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In this paper, a heterogeneous communication system capable of delivering 5G/sub-terahertz signal carriers over an arbitrary long fiber and separated transmission links is presented by employing direct detection, multiplexing techniques, and advanced digital signal processing. In this experiment, the 3.5 GHz and 28.5 GHz carrier frequencies, representing 5G links, deliver 4 Gb/s 16-QAM OFDM signals to separate user ends over a 1-meter wireless link distance. Later, the sub-terahertz wireless communications of 4 to 10 Gb/s QPSK and 8-QAM signals with varying carrier frequencies of 125-,175- and 225 GHz, over wireless distances (< 80 cm) are presented and evaluated. The results indicate that by increasing optical power from 12 dBm to 13 dBm, the bit error rate decreases two orders of magnitude. Eventually, with the assistance of artificial intelligence, a nonlinear equalizer (AI-NLE) prototype is introduced. The results indicate that the AI-NLE successfully decreases the number of errors in received data by one order of magnitude. The proposed heterogeneous system is compatible with radio-over-fiber technology, cost-effective, and easy to deploy, making it a promising candidate for indoor terahertz communication.