on in 3GPP have the following features in common: (1) they use MA signature(s) at the trans- mitter side and (2) they allow multi-user detection at the receiver side. The MA signatures are typically used to differentiate the users. Thus all proposed non-orthogonal MA schemes for the uplink transmission at a high level can be described with the basic diagram shown in Fig. 3.31. As we stated earlier, in non-orthogonal multiple access uplink transmission, multiple UEs share the same time/frequency resources via non-orthogonal resource allocation. There are various non-orthogonal multiple access schemes that can be derived from the general con- cept shown in Fig. 3.31. Fig. 3.32 shows a unified framework for non-orthogonal multiple access based on UE-specific spreading/scrambling/interleaving for the uplink data transmis- sion. For data transmission based on UE-specific spreading, the existing solutions can be classified into two categories: linear spreading and nonlinear spreading. The category of lin- ear spreading includes solutions such as resource spread multiple access (RSMA), MUSA, WSMA, and NCMA, while the category of nonlinear spreading includes SCMA. Linear spreading can be used in conjunction with DFT-S-OFDM and CP-OFDM waveforms. Although receiver implementation relatively less-complex and straightforward in orthogonal MA systems, the successful deployment of non-orthogonal multiple access depends on advanced receivers with inter-UE interference cancellation capabilities [23]. 356 Chapter 3 Input data Transport block segmentation and Channel encoder Rate matching Bit scrambling Modulation CRC addition UE-specific Transform Subcarrier spreading/ Spatial precoding OFDM processing DFT-S-OFDM precoding mapping scrambling Subcarrier Spatial precoding OFDM processing CP-OFDM mapping Figure 3.33 Linear hybrid spreading for non-orthogonal multiple access uplink transmission [23]. Fig. 3.33 shows non-orthogonal multiple access uplink transmission blocks based on linear hybrid spreading. In particular, the assignme