JOURNAL OF TELECOMMUNICATIONS, VOLUME 29, ISSUE 2, FEBRUARY 2015

18

Study of UWB On-Body Radio Channel for Ectomorph, Mesomorph, and Endomorph

Body Types Mohammad Monirujjaman Khan, Ratil Hasnat Ashique, and Md. Raqibull Hasan

AbstractThe effects of different human body sizes and shapes on the ultra wideband (3-10 GHz) on-body radio propagation

channels are investigated. In this paper, three different human body sizes (Ectomorph, mesomorph and endomorph) are

investigated. Experimental investigation is performed using a pair of Tapered Slot Antennas (TSA) in the indoor environment.

Thirty four different receiver locations on the front part of the human body are considered for calculating the path loss. Results

and analysis show that due to three different types of human body shapes and sizes maximum of 31.8% variation in path loss

exponent is observed. The effect of the three different human body sizes and shapes variations on the 8 different ultra

wideband on-body radio channels was also studied.

Index Terms Body-centric wireless communications, body size effects, on-body radio channel; path loss, ultra wideband.

1 INTRODUCTION

ODY-centric wireless communications (BCWCs) is a central point in the development of fourth generation mobile communications. In body-centric wireless

networks, various units/sensors are scattered on/around the human body to measure specified physiological data, as in patient monitoring for healthcare applications. A body-worn base station will receive the medical data measured by the sensors located on/around the human body. Body-centric wireless networks have a range of applications, from monitoring of patients with chronic diseases and care for the elderly, to general well-being monitoring and performance evaluation in sports [1], [2], [3], [4], [5].

The human body is considered an uninviting and

even hostile environment for a wireless signal. The dif-

fraction and scattering from the body parts, in addition to

the tissue losses, lead to strong attenuation and distortion

of the signal. In order to design power-efficient on-body

communication systems, accurate understanding of the

wave propagation, the radio channel characteristics and

attenuation around the human body is extremely impor-

tant. In the past few years, researchers have been tho-

roughly investigating narrow band and ultra wideband

on-body radio channels. In [6], [7], [8], [9], [10], [11], [12],

[13] on-body radio channel characterisation was pre-

sented at the unlicensed frequency band of 2.45 GHz. In

[14], [15] [16] [17] [18] [19], [20], [21], [22], [23] ultra wide-

band (UWB) on body propagation channels have been

characterised and their behaviour has been investigated

in indoor and chamber for stand-still, various postures

and dynamic human body. The shapes and sizes of the

human body will significantly affect the propagation

paths and cause large variations in the path loss for on-

body radio links.

In this paper, ultra wideband on-body radio propaga-

tion study is performed by characterizing the path loss for

three different real human subjects of different shapes

and sizes. The body sizes of the test subjects used in this

study are characterised as Endomorph (thin), Ectomorph

(medium build) and Mesomorph (fatty/larger size). Mea-

surement campaigns were performed in the indoor envi-

ronment using a pair of Tapered Slot antennas. The effect

of the three different body sizes and shapes on the path

loss for various on-body links were investigated and ana-

lysed.

The rest of the paper is organized as follows; section 2

illustrates the measurement setup, section 3 presents

measurement results, radio channel parameters and mod-

elling aspects, and finally section 4 draws the conclusion.

2 MEASUREMENT SETTINGS

For this study, three real human subjects with different body sizes and shapes were used in this measurement campaign (as shown in Fig. 1). Table I shows the dimensions of three different subjects used in this measurement (Male1, Male2, Male3). In this study, a pair of Tapered Slot antennas was used (see Fig. 2) [24]. A HP8720ES vector network analyser (VNA) was used to measure the transmission response (S21) in the frequency range of 3-10 GHz between two antennas of the same type placed on the body. The frequency range was set to 3-10 GHz, with 1601 points and with a sweep time of 800 ms. The network analyser settings were shown in the

Mohammad Monirujjaman Khan is with the Department of Electrical and Electronic Eng. at Primeasia University, Banani, Dhaka, Bangladesh.

Ratil Hasnat Ashique is with the Department of Electrical and Electronic Engineering, Primeasia University, Banani, Dhaka, Bangladesh. Md. Raqibull Hasan is with the Electrical and Electronic Engineering De-

partment, Primeasia University, Banani, Dhaka, Bangladesh.

