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Ultrareliable and Low-Latency Communication Techniques for Tactile Internet Services

Kwang Soon Kim, Dong Ku Kim, Chan-Byoung Chae, Sunghyun Choi, Young-Chai Ko, Jonghyun Kim, Yeon-Geun Lim, Minho Yang, Sundo Kim, Byungju Lim, Kwanghoon Lee, Kyung Lin Ryu

arXiv:1907.04474v1cs.ITeess.SP

TL;DR

URLLC services must deliver heterogeneous video, audio, haptic, and control traffic with stringent latency and reliability requirements, including sporadic medium-to-large packets that current systems do not adequately support. The paper proposes cross-layer URLLC techniques and realistic ray-tracing-based evaluation, with simulations indicating feasible high-reliability, low-latency service at reasonable spectral efficiency in realistic environments.

  • Problem

    Heterogeneous URLLC traffic has diverse packet sizes, rates, arrival patterns, latency requirements, and reliability requirements that current wireless systems do not adequately support.

  • Method

    The paper develops new RRC states and multiple access, waveform multiplexing, low-delay channel coding, synchronization, full-duplex, and ray-tracing-based system-level evaluation techniques.

  • Results

    The proposed schemes are reported to support high reliability and low latency at reasonably high spectral efficiency, with waveform multiplexing achieving an overall gain as high as 1.67 times over conventional LTE-based multiband OFDM in the evaluated setting.

  • Takeaways & Limitations

    Realistic-environment simulations indicate that the proposed techniques are promising for supporting Tactile Internet services while meeting latency and reliability requirements.

Abstract

from arXiv · show

This paper presents novel ultrareliable and low-latency communication (URLLC) techniques for URLLC services, such as Tactile Internet services. Among typical use-cases of URLLC services are tele-operation, immersive virtual reality, cooperative automated driving, and so on. In such URLLC services, new kinds of traffic such as haptic information including kinesthetic information and tactile information need to be delivered in addition to high-quality video and audio traffic in traditional multimedia services. Further, such a variety of traffic has various characteristics in terms of packet sizes and data rates with a variety of requirements of latency and reliability. Furthermore, some traffic may occur in a sporadic manner but require reliable delivery of packets of medium to large sizes within a low latency, which is not supported by current state-of-the-art wireless communication systems and is very challenging for future wireless communication systems. Thus, to meet such a variety of tight traffic requirements in a wireless communication system, novel technologies from the physical layer to the network layer need to be devised. In this paper, some novel physical layer technologies such as waveform multiplexing, multiple access scheme, channel code design, synchronization, and full-duplex transmission for spectrally-efficient URLLC are introduced. In addition, a novel performance evaluation approach, which combines a ray-tracing tool and system-level simulation, is suggested for evaluating the performance of the proposed schemes. Simulation results show the feasibility of the proposed schemes providing realistic URLLC services in realistic geographical environments, which encourages further efforts to substantiate the proposed work.

I. INTRODUCTION

URLLC services combine diverse traffic and stringent latency-reliability requirements that challenge conventional cellular mechanisms. The paper introduces cross-layer techniques and realistic evaluation methods to address these demands.

  • URLLC use cases add haptic, sensing, control, command, and feedback traffic to conventional high-quality video and audio, forming interactive information loops.
  • Tele-surgery and related applications require delivery within about 1 ms and reliability as high as BLER 10^-9, while other scenarios impose similarly tight constraints.
  • Channel variation makes reliable delivery difficult, while LTE scheduling, feedback, AMC, and HARQ introduce delays incompatible with highly latency-sensitive information.
  • The paper develops LSAS-based multiple access schemes, waveform multiplexing, and full-duplex techniques, and evaluates them with system-level simulation combined with ray tracing and real-environment maps.

A. Some Use Cases

Immersive reality, tele-operation, collaborative driving, and UAV applications exchange video, audio, sensing, and haptic information under application-dependent latency and reliability constraints. These use cases therefore require traffic support beyond conventional multimedia streaming.

