f co-scheduled users increases, the decoding complexity of the SIC receiver increases. The message passing algorithm (MPA), as a less-complex decoding algorithm, as well as other low-complexity receiver designs have recently drawn attention. Several code-spreading- based techniques, including SCMA, MUSA, and PDMA and several others were the candi- dates under consideration in 3GPP Rel-16 NOMA study item. It has been shown that one can potentially achieve higher spectral efficiency, larger connectivity, and better user fairness with non-orthogonal multiple access relative to orthogonal MA schemes [50-52]. While the interference-free condition between orthogonally multiplexed users might facili- tate multi-user detection at the receivers, it is widely known that orthogonal MA cannot achieve the sum capacity of a wireless system. The orthogonal MA also has limited granu- larity of resource scheduling, SO it struggles to handle a large number of active connections. Non-orthogonal multi-user transmission/access has been recently investigated in a New Radio Access Physical Layer Aspects (Part 1) 355 Bit-level operations Symbol-level operations Bit-level Forward error Modulated symbol Symbol to interleaver/ sequence resource element correction (FEC) scrambler generator mapping Figure 3.31 High-level block diagram for uplink non-orthogonal multiple-access schemes [22,23]. Input data Transport block Channel encoder UE-specific segmentation and Rate matching Bit scrambling Modulation CRC addition interleaving UE-specific Transform Subcarrier spreading/ Spatial precoding OFDM processing DFT-S-OFDM precoding mapping scrambling Subcarrier Spatial precoding OFDM processing CP-OFDM mapping Figure 3.32 General framework for non-orthogonal multiple access uplink transmission [23]. systematic manner to deal with the above problems. Interference can be controlled by non- orthogonal resource allocation at the cost of increased receiver complexity. The non-orthogonal multiple access schemes that were studied for the uplink transmissi