Multicarrier Spread Spectrum Communications With Noncontiguous Subcarrier Bands for HF Skywave Links

Existing high-frequency (HF) radio systems are becoming increasingly impaired by high levels of interference and traffic due to the growing use of the HF band. Although many HF systems exhibit robust performance against limited amounts of interference, their reliability degrades as more users occupy the same transmission band. To improve reliability in these congested channel conditions, we propose a filter-bank based multicarrier spread-spectrum waveform with noncontiguous subcarrier bands. Using noncontiguous subcarrier bands enables the use of a robust, wideband system while retaining the frequency agility of a narrowband system. In this study, we first modify a filter-bank transmitter structure to accommodate noncontiguous subcarrier bands and consider several impacts of this change, such as elevated peak-to-average-power ratios (PAPRs). We also introduce a receiver architecture to process the noncontiguous spread-spectrum signal, along with details regarding wideband channel estimation. Efficient transceiver structures are developed to support practical system implementations. We conclude by comparing the performance of contiguous and noncontiguous systems through both simulation and over-the-air testing. The results demonstrate that, in typical channel conditions, noncontiguous systems demonstrate comparable performance to contiguous; however, in congested conditions, noncontiguous systems significantly outperform contiguous.