ETSI TR 103 751 V1.1.1 (2021-04)

Smart Body Area Networks (SmartBAN); Implant communications

DTR/SmartBAN-003

General Information

• Status: Not Published
• Technical Committee: SmartBAN - Smart Body Area Network
• Current Stage: 12 - Completion
• Due Date: 10-May-2021
• Completion Date: 16-Apr-2021

Standards Content (Sample)

ETSI TR 103 751 V1.1.1 (2021-04)






TECHNICAL REPORT
Smart Body Area Networks (SmartBAN);
Implant communications

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2 ETSI TR 103 751 V1.1.1 (2021-04)

Reference
DTR/SmartBAN-003
Keywords
health, implants, protocol

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ETSI

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3 ETSI TR 103 751 V1.1.1 (2021-04)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 7
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Symbols . 7
3.3 Abbreviations . 7
4 Introduction and Background . 8
5 Implant UWB Communication System . 9
5.1 Transmitter structure . 9
5.2 Receiver structure . 9
6 Fundamental Performance Evaluation . 10
6.1 Setup . 10
6.2 Results and Discussions . 11
7 Evaluation with Living Animal Experiment . 11
7.1 Setup . 11
7.2 Results and Discussions . 12
8 MIMO Transmission for Implant UWB-IR System . 13
8.1 Antenna Development for Implant Side Polarization Diversity . 13
8.2 Experimental Evaluation on Path Loss Characteristics . 13
8.3 Improvement of communication performance . 14
9 Implantable Device Localization with UWB Communications . 15
9.1 Location Estimation System Based on RSSI . 15
9.2 Experimental Evaluation on RSSI-Based Localization . 16
9.3 Location Estimation System Based on TOA . 17
9.4 Performance Evaluation on TOA-Based Localization . 18
History . 20


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4 ETSI TR 103 751 V1.1.1 (2021-04)
List of figures
Figure 1: Implant UWB-IR system structure . 9
Figure 2: An example of UWB-IR modulated signals . 9
Figure 3: Examples of shapes of transmitted and received signals .10
Figure 4: Path loss characteristics of liquid phantom .10
Figure 5: BER performance evaluation in liquid phantom experiment .11
Figure 6: Overview of living animal experiment .12
Figure 7: BER performance evaluation in living animal experiment .12
Figure 8: Developed diversity antenna for implant UWB communication (a) Planar elliptical loop antenna (b) Bird's-eye
view of the dual-polarized diversity antenna .13
Figure 9: Overview of experimental environment with a living animal .14
Figure 10: Measured path loss performance in the experiment .14
Figure 11: Cumulative distribution function of SNR characteristics.15
Figure 12: Location estimation system .16
Figure 13: Experimental setup for RSSI-based localization system .16
Figure 14: Cumulative distribution function on position estimation error .17
Figure 15: Validation results for relative permittivity estimation model .18
Figure 16: RMSE location estimation error for TOA-based location estimation method .19
Figure 17: c.d.f. of location estimation error for TOA-based localization .19


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5 ETSI TR 103 751 V1.1.1 (2021-04)
List of tables
Table 1: Parameters of communication performance evaluation .14


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6 ETSI TR 103 751 V1.1.1 (2021-04)
Intellectual Property Rights
Essential patents
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pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
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Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Smart Body Area Network (SmartBAN).
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.

