Chapter Summary

Chapter Summary

Key Points

• 1.

  V2X is four overlapping link types: V2I (vehicle-to- infrastructure), V2V (vehicle-to-vehicle), V2P (vehicle-to- pedestrian), V2N (vehicle-to-network). Each has distinct mobility, latency, and throughput requirements. The hardest case is V2V safety: closing speeds to 280 km/h + 1-ms latency

  • $10^{-5}$ reliability. OTFS is the only known waveform that meets all three simultaneously at mmWave.
• 2.

  OFDM fails at mmWave V2V closing speeds. At 77 GHz with 300 km/h closing, Doppler is $\sim 20$ kHz — $\sim 17\%$ of 5G NR mmWave subcarrier spacing, creating severe ICI. BER hits an error floor at $10^{-2}$. OTFS, by working in DD domain, maintains full $P$-order diversity regardless of Doppler; achieves $10^{-14}$ BER at 20 dB SNR. 30-dB advantage at $10^{-6}$ BER.

• 3.

  Cooperative perception via OTFS-ISAC is low-overhead. The DD-domain scene $\hat\Theta = \{(\tau_i, \nu_i, \theta_i, \phi_i, |a_i|)\}$ needs only $\sim 7$ kbps per vehicle — 1000× less than lidar point-cloud sharing. Qualitative benefit (NLOS coverage via neighbor vehicles) exceeds the quantitative $\sqrt{K}$ accuracy gain.

• 4.

  V2X spectrum spans 5.9 GHz to 120 GHz. Current deployment: C-V2X (LTE Sidelink) on 5.9 GHz, 5G NR-V2X extending to mmWave. 6G OTFS-V2X standardization expected 2028+. Sub-6 GHz for long-range safety messages; mmWave for short-range cooperative perception. They complement, not compete.

• 5.

  Platooning requires OTFS's 1-ms latency. String stability for $N = 4$ truck platoon requires $T_{\text{loop}} \leq 1$ ms at $p = 10^{-5}$ reliability. OTFS-V2V at $T_{\text{loop}} = 0.5$ ms comfortably meets the condition; C-V2X at $5$-$10$ ms fails. OTFS-V2V is the prerequisite for scale-up of platooning (from current 3-4 vehicles to 10-20).

• 6.

  Intersection management needs cooperative perception coverage. OTFS-ISAC RSUs + vehicle-to-vehicle scene sharing achieve full intersection coverage with 10-12 cooperating vehicles. Latency 5-10 ms end-to-end; eliminates most intersection collisions via early warning of blind-spot pedestrians/vehicles.

• 7.

  CommIT contributions: Wei-Yuan-Auto 2022 + Xu-Liu-Caire 2024. These two papers establish the quantitative case for OTFS in V2X, from single-link performance (Wei-Yuan) to network-scale applications (Xu-Liu). Combined with Cui-Yuan-Caire 2023 (tracking) and Liu-Caire-SAC 2023 (sensing-assisted comms), they constitute the CommIT group's 6G V2X research program.

• 8.

  Deployment timeline is 2025-2030+. 2024: C-V2X baseline. 2025-2027: NR-V2X (Rel. 17/18) mmWave deployment. 2028: 3GPP Rel. 21 OTFS-V2X standardization. 2028-2030: OTFS-V2X in premium vehicles; mmWave array cost reduction enables mid- market. 2030+: economy vehicles.