IEICE Communications Express, Vol.5, No.8, 272–277

Experimental evaluation of
MIMO transmission on
between human bodies
communication
Tsutomu Mitsui1, Takefumi Hiraguri2a), Kentaro Nishimori1b),
Shunya Yokoyama2a), Kenko Ota2, Tomomi Hiraguri3,
Yoshiaki Morino2, and Naoki Honma4
1

Faculty of Engineering, Niigata University,

8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950–2181, Japan
2

Faculty of Engineering, Nippon Institute of Technology,

4–1 Miyashiro-machi, Saitama 345–8501, Japan
3

Faculty of Health Sciences, Tokoha University,

1–30 Aoi-ku, Shizuoka-shi, Shizuoka 420–0831, Japan
4

Faculty of Engineering, Iwate University,

3–18–8 Ueda, Morioka, Iwate 020–8550, Japana) hira@nit.ac.jpb) nishimori@ie.niigata-u.ac.jp

Abstract: In this paper, we propose multi-input multi-output (MIMO)
transmission using human bodies. The proposed scheme is experimentally
evaluated using test subjects, whose bodies are located at different positions.
A high channel capacity was achieved by using MIMO transmission. The
channel capacity obtained for 2 × 2 MIMO in body-to-body communication
is approximately 1.6 times higher than that obtained when using single-input
single-output transmission. The experimental results indicate the success ofthe proposed method in increasing channel capacity using MIMO. The
presented research is relatively unique, and the results would therefore bea valuable contribution to this ﬁeld of research.
Keywords: MIMO, body-to-body communication, channel capacity
Classiﬁcation: Wireless Communication Technologies
References© IEICE 2016
DOI: 10.1587/comex.2016XBL0096
Received May 2, 2016
Accepted May 19, 2016
Publicized June 2, 2016
Copyedited August 1, 2016[1] T. G. Zimmerman, “Personal area networks: near-ﬁeld intrabody communication,” IBM Syst. J., vol. 35, no. 3–4, pp. 609–617, 1996. DOI:10.1147/sj.353.
0609[2] M. Sasaki and K. Ochiai, “Prsonal and demonstration of intrabody communication with a sensitive electro-opotic sensor,” IEEE Trans. Instrum. Meas.,
vol. 58, no. 2, pp. 457–466, Aug. 2008. DOI:10.1109/TIM.2008.2003307[3] T. Hiraguri and K. Nishimori, “Transmission methods and efﬁciency using
MIMO technologies for wireless LAN systems,” IEICE Trans. Commun.,vol. E98-B, no. 7, pp. 1250–1267, July 2015. DOI:10.1587/transcom.E98.B.
1250

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IEICE Communications Express, Vol.5, No.8, 272–277[4] S. Movassaghi, M. Abolhasan, J. Lipman, D. Smith, and A. Jamalipour,“Wireless body area networks: a survey,” IEEE Commun. Surveys Tuts., vol. 16,
no. 3, pp. 1658–1686, Aug. 2014. DOI:10.1109/SURV.2013.121313.00064[5] A. Goldsmith, S. Jafar, N. Jindal, and S. Vishwanath, “Capacity limits of MIMO
channels,” IEEE J. Sel. Areas Commun., vol. 21, no. 5, pp. 684–702, June
2003. DOI:10.1109/JSAC.2003.810294

1

Introduction

Today’s consumers are surrounded by a wide range of mobile communication
devices, such as smart phones, laptop PCs, mobile game consoles, and so on. In the
future, a uniﬁed communication method will likely be required to link these diverse
mobile terminals. One solution that was proposed by Zimmerman is the concept ofusing the human body as a communication path to link mobile terminals [1]. This
type of communication, called intra-body communication, would offer a beneﬁt ofcommunication without constraint of physical cabling on account of the body being
occupied as a communication medium.
We apply intra-body communication technology in this study and focus on thetransmission of signal between two human bodies. The transmission scheme isherein referred to as body-to-body communication. Unlike intra-body communication, body-to-body communication involves intermediary technology between
wired and wireless communication. Therefore, it has the same advantages of
intra-body communication, while eliminating the need for antennas and device of
wireless communication systems. In related studies, body-to-body communication
results have been minimally obtained through a focus on intra-body communication[2]. Consequently, addressing network conﬁguration and basic evaluation experiments for body-to-body communication is important.
In this paper, we present our experimental evaluations of body-to-body communication. Multiple-input multiple-output (MIMO) transmission [3] is introduced
to increase a channel capacity. The channel capacity by MIMO transmission iscompared with that by single-input single-output (SISO) transmission.
2© IEICE 2016
DOI: 10.1587/comex.2016XBL0096
Received May 2, 2016
Accepted May 19, 2016
Publicized June 2, 2016
Copyedited August 1, 2016

