IEEE Solid-State Circuits Magazine - Fall 2017 - 37

communication protocol and is able
to listen in (eavesdrop) or exchange
data with the medical device to mod-
ify its behavior (man in the middle).
The solution for wireless devices is
to implement encryption and authen-
tication with secure key exchange.
But again such techniques can be chal-
lenging under low power constraints,
and further advances in this area
are needed. Under a denial of service
attack, the wireless medical device is
prevented from communicating either
by RF jamming or by flooding the net-
work with legitimate connection/data
transmission requests. Sophisticated
jamming techniques that exploit pro-
tocol features or weaknesses can
be difficult to detect and have been
demonstrated for wireless medical
systems based on Wi-Fi and Zigbee
[8]. This presents an argument for
wireless medical monitoring devices
to use modified or custom protocols
that cannot be so easily understood
and replicated.

peak transceiver current consump-
tion of 5 mW was achieved to allow
additional overhead for vital-sign
sensing, digitization and process-
ing, and other system housekeeping
functions. The transceiver operates
in the 868/915 MHz ISM bands as
this gives a good tradeoff between
antenna size, range, and power con-
sumption [12] and allows a 30-m range
with a transmit power of ~100 uW.
Key to robust wireless system opera-
tion at very low power levels is a custom
hardware medium access control-
ler, implementing many of the key

control functions in efficient low-power
hardware, including RF channel selec-
tion, channel access, link establish-
ment, forward error correction, data
transfer, and sleep management [13]. In
many other transceivers, such func-
tions would be run at a higher layer
in software, allowing for greater flex-
ibility but with a resulting higher
power usage.
Since the development of this SoC
and system, Bluetooth low energy
(BTLE) has emerged as a popular low-
power wireless technology for wire-
less sensing and the Internet of

SensiumVitals Patch

SensiumVitals Bridge

A Wireless Solution for
General Care Patient Monitoring
Low-power, wearable, and wireless
vital-sign monitors for the early de-
tection of patient deterioration on
general wards are available on the
market. One of the first such devices
to become commercially available as
a CE-marked and FDA 510K-cleared
medical device is the SensiumVi-
tals system, as shown in Figure 1
[9]. At the heart of this system is a
single-use wearable wireless patch
that is attached to the patient's torso
and monitors heart rate, respiratory
rate, and temperature and transmits
up dated readings to wall-mounted
bridges every 2 min.
This patch is based on a dedicated
system-on-chip (SoC) incorporating
a custom wireless protocol designed
to minimize power consumption and
cost and obtain a five-day battery life
from a single CR2032 coin cell [10].
To maximize battery life, the peak
current drain must be lower than
10 mA [11]. In this SoC, peak current
consumption is dominated by the
transceiver when active, and thus a

MG Service
Monitoring
Gateway Service
Controls Bridges
Tracks Patches
No Patient Names

Application
Server
(Provides MAS
and MG Services)
MAS Service
Monitoring
Application Service
Links Patient ID
to Patch
Notifications Sent
Via E-mail
User Interface
(Using https)

Database
Server

Connects to ADT
and EMR System

Wireless Monitoring
Application Screen

Notifications Sent to
Handheld Devices

FIGURE 1: A wireless patient monitoring system for the early detection of deterioration on
general care wards. (From [9], used with permission.)

IEEE SOLID-STATE CIRCUITS MAGAZINE

FA L L 2 0 17

37
Table of Contents for the Digital Edition of IEEE Solid-State Circuits Magazine - Fall 2017
