October 2015
34
E
mbedded
W
ireless
Dual wireless protocol solution
for the Internet of Things
By Tudor St ˘anescu,
Freescale
This article introduces
the Kinetis KW40Z MCU,
an ARM Cortex-M0+ based
ultra-low power wireless
microcontroller platform which is
a solution for addressing
multi-wireless protocol in
the ever-growing IoT space.
The Internet of Things (IoT) is here,
whether we know it or not. More and more,
the everyday objects around us are evolving
to include capabilities that connect the real
world to the virtual universe. From the edge
sensor node in your home to the vast cloud
infrastructure—data is flowing from physical
devices and enabling a virtual representation.
Whether it’s an IPv6 address, a QR code, or
some other means of identification, connec-
tivity capabilities are rapidly enabling a mass
deployment of the IoT.
When designing silicon for these sorts of con-
nectivity solutions, low resource consumption
is key: low power, low cost of materials, and
achieving just the right result with the least
effort. These requirements, plus the prolifera-
tion of terminals for mobile communications,
have made wireless the preferred method of
connecting the objects around us. Various
protocols that were developed for earlier mar-
kets (such as handheld Bluetooth accessories
or Smart Energy ZigBee®/802.15.4, which
met the requirements of the IoT space) were
enriched with technologies such as Bluetooth
Smart and Thread.
The IoT is as vast a concept as the Internet
itself, with the ability to grow and spread like
a living organism. The hardware that makes
up this organism varies in terms of complexity
and function. Sensor networks are vital organs
within the system, acting as organic sensory
appendages for all the data being created. As
in any data network, gateways that bridge two
networks or that connect a network and the
cloud are essential. Protocols such as Thread
define concepts like border routers, which
route IPv6 packets between a sensor network
and a regular LAN or WAN.
Another essential concept for protocol specifi-
cations in the IoT space (particularly inwireless
sensors networks) is network commissioning -
the collection of procedures for creating a net-
work to serve its intended purpose. One of the
procedures in this operation is adding a new
device to an existing wireless network. Usually
this involves a method of authenticating the
new device to the existing network using out-
of-band (OOB) data. The OOB credentials can
be obtained by using a secondary protocol. The
best example of this would be scanning a QR
code on a home automation device that needs
to be commissioned to the home automation
network with a tool, such as a mobile phone.
Gateways and network commissioning pres-
ent the need (and opportunity to fulfill that
need) of wireless sensor network devices to
have dual-protocol capabilities: the ability
to be part of two networks as a gateway, or
the ability to provide OOB data for commis-
sioning. Dual-mode devices are not a new
concept and they have been around since
the first systems-on-chip for mobile phones
that integrated Bluetooth or Wi-Fi. The IoT,
however, presents new challenges when it
comes to combining dual mode capabilities
with resource consumption requirements for
low power and low cost sensors. Because of
these constraints, dual-mode devices in the
wireless IoT space need to achieve the func-
tionality of both protocols via a single radio
frequency front-end through which the pro-
tocols are multiplexed. Multiplexing protocols
in a system with very low complexity (a lim-
ited number of logic gates in the silicon lay-
out) becomes the real design challenge, and an
opportunity for differentiation between man-
ufacturers. To best approach this challenge,
one must consider both the system architec-
ture and the protocols themselves.
The system architecture involves hardware
and software implementation of the layers of
the respective protocol stacks. In most cases
hardware starts at the lowest level (radio
front-end in the case of wireless devices)
and stops somewhere around layer 2, also
known as the data link layer. Above this level,
hardware automation/protocol acceleration
becomes impractical for IoT devices because
of their low resource consuming nature. The
Open Systems Interconnectivity (OSI) model
