There is a big raging debate in the Wi-Fi industry right now about LAA-LTE. This is a proposal by cellular carriers to use the 5 GHz unlicensed band to perform data offload, but using a LTE protocol and not Wi-Fi. Of course the mobile carriers are going to proclaim how wonderful LAA-LTE is for their network operations and sugar-coat the whole Wi-Fi co-existence problem.
LTE, as a protocol, is
designed to work on a licensed spectrum where you do not have to compete
with, or even share, the resources with another network. The "LAA" here stands for "licensed assisted access", which is a wonderful Orwellian term that sounds really good but actually means the complete opposite of what it sounds like. In this context, "licensed assisted access" means that your traffic is traveling over unlicensed spectrum.
Whether licensed or not, wireless radio technology, being half duplex, is all about collision avoidance. LTE uses time division multiplexing, generically known as TDMA. TDMA, and
all of its variations, are designed to work under the central premise
that the network coordinates the usage of the spectrum, in order to
prevent collisions from occurring between two or more radio transmissions on the same frequency. Wi-Fi, by contrast, works by clients
"contending" for the space and the right to transmit. Most people don't understand that when you have a network with an AP and 20 client devices, the AP has to compete for the next transmission slot along with all of the clients, and while QoS modifies the contention rules, it is only a statistical advantage, not a guarantee.
Wi-Fi and LTE are fundamentally conflicting and
mutually exclusive architectures. Even if LAA-LTE allocated a large
portion of the spectrum time to "external Wi-Fi", early studies (see http://www.cablelabs.com/wi-fi-vs-duty-cycled-lte/) have already shown that latency in Wi-Fi
increases astronomically when an LAA-LTE network is present, even under
light duty cycles. There are also no guarantees or requirements that
LAA-LTE has to be configured to "play nicely" in the 5 GHz sandbox.
It is ironic that 2.4 GHz and 5 GHz used to be considered "garbage
bands" that nobody in the cellular space wanted to get close to, until
other companies figured out how to use the bands effectively (and make
money from it). Now, these same carriers want to save money on licensed
bands by seizing control over "free" unlicensed bands with LAA-LTE.
At the same time, the way the FCC rules are currently structured, the
bands are unlicensed and thus there really isn't anything that the
industry can do to stop it. If the 800 lb gorillas in the room want to
bully their way into taking over the spectrum, they have the ability to
make a real go of it.
One idea I've had on this subject is to take the proposed 5.9 GHz band
that Congress wants to open up and dedicate those channels to
applications like LAA-LTE, to keep it unlicensed yet, by mutual
agreement, separated from Wi-Fi. Such an approach is unfortunately way too
logical and reasonable to likely gain any traction.