PaperlayerView exact revision on arXiv

Source-linked AI summary

Waves on the Walls: Empirical Characterization of mmWave Lateral Waves for Enhanced Indoor Coverage

Apala Pramanik, Avhishek Biswas, Sasitharan Balasubramaniam, Christos Argyropoulos, Mehmet C. Vuran

arXiv:2609.04429v1cs.NIcs.SYeess.SY

TL;DR

Indoor mmWave coverage is challenged by walls, while evidence for lateral-wave propagation along engineered building materials has been lacking. This paper experimentally characterizes lateral waves at an air–drywall interface and models their frequency- and distance-dependent path loss. Controlled measurements provide empirical evidence for the interface-guided path and validate the model.

Abstract

from arXiv · show

High-frequency millimeter-wave (mmWave) communication systems are constrained by the surrounding environment, where walls are traditionally treated as obstacles that block or reflect signals indoors. Consequently, current beamforming strategies are tailored to circumvent these obstructions. In this paper, a paradigm shift is introduced that leverages lateral wave propagation along building interfaces to extend mmWave coverage. Unlike traditional reflections, lateral waves travel along the boundary between two media of different refractive indices and decay algebraically with distance, offering a potential alternative path for mmWave connectivity. While well-established at low frequencies in natural media, the existence of lateral waves at mmWave frequencies along engineered building materials has not been demonstrated before. To this end, the first experimental characterization of mmWave lateral waves along a wall is reported. Extensive controlled measurements are employed to characterize the signal-grazing geometry and to establish a frequency and distance-dependent path-loss model for this phenomenon. The results provide the first empirical foundation for a new class of interface-guided mmWave links.

I. INTRODUCTION

Indoor mmWave coverage is challenged by wall attenuation, while lateral waves offer a wall-interface path that this paper experimentally investigates. The paper positions that work against approaches based on reflection and scattering.

I. INTRODUCTION

  • Walls attenuate mmWave signals indoors, making terminals behind them difficult to reach; directional links also face blockage and beam-training overhead.The paper frames indoor coverage as a challenge for fixed wireless access terminals inside homes and offices.Source: §I · p. 1
  • Existing approaches use wall reflections or scattering, including tunable reconfigurable intelligent surfaces that redirect signals.The introduction contrasts these approaches with propagation along the wall interface.Source: §I · p. 1
  • The paper investigates lateral waves traveling along wall surfaces as an alternative way to extend mmWave connectivity.These waves arise at interfaces between media with different refractive indices and decay algebraically with distance because most of their path is in the lower-loss medium.Source: §I · pp. 1–2
  • The paper reports the first experimental demonstration of mmWave lateral waves along a building-material interface and develops a frequency- and distance-dependent path-loss model.The model is validated through controlled measurements.Source: §I · p. 2

A. Propagation Characteristics of Building Materials

Prior building-material studies characterize penetration loss, reflection, and scattering, while lateral-wave theory describes a distinct interface-guided path. The paper reviews these research threads and their differing settings.

A. Propagation Characteristics of Building Materials

  • Building-material studies characterize attenuation, penetration, reflection, and diffuse scattering, but do not resolve waves guided along wall surfaces.Reported measurements span mmWave and sub-terahertz bands; rough surfaces add diffuse scattering.Source: A. Propagation Characteristics of… · p. 2

B. Intelligent Reflecting Surface/Reconfigurable Intelligent Surfaces

  • Reconfigurable intelligent surfaces steer reflected signals with fabricated, powered arrays of tunable elements mounted on walls.The arrays require bias lines, control circuitry, and power.Source: B. Intelligent Reflecting… · p. 2

C. Background on Lateral-Wave Propagation

  • Lateral waves guide energy along an interface rather than reflecting it, but prior measurements described here concern thick, low-loss natural media at lower frequencies.The passage distinguishes lateral waves from bound surface waves and engineered surface plasmons.Source: C. Background on Lateral-Wave… · p. 2

D. Nanonetworks and Internet of Paint

The paper reports mmWave lateral-wave evidence at a building-material interface, addressing a gap in prior wall-propagation studies. Controlled configurations distinguish the interface response from other measured returns.

