LPPa stands for (LTE protocol positioning annex). It might be Ue-associated and non-Ue associated.
For more details check this link.
http://lteworld.org/blog/lte-ue-positioning-e-utran and 3GPP 36.413 release 9
On what parameter basis, eNodeB changes its current transmission mode to different transmission mode for an UE ?
What parameters are considered to take decision on transmission mode ? Does the eNodeB inform to UE about the selected TM ?