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Analysis Of Human Impedance and Channel Propagation
Characteristics in Body Area NetworkFangming Ruan
1
Dept of Electron & Info .Eng. Guizhou Normal University
Guiyang [email protected]
Wu Liang2
School of Economics & Management Univ.of Electronic
Sci.& TechChengdu, China
AbstractBased on description of human body bio-impedance
Transmission property of communication channel on-body is
discussed .In
frequency range of (3-5) GHz human body has a good response to
signal
transportation .Considering bit error rate(BER) of channel
on-body binary
phase switch keying(BPSK) has better performance than other
modulation
for wireless body area network(WBAN).
Keywords-impedance; impulse response ; bit error rate; body
area
network
I INTRODUCTION
Body area central network is a promising potential network
,which can
provide remote healthcare ,patient status monitoring and
controlling in
addition to make various daily entertainment fitness ,and the
like .Channel
feature of communication on body is a basic problem for body
area network
.Addressed in this paper include impedance of human body
,frequency range
to be appropriate for body area network(BAN), response to
impulse in body
,bit error rate(BET) with bi-phase modulation in body area.
II. HUMAN BODY IMPEDANCE
Important physiology and medical information can be obtained fro
variationof impedance of human body .Human body can be represented
with electric
circuit because tissues are made of cells and human body
consists of tissues
.Circuit replacing human body can be seen in FigI which is based
on a model
presented in [1]-[5]. RC circuit of head is supplemented in new
circuit model.
Each part of human body (head , torso ,arms , and legs) is
replaced by an
electrical capacitor in parallel with a resistor.
There are various combinations from circuit in Fig1 to decide
human
body impedance: between two hands , hand-foot, head-foot.Each of
the
options seems to be proper but input impedance is different each
other in
these three cases.
Feng Zhou3
This work was supported by National nature science Foundation of
China
with grant No.60971078, by Guizho Provincial Nature Science
and
Technology Foundation(No.J[2007]2211),by Guizhou Provincial
Foundation
for International Cooperative Research of science and
Technology(No.G[2008]700115) and by PHD Foundation of Guizho
Normal
university.
Comm. Metrol. Center ,Ministry Of Industry & Info. Tech
Beijing ,China
Xiaolu Wang4
Research Institute Of Atomics & Molecules Sichuan Univ.
Chengdu, China
Figure 1. Circuit model of human body
Figure 2. Calculating input impedance with proposed
cylindrical
model of humanbody.
When performing computer simulations ,cylindrical model of human
body is
taken into account. Fig2 gives the method calculating average
impedance
through division of voltage.
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Across two terminals by current passing through the cylinder
.
Where inhe-f is the input impedance between head and foot ,
are
complex voltage and current respectively .
The input impedance may be calculated in the simplest way-the
voltage
drop divided by current flowing through the human body:
inhe-f=
p
E (2)
Results of calculations are presented in Fig3 . Variation of
resistance and
capacitance with dimension of human body to can be roughly
sorted three
phases(see Fig3a and Fig
(a)Resistance varied with object size.
(b) capacitance varied with object size
Figure 3 Results of calculation of cylindrical model in TEM
cell
III. FREQUENCY PROPERTY IN BODY CHANNEL.
Communication between implanted devices ,pacemaker for instance,
needs
to consider response of human body. Signal received at pacemaker
has
relationship with transmission signal and impulse response as
seen formula
(3.1)
r(t)=
(3.1)
In frequency domain transmission function can be expressed
with
formula (3.2) as below
y
Where H(f) is magnitude response and (f) is group delay.
Considering Gaussion pulse as exciting source ,and assuming
receiving
antenna is set 20cm away from torso of body response in
frequency
are shown in Fig.4
(a)
(b)
Body channel ,seen from Fig4. Has a good performance in
frequency range
from 3.1GHz through 5GHz.
For human body typical electric parameters of muscle and fat are
shown in
Table 1.
Dielectric constant has effect on the wavelength of signal
propagated in
medium.In air the wavelength can be found in Equation (3.2)
where
=1.However in different medium
Table 1. Body Electrical Properties
the wavelength is reduced as seen in Equation (3.3).
(3.3)
Where is the wavelength in air with unit in meters and f if
frequency in Hz.
Frequency(MHz) Muscle Fat
(
() ()
100 66.2 0.73 31.6 12.7 0.07 92.4
400 58 0.82 43.7 11.6 0.08 108
900 56 0.97 48.2 11.3 0.11 111
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(3.4)
Where is the wavelength in medium.
Physical size is an important consideration when designing
implanted
antennas .Muscle conductivity is 0.82S, bigger than that in air.
The effectlike sea water surrounding implant device, which can
attenuate signal
passing through muscle and reduced penetration depth. Variation
of muscle
characteristic impedance needs to be calculated at the fat
muscle boundryat which part of the signal is reflected describing
by reflection coefficient
(3.5)
Whereis the impedance in free space (377), and is the
impedancein medium .At muscle-fat boundry =80% majority of incident
power is
reflected .Radiation takes place for implanted device duebto no
grounding.
IV. UWB RADIOO SYSTEM PERFORMANCE IN A BODY-
CENTRIC ENVIRONMENT
Accurate performance prediction of UWB systems requires the
knowledge ofthe propogation channel behavior system modeling of
potential UWB radio
trasceivers for body area radio system modeled using Agilent
DSP
DesignerTM to investigate the effects of on-body channels on UWB
systems
using different pulse modulation technique.
Figure 5 Block diagram of the UWB radio system modeled for
performance analysis of potential transceivers that could be
applied in body area networks
Various modulation schemes are possible for UWB signaling such
as pulse
position modulation (PPM) amplitude shift keying (ASK) on-off
keying (OOK)
phase shift keying (PSK) and frequency shift keying (FSK). The
performance of
PPM and bi phase modulated UWB signals in multipath environment
was
investigated in [9] [10] for different data rates and under
different
requirements. The system model presented here applies 100Mbit/s
data rate
and operates in low signal-to-noise ratio (SNR=0) for
performance analysisunder measured on-body channel data.
Bi-phase modulation can be adopted in designing initial
Potential UWB transceiver designs for wireless body centric
networks since it
provides better performance for UWB systems even for higher data
rates
which also agree with results obtained in [10].
V. CONCLUSIONBody area network(BAN) involves in multiple
challenges including:
overall size and weight of sensor nodes should be tailored to
the human
body total energy consumption of sensor needs to be drastically
reduced to
allow energy autonomy ; intelligence should be added to sensors
so thateach one is capable of storing processing and transferring
signal continuosly
or on an event-triggered basis and the like .Human body
impedance can
reflect physiology and medical qseful information .In frequency
domain
feature of body as transmission channel is discussed briefly as
well as electric
parameters of muscle and fat; for potential UWB radio of body
area network
binary phase switching keying has a better performance than
pulse position
modulation(PPM)and other modulations.
References
[1] R.J. Liedtke,The fundamentals of Bioelectric Impedance
Analysis
,http://www.rilsystem.com/docs/bia info/fundamentals
/fundamentals.PDF February 1998.
[2]
Timing and
coding
Pulse shape
generator
Bit slicer
1000011 1
Correlator
sub-system
PA
Measured on-
bodychannel
+antenna
LNA
Input data
Spreading code
Recovered data
