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A Miniaturized Wi-Fi HaLow-Based Wireless Imaging Transfer System for Capsule Endoscopy

Michele Bertozzi, Lorenzo Amelio, Sebastiano Strangio, Nikita J. Greenidge, Benjamin Calmé, Pietro Valdastri, Giuseppe Iannaccone Fellow, Alessandro Catania

arXiv:2610.13815v1eess.IV

TL;DR

Wireless capsule endoscopy must transmit diagnostic images through tissue despite tight size and energy constraints and a channel with frequency-dependent losses. This paper designs and validates a miniaturized WIT system using sub-GHz Wi-Fi HaLow, alongside preliminary in-vivo link tests. The integrated system transmits 320 × 320 color frames above 12 Mbps, with reported RF and complete-chain energy figures of 20.7 and 39.6 nJ/bit, respectively.

  • Problem

    Capsule imaging must transmit through lossy, dispersive tissue while balancing carrier frequency, antenna size, attenuation, data rate, and the capsule’s limited energy budget.

    Source: §I · pp. 2–3

  • Method

    The authors build a capsule-compatible WIT chain and separately assess Wi-Fi HaLow through-body communication in a porcine model before completing hardware integration.

    Source: §I · p. 3, §III · p. 4

  • Results

    The WIT chain achieved above 12 Mbps and approximately 20.7 nJ/bit RF transmission efficiency; complete-chain consumption was approximately 477 mW or 39.6 nJ/bit.

    Source: §VI · p. 9

  • Takeaways & Limitations

    The measured results support IEEE 802.11ah as a technically viable wireless backbone for next-generation color capsule endoscopy.

    Source: §VI · p. 10

    Further integration with wireless power transfer and fully autonomous capsule operation remains to be completed.

    Source: §VI · p. 10

Abstract

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Wireless capsule endoscopy is constrained by severe limitations in size, available power, and reliable data transmission through biological tissues. Although recent advances in miniature imaging sensors have improved image quality, the wireless transmission of color images at practical frame rates remains a challenging task under the tight capsule constraints. We present the design and the experimental validation of a miniaturized Wireless Imaging Transfer (WIT) system for capsule endoscopy based on a sub-GHz IEEE 802.11ah (Wi-Fi HaLow) wireless link. In addition, a preliminary in-vivo validation of Wi-Fi HaLow communication is reported, showing that a stable through-body wireless link can be established across biological tissues in a clinically relevant porcine model. These in-vivo results provide direct experimental support for the adoption of sub-GHz Wi-Fi HaLow for capsule endoscopy applications. Experimental results demonstrate stable wireless image transmission at a resolution of 320x320 pixels, with measured end-to-end data rates above 12 Mbps and a transmission energy efficiency of 20.7 nJ/bit. We also report a detailed power consumption analysis, with a breakdown of the contributions from the imaging sensor, illumination, digital processing, and RF transmission. When all active subsystem contributions are considered, including the camera, digital processing, RF transmission, and illumination at 60% LED brightness, the total power consumption is approximately 477 mW, corresponding to a complete-chain energy consumption of approximately 39.6 nJ/bit. Overall, the measured performance confirms that sub-GHz Wi-Fi HaLow provides a promising trade-off among throughput, robustness, and energy efficiency for wireless imaging in capsule endoscopy.

I. INTRODUCTION

Capsule endoscopy must transmit diagnostic color images through lossy tissue while sharing a tightly constrained space and energy budget. The paper motivates sub-GHz Wi-Fi HaLow and reports a miniaturized imaging-transfer system plus preliminary in-vivo link validation.