  • A. Some Use Cases: Immersive virtual reality combines vision, audio, and touch traffic, with vision requiring sub-millisecond-to-millisecond air latency, 10 Mbps to 1 Gbps, and 99.9%-99.999% reliability.
  • A. Some Use Cases: Tele-operation requires haptic exchange alongside high-quality video and audio, with highly dynamic environments allowing air latency of 1 ms or less.
  • A. Some Use Cases: Collaborative autonomous driving exchanges sensing information at very low latency and may also require reliable high-quality video and audio among neighboring vehicles.
  • A. Some Use Cases: UAV applications require real-time video, audio, and haptic exchange under low-latency constraints because of highly dynamic environments.

4) Interpersonal Communication:

Interpersonal communication and haptic interpersonal communication require reliable multimedia plus haptic exchange for social and interactive applications. Their haptic interactions can demand air latency of only a few milliseconds.

  • 4) Interpersonal Communication:: Haptic interpersonal communication supports remote co-presence and human-touch exchange for applications including social networking, gaming, education, and training.
  • 4) Interpersonal Communication:: Static dialoguing requires highly reliable video and audio together with haptic information whose air latency can be as low as a few milliseconds.
  • 4) Interpersonal Communication:: The paper classifies traffic by latency, reliability, packet characteristics, and arrival behavior, distinguishing loose, medium, periodic low-latency, and bursty or sporadic classes.
  • 4) Interpersonal Communication:: As latency tightens, traffic-specific mechanisms progress from legacy LTE-style procedures toward semi-persistent scheduling or grant-free multiple access for periodic, bursty, and sporadic traffic.

III. MULTIPLE ACCESS STRATEGY FOR URLLC

The paper proposes traffic-aware RRC control and radio-resource strategies for URLLC, including new user states and multiple access support. These mechanisms are designed to match protocol procedures and resources to traffic latency requirements.

  • III. MULTIPLE ACCESS STRATEGY FOR URLLC: URLLC use cases motivate short-TTI frames, traffic-aware RRC control, radio-resource management, optimization, and novel multiple access techniques.
  • III. MULTIPLE ACCESS STRATEGY FOR URLLC: A new RRC control strategy provides different protocol, core-network, and radio-resource procedures for URLLC traffic classes and partitions DL and UL resources for multiple access schemes.
  • III. MULTIPLE ACCESS STRATEGY FOR URLLC: The proposed design further classifies the inactive state into RRC INACTIVE and RRC INACTIVE CONNECTED according to handshake requirements and allocated radio resources.

RRC_INACTIVE

The proposed RRC strategy introduces traffic-aware connection procedures, ranging from LTE-style handshaking to fast-grant and immediate grant-free access. Dedicated preambles and shared subchannels support faster access for tighter latency classes.

  • RRC_INACTIVE: Three RRC procedures support progressively tighter latency requirements: LTE-style four-way handshaking, two-way FGMA access, and immediate GFMA access.The procedures respectively target loose, medium, and low latency traffic.
  • RRC_INACTIVE: The LTE-style procedure remains appropriate for traffic with loose latency requirements because it is spectrally efficient despite its longer handshaking.It uses common preambles and granted uplink access.

FGMA GFMA

The paper combines FGMA and GFMA with traffic classification, resource partitioning, and latency-aware radio resource management. Large antenna arrays and tailored scheduling are used to address reliability while preserving spectral efficiency.

  • FGMA GFMA: Different multiple-access components partition downlink and uplink resources so traffic with similar characteristics and QoS can be served together.The partitioning supports simultaneous operation of multiple access schemes on a common carrier.
  • FGMA GFMA: Large-scale antenna systems reduce channel uncertainty through channel hardening, supporting reliability when low latency restricts AMC and HARQ.The paper identifies diversity from many antennas as important when feedback and retransmissions are unavailable or limited.
  • FGMA GFMA: FGMA with latency-optimal radio resource management is designed to maximize spectral efficiency while satisfying URLLC latency and reliability requirements.The base station groups users by traffic characteristics and QoS before constructing and allocating subchannels.
  • FGMA GFMA: GFMA handles low-latency grant-free transmissions by combining preallocated resources with large-scale antenna processing that accounts for arrival uncertainty.The approach modifies latency-optimal resource management for transmissions occurring without grants.

