Improving the LPI and self-interference characteristics of the STANAG 4415 very robust HF waveform

STANAG 4415 is a very robust waveform intended to provide communications under extreme HF channel conditions: negative signal to noise ratios, large Doppler spreads, large multipath delay spreads and in interference environments where the interferer may be 40 dB stronger than the signal of interest. The self interference specification provided in the STANAG 4415 document is, at best, achievable over short time periods because of limitations imposed by the STANAG 4415 waveform structure. We show how the STANAG 4415 waveform can be modified to provide improved self-interference rejection capabilities. Two examples where the modifications have significant beneficial impacts are provided. The utility of the modified STANAG 4415 waveform as a low rate, engineering order wire transport in an HF network application is shown. In this application, the improved self-interference rejection translates into an increased probability of successful transmission when two transmissions overlap. These same modifications, used to enhance the self-interference rejection performance, can also significantly enhance the use of STANAG 4415 as a low probability of intercept (LPI) waveform when used appropriately. This aspect is also explored and demonstrated. In particular, the interference environment and other unique characteristics of the HF channel, which are normally impairments to communications, are shown to be of significant benefit for LPI communication, when properly exploited.