Gigabit Wi-Fi Design – More Devices, More Capacity, More Problems.

Fluke 802.11ac

When I first started learning how to deploy Wi-Fi networks I really only had a vague knowledge of how it all really worked. In those days, I relied heavily on friends who were experts to give me a basic idea of how Access Points should be deployed. It was in a way much simpler to design WLANs as well, as usually you were only concerned with covering all the places people usually would use their laptops in a building. This requirement could be ‘we just want conference rooms’ or ‘we just want coverage in the executive suites as everyone else has desktops’. My first major deployment was a college, however, and their requirements were to have coverage everywhere students went with their laptops. This required us to design coverage for over 70 buildings and additional outdoor areas which was a huge undertaking for me. I learned a lot about proper RF design from doing this.

The major change we have seen in the last few years is that the main way people on any device access the network is wireless. We have mobile phones, tablets, laptops and all sorts of other devices using the WLAN and this means that RF design has changed from just making sure coverage is good to making sure the network performs well everywhere. This is a huge change in emphasis from ‘nice to have’ to ‘mission critical’. It’s simply not good enough anymore to throw up APs and hope the WLAN performs acceptably.

This was emphasized for me in the first session at Wireless Field Day 5 with the Fluke Networks AirMagnet Product division presentation. They wanted to talk about the updates to the Survey Pro product they were working on to support 802.11ac, the upcoming Wi-Fi standard. For an excellent overview of the impact of 802.11ac I highly recommend Andrew vonNagy’s Revolution Wi-Fi blog series on 802.11ac Gigabit Wi-Fi. For this blog, I am going to concentrate on the updates to AirMagnet Survey Pro.

First of all I will state that a large part of the driving force behind Gigabit Wi-Fi being marketed to consumers (almost too much hype) is the explosion in wireless devices that are being used. This has resulted in the consumerization of IT and major headaches for most IT departments in handing the load on their WLANs. It is still, however very early days with these devices as the standard is not yet ratified and there is a large amount of inconsistent performance in client devices being sold. Even just that the first phase client devices support 2×2:2 (that’s two transmit and receive antennas and 2 spatial streams) means those devices can potentially do 867Mbps over the air and this could saturate USB2 connections. So from the client side, USB3 is needed and I would say that the biggest gain will be when device manufacturers integrate 802.11ac into their products with PCI-Express cards.

The uneven client performance will eventually be fixed by driver or chip updates but this is just one of the factors to consider. Using older 802.11a clients will substantially slow the network down and there is additional considerations if clients support 1, 2 or 3 spatial streams. From the AP side of things in the WLAN contributing factors are channel allocations, denser deployments to support high modulation rates (256-QAM) and many others. Basically as the environment has gotten more complex and variable it means less predictable performance and that the PHY rate is no longer an accurate predictor of performance. That’s without even adding in the challenges of trying to use 80MHz channels.

AirMagnet Survey Pro is attempting to meet these challenges head on by bringing into their tool features needed to more clearly measure client performance. The reality here is that even for experienced users of Survey Pro, your methodology will incorporate some kind of measuring upstream and downstream performance testing to optimize client networks. Survey Pro incorporates iPerf so that performance data can be gathered as part of an active survey. Fluke believes that doing onsite validation surveys with 802.11ac and incorporating performance testing into that is the way to verify that the network will perform to client specifications.

Other additions to Survey Pro that are more specific to 802.11ac are new heatmap views that show primary and secondary channel overlap. This is particularly needed for 80MHz channels as channel planning will need to account for interference of secondary channels (CCI). Another view shows where APs are getting the new 256-QAM rate, which should give a good overview of the performance dropoff as clients move away from the AP. For those of you with a Gold Support contract for Survey Pro you can go to this page to sign up for the beta and see for yourself some of these features in action. You will of course need a supported 802.11ac adapter.

It will be challenging for WLAN designs as 802.11ac begins to rollout. More thought will need to be put into performance testing by validation engineers to make sure that the design meet’s customer criteria. I expect that client drivers will eventually even out as 802.11ac becomes a more mainstream technology. Unfortunately we will probably have to go through another round of this with MU-MIMO in Phase 2, but more on that in a later blog.

2 Responses to “Gigabit Wi-Fi Design – More Devices, More Capacity, More Problems.”

  1. The problem of AC is to use this huge part of spectrum… We need that all governments create a bigger spectrum to use it better. Nice article. Thanks!

  2. GGR says:

    The main problem with WiFi currently for most is interference on the 2.4ghz frequency.

    I think it will be great when more devices adopt 5ghz compatibility allowing for a more reliable experience at home and at work.

    Great post by the way!

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