Wireless Sensor Networks
Wired networks such as controller
area networks (CAN) for automobiles
would have to experience a BER of no
more than 10-6 in order to have undetected
corrupted messages occur less
than once per year for the vehicle fleet
8 while the popular MIL-STD-1553B
for avionics boosts BERs as low as
10-12. Most IWSN standards leverage a
combination of Time Division Multiple
Access (TDMA), Frequency Division
Multiple Access (FDMA), and Carrier
Sense Multiple Access with Collision
Avoidance (CSMA/CA) of medium access
control (MAC) protocols. The main
difference between wired and wireless
MAC protocols generally stems from
the ability to detect collisions on the
medium while sending (e.g., CSMA/
CD) 9. Since this is not possible over
the wireless medium, quality of service
(QoS) analysis can be leveraged in
IWSNs to measure packet loss, bandwidth,
and delay. Moreover, additional
MAC protocols can be utilized to increase
the determinism of WSN.
Preliminary models are also being
proposed that leverage binary countdown
protocols 9, employ a collisionfree
MAC protocol 10, attempt to
approximate carrier sense multiple
access with collision detection (CSMA/
CD) using the proposed carrier sense
multiple access with collision notification
(CSMA/CN) 11, uses an additional
carrier sensing (ACS) algorithm to
enhance the carrier sensing mechanism
in the IEEE 802.15.4 CSMA/CA protocol
12, and leverages new channel access
mechanism for a low latency deterministic
network (LLDN) superframe
in a star topology 13. The CSMA/CA
protocols generally suffer energy waste
due to collisions and unpredictable
end-to-end delays so TDMA mechanisms
are employed in standards such
as WirelessHART and ISA100.11a for
a more assured QoS with reservationbased
medium access. Improvements
over these standards are proposed that
use a time-synchronized mesh network
with short time slots where the device
and overarching network operations are
synchronized 14.
SECURITY
Security ranks amongst the top concerns
for IWSN end users (Figure 2).
As shown in Table 1, there are several
major aspects to security including
data confidentiality, integrity, availability,
freshness, and authenticity 15.
Strengthening all these aspects of
security protect an IWSN against both
passive (e.g., transmission eavesdropping
and sniffing) and active attacks
(e.g., physical modification, Denial of
Service, data falsification, and interruptions
of service).
WSN STANDARDS
As shown in Figure 3, as of 2014 one in
four WSN adopters utilize the WirelessHART
topology with the high 99%
network reliability while one in ten are
leveraging the ISA100.11a specification.
However, in the past two years,
ISA100.11a adoption has increased
67% for its flexible time scheduling and
software tunneling 16. For low powered
and long reach Low Power Wide
Area Network (LPWAN) technology has
growing interests. This topology boasts
up to 10-year battery-powered wireless
sensors with communication links up
to 20 miles. While this technology may
not be best-suited for secure, timesensitive
and high reliability applications,
it ranks highly in ease of use and
scalability.
CONCLUSION
From environmental sensing, to condition
monitoring, and process automation,
IWSN service a broad range
of applications. While ZigBee and
MiWi generally service home automation
applications, WirelessHART and
ISA100.11a are specifically designed for
an industrial environment. Traditional
wired industrial architectures do experience
a greater level of determinism and
a level of scalability with industrial Eth -
ernet. Still, IWSNs surpass any wired
network in modularity, ease of use, and
cost-effectiveness.
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