We present a new OFDM-based hybrid transmission scheme which is suitable for robust transmission in fast fading environments, where a reliable channel estimate is impossible or very difficult to obtain. Our scheme is based on the combination of noncoherently detected MFSK (M-ary frequency shift keying) and OFDM (orthogonal frequency division multiplexing). Furthermore, the subcarrier phases of this OFDM-MFSK scheme can be differentially modulated, leading to a hybrid transmission scheme where additional data can be transmitted, without affecting the robustness of the underlying noncoherently detected OFDMMFSK. A channel estimate is not needed both for the pure OFDM-MFSK and the hybrid modulation scheme. We also consider a coded system, where the two data streams using the MFSK and the phase component are separately encoded.
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