An Extension of Wideband HF Capabilities

This paper describes the implementation and performance of extensions to the MIL-STD-188-110C Appendix D wideband high frequency (HF) waveforms. Appendix D specifies waveforms to provide data rates from 75 bps to 120 kbps in bandwidths of any integer multiple of 3 kHz from 3 to 24 kHz, providing a range of capabilities that can be supported and tailored to the available spectrum. When more than 3 kHz of spectrum is available, radios and modems implementing the standard can use the unoccupied spectrum to obtain higher data rates with lower transmitted power than would be possible in a traditional 3 kHz channel. The higher data rates supported by the Appendix D waveforms are sufficient to support some services not previously practical over HF radio. This includes real-time video transmission and ad-hoc Internet Protocol (IP) networking. The extensions described in this paper provide for four additional bandwidths, 30, 36, 42 and 48 kHz, featuring data rates up to 240 kbps when a good 48 kHz channel is available. These waveforms have been implemented and tested on a variety of mid-latitude skywave links, and the results of those tests are described. The paper concludes with a discussion of the potential value of the wider bandwidths in supporting ad-hoc networking protocols.