Back802.11ac – The New Kid On The Block
802.11ac is the newest Wi-Fi standard in the market. It is more powerful and advanced than each of its predecessors – and there are a few of them. The new 802.11ac offers faster speeds, improved range and reliability, lower power consumption, as well as a free puppy. (Alright, I lied about the free puppy). 802.11ac will be released in two waves. Wave One is already out as of Q3 of 2013. Wave Two will bring even more advancements and is expected to hit the market late 2014.
Introduction:
To better understand and appreciate the features of Wi-Fi I want to explain how Wi-Fi works first. Wi-Fi as we all know is a “wireless” connection, and unlike your desktop Wi-Fi devices can obtain a network connection without any wires. In a desktop the physical connection medium is the copper wire (fiber is quite popular these days as well, but for local networks, copper still has the vast majority). In the Wi-Fi world it’s the Radio Waves traveling in the air, through the window, and through various other mediums. The Radio Waves work similar to sound and light – there is no wire or pipe to contain them. Now there is a decrease of signal from the waves having to go through any obstacles like doors, glass and even air itself, but that is a whole different discussion. This would be very similar to trying to talk to someone face to face, versus talking to someone in a different room with the door closed between you. You will still hear each other, but poorly, and may have to talk slower and repeat certain things.
Going back to how signal is transmitted, in Wi-Fi only one device can transmit OR receive at any time but cannot do both at once. This is what we call Half-Duplex in the technical world. Wired networks on the other hand work in Full-Duplex, because a device can send and receive at the same time. In Wi-Fi this is a very large limitation compared to a regular wired network, because right from the start the connection has half (in reality it’s even less than half) the potential of a wired network. To better understand this, think of Wi-Fi as two or more people having a conversation. One person says something, while everyone else listens. When another person says something, the other people listen. The key here is to always take turns, and NEVER talk at the same time – it’s very rude for one. If two people were to talk at the same time, neither will be understood. Wi-Fi is the exact same way. Only one device must transmit or “talk” at a time for the communication process to work. If there were two devices transmitting at the same time, whether it is two user devices, or an Access Point (AP) and an end user device, the communication will not work because a collision (clash of two or more signals) will occur. In Wi-Fi if a collision were to occur, it cannot be detected. So how do we know a collision occurred? Well, we do not. The signal is just not received – OK it is actually received, but the devices cannot understand it because the collision altered it, and is discarded as if it were never received. To achieve all this, all Wi-Fi devices have a feature called Collision Avoidance. Collision Avoidance is a very strict and exciting set of rules regulating who talks at what time, and when the devices should be quiet and listen only. But again, that is a whole other topic that we do not need to get into detail right now.
MIMO and concurrent Spatial Streams (also referred to as Spatial Multiplexing) is something that was introduced in the 802.11n standard. MIMO stands for Multiple Input Multiple Output, meaning there are several transmitter and several receiver antennas. Concurrent Spatial Streaming means several streams of different data are sent at the same time. Currently with 802.11n the maximum number of concurrent Spatial Streams is three, and a theoretical maximum of four. In 802.11ac, there is an increase, with maximum theoretical Spatial Streams of eight, although three is the current maximum.
The above are often denominated as 2×2:2 or 3×3:3, or 3×3:2, etc. The way to read them is as follows:
Fist number shows how many Transmitters (Tx), second number shows the number of Receivers (Rx), and the third number is the Spatial Streams.
So a 3:3:2 AP would have three Transmitters, three Receivers, and two Spatial Streams. Similarly, a 3×3:3 AP would have three Transmitters, three Receivers and 3 Spatial Streams.
Channel bonding is something that is present even with 802.11n. This has been further improved or I should say increased with 802.11ac. Channel bonding is exactly what it sounds – you combine channels. Combining channels increases the bandwidth and allows for higher data rates. For the 5GHz band, you start with all available twenty-one, non-overlapping channels which are all 20MHz wide. Twenty-one channels is the set maximum in the FCC regulatory domain (North America). If you combined these 20MHz channels, now you have 10 non-overlapping 40MHz channels (because 21 divided by 2 is equal to 10 plus 1.) With 802.11ac Wave One you can go a step further. We take the ten 40MHz channels and combine them to create five 80MHz channels.
In Wave Two, things get even more exciting. You would be able to take two 80MHz channels and combine them to form a 160MHz channel. (Combining two 160MHz channels into a signal 320MHz channel is currently not supported.) How awesome is having 160MHz wide channels!? A lot of bandwidth and potential throughout here. Again, the larger the channel, the more data throughput you can have. A good analogy is a highway. A two lane highway will not be able to accommodate as many cars as a let’s say a six lane highway.
