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processing capability. For instance,
the Nordic nRF51822 uses an
ultra-low-power consumption ARM
Cortex M0 core for maximum power
efficiency, while the nRF52832 has
a Cortex M4 to support a broader
variety of applications. For a
majority of wearable applications,
an SoC design will provide the best
power efficiency, ease of integration
and development cost. As a single
chip design, SoC devices also lend
themselves to small form factor,
thin and light wearables.
With
its
ultra-low
power
consumption,
widespread
compatibility, and ease of
implementation using SoC modules,
it's no wonder Bluetooth Smart is
the number one wireless protocol
for wearable devices today.
NFC
While Bluetooth Smart is undeniably
important for wearables, it's not
the only game in town. Near-
Field Communication(NFC) plays
an important role as another,
often complementary wireless
communication protocol.
Unlike Bluetooth which allows
devices up to 30 feet away to
connect, NFC requires devices
to be within 10cm or even less -
practically touching. On the surface,
NFC's limited range seems like a
drawback, but in fact it's key to its
success.
By requiring devices to be in
extremely close proximity, NFC
inherently makes sure that the right
devices are connected. Whereas
Bluetooth has a complicated pairing
process involving selecting the right
device and entering passcodes, NFC
connections are "tap and go". Users
simply tap the devices together
connection, transmit a message,
and close the connection in tens of
milliseconds. This fast messaging
doesn't just make for responsive
devices, but also helps Bluetooth
Smart minimize power consumption
by maximizing the time the radio is
turned off. Combined with a peak
transmit power of about 15mA, this
allows extremely efficient power
usage, and there are Bluetooth
Smart devices which can last
months or even years off coin cell
batteries.
Security is essential for medical
applications and Bluetooth Smart
doesn't disappoint. It uses robust,
128-bit AES-CCM encryption, and
Elliptic curve Diffie-Hellman key
generation for protection against
eavesdropping.
Implementing Bluetooth Smart can
be done using network processors,
HCI modules, or SoC chips.
Network processors, also known
as connectivity ICs, are Bluetooth
radio modules with low power MCUs
which implement the Bluetooth
stack, minimizing the load on the
host processor. This makes them
appropriate for devices with a low
power MCU.
HCI modules are bare-bones
Bluetooth radio modules which
implement physical and link layer,
and rely on the host system to
implement the upper layers of the
Bluetooth stack. HCI modules are
appropriate for devices which have
a powerful host processor with the
resources to run the Bluetooth stack
in addition to application logic.
SoC chips combine Bluetooth radios
with relatively powerful MCUs which
can run the entire Bluetooth stack
along with application logic all on the
same chip. These can range in their
Medical Devices
Special Edition
and a connection is automatically
established, messages transmitted,
and the connection closed.
The quick and intuitive usage of
NFC makes it particularly attractive
for elderly populations as well
as hospital staff, as it means
equipment can be deployed with
minimal training.
The quick tap and go connections
used by NFC are also well suited
for clinical settings where multiple
devices might need to be read
by a centralized smartphone or
other NFC reader. With Bluetooth,
a connection would have to be
manually setup for each separate
device sequentially, but with NFC,
each device is simply tapped as it
needs to be read, without having
to wade through a list of possibly
dozens of devices in the vicinity.
NFC's other main draw is its
extremely
attractive
power
consumption characteristics. NFC
devices can often be passively
powered - meaning the NFC device
is powered by the RF field generated
by the NFC reader. The amount of
power generated is small, with a
typical figure of 4mA at 3.3V, but
it's enough to power simple sensor
readings.
Without the need for a battery,
incredibly small and thin form
factors can be made, making NFC
an ideal technology for skin patch
sensors, implantables, or clothing.
Because of its need for close
proximity between devices, NFC
provides a basic yet effective form of
physical security and authentication,
and greatly reduces the possibility
of Man-in-the-Middle attacks. Like
Bluetooth Smart, NFC also supports
AES encryption, and Diffie-Hellman
key exchange if an additional level
44 l New-Tech Magazine Europe