Performance Comparison of Spread Spectrum Methods in an Hf Interference Environment

Since the interfering signals from other users of the spectrum is a main problem in HF communication, it is necessary to consider them when evaluating HF radio systems. Based on the Laycock-Gott congestion model, a statistical HF interference model is derived and brieey compared to real measurements. The two basic methods to apply spread-spectrum modulation in radio communication are frequency-hopping (FH) and direct-sequence (DS) modulation. In this work we compare these two methods, with respect to the uncoded bit error probability, on an interference-limited HF channel. The results show that the FH system performs better than the DS system on this channel. The FH system is inherently well suited for the HF environment with predominantly narrowband interferers. The interference rejection capabilities of the DS system are not suucient to handle the high dynamic range of the interfering power. Additional narrowband rejection capabilities would be required to create useful DS systems.