Comparing Different Wireless Types
The following table compares performance between fixed frequency, FHSS and DSSS, assuming the same level RF power and frequency.
DSSS is normally used where high data rate is important. A good example is 802.11 WiFi devices. DSSS combined with the wide bandwidth of the 2.4GHz and 5GHz bands enables a very high data rate, however reliable distance is very short.
Most 900MHz products use FHSS technology as they are used for lower data rate applications where the ability to penetrate through congested industrial environments is important.
Common Wireless Standards
WiFi 802.11
The 802.11 standard specifies requirements for wireless Ethernet devices using DSSS within the 2.4GHz and 5MHz ISM bands. This standard has become popularly known as WiFi (“wireless fidelity”). WiFi devices have been in the market since the late 1990’s, and several 802.11 standards have emerged, from 802.11a to 802.11n. The most commonly used is 802.11b with data rates up to 11Mb/s.
Although WiFi is predominantly a commercial wireless standard, WiFi devices have been used extensively in industry, for high data rates over very short distance. Industrial WiFi units are available with extended temperature ranges, and additional functionality to improve operating reliability.
Bluetooth
The “Bluetooth” standard provides FHSS operation in the 2.4GHz band with data rates of 800Kb/s. Distances are very short because of reduced transmitter power. Bluetooth devices are generally used for transferring data between personal computer peripherals and mobile/cellular telephones. Although there are some Bluetooth industrial products, this standard is not commonly used in industry.
Zigbee 802.15
Zigbee is a very recent standard, designed predominantly for battery-powered wireless sensors. Zigbee devices can use either 868/900MHz or 2.4GHz ISM bands and have low transmitter powers to suit small imbedded batteries.
An important feature of this standard is a “wireless mesh” whereby devices pass information from one unit to another.
Zigbee devices are emerging in building management and HVAC systems, and are expected to be used in industrial applications.
WiMax 802.16
WiMax is a recent wireless standard for fixed broadband data services operating in the 11 – 66 GHz band. WiMax will generally be delivered through commercial supplier networks, although private networks are also envisaged.
Cellular Wireless
GSM, GPRS, CDPD, CDMA – these are different cellular standards used for transmitting data. Although they are used in industrial environments for inventory management, they are generally not used for internal plant or factory applications.