Everything you need to know about Wireless 802.11ac networking

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Everything you need to know about Wireless-AC

Note: This article was first published on 29th November 2014, updated again late in 2015 and re-published on 12th July 2016 as it is one of our popular reads and covers several networking basics.

Get the Basics Right

ASUS' RT-AC66U from 2012 was one of the first routers in the market to support Wireless-AC.

The latest wireless standard is Wireless-AC (also known as Wireless 802.11ac officially). The first routers to support Wireless-AC hit the stands around two years ago, but it is only very recently that manufacturers of smartphones, tablets and notebooks began offering support for it in their devices. From what we have observed on our social media channels, there seems to be a lot of confusion and misunderstanding surrounding this new standard so before we begin, let’s get the basics right.

How routers are advertised.

To be able to properly evaluate a router’s performance, it is first necessary to understand how router manufacturers arrive at the figures that they put on their boxes - it is usually the combined data transfer rates of both the 2.4GHz and 5GHz bands. The fastest first generation Wireless-AC routers were capable of a maximum combined data transfer rate of 1900Mbps. This figure is actually derived from the combined throughput of its 2.4GHz and 5GHz band. To break it down further, these devices supported a maximum data rate of 1300Mbps on the 5GHz Wireless-AC band, while the 2.4GHz band supported Wireless-N and a maximum data rate of 600Mbps - add these two together and you get a combined data rate of 1900Mbps.
Exclusive to the 5GHz band.

Wireless-AC operates only on the 5GHz band and offers much improved speeds thanks to its support for up to 160MHz channel bandwidths and a maximum of 8 spatial streams. According to the specifications, Wireless-AC could potentially offer maximum data transfer rates of up to 6900Mbps. But before you get too excited, in the real world, due to our congested frequency spectrum and hardware limitations, Wireless-AC maximum data rates would not be anywhere near that fast - but it will still be considerably quicker than Wireless-N, whose theoretical maximum data transfer rate was just 600Mbps. Additionally, when setting the router up, it is important to lock the 5GHz band in AC mode to ensure utmost performance.
All about the streams.

The performance of your Wi-Fi network is dependent on a lot of things, but the first thing is the number of spatial streams that your router supports. Currently, the Wireless-AC standard supports up to 433Mbps on a single stream and current radio chipsets typically support three streams, allowing for a maximum data transfer rate of 1300Mbps, as seen on AC-1900 class routers. The lone exception is Quantenna’s QSR1000, found in the latest routers like the ASUS RT-AC87U and Linksys E8350, which is the first chipset to support four streams, enabling a maximum data rate of 1733Mbps and so give rise to AC-2400 class routers. Router aside, performance is also dependent on the receiving end. If you connecting device - smartphone or notebook - only supports two streams, then the maximum data transfer rate is capped at 867Mbps on a Wireless-AC network.
Compatibility

Another important point to note that Wi-Fi performance is not determined solely by your router, but also by the device connected to it. To begin, to take advantage of Wireless-AC router requires a connecting device that supports Wireless-AC. If your device is not Wireless-AC compatible, it will not be able to enjoy the high speeds provided by a Wireless-AC router. Adding to this confusion is that despite Wireless-AC being around for quite some time, it is only very recently that manufacturers of smartphones, tablets and notebook began offering support for it in their devices. And even today, there are new devices released that still do not support Wireless-AC, such as Apple’s latest iPad Mini 3.

A corollary to this point is that not all Wireless-AC devices are similar. Remember our earlier point on spatial streams? In fact, most smartphones and tablets that are Wireless-AC compatible actually have wireless chipsets that support either one or two spatial streams - meaning that their maximum data transfer rate is capped at 867Mbps for devices support two spatial streams. That said, 867Mbps is already beyond what Wireless-N could offer.
MIMO

MIMO is Multiple Input Multiple Output and refers to the use of multiple antennas at both the transmitting and receiving ends to improve wireless performance. Using multiple antennas to transmit and receive data improves reliability and speed. And today, all modern wireless devices make use of MIMO. However, current wireless devices are typically SU-MIMO. SU stands for Single User and refers to the fact that routers today can only transmit data to one device at any one time. This is why performance degrades rapidly as more and more devices are connected to the router. The router has to quickly serve one device and go on to the next, and if there are many devices connected, the “waiting time” is increased. The latest Wireless-AC devices will attempt to address this shortcoming, but more on this later in the article.

Now that we understand some basics of networking and Wireless-AC, let’s see how this applies to the newest Wireless-AC routers today that support maximum data rates of 2400Mbps and 3200Mbps.

