Performance comparison of spread-spectrum methods on an interference-limited HF channel

A severe problem with radio communication in the high-frequency range is the large amount of typically narrowband, interfering signals from other users. A statistical description of the interfering signals is employed in evaluating different spread-spectrum HF radio systems. In particular, when a frequency-hopping (FH) and a direct-sequence (DS) system are compared, the FH system performs better than the DS system under the author´s assumptions. The FH system is inherently well suited for the HF environment with its predominantly narrowband interfering signals. The interference rejection capability that the DS systems normally possess is not sufficient to handle the large dynamic range of the HF interfering power. Additional narrowband interference rejection would be required to create useful DS systems for the HF channel. Furthermore, the author demonstrates the dramatic gain connected with adaptive frequency-hopping, which uses an adaptively selected pool of the channels with least interference for the communication