RF Performance Implications of Wideband HF Waveforms

Emerging approaches to HF communications aim to increase the range of missions and applications HF can support by using higher bandwidths to achieve higher on-air data rates and/or improved communications robustness. Current proposals achieve this in either of two ways: by (i) increasing the bandwidth allocated to a single-carrier modulated waveform, to up to 24 kHz (or possibly higher), or (ii) using existing modulation formats to simultaneously modulate up to 16 carriers in noncontiguous 3 kHz channels. Each of these approaches has inevitable consequences for both radio system performance and spectrum utilization and availability. Both the US Department of Defense and NATO have standards documents (respectively, MIL-STD-188-141C and STANAG 4203) intended to specify the performance and spectral occupancy characteristics of military HF radios. However, these standards have been primarily focused on operation on traditional 3 kHz channels, and do not fully address either of the two proposed Wideband HF (WBHF) approaches. This paper analyzes some key performance impacts of the two WBHF approaches, uses a simple system model to predict the spectrum occupancy and efficiency of the two approaches, and provides recommendations for new and revised requirements to address Wideband HF systems in the applicable US and NATO standards.