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Maximum Practical Datalink Spectral Efficiency
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ogden:

--- Quote from: NiHaoMike on June 14, 2019, 06:18:34 pm ---Even a fairly small dish antenna like the ones used for residential satellite communications are on the order of 30dBi or more. The really big ones used for radio astronomy can do as much as 80dBi.

--- End quote ---

My question was - are antenna beams narrow enough so they can get away w/o any actual MIMO DSP math in the modems? Antenna gain alone does not answer this question. What we need to know is radiation pattern at 1.5km distance.


--- Quote from: coppice on June 14, 2019, 02:24:33 pm ---The potential of MIMO, given enough room for the antennae, is so huge that 50 bits/Hz just takes effort, but little innovation, to achieve.

--- End quote ---

DSP engineering quote of the year :) Search patents for just MIMO keyword. If this is not convincing enough then I simply give up.
TheUnnamedNewbie:

--- Quote from: ogden on June 14, 2019, 06:47:43 pm ---
--- Quote from: NiHaoMike on June 14, 2019, 06:18:34 pm ---Even a fairly small dish antenna like the ones used for residential satellite communications are on the order of 30dBi or more. The really big ones used for radio astronomy can do as much as 80dBi.

--- End quote ---

My question was - are antenna beams narrow enough so they can get away w/o any actual MIMO DSP math in the modems? Antenna gain alone does not answer this question. What we need to know is radiation pattern at 1.5km distance.


--- Quote from: coppice on June 14, 2019, 02:24:33 pm ---The potential of MIMO, given enough room for the antennae, is so huge that 50 bits/Hz just takes effort, but little innovation, to achieve.

--- End quote ---

DSP engineering quote of the year :) Search patents for just MIMO keyword. If this is not convincing enough then I simply give up.

--- End quote ---

I seem to recall a rule of thumb that 1 degree beamwidth equals about 46 dB with a parabolic dish. Going by that assumption, the antennas would have to be about 20 meters away from each other at 1 km to have 6 dB (assuming both antennas have that gain) less received power than the neighbouring antennas, so I am going to go with these needing quite a lot of DSP to get going. It could be that they actually get even narrower beamwidths, which would help, but I am not sure. (I don't know if the 45 dBi I was given included efficiency of the antenna etc - which at 70 GHz is going to be nothing to write home about).

Would be interesting to find out, but I don't know how much these people can share. I'll look up some publications by those groups later to see if that has any info.



The thing that is impressive here is that, to my knowledge, these are not big parabolic dishes, but arrays.
coppice:

--- Quote from: TheUnnamedNewbie on June 15, 2019, 07:39:11 am ---
--- Quote from: ogden on June 14, 2019, 06:47:43 pm ---
--- Quote from: NiHaoMike on June 14, 2019, 06:18:34 pm ---Even a fairly small dish antenna like the ones used for residential satellite communications are on the order of 30dBi or more. The really big ones used for radio astronomy can do as much as 80dBi.

--- End quote ---

My question was - are antenna beams narrow enough so they can get away w/o any actual MIMO DSP math in the modems? Antenna gain alone does not answer this question. What we need to know is radiation pattern at 1.5km distance.


--- Quote from: coppice on June 14, 2019, 02:24:33 pm ---The potential of MIMO, given enough room for the antennae, is so huge that 50 bits/Hz just takes effort, but little innovation, to achieve.

--- End quote ---

DSP engineering quote of the year :) Search patents for just MIMO keyword. If this is not convincing enough then I simply give up.

--- End quote ---

I seem to recall a rule of thumb that 1 degree beamwidth equals about 46 dB with a parabolic dish. Going by that assumption, the antennas would have to be about 20 meters away from each other at 1 km to have 6 dB (assuming both antennas have that gain) less received power than the neighbouring antennas, so I am going to go with these needing quite a lot of DSP to get going. It could be that they actually get even narrower beamwidths, which would help, but I am not sure. (I don't know if the 45 dBi I was given included efficiency of the antenna etc - which at 70 GHz is going to be nothing to write home about).

Would be interesting to find out, but I don't know how much these people can share. I'll look up some publications by those groups later to see if that has any info.



The thing that is impressive here is that, to my knowledge, these are not big parabolic dishes, but arrays.

--- End quote ---
The cellular industry has driven some pretty impressive developments in what can be achieved with a compact low cost antennae elaborately formed from simple stamped sheets. That said. the need for extensive DSP, and tight constraints on receiver front end performance, are a given for this type of system. Forget any idea of focussing an RF beam at an antenna so well that it won't significantly spill into adjacent ones. The antennae needed to do that at such low frequencies are largely impractical, even at the high end of the RF band. Even at optical frequencies, where its easy to make a diffraction limited beam, the atmosphere can still fuzz it up enough to cause trouble at the receiver. However, even small amounts of physical isolation can substantially reduce the processing problems at the receiver, so they have a big payoff.
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