Software-Defined Radio Techniques for Enhanced OFDM Transmission in NVIS Propagation

This study presents the development of a data communication system that operates in the high frequency (HF) frequency range using the Orthogonal Frequency-Division Multiplexing (OFDM) modulation technique. The system consists of a transmitter and receiver built on Software-Defined Radio (SDR) platforms and uses the GNU Radio software framework. The NVIS (Near Vertical Incidence Skywave) communication system has been designed and tested under both laboratory and real field conditions over a link distance of 180 kilometers. The laboratory tests evaluated the performance of OFDM modulation, considering factors such as signal-to-noise ratio (SNR), packet error rate (PER), packet length, number of subcarriers, and bandwidths ranging from 3 kHz to 24 kHz.