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6G Enabled Advanced Transportation Systems

Ruiqi Liu, Meng Hua, Ke Guan, Xiping Wang, Leyi Zhang, Tianqi Mao, Di Zhang, Qingqing Wu, Abbas Jamalipour

arXiv:2305.15184v3cs.ITcs.NIcs.SYeess.SPeess.SYmath.IT

TL;DR

Because 6G and ITS are emerging and dynamic topics, little survey coverage addresses their interplay. The paper surveys recent 6G research and standardization on transportation connectivity and candidate technologies including localization, integrated sensing and communications, and security. The paper concludes that 6G could connect previously unconnected transportation devices, including on high-speed trains and airplanes, and enable more intelligent, robust, and secure transportation.

  • Problem

    Because 6G and ITS are emerging and dynamic topics, little survey coverage addresses their interplay.

    Source: §I · p. 2

  • Method

    The paper surveys recent 6G research and standardization on transportation connectivity and candidate technologies including localization, integrated sensing and communications, and security.

    Source: §I · p. 2, 1) Localization approaches · p. 9

  • Results

    The paper concludes that 6G could connect previously unconnected transportation devices, including on high-speed trains and airplanes, and enable more intelligent, robust, and secure transportation.

    Source: §IV · p. 13

  • Takeaways & Limitations

    The paper presents 6G as a potential means to improve transportation services, provided implementation challenges are overcome.

    Source: §IV · p. 13

    6G remains under study, and the reported early results only indicate that some candidate technologies might prevail.

    Source: §I · p. 2

Abstract

from arXiv · show

With the emergence of communication services with stringent requirements such as autonomous driving or on-flight Internet, the sixth-generation (6G) wireless network is envisaged to become an enabling technology for future transportation systems. In this paper, two ways of interactions between 6G networks and transportation are extensively investigated. On one hand, the new usage scenarios and capabilities of 6G over existing cellular networks are firstly highlighted. Then, its potential in seamless and ubiquitous connectivity across the heterogeneous space-air-ground transportation systems is demonstrated, where railways, airplanes, high-altitude platforms and satellites are investigated. On the other hand, we reveal that the introduction of 6G guarantees a more intelligent, efficient and secure transportation system. Specifically, technical analysis on how 6G can empower future transportation is provided, based on the latest research and standardization progresses in localization, integrated sensing and communications, and security. The technical challenges and insights for a road ahead are also summarized for possible inspirations on 6G enabled advanced transportation.

I. INTRODUCTION

Because 6G and intelligent transportation systems (ITS) are emerging fields with little survey coverage of their interplay, the paper reviews how 6G may support transportation connectivity and smarter, more secure systems. It situates this review in the shift toward data-driven transportation and 6G’s expanded usage scenarios and capabilities.

I. INTRODUCTION

  • Data-driven ITS uses sensor and device inputs to inform directives, while heterogeneous data and future transportation demands challenge rate and latency beyond 5G.Video, GPS, and sensor data support detection, recognition, tracking, and AI-based traffic analysis.Source: §I · pp. 1–2
  • 6G is envisaged to enhance 5G’s three usage scenarios and add integrated sensing and communication, AI and communication, and ubiquitous connectivity.For data rate, connection density, and efficiency, 6G targets are around five times 5G values; the exemplary targets need not be met simultaneously.Source: §I · p. 2
  • The paper surveys early 6G candidate technologies intended to connect transportation in remote or extreme conditions and contribute to greener, smarter, more secure, and more robust systems.The field remains under study, with early results pointing to candidate technologies for the envisaged scenarios and capabilities.Source: §I · p. 2
  • The paper addresses the limited survey coverage of the interplay between emerging 6G networks and ITS through a comprehensive survey and area-specific insights.It reviews ubiquitous connectivity and candidate technologies for more intelligent, robust, and secure transportation.Source: §I · p. 2

II. UBIQUITOUS CONNECTIVITY FOR ALL TRANSPORTATION

The section considers how 6G could extend connectivity across transportation, including remote areas, and details the railway scenarios that demand high data rates and uninterrupted service. For railways, it identifies channel characterization and sounding as part of the technical analysis.

