A transmitter and receiver designed with resonant tunneling diodes (RTDs) achieved 1.2 Gbit/s over a 0.5 cm wireless link using on-off-keying (OOK) modulation at 860 GHz, marking the first-ever demonstration of wireless communication beyond 850 GHz using all-electronic oscillators. Each oscillator in the transmitter (Tx) and receiver (Rx) employs two RTDs , a cavity resonator formed by a low-loss air-bridge transmission line, a ring-slot antenna, and a silicon lens. The Tx generated terahertz radiation with 0.23 mW output power and a DC-RF efficiency of 0.2%. The Rx frequency is biased close to the Tx frequency, resulting in injection locking of both oscillators for coherent detection. Improvements in device packaging could further enhance the data rates, paving the way for high-speed communication applications.