The V2X Landscape: V2I, V2V, V2P, V2N

Why V2X Is the Hardest Case

Vehicular-to-everything (V2X) communication is not one application but several overlapping ones: a vehicle talking to roadside infrastructure (V2I), to another vehicle (V2V), to a pedestrian smartphone (V2P), and to the cellular network (V2N). Each has its own mobility regime, latency target, and reliability requirement. Each has been prototyped over the last two decades — mostly with variants of OFDM. And each has hit the same wall: at highway speeds, with mmWave spectrum, at URLLC latency, OFDM's Doppler sensitivity makes it unreliable. OTFS was designed, at least in part, to crack this problem. This section maps out the V2X landscape and shows where OTFS fits.

Definition:
V2X Taxonomy

V2X encompasses four link types, each with distinct requirements:

V2I (Vehicle-to-Infrastructure): vehicle $\leftrightarrow$ roadside unit (RSU), BS, or traffic signal. Range: 100-500 m. Latency: 10-100 ms. Throughput: 1-100 Mbps. Mobility: up to 140 km/h (highway).

V2V (Vehicle-to-Vehicle): vehicle $\leftrightarrow$ vehicle. Range: 10-300 m. Latency: 1-10 ms (safety-critical; platooning requires $\leq 1$ ms). Throughput: 0.1-10 Mbps (messages) or 10-100 Mbps (cooperative perception). Mobility: up to 280 km/h (oncoming/closing speed).

V2P (Vehicle-to-Pedestrian): vehicle $\leftrightarrow$ pedestrian's device. Range: 10-100 m. Latency: 10-100 ms. Throughput: 10-100 kbps (notifications). Mobility: slow (pedestrian 1-2 m/s), but vehicle velocity creates large relative Doppler.

V2N (Vehicle-to-Network): vehicle $\leftrightarrow$ cellular core. Range: cellular coverage. Latency: 10-100 ms. Throughput: 1-1000 Mbps (streaming, software updates). Mobility: tested through 5G NR.

Collectively: V2X = V2I + V2V + V2P + V2N.

Theorem: V2X Mobility-Latency-Throughput Triangle

The four V2X link types occupy distinct points in the $(v_{\max}, T_{\text{latency}}, R)$ space:

Link	$v_{\max}$	$T_{\text{latency}}$	$R$
V2I	140 km/h	10-100 ms	1-100 Mbps
V2V (safety)	280 km/h	1-10 ms	0.1-10 Mbps
V2V (perception)	280 km/h	10-100 ms	10-100 Mbps
V2P	140 km/h	10-100 ms	10 kbps
V2N	140 km/h	10-100 ms	1-1000 Mbps

Consequence. V2V (safety, platooning) has the tightest constraint triangle: 280 km/h closure + 1-ms latency + 10 Mbps. No 5G NR waveform (nor DSRC, nor C-V2X) reliably hits all three corners of this triangle. OTFS-ISAC is the only known candidate — in academic/prototype testbeds — to meet all three simultaneously.

The point is that the V2V safety use case is qualitatively different from V2I or V2N. The Doppler from closing vehicles can push $\nu$ to $\sim 10$ kHz at 5.9 GHz (DSRC band) or $\sim 100$ kHz at 77 GHz mmWave. At OFDM subcarrier spacings (15 kHz at 5G NR low-band, 120 kHz at 5G NR mmWave), this creates severe inter-carrier interference — the channel coherence band is below the subcarrier spacing. OTFS, by working in the DD domain, sidesteps this problem entirely: the channel is sparse in DD, regardless of its non-sparsity in frequency.

Proof

Doppler at closing speed

For two vehicles approaching each other: $v_{\text{rel}} = v_1 + v_2$ . Doppler: $\nu = v_{\text{rel}}/\lambda$ . At 300 km/h closing (150+150) and 5.9 GHz: $\nu = 84/0.05 = 1680$ Hz. At 77 GHz: $\nu = 84/0.004 = 21{,}000$ Hz = 21 kHz.

OFDM ICI threshold

OFDM carries interference when $\nu$ exceeds a few percent of the subcarrier spacing $\Delta f$ . At 5G NR mmWave ( $\Delta f = 120$ kHz), 21 kHz is $\sim 18\%$ — severe ICI.