I. INTRODUCTION

  • The tissue channel’s frequency-dependent losses create a trade-off among carrier frequency, antenna size, attenuation, data rate, and link robustness.Image fidelity and frame rate also compete with the capsule’s limited energy budget.Source: §I · p. 2
  • Wi-Fi HaLow combines sub-GHz operation with 1–16 MHz channels and single-stream data rates up to approximately 86.7 Mbps, supporting multi-megabit imaging links.By comparison, IEEE 802.15.6 HBC supports up to approximately 1.3 Mbps, which the paper describes as insufficient for the targeted uncompressed imaging stream.Source: §I · p. 2
  • Prior experimental evidence for Wi-Fi HaLow through living tissue and capsule-compatible WIT systems with subsystem-level power analysis is limited.Existing studies of IEEE 802.11ah for healthcare monitoring primarily rely on analytical path-loss models.Source: §I · pp. 2–3
  • The work designs a miniaturized WIT chain with a NanEyeC color camera, STM32U575 microcontroller, and SX-SDMAH Wi-Fi HaLow transceiver on capsule-compatible hardware.The chain is validated in a colon phantom using an oloid-based magnetic actuation platform.Source: §I · p. 3
  • The paper reports preliminary in-vivo Wi-Fi HaLow validation, an end-to-end WIT chain sustaining data rates above 12 Mbps, and subsystem-level current analysis.The imaging chain is also benchmarked against a wired Olympus reference colonovideoscope under laboratory manipulation.Source: §I · p. 3

II. ELECTROMAGNETIC CONSTRAINTS AND LINK DESIGN RATIONALE

The section analyzes tissue-dependent propagation to motivate a sub-GHz link design. Its penetration-depth analysis supports operation around 0.9 GHz as a compromise between lower attenuation and multi-megabit throughput.

II. ELECTROMAGNETIC CONSTRAINTS AND LINK DESIGN RATIONALE

  • Penetration depth δ is evaluated as a measure of how deeply electromagnetic radiation enters a material, using frequency-dependent tissue dielectric properties.The analysis uses tabulated dispersive datasets from literature and public databases.Source: §II · p. 3
  • Penetration depth decreases monotonically with frequency; muscle and large intestine attenuate more strongly than fat because of higher conductivity.The trend is attributed to conductive losses represented by σ/(fεr).Source: §II · p. 3, Figure 1 · p. 3
  • Around 0.9 GHz, penetration depth remains several centimetres for most tissues, while depth rapidly decreases in the 2–3 GHz range.The paper describes this sub-GHz choice as retaining data rate without narrow-bandwidth limitations and keeping antenna size capsule-compatible.Source: §II · p. 3
  • The reported communication results show negligible packet loss and throughput of 12–13 Mbps, which the paper considers compatible with capsule imaging.This result is offered in support of the IEEE 802.11ah selection.Source: §II · p. 4

III. IN-VIVO VALIDATION OF WI-FI HALOW

The in-vivo campaign tests whether Wi-Fi HaLow can communicate through tissue under realistic conditions, before the integrated capsule hardware was available. The authors report reliable multi-megabit communication in a porcine model, while characterizing this as preliminary channel validation.

III. IN-VIVO VALIDATION OF WI-FI HALOW

  • The campaign used an earlier SX-NEWAH platform and kept its transceiver electronics outside the body to test the wireless channel independently of final hardware integration.The WIT system later adopted the SX-SDMAH module based on the MM6108.Source: §III · p. 4
  • The porcine-model setup placed a flexible antenna at a colonoscope tip inside the animal and an external access-point antenna over the abdomen.A custom 3D-printed add-on hosted the internal antenna; the setup used a coaxial cable to connect it to the station board.Source: §III · p. 4, Figure 2 · p. 5
  • At 915 MHz with 4 MHz bandwidth and approximately 15 cm antenna separation, measured throughput ranged from 1.8 to 5.3 Mbps across transmit-power settings.Average current ranged from 54 to 126 mA at 3.3 V, corresponding to 178–415 mW; values depend on the evaluation-kit configuration.Source: §III · p. 4
  • Throughput remained in the multi-Mbps range in both laboratory and in-vivo tests, directly validating stable Wi-Fi HaLow transmission through biological tissues.Small differences were attributed in part to link distance and the transceiver’s adaptive transmission parameters.Source: §III · p. 4, Figure 3 · p. 5
  • The authors characterize the in-vivo campaign as a preliminary proof of communication feasibility, not validation of the integrated WIT prototype.They associate the relatively high power observed in those tests mainly with the earlier transceiver generation.Source: §III · p. 4