II. UBIQUITOUS CONNECTIVITY FOR ALL TRANSPORTATION

  • 6G is envisaged to provide connectivity to passengers and devices across transportation types, including remote areas where connectivity is currently scarce or bandwidth limited.The need spans large bandwidth, low latency, and high reliability.Source: §II · p. 3

A. Railway transportation

  • Smart rail mobility comprises five high-data-rate scenarios: train-to-infrastructure, inside station, train-to-train, infrastructure-to-infrastructure, and intra-wagon.Bandwidth needs range from hundreds of MHz to several GHz, with dozens of GHz needed in train-to-train and intra-wagon scenarios; train-to-infrastructure is the greatest challenge, requiring uninterrupted high-rate, low-latency service.Source: A. Railway transportation · p. 3
  • The railway discussion examines channel conditions for the five scenarios at 300 GHz using channel sounding, ray tracing, and channel characterization.It considers how channel characteristics can inform communication-system design and deployment.Source: A. Railway transportation · p. 3

1) Channel characterization:

Railway channel measurements at 300 GHz indicate sparser multipath than a similar 60-GHz scenario, while channel-dependent angular spreads and severe Doppler motivate adaptable beamforming and compensation approaches.

1) Channel characterization:

  • At 300 GHz, the T2I/IS RMS delay spread is 8.92 ns, half the 16 ns mean measured in a similar 60-GHz scenario.The measurements indicate considerably sparser multipath at 300 GHz, but limited degrees of freedom leave a need for measurement-validated real-time simulations.Source: 1) Channel characterization · p. 3

2) Fast and adaptive beamforming:

  • Railway angular spreads vary by scenario: IS and IW have wider azimuth than elevation spreads, while T2T has larger mean elevation than azimuth spreads.This points to different multipath distributions and a need for beamforming algorithms flexible enough to adapt to each scenario’s propagation conditions.Source: 2) Fast and adaptive beamforming · pp. 3–4

3) Mechanisms against the Doppler effect:

  • At 300 GHz, mean Doppler shifts reach 72.32 kHz in T2I and 8.25 kHz in T2T, motivating mechanisms beyond current 5G calibration.Proposed directions include larger subcarrier spacing, tunable RIS-based mitigation using train location, direction, and velocity, and machine-learning Doppler estimation from repeated HST routes.Source: 3) Mechanisms against the Doppler effect · p. 4

4) Proper modulation and channel coding:

The section relates railway modulation and coding choices to channel conditions, then describes airborne connectivity through cellular air-to-ground networks. It also notes limits and technical challenges for connectivity in flight.

4) Proper modulation and channel coding:

  • For railway links, a lower Rician K-factor indicates stronger multipath, and lower-order modulation with lower coding rates is suggested for such cases.The mean K-factor exceeds 5 dB in most LoS smart-rail scenarios, with C-NT and C-T as exceptions; the IW LoS range is 4.27–6.90 dB.Source: 4) Proper modulation and channel coding · p. 4
  • Above 200 km/h, OTFS can provide lower-complexity channel estimation, higher diversity, and higher reliability for high-speed-train communications.For HST mIoT, simulations in prior work report that OTFS-TSMA can achieve high user connectivity and transmission reliability.Source: 4) Proper modulation and channel coding · p. 5
  • Novel coding designs include polarization-adjusted convolutional codes with rate matching for HRLLC and APSK-based schemes for immersive communication.The cited studies describe these as potential 6G coding designs for different deployment scenarios.Source: 4) Proper modulation and channel coding · p. 5

B. Air to ground communication

  • NTN can reach nearly every location, but its latency and data rate generally limit in-flight service to email and chat rather than video conferencing, streaming, or gaming.Cellular ATG is presented as a candidate for more satisfactory data rates and latency, using ground-network base stations to serve aircraft.Source: B. Air to ground communication · p. 6
  • Long aircraft-to-base-station distances and high mobility make Doppler shift a challenge for ATG, alongside the need for enhanced coverage, beam tracking, and high-performance antennas.The cellular ATG architecture routes signals from ground base stations to an airborne antenna, then through a CPE to cabin Wi-Fi.Source: B. Air to ground communication · p. 6

1) Enhanced cell coverage:

The section describes ways to maintain cellular air-to-ground links despite aircraft mobility, and presents non-terrestrial networks as a complement for transportation in remote areas.

