23-08-2012, 05:15 PM
Performance of ZigBee-Based wireless sensor nodes for real-time monitoring of fruit logistics
Performance of ZigBee-Based wireless sensor nodes.pdf (Size: 1.53 MB / Downloads: 68)
Abstract
Progress in fruit logistics requires an increasing number of measurements to be performed in refrigerated chambers and during transport.
Wireless sensor networks (WSN) are a promising solution in this field. This paper explores the potential of wireless sensor
technology for monitoring fruit storage and transport conditions. It focuses in particular on ZigBee technology with special regard to
two different commercial modules (Xbow and Xbee). The main contributions of the paper relate to the analysis of battery life under
cooling conditions and the evaluation of the reliability of communications and measurements. Psychrometric equations were used for
quick assessment of changes in the absolute water content of air, allowing estimation of future water loss, and detection of condensation
on the product.
2008 Elsevier Ltd. All rights reserved.
Keywords: Perishable products; Postharvest; Information technologies; Motes; Cold chain
1. Introduction
Fruits and vegetables are submitted to a variety of risks
during transport and storage that are responsible for material
quality losses. Among them are intrinsic biological and
chemical processes that fresh produce undergoes after harvest,
related to a lack of appropriate control on duration,
temperature and humidity, which causes senescence and
rot. As a consequence, effective cold-logistics monitoring
is fundamental for ensuring product quality along the supply
chain (Rodrı´guez-Bermejo et al., 2007).
Wireless sensors networks (WSN) is a very promising
technology in this field. A wireless sensor network is a
system comprised of radio frequency (RF) transceivers,
sensors, microcontrollers and power sources (Wang et al.,
2006). Instrumented with a variety of sensors, such as temperature,
humidity and volatile compound detection, WSN
allow transport monitoring of perishable food products to
be accomplished in a distributed way (Callaway, 2004).
The use of wireless intelligent sensors inside refrigerated
vehicles was proposed in 2004 by Qingshan et al. (2004).
Subsequently, Fuhr and Lau (2005) tested a RF device in
a metal cargo container and demonstrated that it is possible
to communicate with the outside world. Craddock and
Stansfield (2005) proposed sensor fusion for the development
of smart containers in order to improve security,
gathering data from several sources in order to trigger
the alarms. Containers may incorporate a variety of sensors
to detect, identify, log and communicate what happens
during their journeys around the world. Jedermann et al.
(2006) presented a system for intelligent containers combining
wireless sensor networks and RFID (Radio Frequency
Identification). Ruiz-Garcia et al. (2007) analyzed
monitoring intermodal refrigerated fruit transport, facing
the integration of wireless sensor networks with multiplexed
communications and fleet management systems.
Such devices can be placed in transport vehicles in order
0260-8774/$ - see front matter 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jfoodeng.2007.12.033
* Corresponding author.
E-mail address: luis.ruiz[at]upm.es (L. Ruiz-Garcia).
www.elsevierlocate/jfoodeng
Available online at www.sciencedirect.com
Journal of Food Engineering 87 (2008) 405–415
to monitor the on-the-go environment and can be the basis
for distributed systems, enabling environment sensing
together with data processing. Behrens et al. (2007) studied
the relation of battery lifetime and temperature in WSN,
controlling the topology of the network in order to optimize
energy-efficiency.
To date there has been no experimentation regarding
fundamental factors in this field, such as node location
inside the cargo, battery life and reliability of instrumentation
under cooling conditions. Thus, experimentation
in conventional refrigerated chambers could provide valuable
information for near-future implementation in
transports.
WSN can operate in a wide range of environments and
provide advantages in cost, size, power, flexibility and distributed
intelligence compared to wired ones. Wireless sensor
networks offer permanent online access to the condition
of freight. In a network, if a node cannot directly contact
the base station, the message may be forwarded over multiple
hops. By auto configuration set up, the network could
continue to operate as nodes are moved, introduced or
removed. Monitoring applications have been developed
in medicine, agriculture, environment, military, machine/
building, toys, motion tracking and many other fields
(Akyildiz et al., 2002; Baronti et al., 2007; Jedermann
et al., 2006). Architectures for sensor networks have been
changing greatly over the last 50 years, from the analogue
4–20 mA designs to the bus and network topology of
today. Bus architectures reduce wiring and required communication
bandwidth. Wireless sensors further decrease
wiring needs, providing new opportunities for distributedintelligence
architectures (Maxwell and Williamson, 2002;
Wang et al., 2006).
