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Integration of Communication and Sensing in 6G: a Joint Industrial and Academic Perspective

Henk Wymeersch, Deep Shrestha, Carlos Morais de Lima, Vijaya Yajnanarayana, Björn Richerzhagen, Musa Furkan Keskin, Kim Schindhelm, Alejandro Ramirez, Andreas Wolfgang, Mar Francis de Guzman, Katsuyuki Haneda, Tommy Svensson, Robert Baldemair, Stefan Parkvall

arXiv:2106.13023v1eess.SPcs.ITmath.IT

TL;DR

The paper addresses the gap between 5G capabilities and the extreme localization and sensing needs of envisioned 6G use cases. It presents the Hexa-X vision and cross-layer enablers for integrating these capabilities with communication. The paper concludes that this integration is central to the envisioned 6G performance and applications, while noting hardware and channel challenges.

  • Problem

    5G has treated localization as a service layered over communication, while future use cases call for integrated capabilities that meet accuracy, latency, reliability, and availability requirements.

    Source: B. Localization Solutions in 5G and… · p. 2, §III · p. 3

  • Method

    The paper presents the Hexa-X vision, use cases, technical enablers, and research challenges for integrating localization and sensing across 6G system design.

    Source: §I · p. 2, §VI · p. 5

  • Results

    The paper concludes that integrating localization and sensing from 6G's outset is intended to support the performance and latency needs of identified use cases and tightly integrate radar, communication, computation, localization, and sensing.

    Source: §VI · p. 5

  • Takeaways & Limitations

    The Hexa-X vision treats localization, radar, and sensing as intrinsic parts of 6G and considers enablers across channel, hardware, waveforms, algorithms, and protocols.

    Source: §I · p. 2, §VI · p. 5

    Hardware imperfections affect the estimation of additional signal parameters used for accurate localization and sensing, making robust estimation a challenge.

    Source: A. Hardware Limitations · p. 5

Abstract

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6G will likely be the first generation of mobile communication that will feature tight integration of localization and sensing with communication functionalities. Among several worldwide initiatives, the Hexa-X flagship project stands out as it brings together 25 key players from adjacent industries and academia, and has among its explicit goals to research fundamentally new radio access technologies and high-resolution localization and sensing. Such features will not only enable novel use cases requiring extreme localization performance, but also provide a means to support and improve communication functionalities. This paper provides an overview of the Hexa-X vision alongside the envisioned use cases. To close the required performance gap of these use cases with respect to 5G, several technical enablers will be discussed, together with the associated research challenges for the coming years.

I. INTRODUCTION

The introduction traces how wider bandwidths and higher frequencies have expanded 5G localization, then frames 6G as integrating communication, localization, and sensing. Hexa-X presents this as a cross-layer vision for extreme-performance use cases, alongside technical enablers and research challenges.

I. INTRODUCTION

  • Wider bandwidths and directional transmissions at higher carrier frequencies support more accurate localization and have spurred dedicated 5G signal designs and new use cases.The introduction notes 5G bands around 24–28 GHz and continuous bandwidths up to 400 MHz.Source: §I · p. 1
  • 5G localization includes bistatic and monostatic modes, with TDoA, AoA, and AoD measurements; RTT can avoid base-station synchronization at the cost of higher signaling overhead.Multipath exploitation is being explored at mmWave, while localization and sensing resolution is fundamentally limited by bandwidth and antenna aperture.Source: §I · p. 1, Figure 1 · p. 1
  • Monostatic joint radar and communication can map environments and track moving objects, but requires strong transmit-receive antenna isolation.The paper notes full-duplex operation or physical separation as ways to provide isolation.Source: Figure 1 · p. 1
  • 6G is expected to use 100–300 GHz and potentially 300–3000 GHz bands, with 2–10 GHz bandwidths, for demanding use cases and communication in dynamic environments.The paper proposes joint radar communication, computation, localization, and sensing (JRC2LS), alongside related concepts ICAS and JCS.Source: §I · p. 1
  • Hexa-X presents use cases requiring extreme localization performance and a vision that considers localization and sensing across channel, hardware, waveform, algorithm, and protocol design.The consortium comprises 25 industry and academic partners across the 6G vertical.Source: §I · p. 2

II. USE CASES AND GAP ANALYSIS

The section groups representative Hexa-X 6G use cases into five families and sets out their localization and sensing requirements. It introduces selected use cases and considers whether 5G can meet those requirements.

II. USE CASES AND GAP ANALYSIS

  • Hexa-X clusters its representative 6G use cases into sustainable development, massive twinning, telepresence, cooperating robots, and local trust zones.Table I summarizes functional and non-functional localization and sensing requirements.Source: §II · p. 2
  • The section describes selected use cases in these families and how they use envisioned 6G localization and sensing capabilities.Source: §II · p. 2
  • The analysis considers how far 5G can meet the localization and sensing requirements of the selected use cases.Source: §II · p. 2

1) Massive twinning:

The use cases connect radio-based localization and sensing to digital replicas, immersive interactions, and cooperative robotics. Their requirements range from precise mapping and gesture detection to reliable, high-integrity localization and SLAM.

