3 ms·

A traditional radio would be like an LED and a photocell; you can blink the LED and detect it with the photocell, but the maximum data rate is fairly small. MI

by p1mrx 12y ago

A traditional radio would be like an LED and a photocell; you can blink the LED and detect it with the photocell, but the maximum data rate is fairly small. MIMO is more like vision. With a 2D array of pixels and a 2D array of photocells, you can transmit a vast amount of information through the same volume of space, and nearby equipment can reuse the same colors without much interference. With smarter radios and more antennas, radio still has a long way to go before we hit the universe's data cap.

Geee 12y ago
Expect everything bounces around, so it's like trying to decipher TV by watching the flickering on the wall. :) Actually, MIMO makes use of this (it works better in 'bouncy' non-line-of-sight multipath environments). By just a small antenna separation, the spatial channel characteristics can vary a lot as the signals might take a completely different paths, and the receiver is able to separate them from each other.
- IvyMike 12y ago
  > decipher TV by watching the flickering on the wall. Off topic, but... this has been done. Amazes me to this day. "Optical Time-Domain Eavesdropping Risks of CRT Displays" http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf
foobarqux 12y ago
That's a bad analogy. Just adding a transmitter doubles your power usage. MIMO is more efficient at the same power.
- jrockway 12y ago
  It's a good way of understanding spatial streams. Each pixel is a highly-directional transmit antenna, and each of your rods and cones is a highly-directional receiver. The result is 1920x1080 streams that you can interpret all at once! (Of course, given the extremely wide bandwidth of visible light and the high SNR between your TV and other light sources, you don't need that many spatial streams to beam the information representing HDTV across space. But humans.)
  - foobarqux 12y ago
    MIMO doesn't operate via "spatial" streams, the antennas are not "highly directional" to the extent that a tx antenna and an rx antenna get an interference free channel.
    - jrockway 12y ago
      True on a very technical level. MIMO is required to implement spatial streams. It's also the foundation for beamforming and diversity coding. But technically, MIMO itself is not beamforming or spatial streams. So while not a 100% perfect example, I don't think the original comment is all that terrible.

by p1mrx 12y ago

Geee 12y ago

Expect everything bounces around, so it's like trying to decipher TV by watching the flickering on the wall. :) Actually, MIMO makes use of this (it works better in 'bouncy' non-line-of-sight multipath environments). By just a small antenna separation, the spatial channel characteristics can vary a lot as the signals might take a completely different paths, and the receiver is able to separate them from each other.

IvyMike 12y ago
> decipher TV by watching the flickering on the wall. Off topic, but... this has been done. Amazes me to this day. "Optical Time-Domain Eavesdropping Risks of CRT Displays" http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf

foobarqux 12y ago

That's a bad analogy. Just adding a transmitter doubles your power usage. MIMO is more efficient at the same power.

jrockway 12y ago
It's a good way of understanding spatial streams. Each pixel is a highly-directional transmit antenna, and each of your rods and cones is a highly-directional receiver. The result is 1920x1080 streams that you can interpret all at once! (Of course, given the extremely wide bandwidth of visible light and the high SNR between your TV and other light sources, you don't need that many spatial streams to beam the information representing HDTV across space. But humans.)
- foobarqux 12y ago
  MIMO doesn't operate via "spatial" streams, the antennas are not "highly directional" to the extent that a tx antenna and an rx antenna get an interference free channel.
  - jrockway 12y ago
    True on a very technical level. MIMO is required to implement spatial streams. It's also the foundation for beamforming and diversity coding. But technically, MIMO itself is not beamforming or spatial streams. So while not a 100% perfect example, I don't think the original comment is all that terrible.