An HF Digital Communication System Based on Software-Defined Radio

High Frequency (HF) communication systems use radio waves at frequencies in the range of 3-30 MHz propagating in the form of skywave with the help of the ionosphere. For emergency communication applications, the HF communication system is expected to send text messages by implementing a digital communication system. This paper presents the design of the HF digital communication system on a Software-Defined Radio (SDR) platform for easy implementation. To achieve a good error rate performance, the AX.25 protocol is used at the data link layer. The system performance is evaluated by measuring Signal to Noise Ratio (SNR), Bit Error Rate (BER), Character Error Rate (CER), and Frame Error Rate (FER) with and without the AX.25 protocol. The results show that the system has been successfully implemented on the USRP platform with LabView as the user interface, while the use of the AX.25 protocol generates a zero error rate.