Wireless personal-area
networks (WPANs)
are exceptionally useful
for sensing, monitoring,
and control applications.
Cost-effective WPANs have the
unique potential to implement wireless
connectivity in many end products
where this functionality wasn’t
considered previously. A thorough,
fact-based, logical, and organized
evaluation of key WPAN design
factors can closely manage system
financial objectives, increasing end
product value with a positive rate
of return, while still achieving key
wireless design objectives.
Sensing, monitoring, and control solutions drive specific
consideration factors for WPAN implementation. Ranges
for low-cost wireless networks in sensing, monitoring, and
control applications encompass those distances of 300 m
or less and data rates of 250 kbits/s or less. In WPAN end
node designs, it’s often necessary to extend battery life to
the optimum to meet product needs.
By proactively analyzing several key factors before
design work begins, the embedded engineer can enhance
the results of the final wireless network implementation.
Developing and examining these key factors in a matrix
format will aid the design engineer in the component and
solution selection analysis process.
Reference design schematics, bills of materials, and
other application information may also be gathered as a
baseline for design initiation. An example wireless UART
(universal asynchronous receiver/transmitter) reference
design is included with this article.
It’s recommended that the embedded engineer consider
review of the following areas in relation to WPAN design
requirements: integration, wireless networking topologies,
radio (RF modem or transceiver), performance, operating
voltage, data rates, range, channel flexibility, output power,
sensitivity, power management, peripherals, clocking, multitier
software, ease of hardware and software design,
antenna design, and packaging.
Also, when considering an integrated solution or a discrete
solution, the microcontroller (MCU) should be evaluated
with the following factors in mind: CPU features, performance,
memory options, power management, clock
source options, analog-to-digital conversion, peripherals,
packaging, in-circuit debug and programming capabilities,
and ease of software and hardware design. Such analysis
will provide an organized perspective for engineering decisions,
an avenue toward design success, a fast time-tomarket,
and an easier implementation of cost-effective
wireless networking.
INTEGRATION
A variety of implementation alternatives for low-cost wireless
networking can offer the engineer a high level of flexibility
in the design process. As one alternative, consider
solutions from one-stop-shopping providers that offer various
configurations of standalone transceivers to be used
with a wide selection of microcontrollers (Fig. 1).
As a second and equally effective alternative, consider
the newest solutions that offer integrated transceiver/MCU products. Reusing design components
and engineering investment
may be important as designers
work on multiple, yet similar, end
products. Therefore, a structured
evaluation of solution options can
be both cost- and resource-efficient.
Well-thought-out research
can mold a basis for several end
products to be designed from a
single foundation (Fig. 2).
WIRELESS NETWORKING
TECHNOLOGIES
The 2.4-GHz ISM band supports multiple
short-range wireless networking
technologies. Each alternative has been
developed to optimally serve specific
applications or functions. The networking
topologies most commonly associated to
the 2.4-GHz frequency range are Bluetooth,
Wi-Fi, and ZigBee, as well as other
proprietary solutions (see the table).
Each solution is suitable for WPANs.
However, some offer extended capabilities
that align best with sensing, monitoring,
and control application needs.
Non-standards-based proprietary solutions
may be considered, too. But such
solutions may pose some risk to the
designer since they’re vendor-dependent
and could be subject to change.
ZigBee, an IEEE 802.15.4 standardsbased
solution as defined by the ZigBee
Alliance (www.zigbee.org), was created
to address networks that require low
power consumption, low data rates, reliability,
and security. The ZigBee solution
accommodates network-specific support
mesh networking, network recovery
and healing, device interoperability,
and vendor independence. The ZigBee
solution frequencies are typically in the
868/915-MHz or 2.4-GHz spectrums.
ZigBee technology solutions have a
250-kbit/s data rate. Power consumption
must be extremely low to optimize
battery life for months or even years of
operation (often equivalent to the shelf
life of the battery) using alkaline or lithium
cells. ZigBee technology theoretically
supports up to 65,000 nodes. Common
applications in sensing, monitoring,
and control that are best supported by
a ZigBee technology solution include
personal and medical monitoring;
asset management, status, and tracking;
security, access control, and safety
monitoring; fitness monitoring; process
sensing and control; energy management;
home automation; heating, ventilation,
and air-conditioning sensing and
control; building automation; industrial
automation; and many others.
Some WPANs may be as simple as
single point-to-point or star configurations.
Depending on the application, other
proprietary wireless solutions similar
to ZigBee may offer the best match of
ease of design versus system capability.
One low-complexity example is the
simple media access controller, or SMAC.
Look for solutions in this space where the
vendor offers easy-to-use source code
to speed time-to-market for simple networks.
The IEEE802.15.4 standard-compliant
media-access-controller (MAC)
solution supports more complex configurations
with packet and streaming data
modes, beaconed and non-beaconed
networks, and 128 AES data encryption.
Providers that offer multiple levels of
stack capability give embedded engineers
the opportunity to reuse their
design software for a variety of WPANs,
including those with varying levels of
complexity. Multiple stack solutions act
as the foundation on which the embedded
engineer can easily set up the radio
and focus most of the design effort on
the application software.
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