Sparse Code Multiple Access (SCMA) is one of Non Orthogonal Multiple Access (NOMA) candidates for 5G, the fifth generation mobile network. Multiple overlapped blocks of SCMA code are transmitted per frequency layer which compels the receiver to cancel unwanted SCMA code blocks. Thanks to the sparsity of SCMA, Message Passing Algorithm (MPA) achieves near-optimal performance. Nevertheless, this process is time-consuming and has a high degree of complexity even if Max-Log Algorithm is used. The major contribution of this paper is to propose a new decoding scheme called Hybrid Interference Cancellation (HIC) to reduce time processing without degrading a target Bit Error Rate (BER). The HIC decodes and removes the strongest user, reducing the complexity of Log Domain MPA decoding of remaining users, followed by a Low Density Parity Code (LDPC) decoder. The interference cancellation decoder is either a hard interference cancellation or a soft interference cancellation. The originality of the paper is to calculate a threshold value based on power measurements to decide whether hard decoder or soft decoder should be used to reach the BER target with a lower complexity. Results show a significant reduction in terms of complexity as compared to the traditional MPA process for the same values of BER.

稀疏码多址 (SCMA) 是第五代移动网络 5G 的非正交多址 (NOMA) 候选方案之一。每个频率层传输多个重叠的 SCMA 码块，这迫使接收器取消不需要的 SCMA 码块。由于 SCMA 的稀疏性，消息传递算法 (MPA) 实现了近乎最佳的性能。然而，即使使用 Max-Log 算法，这个过程也很耗时并且具有高度的复杂性。本文的主要贡献是提出了一种称为混合干扰消除 (HIC) 的新解码方案，以在不降低目标误码率 (BER) 的情况下减少时间处理。HIC 解码并去除最强用户，降低剩余用户的对数域 MPA 解码的复杂性，然后是低密度奇偶校验码 (LDPC) 解码器。干扰消除解码器是硬干扰消除或软干扰消除。论文的独创性是根据功率测量计算一个阈值来决定是使用硬解码器还是软解码器来达到更低复杂度的BER目标。结果表明，对于相同的 BER 值，与传统 MPA 过程相比，复杂性显着降低。