IV. SYSTEM ARCHITECTURE OF THE WIT MODULE

The WIT module combines capsule-side image acquisition, processing, and sub-GHz wireless transmission with an external receiver and control path. Its architecture is designed around compact size, reduced average power, and sustained multi-megabit throughput.

IV. SYSTEM ARCHITECTURE OF THE WIT MODULE

  • The capsule-side chain combines a miniaturized NanEyeC white-light imaging front end, a microcontroller, and a sub-GHz IEEE 802.11ah transceiver.The microcontroller handles acquisition, buffering, packetization, and local control; the external access point receives packets and reconstructs frames.Source: §IV · p. 5
  • The system-level block diagram presents the WIT subsystems and their interconnections, with the architecture assembled from three PCBs.The design targets compact form factor, reduced average power, and sustained multi-megabit throughput.Source: Figure 4 · p. 5, §IV · p. 5
  • The external unit supports a reverse control path for adjusting capsule-side parameters such as exposure time and LED intensity.The same external unit handles image visualization and storage.Source: §IV · p. 5

A. Imaging Front-End

The imaging front-end pairs a miniature color sensor with integrated illumination, while the microcontroller handles acquisition, data preparation, and remote camera and LED control.

A. Imaging Front-End

  • The low-power NanEyeC miniature CMOS color camera module measures 1 mm × 1 mm × 2 mm, provides a native resolution of 320 × 320 pixels, and supports programmable exposure times for low-light in-body conditions.Source: A. Imaging Front-End · p. 6
  • The camera’s single-ended digital output enables direct microcontroller connection, avoiding interface electronics and reducing PCB area, routing complexity, and static power.Source: A. Imaging Front-End · p. 6
  • The camera and illumination LEDs share a custom rigid-flex PCB, with PWM control enabling dynamic LED-brightness trade-offs between illumination quality and average power.Source: A. Imaging Front-End · p. 6

B. Microcontroller and Data Handling

C. Sub-GHz IEEE 802.11ah Transceiver

The WIT system uses a sub-GHz IEEE 802.11ah radio connected to the microcontroller, assembled with the imaging front-end as a compact stacked module.

C. Sub-GHz IEEE 802.11ah Transceiver

  • The MM6108-based SX-SDMAH transceiver supports 1–16 MHz channels and adaptive data rates, while autonomously managing modulation, channel access, framing, and retransmissions.It connects to the STM32U575 via high-speed SPI and uses a flexible sub-GHz antenna suited to the capsule geometry.Source: C. Sub-GHz IEEE 802.11ah Transceiver · p. 6
  • The commercial radio module is the prototype’s largest single component; the authors chose it to demonstrate protocol feasibility before further miniaturization.The authors note that SoC-level integration could potentially reduce footprint and parasitic losses.Source: C. Sub-GHz IEEE 802.11ah Transceiver · p. 6

D. Miniaturized Stack Implementation

  • The imaging board has the smallest footprint, the radio-hosting WDT board is the most volumetrically demanding subsystem, and the total stacked height is below 1 cm.Source: D. Miniaturized Stack Implementation · p. 7
  • The prototype stacks the rigid-flex imaging board distally and the MCU and radio boards proximally, using board-to-board connectors to limit lateral footprint.The assembled WIT module fits a dedicated compartment incorporated into the oloid-shaped capsule used in the experiments.Source: D. Miniaturized Stack Implementation · p. 7

V. EXPERIMENTAL VALIDATION OF THE PROPOSED WIT PROTOTYPE

Benchtop validation assessed wireless throughput, image reconstruction, and subsystem power using a colon phantom and an oloid-based magnetic actuation platform.

