A resonant-tunneling-diode terahertz (THz) oscillator chip for frequency- and polarization-division multiplexing was fabricated. Wireless data transmissions using 2-channel frequency-division multiplexing with ranges of 500 and 800 GHz and polarization-division multiplexing at 500 GHz range were demonstrated. Transmissions up to a data rate of 28 Gbit/s for each channel under an error-correctable error rate were achieved in both the multiplexing technologies.