Editor’s note: This is the fourth part of a series about Wireless Local Area Networks. Matt Gunter, a radio frequency engineer, founded Goose Creek Technologies.We have seen headlines ranging from “802.11 will be the end of 3G cellular” to “Bluetooth will vanquish 802.11” to “WiMax will overcome 3G cellular and 802.11”.
Truth be told, 802.11, 3G Cellular, Bluetooth, and WiMax are NOT competing technologies. Each has is unique niche and purpose. Although these are not competing technologies, someday a user will use a single device to access the Internet via whichever of these technologies are readily available. That is how these technologies will converge.
To define how each of these technologies co-exists we need to define different types of wireless networks. You can basically classify the technologies by the coverage radii unique to each. The coverage radii is mostly dictated by the transmit power levels of the base and receiving wireless devices. Bluetooth should be considered a WPAN (wireless personal area network), because it has a limited range of a few meters. 802.11 should be considered a WLAN (wireless local area network) because it generally extends to less than 100 meters. WiMax and 3G Cellular are both WWAN (wireless wide area networks) because they extend for several kilometers.
Bluetooth as a WPAN is mainly intended to be a low-bandwidth short range wireless communication method. The Bluetooth standard was created by a consortium of hardware vendors and later adopted by the IEEE as 802.15. Since it is for short-range communication only, it is mainly used for communication cable replacement. For instance, Bluetooth is used to connect your cell-phone to your hands-free headset without the need of a wire.
Designed as a wired Ethernet (802.3) replacement, 802.11 originally came in three flavors: Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and Infrared. Both the FHSS and Infrared versions of 802.11 fell by the wayside when the IEEE adopted 802.11a and 802.11b. Watch out for legacy 802.11 FHSS devices because they will wreak havoc on the performance of an 802.11b system.
Last year 802.11g was approved as a speed enhancement to 802.11b. Both 802.11b and 802.11g use the 2.4 Ghz frequency band while 802.11a used the 5.7 Ghz band. The majority of the installed hardware base for WLAN is 802.11b, with 802.11g growing in popularity. 802.11a is not very useful due to its high frequency and thus less coverage range. Wi-Fi is the name given to 802.11b by the Wi-Fi Alliance. Standards other than 802.11b are often incorrectly called Wi-Fi.
WiMax is a trade name for IEEE 802.16 point to multipoint broadband wireless access. It is meant to provide wide area wireless access in the frequency ranges of 10 to 66 Ghz. Because this standard is still evolving and vendors have not fully achieved compatibility testing, there are only limited deployments on WiMax. WiMax is mainly intended to be a fixed broadband wireless system providing very high data rates. As is such it is really not competing with 3G cellular and its inherent mobility.
Although WLAN uses unlicensed frequencies, it does not mean this is an unregulated field. In fact, it is highly regulated in terms of the wireless devices that can be used. The main governing law for the wireless devices is Part 15 Title 47 of the Code of Federal Regulations. This law governs how wireless devices using the unlicensed spectrum must comply with certain power output level. The goal is to make the spectrum usable by everyone who desires to use it.
In a nutshell, Part 15 simply says that you are not allowed to produce harmful interference. Although the laws of Part 15 are strict there is not very much enforcement, yet. One of the ways the FCC enforces Part 15 is to require hardware vendors to have their ‘antenna systems’ be FCC certified. The FCC does not certify each individual component. The whole system (access point, cabling, and antenna) is certified as 1 unit. This means that if you unscrew an antenna from an access point and put your own antenna on it, you are breaking the law.
Part 15 violations occur all of the time when people modify access points but placing new antennas on them. Most people are unaware of the laws they are breaking. If someone files an interference complaint against your unlawful system then you could be in big trouble. The FCC can enter your premises and confiscate your equipment without the need of a search warrant or your permission. So it’s best not to modify your equipment. If you need to have a different system configuration, you had better purchase a new system that is completely FCC Part 15 certified.
Another regulatory code that is often broken during WLAN installations is the electrical code. Too many times, an access point that is not plenum rated is placed above a ceiling tile. This is a major fire and smoke hazard and a violation of most building electrical codes in any jurisdiction. The plenum is the air-return space above the acoustical ceiling tiles. This air is circulated throughout the building’s air handling system. If the non-plenum rated access point were to catch fire, extremely poisonous gases would be released. The plenum-rating requirement applies to the Ethernet cabling connected to the access point. It should also be plenum rated.
The EPA and OSHA govern other regulations regarding wireless transmitters inside buildings. In most instances you will not have to worry about these regulations if you are installing commonplace WLAN hardware, but there are some instances where the occupational exposure limits could be exceeded. The limits depend on the power levels being transmitted and the proximity and time-duration exposure to humans.
Hopefully, many of the realities of implementing a WLAN have been exposed in this article series. The misleading WLAN ads can be very seductive so you need to take a step back and reasonably look at the whole picture. Do you really need a WLAN? Will it make your enterprise more efficient? Like any technological upgrade, WLAN has its positives and negatives. You have to weigh the risk against the advantage you may gain.