ion, which gives the probabilities contingent upon the values of the other vari- ables. Marginal variables are those variables in the subset of variables being retained. The distribution of the marginal variables (the marginal distribution) is obtained by marginalizing; that is, focusing on the sums in the margin, over the distribution of the variables being discarded, and the discarded variables are said to have been marginalized. New Radio Access Physical Layer Aspects (Part 1) 359 Table 3.6: Rel-16 non-orthogonal multiple-access use cases and features supported by different operation modes [23]. Dynamic Operation Mode MCS Support Characteristics Use Case RRC_INACTIVE, grant-free with Reduction in system overhead, mMTC and contention, tracking area-free latency, and power consumption (asynchronized) RRC_CONNECTED Grant-free with Reduction in system overhead and mMTC, (Synchronized) contention latency URLLC, and Grant-based Limited downlink overhead with overloading reduction the network operates in grant-based mode, transmission schemes proposed for NOMA can be applied to MU-MIMO; however, the relative spectral efficiency advantage of NOMA over MU-MIMO is not clear under underloaded scenarios. When the network operates in grant-free mode and the uplink access is contention-free, the relative gain of NOMA over MU-MIMO in terms of spectral efficiency is not proven. The most significant gain of NOMA over MU-MIMO may be attributed to contention-based, grant-free transmission and small data transmission in RRC_INACTIVE state scenarios. 3.3.3.1 Sparse Code Multiple Access SCMA is a frequency-domain non-orthogonal multiple-access scheme, which can improve the spectral efficiency of wireless radio access. In SCMA, different incoming data streams are directly mapped to codewords of different multi-dimensional cookbooks, where each codeword represents a spread transmission layer. Each layer or user has its own dedicated codebook. Multiple SCMA layers share the same time-frequency resources of OFDMA. The sparsity of codew