Superimposed asymmetric modulation in narrowband fading channels using orthogonal codes

The asymmetric signal constellation (ASC) method to break isometry is analyzed in a superimposed symbol framework with a Kalman filter estimator (KF) / maximum-likelihood (ML) detector as the receiver. Direct application of the ASC method led to a bit error floor, which motivates the proposal of combining orthogonal spreading codes with ASC to solve this problem. The proposed scheme generalizes previously proposed ASC and pilot-assisted solutions in a systematic way and results in coherent detection schemes without set bit error floors and better performance