Experimental methodology of intra-body communication andbody-to-body communication

In Sect. 3, we compare respective electric power (the received power) in SISO byinter-body communication and body-to-body communication. An electrode isrequired to respective communications. Therefore, body-to-body communicationis conﬁrmed by prototype electrode. In addition, body-to-body communication in
SISO is evaluated to verify that an input signal is transmitted to different bodies via
a radio medium. The transmission of electric power is additionally conﬁrmed in theexperiment and results are compared. In Sect. 4, an experimental by body-to-bodycommunication using MIMO transmission is employed in order to increase thechannel capacity. Low frequencies, those below the microwave, are sufﬁciently
effective to enable signals to be transmitted in the human body [4]. However, when
low frequencies are used, it is difﬁcult to obtain wideband performance by small

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antennas. If SISO transmission is used, a high transmission rate may not be
obtained. In this study, this issue is solved by using a 2  2 MIMO transmission.
The channel capacity by MIMO and SISO transmissions are evaluated in terms ofbody-to-body communication.

Fig. 1.

3© IEICE 2016
DOI: 10.1587/comex.2016XBL0096
Received May 2, 2016
Accepted May 19, 2016
Publicized June 2, 2016
Copyedited August 1, 2016

Human body(s) communication conﬁguration and evaluation
results.

Evaluation of intra-body communication and the body-to-bodycommunication with SISO

In our initial tests, we evaluated whether signal could be transmitted within the
body of test subject, as shown in Fig. 1(a), in order to conﬁrm the received powerof intra-body communication. Fig. 1(c) shows electrodes of the prototype. The
electrodes are probe type. The electrode surface was in contact with the wrist. For
the experiments on intra-body communication, we applied the electrodes directly
to both wrists of test subject, as shown in Fig. 1(d). We used a vector network
analyzer (VNA) to measure the received power of transmitted signals. The
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measurement was performed with subject’s electrode-ﬁtted arms which are horizontally extended and maintained in a static state. The electrodes and ground cables
were attached to both wrists and ankles of the subject and held in place withmasking tape. The received power was measured at a frequency band of
500 KHz–500 MHz. Ground terminals were wound around subject’s ankles andconnected with cables to place them at a sufﬁcient distance from the electrodes.
Fig. 1(b) illustrates the experimental method used for body-to-body communication. Like intra-body communication experiments, body-to-body communication is also evaluated by measuring the received power when signals are transmitted
from S1 to S2 by VNA. The signals by SISO transmission were transmitted between
two bodies of test subjects. The electrode was used for the wrist of each subject inorder to conﬁrm whether signals were transmitted between their bodies. As shownin Fig. 1(b), transmit distance, d between test subjects was set to be 1 m.
Fig. 1(e) shows the received power measured for intra-body and body-to-bodycommunications. These results are compared to the received power when electrodes
were not attached. The frequency is shown on the horizontal axis, and jS21 j as thereceived amplitude is depicted on the vertical axis. The range of frequency is from500 kHz to 500 MHz. The noise level is indicated at approximately −80 dB whenelectrodes are not attached (uninstalled). Intra-body communication shows a highreceived power level of −40 to −30 dB in all the frequency band, while body-tobody communication shows a received power level of −45 to −30 dB: these power
levels are much higher than the noise power level. These results conﬁrm thatsignals can be transmitted by both intra-body and body-to-body communications.
4© IEICE 2016
DOI: 10.1587/comex.2016XBL0096
Received May 2, 2016
Accepted May 19, 2016
Publicized June 2, 2016
Copyedited August 1, 2016

