Orthogonal principle in details :-
Signals are Orthogonal if they don’t interfere with each other. This interference can be avoided by controlling the transmission of the signals in one of the several domains. The most prominent domains are frequency, time and space.
So the OFDM is achieved under following guidelines.
A) Separate the sub-carriers within a OFDM symbol by inverse of modulation rate.
B) Make sure modulation rate is consistent for all sub-carriers within a modulation symbol.
LTE RF link:
In LTE radio link between transmitter and receiver its done by following approach. Synchronize UE local frequency oscillator with the eNodeB and hence insure Orthogonal relation in-between sub-carriers. This results in theoretical zero inter-symbol-interference. This is very important requirement of OFDM systems.