B

19

Table II. During the measurement, the transmitter Tapered Slot antenna connecting with the cable was placed on the left waist and the receiver Tapered Slot antenna was successively attached on 34 different locations on the front part of the body as shown in Fig. 3. The test subjects were standing still during the measurements and, for each receiver location and measurement scenario, 10 sweeps were considered. The effects of the cable were calibrated out.

The measurement campaigns were performed in the Body-Centric Wireless Sensor Laboratory at Queen Mary, University of London [25]. The total area of the lab is 45 m2 which includes a meeting area, treadmill machine,

workstation and a hospital bed for healthcare applications

3 ULTRA WIDEBAND ON-BODY PARAMETERS FOR DIFFERENT HUMAN BODY SHAPES

The path loss for each receiver location is directly calcu-lated from the measurement, averaging over the frequen-cy band of 3~10 GHz. It is well known that the average received signal decreases logarithmically with distance for both indoor and outdoor environments as explained in [26].

X

d

ddPLdPL dBdB )log(10)()(

0

0 (1)

where d is the distance between transmitter and receiver,

0d is a reference distance set in measurement (in this study it is set to 10 cm), )( 0dPLdB is the path loss value at the reference distance, and X is the shadowing fad-ing. The parameter is the path loss exponent that indi-cates the rate at which the path loss increases with dis-tance. A least-square fit method is applied on the measured path loss data for 34 different receiver locations to extract the path loss exponent for three test subjects, as shown in Fig. 4. Table III lists the values of path loss exponent ob-tained for different test subjects. It can be noted that the path loss is affected by the body size. Due to different

TABLE 2 NETWORK ANALYSER SETTINGS

Frequency Band 3 to 10 GHz

Frequency Points 1601 Sweep Time 800 ms Number of Sweep 10 VNA Transmit Power

0 dBm

Fig. 3. Ultra wideband on-body radio propagation measurement settings showing the transmitter antenna is on the left waist while the receiver antenna is on 34 different locations of the body.

(a)Male 1 (b) Male 2 (c) Male 3 Fig. 1. Photographs of the three test male subjects used for ultra wideband on-body radio propagation channel measure-ment (dimensions are shown in Table I).

TABLE 1 THE DIMENSIONS OF THREE REAL HUMAN TEST SUB-

JECTS USED IN THIS STUDY

Dimensions Male 1 Male 2 Male 3

Height (cm) 182 178 188 Weight (kg) 70 78 120 Chest Circum-ference (cm)

87 93 124

Waist Circum-ference (cm)

79 86 130

Fig. 2. The Tapered Slot antenna used in this experiment [16].

20

body sizes and shapes, the path loss exponent and the mean path loss )( 0dPLdB at the reference distance vary for the three different human bodies. Maximum of 31.8% variation in path loss exponent is noticed for the three different body shapes (thin, medium-build and fat-ty/larger size). Results show that the path loss exponent increases with the body size. In the case of subjects with the low value of body chest and waist circumference such as male 1 and male 2, the path loss exponent is lower and with the high value of chest and waist circumference for male 3, the path loss exponent is higher. In this case for thinner subject (male 1), the propagation between the transmitter and receiver is more line of sight (LOS) than the body with higher volume of the chest and waist cir-cumference leads to lower value of path loss exponent ( =1.91). For subject with higher curvature radius trunk such as (male 3), the wave reaches the receiver through creeping wave propagation, which has higher signal at-tenuation, thus leading to higher value of exponent ( =2.80). For the subject with higher volume of chest and waist circumferences, the communications for some of the receiver locations is heavily blocked by the different body parts, compared to the subject with lower value of chest and waist circumferences. In addition, the body tissues are also different for various subjects which also contri-bute for the variation of the path loss. X is a zero mean, normal distributed statistical vari-able, and is introduced to consider the deviation of the measurements from the calculated average path loss. Fig. 5 shows the deviation of measurements from the average path fitted to a normal distribution for three different test subjects cases. Table III lists the values of standard devia-tion of the shadowing factor obtained for three different test subjects. Results indicate that the standard deviation

value varies for different subjects.