D. Nanonetworks and Internet of Paint

  • Prior Internet of Paint work modeled lateral paths, but empirical evidence at mmWave along engineered building materials had not been provided.The paper identifies its result as the first experimental evidence of mmWave lateral waves.Source: D. Nanonetworks and Internet of Paint · pp. 2–3
  • The three setups test the response without drywall, with a drywall interface and air beyond it, and with an absorber contacting the far face.The lateral wave’s grazing geometry is present only in the drywall-and-air configuration.Source: Figure 2 · p. 3
  • A high-incidence SNR peak appears only with drywall present and the RF absorber 5 inches behind it; the peak vanishes when the absorber contacts drywall’s far face.Source: Figure 3 · p. 3

III. OVERVIEW

The paper experimentally probes the air–drywall interface with a 60 GHz beamforming module and a gypsum drywall sheet. A high-incidence return appears with drywall, matching the predicted lateral-wave grazing geometry.

III. OVERVIEW

  • A distinct high-incidence return appears only when drywall is present, matching the lateral wave’s grazing geometry at the far air–drywall interface.The return provides evidence that validates the model developed in Section IV.Source: §III · p. 3
  • The experiment places the transmitter and receiver in air on the same side of the drywall and probes the interface with a bistatic beam sweep.The lateral wave couples through the drywall, grazes the far interface, and penetrates back into the wall.Source: §III · p. 3
  • The study uses a 60 GHz beamforming module and standard gypsum drywall, with dielectric properties used to determine the critical coupling angle.Signal-to-noise ratio is recorded across transmitter and receiver beam pairs.Source: §III · p. 3

A. Dielectric Properties of Drywall

The drywall is described as a low-loss dielectric, with measured-material properties differing from the generic plasterboard model. Those refractive indices imply different critical angles.

A. Dielectric Properties of Drywall

B. Lateral Wave Propagation

Controlled 60 GHz beam sweeps show a high-incidence return at the air-drywall interface that disappears when an absorber contacts the drywall’s far face. The measurements distinguish this return from the absorber response and back-face reflection.

B. Lateral Wave Propagation

  • A bistatic beam sweep measures mean SNR over 2,000 samples per beam pair, resolving return power against incidence angle and RX beam angle.The sweep spans TX and RX beam codebooks; rotating TX boresight extends incidence toward grazing angles.Source: B. Lateral Wave Propagation · pp. 3–4
  • RF-absorber-lined enclosures suppress back- and side-lobe radiation, and the absorber behind the drywall suppresses back-face reflection in the wall-and-absorber setup.Source: B. Lateral Wave Propagation · p. 4
  • The wall-and-absorber setup produces a 9.15 dB peak at high incidence, while contacting the absorber to the drywall’s far face removes the return.The absorber-only setup stays at ≈7.5 dB across the measured incidence range, with no distinct peaks.Source: B. Lateral Wave Propagation · p. 4

IV. LATERAL WAVE PROPAGATION CHANNEL MODEL

The channel model represents the lateral wave as a path coupling through the wall, traveling along the far air-wall interface, and exiting through the wall again. It separates frequency- and distance-dependent interface losses from fixed coupling and crossing terms.

IV. LATERAL WAVE PROPAGATION CHANNEL MODEL

  • The model adapts the IoP channel formulation for TX and RX in air, with wall thickness t as the dense-medium path depth.The total path loss sums spreading, interface-leg loss, two-crossing transmission loss, and air-leg loss.Source: §IV · pp. 4–5
  • The path comprises two air legs, two wall crossings, and an interface leg of length dLW; lateral-wave formation approaches grazing incidence and critical-angle refraction.Across a distance sweep, dLW differs from TX–RX separation ρD by a fixed offset.Source: §IV · p. 4
  • Air-leg coupling is treated as a distance-independent loss LA when terminals are close to the wall; the two drywall crossings add spreading and bulk absorption.The crossing path lengths are t/cos θr and t/cos θd.Source: §IV · pp. 4–5
  • Near grazing, plane-wave Fresnel transmittance falls to zero and the corresponding loss diverges, although the lateral wave is a head wave; at the critical angle, transmittance is small but finite.Source: §IV · p. 5
  • The interface leg combines spreading with air absorption and leakage; its general spreading exponent covers 20 or 40 dB per decade, while leakage adds 4.343 αL dB per meter.The finite sheet leaks energy by re-radiating through the slab; αL = 0 recovers the cited spreading models.Source: §IV · p. 5
  • At fixed frequency, distance-dependent path loss follows 20 log10(ρD/ρD0) for nLW = 2 or 40 log10(ρD/ρD0) for nLW = 4, with leakage adding a linear term.Source: §IV · p. 5
  • Relative frequency loss removes frequency-independent terms; spreading gives effective frequency exponent nf = 4, drywall absorption scales linearly with frequency, and atmospheric absorption adds a small correction.The model assumes a dispersion-free wall refractive index.Source: §IV · p. 5

V. MODEL COMPARISON AND VERIFICATION

This section describes experimental validation of the Section IV lateral-wave channel model by comparing it with measured path loss across frequency and distance.