ETSI

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7 ETSI TR 103 751 V1.1.1 (2021-04)
1 Scope
The present document has the scope to evaluate ultra-low power, Ultra-WideBand technology (UWB) for a
swallowable, pill-camera, wireless medical device operating in the 3,1 GHz to 10,6 GHz frequency band within the
context of Smart Body Area Networks (SmartBAN).
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
Not applicable.
3 Definition of terms, symbols and abbreviations
3.1 Terms
Void.
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ADC Analog-to-Digital Converter
BAN Body Area Network
BER Bit Error Rate
BPF Band Pass Filter
BPSK Binary Phase Shift Keying
CMOS Complementary Metal Oxide Semiconductor
CT Computed Tomography
FDTD Finite-Difference Time-Domain
FPGA Field Programmable Gate Array
FSK Frequency Shift Keying
IR Impulse Radio
MICS Medical Implant Communication Service
MIMO Multiple-Input Multiple Output
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8 ETSI TR 103 751 V1.1.1 (2021-04)
ML Maximum Likelihood
MPPM Multi Position Pulse Modulation
MRC Maximum Ratio Combining
MRI Magnetic Resonance Imaging
OFDM Orthogonal Frequency Division Multiplexing
RF Radio Frequency
RMS Root Mean Square
RMSE Root Mean Square Error
RSSI Received Signal Strength Indicator
SNR Signal-to-Noise power Ratio
TOA Time Of Arrival
UWB Ultra WideBand
WCE Wireless Capsule Endoscope
4 Introduction and Background
BANs attracted a lot of attention as a future technology for wireless networks. Typical applications of wireless BANs
include healthcare, medical treatment and medical monitoring Generally, wireless BANs are classified into two groups:
wearable BANs and implant BANs. Wearable BANs are mainly used to monitor a person's healthy condition in daily
life, whereas Wireless Capsule Endoscopy (WCE) has been one of the most important applications in implant BANs.
WCE involves swallowing a small capsule by a patient, which contains a colour camera, light source, battery and
transmits images to the outside receiver in order to assist in diagnosing gastrointestinal conditions such as obscure
malabsorption, gastrointestinal bleeding, chronic diarrhoea and abdominal pain. The present document focuses on
implant BAN applications. Such a medical application requires a reliable wireless communication channel and
extremely low power consumption for increasing device longevity.
To realize the implant communications, the 400 MHz band and 2,4 GHz band are usually chosen. For example, a
commercially available implant communication chip for cardiac pacemaker employs the 400 MHz band for data
transmission and the 2,4 GHz band for waking-up and control. It has been reported that all of WCE techniques employ
400 MHz, 2,4 GHz or dozens of MHz band with narrow-band modulation schemes, such as Frequency Shift Keying
(FSK) or Binary Phase Shift Keying (BPSK). The data rate is limited to several hundred kbps. However, in view of the
implant communication application, for instance, WCE requires a higher data rate for a real-time image and video
transmission.
In order to satisfy the above requirements, the present document pays attention to Ultra-Wideband (UWB) transmission.
As UWB transmission schemes, UWB-Impulse Radio (UWB-IR), direct sequence-UWB (DS-UWB), and multiband-
Orthogonal Frequency Division Multiplexing (multiband-OFDM) have been considered so far. Of all UWB schemes,
UWB-IR is a technique that iteratively transmits extremely short pulses on the nanosecond time duration per bit.
Therefore, it has merit in respect of low power consumption. Furthermore, coherent detection, namely correlation
detection, claims to be one of the most suitable solutions for the UWB-IR communication system. Although the
coherent detection needs to generate a template signal in the receiver side, the reliability of the coherent detection is
generally superior to that of a non-coherent detection.
In implant BANs, the UWB-IR signals suffer from large attenuation, which may lead to undesired performance
degradation. Therefore, it is important to investigate the transmission performance of the implant BANs. The present
document aims to analyse the basic characteristics of the UWB-IR communication system by a liquid phantom
experiment and then, evaluate the realistic performance of the implant UWB-IR system in a living animal experiment.
In addition, Multiple-Input Multiple-Output (MIMO) technology is then considered for further improving the implant
UWB communications. For this purpose, an example of implant side diversity antenna is developed, and the
fundamental performance of the developed implant antenna is experimentally evaluated. Based on the measurement
results, the communication performance improvement is discussed.
In the present document, the location estimation of an implantable device in UWB communications is also discussed. In
medical treatments with implantable devices, it is important to estimate their locations accurately. So far, several kinds
of localization methods have been proposed, such as magnetic field-based, Radio Frequency (RF) wave-based, and
acoustic-based technologies. The present document pays attention to the Received Signal Strength Indicator (RSSI)-
based localization because RSSI can be measured by a fundamental function in modern wireless communication
systems without any additional special devices. High distance resolution of UWB (Ultra Wideband) communication
signals is expected to achieve, as compared with a typical 400 MHz MICS band. In addition, this paper introduces an
example of implant device localization systems based on UWB communications, and then discuss the achievable
location estimation accuracy in a real environment.
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9 ETSI TR 103 751 V1.1.1 (2021-04)
5 Implant UWB Communication System
5.1 Transmitter structure
The structure of the transmitter is shown in Figure 1(a). As a UWB-IR pulse, the first order Gaussian monocycle pulse
is employed, and this transmitter uses a Multi-Pulse Position Modulation (MPPM) scheme, which can control the trade-
off relationship between the data rate and the reliability of the transmission. Figure 2 shows an example of MPPM
signals when the number of chip slots L is set to 4, in which two UWB-IR pulses are assigned to each transmitted
symbol. It is possible to control the data rate by changing the number of chip slots L. It is noted that the IR-type
transmitter does not need a carrier signal and amplifiers. It employs a clock generator and some CMOS gates to produce
pulses and a Band Pass Filter (BPF) for spectrum forming. Since CMOS gates consume low power and the passive BPF
does not consume power, the total power consumption in the transmitter can be expected at a quite low level.
UWB-IR front-end
Frequency r(t)
Bit sequence b s(t)
k
Comparator
LNA BPF
MPPM
down-converter
generator
p(t)
Symbol timing Template signal
Pulse generator
synchronization generator
(a) Transmitter (b) Receiver