1) Enhanced cell coverage:

  • Some 5G cellular ATG networks have a reported maximum cell radius of 300 km, while enhanced coverage is intended to reduce handovers and stabilize aircraft connections.The passage identifies frame-structure design, PRACH timing adjustment, HARQ, and interference suppression as technologies that can help increase coverage.Source: 1) Enhanced cell coverage · p. 6

2) Precise beam tracking:

  • For predictable cruise paths, machine-learning beam tracking can use historical positions and velocities to predict beamsteering angles with less overhead than periodic training.Adaptive beam-width adjustment is also proposed to select an optimal width at cell center or cell edge.Source: 2) Precise beam tracking · p. 6

C. Complementary coverage for transportation in remote areas

  • NTN is proposed to complement ground networks for transportation in remote areas, using heterogeneous platforms that include LEO satellites, HAPS, and UAVs.The passage identifies ships at sea and travelers crossing deserts as examples of transportation beyond typical terrestrial coverage.Source: C. Complementary coverage for… · pp. 6–7

1) HAPS as IMT Base Stations:

The section surveys HAPS and LEO satellite approaches to extending connectivity, including their propagation and backhaul challenges and proposed communication techniques.

1) HAPS as IMT Base Stations:

  • HAPS can remain quasi-stationary in the stratosphere for weeks or months, supporting stable line-of-sight access for remote areas and transportation such as ships.The passage defines HAPS as airships or balloons operating at 20–50 km altitude and describes HAPS as IMT base stations as a complement for 6G coverage.Source: 1) HAPS as IMT Base Stations · p. 7
  • Atmospheric inhomogeneity across the lower near space complicates HAPS channel modeling and beam alignment through refraction, scattering, diffraction, and absorption.Existing stochastic channel models are described as not fully accounting for the complex HIBS channel factors; neural networks are proposed as a possible approach given sufficient measurement data.Source: 1) HAPS as IMT Base Stations · p. 7
  • THz links can provide Tbps transmission, whereas microwave frequencies can hardly support inter-HIBS backhaul over 100 Gbps; metasurface transmitters are proposed to reduce hardware overhead and energy consumption.The passage attributes the metasurface benefit to digital modulation and beamforming without RF chains or a feeding network.Source: 1) HAPS as IMT Base Stations · p. 7

2) LEO satellite-based communication:

  • LEO satellite communication is presented as a way to extend broadband connectivity to ocean and remote areas beyond the reach of ground networks and relays, with lower latency than GEO satellites.The passage reports ground-based coverage limited to 15 km from the coastline and ship- or aircraft-relay coverage extended to 60 km.Source: 2) LEO satellite-based communication · p. 7
  • Iterative frequency-offset estimation and compensation in both uplink and downlink can mitigate satellite Doppler effects, with trajectory and heading information as potential prior knowledge.The passage also identifies OTFS, AFDM, and resource-sparsity-based technologies such as NOMA as emerging ways to address Doppler side effects.Source: 2) LEO satellite-based communication · p. 8
  • Combining free-space optical and RF communications is proposed for heterogeneous TN–NTN networks to address frequency scarcity; Starlink uses laser inter-satellite links to reduce latency and interference.The passage also states that narrower laser beams eliminate interference and ensure higher transmission security.Source: 2) LEO satellite-based communication · pp. 8–9

3) Standardization efforts for NTN:

The section reviews NTN standardization across 3GPP and other organizations, noting both the evolution of the work and its current focus.

