Multicarrier HF modems with turbo structures for data transmission

In this contribution, the comparison of two HF modems with coding and either OFDM or OFDM-CDM modulation, is carried out. The analysis of these techniques for low-latency applications showed clear advantage of OFDM-CDM technology. Nevertheless, its suitability is not so clear in front of coded OFDM with interleaving when applications insensitive to delay are considered, as will be the case in this contribution. Therefore, a comparison of OFDM and OFDM-CDM under equivalent conditions in this scenario is performed. The proposed system uses advanced turbo detection strategies at receiver to confront realistic HF channels impairments. The advanced system has been also designed to consider the possibility of multiband transmission to reach the desired target data rate, constrained by a maximum available transmit power and the number of usable channels. The possibility of using multiple bands enables reaching higher data rates whenever the channel conditions in two or more bands are favorable. The innovative contribution of this paper is twofold: on one hand, the multiband, adaptive HF transmission according to the overall channel knowledge is defined. On the other hand, the aforementioned comparison of two multicarrier technologies in realistic HF channels taking into account different aspects like trade-off between complexity and performance, power allocation among channels and turbo principles is performed.