IV. MORE PHY TECHNOLOGIES

Beyond multiple access, the paper proposes physical-layer technologies addressing waveform coexistence, processing delay, channel coding, and duplexing. These mechanisms target the combined spectral-efficiency, latency, and reliability demands of URLLC.

  • IV. MORE PHY TECHNOLOGIES: Waveform multiplexing matches waveform types and numerologies to users’ channel environments and latency requirements while multiplexing them on shared resources.The design considers cyclic-prefix length, subcarrier spacing, and filter length.
  • IV. MORE PHY TECHNOLOGIES: Channel encoding and decoding are major contributors to processing delay, motivating codes that combine low latency with strong high-reliability performance.The target high-reliability regime includes FER values from 10^-3 to 10^-7.
  • IV. MORE PHY TECHNOLOGIES: Full-duplex communication is proposed to increase spectral efficiency and reduce delay between downlink and uplink transmissions.The paper notes that LSAS-based systems require channel reciprocity for efficient channel estimation.

A. Waveform Multiplexing

The proposed waveform multiplexing system adapts numerology and filtering to channel and service conditions, while synchronization and coding-related mechanisms address practical URLLC constraints. The uplink synchronization approach is reported to outperform prior approaches.

  • A. Waveform Multiplexing: Different numerologies can coexist through resource partitioning, but inter-numerology interference and filter design for low out-of-band emission must be addressed.These requirements constrain practical multiplexing designs.
  • A. Waveform Multiplexing: Waveform multiplexing selects subcarrier spacing, cyclic-prefix length, and waveform filters according to mobility, delay spread, latency, and out-of-band-emission requirements.The design aims to minimize cyclic-prefix overhead and guard-band requirements.
  • A. Waveform Multiplexing: Downlink synchronization can use legacy time and frequency synchronization on each user’s subband despite differing numerologies and waveform filters.The paper identifies uplink synchronization as the more significant issue under mobility and higher carrier frequencies.
  • A. Waveform Multiplexing: The uplink interference-cancellation approach provides better performance than the cited alternatives for synchronization errors and frequency offsets.The comparison is reported in Fig. 7(b).

C. Channel codes for URLLC

The paper identifies error-floor limitations in raptor-like QC-LDPC codes for stringent URLLC reliability and proposes ARACA codes to address them.

  • C. Channel codes for URLLC: Raptor-like QC-LDPC codes may have poor error-floor performance at low code rates because they lack linear minimum distance growth and contain too many degree-1 variable nodes.This limitation is especially relevant when URLLC requires FER between 10^-3 and 10^-7 without retransmissions.
  • C. Channel codes for URLLC: ARACA codes target high reliability by combining linear minimum distance growth with good waterfall performance and efficient encoding.Their protograph uses two outer and two inner code parts, with outer connections supporting low-complexity encoding.

D. Full-duplex Cellular Communication: code-division duplexing spatial-division multiple access (CDD-SDMA)

The paper addresses full-duplex cellular interference by proposing CDD-SDMA, which aligns uplink interference away from downlink signal dimensions while preserving spatial multiplexing.

