right side of y-axis, for BPSK, it will be decoded as S2, and then removed from the composite signal, which only has S1 left. Notice that the symbols can use the same modulation scheme as long as they have different power. Most NOMA works, however, do not consider any specific modulation, rather they apply the Gaussian coding and perform analysis based on information-theoretic perspective. The disadvantage of NOMA, however, lies in the following aspects. Firstly, NOMA requires a more complicated receiver structure to perform SIC; hence, the cost will be higher and receiver architecture will also be changed accordingly. Secondly, during SIC procedure, one user will decode signal from others; this will cause security and privacy concerns. Lastly, depending on implementation, this successive decoding will impose certain delays for users. Starting from 3rd Generation Partnership Project (3GPP) LTE Release-13, NOMA, as one of the techniques in multi-user superposed transmission (MUST), has become part of the standardization. In 2017, with LTE Release-14, 15 MUST schemes have been proposed for the uplink NR. Additionally, NOMA has attracted extensive attention from industry. NTT DoCoMo and MediaTek collaborated to have a field test of NOMA in Nov. 2017. With a sim- ple scenario of one base station and three users, they were able to achieve 2.3 time spectral efficiency compared with current technology.1 1 MediaTek Newsroom, Nov. 2017. 1.2 Enabling Technologies Nevertheless, we have applied NOMA in many schemes and systematically studied its performance, for example NOMA with D2D, with MIMO, relay networks, and cognitive radio. More importantly, we have reviewed the fundamental principle of NOMA and pointed out the error propagation phenomenon. Furthermore, we have also considered the channel imperfection and its impact to NOMA performance. 1.2.1.2 Channel Codes Channel coding is instrumental for achieving higher capacity and reliability. For example, low-density parity-check (LDPC) has been extensively used in 4G, repla