Over the last few years there has been a lot of talk about the benefits of 802.11n and one of the key benefits this new standard gives us: MIMO. MIMO stands for Multiple-Input Multiple-Output. This directly relates to the amount of antennas an access point has – and the important thing to remember is that there is a distinction between a transmitting antenna vs. a receiving antenna. Confused yet? It gets worse. The numbers don’t have to match up. Depending on the Access Point (AP), there can be many combinations – starting with 1x1 (transmit is first) to 2x1 to 2x2 and all the way up to 4x4 – though I am unaware of any 4x4s out there.
In the majority of indoor WLAN implementations though, you have wide-open areas and lots of variables that affect Radio Frequency (RF) behavior. Take a hospital for instance – or really any standard indoor office environment. There are now many obstructions between the transmitting AP and receiving clients (laptop). Walls, elevators, cubes etc. These all reduce the signal strength of the radio signal as it is sent out. A MIMO AP sends out multiple signals – each from a transmitting antenna. Because those transmitting signals can (and always will) reach the intended receiver via slightly different routes (reflecting off different surfaces), the receiver gets these multiple signals not all at once, but over the course of a few nanoseconds. The ability for a MIMO receiver to collect these multiple streams, and process and use all of them is another large benefit with this technology. Again this benefit is predicated on having a MIMO transmitter and a MIMO client.
What is the benefit to all of this? The majority, if not all, client adapters being shipped out now are 802.11n MIMO capable. There are still a huge number of legacy 802.11a/b/g clients out there and will be for a few years anyway. The good from all of this is that they can all cohabitate. The new 802.11n APs being deployed must take into account the legacy devices while also provide the enhanced capabilities mentioned above. Even in an environment that had 100% legacy, clients are still going to see an increase in throughput, range, and data rates. Beyond that, the more clients used in the space the better off you will be.
As a side note – with these more powerful APs out there that are now capable of 450Mbps+ throughputs, you need to ensure you are giving them Gigabit Ethernet wired handoffs. Kind of senseless if you have your LAN be the bottleneck – for once!