Body-Centric Wireless Communications

Gunjan Gupta

10BEC112

Electronics and Communication Dept.

Institute of Technology, Nirma University

Abstract - The continuous minimization of

electronic devices, combined with recent

developments in wearable computer

technology, is leading to the creation of a wide

range of devices that can be carried by their

user in a pocket or otherwise attached to their

body. This can be seen as a continuation

improvement in the mobile phone, which has

become smaller and more convenient for

personalized operation over the last few

years. Alongside this trend, there have been a

number of body-centric communication

systems for specialized occupations, such as

paramedics and fire fighters, as well as

continuing interest for military personnel. The

development of the mobile phone can be

characterized from the user perspective by

three phases. The first equipment was large

and heavy, and was used only by those people

whose job required it. Then, the business

community saw it as a way of improving

business operations. Finally, the mobile phone

became popular with the general population,

who used it for social and entertainment

purposes, and, more recently, as a fashion

accessory. It is quite possible that body area

networks (BANs) will follow the same path.

Figure 1.1 shows a wearable computer, an

early form of BAN, as a test bed for a wide

range of studies into hardware and software

architectures, and user applications. It is

obviously bulky and inconvenient to use and

has wired interconnections. However, further

minimization has taken place; as a result, it

was clearly desirable to remove the wired

interconnections. It is also likely that power

will be provided at each body unit and that

data transfer will use high capacity wireless

communications. Other current uses of such

systems include warehouse operators and

garage mechanics. Wearable computers are

also used as a fashion accessory. Body-worn

equipment is also used for health monitoring

[1] like as in smart wireless

electrocardiography (ECG) patch. It is a hybrid

system, combining electronic assembly on a

flexible substrate with textile integration. The

wireless ECG patch measures a bipolar ECG

signal between two electrodes separated by a

distance varying for 3 to 4 cm.

Figure 1.1[7] Wearable computer (a) headset with video display, microphone, and earpiece and (b) miniaturized PC.

INTRODUCTION Medical implants for monitoring, diagnosis, and activity have been studied for some time. The opportunities created by nanotechnology and micro technology now open up the possibility of much more widespread use and application. In addition to sensors and drug delivery mechanisms, communication is a vital part of this implementation process, for monitoring of internal body conditions and for signalling actions to be taken by the implant. These implants might also be used in conjunction with a body area network, as shown in Figure 1.2 [2]. Optimum design of such BANs and implants means that a full understanding of antennas and propagation into and through the body is needed.

Figure 1.2[7] Wearable medical support network.

Body-centric communication takes its place firmly within the sphere of personal area networks (PANs) and (BANs). The content of a BAN or PAN contains a range of communications needs and requirements. These can be classified as:

Off-body: because the channel is off of the body and in the surrounding space, only one antenna in the communications link is on the body. This is referred to as the off-body domain.

On-body: most of the channel is on the surface of the body and both

antennas will be on the body. This is called the on-body domain.

In-body: a significant part of the channel is inside the body and implanted transceivers are used. This is called the in-body domain.

This nomenclature implies a partitioning of the PAN and BAN space into three areas. The first is where most of the channel is off the body and in the surrounding space, and where only one antenna in the communications link is on the body, which we call the off-body domain. The second is where most of the channel is on the surface of the body, and both antennas will be on the body, called the on-body domain. The last is where a significant part of the channel is inside the body and implanted transceivers are used, and we call this the in-body domain. While this is not a perfect subdivision, it does serve to highlight some of the different challenges for antennas and propagation in the body-centric system. Off- to On-Body Communications Communications from localized base stations, or broadcast stations, to transceivers located on the body have been used extensively. In the mobile phone area, such investigations include studies of the propagation characteristics of urban and rural environments and the performance of body worn antennas in the face of variations of body proximity and orientation. Fabric-based antennas can significantly increase the performance of body-worn equipment in communications to local base stations. Such antennas need to orient the radiation pattern away from the body while simultaneously providing all around coverage. In addition, it is important to screen the antenna from the body in order to prevent the losses in the tissue from degrading the antenna efficiency. This can be achieved by using larger ground planes than are possible in miniaturized equipment. The challenges for fabric-based antennas are to maintain good performance in the face of changes in the body posture and to be unobtrusive.

On-Body Communications There are now many examples of wearable computers in general use today, some of which still incorporate wired interconnections. This is undesirable, due to reliability issues surrounding constantly flexing cables and connectors, the weight of such cables, and the general inconvenience to the user. A number of other connection methods have been proposed for this purpose, including smart textiles and communication by the currents in the user’s body. Each of these methods has its own advantages and drawbacks. Among the drawbacks of the smart clothes, for example, is the need for a special garment to be worn, which may conflict with the user’s personal preferences. Similarly, body current communication is limited because it has a relatively low capacity. For real-time video transfer around the body, very high data rates are required.

