Constellation folding for sub-optimum maximum-likelihood method in blind modulation detection

Adaptive Orthogonal Frequency Division Multiplexing (OFDM) system is effective for radio communications. In the system, the receiver needs to know the modulation schemes used by the transmitter. The sub-optimum maximum-likelihood (ML) method is useful for the modulation detection. In this paper, we propose constellation folding as a new technique to implement the sub-optimum ML method efficiently. Two types of the constellation folding scheme are derived. The validity of the proposed methods is demonstrated by computer simulations.