Figure 1: Implant UWB-IR system structure

Figure 2: An example of UWB-IR modulated signals
5.2 Receiver structure
Figure 1(b) shows the structure of the receiver. From pre-measurement of the implant channel characteristics, it is found
that the power delay profile can be well represented as a two-path model with a very small mean time interval in the
order of nanoseconds. This means that the multipaths are almost indistinguishable in the received signal and the
multipath fading effect is not dominative. Therefore a detection system without any channel estimation is suitable for
the implant communications, so the correlation detection is herein considered as the receive detection scheme. In the
correlation detection, since the binary MPPM chooses one from two location assignments, two kinds of energies for the
corresponding pulse locations from the received signal are calculated. It is noted that the receiver requires no threshold
for the detection. In Figure 1(b), the symbol timing synchronization is realized with pilot signals sent from the
transmitter.
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10 ETSI TR 103 751 V1.1.1 (2021-04)
6 Fundamental Performance Evaluation
6.1 Setup
This clause demonstrates the fundamental performance of the implant UWB-IR communication system. For this
purpose, the fundamental characteristics are experimentally measured in a liquid phantom environment simulating a
human body. In this experiment, the helical antenna as an on-body receive antenna is used on the liquid phantom
surface with a spacing of 1 cm. The in-body transmit antenna is a one-wavelength loop antenna. A type of glue is coated
to the antenna and feeding part for preventing a direct contact of the antenna to the liquid. The transmit antenna was
inserted in the liquid phantom. The liquid phantom was produced to simulate muscle-like dielectric properties. It is
confirmed that the dielectric properties of the vessel and found that its loss is almost ignorable. The transmit and receive
antennas are connected to a network analyser with coaxial cables. The two coaxial cables were arranged at a right angle
each other for removing possible direct coupling between them. Figure 3 shows examples of shapes of the transmitted
and received UWB signals. The S performance is measured, namely the path loss characteristic, as a function of the
21
distance from the implant transmit antenna to the phantom surface at the frequency band of 4 GHz. The measured path
loss characteristics are shown in Figure 4. It is found that at a depth of 70 mm from the body surface, the path loss is
around 80 dB. Such a path loss level may be acceptable in present transceiver design technology.
0.4
0.3
0.2
1.5 V
0.1
0.0
100 psec
-0.1
0 10 203040 50
Time (usec)
(b) received signal
(a) trasnmitted signal

Figure 3: Examples of shapes of transmitted and received signals
90
Frequency band: 4 GHz
80
70
60
50
40
30
20 30 40 50 60 70 80 90
Distance from phantom surface (mm)

Figure 4: Path loss characteristics of liquid phantom
ETSI
Path loss (dB)
Voltage (V)

