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Non-orthogonal multiple access(NOMA) is proved to be useful to satisfy the requirements of beyond 5th generation such as massive multi-user connection. Here we compare the performances of two NOMA schemes: low code rate spreading (LCRS)scheme and interleaver division multiple ac-cess (IDMA) scheme. It is found that LCRS is superior to IDMA when number of users is small due to coding gain achieved. While IDMA is preferred when number of users is high because repetition applied in IDMA can suppress multi-user interference effectively.And interleaver is important in IDMA for randomizing the interference. Also, this paper evaluates the impact of channel decoder. It is observed that Log-MAP decoder has much better performance than that of Max-Log-MAP when number of users is large. Thus, it is recommended to use Log-MAP decoder in NOMA in high user overloading case. We also compared the performance of NOMA by using different type of channel codes. We find that NOMA using specific convolutional code has a better performance than that of using specif-ic LDPC code when number of users is high.