This paper investigates the energy-efficient communications and user capacity in the cognitive multiple input multiple output (MIMO) symmetric system of underlay mode. The advantage of the improved energy efficiency provided by the orthogonal slot allocation for time division multiple access (TDMA) has a side effect of restricting the number of users accessing the system. To tackle the above problem, this paper proposes a nonorthogonal time resource allocation method with sparse code multiple access (SCMA), which allows one to convert the orthogonal slot units of TDMA into non-orthogonal shared slot units for multiple secondary users (SUs). The method of adding virtual users is adopted, wherein each SU is treated as multiple SUs who occupy a shared unit, to facilitate the packet access. Finally, the greedy algorithm is applied to optimize the time slot allocation of unoccupied shared slot units. The simulation results show that SCMA-based nonorthogonal slot allocation can reduce not only the energy consumption by nearly 40%, but also the average power interference from SUs to primary users by nearly 2 dB if their number is relatively high. Moreover, in the case of satisfying the rate requirement of the users, the system user capacity increased by more than 50%.

中文翻译：

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通过基于 SCMA 的非正交时隙分配优化认知 MIMO 系统的能量效率和用户容量

本文研究了底层模式的认知多输入多输出 (MIMO) 对称系统中的节能通信和用户容量。时分多址 (TDMA) 的正交时隙分配所提供的改进能源效率的优势具有限制访问系统的用户数量的副作用。针对上述问题，本文提出了一种具有稀疏码多址（SCMA）的非正交时间资源分配方法，该方法允许将TDMA的正交时隙单元转换为多个次级用户（SU）的非正交共享时隙单元。采用添加虚拟用户的方法，将每个SU视为多个SU，占用一个共享单元，方便分组接入。最后，应用贪心算法优化未占用共享时隙单元的时隙分配。仿真结果表明，基于SCMA的非正交时隙分配不仅可以降低近40%的能耗，而且如果数量较多的话，SU对主要用户的平均功率干扰也可以降低近2dB。而且，在满足用户速率要求的情况下，系统用户容量增加了50%以上。