Wireless LAN

Flexibility: Within radio coverage, nodes can communicate without further restrictions. Radio waves can penetrate walls, senders and receivers can be placed anywhere.
Planning: Only wireless ad hoc network allows for communication without planning. Any wire network needs wiring plans, as long as devices follow same standard, they can communicate.
Design: Only wireless network allow for the design of small, independent device which can be put into pocket.
Robustness: wireless network can survive disasters; earthquakes or user pulling a plug.
License free: LAN operators don’t want to apply for a special license in order to be able to use the product. The equipment usually operate in the license free band.

WLAN Technology
Wireless LAN standards that are currently being explored in the field of communications technology are:
1. IEEE 802.11.
a. 802.11a
b. 802.11b
c. 802.11g
2. HiperLAN/2.
3. Bluetooth.
4. HomeRF.

IEEE 802.11
The IEEE finalized the initial standard for wireless LANs, IEEE 802.11 in June 1997.
This initial standard specifies a 2.4 GHz operating frequency with data rates of 1 and 2 Mbps.
With this standard, one could choose to use either frequency-hopping or direct sequence (two non compatible forms of spread spectrum modulation).
Because of relatively low data rates (as compared to Ethernet), products based on the initial standard did not flourish as many had hoped.

The 802.11a standard (High Speed Physical Layer in the 5 GHz Band) specifies operation in the 5 GHz band with data rates up to 54 Mb/s.
The advantages of this standard (compared to 802.11b.Higher Speed Physical Layer Extension in the 2.4 GHz Band) include having much higher capacity. 802.11a isn't compatible with
802.11b and 802.11g products. As with the initial standard

802.11b (Wi-Fi)
802.11b operates in the 2.4 GHz band, but it includes 5.5 and 11 Mb/s in addition to the initial 1 and 2 Mb/s.
The 802.11b standard only specifies direct sequence modulation, but it is backward compatible with the initial direct sequence wireless LANs.
The IEEE 802.11b standard is what most companies choose today for deploying wireless LANs.

The 802.11 working group is currently working to extend the data rates in the 2.4 GHz band to 54 Mb/s using OFDM (orthogonal frequency division multiplexing), which is the 802.11g standard.
Companies should be able to easily scale their existing 802.11b products to become 802.11g-compliant through firmware upgrades.
This enables companies having existing 802.11b infrastructures to scale up their network via relatively simple cost-effective changes.

HiperLAN 1
European Telecommunications Standards Institute, ETSI, ratified in 1996 with High Performance Radio LAN (HiperLAN 1) standard to provide high-speed communications (20Mbps) between portable devices in the 5GHz range.
Similarly to IEEE802.11, HiperLAN/1 adopts carrier sense multiple access protocol to connect end user devices together.

HiperLAN 2
A flexible Radio LAN standard called HiperLAN 2, designed to provide high speed access (up to 54 Mbps at PHY layer) to a variety of networks including 3G mobile core networks, ATM networks and IP based networks, and also for private use as a wireless LAN system
HIPERLAN/2 [5] has a very high transmission rate up to 54 Mbps.
This is achieved by making use of a modularization method called Orthogonal Frequency Digital Multiplexing (OFDM). OFDM is particularly efficient in time-dispersive environments,


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