The detection of arrivals is a crucial step in communication and localization systems, in order to achieve frame synchronization for demodulation and to identify the emitter. When multiple users are transmitting in the same environment, this detection becomes more difficult as the different signals can interfere with each other. To overcome this issue, CodeDivision Multiple Access (CDMA) can be used to obtain good auto-correlation and cross-correlation properties. In this work, a CDMA scheme is used to identify two Autonomous Underwater Vehicles by modulating a companion pair of Complementary Set of Sequences (CSS) in Orthogonal Frequency-Division Multiplexing (OFDM). The detection is performed in two steps to obtain robustness against interferences, as well as to save computing time in a practical system. First, frame synchronization is obtained with a preamble, and next the arrival is validated and the emitter identified with the CSS, which is attached to the preamble. The results show that the correlation peaks of the CSS are easily detected even in challenging conditions of multipath, Doppler, noise and interference.