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11 ETSI TR 103 751 V1.1.1 (2021-04)
6.2 Results and Discussions
The BER performance of the UWB-IR transceivers is calculated based on the path loss measurement results in the
liquid phantom experiment. It is assumed that the transmitter and the receiver were connected with an attenuator in
order to accurately control the path loss according to the distance between transceivers, and then the BER is calculated
from the comparison between the transmitted bit sequence and the received bit sequence. As for the symbol timing and
sampling clock synchronization, it is almost perfectly performed with a proper length of pilot signals in the experiment.
Moreover, the optimal detection time is also determined before conducting the experiment.
Figure 5 illustrates the average BER performances by the experiment and the theoretical analysis against the distance
between transceivers. Good agreements are observed between the results of the experiment and the theory. Furthermore,
as seen from Figure 5, the BER performance is improved as the data rate decreases (namely, L increases). Note that the
-2
BER performance of 10 is accomplished at the distance of around 70 mm when L = 16 (namely, the data rate is
-2 -3
1 Mbps). The achievement of the BER performance of around 10 to 10 means that it is possible to obtain an error-
-10
free BER (< 10 ) if an adequate forward error correction code is adopted. This error-free BER satisfies the requirement
for almost all implant BAN applications. Therefore, the developed UWB-IR communication system can establish a
reliable communication link at the maximum distance of 70 mm in the biological-equivalent liquid phantom.
0
10
Experiment (8Mbps, L = 2)
Theory (8Mbps, L = 2)
Experiment (2Mbss, L = 8)
Experiment (1Mbps, L = 16)
-1
10
-2
10
Theory (2Mbps, L = 8)
-3
10
Theory
(1Mbps, L = 16)
-4
10
60 61 62 63 64 65 66 67 68
Distance from phantom surface (mm)

Figure 5: BER performance evaluation in liquid phantom experiment
7 Evaluation with Living Animal Experiment
7.1 Setup
Figure 6 shows an overview of the living body experiment with the developed UWB-IR system. In the living body
experiment, a living animal (pig) is used instead of a human body because it is difficult to conduct an experiment with a
living human body in our environment. The transmit antenna is implanted into the pig, and the receive antenna is put on
the pig-body's surface. The transceivers and each antenna are connected with coaxial cables. For the received data
capture, a laptop computer is connected to the receiver. The insertion points of the transmit antenna and the positions of
the transmit antennas are shown in Figure 6, which indicates the transmit antenna positions when the insertion point is
in the centre of the abdomen and the thorax (chest). In the experiment, the transmit antenna is covered with a vinyl
material for insulation. The receive antenna is just above the transmit antenna on the body surface.
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BER

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12 ETSI TR 103 751 V1.1.1 (2021-04)
Insertion point
Head Head
of transmit antenna
Receiver Laptop computer Position of
B
D, E
C
transmit antenna
Distance between tranmi t
A
and receive antennas
Transmitter
Living animal body
Body
Body
Center of the abdomen Thorax (chest)

Figure 6: Overview of living animal experiment
7.2 Results and Discussions
Figure 7 illustrates the BER performance against the distance between transmit and receive antennas in the case of the
Vivaldi-type receive antenna and the helical-type receive antenna. In this figure, the antenna position IDs are also
indicated. Note that, in both antenna cases, no bit error is observed at the distance of 22 mm (Position ID: A), and
moreover, in the helical antenna case, no bit error is observed also at the distance of 33 mm (Position ID: D). As for the
-3
reason that there is a sharp drop after 10 at 2 Mbps and 1 Mbps, it is because that the transmitted data number is not
sufficient for giving an average BER in this order. Similarly to the result of the fundamental characteristic investigation
in the previous clause, the evaluation results illustrate that the BER performances are inversely proportional to the data
rate. Furthermore, as the distance between the antennas increases, the BER performance is getting worse due to the
corresponding path loss in the biological tissues.
However, the BER at a distance of 80 mm exhibited a worse performance compared to that at 120 mm, which means
that the BER performances are not always getting worse when the communication distance increases. This is because of
the difference in the types and thickness of the tissue between the transceivers. A high-water-content tissue such as
muscle and peritoneal fluid has a larger path loss, whereas a low-water- content tissue such as fat and bone has a
smaller path loss. The implant communication performance is therefore dependent on not only the distance but also the
types and thickness of the tissue between the transceivers, which explains why the results for the antennas place
...