In the frequency arrangements currently considered in 3GPP, several TDD carriers possibly belonging to different operator can be allocated next to each other. To handle interference between UL and DL of adjacent carriers, on the eNodeB side, one may at least use filtering to reduce interference between UL and DL on adjacent carriers.
Some guard band is needed and the requirement on the filters is very tough as compared to FDD, especially in the case with co-siting, probably leading to specific analog filter design for the particular carriers.
However, a more efficient approach is to synchronize the carriers to a common reference and allocate resources to UL and DL on each carrier so there is no overlap between them in time. This requires the frame structures of the two TDD systems to be sufficiently compatible. The main advantage of such a solution is that interference, and more importantly, radio requirements are similar to FDD which means that it is possible to design and build eNodeBs and UEs for entire frequency bands allocated to TDD rather than for specific carriers.
The frame structure allows setting the total lengths of the downlink and uplink levels with a more finer granularity than 1ms sub-frame levels by also adjusting the lengths of DwPTS and UpPTS.