What they have in common TDMA and GPS ?
TDMA (Time Division Multiply Access) until recently was associated more with mobile networks, or satellite, rather than with Wi-Fi networks. Ubiquiti's AirMax protocol has introduced this alternative method of accessing the media along with some other manufacturers like Mikrotik - NV2 or Motorola's Canopy.
Why a GPS receiver in Ubiquiti Rocket M ?
TDMA transmission works in the way that Access Point is allocating time slots for the stations, - short stretches of time in which they can transmit and receive data. The TDMA access to the media has a very big advantage over the traditional CSMA approach as there is no hidden node issue (the stations don't have to "fight' for transmission and they get more time
slots if they require more bandwidth - dynamic allocation of resources) which increases the overall network capacity.
Along with introducing the GPS receiver the Rocket M series has made new level of the wireless networking. Why?
Time is the answer. GPS is used not to provide the position of the device (even though it could be). It is needed for something else.
The problem with congested networks is the same everywhere - there is situation where on the mast or pole there are several wireless devices (base stations) that are broacasting in the same frequency (or close to each other). If the number of these devices is bigger that the non overlapping channels (only 3 such channels in 2.4GHz) then they start to interfere with each other. In such case even the TDMA is not working well. That's why Ubiquiti mage the GPS Rocket M.
Each Rocket M with GPS synchronizes its time with the satellite via GPS (each sattellite has very accurate clock) so the timing is very precise. If one of the Rockets is set up as a master then and the other need to be working in slave mode (so they share the timing) and that way the slave devices are very precisely synchronizing time slots with the Master (Master makes the time slots for all the stations). Thanks to that solution (Airsync) the Master devices are not interfering with each other and they can even work on the same channel! The synchronization doesn't affect the network speed or capabilities in any way.
On the other hand Mikrotik is working on similar approach with it's NV2.