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White Paper on Critical and Massive Machine Type Communication Towards 6G
Nurul Huda Mahmood, Stefan Böcker, Andrea Munari, Federico Clazzer, Ingrid Moerman, Konstantin Mikhaylov, Onel Lopez, Ok-Sun Park, Eric Mercier, Hannes Bartz, Riku Jäntti, Ravikumar Pragada, Yihua Ma, Elina Annanperä, Christian Wietfeld, Martin Andraud, Gianluigi Liva, Yan Chen, Eduardo Garro, Frank Burkhardt, Hirley Alves, Chen-Feng Liu, Yalcin Sadi, Jean-Baptiste Dore, Eunah Kim, JaeSheung Shin, Gi-Yoon Park, Seok-Ki Kim, Chanho Yoon, Khoirul Anwar, Pertti Seppänen
TL;DR
The paper addresses the gap between diverse, demanding MTC requirements and the limitations of existing wireless systems designed primarily for human communications. It develops a holistic view of 6G MTC, covering use cases, requirements, service classes, and technical enablers across the protocol stack. Its central outcome is a broad 6G MTC framework that emphasizes energy efficiency, end-to-end optimization, mission-critical dependability, intelligence, and long-term security.
Problem
Existing wireless systems adapted from human communications are inefficient and unscalable for the fundamentally different and diverse requirements of MTC.
Method
The paper provides an overarching, holistic analysis of MTC toward 6G, spanning drivers, use cases, requirements, service classes, and technical enablers from physical to application layers.
Results
The paper identifies energy-efficient devices, on-device intelligence, end-to-end design, mission-critical service, and lightweight long-term security as key directions for 6G MTC.
Takeaways & Limitations
6G MTC is presented as an intelligent and end-to-end optimized network serving diverse massive and critical machine communication needs.
Takeaways & Limitations
Grant-free designs still face synchronization, privacy, and security challenges, including time- and frequency-offset correction for randomly superimposed pilots.
Abstract
from arXiv · showhide
The society as a whole, and many vertical sectors in particular, is becoming increasingly digitalized. Machine Type Communication (MTC), encompassing its massive and critical aspects, and ubiquitous wireless connectivity are among the main enablers of such digitization at large. The recently introduced 5G New Radio is natively designed to support both aspects of MTC to promote the digital transformation of the society. However, it is evident that some of the more demanding requirements cannot be fully supported by 5G networks. Alongside, further development of the society towards 2030 will give rise to new and more stringent requirements on wireless connectivity in general, and MTC in particular. Driven by the societal trends towards 2030, the next generation (6G) will be an agile and efficient convergent network serving a set of diverse service classes and a wide range of key performance indicators (KPI). This white paper explores the main drivers and requirements of an MTC-optimized 6G network, and discusses the following six key research questions: - Will the main KPIs of 5G continue to be the dominant KPIs in 6G; or will there emerge new key metrics? - How to deliver different E2E service mandates with different KPI requirements considering joint-optimization at the physical up to the application layer? - What are the key enablers towards designing ultra-low power receivers and highly efficient sleep modes? - How to tackle a disruptive rather than incremental joint design of a massively scalable waveform and medium access policy for global MTC connectivity? - How to support new service classes characterizing mission-critical and dependable MTC in 6G? - What are the potential enablers of long term, lightweight and flexible privacy and security schemes considering MTC device requirements?
1 Introduction
The paper frames 6G MTC as an evolution beyond systems adapted from human communications, targeting scalable connectivity for diverse machine applications and requirements. It surveys 5G capabilities and proposes a holistic, intelligent, end-to-end optimized network perspective.
- 6G MTC must address diverse applications ranging from best-effort sensors to highly reliable, real-time vehicle connectivity.
- 5G NR supports mMTC through high connection density and URLLC through 99.999% reliability at 1 ms user-plane latency.
- NR adds configurable numerology, short mini-slots, and grant-free transmission to reduce latency and signaling overhead for URLLC and mMTC.
- Existing systems remain power-hungry or costly for many MTC applications, while LPWANs trade efficiency and range against data rates and supported use cases.
- The paper argues that modifying human-type communication systems for IoT is inefficient and unscalable because MTC has fundamentally different requirements.
- It presents an intelligent, unified, holistic network optimized end to end from the physical layer through the application layer.
2 MTC Megatrends Towards 2030
MTC is positioned as a key technology enabler amid rapid societal transformation toward 2030. The paper therefore organizes its discussion around emerging drivers, use cases, requirements, and service classes.
- Rapid societal transformation toward 2030 is identified as a central driver of MTC evolution.