An interesting feature of channel bonding is that you can do two types of bonding. One is the combining of adjacent channels, and the other being able to combine channels that are spaced apart.
Before we get started I with the juicy details I want to give you an idea of what came before 802.11ac
*These are the maximum values assuming all possible Spatial Streams are being used with the highest data rate possible. The maximum number of Spatial Streams right now are 3 for 802.11n and 3 for 802.11ac Wave One.
** These are values that are typical maximum when downloading raw data from a file server. Different applications and protocols like likely further decrease this number. It is still however a realistically achievable number.
Key Features of 802.11ac Wave One
Now that we have a good base understanding of how Wi-Fi works and some of its features and capabilities, let’s get into what 802.11ac offers over the predecessors.
It is important to understand that 802.11ac will come in Two Wave releases, with Wave One already out (Q3 of 2013) and Wave Two is expected to be released in late 2014. Wave two will bring a completely new hardware and capabilities. The difference in the waves is so large in fact, it might as well be called a different standard, but it isn’t.
Let’s finally get to the details of 802.11ac
– 5GHz Only – Since 802.11ac is only on 5GHz – this will force the use of the cleaner 5GHz band only. Currently the 5GHz band is much cleaner than the 2.4GHz band. If you were to use a spectrum analyzer and compare the two frequency bands, you would see a lot of noise and disturbances on the 2.4GHz band. On the 5GHz band there isn’t a whole lot going on usually. This is because a lot, if not most Wi-Fi networks, cordless phones, microwaves, Bluetooth and so many other devices all operate on the 2.4GHz band primarily. Of course this is subject to change in the future, but for now, the 5GHz band is the place to be. If you did not already catch on, the less interference and noise you have the better and faster your network will be.
– 80MHz Channels – Wider channels allow for more bandwidth.
– 256 QAM (Quadrature Amplitude Modulation) – This is increased from the 64 QAM possible on the 802.11n standard. More QAM allows a higher density of data to be transmitted over the same size pipe at a time. The denser the data, the more data you are sending over the same time frame.
– 802.11ac 3×3:3 Spatial Stream MIMO – MIMO increases speed and throughput
– 800 Mbps Realistic Throughput – This is achieved through a wider 80MHz channel, 3 Spatial Streams and 256 QAM Technology. This is significantly higher than the realistic throughput of 802.11n, which is is about 340 Mbps. Yes, the maximum theoretical speed you hear of is about for 802.11ac is 7Gbps. Truth is, we will never see these numbers – ever. (Max is actually a bit less than 7Gbps, but we will round it up for ease of use)
– Longer Range – We will get a bit of a boost in the range, thus increasing the distance we can be from the AP and still get signal. Can you hear me now?
– Lower Power Consumption – This will likely be achieved by the new, more efficient hardware, rather than the 802.11ac standard itself. Whatever it may be, no complaints here.
802.11ac Wave Two
Wave Two will have even more new and exciting features
– Everything from Wave One – Pretty self-explanatory, all features in Wave One will be present in Wave Two
– 160MHz Channel Support – Although the 80MHz channels are present in Wave One, 160MHz is brand new addition in Wave Two. This will further increase the throughput potential
– 3+ MIMO Spatial Streams – Three Spatial Streams is something that is present in 802.11n and 802.11ac Wave One. However, 3+ (4 and possibly more) Spatial Streams is something completely new. We expect 4 Spatial Streams to be present at the start of 802.11ac Wave Two. Just like stated above, Spatial Streams are what enables us to take advantage and increase the throughput. The more Spatial Streams, the more potential data throughput. We hope to see more spatial streams added with the progression of Wave Two as well.
– MU-MIMO (Multi-User-MIMO) Will Be Available – This is definitely and advancement in technology to take a note of. Currently in 802.11n and 802.11ac Wave One, only Single-User-MIMO is supported. At this point in time, most phones and tablets are only Single Spatial Stream, so if an AP supports multiple Spatial Streams, all but one are going to waste. With a four Spatial Stream MU-MIMO AP, we will be able to utilize these same Spatial Streams to several devices. (There will no longer be a waste of Streams). So for example, we will be able to have four separate Single Stream devices that share the Spatial Streams – one per person. It would also be possible to have two users on a Single Stream phones utilizing one stream each, and another user on a laptop utilizing the other two streams. This is a very good feature to be mindful of.
