandwidth data. To achieve the highest data rates available in 11ac requires the use of up to eight RF transmitters. Compare this to 11n today, which allows for up to four transmit streams, but where the number of devices capable of four-stream transmission remains extremely low, mainly due to power and other RF challenges. It is likely to be a long time before the full capabilities of 11ac can be realized.
The number of transmitters and the power to drive them isn't the only implementation challenge. Beam forming, which is a yet-to-be-delivered feature of 11n, is also part of 11ac. This is just one example of some of the complex technology that needs to be implemented to achieve the maximum data rates, and just because the technology is specified in a document it does not mean it is easy to implement.
So the one complexity we haven't addressed yet fortunately only pertains to the manufacturers, but it's pretty ugly. There are significant geographic differences in the frequency allocations for the 5GHz band, with entirely different sets of allocated frequencies for primary channels and channel bonding, leading to differences in the availability and number of wide-bandwidth channels. This will significantly increase the manufacturing complexity of devices that are expected to be shipped worldwide, not to mention the marketing challenges, since equivalent hardware will have different capabilities in different geographic regions. We'll let the manufacturers handle this one!
So, when does 11ac equipment reach your loading dock?
It will be a long time coming. Although the new standard might be ratified in a year or two, manufacturers are going to have to work through some serious technological issues before 11ac equipment hits the market.
So if you're just planning to, or just recently upgraded to 11n, don't worry. And it's probably not worth putting off an upgrade to leapfrog to 11ac. Just remember that when 11ac starts knocking on your door that planning a wireless network takes careful consideration. As with 802.11n, it will be imperative to design your network to meet application requirements and purchase equipment that allows you to get full use out of your enterprise wireless network.