Interference Mitigation in Mixed-Numerology System Using Hybrid Waveforms

The coexistence of mixed numerologies with OFDM introduces significant inter-numerology interference (INI) due to high out-of-band emission (OOBE). This interference worsens with increasing offset between numerologies, negatively impacting system performance. To address this issue, this paper proposes the use of a Hybrid Waveforms (HW) technique to mitigate the effects of INI in mixed-numerology systems. Specifically, f-OFDM, UFMC, and WOLA waveforms are employed instead of OFDM to suppress OOBE for users with higher numerology. The effectiveness of the proposed technique is evaluated using the Vienna 5G link-level simulator. Simulation results demonstrate that utilizing f-OFDM, UFMC, and WOLA waveforms for higher numerology users is more efficient in reducing INI compared to OFDM. By implementing the proposed framework, user throughput increases and Bit Error Rate (BER) decreases. Among the hybrid waveforms, f-OFDM proves to be the most effective, providing the highest throughput and the lowest BER when compared to UFMC, WOLA, and OFDM. For instance, in the case of f-OFDM, when the power of the second user is ten times that of the first user, the user BER in the uplink can be reduced by 63.3%, and its throughput can be increased by 47.3%. Similarly, in the downlink, the user BER can be reduced by 60.9%, and its throughput can be increased by 43%. These improvements are observed when comparing against the traditional system (OFDM), where the first user uses a subcarrier spacing of 15 kHz and the second user uses a 60 kHz spacing with a 180 kHz guard band.