Each of the various technologies being investigated for
wireless use has its own advantages and disadvantages. Bluetooth
is typically used over short ranges of less than 10
m and uses very little power. A master-slave structure is
implemented to provide some contention management and adhoc
networks are the expected usage. It also implements a
frequency-hopping algorithm to minimise interference and to
allow multiple Bluetooth networks to operate within the same
physical area. A variety of different packet types are specified,
with differing lengths, coding strategies and retransmission
allowances. Like Bluetooth, ZigBee also focusses on low
power transmissions over relatively short distances, but is
tailored towards static networks with infrequent transmissions
and small packet sizes. ZigBee devices can be either fully
functional or feature reduced functionality. Fully functional
devices are able to communicate in a peer-to-peer manner and
act as contention masters for reduced devices. Reduced devices
can only communicate with master devices, through managed
and unmanaged contention systems. WLAN is technically a
collection of standards, each defining various physical layers
and media access control strategies. Examples of this are
802.11b, 802.11g and 802.11n, each of which feature differing
modulation schemes and data throughputs. 802.11e is also under
development with the goal of providing better support for
time-critical functions. WLAN networks can be implemented
ad-hoc, or, more popularly, through a central access point.
WLAN features much higher data rates that Bluetooth or
ZigBee, but is very inefficient when transmitting small data
packets [32].