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Message: <blockquote data-quote="knutinh" data-source="post: 62910" data-attributes="member: 14776">The main benefit of 802.11n seems to be MIMO with the promised ability to:-avoid local variation due to fading-optimally use of the "envelope" given by max radiated power and max bandwidth usage through spatial mechanismsIn all radio communications, the received signal level is important because it is what allows us to receive a waveform that can be decoded into ones and zeros. Actually, it is usually the system signal-to-noise ratio that is most important, but since signal and noise is uncorrelated, and noise may either be white noise from electronics or interference from other radios, we cant do a lot about it.Anyways, the signal level is usually a function of distance. Greater distance means that a radiated wave "thins out" just like the sun is weaker on Pluto than on Earth. The signal level will also drop if we have an object blocking the free line of sight to the transmitter. Try closing the window to a (acoustically) noisy street for an example. But on top of this, we get what is known as "fading". Real environments, especially human-made, contains a lot of flat structures that reflect radio waves well. When you are listening to a transmitter you are actually listening to a sum of many reflected echos that are shifted in time and attenuated. This fading patter can occur as a function of position (the pattern changes if the distance to the reflectors changes) or time (if the reflectors themselves are moving). This pattern can look like:<img src="http://upload.wikimedia.org/wikipedia/en/thumb/5/5c/Rayleigh_fading_doppler_100Hz.svg/765px-Rayleigh_fading_doppler_100Hz.svg.png" alt="" class="fr-fic fr-dii fr-draggable " style="" />Now, if the receiver by accident is in a deep "null", the SNR may be very low, even though the averaged SNR over time and position is good enough. Moving by a halv wavelength often is enough to get out of this null, and a wavelength at 2.4 GHz isnt much.Now, I have understood it as MIMO technology sees several spatial "channels" and tries to optimize a budget where the total transmitted power is balanced against each other. The simplest modus would be simply selecting the antenna that has the best SNR at every instant. That is similar to classic antenna diversity. But if antenna #1 and antenna #2 have paths to receiver antenna #1 and #2 that are different, one may benefit from dividing power between those two, and then using error correction to remove interference.regardsknut</blockquote>

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