2.1 Drivers
The paper identifies automation, ubiquitous connectivity, new human-machine interaction, zero-energy operation, data markets, and sustainability as drivers shaping MTC toward 2030.
- MTC supports increasing automation and intelligence in transportation, where higher driving automation requires more sensors, edge processing, and real-time connectivity.
- Forecasted growth to 30 billion connected IoT devices by 2030 supports ubiquitous connectivity and increasingly autonomous city services.
- Industry 5.0 will require MTC to support customized production and more interactive local and remote sensing, actuation, and haptics.
- XR, brain-computer interaction, and multisensory interfaces are expected to drive widespread machine-enabled human-machine interaction.
- Zero-energy trends demand higher performance at very low energy consumption, including zero-latency and zero-error capabilities for real-time control and emergency IoT.
- Emerging data markets introduce data-centric KPIs such as age of information, privacy, and localization accuracy.
- These societal and technological trends are linked to the 2030 Sustainable Development Goals for an inclusive, trustworthy, and self-sustainable society.
2.2 Use Cases
The paper presents representative 6G MTC use cases spanning factories, autonomous-device swarms, personalized body networks, extreme-edge sensing, immersive interaction, and distributed sensing services.
- The paper selects plausible use cases to represent diverse MTC possibilities because forecasting 6G use cases is not straightforward.
- Industry 4.0 and Industry 5.0: Future factories will need massive connectivity for mobile production assets as manufacturing becomes more agile, adaptable, personalized, and data-driven.
- Autonomous Vehicle Swarms: Autonomous vehicle swarms will coordinate distributed tasks across shop floors, logistics, transport, and emergency response, requiring robust connectivity.
- Personalized Body Area Networks: Wearables are expected to evolve into clothing-integrated, implanted, and personalized body-area-network devices.
- Extreme-Edge IoT: Extreme-edge sensors have constrained power, computing, and storage, motivating wireless energy transfer and backscatter technologies.
- Internet of Senses: Internet of Senses applications may require ultrareliable, ultrabroadband, ultraresponsive connectivity for immersive remote control and interaction.
- Distributed Sensing: Distributed sensing services may use MTC and distributed ledgers to exchange authenticated sensor data, services, or micropayments between devices.
2.3 Requirements
6G MTC requirements will retain stricter versions of 5G KPIs while adding metrics for information freshness, interoperability, dependability, positioning, sustainability, and end-to-end energy efficiency.
- Existing and Evolving KPIs: 6G will impose more stringent requirements on existing 5G KPIs while evolving quality-of-service demands toward end-to-end guarantees.Industrial closed-loop control may require up to 1 −10−7 E2E reliability at 1 ms E2E latency, with around 1−10−9 per-link reliability and 0.1ms user-plane latency.
- Energy and Sustainability: Ultra-dense industrial IoT deployments may require 3D connectivity supporting up to 100 connections per m3, alongside a zero-energy-device vision.The zero-energy vision combines efficient hardware design with energy harvesting.
- Novel KPIs: New 6G KPIs include AoI, interoperability, dependability, positioning, sustainability, and E2E EE.AoI measures information freshness for networked monitoring and control, while dependability encompasses availability, reliability, security, and system integrity.
- Novel KPIs: Interoperability must span heterogeneous wired and wireless access technologies and deployment scenarios.Positioning accuracy is relevant to applications such as controlling automated guided vehicles on factory floors.
- Energy and Sustainability: 6G sustainability must account for total cost and energy consumed per successfully delivered application-level bit, including environmental impact.This extends beyond device energy efficiency to infrastructure and end-to-end concerns.
2.4 MTC Service Classes
6G MTC expands beyond 5G’s critical and massive categories into service classes spanning zero-energy operation, dependable and broadband critical communication, scalable critical connectivity, and globally scalable massive connectivity.
- Service-class evolution: MTC will face more stringent and heterogeneous constraints from industrial use cases and verticalized service provision, requiring multidimensional optimization and scalable design.The evolution extends 5G’s URLLC and mMTC categories toward diverse applications.
- Critical MTC classes: Dependable cMTC supports extreme reliability and low latency together with dependability measures, precise positioning, and security.It is described as a direct evolution of 5G URLLC for applications such as autonomous driving.
- Critical MTC classes: Broadband cMTC combines mobile-broadband data with high reliability and low latency for applications including XR, cloud gaming, and robot-assisted surgery.
- Critical MTC classes: Scalable cMTC supports massive connectivity with high reliability and low latency for critical medical monitoring and factory automation.
- Globally scalable mMTC: Globally scalable mMTC provides ultra-wide coverage across all spatial dimensions, including volumetric device density.UAV swarms and non-terrestrial networks are identified as fundamental to global mMTC connectivity.
