Chapter Summary

Chapter Summary

Key Points

• 1.

  6G's 1000-km/h mobility target exceeds OFDM's ceiling. Enhanced OFDM numerologies can push to 500 km/h at a rate cost; OTFS handles arbitrary mobility natively. This structural limit of OFDM is the core case for OTFS in 6G.

• 2.

  Dual-waveform 6G is the likely architecture. Neither OFDM nor OTFS dominates all scenarios. Dual-waveform scheduler achieves $\geq 95\%$ of the best-per-UE choice. OFDM for low-mobility (70-80% of use cases), OTFS for high-mobility, NTN, ISAC (20-30%).

• 3.

  OTFS pays 2 dB PAPR cost over DFT-s-OFDM. Matters for UE mmWave uplink. Absorbed by OTFS's mobility + reliability gain in vehicular/LEO scenarios. Low-mobility: DFT-s-OFDM wins.

• 4.

  MDMA multiplies user capacity by ~64×. DD + spatial domains add orthogonal dimensions beyond OFDMA's time-frequency. Enables 6G's $10^7$-devices/km² target. OTFS is the enabling waveform.

• 5.

  OTFS is 1.5× compute of 5G NR. Modern silicon (3nm, 2nm) easily absorbs this: ~20% area, ~30% power. Chip cost +~$20 per UE, +~$500 per BS — negligible in system cost.

• 6.

  Energy: OTFS is more efficient under mobility, less under static. PAPR penalty dominates at static; retransmission savings dominate at mobility. Waveform selection (dual-mode) optimizes per UE.

• 7.

  IPR: Cohere FRAND + academic alternatives. License cost ~0.5-1% of chip revenue. Comparable to LDPC. Not a blocker. CommIT contributions (Chapters 17-18) provide IPR-free academic anchors.

• 8.

  Standardization timeline: Rel. 20 (2026-2028) Study Item, Rel. 21 (2028-2030) Work Item, first commercial 2030+. Mass deployment 2032+. 1-2 year risk of slippage to Rel. 22 if vendor consensus falters.

• 9.

  Ecosystem health is strong (2026). Qualcomm committed, 20+ academic groups active, $\sim 80\%$ industry probability of 6G adoption. CommIT's Mohammadi-Caire and Buzzi-Caire contributions (cell-free, LEO) are the quantitative anchors driving adoption.