稀疏码多址接入系统中基于分层编码的多播资源分配算法

稀疏码多址接入(sparse code multiple access，SCMA)技术被认为是一种能有效提高频谱效率的技术。将稀疏码多址接入技术应用于无线多播通信中可以扩展多播系统的容量。对多播系统的容量进行了推导，采用分层编码技术应用在SCMA系统的多播传输中，使得系统容量不再受限于多播系统中最差用户的信道质量，采用资源分配算法来最大化多播系统容量。为了减少最优化问题的计算复杂度，又提出了快速次优化算法(fast suboptimal algorithm， FSA)，该算法分为码本分配和功率分配2个阶段。仿真结果显示，提出的快速次优化算法在SCMA系统中的多播系统功效要优于正交频分多址接入(orthogonal frequency division multiple access， OFDMA)系统中的多播系统功效。并且，在SCMA系统和OFDMA系统中，提出算法的系统功效都要远优于传统多播(conventional multicast， CM)策略的系统功效。

Multicast resource allocation algorithm based on layered coding in sparse code multiple access systems

Sparse code multiple access (SCMA) is considered as a promising technique for improving spectral efficiency. we apply SCMA to wireless multicast communication with the purpose of taking the advantage of SCMA to expand multicast capacity.Firstly, we formulate the capacity of the multicast systems;Secondly, we exploit layered coding scheme in the SCMA systems which is no longer constrained by the user with the worst channel quality in the multicast group; Finally, multicast resource allocation algorithm for the SCMA systems is optimized with the objective of maximizing the capacity of the systems. In order to reduce the computational complexity of optimal question, a fast suboptimal algorithm (FSA) is proposed by separating the power allocation and codebook assignment. Simulation results show that the performance of SCMA systems with FSA is better than the performance of orthogonal frequency division multiple access (OFDMA) systems with FSA. The proposed algorithm significantly outperforms conventional multicast (CM) scheme in SCMA systems and OFDMA systems.