Image Processing Reference
In-Depth Information
29.5.5 IEEE 802.15.4 and ZigBee
Wireless communication has many interesting applications in the field of building (as well as home)
automation. For management functions such as log file access for service technicians or presenting
user interfaces to occupants on their personal mobile devices, Wireless LAN and Bluetooth are well
suited. For purposes of process data exchange, however, they do not provide the required energy
efficiency and cost efficiency, especially for wireless sensors.
The focus of IEEE .. and ZigBee is to provide general purpose, easy-to-use, and self-
organizing wireless communication for low cost and low power embedded devices. While IEEE
.. defines the physical and the MAC layers, ZigBee defines the layers above. Strictly speak-
ing, IEEE .. is therefore an entirely independent protocol, and ZigBee is certainly not the only
protocol to build on it—although it is one of the very few published, another notable case being a
specification for IPv over IEEE .. []. However, IEEE .. and ZigBee are actually not
only complementary, but have mutually influenced the development of each other.
29.5.5.1 IEEE 802.15.4
The IEEE .. [] physical layer (PHY) focuses on three frequency bands: MHz, MHz,
and . GHz. he . GHz band is available license-free almost worldwide. However, this also means
it is very crowded, for example, Wireless LAN and Bluetooth use it. BA applications require far less
throughput.hisenablestheuseoflowerfrequencies,whichhavetheadvantageofbetterradiowave
propagation with the same amount of power spent. Unfortunately, the frequency ranges for license-
free radio communication in the MHz region differ in Europe (- MHz) and United States
(- MHz). However, they are close enough to allow a single transceiver design which can be
adapted by adjusting the oscillator only.
Although narrower than its U.S. counterpart, the European - MHz range is particularly
attractive since it is well regulated. For example, channel-hogging audio applications such as cordless
headphones are not allowed between and MHz, but have their own frequency at MHz.
he-MHzsubrangeisfurthersubdividedintosectionswithvaryinglimitationsonduty
cycle and transmission power. In contrast, devices using the U.S. - MHz range are only
subject to a transmit power limit of W. Therefore, e.g., cordless phones are a major source of
interference.
Both frequency bands are supported by IEEE ... A variety of modulation schemes with mul-
tiple data rates are available. A recent amendment (IEEE ..a-) also specifies ultra-wide
band communication in various frequency ranges.
In IEEE .., devices are classified as full function devices (FFDs) and reduced function devices
(RFD) according to the complexity of the protocol stack. While FFDs can communicate in peer-to-
peer fashion, RFDs can only communicate with coordinators, resulting in a star topology.
IEEE .. defines two different kinds of personal area networks (PANs): beacon enabled and
non-beacon enabled networks. In a beacon enabled network, a superframe structure is used. The
superframe is bounded by network beacons which are sent by the PAN coordinator periodically.
Between these beacons, the superframe is divided into slots (contention access period) which can
be used by the PAN members to communicate using a CSMA/collision avoidance (CA) scheme.
Optionally, the PAN coordinator can assign guaranteed time slots (GTS) to devices, providing them
withaixedcommunicationslot.Inanon-beaconenablednetwork,allPANmemberscancommu-
nicate at any time using CSMA-CA. In contrast to other wireless protocols that consider security
an application matter, IEEE .. specifies different security services despite its low position in
the protocol stack. These services rely on AES and include access control, message confidentiality,
message integrity, and replay protection.
IEEE .. was first published in . In late , ..b added additional PHY layers as
well as MAC improvements (e.g., reduced association time in non-beacon networks). It also included
