The next generation of Wi-Fi - short for 802.11ac

At the end of last year when 802.11n finally pidim'yav themselves (at least in terms of supply chipsets), all previous standards for Wi-Fi - some experts voiced figures about 70%. Rozsmakuvavshy high speeds audience wants more, and the heirs predict 802.11ac, promising to Gigabit speed. Let's see what we get in reality.
What speeds?802.11n uses the following to increase capacity:Optimized mezanyzma modulation and transmission of packets allowed to "break" from 54Mbps to ~ 75MbpsThen incorporated Channel Bonding - channels width 40Mhz (twice more traditional 22Mhz) provide double the speed - up to 150Mbps.Then the mechanism incorporated Multiple Spatial Streams, which according to the standard can be up to four, which allows to achieve in theory 150 * 4 = 600Mbps802.11ac going to "catch up and overtake" the following ways:Channels width 80Mhz and 160Mhz, which allows you to instantly double / pochetveryty results 802.11n.Maximum Number of Spatial Streams increased to 8, allowing more time to double speed.Optimization of modulation methods and transmission of packets can squeeze some more life and to achieve that high speeds will be available not only within 4m of the access point.However, accounting for all factors, we can get the velocity in the theory of eight-plus times higher than 802.11n - about 5Gbps. Marketers are happy people not understanding Hava. In practice, the same, this speed is almost impossible:New channels will not fit into the range of 2.4Ghz, so 802.11ac will work only in 5Ghz. But in 5Ghz not so simple. In the same trouble-free Europe can only work on the first four channels: 36/40/44/48 - must be included on other DFS / TPC (coexistence with radars), which excludes the possibility of building more or less reliable network. And in these 4 channels goeth only 1 channel 802.11ac, and then "only" at 80Mhz. As an exercise try to count how many 160Mhz-channels fit in a whole range 5Ghz in different regions. Some hope in the 802.11ad - version of the standard that works in the 60Ghz, where available megahertz little more, but this frequency range while clearly designed in the U.S. alone, and communication range it tens of meters (which is very good to lose video from phone to TV or use a wireless mouse, but not for serious networks). So, divide the rate in half.8 Spatial Streams require radiomodulya with 8 antennas and a suitable environment (for all 8 flows as a result came on the client). As will appear Dual-Radio Access Point with 8x8: 8 MIMO (16 antennas with Dual Radio!) One can only guess. :) Mobile devices, most likely will not go further 4x4: 4 because of the need to save energy and space in the trunk. So, cut in half speed yet.Together we get a maximum duplication speed 802.11n - which in itself is still not bad.
Why do we still move on 802.11ac?In addition to speed, 802.11ac offers two key improvements:Beamforming - can dynamically change the chart orientation of the antennas (which is actually for an antenna array with 8 elements). Ideally, this means that the access point coverage area optimally adapts to the current location of customers. Beamforming is not new to Wi-Fi, it even made part of the standard 802.11n. But part optsyonalnoy! In 802.11ac it will become part of mandatory.While it is unclear how the work Beamforming in 802.11ac and whether as a result of it at least some benefit, but it is clear that he is introduced to maximize the effect of the next (and main) improvement.In 802.11ac finally appears MU-MIMO! Networks Wi-Fi - half-duplex: until one passes - others listen. Packets are transmitted consecutively - at a time one packet is transmitted. If by "pipe" at 450Mbps (802.11n 3x3: 3 MIMO) is the flow of 1Mbps - uses 1 / 450 bandwidth. If this data arrive for another client - use unused bandwidth can not. As a result of persuasion from ultra high-speed 802.11n networks with many clients neshvydkyh (ie corporate) is very small.MU-MIMO allows smash "pipe" into several "smaller diameter tubes" and transmit data on them in parallel. This technology is well known telekomschykamy. So far, say about two versions of MU-MIMO in 802.11ac: SDMA (Space Division Multiple Access) allows to transmit data to various clients on various Spatial Streams (that's where you need Beamforming!), Downlink MIMO OFDM podnesuschye can break into groups, and dynamically(if-b) to provide each customer the right amount pidnesut. Thus, even if the access point clients sit 2x2: 2 MIMO - can still make full use of "pipe.TogetherApparently, even if the maximum speed limit one Gbps, standard 802.11ac promises significant benefits for both home (high speed), and corporate networks (effective utilization of the highest speeds in networks with many clients). In addition, to support new radiorezhimov to completely replace all equipment that promises significant benefits vendors and integrators - all satisfied, in general:) Currently it is expected that the standard will be ratified at the end 2012/nachale 2013, but nabolee optimistic vendors have already introduced chipsets and products based on them at CES-2012. Uhotovana or 802.11ac fate 802.11n, adopted a few years later than expected, time will tell.