Non-orthogonal Multiple Access (NOMA) has been envisioned as one of the key enabling techniques to fulfill the requirements of future wireless networks. The primary benefit of NOMA is higher spectrum efficiency compared to Orthogonal Multiple Access (OMA). This paper presents an error rate comparison of two distinct NOMA schemes, i.e., power domain NOMA (PD-NOMA) and Sparse Code Multiple Access (SCMA). In a typical PD-NOMA system, successive interference cancellation (SIC) is utilized at the receiver, which however may lead to error propagation. In comparison, message passing decoding is employed in SCMA. To attain the best error rate performance of PD-NOMA, we optimize the power allocation with the aid of pairwise error probability and then carry out the decoding using generalized sphere decoder (GSD). Our extensive simulation results show that SCMA system with “ 5×105\times 10 ” setting (i.e., ten users communicate over five subcarriers, each active over two subcarriers) achieves better uncoded BER and coded BER performance than both typical “ 1×21\times 2 ” and “ 2×42\times 4 ” PD-NOMA systems in uplink Rayleigh fading channel. Finally, the impacts of channel estimation error on SCMA, SIC and GSD based PD-NOMA and the complexity of multiuser detection schemes are also discussed.

中文翻译：

---

功率域非正交多址与稀疏码多址的误码率比较


非正交多址 (NOMA) 已被视为满足未来无线网络要求的关键支持技术之一。与正交多址 (OMA) 相比，NOMA 的主要优点是更高的频谱效率。本文对两种不同的 NOMA 方案（即功率域 NOMA (PD-NOMA) 和稀疏码多址接入 (SCMA)）进行了错误率比较。在典型的PD-NOMA系统中，接收器采用连续干扰消除（SIC），但这可能导致错误传播。相比之下，SCMA 中采用消息传递解码。为了获得 PD-NOMA 的最佳错误率性能，我们借助成对错误概率优化功率分配，然后使用广义球解码器（GSD）进行解码。我们的大量仿真结果表明，采用“5×105\times 10”设置（即十个用户通过五个子载波进行通信，每个用户在两个子载波上进行通信）的 SCMA 系统比典型的“1×21\上行瑞利衰落信道中的“2×42×4”PD-NOMA系统。最后，还讨论了信道估计误差对基于SCMA、SIC和GSD的PD-NOMA的影响以及多用户检测方案的复杂性。