Wireless AC 802.11ac
Wireless has freed us from the burden of cords and cables and given us unprecedented mobility. Video is a huge strain on wireless, with higher quality videos requiring more bandwidth. 802.11n is fast, but innovation marches on. The demands will never stop increasing so we need something faster, or it’s back to wire. Now that we’ve tasted the freedom of wireless, there is no going back. We’ve got an answer, and that’s where the 802.11ac come sin.
AC is an emerging standard coming out of the IEEE. It’s VHT, or very high throughput. This means that it operates below six gigahertz with modes of operations for a maximum multi-station throughput of at least 1Gbps and a maximum single link throughput of at least 500Mbps. For sure mileage may vary based upon product once it starts coming out. The standard requires every station to support a 5 data rate of 290 Mbps or faster, and your middling devices around 850Mbps. High end devices can reach up to 1.3Ghz, and that’s jus tthe first generation of 802.11ac.
Do understand that 802.11ac does not replace 802.11n – it actually builds on top of all the breakthrough advancements events which really streamlines a standard process with just a few tweaks. The real question is: Where is this fifth generation wireless getting all this new speed? The first thing that was done was to move away from the crowded interference prone 2.4GHz band to go directly to 5Ghz, where there is more room. With an extra breathing space, we can widen the channels to 80Mhz, which gives us 234 data subcarriers – that is more than double the 108 we have in 802.11n! The AC standard has even an option to bond two of these channels together for 160Mhz.
With tweaks to RTS and CTS, this wider band allows us to transmit more data efficiently by shutting down the transmitter sooner to decrease power usage, which translates to both speed and battery life improvement. Some features of 802.11ac includes Multi User – Multi Input Multi Output, or MU-MIMO. 802.11ac doubles our spatial stream from 4 to 8. With this and MU-MIMO, we can accomplish some really cool things. For example, instead of 1 frame for 1 receiver, we can send multiple simultaneous frames to multiple receivers. MU-MIMO is switch like technology versus 802.11n’s single user MIMO, which is more hub like technology. This means an access point (AP) with four antennas can send one stream to 3 devices downstream at the same time.
802.11ac is home to beam forming to a single explict method beam forming with feedback. The 802.11ac transmitter sends a special sounding frame to the receiving device asking for feedback. The receiving side returns the beam forming matrices to the trasmitter for effective signal shaping. No more multiple methods to cause chipset confusion – one method to rule them all. Beam forming is a powerful tool for increasing link budget and extending reach if implemented. Don’t be surprised if you see gains of at least 5dB across your SNR range.
802.11ac brings even more advances to 802.11n. Features like High Order Modulation, 256 QAM – up from 64 QAM in 802.11n – that’s a 33% speed bump. Speaking of modulation, coding scheme MCS 0-7 is fully supported, Fast Fourier Transform (FFT) up to 512 – that’s a quantum leap from 128 in 802.11n, and a new set of PPDUs. Procedural Protocol Data Units support the new VHT preamble improve automatic gain control for MIMO, auto detection. 802.11ac is backward compatible with other 802.11n wireless technologies. There is no new Greenfield preamble to make life more difficult. Wireless innovations are moving so fast that the IEEE actually ran of of letter so they had to start over.
Increased throughput requires change in at least one of three areas. You can do higher order modulation, wider channel bandwidth, or more spatial streams.