Multicarrier CDMA for Data Transmission over HF Channels: Application to "Digital Divide" Reduction

High-Frequency (HF) ionospheric transmission has been employed for many years for long-distance radio bridging both in military and civil applications. In these last decade, the employment of the most advanced transmission techniques to HF channels raised a considerable interest in R&D. Orthogonal Frequency Division Multiplexing (OFDM), Direct Sequence Spread Spectrum (DS/SS) and Frequency Hopping Spread Spectrum (FH/SS) are practical examples of attempts to exploit wideband transmission techniques based on diversity concepts in the low-frequency HF context. In this paper
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we are proposing the use of multicarrier Code Division Multiple Access (MC-CDMA) techniques for multi-user communications in HF ionospheric channels. The study reported here is related to part of a project aimed at providing cheap and robust wireless connections to isolated rural areas located in central Africa. We analyzed all the problems related to system design and implementation in the context of the considered application environment. A feasible solution has been studied and tested by means of laboratory simulation. Experimental results pointed out the real possibility of exploiting MC-CDMA techniques for high-data rate communications over HF channels due to the robustness and the flexibility inherent to the physical layer technology considered.