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A Review of Wireless Body Area Networks for Medical Applications
Sana Ullah, Pervez Khan, Niamat Ullah, Shahnaz Saleem, Henry Higgins, Kyung Sup Kwak
TL;DR
WBANs address the need for unobtrusive, long-term ambulatory health monitoring with real-time patient-status updates. This review synthesizes WBAN infrastructure, in-body antenna design, low-power MAC protocols, and applications, concluding that existing MAC protocols do not reliably accommodate heterogeneous traffic and that new power-efficient solutions are needed.
Problem
WBANs require reliable, low-power communication for heterogeneous medical and non-medical traffic, especially for implanted nodes and emergency events.
Method
The paper reviews WBAN traffic classification, infrastructure, in-body antenna design, low-power MAC protocols, and applications.
Results
Existing low-power MAC protocols have limitations in accommodating heterogeneous WBAN traffic reliably, including power-consumption and QoS issues for medical traffic.
Takeaways & Limitations
New power-efficient solutions are needed for in-body and on-body sensor networks.
Abstract
from arXiv · showhide
Recent advances in Micro-Electro-Mechanical Systems (MEMS) technology, integrated circuits, and wireless communication have allowed the realization of Wireless Body Area Networks (WBANs). WBANs promise unobtrusive ambulatory health monitoring for a long period of time and provide real-time updates of the patient's status to the physician. They are widely used for ubiquitous healthcare, entertainment, and military applications. This paper reviews the key aspects of WBANs for numerous applications. We present a WBAN infrastructure that provides solutions to on-demand, emergency, and normal traffic. We further discuss in-body antenna design and low-power MAC protocol for WBAN. In addition, we briefly outline some of the WBAN applications with examples. Our discussion realizes a need for new power-efficient solutions towards in-body and on-body sensor networks.
I. INTRODUCTION
WBANs support unobtrusive, long-term monitoring of body functions and communication of patient information for healthcare and other applications. The review situates WBANs within emerging monitoring systems and outlines the paper’s organization around infrastructure, antennas, MAC protocols, and applications.
- Motivation: The motivation includes cardiovascular disease burden and the potential for ambulatory vital-sign monitoring with real-time medical-record updates.The introduction reports cardiovascular disease as a foremost cause of death in the United States and Europe and describes monitoring as an economical healthcare solution.
- WBAN concept: WBANs use portable, miniaturized, autonomous sensor nodes to monitor body functions without constraining normal activities.In-body networks additionally support communication between implanted devices and remote monitoring systems.
- Medical monitoring: WBAN systems can collect information from Implantable Cardioverter Defibrillators to detect and treat ventricular tachyarrhythmia and help prevent Sudden Cardiac Death.
- Related systems: Projects including CodeBlue, Mobi-Health, iSIM, UbiMon, and MIThril have contributed to proactive, real-time, wearable, or affordable healthcare systems.
- Paper scope: The paper reviews WBAN infrastructure, in-body antenna design, low-power MAC protocols, and applications in successive sections.
II. WBAN INFRASTRUCTURE
The proposed WBAN infrastructure organizes traffic into on-demand, emergency, and normal classes and uses a coordinator to manage communication and connect applications to relevant servers.
- Communication bands: WBANs use WMTS, ISM, UWB, and MICS bands, with MICS at 402–405 MHz dedicated to implant communication.WMTS is licensed for medical telemetry, while its restricted bandwidth cannot support video and voice transmissions.
- Traffic classes: WBAN traffic is categorized as on-demand, emergency, or normal according to its source and timing requirements.On-demand traffic is initiated by a coordinator or doctor; emergency traffic is initiated by nodes; normal traffic covers routine monitoring.
- Traffic classes: Emergency traffic is unpredictable and should be accommodated in less than one second after a node exceeds a predefined threshold.
- Coordinator: The coordinator combines a wakeup circuit, main radio, bridging function, and data interface to manage heterogeneous WBAN communication.The wakeup circuit accommodates on-demand and emergency traffic, while bridging connects nodes operating on different frequency bands.
- Applications: The coordinator connects WBANs to telemedicine, game, and medical servers for relevant recommendations.
III. IN-BODY ANTENNA DESIGN
In-body antenna design must address severe size constraints and the electrical effects of body tissue on propagation, impedance, and signal absorption.
- Design constraints: At 403 MHz, a half-wave dipole would be 372 mm long, making that antenna dimension impractical for implantation.The wavelength in space at this frequency is 744 mm.
- Tissue effects: Body tissue increases antenna electrical length, absorbs some signal because it is partly conductive, and can act as a parasitic radiator.
- Design constraints: The high dielectric constant of body tissue and its conductivity make the available antenna size much smaller than the optimum.
A. Dipole Antenna
The section compares dipole, loop, and patch antenna options for in-body communication, emphasizing tissue interaction, integration, and the compromises of electrically small designs.
- Dipole antenna: A 10 mm dipole at 403 MHz has radiation resistance of 45 mΩ in air, while surrounding high-dielectric material increases its electrical length.
- Loop antenna: A 10 mm-diameter loop has radiation resistance of 626 µΩ and is useful in-body because its magnetic field is less affected by tissue.The loop can also be readily integrated into existing structures.
- Patch antenna: A patch antenna can be integrated into an implant surface and acts as a λ/2 parallel-plate transmission line with impedance inversely proportional to width.
