In the context of a competition, I need to set up a wireless link between a base station and a mobile target.

The mobile target:

-> will always be within the same 180 degree cone from the base station's perspective (i.e. the mobile target will always be 'in front of' the base station and never 'behind')

-> will go out pretty far (1 km - 2 km) away from the base station

-> needs to stream low-quality video back to the base station

-> may be NLOS sometimes; the mounds behind which the mobile target will go that make it NLOS aren't very big (1 m - 2 m)

-> is in a desert-like setting (no trees, no structures, no giant rocks) so the signal shouldn't be bouncing (thus no multi-path problem)

One of my thoughts was to use a hardy wireless router that runs 802.11n and thus MIMO and change it's 4 omnidirectional antennas for 4 large directional ones, placed a few meters up on a mast. I would select the antennas to each have about a 60 degree cone and place them so that they cover the 180 degrees.

I know MIMO is better known for solving the signal multi-path problem but I was hoping my idea was sound and that by using 4 directional antennas (with higher gain than 4 omnidirectional ones), I could effectively handle the 180 degrees that need to be covered; the MIMO technology would be used to coalesce the signal received at the antennas.

In other words, I was hoping the MIMO technology would make sure that whichever directional antenna the signal from the mobile target is hitting, the wireless router would reconstruct it as one signal. This would effectively be the same as having 1 giant 180 degree directional antenna.

How wrong am I doing this?

  • 1
    \$\begingroup\$ How much more gain are you going to get from your antenna configuration you are considering compared to a dipole? If it's less than 20dB +plus complications, then maybe pumping out 20dB more power from the mobiles might be the answer. What bandwidth are you transmitting per mobile? Do you have any licencing problems? \$\endgroup\$ – Andy aka Sep 26 '13 at 20:34
  • \$\begingroup\$ Sorry about this late reply, I somehow expected to be automagically notified when someone posted but it seems I wasn't. Well, competition is in the US where the law stipulates maximum EIRP of 4 Watts (36 dBm) on 2.4 GHz, while the maximum transmission power before antenna and cable loss is 1 Watt (30dBm). \$\endgroup\$ – Alex Teodor Oct 3 '13 at 6:38
  • \$\begingroup\$ Given the single mobile platform can output no more than 4 Watts (36 dBm) in any configuration. I'm not sure any licensing can increase this legal limit. However, the 4 directional antennas would be sitting at the base station, providing gain on the receiving side. The omnidirectional antenna with the greatest gains I've found had 15 dBi (which really seems like a lot). Using the MIMO + directional technique I described would have 18 dBi directional antennas. \$\endgroup\$ – Alex Teodor Oct 3 '13 at 7:03
  • \$\begingroup\$ In fact, the more I think about it, the more surprised I am that directional antennas only provide 3 extra dBi, although I guess 3 dBi is twice the power. \$\endgroup\$ – Alex Teodor Oct 3 '13 at 7:04
  • \$\begingroup\$ you should be able to get a lot more than 3dBi. \$\endgroup\$ – Andy aka Oct 3 '13 at 7:17

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