2   k bit / s ▁in ▁an ▁expanded ▁ 1 5 0   k Hz ▁channel . ▁To ▁overcome ▁the ▁limitations ▁many ▁software ▁vend ors ▁have ▁begun ▁to ▁consider ▁hy brid ▁solutions ▁where ▁T ET RA ▁is ▁used ▁for ▁critical ▁sign alling ▁while ▁large ▁data ▁synchron ization ▁and ▁transfer ▁of ▁images ▁and ▁video ▁is ▁done ▁over ▁ 3 G ▁/ ▁L TE . ▁ ▁T ET RA ▁usage ▁▁ ▁there ▁were ▁ 1 1 4 ▁countries ▁using ▁T ET RA ▁systems ▁in ▁Europe , ▁Middle ▁East , ▁Africa , ▁Asia ▁Pacific , ▁Car ib bean ▁and ▁Latin ▁America . ▁ ▁The ▁T ET RA - system ▁is ▁in ▁use ▁by ▁the ▁public ▁sector ▁in ▁the ▁following ▁countries . ▁Only ▁T ET RA ▁network ▁infrastr ucture ▁install ations ▁are ▁listed . ▁T ET RA ▁being ▁an ▁open ▁standard , ▁each ▁of ▁these ▁networks ▁can ▁use ▁any ▁mix ▁of ▁T ET RA ▁mobile ▁terminal s ▁from ▁a ▁wide ▁range ▁of ▁supp liers . ▁ ▁Techn ical ▁details ▁ ▁Radio ▁aspects ▁ ▁For ▁its ▁mod ulation ▁T ET RA , ▁uses ▁ ▁differential ▁quadr ature ▁phase - shift ▁key ing . ▁The ▁symbol ▁( ba ud ) ▁rate ▁is ▁ 1 8 , 0 0 0 ▁symbols ▁per ▁second , ▁and ▁each ▁symbol ▁maps ▁to ▁ 2 ▁bits , ▁thus ▁resulting ▁in ▁ 3 6 , 0 0 0   bit / s ▁gross . ▁ ▁As ▁a ▁form ▁of ▁phase ▁shift ▁key ing ▁is ▁used ▁to ▁transmit ▁data ▁during ▁each ▁burst , ▁it ▁would