Here is what the General Instruction of the Roman Missal says:
The Entrance
There are four options for the Entrance Chant: (1) the antiphon from the Missal or the antiphon with its Psalm from the Graduale Romanum, as set to music there or in another setting; (2) the antiphon and Psalm of the Graduale Simplex for the liturgical time; (3) a chant from another collection of Psalms and antiphons, approved by the Conference of Bishops or the Diocesan Bishop, including Psalms arranged in responsorial or metrical forms; (4) another liturgical chant that is suited to the sacred action, the day, or hte time of year, similarly approved by the Conference of Bishops or the Diocesan Bishop.
If there is no singing at the Entrance, the antiphon is recited either by the faithful, or by some of them, or by a reader; otherwise, it is recited by the Priest himself, who may even adapt it as an introductory explanation.