te sufficiently large difference among the signals of different UEs in the power domain in order to enable signal separation at the (SIC) receiver. For the uplink, due to different channels experienced by signals transmitted via different UEs, the received sig- nal powers of different UEs already have differences in the power domain. On the other hand, when NOMA is applied in the uplink, the ICI greatly increases since multiple UEs are allowed to simultaneously transmit, whereas in the downlink, ICI does not increase when NOMA is applied because generally the base station has fixed transmission power regardless of the number of multiplexed UEs [23]. 3.3.3.3 Scrambling-Based and Spreading-Based NOMA Schemes In addition to the NOMA schemes discussed in the previous sections, there are other schemes proposed as part of 3GPP Rel-16 study item on NOMA. Scrambling-based NOMA schemes use different scrambling signatures for each user and utilize a low-rate forward error correction code or code repetition for multi-user decoding. The scrambling operation is carried out after the modulation. MMSE with SIC (MMSE-SIC) and ESE are used for the multi-user detection. RSMA is one of the scrambling-based schemes under consideration which utilizes low cross-correlation properties of long pseudo-random scrambling codes. Long scrambling sequences are used in RSMA. However, a long user signature causes high- decoding complexity and latency. Following the descrambling step, the ratio of signal-to- interference power is directly proportional to the scrambling code length. It must be noted that each user can transmit signal at any time using the asynchronous RSMA. Depending on the application scenarios, single-carrier RSMA or multicarrier RSMA can be utilized. Single-carrier RSMA can be used in the uplink access to reduce the PAPR of the UE. Multicarrier RSMA can be utilized in the downlink access to simplify the receiver complex- ity in the frequency-selective wireless fading channels. RSMA can be extended to multi- ple layers. Treatin