[awelkie]

I feel like limits on EIRP are overly conservative and restrict the usefulness of phased arrays. If the limit were on total radiated power, then your 1 watt WiFi router could have the range of a kilowatt transceiver with a reasonable number of antenna elements, while emitting the same total power as interference. But since the limit is on EIRP, the phased array is limited to the same range, and so there's no point in using a phased array over a single antenna.

Does anyone know if there's a good reason to use EIRP that I'm missing? I figure satellite communication terminals can have huge EIRPs because they're all pointed at the sky, but the FCC can't guarantee that the beams won't cross for other bands, so they limit the EIRP, but I still think we would all be better off of our systems were spatially selective.

[adrian_b]

If you use a directive antenna to concentrate the radiated power into a small solid angle, to reach a distant receiver, you also increase in the same proportion the interference for another receiver that is located in the same direction as yours, but which does not want to receive your signal.

So limiting EIRP provides a limit for the interference suffered by a receiver that happens to be in the direction towards which you transmit, for which it does not matter at all which is the total power that you transmit in all directions.

[tyzoid]

True, but it dissuades folks from using directional signals, broadcasting RF energy in more directions and increasing the noise floor for everyone. I feel like there should be some sort of middle point here.

[pc486]

EIRP is good at reducing uintentional interference. After all, you'd probably wouldn't like me pointing a 20 element yagi antenna through your house, denying your ability to use the spectrum in a reasonable manner, just so I could do a point-to-point fixed link.

EIRP minimizes regulations. It's a good trade-off over operator and installation licencing.

[MPSimmons]

It sounds like this is very definitely targeted at high speed personal-area-networks.

[ballooney]

Yes, for the same reason that I can look into a 5mW LED but 5mW of laser can blind me. Your neighbour's WiFi routewr might be entirely DoS'd by the Maser of RF coming through the wall at it from your phased array, even thoughh it's only 100mW.

[awelkie]

Sure, but the probability would be low-ish of that happening, and the other system could either switch frequencies or beamform a null in the direction of the interferer if they were also a phased array.

Maybe the EIRP shouldn't be unlimited, but I still think it would be beneficial to encourage spatially selective systems.

[palata]

This (and the parent) really sound super interesting to me, but I don't understand. Before I spend hours on Wikipedia reading about EIRP and phased array (and probably give up), is there a chance one of you could explain this briefly in words I may understand? :)

[Aurornis]

Modern MIMO is about utilizing the combined channel efficiently, not necessarily beam forming. In most cases you can still extract more capacity from a channel with two or more antennas within the same EIRP envelope as a single antenna.