– ~1.6Gbps Of Throughput, Maybe Even Higher – Even more than Wave One! Now, we are speculating on the number, but this is our “educated guess”. With time this will probably increase to even more, so we will have to wait and see. We can accredit this high speed to the above listed features. Again, even with all these added features and capabilities, we still will never get close to the theoretical 7Gbps.
The Ugly Side of 802.11ac
Unfortunately, not everything is shinny and sweet with 802.11ac. Currently, there are several issues to take note of.
– Presence of Clients – Even if you were to deploy 802.11ac APs, do you have clients capable of connecting to them? There are not many devices that support 802.11ac currently. The newest MacBook Pro and MacBook Air support it. There are also some USB2.0/USB3.0 and PCI/PCI-E network cards which can be added to computers in order to support 802.11ac. Even so, most of the available 802.11ac network cards do not offer the full capabilities at this time. The drivers they use are new and unrefined. Users often suffer dropped connections and speed throughput is also very limited. Some examples of that would be the USB2.0 network cards, which are limited by the USB2.0 Bus at a maximum of 480Mbps theoretical throughput, which in reality is less. In this case, there would be absolutely no advantage of getting the network card, as it offers no increased speeds. Although USB3.0 ports and PCI/PCI-E slots can support the high data throughput, most network cards are still not build and configured to do so. So in most of the cases, you would be spending money on something that offers little or not improvement, other than being able to say “I am on 802.11ac! Wow!”. There ARE some network cards that are actually capable and offer the higher throughput speeds, but research is necessary to fish them out. Overall, there just aren’t very many users utilizing the 802.11ac at this point.
– New Hardware – One of the major problems like stated briefly is the Wave releases. There will be a completely different chip architecture used in Wave Two. While this may not sound really bad, it actually is. Every piece of hardware that you buy right now, which has 802.11ac Wave One chip, will not be able to handle the new features of Wave Two. Don’t worry, you will still be able to connect to the Wave Two APs and devices, you just will not be enjoying the extra benefits and increased speeds that they support. So are you going to buy 802.11ac APs and devices, and replace them all in about a year? Maybe, maybe not. I wouldn’t.
– Channel Bonding – There is a limitation you may not want to hear about. Although channel bonding will provide increased throughput which is absolutely amazing, it will also limit the number of channels you have available. If you were to start with all twenty-one 20MHz channels, this gives you a lot of flexibility of AP placement in a large scale deployment. When you combine the 20MHz channels to form 40MHz channels you now only have ten separate channels to utilize. This may still be usable in large scale deployments, but it really depends on factors I will describe a little bit later. When you start dealing with 80MHz you are only left with 5 different channels. This is usually not feasible for a large scale deployment. With 160MHz you are left with only two channels and this is definitely not possible in large scale deployments.
Now let me explain why you cannot use large channels in larger deployments. The most obvious fact is as the number of channels decreases, the placement planning gets very difficult and in some cases impossible. The reason for the previous statement is APs operating on the same channel cannot be next to each other. Having neighboring APs on the same channel will create interference and result in poor or no network connectivity. Channels must alternate – which is why the more channels you have the easier it is to create a placement plan. With two or even five channels available it may be impossible to achieve this alternate placement. Also, in a dense environment, the more users you have utilizing a specific channel, the slower it will get. If you have a lot of users, it is better to use the 40MHz and even the standard 20MHz channels as opposed to the wider channels. Ok, so “WHERE can I use the wide channels that support the super-fast speeds?” you might ask. Well, at a place where there are a few users with a large demand for throughput. Some examples would be gaming, video streaming, media studio, etc.
– Price – Generally, there is a higher cost associated with the latest and greatest, and 802.11ac capable APs and devices are no different. The new technology comes with a new and improved price tag. Eventually the price will subside, but for now expect to pay about extra 50% more than you would for the older 802.11n capable device.
– 256 QAM Is Short Range – The use of the 256 QAM allows for very high data speeds. Unfortunately, it will only be possible within a close range of the AP. How close, well, we are not able to provide an exact number as it depends on the environment, signal strength, noise level, and other interferences. You will probably have to be fairly close to the AP, but not so close that you would be placing your laptop on top of it. When you move out of the range of 256 QAM, you will drop down the 64 QAM and use a lower speed.
The Final Word
There are certainly many improvements with 802.11ac, as well as some limitations that come along. It can’t all be good. But overall, we will see a major step up from the previous 802.11n standard. Wave Two of 802.11ac will offer even more features and higher-yet speeds. I will definitely be upgrading, but probably not right away.
I hope this has been helpful and informative enough to have been worth your time. Questions and comments are welcome.
Peter Yordanov, Signing Out.
