Over many years of working with wireless, one thing I have been overwhelmed with is the time and effort that can go into the selection of a Wireless LAN infrastructure. Research into each and every Wireless LAN vendor, and there are a number of us, is tirelessly (or so it seems) undertaken, trials and proofs of concept are run, references are taken, and then the most suitable technology (hopefully) is chosen. This is as it should be. The thing that surprises me however, is how often little or no time or effort goes into investigation of the other half of the equation - the WiFi chipset within the mobile device.
But 802.11n is 802.11n, right?
Not quite.... I am sure many of you know this, but I thought it would be good to just give a brief overview of what difference there is in the capabilities of different implementations of the 802.11n standard.
Firstly, with 802.11n, we have the ability to run within either the 2.4GHz or 5GHz frequency bands; commonly known as 11bgn and 11an, respectively. Each of these runs separately from the other, and most enterprise class WiFi vendors would specify dual band access points for educational campuses.
Secondly, 802.11n added MIMO (Multiple In/Multiple Out) capability. By utilising multiple antenna chains per radio, it is possible to send multiple data streams simultaneously, each carrying additional data. The standard allows for up to 4 spatial streams. Most enterprise WiFi vendors would specify either dual or triple stream access points for educational campuses.
Thirdly, 802.11n allows for the use of varied channel widths. Both 20MHz and 40MHz channel widths are configurable. The benefit of a 40MHz channel width being slightly greater than 2x performance over 20MHz.
So what does that mean for me???
The easiest way to show the impact of this variance in implementation of 802.11n is by looking at the achievable data-rate for each combination of Spatial Streams and Channel Widths.
Datarate based on Channel Width and Number of Spatial Streams
# Spatial Streams
20MHz (With SGI)
**As there are no commercial implementations of 4 spatial streams that I am aware of (happy to stand corrected), any comparisons to follow will be based on 1, 2 and 3 spatial stream implementations.
So, as you can see, there is huge potential for variance in performance of your wireless network based on the devices you choose. If you were to choose, for example, a Broadcom 4313 WiFi chipset, you would be limited to 20MHz operation and a single spatial stream in just the 2.4GHz band. If, however, you were to choose instead the Intel 6300 chipset, you would have access to 40MHz operation and three spatial streams in both spectra. In a standard classroom deployment with 30 devices running on a single AP, the BCM4313 solution would be limited to 65Mbps (or 72 with SGI) aggregate across all devices, whereas the Intel 6300 based solution would achieve up to 450Mbps aggregate on each of the bands, totalling up to 900Mbps. This equates to an increase to 12.5x (with SGI) performance through the use of a different '11n' device.
Finding out which WiFi chipset your device vendor has chosen to implement isn't always that straight forward - but worth it if you can see a 13x performance increase wouldn't you say? In order of preference, I would demand dual band as a minimum. Dual band WiFi chipsets are available in Mobile Phones, Tablets, Netbooks and Laptops. Then I'd look to push for multiple spatial stream capability, but remember, if you have a dual stream AP, then a triple stream client won't help! 40MHz capability is normally a given on 5GHz capable devices, but not all - so worth checking for!
Where do you check???
Well, the WiFi alliance is a great place to start. They have a search facility available at Certified Products Advanced Search | Wi-Fi Alliance . If you speak to your device vendor, and find out the 1500 notebooks you are looking to purchase contain the Realtek 8192CE WiFi chipset, then goto this page and search for 8192CE where you can then view the WiFi certificate for the device. Within this certificate, you can see that the device is only certified for 2.4GHz, but that it does support 2 spatial streams, both for transmit and receive. It's not the slowest device on the market, but maybe you should at this point consider checking with the laptop vendor if they have an alternative WiFi chipset available that supports both 2.4GHz and 5GHz - after all, it'll allow you at least twice the performance from your WiFi infrastructure than the 2.4GHz only device, and typically shouldn't be too much more expensive.
What about 11ac?
Well, 802.11ac both simplifies and complicates things (if that's possible!). The good news, is that 802.11ac mandates 5GHz operation. It is however possible to have a 5GHz only device, although all implementations I have seen to date include 2.4GHz operation for 802.11bgn. On the flip side, there is a greater variance in the numbers of spatial streams (1-8 by the standard) and the channel widths available (20MHz, 40MHz, 80MHz and even 160MHz when 2nd Generation 11ac chipsets hit the market).
The key thing here will be to ensure that any 802.11ac access points you are looking at today support the current maximum capability - 3 spatial streams and 80MHz wide channels (this is based on my current understanding of the market; 4 spatial streams and 160MHz channels are expected in late 2014 or even early 2015). The same principles will exist for your client devices as above.
I guess the key thing I am getting at here is that It Takes Two to WiFi. You can buy the meanest, fastest, most capable WiFi infrastructure in the world, but if you load it up with single band, single stream WiFi devices, it's just a waste!
I am not sure if you will find this post useful, however I am happy to answer any questions you may have on the subject!
The comments and opinions here are my own and do not necessarily reflect the views of my employer!
Last edited by wotnowires; 29th October 2013 at 09:24 PM.
Some good information here. Just like to add that when selecting a wireless product you want to ensure that your solution is going to be viable in the BYOD environment we are in. Admins of the wireless network should push for their organization to purchase 5Ghz capable devices with good NICs, however, there should be the understanding that now or in the future the wireless network will likely be opened up to any wireless device that desires to connect. Expanding the width of your channels can increase speeds, but it does open the network up to more possibilities of wireless interference and can reduce the ability to mitigate it by moving to a less cluttered channel since your options will be more limited and expanded channels will have more overlap on the spectrum. That said, having wider channels and devices that can utilize them not only improves connectivity speeds it will reduce the AP and channel utilization since those devices can push more data in a shorter amount of time freeing the air time for other transmissions.
All of this shows why it's even more important to understand wifi before making any buying decisions.
Professional WLAN designers use design tools to balance all of these requirements in order to show the most effective design to meet the requirements, and it's sometimes tricky. It takes a big investment in time, tools and experience to become proficient at WLAN design. I wish that more people would consult with WLAN professionals before ordering enterprise equipment and just randomly sticking them up.