In order to compare the path loss of three different hu-

man bodies, 8 different ultra wideband on-body chan-

nels have been chosen (Fig. 6). Fig. 7 shows variation in

path loss for 8 different ultra wideband on-body links of

three different human bodies. For the considered 8 dif-

ferent on-body links due to different human body sizes

and shapes, maximum of 13 dB variation of path loss of

an on-body link is occurred. It was noted for the trans-

mitter to right wrist link (Rx 19) of male 01 and male 03,

where the variation of path loss for this link of three dif-

ferent subjects is mainly due to different trunk size of

the different subjects. In the case of male 01, the trunk

size is much smaller than the trunk of male 03, which

creates less NLOS and less blocked communication, re-

sulting in a lower path loss value for this link of the

male 01.

-15 -10 -5 0 5 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Deviation from average path loss (dB)

Cu

mu

lative

pro

ba

bility

Male 1

Normal fit(=7.36 )

Male 2

Normal fit(=7.61 )

Male 3

Normal fit(=6.60 )

Fig. 5. Deviation of the measurements from the average path loss for three different test subjects.

0 1 2 3 4 5 6 7 8 9 10

30

40

50

60

70

80

10 log(d/d0)

Pa

th L

oss (

dB

)

Male 1

Least Square Fit (=1.91)

Male 2

Least Square Fit (=2.19)

Male 3

Least Square Fit (=2.8)

Fig. 4. Measured and modelled path loss for ultra wideband on-body channels versus logarithmic Tx-Rx separation distance of different human body (Male 01-Male 03).

Transmitter (Tx) Antenna Position

2419

11

33

9

34

2832

Receiver (Rx) Antenna Position

Fig. 6. Considered 8 different on-body links choosen for path loss comparison of different test subjects.

TABLE 3 ON-BODY PATH LOSS PARAMETERS FOR THE 3 DIFFER-

ENT TEST SUBJECTS

Path Loss Parameters

Male 1 Male 2 Male 3

1.91 2.19 2.80 )( 0dPLdB (dB)

51.2 51.8 49.0 (dB) 7.36 7.61 6.60

21

7 CONCLUSION

Ultra wideband on-body radio propagation for three

different real human test subjects of various sizes and

shapes was investigated in this paper. Experimental

investigation was made in the indoor environments

using a pair of Tapered Slot antennas. Results and

analysis showed that due to the different body sizes

and shapes a maximum variation of 31.8% in path loss

exponent occurred. The path loss exponent generally

increases with the body size. The effect of the three

different human body sizes and shapes variations on

the 8 different ultra wideband on-body radio channels

was studied where results demonstrated that, for

certain on-body links (e.g. waist to right wrist) the

changes in body size and shape can lead to a

significant variation (up to 13 dB) in path loss.

ACKNOWLEDGMENT

The authors of this paper would like to thank John

Dupuy for his help with the antennas fabrication. The

authors also would like to thank Sanjoy Mazumdar for

his help during the measurement.

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Mohammad Monirujjaman Khan received his BEng. and PhD de-grees from Queen Mary University of London (QMUL) in 2008 and 2012, respectively. He is working as an Assistant Professor and Head of Electrical and Electronic Engineering department at Primea-sia University, Dhaka, Bangladesh. He received best paper award in the IEEE international conferences in 2013. He also received best presentation award in the International IEEE conference in 2014. His main research interests include compact and efficient antennas for medical and sports applications in wireless body area networks and wireless personal area networks, radio propagation channel model-ling and characterization, small antennas design, cognitive radio and system and wearable systems. He has authored and co-authored more than 50 technical papers in leading journals and peer-reviewed conferences. Dr Khan is acting as a reviewer for many leading IEEE and IET journals in the area of antennas, radio wave propagation and communication systems. Ratil Hasnat Ashique is a lecturer at the Primeasia University, Ban-gladesh. He received his B.Sc. Engineering degree in Electrical and Electronic Engineering from Bangladesh University of Engineering & Technology (BUET) in 2011. His research interest includes wireless communication, microwave and RF engineering, antenna design and radio channel modelling and characterization. Md Raqibull Hasan is a lecturer at the Primeasia University, Ban-gladesh. He received his B.Sc. Engineering degree in Electrical and Electronic Engineering from Bangladesh Khulna University of Engi-neering & Technology (KUET) in 2013. His research interest includes wireless communication, microwave and RF engineering, antenna design and radio channel modelling and characterization, microcon-troller, nanao technology.

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