11-09-2013, 04:52 PM
Radio-Frequency Technologies for WSNs
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Abstract
Many wireless monitoring and control applications are available for
the industrial and home markets. Some hardware platforms are specialized for
optimizing only one feature (e.g., high data rate, long transfer range, or low-
power mode). However, the most restrictive parameters for WSNs are both
power consumption and distance. This chapter briefly describes different radio-
frequency technologies, although many of them are not appropriate or are not
yet fully developed for WSNs. Therefore, only appropriate technologies are
discussed in depth, and a brief overview of several integrated circuits from
different manufacturers is included.
Bluetooth Technology (IEEE 802.15.1)
The Bluetooth wireless communications technology provides a personal area
network (PAN) for exchanging data between Bluetooth-capable devices within
a certain proximity.
Bluetooth technology has a low-power mode and high integrated devices and
operates in the unlicensed 2.4-GHz band, but it is limited to short-distance
communications. Therefore, this technology is not the most appropriate for
developing a WSN. For this reason, Bluetooth is just mentioned and described
as an existing technology (Bluetooth SIG).
UWB Technology (IEEE 802.15.3)
The Ultra Wideband (UWB) technology allows information to be transmitted
at a large bandwidth in precise pulses that are typically 1 to 2 nanoseconds in
length and occupy at least 25% of the center frequency, much more than other
systems. The use of this technology is limited to the range of frequencies from 3.1
to 10.6 GHz. Another remarkable characteristic of UWB is its better behavior
regarding interferences than other technologies due to the use of spread-spectrum
modulation techniques.
Despite having a greater ratio of transmission velocity over power consump-
tion than other similar technologies like Wi-Fi, UWB is limited to short-range
applications. It is therefore appropriate for portable devices, to get long battery
life, but not for WSNs requiring larger distances. This is the main reason for not
going into further details on UWB technology (Intel UWB).
Wavenis Technology (EN300–220 and FCC15.247—Coronis
Systems)
The Wavenis technology, developed by Coronis Systems, provides long-range
data connections and services for autonomous devices with extremely limited
battery resources and is intended for ultra low-power (ULP) and long-range
wireless communications. Wavenis extends the industry standard Bluetooth
protocol to provide robust wireless solutions for building ad hoc and fixed
networks using autonomous, battery-powered devices.
Wibree Technology (Nokia)
Wibree technology is a short-range wireless communications protocol intended
to compliment Bluetooth by implementing most of the Bluetooth functions
with less power consumption. The Wibree open standard is able to work in
applications where reliable Bluetooth data transmission is not possible,
although the maximum data transmission rate is three times lower than that
of Bluetooth 2.0 (1 Mbps versus up to 3 Mbps).
The Wibree specifications are being defined by a group of important com-
panies from different sectors such as semiconductor manufacturers, service
providers, and vendors, with Nokia in the lead. (The list of such companies
includes Broadcom, Casio, CSR, Epson, ItoM, Nordic Semiconductor, STMi-
croelectronics, Suunto, Taiyo Yuden, and Texas Instruments.)
This technology is designed to operate with either a standalone chip or a
dual-mode chip. While the standalone chip is a small device able to operate
with very low power consumption, the dual-mode Bluetooth Wibree is able to
communicate with Bluetooth standard devices with less power consumption
and at distances of 5 to 10 meters using the 2.5-GHz band.
The main characteristics of Wibree are the ultra low-power IDLE mode
operation, power-saving technology, device discovery, reliable point-to-multipoint
data transfer, and encrypted communications (Nokia, 2007).
ZigBee System-on-Chip (SoC)
In most cases, solutions are formed by a transceiver plus a low-power micro-
controller, enough to satisfy the wireless sensor’s designer’s needs. On other
applications, a high scale of integration is required. For this purpose, some
manufacturers have developed a System-on-Chip (SoC), integrating a micro-
controller and a transceiver in the same package. With these integrated circuits
(ICs), only a few external passive components are required to build a fully
compliant ZigBee device in minimum space.
Silicon Laboratories
The IC-specialty firm Silicon Labs offers several solutions for the ZigBee and
802.15.4 protocols (SiLabs Home Page). The microcontrollers of the 8051
family from Silicon Labs are optimal for low-power wireless applications like
ZigBee. Silicon Labs has developed microcontroller kits that are available in
order to test the platforms and implement future applications. As an example,
the ZigBee-2.4-DK is a development kit that allows the user to create ZigBee
applications from scratch. It has six target boards and the necessary accessories
and software to make it work; each board consists of a Chipcon CC2420
transceiver connected to a C8051F121 microcontroller including USB and
JTAG interfaces (SiLabs ZDK; SiLabs AN222). The software tool also consists
of an integrated development environment based on the Keil C compiler and
software stack, including the ZigBee and 802.15.4 MAC layers. It also includes
an application programming interface (API) for personal computers, which has
the necessary network primitives to build applications that can manage a
ZigBee-based network (SiLabs AN241; SiLabs AN242).