Rotation Invariant Subcarrier Mapping: A novel technique enabling quasi-constant OFDM envelope

We propose a novel method that considerably reduces the Peak-to-Average Power Ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) systems, yielding a quasi constant signal envelope in the time domain (PAPR close to 1 dB). The proposed technique, named Rotation Invariant Subcarrier Mapping (RISM), is a novel scheme for subcarriers data mapping, where the symbols belonging to the modulation alphabet are not anchored, but maintain degrees of freedom. In other words, a bit tuple is not mapped on a single point, rather it is mapped onto a geometrical locus, which is totally or partially rotation invariant. The final positions of the transmitted complex symbols are chosen by an iterative optimization process to minimize the PAPR of the resulting OFDM symbol. Numerical results confirm that RISM makes OFDM usable even in severe non-linear channels.