The classical procedures which define the relativistic notion of space-time can be implemented in the framework of Quantum Field Theory. Only relying on the conformal symmetries of field propagation, time-frequency transfer and localization lead to the definition of time-frequency references and positions in space-time as quantum observables. Quantum positions have a non vanishing commutator identifying with spin, both observables characterizing quantum localization in space-time. Frame transformations to accelerated frames differ from their classical counterparts. Conformal symmetry nevertheless allows to extend the covariance rules underlying the formalism of general relativity under an algebraic form suiting the quantum framework.