Impact of SC-FDMA and Pilots on PAPR and Performance of Power Domain NOMA-UFMC System

Non-Orthogonal Multiple Access (NOMA) is envisioned as promising 5G multiple access technology due to its throughput gain achieved through grouping mobile nodes having substantial difference in channel conditions and capability to serve large number of users simultaneously at same time, frequency, or code, but with different power levels. Furthermore, modifications in OFDM waveform for relaxed synchronization and supporting short burst communications for Internet of Things (IoT) devices has paved the way for Universal Filtered Multi-Carrier (UFMC) waveform. However, a major disadvantage in deployment of Non-Orthogonal UFMC is the high Peak-to-Average-Power-Ratio (PAPR) being comparable to that of OFDMA. As such, additional PAPR reduction techniques are required for reducing the dynamic range of power amplifier deployed in communication system. We take up Power Domain NOMA (PD-NOMA) in which available power is sliced between users and investigate the performance of SC-FDMA for PD-NOMA UFMC systems for PAPR reduction. UFMC is known to provide additional diversity to transmitter in uplink and facilitates relaxed synchronization at the receiver side in downlink scenario. Simulation results show that in flat-fading scenario, BER performance of proposed system is found to be significantly better than OFDM and UFMC. However, BER performance of proposed system in AWGN channel is seen to be traded off as the extent of SC-FDMA precoding increases. Also, increasing pilots per subband leads to increased PAPR with OFDM, UFMC whereas SC-FDMA for PD-NOMA UFMC system shows stagnation and significant comparative reduction in PAPR values.