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WLAN technology involves linking devices through a wireless distribution method by which one can connect to a network. Users will have the mobility to connect to a network anywhere within the coverage area. This technology had become popular due to the increase in laptop users. Speaking in laymen terms, user's having a laptop, Mobile or any device which has the wireless competence will act as a receiver while the access point would act as a sender transmitting wireless signals. Access point is a device that concedes the wireless devices to connect to a network.
To gain the customer satisfaction Public Businesses, Malls, Coffee shops have begun offering free wireless access to their customers by the help of this technology.
Present wireless networks consists heterogeneous wireless networks for example wireless cellular networks, wireless Local Area Networks (WLAN), wireless mesh networks, etc. For the reason that wireless network has its own strengths and disadvantages in spectral efficiency and mobility, the integration of heterogeneous networks can provide more efficient wireless services to mobile terminals (MTs) [1.1]. For this reason, many recent studies are focusing on the integration of heterogeneous networks, e.g., WiMAX-WLAN [2, 3] and 3G-WLAN [4, 5, 6, 7, 8].
Let's talk about the characteristics of Radio frequency transmission. These frequencies are radiated in to air via antenna and that creates radio waves. They are absorbed when the waves are propagated through objects (Walls..Etc.,) and are reflected by objects like metal surfaces. Bottom line is this absorption and reflection can cause areas of low signal strength/Quality which we have to deal with.
 According to the accuracy of the spectrum sensing, both the secondary data rate and the interference to primary users can be optimized by adjusting the spreading gain. Its performance is analyzed and demonstrated by simulations.
Higher data rates have shorter data range. This means that the receiver needs more signal strength and more signal to noise ratio to receive better information. Higher frequencies allow higher data rates and have a shorter transmission range.
We can see the Frequency spectrum in this picture. We have 3 unlicensed bands. The first two bands 900 & 2.4 GHz together are referred to the ISM bands (Industrial, Scientific and Medical Frequency bands) and the 5GHz band is referred to unlicensed national information infrastructure.
These factors make the unlicensed spectrum a perfect environment for producing a disruptive technology, which, in the case of wireless LAN (WLAN), it has.
802.11b was approved in 1999 and it became the effective standard for wireless and it was adopted rapidly in the market. It operates in the worldwide available 2.4GHz ISM band. It provides 4 data rates up to 11Mbps.it is the most commonly wireless standard virtually approved for worldwide use. There are 13 ETSI (European Telecommunications Standard Institute) 2.4MHz channels.
IEEE 802.11 is a widely used standard for MAC and PHY layers of WLANs.
In the above diagram, 2.4GHz 802.11 b/g has 3 non overlapping channels which mean that three access points can operate in the same cell area without sharing the Media. Access point1 doesn't share time with Access point 6 or 11 as they have different frequencies.
Security of WLAN is like security for any other network. Obvious security fixes should be implemented first such limiting access and disabling 'open' access. To ensure the wireless Network security, Encryption and Authentication are the technologies used. This technology allows the authorized users to access the wireless network and also allows the data encryption information to be received by the desired users only.
Wireless authentication and data encryption includes WEP, TKIP and CCMP. If you are working with a security policy server then the devices can support security supervision functions such as vibrant control of user rights.
There is a possibility for the hackers or intruders to access or corrupt the data as WLAN transmits and receives data through open air. Secured WLAN along with greater speeds has improved dramatically in recent years.
In most of the offices 802.11g products with a maximum data rate of 54Mbps are deployed. The throughput is about 50% of the data rate. 7Users per access points with no conference rooms provide 3.8 Mbps throughput per user. Now 7 users+1 conference room (10 members) provides 1.5 Mbps throughput per user.
This technology is a personal area network - a network used for connecting devices which are centred on a person's workspace through wireless connectivity. Predictably, a WPAN network uses a technology which permits communication at a range of about 10 meters, a very short range. One such technology is Bluetooth, which uses a new IEEE standard, IEEE 802.15.
A WPAN supplies interconnect to all the ordinary computing and communicating devices or can serve a more focused purpose such as allowing a team member to communicate more efficiently. It was introduced as a new concept for next generation wireless systems.
Basic concept in WPAN technology is known as plugging in. In idyllic situation, when two devices having the WLAN capability comes into a range closer (Approx 10mt) to a central server, they can communicate with each other similar to devices communicating with each when connected through a cable. One excellent feature of this technology is the ability to lock out each device selectively, avoiding interference or unauthorized access
The WPAN technology is in its early stage and is enduring a rapid development. Projected operating frequencies are around 2.4 GHz. WLAN and WPAN networks provide approving services in the same unlicensed radio frequency band of operation.
The intent is to smooth the process of seamless operation for home or business devices and systems. Every device having WPAN capability can plug in to any other device in the same WPAN, provided they are within the substantial range of one another
Bluetooth wireless communication is the main or can say that it is one of the instance of a WPAN technology. Different technologies like infrared, Home RF can also be used in WPANs but each technology is optimized for specific application, usage, or domain. As we mentioned earlier, Due to the rapid growth of the laptop users these technologies are developed for communicating wirelessly.
 Bluetooth networks can be referred to as Cognitive Personal Area Networks, or CPANs. While all devices in a Bluetooth piconet follow the same pseudo-random hopping sequence.
"Bluetooth was named after the 10th century Danish king Harold Bluetooth who unified scandinavia"
IEEE 802.15.1-was endorsed in 2002 standard is an additional resource for those who implement Bluetooth devices. Here the transport layers (L2CAP, LMP, Baseband, and radio) of the Bluetooth technology are defined.
802.15.2- Was endorsed in 2003 has developed a Coexistence Model to enumerate the mutual interference of a WLAN and a WPAN.
802.15.3,3b,3c- Was endorsed in 2003 to draft and publish a new standard for high-rate (20Mbit/s or greater) WPANs. 3c developed a millimetre-wave-based physical layer to the existing 802.15.3 Wpan. It operates at 57-64 GHz unlicensed band.
802.15.3a was withdrawn.
802.15.4,4a,4b,4c- Was ratified in 2006 to investigate a low data rate solution.
802.15.5 was ratified to enable Mesh network Capability in WPANs