V. MODEL COMPARISON AND VERIFICATION

  • The section proceeds from describing the setup to comparing the model with measurements and analyzing path-loss exponents.Source: §V · pp. 5–6
  • The experimental setup places TX and RX in air on one side of the drywall, with an absorber behind it.Source: Figure 5 · p. 6
  • The model comparison evaluates measured path loss under frequency and distance scaling.The section also analyzes the resulting path-loss exponents.Source: §V · p. 6

A. Experimental Setup

The setup uses a drywall interface and controlled beam steering to probe lateral-wave behavior, then evaluates path loss across incidence angles, frequencies, and distances.

A. Experimental Setup

  • TX and RX are in air on the same side of an 8 ft × 4 ft gypsum drywall sheet, with absorbers suppressing side, back-lobe, and far-face reflections.The absorber placement leaves the far air–drywall interface intact for lateral-wave propagation.Source: A. Experimental Setup · p. 6
  • Beam steering spans 0°–90° incidence, with TX boresight rotations from 0° to 90° to reach near-grazing angles.Intermediate boresight angles include 30°, 45°, 60°, 70°, 75°, and 85°.Source: A. Experimental Setup · p. 6
  • In WA at 60 GHz, peak SNR over RX beams occurs near grazing incidence, where the lateral wave forms.Shaded regions show standard deviation across five measurements at each incidence angle.Source: Figure 6 · p. 6
  • Path loss is averaged across five trials, measured at 75°–90° incidence using the strongest beam pair, and referenced to 58 GHz or ρD0 = 1.02 m for frequency or distance sweeps.Least-squares fits against log10 frequency or distance yield the experimental path-loss exponent.Source: A. Experimental Setup · p. 6

B. Evaluations

Controlled measurements identify near-grazing lateral-wave returns and characterize path loss across frequency and distance. The measured exponents vary with boresight, with direct and reflected components contributing alongside the lateral wave.

B. Evaluations

  • The high-incidence SNR peaks are suppressed when an RF absorber contacts the drywall’s far face, while peaks at 57° and 69° are attributed to higher-order specular multipath.The absorber-contact and absorber-only configurations help distinguish the interface return from multipath and direct/reflected signals.Source: B. Evaluations · p. 7
  • The fitted frequency exponent is nf ≈ 5.3, above the nf = 2 expected for a purely in-air return; drywall absorption growth contributes 1.3 to the exponent.The air-absorption term reduces the fitted exponent by only 0.02.Source: B. Evaluations · p. 7
  • nexp = 4.11 at 45°, 1.54 at 60°, and 1.83 at 75°; wider-boresight measurements include strong direct and reflected signals alongside the lateral wave.At 45°, the measured exponent exceeds the nf = 2 expected for an in-air return; at 60° and 75°, the values are near 2.Source: B. Evaluations · p. 7, Figure 7 · p. 7
  • Distance-sweep exponents are 1.19 at 45°, 0.30 at 60°, and 0.83 at 75° boresight, below 2 and consistent with slower attenuation over the measured range.The measurements combine direct, specular-reflected, and lateral-wave fields; wider-boresight reflected components contribute to the gap from theoretical values.Source: Figure 8 · p. 8, B. Evaluations · p. 8
  • A boresight-stable SNR peak occurs at 7°–9° grazing angle, corresponding to 81°–83° incidence, where the beamwidth overlaps the near-grazing region for lateral-wave formation.The 6° beamwidth spans 82°–88° incidence at 84.5° incidence, and the discrete beam codebook yields its strongest response at 81°–83°.Source: B. Evaluations · pp. 7–8
  • The characterization uses drywall at the low-contrast, low-loss end; the authors expect higher-contrast concrete, brick, and glass to raise crossing loss and pull the exponent toward n = 4.Additional materials, finishes, corners, and layered partition walls are identified as future scenarios.Source: B. Evaluations · p. 8

VI. CONCLUSION

The paper demonstrates mmWave lateral waves along drywall and models their frequency- and distance-dependent path loss against controlled measurements. These results establish walls as surfaces that can guide RF energy and motivate testing additional materials and geometries.

VI. CONCLUSION

  • Controlled experiments demonstrate mmWave lateral waves along drywall, and validate a frequency- and distance-dependent path-loss model against measurements.The work presents walls as surfaces that can guide RF energy as a lateral wave, motivating further study across materials, frequencies, and surface geometries.Source: §VI · p. 8
Loading 2609.04429v1…