The present document defines the Air Interface (AI) for the Terrestrial Trunked Radio (TETRA) system supporting Voice plus Data (V+D) and contains the specifications of the physical layer, the data link layer and the network layer according to the ISO model.First, it establishes the TETRA radio aspects (layer 1):• it defines and specifies the modulation;• it defines and specifies the radio transmission and reception;• it defines and specifies the synchronization;• it defines and specifies the channel coding;• it defines and specifies the channel multiplexing;• it defines and specifies the control over the radio link.Secondly, it establishes the services, me