They asked me technical questions about the Digital Communication blocks (scrambling, interleaving, modulation, etc.) They also asked what I knew about OFDM, cyclic prefix, etc. If you're preparing for an interview for the 5G diploma or an internship in that department, I would recommend that you study these topics: Wired topics (ORAN) and Wireless (OFDM, MIMO, IQ samples, constellation diagram, etc.) Familiarize yourself with the 3GPP standard and what it does. Good luck!