overview of RAN solutions?

I am wrapping my mind around the myriad of RAN solutions out there,
and I would appreciate it if someone had a good overview of the
subject or could direct me to new vendors worth investigating.

So far, I see ones that are designed to (a) increase coverage, (b)
increase capacity, or (c) do some combo of (a) and (b).

Some solutions suck in the donor signal (antennas on top of roof) and
then blow it back indoors on various frequencies. A good example of
this is something like Axell, which doesn't appear to add much
capacity, just stretch the existing uplink's capacity by amplifying
the signal indoors. Other solutions (IP-RAN, E-RAN, etc) have an
Internet / IP component and allow for all sorts of cool things
(synchronization between units for soft handoff, etc). SpiderCloud
seems to be a good play here. Then there are other niche plays that
don't do everything, but seem to be good enough for various
applications, like SMS texting. If I remember right, IPAccess did
this sort of thing for schools (which is perfect for emergencies).

Any others I should look into? I'm primarily interested in
carrier-grade ones...