MIMO transmission in the frequency domain over the HF channel

This paper deals with some highlights showing why Spread Spectrum Multicarrier Technologies as MC-CDMA are very robust for HF communications in front of plain OFDM for delay sensitive transmissions. Several steps of this research line have been published by the authors showing that uncoded interactive digital voice transmissions is feasible over the HF channel if proper modulation is selected. The modulation choice, MC-CDMA, comes up from the intuition and simulations but this is the first time that some theoretical insights are presented using a borrowed analysis originally developed for spatial MIMO (Multiple Input Multiple Output) applications. The recognition that MC-CDMA could be interpreted as a sort of correlated spatial MIMO where now the mixture comes in the frequency domain, provides powerful theoretical tools using asymptotic analysis that show the benefits of this modulation and also suggest improved detectors equivalent to those used in spatial MIMO communications.