It doesn't have enough energy for that, precisely my point. Wireless beam forming demands a multiple antenna/DAC activation energy (even if just "listening" RF

It doesn't have enough energy for that, precisely my point. Wireless beam forming demands a multiple antenna/DAC activation energy (even if just "listening" RF) two orders or three above the energy harvested for the muC as cited in these works. Even if we want to say schedule things correctly, it's very difficult in practice for commercially available muC's to keep accurate timer without skew in very low power modes for the once-a-day reactivation which will eat 99% of your condensator energy. If such a low activation energy specialised transceiver antenna exists commercially, I shudder at its price. And then of course the packet emission could fail to be received at that precise moment for any number of reasons. Beamforming is a high-power, high bandwidth, always-on high-computation sport, AFAIC.