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V2X Meets NOMA: Non-Orthogonal Multiple Access for 5G Enabled Vehicular Networks

Boya Di, Lingyang Song, Yonghui Li, Zhu Han

arXiv:1705.08709v1cs.ITcs.NI

TL;DR

Massive V2X connectivity creates access collisions and distributed interference-management challenges. This paper introduces NOMA into LTE-based vehicular networks, designs scheduling and resource-allocation mechanisms, and extends them to safety-critical broadcast; the proposed NOMA-MCD scheme performs better than OMA and reduces resource collisions.

  • Problem

    Massive connectivity creates access collisions, while distributed interference management remains challenging for users.

    Source: §I · p. 3, 2) Distributed Power Control of the… · p. 10

  • Method

    The paper introduces NOMA into LTE-based vehicular networks and designs multiplexing, scheduling, resource-allocation, and network-control mechanisms, extending NOMA-MCD to safety-critical V2X broadcasting.

    Source: §V · p. 16

  • Results

    The NOMA-MCD scheme performs better than the OMA-based scheme and efficiently reduces resource collisions.

    Source: C. Performance Evaluation · p. 12, §V · p. 16

  • Takeaways & Limitations

    NOMA shows potential to enhance cellular V2X services and support massive connectivity through power-domain or code-domain multiplexing.

    Source: §V · pp. 16–17

Abstract

from arXiv · show

Benefited from the widely deployed infrastructure, the LTE network has recently been considered as a promising candidate to support the vehicle-to-everything (V2X) services. However, with a massive number of devices accessing the V2X network in the future, the conventional OFDM-based LTE network faces the congestion issues due to its low efficiency of orthogonal access, resulting in significant access delay and posing a great challenge especially to safety-critical applications. The non-orthogonal multiple access (NOMA) technique has been well recognized as an effective solution for the future 5G cellular networks to provide broadband communications and massive connectivity. In this article, we investigate the applicability of NOMA in supporting cellular V2X services to achieve low latency and high reliability. Starting with a basic V2X unicast system, a novel NOMA-based scheme is proposed to tackle the technical hurdles in designing high spectral efficient scheduling and resource allocation schemes in the ultra dense topology. We then extend it to a more general V2X broadcasting system. Other NOMA-based extended V2X applications and some open issues are also discussed.

I. INTRODUCTION

LTE-based V2X offers broad coverage and controllable latency, but orthogonal access becomes congested in dense networks. The paper examines NOMA to support massive connectivity, reduce collisions, and improve V2X latency and reliability.

  • LTE is considered promising for V2X because it offers large coverage, controllable latency, and high data rates.Source: §I · p. 2
  • OMA-based LTE suffers resource collisions, difficult access-rate guarantees, and severe packet loss in dense V2X topologies.Source: §I · p. 2
  • NOMA allows multiple users to share channels through power- or code-domain multiplexing, improving spectrum efficiency and alleviating congestion.Source: §I · p. 3
  • NOMA-based V2X introduces distinct scheduling, spectrum-management, power-control, and signaling challenges because of mobility, interference, and CSI requirements.Source: §I · pp. 3–4
  • The article studies NOMA-based V2X unicast systems, proposes a mixed centralized/distributed scheme, and discusses extensions including broadcasting, uplink V2I, and multi-operator V2V.Source: §I · pp. 4–5

A. LTE-supported V2X Services

LTE-supported V2X uses direct and cellular communication modes for safety-critical and traffic-efficient services. Dynamic and semi-persistent scheduling address different latency and traffic patterns, while mobility and dense topology create interference and scheduling challenges.

B. Non-Orthogonal Multiple Access Technique

NOMA supports overloaded transmission by multiplexing users in the power or code domain. The paper describes PD-NOMA with SIC and CD-NOMA with sparse codebooks and spreading sequences.

III. NOMA APPLICABILITY TO CELLULAR V2X

The paper applies PD-NOMA to cellular V2X, beginning with a unicast model and addressing interference, mobility, scheduling, power control, and signaling. It proposes a mixed centralized/distributed design that combines BS scheduling with distributed user power control.

  • The proposed NOMA-MCD approach targets resource-collision reduction and low latency in cellular V2X, then extends toward broadcast scenarios.Source: §III · p. 7

NOMA-based V2X Unicast System Model

Key Problems and Solutions of Resource Allocation and Signaling Control

1) Centralized Spectrum Management of the BS:

The BS formulates centralized spectrum allocation using partial CSI and solves the resulting non-convex assignment through many-to-many swap matching.

2) Distributed Power Control of the Users:

Users perform distributed power control through iterative Tx-Rx signaling, balancing target-link decoding against interference across neighboring receivers.

C. Performance Evaluation

The proposed NOMA-MCD scheme combines centralized resource allocation with distributed power control and is evaluated against an OMA-based LTE-D scheme.

1) Tx-Rx selection and time-frequency resource allocation of the BS:

The paper considers BS scheduling and resource allocation for V2X broadcasting and uplink V2I, including SCMA-based grant-free access for dense connectivity.

1) Tx-Rx selection and time-frequency resource allocation of the BS:

2) Power control strategy of each Tx user:

B. NOMA-based Uplink V2I Networks

C. NOMA-based V2V Networks with Multiple Operators

The multiple-operator V2V setting shares carriers across vehicles subscribed to different operators, creating resource-collision and coordination challenges. NOMA-based joint transmission and reception is proposed to improve cell-edge spectrum efficiency, while mobility and imperfect beam fitting remain design concerns.

V. CONCLUSIONS AND FUTURE OUTLOOK

The paper introduces NOMA into LTE-based vehicular networks to reduce resource collisions and support diverse V2X applications, extending a unicast scheme to safety-critical broadcasting. It reports reduced collisions versus OMA and identifies synchronization, coexistence, coordination, and mobility-related issues for future work.

  • The paper introduces NOMA into LTE-based vehicular networks to support massive connectivity and high spectrum efficiency.Source: §V · pp. 16–17
  • The NOMA-MCD scheme is developed for V2X unicast and extended to a more general safety-critical V2X broadcast scenario.Source: §V · p. 16
  • The proposed NOMA-MCD scheme efficiently reduces resource collision compared to the traditional OMA-based scheme.Source: §V · p. 16
  • Open issues include synchronization under high mobility, LTE–WiFi coexistence, and coordination among services and devices with different requirements.Source: §V · p. 17
  • NOMA applications discussed include cooperative V2X, cognitive V2X, networking NOMA, and contention-based SCMA.Source: §V · pp. 16–17
  • Cognitive NOMA lets vehicles opportunistically access cellular-user channels while protecting cellular services through coordinated power control and user coordination.Source: §V · p. 17
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