Comparison of channel capacity in body-to-body communication
using MIMO and SISO

In Sect. 3, body-to-body communication using SISO transmission was conﬁrmed
by jS21 j. In this section, the channel capacity of body-to-body communication byusing MIMO transmission is experimentally evaluated. The purpose of this experiment is to conﬁrm whether MIMO transmission can be utilized to improve thechannel capacity in terms of body-to-body communication. In this experiment, weused a four-port VNA for MIMO transmission. Fig. 2(a) illustrates an experimental
conﬁguration used for body-to-body communication by MIMO transmission. As
shown in Fig. 2(a), electrodes are applied to both wrists of each test subject. It is
veriﬁed whether signals were transmitted between their bodies, which are separated
by the distance of d ¼ 1 m. Therefore, unlike SISO measurements, four electrodes
were used and 2  2 MIMO transmissions were considered.
To reduce errors caused by the differences between individual test subjects,
three pairs of test subjects are evaluated (test subjects A, B, and C). We evaluatedthree different test subject pairs: A–B, B–C, and C–A. Fig. 2(b) shows the
propagation path of the 2  2 MIMO transmission. The right wrists were connected
to VNA ports S1 and S3 ; the left wrists were connected to S2 and S4 . Fig. 2(c)illustrates an experimental scene of body-to-body communication using MIMO
transmission. The measurement was performed with two subjects facing each otherwhile their arms were horizontally extended. Electrodes were attached to both arms.

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Fig. 2.

Body-to-body communication conﬁguration using MIMO
transmission

Body-to-body communication using SISO transmission was performed using thesame conﬁguration described in Sect. 3 and S1 and S4 were used in Fig. 2(b). In
addition, electrodes were in contact with the wrists. The copper wires connected to
the ground terminals were placed at an adequate distance from the wrist electrodes
by winding them around the ankles and connecting them with cables to eliminate
any potential difference. The measurement time was 60 s per measurement. The
measurement was performed ten times, and the average value of those ten measurements was obtained. The channel capacity by SISO and MIMO transmission was
obtained when the frequency bandwidth was changed.
Using Shannon capacity formula [5], Shannon capacity in SISO channel isexpressed as
CSISO ¼ log2 ð1 þ Þ ½bits=s=Hz:© IEICE 2016
DOI: 10.1587/comex.2016XBL0096
Received May 2, 2016
Accepted May 19, 2016
Publicized June 2, 2016
Copyedited August 1, 2016

Shannon capacity in MIMO channel is expressed as
CMIMO ¼ log2 det I þ HHH ½bits=s=Hz;
M
!
2
2


j
þ
jh
j
h
h
þ
h
h
jh
11
12
11
12
21
22
;
HHH ¼
h21 h11 þ h22 h12 jh21 j2 þ jh22 j2

ð1Þ

ð2Þ

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IEICE Communications Express, Vol.5, No.8, 272–277

where hij denotes the channel response for j-th and i-th transmitter and receiver. γ
is the signal-to-noise ratio (SNR), I is an identity matrix, and M is the number ofantennas (electrodes). Because our experiment was employed by 2  2 MIMO,
M ¼ 2 and HHH is a 2  2 channel matrix.
In these evaluations, the frequency range was 500 kHz to 500 MHz. The
measurement results of SISO and 2  2 MIMO transmission were compared, as
shown in Fig. 3. The channel capacity in SISO channel is obtained by using
the channel between S1 and S4 in Fig. 2. The SNR is 20 dB. The measurement
results are shown when the distance between test subjects is ﬁxed at d ¼ 1 m. For
three pairs of test subjects, the channel capacity is obtained at approximately
12 bits/s/Hz when using SISO transmission. For the MIMO transmission, thechannel capacity of approximately 20 bits/s/Hz is obtained. The channel capacity
obtained for 2  2 MIMO is approximately 1.6 times higher than that obtained
when using SISO. These results show that the channel capacity is increased by2  2 MIMO transmission, even for body-to-body communication.

Fig. 3.

5

Channel capacity using SISO and MIMO in the body-to-bodycommunication

Conclusion

In this paper, body-to-body communication was evaluated using 2  2 MIMO
channel. The experimental results indicate that MIMO transmission can provide achannel capacity at approximately 1.6 times higher than that of SISO transmission.
Therefore, it is conﬁrmed that MIMO transmission is effective for transmission rate
improvement, even when using the human body communication.

© IEICE 2016
DOI: 10.1587/comex.2016XBL0096
Received May 2, 2016
Accepted May 19, 2016
Publicized June 2, 2016
Copyedited August 1, 2016277