1) Massive twinning:

  • Manufacturing digital twins require precise localization and mapping of moving and stationary factory scatterers, potentially using communication links already present in the environment.The massive-twinning family also includes smart-city replicas with real-time traffic, pollution, and utility information, relying on city and entity monitoring.Source: 1) Massive twinning · p. 2

2) Immersive telepresence for enhanced interactions:

3) From robots to cobots:

  • Robots, cobots, and flexible manufacturing require robust localization and SLAM, with high service availability, reliability, and estimate integrity.Source: 3) From robots to cobots · p. 2

4) Local trust zones for humans and machines:

Local trust zones include applications that use network infrastructure as a sensor web, including cooperative localization for out-of-coverage devices. The section contrasts 5G positioning capabilities with the need to make localization and sensing integral to future RANs.

4) Local trust zones for humans and machines:

  • Local trust-zone applications include precision healthcare, network infrastructure as a sensor web, and cooperative localization for out-of-coverage devices such as vehicles in harvesting platoons.Source: 4) Local trust zones for humans and… · p. 2

B. Localization Solutions in 5G and Gap Analysis

  • Under ideal simulated conditions, TDoA localizes 90% of UEs within 3.4 m in urban macro, 1.5 m in urban micro, and 1.4 m in indoor open office scenarios.RTT reaches 0.8 m horizontal accuracy indoors in 90% of cases; base-station deployment geometry also affects accuracy.Source: B. Localization Solutions in 5G and… · p. 2
  • The paper argues that future RANs should integrate localization and sensing with communication and address latency, reliability, and availability as well as accuracy.It contrasts this with 5G's approach of providing localization as a service on top of communication.Source: B. Localization Solutions in 5G and… · p. 2

III. HEXA-X VISION

Hexa-X frames 6G localization and sensing around extreme performance and JRC2LS, addressing use cases that span multiple frequency bands and functions. Its vision calls for integrated, adaptable communication and sensing design with broader localization metrics.

III. HEXA-X VISION

  • The envisioned 6G systems combine sub-6 GHz and 24 GHz bands with 100 GHz–1 THz bands to meet demands beyond conventional user localization.Source: §III · p. 2
  • 6G localization targets accuracy, latency, and integrity beyond 5G and comparable to or better than radar, lidar, and cameras, including 3D orientation and its derivatives.The envisioned integrated design includes waveforms, measurements, interfaces, signals, and protocols.Source: §III · p. 3
  • Meeting extreme bit-rate, latency, localization, and sensing targets is expected to support services merging digital, physical, and human domains.Source: §III · p. 3
  • JRC2LS expands joint radar and communication into computation, localization, and sensing across monostatic, bistatic, and multistatic modes, with edge computing and high-rate communication.The vision also considers tailor-made localization and sensing signals or a common agile signaling framework.Source: §III · p. 3
  • Accuracy means the 90% confidence interval on localization error; latency runs from request to result, including measurements and algorithm execution but excluding signaling.The paper also defines range, update rate, reliability, and availability, and notes agility and scalability as additional metrics.Source: §III · p. 3
  • Hexa-X proposes a common agile signaling framework that can be dynamically parameterized for different JRC2LS needs, a shift from earlier mobile generations.Source: §III · p. 3

IV. TECHNICAL ENABLERS

The technical-enabler discussion argues that sensing should span frequency bands and functions rather than focus only on mmWave and higher frequencies. Lower-band bandwidth and multi-carrier fusion can also support sensing performance.

IV. TECHNICAL ENABLERS

  • Large-coverage deployments are expected below 6 GHz, so sensing research should include lower frequencies alongside mmWave and beyond.Source: §IV · p. 3
  • Wide bandwidth supports accurate sensing, and lower-band mobile systems can access large bandwidths; results from multiple operator carriers can be fused to improve performance.Source: §IV · p. 3
  • Sensing use cases should extend beyond object location and mapping to spectroscopic sensing of environmental data where feasible at each frequency range.The passage notes that technical advances will enable these multifunctional applications.Source: §IV · p. 3

A. High-resolution Angle, Range, Doppler Processing

Localization, radar, and sensing depend on resolving multipath in angle, range, or Doppler. Higher-frequency systems offer fine spatial resolution but bring synchronization, calibration, and channel-tracking challenges.

A. High-resolution Angle, Range, Doppler Processing

  • Multipath resolution in angle, range, or Doppler underlies localization, radar, and sensing; massive arrays support angle resolution, while large bandwidths support range resolution.Source: A. High-resolution Angle, Range,… · p. 3
  • THz signals’ short wavelengths enable massive arrays with fine spatial and delay resolution for directional sensing and imaging, including gesture detection and 3D mapping.The passage says these signals are less susceptible to ambient light and weather than light and infrared technologies.Source: A. High-resolution Angle, Range,… · p. 3
  • Accurate sensing at these frequencies requires careful synchronization and antenna calibration, while shorter channel coherence times demand more frequent channel estimation.Source: A. High-resolution Angle, Range,… · p. 3
  • Higher Doppler shifts at THz frequencies motivate new estimation algorithms to calculate position and velocity as channels change more quickly.Source: A. High-resolution Angle, Range,… · p. 3

B. Highly Directional Beamforming and Context Awareness

Directional high-frequency beams support detailed sensing and localization, while shared hardware and joint waveforms bring communication and sensing onto a common platform. The design must account for propagation, interference, and waveform trade-offs.