V. EXPERIMENTAL VALIDATION OF THE PROPOSED WIT PROTOTYPE

  • The campaign evaluated throughput, image transmission and reconstruction, and subsystem power under benchtop conditions using a colon phantom and magnetic actuation platform.Source: §V · p. 7

1) Colon Phantom and Robotic Manipulation:

2) Throughput Measurement Methodology:

  • Application-layer throughput was measured with UDP iperf between the capsule-side transceiver and a Raspberry Pi gateway, which reconstructed data and monitored throughput.The gateway also sent bidirectional exposure-time and LED-intensity control commands.Source: 2) Throughput Measurement Methodology · p. 7

V. EXPERIMENTAL VALIDATION OF THE PROPOSED WIT PROTOTYPE

3) Power Measurement Methodology:

The section describes subsystem power measurement and reports wireless-link performance, including throughput, image reconstruction, and frame-rate implications.

3) Power Measurement Methodology:

  • Power characterization separately identified baseline digital consumption, illumination-dependent variation, and RF analog-front-end current bursts.Average power was calculated from the averaged measured current waveform multiplied by supply voltage.Source: 3) Power Measurement Methodology · p. 7

1) Wireless Link Performance:

  • 12–13 Mbps application-layer throughput, roughly three times the previous SX-NEWAH platform, accompanied a dissipated-power reduction from about 400 mW to about 250 mW.The comparison is shown in Fig. 8.Source: Figure 8 · p. 8, 1) Wireless Link Performance · p. 8
  • The available bandwidth supports frame rates above 10 fps in principle, while typical capsule operation at 1–5 fps can reduce average power through duty cycling.Adaptive frame-rate strategies can increase acquisition speed during rapid capsule motion, increasing mucosal sampling density and reducing missed-detection risk.Source: 1) Wireless Link Performance · p. 8

B. Experimental Results

2) Image Transmission Performance:

The WIT module transmitted 320 × 320 color frames and produced recognizable full-color images, though the wired reference scope showed finer detail. The imaging acquisitions did not require LED brightness above 60%.

2) Image Transmission Performance:

3) Power and Energy Characterization:

The complete imaging and transmission chain drew approximately 477 mW and used approximately 39.6 nJ/bit at 60% LED brightness. Measurements separate the digital baseline, illumination, camera, and RF contributions.

3) Power and Energy Characterization:

VI. CONCLUSIONS

The paper presents a miniaturized Wi-Fi HaLow imaging system for capsule endoscopy and reports both through-body communication tests and colon-phantom validation. The measured chain transmitted uncompressed color frames above 10 fps, while prototype footprint and power remain partly tied to the commercial transceiver module.

VI. CONCLUSIONS

  • The authors report a preliminary porcine in-vivo demonstration of Wi-Fi HaLow communication through biological tissues for a WCE application.Source: §VI · p. 9
  • The capsule-compatible architecture combines a NanEyeC imaging front-end, STM32U575 microcontroller, and IEEE 802.11ah transceiver on a stacked PCB, and was validated in a colon phantom.The phantom validation used the oloid-based magnetic actuation platform.Source: §VI · p. 9
  • Application-layer throughput exceeded 12 Mbps, supporting uncompressed 320 × 320 color frames above 10 fps; the complete chain used approximately 477 mW and 39.6 nJ/bit at 60% LED brightness.The paper concludes IEEE 802.11ah offers a favorable compromise among robustness, throughput, and energy efficiency for in-body wireless imaging.Source: §VI · p. 9
  • The prototype’s footprint and power are partly determined by the integration level of its commercial transceiver module.More highly integrated Wi-Fi HaLow SoCs and modules are expected to reduce board area and power overhead.Source: §VI · pp. 9–10
  • Integration with wireless power transfer and fully autonomous capsule operation remains to be completed.Source: §VI · p. 10
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