Performance Comparison of NOMA‐OFDM and NOMA‐OTFS in Advanced Wireless Systems

ABSTRACT With the growing demand for ultra‐reliable and high‐speed communication in next‐generation wireless networks, advanced multiple access and modulation schemes are becoming increasingly popular. Non‐orthogonal multiple access (NOMA) exploits the power‐domain superposition coding paradigm that enhances spectral efficiency while orthogonal time frequency space (OTFS) modulations show improved resilience compared with classical orthogonal frequency division multiplexing (OFDM) schemes in highly dynamic time and frequency dispersive channels. Using OTFS and OFDM waveforms, this work compares the performance of downlink NOMA systems with the use of pilot‐assisted channel estimating methods, Least Squares (LS), and Minimum Mean Square Error (MMSE) estimators. The performance metrics, bit error rate (BER), sum rate, peak‐to‐average power ratio (PAPR), and outage probability over a range of signal‐to‐noise ratios (SNRs) are given using a two‐user NOMA system with successive interference cancellation (SIC). Simulation results demonstrate that MMSE estimation achieves consistently lower BER than LS, particularly at low‐to‐moderate SNR levels. The NOMA‐OTFS system shows improved BER performance under high‐mobility and doubly dispersive channel conditions due to reduced Doppler‐induced interference. OTFS and OFDM have similar sum‐rate behavior with SNR, and outage probability study results suggest that OFDM with MMSE is more reliable when the rate is highly demanded. All in all, the findings show that the NOMA‐OTFS using MMSE channel estimate offers a good tradeoff between reliability and performance capability in the next generation of wireless communication system.