OTFS DD structure

OTFS with $N = 256$ Doppler bins at frame duration $T = 100$ ms: $\Delta\nu = 10$ Hz. A Doppler spread of 21 kHz occupies 2100 Doppler bins — still sparse (few paths, finite support). The DD structure handles it naturally.

Conclusion

OFDM fails the triangle; OTFS hits all corners. This is the rationale for OTFS in V2X. $\blacksquare$

The V2X Use Cases Where OTFS Matters

OTFS's advantage is not uniform across V2X. The DD-domain processing is essential where:

V2V safety (platooning, collision avoidance): closing speeds, 1-ms latency, mmWave. OTFS wins decisively.
V2I mmWave handover: mmWave BS with rapidly moving UE. OTFS maintains link stability through beam changes.
V2P warning: V2V pedestrian detection through LOS-NLOS transitions. OTFS's DD channel is robust to these transitions.

The DD-domain processing is not essential for:

V2N (cellular-grade mobility): 5G NR with OFDM works fine for highway-speed V2N.
V2I in sub-6 GHz: coherence time is long enough that OFDM handles it.

The clear deployment win for OTFS is in the mmWave V2V and safety domains — precisely where 6G V2X will concentrate.

Example: V2V Safety: 300 km/h Closing at 77 GHz

Two vehicles approaching each other at 150 km/h each (300 km/h closing) on a highway. 77 GHz mmWave. Safety message: 100 bytes, latency target 1 ms, reliability $10^{-4}$ (one error in 10,000 transmissions).

(a) Compute the Doppler spread. (b) Evaluate 5G NR mmWave OFDM feasibility. (c) Show why OTFS handles it.

Solution

Doppler

$\nu = 300 \cdot 10^3/3600 / 0.004 = 20.8$ kHz.

OFDM feasibility

5G NR mmWave: $\Delta f = 120$ kHz, $N = 64$ subcarriers/symbol. $\nu/\Delta f = 17\%$ : severe ICI. Achievable BER at 20 dB SNR: $\sim 10^{-2}$ , not $10^{-4}$ . OFDM fails.

OTFS

$N = 256$ Doppler bins at $T = 12.8$ ms: $\Delta\nu = 78$ Hz. $\nu_{\max} = 20.8$ kHz / 78 Hz = 267 bins — but still sparse (few paths). OTFS maintains full diversity, achieves $10^{-5}$ BER at 20 dB SNR. Hits the triangle.

Latency check

$T = 12.8$ ms frame + 0.5 ms processing < 13.3 ms. Doesn't meet 1 ms safety target! Need shorter frames: $T = 1$ ms gives $\Delta\nu = 1$ kHz — too coarse for fine tracking. Real solution: dedicated 1-ms URLLC frame for safety messages, fused with 12.8-ms frame for data/sensing.

Summary

V2V safety needs (i) short URLLC frame for latency, (ii) OTFS structure for Doppler robustness. Both deliverable by the SAC + PRA framework of Chapters 12-14.

Definition:
Current V2X Standards (2024)

Three standards compete for V2X deployment:

DSRC (IEEE 802.11p): OFDM-based, 5.9 GHz ITS band, 10 MHz bandwidth. Deployed in some US/European vehicles since 2015. Max throughput 27 Mbps, range 300 m.

C-V2X (LTE Mode 4 & 5G NR Sidelink): cellular-based, 5.9 GHz or mmWave. OFDM + SC-FDMA. 4G variant deployed; 5G NR variant being rolled out 2022-2026. Better reliability than DSRC at high mobility.

NR-V2X (3GPP Release 17/18): mmWave-capable, supports both sidelink (V2V) and uplink/downlink (V2I/V2N). Deployed in 2024+ premium vehicles. Still OFDM-based; mmWave sidelink uses PRBs with $\Delta f = 240$ kHz or higher.

Candidate: OTFS for 6G V2X (3GPP Release 21+, 2028+). Not yet standardized; positioned as replacement for mmWave OFDM in high-mobility scenarios.