B. Highly Directional Beamforming and Context Awareness

  • High attenuation, power constraints, and blockage at mmWave and THz motivate pencil-like beams that can scan beam space into real-time 3D maps for industrial digital twins or gesture interfaces.Source: B. Highly Directional Beamforming and… · p. 4
  • Combining beam-space imaging with range metrics can support precise localization without prior environmental knowledge, although beam-point errors degrade performance.Location information can also support beam tracking and proactive resource allocation with low overhead.Source: B. Highly Directional Beamforming and… · p. 4

C. Joint Waveforms and Joint Hardware

  • JRC2LS reuses communication hardware and signals for sensing on a joint platform; monostatic full-duplex operation requires digital and RF cancellation for sufficient TX/RX isolation.Source: C. Joint Waveforms and Joint Hardware · p. 4
  • Jointly optimized dual-functional waveforms can serve multiple downlink users and estimate targets, but high-mobility OFDM radar faces inter-carrier interference that degrades conventional FFT-based algorithms.Source: C. Joint Waveforms and Joint Hardware · p. 4
  • Single-carrier waveforms can be attractive for hardware but need careful design to avoid high sidelobes; all waveforms should be evaluated with the range-Doppler ambiguity function.That function reveals waveform characteristics related to resolution, accuracy, and clutter rejection.Source: C. Joint Waveforms and Joint Hardware · p. 4

D. Intelligent Infrastructure

Intelligent infrastructure can redirect signals to support connectivity and localization, while 6G’s high-resolution, site-dependent channels call for complementary model-based and data-driven algorithms.

D. Intelligent Infrastructure

  • An RIS can redirect signals around absent line-of-sight paths, and a known RIS position adds localization information.RIS implementations include reconfigurable metamaterials and discrete antennas; large active surfaces with many antennas are a natural evolution of massive MIMO.Source: D. Intelligent Infrastructure · p. 4

E. Algorithmic Developments

  • High bandwidth and large MIMO can resolve multipath and reveal scatterer geometry or material properties, but high-frequency channels depend strongly on local geometry and materials.The paper says predefined channel parameters such as macro, micro, or rural are ineffective for these site-dependent realizations.Source: E. Algorithmic Developments · p. 4
  • The paper foresees complementary model-based and AI-based algorithms, with data-adaptive methods useful for hardware impairments or intractable channel-to-position mappings.Examples include radio analytics for environmental changes, SLAM loop closure and data association, and location and orientation estimation from fingerprints.Source: E. Algorithmic Developments · p. 4

V. CHALLENGES IN CLOSING THE GAP

Closing the localization and sensing performance gap depends on addressing challenges that cut across the technical enablers, particularly hardware imperfections and propagation-channel properties.

V. CHALLENGES IN CLOSING THE GAP

  • Hardware impairments at higher frequencies and propagation-channel properties across frequency bands can affect all the presented enablers.The paper identifies these as fundamental challenges to meeting the requirements in Table I.Source: §V · p. 5

A. Hardware Limitations

  • Phase noise, antenna non-linearities and mutual coupling, signal distortion, and frequency-dependent IQ imbalance can degrade parameter estimation for localization and sensing.The passage links these impairments respectively to Doppler processing and integration, angle estimation, range resolution, and SNR and AoD/AoA estimation.Source: A. Hardware Limitations · p. 5
  • The research challenge is to determine how hardware imperfections affect localization and sensing accuracy and design signals for robust estimation.Some impairments may be calibrated, while phase noise requires dynamic compensation.Source: A. Hardware Limitations · p. 5

B. The Propagation Channel

Propagation changes with frequency and object scale, shaping multipath visibility and localization prospects. The paper also identifies open channel-characterization challenges and presents the Hexa-X vision of integrated localization, radar, sensing, and communication.

B. The Propagation Channel

  • At 100 GHz and above, visible multipath is mainly associated with metallic objects, while diffuse multipath can impair mapping by making objects intermittently visible.At sub-6 GHz, small movements can cause large power fluctuations; at mmWave, reduced penetration and greater multipath resolvability favor localization.Source: B. The Propagation Channel · p. 5
  • The 140 GHz measurements show recurring specular reflections from planar surfaces and cylindrical pillars, while angular, delay, and Doppler spreads, absorption, link gains, and mobility remain characterization challenges.The paper suggests relating physical objects to link gains in site-specific models with temporal and spatial consistency, rather than partially stochastic models.Source: Figure 2 · p. 5

VI. CONCLUSIONS

  • The Hexa-X vision places localization, radar, and sensing within 6G from the outset, tightly integrating them with communication and computation.The paper frames localization, tracking, and sensing of physical objects as a bridge between human, physical, and digital worlds.Source: §VI · p. 5
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