- Zero-energy mMTC: Zero-energy mMTC targets massive deployments of energy-efficient radios with very long battery and network lifetimes.Relevant techniques include energy harvesting, backscatter communication, zero-energy radios, and extreme energy-efficient resource allocation.
3 Potential Enabling Technologies
The paper surveys potential MTC enablers across the protocol stack, from efficient hardware and zero-energy interfaces to scalable connectivity, mission-critical services, privacy, and security.
- Scope: Potential MTC enablers span protocol-stack layers from efficient hardware design through application-layer considerations.
- Architecture and interfaces: A holistic network architecture frames the solution landscape before discussions of zero-energy air interfaces and globally available, massively scalable MTC services.
- Mission-criticality and security: The paper also addresses mission-critical MTC for industrial and related verticals, alongside privacy and security for heterogeneous devices and applications.
3.1 Holistic MTC Network Architecture
The proposed holistic MTC architecture addresses fragmented, heterogeneous connectivity through harmonized, sustainable, technology-agnostic orchestration driven by end-to-end application QoS.
- Motivation: No single MTC radio-access technology can serve a significant share of the diverse envisaged applications, and a universal solution is unlikely soon.
- Motivation: Coexisting MTC networks are often disjoint across administrative domains, while unlicensed-band radios may compete for the same radio resources.
- Architectural objective: The architecture must harmonize connectivity sustainably while maximizing performance for machines, networks, and the services they support.
- Architectural trends: Key architectural trends include zero-energy interfaces, cell-free networking, greater heterogeneity, infrastructure-less critical networks, and more diverse traffic patterns and service classes.Cell-free networking can reduce signaling overhead and improve reliability through multiple-base-station demodulation.
- Holistic architecture: The future architecture should be efficient, edge-intelligent, and software-defined, with dynamic collaborative orchestration across heterogeneous domains and stakeholders.
- Orchestration and optimization: Open algorithms should select and configure radios using application E2E QoS and fairness, supported by machine learning and real-time localization and optimization.These mechanisms may be centralized, distributed, edge-deployed, or moved to individual devices.
- Orchestration and optimization: The architecture should support manageable control and emergency traffic, backward compatibility, cross-domain interoperability, and software-based updates.
3.2 Energy Efficient MTC Devices
Energy-efficient 6G MTC devices require ultra-low-power receiver architectures, energy harvesting, zero-energy communication, and device-level intelligence for scalable massive and critical connectivity.
- Design priorities: Energy efficiency is a central mMTC KPI, supported by ultra-low-power receivers, enhanced energy harvesting, and zero-energy communication schemes.The paper also identifies collaborative and distributed intelligence as an enabler for critical MTC.
- Ultra-Low Power Receiver Architecture: Whole-device optimization combines antenna packaging, RF-interface co-design, and selective narrower-band radiators to reduce power and improve blocking robustness.The antenna and transceiver should be designed as an intimate, optimized connection rather than as separate components.
- Ultra-Low Power Receiver Architecture: Below 100 nW power consumption at less than −80 dBm sensitivity is demonstrated as a promising target for sub-GHz receivers using simple noncoherent modulation.The comparison covers receiver power consumption versus sensitivity across frequency bands and design types.
- Ambient Backscatter Communications for 6G mMTC: Ambient backscatter reduces power and spectrum occupancy by modulating and reflecting ambient RF signals without a voltage-controlled oscillator or power amplifier.Key challenges include strong direct-path interference, changing ambient-signal amplitude and phase, severe backscatter path loss, energy supply, and coexistence with legacy receivers.
- Zero-Energy and Wake Up Radios: A zero-energy wake-up radio can support approximately 40 years of battery life, improving device life by more than three decades over 5G under the considered parameters.The example uses legacy DRX cycles of 10.24 s and 43.69 min, a 2.56 s measurement cycle, and a 25% PSM duty cycle.
- Zero-Energy and Wake Up Radios: Future zero-energy air interfaces may enable battery-less IoT devices through limited downlink payload reception and backscatter-based uplink transmission.On-device intelligence further spans context adaptation, compressed sensing, event-driven interfaces, and adaptive communication protocols, but integrating these functions within power limits remains challenging.
3.3 Global Massively Scalable MTC
Global massively scalable MTC requires coordinated evolution across coverage, PHY, MAC, coding, higher layers, and energy-aware multicast operation. The paper highlights heterogeneous access, uncoordinated massive traffic, and application-specific access strategies as central design concerns.
- Global coverage and cross-layer design: Global MTC scalability requires interoperability across heterogeneous networks and protocol-stack designs spanning global coverage, PHY, MAC, and higher layers.The paper identifies spectrum harmonization and non-terrestrial networks alongside grant-free access, coding, random access, scheduling, and higher-layer simplification.