  • D. Full-duplex Cellular Communication: code-division duplexing spatial-division multiple access (CDD-SDMA): Without elaborate interference management, full-duplex uplink interference prevents meaningful improvement in user-rate distribution even with perfect base-station self-interference cancellation.The limitation arises from uplink users interfering with downlink users.
  • D. Full-duplex Cellular Communication: code-division duplexing spatial-division multiple access (CDD-SDMA): CDD-SDMA aligns uplink interference into a null space orthogonal to the downlink multiuser signal subspace.The scheme uses orthogonal downlink-uplink codes and antenna reconfiguration to align uplink interference into one downlink-signal dimension.
  • D. Full-duplex Cellular Communication: code-division duplexing spatial-division multiple access (CDD-SDMA): The feasibility evaluation models indoor hotspot channels with adjacent-channel, in-band blocking, co-channel interference, and finite-resolution converter effects.The scenario uses 40 baseband streams and 100 physical base-station antennas.

V. EVALUATION METHODOLOGY AND SIMULATION RESULTS

The evaluation combines realistic geographical channel modeling with system-level simulation to assess URLLC multiple access and waveform multiplexing. Results show that the proposed schemes improve latency, reliability, and spectral efficiency under appropriate traffic conditions, while combined-gain estimates remain optimistic.

  • V. EVALUATION METHODOLOGY AND SIMULATION RESULTS: The evaluation methodology combines high-resolution digital maps, real base-station deployment data, ray tracing, and generated 3D wireless channels.The strategy evaluates uplink multiple access and downlink waveform multiplexing in realistic geography.
  • V. EVALUATION METHODOLOGY AND SIMULATION RESULTS: The channel evaluation uses 6000 users, 12 real base stations with 128-element antenna arrays, 8 KB packets, 2 ms latency, and 99.999% reliability constraints.Traffic follows sporadic Poisson arrivals at 100 packets per second, with variable-length mini-slots and 25% CP overhead.
  • V. EVALUATION METHODOLOGY AND SIMULATION RESULTS: GFMA performs best for tight-latency, sporadic traffic, while FGMA can provide much higher spectral efficiency for periodic arrivals with guaranteed latency and reliability.GFMA increasingly outperforms FGMA as latency becomes tighter or more base-station antennas are added.
  • V. EVALUATION METHODOLOGY AND SIMULATION RESULTS: The proposed GFMA and FGMA guarantee high reliability and low latency at reasonably high spectral efficiency according to traffic class and QoS, unlike LTE-style access.The evaluation uses realistic deployments and large antenna arrays in the GangNam station area.
  • V. EVALUATION METHODOLOGY AND SIMULATION RESULTS: 1.67 times is the reported upper-bound spectral-efficiency gain of waveform multiplexing over conventional LTE-based multiband OFDM.The gain combines ideal waveform selection with optimal CP length and OFDM-parameter selection.
  • V. EVALUATION METHODOLOGY AND SIMULATION RESULTS: Combining waveform multiplexing, CDD-SDMA, and proposed multiple access may yield up to 100% further spectral-efficiency gain, but the paper describes this estimate as potentially too optimistic.The estimate directly combines results from separate figures rather than reporting a joint experiment.

VI. CONCLUSION

The paper develops a suite of URLLC techniques spanning user states, radio-resource strategies, physical-layer technologies, and realistic evaluation to support Tactile Internet services. Simulations indicate that the proposed schemes can jointly provide high spectral efficiency, low latency, and high reliability.

  • It proposes multiplexing multiple access schemes over radio resources and latency-optimal resource management for diverse URLLC traffic and QoS requirements.The goal is to maximize spectral efficiency while maintaining latency and reliability guarantees.
  • The paper introduces new low-latency user states, corresponding RRC protocols, and radio-resource allocation strategies.These mechanisms are designed around the latency requirements of URLLC traffic.
  • The proposed schemes support URLLC services with high spectral efficiency while guaranteeing latency and reliability requirements in realistic environments.The evaluation combines refined digital maps, realistic node distributions, ray-tracing data, and deterministic or stochastic 3D channel models.
  • Additional PHY contributions cover waveform multiplexing, synchronization, low-delay high-reliability channel codes, and practical full-duplex MU-MIMO.The full-duplex concept combines downlink/uplink MU-MIMO with interference alignment, and each technology is reported to provide significant performance improvement.
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