- Patch antenna: A full-size patch is impractical in-body, while an electrically small patch has low real impedance and impaired performance.Body tissue with dielectric constant around 50 makes the patch electrically larger than it would be in air, but does not remove the small-antenna performance trade-off.
- Alternative designs: Alternative in-body antenna designs include PIFA, loaded PIFA, bow tie, spiral, and trailing-wire antennas.
D. Impedance Measurement
Implant antenna impedance is difficult to measure definitively because body tissue, implant position, and individual anatomy vary over time. Phantom measurements provide only an approximation, while trimming is used to maintain performance.
- D. Impedance Measurement: Body tissue and changing implant position make definitive antenna impedance measurements of limited value.Individual differences in fat and muscle further affect the measurement conditions.
- D. Impedance Measurement: Phantom measurements can approximate the impedance of an antenna immersed in body-like conditions.
- D. Impedance Measurement: The trimming routine should run at power-up or regular intervals to maintain optimum performance.
IV. MAC PROTOCOL
WBAN MAC design must support heterogeneous medical traffic while conserving energy, especially for implanted nodes. Existing approaches face synchronization, power, reliability, interference, and channel-access limitations, motivating TDMA-based alternatives.
- IV. MAC PROTOCOL: In-body nodes require power-efficient MAC operation, while medical traffic needs higher priority and reliability than non-medical traffic.Emergency nodes should access the channel in less than one second.
- IV. MAC PROTOCOL: Existing MAC protocols provide limited support for heterogeneous WBAN traffic and the stringent requirements of in-body nodes.
- IV. MAC PROTOCOL: IEEE 802.15.4 does not achieve the required power level for in-body nodes and has power-consumption and QoS issues for medical traffic.
- IV. MAC PROTOCOL: CSMA/CA can produce improper clear-channel assessment because human-body path loss prevents on-body nodes from detecting in-body activity at three meters.The cited thresholds are -85dBm and -95dBm.
- IV. MAC PROTOCOL: The paper analyzes a preamble-based TDMA protocol for an on-body sensor network using extensive ns-2 simulations.Residual energy at on-body nodes is presented as the simulation focus.
V. WBAN APPLICATIONS
WBANs support diverse in-body and on-body applications spanning medical monitoring, implanted-device control, rehabilitation, entertainment, and military use. The paper illustrates these applications through examples and a real-time telemedicine infrastructure.
- V. WBAN APPLICATIONS: In-body applications include pacemaker and implantable cardiac-defibrillator monitoring and programming, bladder control, and limb-movement restoration.
- V. WBAN APPLICATIONS: The reviewed applications include remote medical diagnosis, interactive gaming, and military uses.
- V. WBAN APPLICATIONS: A real-time telemedicine infrastructure is presented for patient rehabilitation.
- V. WBAN APPLICATIONS: On-body medical applications monitor heart rate, blood pressure, temperature, and respiration.
- V. WBAN APPLICATIONS: On-body non-medical applications include monitoring forgotten things, establishing social networks, and assessing soldier fatigue and battle readiness.
A. Cardiovascular Diseases
WBANs are presented as a technology for monitoring cardiovascular and other abnormal conditions during ambulatory health care. The section also describes sensor-based cancer monitoring as a possible diagnostic application.
- A. Cardiovascular Diseases: WBANs can monitor episodic events and abnormal conditions during ambulatory health monitoring.
- A. Cardiovascular Diseases: The paper identifies cardiovascular disease as a major health concern motivating improved monitoring solutions.
- A. Cardiovascular Diseases: Miniaturized sensors integrated into WBANs can monitor cancer cells and allow physicians to diagnose tumors without biopsy.
C. Asthma
WBANs support asthma monitoring by detecting allergic environmental factors and providing real-time physician feedback. They also address telemedicine limitations that can restrict prolonged, unobtrusive health monitoring.
- C. Asthma: WBANs can monitor allergic agents and provide real-time feedback to physicians for patients with asthma.A GPS-based device can monitor environmental factors and trigger an alarm when information allergic to the patient is detected.
- C. Asthma: Existing telemedicine systems use dedicated wireless channels or power-demanding protocols such as Bluetooth.These approaches may be exposed to interference from other devices using the same frequency band.
- C. Asthma: These channel, power, and interference characteristics limit prolonged health monitoring.WBAN integration with telemedicine supports unobtrusive ambulatory monitoring over long periods.
E. Artificial Retina
WBAN applications include implanted retina prostheses that assist people with limited or no vision. The review places this example alongside broader WBAN application areas and identifies a need for more power-efficient solutions.
- E. Artificial Retina: Retina prosthesis chips can be implanted in the human eye to assist patients with limited or no vision.The stated benefit is helping patients see at an adequate level.
- E. Artificial Retina: WBANs also support military applications by connecting soldiers and reporting activities to commanders.The passage specifies activities including running, firing, and digging, while requiring secure communication to prevent ambushes.
- E. Artificial Retina: The review covers traffic classification, in-body antenna design, MAC protocols, and WBAN applications.It specifically discusses supported patch antennas for in-body communication and low-power MAC protocols.
- E. Artificial Retina: Existing low-power MAC protocols have limitations in reliably accommodating heterogeneous traffic, motivating new power-efficient solutions.The conclusion frames this need across in-body and on-body sensor networks.