- Global coverage and cross-layer design: Spectrum-regulation differences across countries obstruct global machine roaming, while higher-frequency harmonization and sub-GHz political coordination are proposed as complementary directions.Regulatory differences include frequency bands, transmit power, duty cycle, access mechanisms, and permitted applications.
- Global coverage and cross-layer design: Non-terrestrial networks using LEO satellites, drones, HAPs, and UAVs can offload terrestrial traffic and reach otherwise unserved areas.
- PHY and access: Massive grant-free traffic motivates NOMA, compressed-sensing pilot detection, low-complexity multi-user detection, iterative interference cancellation, and joint activity detection and decoding.NOMA reliability depends on both user detection and data decoding over shared resources.
- MAC and traffic adaptation: Random access is preferable to conventional scheduling for intermittent massive traffic, but ALOHA is inefficient; unsourced random access, persistent grant-free scheduling, and traffic-specific slicing offer alternatives.Sporadic, periodic, and event-driven traffic can use random, persistent, or hybrid access schemes respectively.
- Higher-layer and energy considerations: Point-to-multipoint support and on-demand paging can reduce IoT energy use during massive software updates by avoiding continuous service-announcement monitoring.
3.4 Mission Critical MTC
Mission-critical MTC in 6G is framed around dependable, application-aware service rather than simply tighter conventional URLLC parameters. The paper proposes service classes, multi-RAT resource management, prediction, brokers, digital twins, and collision-tolerant designs.
- Mission-critical requirements: 6G mission-critical MTC is expected to prioritize dependable latency and error performance for applications such as life-critical alarming and control.The paper gives target values of 0.1 ms latency and BLER of 10^-9 in connection with URLLC requirements.
- Mission-critical requirements: “Taming the tail” allows higher absolute time bounds when time-bound violations and jitter remain near zero, enabling more resource-efficient and application-aware solutions.
- Service classes and adaptation: Tweaking 5G with shorter TTIs and duplication is described as neither scalable nor efficient for cMTC, motivating application-domain information and new cMTC service classes.
- Resource management: A cMTC management function should allocate resources across multi-RAT and multi-link options while associating time bounds with spectrum and energy costs.The function uses resource-awareness information from devices and the network environment, including antennas and RIS.
- Resource management: A cMTC broker can shift resource-intensive decisions away from constrained devices, manage radio resources across RATs, and operate a digital twin to evaluate decisions before implementation.
- Resource management: Fixed reservations can waste resources, while semi-persistent scheduling and collision-friendly transceivers are needed for distributed, rapidly changing, or highly dense environments.
3.5 Privacy and Security for MTC
MTC privacy and security must address massive, heterogeneous, low-cost deployments with limited human involvement and long-lived data protection needs. The paper surveys authorization, distributed trust, anomaly detection, lightweight authentication, and post-quantum protection.
- Requirements and threats: MTC security differs from conventional solutions because deployments are massive, devices have diverse cost and complexity constraints, and human involvement is limited.
- Requirements and threats: MTC privacy threats include exposure of location, health, and industrial personal data, requiring privacy considerations in solution development and regulatory compliance.
- Privacy and authorization: OAuth-based authorization, digitally signed consent, and privacy-management architectures are presented for controlled personal-data reuse.
- Distributed trust: Smart contracts and blockchains can provide decentralized trust, privacy, authentication, transparency, and auditability, but resource-constrained devices and uplink-oriented MTC create integration challenges.
- Security monitoring: Zero-day vulnerabilities cannot all be mitigated by design, so anomaly identification remains necessary; SPHINX is cited but not comprehensive against several attack classes.
- Lightweight authentication: Massive low-power deployments make SIM-based authentication unsuitable, motivating group-based, anonymous, physical-layer, RF-signature, and access-integrated authentication schemes.
- Long-term security: Lightweight post-quantum encryption and authentication are needed to protect long-term confidentiality, authenticity, and integrity against quantum-computing threats.NIST standardization of quantum-resistant cryptosystems is ongoing.
4 Conclusions
The paper positions MTC and IoT networks as central to 6G connectivity and examines their evolution across service classes, requirements, and technical layers. Its conclusions are synthesized through six research questions spanning the MTC solution landscape.
- 6G will optimize established URLLC, mMTC, and eMBB services while introducing new use cases and service classes.
- MTC and IoT networks are presented as foundational to 6G wireless connectivity in everyday life.
- The paper surveys MTC drivers, use cases, requirements, service classes, and future research directions across the physical-to-application-layer stack.
- Six research questions synthesize the paper’s key discussion points and takeaways.