Wireless Networking for the Rest of Us

Wireless networks are everywhere and have become a part of our everyday lives because they allow people to remain connected without sacrificing mobility.Their popularity really skyrocketing in the past six months and I couldn’t be happier about that since I am a bit of a wireless junkie.  

I think a large contributor to the success of wireless networking is their relative ease-of-use. It is very easy for someone with very little wireless knowledge to setup and connect to a basic wireless network; this makes them very attractive.  Unfortunately, it is the apparent ease-of-use that masks the fact that wireless networks are incredibly complex and that they require a lot technical skill and planning to fully understand and deploy properly. With that in mind, consider this my first post in a series designed to explain the inner-working of wireless networks in language that anyone can understand. Basically, I want to take the technical-mystery out of wireless networks and help people understand how they work.

The remainder of this post is actually a republishing of a post I created for my, now retired, personal blog several months ago. Posts to follow will contain explanations of how antennas work, understanding radio frequencies (RF), and authentication and encryption. Without further ado, I give you “What You Thought You Knew About Your New 802.11n Router”:

If you have recently purchased a new wireless router, the odds are good you are the proud owner of an 802.11n router. Odds are equally as good that the sales person told you all about the increased range, reliability, and speed that you will experience with your new purchase. It’s during the speed pitch that the sales person, usually a high school kid with no wireless networking background, will introduce you to the term 3×3 MIMO and make one of the following claims:

  1. “3×3 MIMO means the router can send and receive three times as much as the older wireless routers could.”
  2. “3×3 MIMO means you can send and receive three streams of data (spatial streams) at the same time, effectively tripling your speed.”
  3. “This router has three antennas so three different computers can connect without interfering with each other since they will each have their own dedicated antenna.”

The first two statements actually contain tiny shreds of truth but are incredibly over-simplified and misleading. The third statement is a piece of creative genius which, from the look on the teenager’s face when I asked him what 3×3 MIMO meant, was thought up on the fly. After I left the store, I’m sure he gave himself a pat on the back for thinking so quickly on his feet. Unfortunately, all of this quick thinking means you probably bought an 802.11n router with a slight misunderstanding of its capabilities. 

True, your new 802.11n router may indeed say 2×2 MIMO, 2×3 MIMO, or 3×3 MIMO on it. Also true, those number do refer to the number of radio chains in the router. Here’s the skinny on radio chains and MIMO terminology:

2×3 – This refers to the number of transmitters and receivers in your access point or router, respectively. In this case, the router would have two transmitters and three receivers.

MIMO – This means multiple-input multiple-output. Your router is capable of sending and receiving multiple signals at the same time because it has multiple radios and antennas.

Radio Chains – A radio chain is comprised of a radio, and all of the supporting components for that radio. A radio chain does not need to have both a transmitter and a receiver. Here are a few examples of MIMO systems with the number of radio chains shown:

  • 2×2 MIMO – Two radio chains. Each radio chain has a transmitter and a receiver.
  • 2×3 MIMO – Three radio chains. Two radio chains are comprised of a transmitter and receiver, and one of the radio chains only has a receiver.
  • 3×3 MIMO – Three radio chains. Each radio chain has a transmitter and a receiver.

Understanding this terminology, you can now see that there may have been some truth in what the sales person told you in the store. A 3×3 MIMO system may actually be capable of supporting three spatial streams. If that was the case, you would definitely see a theoretical tripling of your wireless speeds. Unfortunately, as I’ve shown above, the term 3×3 only refers to the number of transmitters and receivers; it does not speak to the capabilities of the access point or router itself. Most 3×3 access points and routers on the market today actually only support two spatial streams. This means that, while they may have three transmitters, they were not given the capabilities of using all three transmitters to broadcast discrete streams of data simultaneously, so you’ll only really see a theoretical doubling of your wireless speeds instead of the tripling you were told about at the store.

Dan C.

Did this post explain MIMO and 802.11n in a way that you could understand? If not, please let me know which parts I could explain better and I promise to try and clarify my explanations.

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