Waveform design considerations for transmission of digital voice over HF

The development of digital voice (DV) technology has had a significant impact on high frequency (HF) voice communications. The secure features of DV in combination with the benefits of modern digital signal processing (i. e. equalization, narrow-band interference suppression, FEC, interleaving, etc) have provided users with some great advantages when communicating over challenging HF links. A new, higher quality, DV algorithm (vocoder) called mixed excitation linear prediction enhanced (MELPe) was recently developed and standardized. This new vocoder operates at data rates of 2400 bits per second (bps) and 1200 bps with a goal of providing higher quality DV in applications where limited bandwidth is available to users. However, the MELPe development focused only on the vocoder algorithm and no work was done in the specific area of physical-layer waveforms that would be used to convey the DV bits over wireless links (i.e. in HF, independent of the actual waveform which would be used to carry the data over-the-air). This paper considers how to best combine MELPe with current standardized HF waveforms and also investigates if new waveforms needs to be developed to carry MELPe over HF links.