Wireless radio connectivity is an obvious option for connecting body-worn devices. Several standards for wireless connections between small, closely spaced devices have been developed, including Bluetooth, BodyLAN, and Zigbee. These types of connection can provide high levels of flexibility and comfort to the user, and therefore have received a lot of attention. There are three primary criteria for wireless modules for on-body communications. Firstly, they must support the high data rates expected in the future. Secondly, they must be small and lightweight. Both of these suggest the use of high frequencies. Thirdly, they must consume minimum power, which implies highly efficient links. In terms of antennas and propagation, efficient design requires a good understanding of the properties of the propagation channel involved and the development of optimized antennas. Medical Implants and Sensor Networks In recent years, several exciting developments, such as submicron electronics, nanotechnology and microelectromechanical systems (MEMS), have emerged, which will have a profound impact on medicine. These

technologies will allow the construction of intelligent microscopic implantable sensors, mobile robots, and drug release devices, which will perform in vivo diagnostic and therapeutic intervention. Such devices offer great potential to improve the quality of life for many patients; there are now a number of conditions where implants are used to improve patient lifestyle, such as pacemakers [3] and cochlea implants [4]. There are also significant future aspirations, such the projects within the EC Integrated Project, Healthy Aims, [5] which include pressure sensing in the brain cavity, glaucoma sensor, and retinal implants. Other future aims are the lab-on-a-chip for internal diagnosis or automatic drug delivery [6] and interfacing to nerve endings for communications to the brain. As an example of the significance of such developments, current stats indicates that there are patients with severe spinal injuries who are fully aware but unable to communicate because they have no muscular control. Implanted sensors connected to the spinal cord, or even the brain, could give them back the ability to communicate. This would have an immeasurable impact upon the quality of life for these patients.

There are, however, many problems that must be overcome if this implant technology is to be widely exploited and used commercially. There is now much work to develop new sensor technology, much of which is being enabled by nanosystem and microsystem research. There is less work being done on other important aspects of the implant system, namely communications. This will have a crucial effect on the practicability of future implant systems, where the potentially very small size of the sensor needs to be matched by miniaturization in the communication technology. Electromagnetics is one of the enabling technologies that has to be applied within the framework of communications networks and user needs. There is also the concept of a hierarchy of implants, as shown in Figure 1.3, applied to the head, where the higher levels, some of which may be outside or on the body, have high intelligence. Because of this, high communication rates are

Figure 1.3[7] Communications to medical implants.

needed, while those at the lower levels become smaller and have less communication requirements. The subdermal sensors could read body data, as well as being relays to the single, or group, neuron (or other body data) sensors which are ideally at the submicron scale. At this size, sensor noise, be it electrical or mechanical, will limit performance. The larger implants may be active—that is to say, with internal power sources—and the smaller ones may be passive; in either case, communications are important. Sensors are now becoming available for all levels. The feasibility of providing communications will be limited both by the fundamentals of electromagnetics and the antenna and transceiver technology needed to implement it.

Overview of Applications Body-centric wireless communications are aimed at providing systems with constant availability, reconfigurability, and unobtrusiveness. High levels of processing and complex network protocols are needed to provide the powerful computational functionalities required for advanced applications. These requirements have led to increasing research and development activities with the main interests being healthcare, patient monitoring, personal identification, navigation, personal multimedia entertainment, and task-specific/fully compatible wireless wearable computers. Body-centric wireless communications can be applied to many fields and a summary of their applications can be found in table [7]. Some of them include:

Medical applications: smart diagnosis, treatment, drug delivery system, patient monitoring, and aging care;

Wireless access/identification systems: wireless transactions and identification of individual peripheral devices;

Navigation support and location based services: tourism, security, and intelligent transportation system;

Personal multimedia entertainment: wireless DVD and wearable computing;

Military and space applications: smart suits, battlefield personnel care and intelligence, and biosensors for astronaut monitoring.

References [1] Yang, G. Z, Body Sensor Networks, Springer, 2006.

[2] Spratley, J. P. F., P. S. Hall, M. C. Ward, Y. Hao, and

A. Alomainy, “Communications for In-body Microsensor

Applications,” International Workshop on Wearable and

Implantable Body Area Networks, Cambridge, MA:

Media Lab, MIT, April 2006.

[3] Perrins, J, “Types of Sensor for Rate Responsive

Pacemakers,” IEEE Colloq on International Cardiac

Implants, January 1993.

[4] Loizou P. C., “Introduction to Cochlear Implants,”

IEEE Signal Processing Magazine, September 1998, pp.

101–130.

[5] www.healthyaims.org

[6] Figeys, D., “Lab-on-a-chip: A Revolution in

Biological and Medical Sciences,” Anal Chem, May 2000,

72(9):330A–335A.

[7] Book: Antennas and Propagation for Body-Centric

Wireless Communications Second Edition Peter S. Hall

Yang Hao

Standard Applications

Scenarios Wave

Propagation

Mechanism UHF/VHF Medical implants,

personal access,

personal

identification

system

Inductive and

near field

coupling

Medical

implant

(licensed)

Medical implants,

telemedicine Near/far field,

lossy media

BodyLAN Telemedicine Free space wave Bluetooth/

ZigBee/

WLAN

Personal multimedia

entertainment,

security,

smart clothing,

location-based

services

Space/surface

waves

UWB Wireless DVD,

wearable and

ubiquitous

computing

Space/surface

waves