Among the various wireless
standards, the standard for wireless LAN, IEEE802.11b (“WiFi”) (IEEE, 1999b) and
wireless PAN, IEE 802.15.1 (Bluetooth)(IEEE, 2002) and IEEE 802.15.4 (ZigBee)
(IEEE, 2003, are used more widely for measurement and automation applications.
All these standards use the instrumentation, scientific and medical (ISM) radio
bands, including the sub– GHz bands of 902-928 MHz (US), 868 - 870 MHz (Europe),
433.05 - 434.79MHz (US and Europe) and 314 - 316MHz (Japan) and GHz bands of
2.400-2.4835 GHz (worldwide acceptable). In general, lower frequency allows a
longer transmission range and a stronger capability to penetrate through walls
and glass. However, due to the fact that radio waves with lower frequencies are
easier to be more easily absorbed by various materials, such as water and trees,
and that radio waves with higher frequencies are easier to scatter, effective
transmission distance for signals carried by a high-frequency radio wave may not
necessarily be shorter than that by a lower frequency carrier at the same power
rating. The 2.4GHz band has a wider bandwidth that allows more channels and
frequency hopping and permits compact antennas.
Wireless LAN (IEEE 802.11) is a flexible data communication protocol implemented to extend or substitute for a wired local area network, such as Ethernet. The bandwidth of 802.11b is 11Mbits and it operates at 2.4 GHz frequency. Bluetooth (IEEE 802.15.1) is a wireless protocol that is used for short-range communication. It uses the 2.4GHz, 915 and 868MHz radio bands to communicate at 1Mbit between up to eight devices. The Bluetooth is considered a cable replacement for mobile devices. It is mainly designed to
maximize the ad hoc networking functionality. ZigBee is established by the ZigBee Alliance that is supported by more than 70 member companies. ZigBee is considered the most promising for wireless sensors. Table 1 compares the three wireless standards that are most suitable for wireless sensor network.