For fieldbus architecture, the risk that cutting the bus
that connects all the sensors persists. WSN eliminates all
the problems arising from wires in the system. This is the
most important advantage of using such technology for
monitoring.
New miniaturized sensors and actuators based on microelectromechanical
systems (MEMS) are in the development
stage. Available MEMS include inertial, pressure, temperature,
humidity, strain-gage, and various piezo and capacitive
transducers for proximity, position, velocity, acceleration
and vibration measurements (Wang et al., 2006). According
to several research works, connecting wires to these devices
can be more problematic than doing it by means of wireless
designs (Jackson et al., 2008; Wise, 2007).
Another advantage for wireless sensor devices is the feasibility
of installation in places where cabling is impossible,
such as large concrete structures (Norris et al., 2008) or
embedded within the cargo, which brings their readings
closer to the true in situ properties of perishable products.
Wired networks are very reliable and stable communication
systems for instruments and controls. However, wireless
technology promises lower installation costs than wired
devices, because required cabling engineering is very costly
(Maxwell and Williamson, 2002; Wang et al., 2006).
At the current stage there are two available standard
technologies for WSN: ZigBee and Bluetooth. Both are
within the Industrial Scientific and Medical (ISM) band
of 2.4 GHz, which provides license-free operations, huge
spectrum allocation and worldwide compatibility. ZigBee
is more suitable for WSN, mainly because of its low power
consumption derived from its multi-hop communication.
The power consumption in a sensor network is of primary
importance and it should be extremely low. The ZigBee
protocol places primary importance on power management.
It has been developed to allow low power consumption
and years of battery life. The suitability of this
standard for monitoring has been proposed by various
authors (Qingshan et al., 2004; Baker, 2005; Wang et al.,
2006; Jedermann et al., 2006; Ruiz-Garcia et al., 2007).
Bluetooth works better in applications where large data
rates are important, though it requires more energy (Shih
et al., 2001). Bluetooth devices have lower battery life compared
to ZigBee as a result of the processing and protocol
management overhead which is required for ad hoc
networking.
ZigBee provides higher network flexibility than Bluetooth,
allowing different topologies such as star, cluster tree
or mesh networks. ZigBee allows a larger number of nodes
– more than 65,000 – according to specification. Transmission
range is also longer (1–100 m) for ZigBee than for
Bluetooth (1–10 m) (Baronti et al., 2007).
The main objective of this paper is to study the performance
of ZigBee motes for monitoring the refrigerated
conditions in fruit chambers with low temperatures, high
humidity and different cargo densities. Reliability of communications
and measurements, together with battery life,
are major issues in this work.
2. Materials and methods
2.1. The standard ZigBee and 802.15.4 characteristics
ZigBee is an open specification that enables low power
consumption, low cost and low data rate (250 kb/s) for
short-range wireless connections between various electronic
devices. The ZigBee Alliance is an association of
companies which develops standards and products for reliable,
cost-effective, low power wireless networking. Major
players in the electronics industry are members of the
ZigBee Alliance (ZigBee Alliance, 2005).
The ZigBee standard is built on top of the IEEE
802.15.4 standard. The IEEE 802.15.4 standard defines
the physical and MAC (Medium Access Control) layers
for low-rate wireless personal area networks (IEEE,
2003). The physical layer supports three frequency bands
with different gross data rates: 2450 MHz (250 kbps), a
915 MHz (40 kbps) and 868 MHz (20 kbps). It also supports
functionalities for channel selection, link quality estimation,
energy measurement and clear channel assessment.
ZigBee standardizes both the network and the application
layer. The network layer is in charge of organizing and
406 L. Ruiz-Garcia et al. / Journal of Food Engineering 87 (2008) 405–415
providing routing over a multi-hop network, specifying
different network topologies: star, tree and peer to peer.
The Application Layer provides a framework for distributed
application development and communication.