V2X Standards Comparison

Property	DSRC (802.11p)	C-V2X (Rel. 16)	NR-V2X (Rel. 17)	6G OTFS (Rel. 21+)
Band	5.9 GHz only	5.9 GHz, sub-6 GHz	Sub-6, mmWave	Sub-6, mmWave
Modulation	OFDM	OFDM + SC-FDMA	OFDM + SC-FDMA	OTFS
Max throughput	27 Mbps	300 Mbps	1 Gbps	1+ Gbps
Max mobility	200 km/h	250 km/h	300 km/h (mmWave issue)	500+ km/h robust
Min latency	20 ms	5 ms	1 ms (Rel. 17)	0.5-1 ms
Deployment	Partial since 2015	2020+	2024+	2028+ (expected)
ISAC	No	No	Partial (Rel. 18)	Native

V2V BER vs Closing Velocity

Plot uncoded BER vs closing velocity (0-500 km/h) for three schemes: 5G NR OFDM at 77 GHz, OTFS at 77 GHz, and OFDM at 5.9 GHz (DSRC). Sliders: SNR, bandwidth.

Parameters

SNR (dB)15

Bandwidth (MHz)100

f_0

(GHz)77

Historical Note: The 5.9-GHz Band Saga

The 5.9-GHz Intelligent Transport Systems (ITS) band was allocated globally in the 1990s for DSRC. Two decades later, DSRC (802.11p) had partial deployment, but no industry-wide rollout — the standard was technically solid but commercially stalled.

In 2016, cellular operators proposed C-V2X, an LTE-sidelink variant using the same 5.9-GHz band. The FCC initially supported DSRC; in 2020, it reallocated 5.9 GHz: 45 MHz for C-V2X, 30 MHz for unlicensed Wi-Fi, eliminating 7 MHz of DSRC spectrum. This effectively killed DSRC in the US market.

The 5G NR Sidelink (C-V2X Release 16+, 2020+) is now the dominant V2V standard in the US, Europe, and Asia. But the 5.9-GHz band is crowded (max 10 MHz per operator), so V2X throughput is limited to $\sim 300$ Mbps — inadequate for cooperative perception (which needs 100+ Mbps per vehicle, and many vehicles per cell).

For 6G V2X, the industry is looking to mmWave bands (77 GHz for sidelink, 24-28 GHz for V2I) and next-gen waveforms (OTFS). 5.9-GHz is the legacy layer; mmWave OTFS is the future.

🔧Engineering Note

V2X Deployment Maturity (2024)

Current V2X deployment status:

US market: C-V2X rolled out in 2024+ premium vehicles. DSRC deprecated. NR-V2X Release 17 available. OTFS not yet.
European market: ITS-G5 (DSRC variant) deployed 2020+ in premium cars. Gradual migration to C-V2X Rel. 16. NR-V2X Rel. 17 expected 2025-2026. 5G-V2X consortium backs C-V2X evolution.
Chinese market: C-V2X dominant. Significant government investment. Some OEMs testing OTFS prototypes for 6G V2X (2025+).
Japanese market: ETC-like DSRC for tolling; C-V2X for V2V gradually emerging.

Convergence: C-V2X (LTE + 5G NR sidelink) is the dominant standard globally. 6G OTFS is the future aspirant but not yet deployed.

Operational pattern: V2X is a "slow-burn" standard — deployment requires both vehicle OEM cooperation and infrastructure (RSU, BS) deployment. Typical rollout timeline: 5-10 years from standardization to mass adoption.

Practical Constraints

•
Current: C-V2X (LTE Sidelink) dominant globally
•
5G NR-V2X Release 17 deploying 2024+
•
OTFS V2X: prototype stage (2024), standardization Rel. 21+
•
Full adoption: 2028-2030

Common Mistake: The Standards Fragmentation Risk

Mistake:

Assuming that OTFS will obsolete all V2X standards. In reality, deployed vehicles (hundreds of millions globally) run legacy DSRC, C-V2X, or NR-V2X. Any new waveform must coexist or provide forward-compatibility.

Correction:

6G V2X designs should explicitly include:

Dual-mode operation: vehicle supports both OTFS and OFDM; selects based on service (safety → OTFS, infotainment → OFDM).
Gateway architecture: OTFS for V2V + V2I, then gateway to existing cellular (OFDM-based) for V2N.
Backwards compatibility: OTFS frames can be received by legacy OFDM receivers as "pilot + data", even if they can't achieve OTFS gains.

Recognize that OTFS is not a replacement but an enhancement — adding DD-domain processing for the most demanding scenarios, while legacy systems continue running for the easier cases.

Prerequisites & Notation V2V Channels and Why OFDM Fails