Information Technology Reference
In-Depth Information
transition from wired to wireless connections, allowing for ubiquitous
connectivity at all levels and distances.
3.1.1
Bluetooth
Bluetooth was developed as a short-range connectivity standard to replace
wired networks of small dimensions. It allows successive interactions more
efficiently and it allows for localization in the area of limited extension.
It consumes a very small amount of energy, which makes it fit the stringent
energy requirements of mobile devices. Dedicated USB dongles may be
employed to enable Bluetooth in devices that do not have it natively.
Its operating range is of about 10 m at 1 mW of power. Bluetooth devices
transmit on ISM (industrial, scientifical and medical) band, in the range
2.4-2.48 GHz, with an effective bandwidth of 79 MHz.
It uses spread spectrum transmission to reduce interference with other
devices operating on the same frequencies. Specifically, Bluetooth uses the
frequency hopping spread spectrum (FHSS) that divides the available
bandwidth into 79 bands of 1 MHz each and then define a pseudorandom
hopping scheme among the 79 channels that is known only to the devices
involved in the communications, thus improving the resiliency to interference.
3.1.2
IrDA
The IrDA pretty much attempts to address the same applications as
Bluetooth, simple and quick communications between peripherals. To the
purpose of enabling stable communications between mobile devices,
however, this technology fails as it requires that the two communicating
devices be in
line-of-sight
. This major requirement is due to the fact that it
employs infrared light to carry the communication, which is blocked by solid,
non-transparent objects. Other limitations are the very short range (below
1 m) and view angle (less than 30°). IrDA devices are typically found on
cellular phones, some portable PCs, personal digital assistants (PDAs) and
printers. IrDA data rates are normally 4 Mbps, which becomes 16 Mbps with
the new fast infrared (FIR) standard.
3.1.3
HomeRF
HomeRF is a wireless technology developed for domestic uses by the
HomeRF Working Group. It operates on the same frequency as Bluetooth
(2.4 GHz) and employs the Shared Wireless Access Protocol (SWAP),
originally capable of 2 Mbps and then extended to 10 Mbps (SWAP2.0). As
for Bluetooth, it uses the FHSS technology over six digital enhanced cordless
telephone (DECT) voice channels and one data channel following the IEEE
802.11 wireless standard. It does not require dedicated access points as for
Wi-Fi, with individual devices connected point-to-point. Major limitation is
