Multi-User Communications in HF Band with Power Control

A long-distance communication system with low-cost infrastructure and easy installation is required in isolated areas, especially for emergency case. High frequency (HF) communication system (3-30MHz) is proposed as emergency communication, which can achieve long-distance signal transmission by utilizing the ionospheric reflections. However, the channel bandwidth of a single HF radio transmission is limited to 3-20kHz typically. Therefore more ingenuity is required to achieve sufficient channel capacity. To overcome the limitation, this paper attempts to make possible multi-user communications with low interference in HF digital radio communications. The study reported herein investigates the potential use of time-reversal division multiple access (TRDMA) uplink scheme to implement HF multi-user communications. Simulation results show that SIR is relatively uniform in a range of 4 dB by employing a power control mechanism, regardless of the distance between a base transmitter and the user.