WLAN technology is a term used for a wide range of Wireless Local Access Network technologies. Those technologies aim to provide connectivity and wireless access at a high bandwidth to IP-based networks in a similar way or better than wired connections (e.g. Ethernet) provide nowadays. The different options that are currently available in the market have appeared accordingly to the progressive increase of higher bandwidths.The first WLAN standard was created within the IEEE in 1997, the reference for this one is 802.11 (Table 2.4) [25]. The possibilities provided by this standard were to support a maximum of 2Mbps using the unregulated radio-signaling frequency of 2.4 GHz. A drawback when using this unregulated radio-signaling frequency is that WLAN radio signals can be interfered by other equipment working in the same frequency range such as microwaves oven, cordless phones, etc.; in any case, by keeping these at a reasonable distance interference can be avoided. The benefit of using this unregulated radio frequency band is that the cost of the equipment can be lowered as there is no need to pay radio
frequency licenses. The 2Mbps provided by 802.11 were appropriated but are too slow for lots of applications. This triggered the creation of a new IEEE standard, the 802.11b as an extension of 802.11. In September 1999, 802.11b was already supporting up to 11Mbps, providing a bandwidth comparable to traditional Ethernet. 802.11b uses also the same radio frequency band (i.e. 2.4 GHz) as 802.11, having the same drawbacks and benefits derived from free spectrum, but providing a much more convenient bandwidth enough for the majority of applications.
WLAN Standard version
· IEEE 802.11 Standard for WLAN operations at data rates up to 2Mbps in the 2.4GHz ISM Industrial, Scientific and Medical (ISM) band.
· IEEE 802.11a Standard for WLAN operations at data rates up to 54Mbps in the 5GHz Unlicensed National Information Infrastructure (UNII) band.
· IEEE 802.11b Standard for WLAN operations at data rates up to 11 Mbps in the 2.4GHz ISM band.
· IEEE 802.11g High-rate extension to 802.11b allowing for data rates up to 54Mbps in the 2.4 GHz ISM band.
At the same time that 802.11b was being standardized in IEEE, another standard 802.11a was generated as an extension of the 802.11. The 802.11a standard was released in September 1999 supporting a bandwidth of 54Mbps, providing a bandwidth more than enough for the majority of applications; actually, it provided enough bandwidth for several users at the same time. However, 802.11a needs the utilization of a higher frequency band to provide higher bandwidth, and it uses the 5GHz radio frequency band, which is a regulated frequency band. The utilization of a higher frequency has several drawbacks: the achieved distance range is smaller compared to 802.11b, and also penetration of walls and obstacles is more difficult. Despite of providing higher bandwidth, 802.11a products came into the market later than 802.11b because the equipment was more expensive due to regulated band usage constrains. Commonly, 802.11b technology is used in domestic market and 802.11a is used in business market. Between 2002 and 2003, a new standard called 802.11g was generated in IEEE. The 802.11g tries to combine the main advantages of 802.11a and 802.11b, so it is able to support a bandwidth up to 54Mbps using the 2.4 GHz frequency band. The new standard was created to be backward compatible with 802.11b access points, so old devices can still work with new equipment, but at lower rates. All the 802.11 technologies are commonly known as Wi-Fi (Wireless Fidelity). Wi-Fi
is an entity that certifies that vendor’s products follows the different 802.11 specifications. It certifies 802.11, 802.11a, 802.11b and 802.11g.
Bluetooth is another wireless network technology developed in a different path than 802.11 technologies. Bluetooth supports a very short range of approximately 10 meters, providing up to 1Mbps. The most attractive point of Bluetooth is its low manufacturing cost, otherwise it is not a technology that can be considered for general-purpose networking due to the coverage and bandwidth restrictions. However, the range of application for controlling and messaging remote device is very wide. Nowadays it starts to be very common in cell phones or computers as a fast and easy way to connect with remote devices such as earphones,GPS, PDAs, etc.
Complementary WLAN Access Technology for Cellular Networks
The high data rates provided by WLAN technologies are very attractive for different purposes, and cellular network industry has started to put an eye on it as a good possibility to increase data rates provided to their customers. Maximum data rates provided by traditional cellular network technologies are poor compared to maximum data rates provided by any of the 802.11 families. As an example, the maximum throughput that can be achieved by an MS using legacy 2.5G EGPRS terminals is 59.2 kbps in single slot mode, or up to roughly 220 kbps with current 4 TSLs devices in best conditions. For WCDMA, this limit is set up to 384 kbps for current starting networks, although 2Mbps would be also possible. This fact makes the WLAN technology very attractive for new upcoming 3G services that in general would require a high throughput. However, the main limitation is the coverage provided by WLAN equipment, which is remarkably shorter than the one provided by traditional cellular networks. This led to the conclusion that WLAN could be used to access upcoming new set of 3G services, but with a different scope as that of the so-called 3G cellular networks. Based on these assumptions, WLAN AN was also raised as a new complementary access technology to provide 3G services.
WLAN ANs are well suited to hotspot coverage, where there is a high density of high data rate services, such as 3G services, requiring a limited mobility (e.g. located in airports, cafeterias,etc.). But looking at the other side of the coin, 3G systems allow voice, support wide coverage area and provide high possibilities to mobility; 3G systems are more suitable for wider areas with
relatively low to moderate demand of high data rate services but with more mobility needs. This implies that WLAN ANs and 3G systems may compete in certain market niche but more often the market niche for WLAN AN and 3G systems are complementary, which should enable a