The Basics of AC-3200

The Netgear Nighthawk X6 was one of the first routers to be released to use Broadcom's 5G XStream chipset.

The current crop of AC-3200 routers are also called tri-band routers because they broadcast three separate networks. These routers are typically based on Broadcom’s new 5G XStream chipset, which broadcasts of two independent 5GHz networks on top of a single 2.4GHz network.

Maximum data rates remain at 600Mbps for the 2.4GHz band and 1300Mbps for the 5GHz band. But since there are two 5GHz bands now, the total combined data rate of all three frequency bands is 3200Mbps. What this means is that, from a pure speed perspective, these new AC-3200 are theoretically no faster than AC-1900 routers - the 5GHz band still manages a maximum data transfer rate of 1900Mbps. However, what the additional 5GHz band does is increase total bandwidth and this will help especially if you have lots of Wireless-AC compatible devices connected to the router.

To elaborate further, the idea behind this and the Broadcom 5G XStream chipset is to split the fast and slow devices between the two independent 5GHz band. While Wireless-AC devices are going to be faster, not all Wireless-AC devices are equal. Remember that we mentioned that their performance is determined by how many spatial streams they support. Notebooks are typically the quickest as their chipsets usually support up to three spatial streams, whereas tablets and phones vary between one and two streams.

Most routers today are SU-MIMO only, which means regardless of the receiving device, the router can only transmit data to one device at a time. You can imagine how inefficient this can be if multiple devices are connected to the router.

This causes congestion because most routers in the market right now do not support MU-MIMO (Multiple-user Multiple Input Multiple Output) and so can only transmit data to one device at any one time. So the best way to make use of the available bandwidth is to put the fast devices on one 5GHz band and the slower ones on the other. This way, on the faster band, the amount of time needed to serve each device will be kept down to a minimum, allowing it to quickly serve one device and then the next.

So to sum up AC-3200, while they may not offer higher data transfer rates, they do provide greater bandwidth, which can be beneficial especially if you have many wireless devices connected to your router.

The Basics of AC-2400 (802.11ac Wave 2)

The ASUS RT-AC87U is one of the new "wave" of 802.11ac Wave 2 routers.

Along with AC-3200 routers, we are also seeing more AC-2400 class routers entering the fray. AC-2400 routers are markedly different from AC-3200 and they are the first wave of what is unofficially known as “802.11ac Wave 2” devices. What’s the difference then between these devices and older Wireless-AC devices?

Firstly, the latest 802.11ac Wave 2 devices that are in the market now will support up to four spatial streams allowing for a maximum data transfer rate of 1733Mbps - each stream still supports a maximum data transfer rate of 433Mbps. This means that technically, an AC-2400 router will be able to provide faster speeds than an AC-3200 router, although the latter has the upper hand if you were to look at overall combined throughput.

Wider 160MHz channels will offer greater throughput on a single stream, which in turns increase overall data transfer rates.

Secondly, 802.11ac Wave 2 devices will be able to offer wider 160MHz channels to further increase throughput. With 160MHz wide channels, single stream data transfer rates could be doubled from 433Mbps to 866Mbps. In practice, however, we are unlikely to see many users running channels this wide because of interference from other wireless networks from neighboring households.

An illustration of how 802.11ac Wave 2 can help speed up performance on busy networks by transmitting to multiple devices at once. Source: Qualcomm.

Thirdly and arguably the most important feature of 802.11ac is support for MU-MIMO (Multiple-user Multiple Input Multiple Output). Remember we mentioned that most routers these days are SU-MIMO devices and can only serve a single device at any one time? MU-MIMO will allow the router to serve multiple clients at once. This could also help ease congestion, since it reduces the “waiting time” of devices by making better use of its available resources. For example, in what would normally take four “cycles”, a router supporting MU-MIMO with four spatial streams could transmit to four single stream smartphones in a quarter of the time.

802.11ac Wave 2 devices are the future, but they are restricted in their usefulness for the time being. Chiefly this is because to be able to enjoy its maximum speeds and MU-MIMO requires clients with compatible 802.11ac Wave 2 chipsets that also support four spatial streams and MU-MIMO. And, at the time of writing, there are no such devices in the market yet. The current work around to this is to get two routers and have the other one operate as a bridge and connect your devices via Ethernet. It's costly and impractical for sure, but that is the only way for the time being. That said, if you want the best in terms of sheer speed, the new AC-2400 class routers are the way to go.

To know more about networking and for some networking tips to improve your home network performance, be sure to check out our newbie's guide to home networking.