RRU stands for Remote radio unit. On previous versions the radio unit was on the ground and all radio signal was sent up the tower using coaxial cable. This caused a lot of signal loss and required a TMA (tower mounted amplifier) . This causes both a degradation of signal quality, and a higher power consumption. Also, this took up more ground space. With new technology, they have one small control unit mounted on a rack that runs up a fiber cable to the top. Then the fiber is terminated at the RRU where that is connected to the antenna via one 3 meter (usual) jumper with no loss whatsoever. I see both advantages and disadvantages. I hope the are highly stable, as all maintenance will have to be done by a climber, where as before radio failures were fixed with cell techs. I saw a lot of lightning strikes cause a lot of damage. I saw a good amount of RRU failures at launch, but they see to be getting better. We will be doing our first AIR install next week and I must admit, I a skeptical.
BTW this is for AT&T upgrade.