3) Standardization efforts for NTN:

  • 3GPP NTN work has progressed from Rel-15 deployment and channel modeling studies to Rel-17 standardization and Rel-18 enhancements, while Rel-19 is expected to address a satellite-based core network and broader NTN types.The passage says current discussions remain mostly focused on satellite communication, especially LEO, and anticipates more attention to HAPS and HIBS in future releases.Source: 3) Standardization efforts for NTN · p. 9
  • ITU-R SG4, through ITU-R M.2460-0, and ETSI, through TR 103 611, are among the organizations and deliverables addressing satellite communications and network coordination.The passage describes ITU-R M.2460-0 as outlining satellite use cases and technical elements for integration into next-generation access networks.Source: 3) Standardization efforts for NTN · p. 9

III. INTELLIGENT TRANSPORTATION EMPOWERED BY 6G

6G can digitize transportation and support intelligent, efficient systems. Localization methods estimate range and direction, while high-speed vehicles require Doppler compensation.

III. INTELLIGENT TRANSPORTATION EMPOWERED BY 6G

  • 6G can digitize transportation and support intelligent, efficient systems.Transportation can benefit from both 6G communication and beyond-communication scenarios.Source: §III · p. 9

1) Localization approaches:

  • RSS, ToA, and TDoA estimate range, while AoA provides complementary direction information.ToA uses signal travel time; TDoA uses arrival-time differences and does not require strict transmitter–receiver synchronization.Source: 1) Localization approaches · p. 9
  • For higher-speed vehicles, Doppler effects must be compensated, with speed estimated from transmitted and received echo frequencies.Combining localization techniques can improve accuracy.Source: 1) Localization approaches · pp. 9–10

2) Improvement of localization accuracy:

6G localization is estimated to reach 1–10 cm accuracy, depending on configuration, while RIS and integrated sensing and communication address propagation and system-design challenges.

2) Improvement of localization accuracy:

  • 1–10 cm positioning accuracy is estimated for 6G, depending on configuration; ultra-massive MIMO and cooperative sensing can improve accuracy.More antennas increase beamforming and diversity gains, while multiple deployed transmitters and receivers can illuminate additional signal paths.Source: 2) Improvement of localization accuracy · p. 10
  • RIS can provide virtual LoS paths around blockage, illuminating shadowed vehicles and adding reflected paths for localization.RIS-side sensors and echo fusion with a base station offer additional estimation and detection degrees of freedom; deployment, phase shifts, and resources require joint optimization.Source: 2) Improvement of localization accuracy · p. 10, Figure 6 · p. 10

B. Integrated sensing and communication

3) The cost of hardware is high:

  • ISAC integrates sensing and communication on common hardware, improving resource utilization while supporting communication and high-precision sensing.Integration also reduces interference links and limits information exchange coordination to the integrated receiver.Source: 3) The cost of hardware is high · p. 11

1) Information exchange signaling overhead is low:

ISAC combines communication and sensing on shared resources and hardware, reducing coordination overhead while introducing joint design choices and coverage challenges.

1) Information exchange signaling overhead is low:

  • Integrating communication and radar reduces interference links and confines information-exchange coordination to the integrated receiver.A special coordination control unit is not needed.Source: 1) Information exchange signaling… · p. 11

2) Integrated gain is high:

1) Resource allocation management in ISAC systems:

  • ISAC waveform design must balance communication rates and sensing performance, with approaches varying by service scenario.Communication-centered designs can sense with communication signals but may have weak sensing ability; high-rate, high-accuracy scenarios can jointly optimize the waveforms.Source: 1) Resource allocation management in… · p. 11
  • ISAC has asymmetric coverage: target-echo attenuation and LoS blockage can make sensing range shorter than communication range.RIS can create virtual LoS for sensing and additional NLoS paths for multi-user communication; joint waveform and RIS-phase design can meet specified SINR constraints.Source: 1) Resource allocation management in… · p. 11, Figure 7 · p. 11
  • Open ISAC issues include optimal base-station deployment, base-station coordination, and system architecture and protocol design.The research remains ongoing.Source: 1) Resource allocation management in… · p. 12

2) Sensing-assisted communication:

For autonomous driving, ISAC can use sensing echoes to train and track communication beams. V2X also requires stringent latency, reliability, and uplink capacity.

