基于相位旋转的SCMA码本优化方法

To solve the high bit error ratio (BER) problem under the condition of high overload of sparse code multiple access (SCMA), the influence of phase rotation on the SCMA code is studied firstly. Two schemes of optimizing the phase rotation angle are then proposed based on the controlled-distance among the constellation points of synthetic constellation. The first scheme is called the rotation based on maximizing minimum euclidean distance (M-rotation) and the second is the rotation based on exponential average (E-rotation). E-rotation achieves better BER performance than M-rotation, but M-rotation is outstanding at the case of high signal-to-noise ratio (SNR). With respect to the decoding complexity, both schemes have no distinction but E-rotation gets better performance than M-rotation when the partial extrinsic information transmission of MPA (PEIT-MPA) is adopted.