2) Sensing-assisted communication:

  • ISAC can use detection echoes to train a dual-functional base station’s communication codebook and predict subsequent beams for real-time tracking.An extended Kalman filtering framework has been studied to track and predict vehicle kinematics for vehicle-to-infrastructure beamforming.Source: 2) Sensing-assisted communication · p. 12

C. Autonomous driving

  • Localization and sensing, alongside communication, are described as supporting the progression of autonomous driving.The passage notes that full autonomous driving requires new communication paradigms for 6G.Source: C. Autonomous driving · p. 12

1) V2X communication:

  • 6G is expected to provide 0.1 to 1 ms air-interface latency for V2X information exchange among necessary nodes.The required reaction time depends on physical distance, processing capacity, and whether decisions use data from multiple vehicles and roadside infrastructure.Source: 1) V2X communication · p. 12
  • V2X is expected to need reliability potentially reaching 1 −10−6 and typical-case uplink rates up to 750 Mbps if all vehicle sensor data goes to cloud service centers.The passage says typical autonomous-driving mobility can be served by both 5G and 6G without posing major cellular-network challenges.Source: 1) V2X communication · p. 12

2) Mobile edge computing:

Mobile edge computing moves autonomous-driving decisions closer to vehicles to reduce latency, while network slicing separates the different communication and quality-of-service needs of transportation. Flexible slice configuration and timely management remain challenges, with AI identified as a potential aid.

2) Mobile edge computing:

  • Centralized decisions can increase end-to-end latency with physical distance, motivating mobile edge computing near vehicles.The proposed setting includes many information sources, such as vehicles, traffic lights, and roadside sensors.Source: 2) Mobile edge computing · p. 12
  • 6G base stations and roadside units can host edge tasks, while nearby parked cars may add capacity at busy times.Challenges include smart scheduling, dynamic allocation, and coordinating mobile edge computing with other 6G technologies.Source: 2) Mobile edge computing · p. 13

3) Network slicing:

  • Network slicing creates logically independent networks on shared infrastructure to meet autonomous driving's differing latency, bandwidth, and reliability demands.Slices can support distinct quality of service, including very low latency or ultra-large uplink bandwidth.Source: 3) Network slicing · p. 13
  • 6G slicing must support flexible, timely configuration and management of different RAN slices; AI may offer opportunities to address this challenge.Source: 3) Network slicing · p. 13

D. Security for intelligent transportation systems

As intelligent transportation systems grow more complex and face security threats, this section surveys academic work, ITU-T recommendations, and ongoing standards work addressing emerging requirements. The conclusion describes 6G's potential to connect high-speed trains and airplanes and enable more intelligent, robust, and secure transportation.

D. Security for intelligent transportation systems

  • Research explores blockchain, machine learning, and quantum-related ITS security –, while ITU-T SG17 recommendations address threats, implementation guidance, and security requirements.Examples include threat identification for connected vehicles and V2X, intrusion detection for in-vehicle networks, and misbehavior detection for connected vehicles.Source: D. Security for intelligent… · p. 13
  • Ongoing work broadens software-update guidance to in-vehicle procedures and adds public-5G deployment scenarios for C-V2X services targeting 5G URLLC.These updates revise X.1373 and supplement X.1813, respectively.Source: D. Security for intelligent… · p. 13
  • New guidance addresses vehicular-edge-computing risks such as data leakage and manipulation, while separate work analyzes vulnerabilities in over-the-air vehicle updates.The work items propose security requirements and use cases for vehicular edge computing, and methodologies for automotive-industry security functions.Source: D. Security for intelligent… · p. 13

IV. CONCLUSIONS

  • 6G can connect previously unconnected transportation devices, including high-speed trains and airplanes, and enable more intelligent, robust, and secure transportation.Source: §IV · p. 13
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