A Wireless LAN is a Wireless local area network which is used to connect two or more computers without wires. This is an extension of wired LAN which reduces the need of wires and gives mobility within the local area and still be connected to a particular network. Using radio frequency (RF) technology they transmit and receive data over the air to get the network access without using wires. This gives ease to the people who use handheld devices like cell phones, notebook computers etc. For home user and business wireless LAN became popular as people do not need to stay at a place to access the internet. Spread spectrum technology is used for wireless LAN to connect devices to the network.
Why wireless (wireless vs. wired networks):
Both wired and wireless networks have advantages over each other. Few differences are below:
Installation: Installing wired network is a bit difficult task as we need to pull wires connect them and give connections, but when compared to wireless it consumes less time as wireless networks take time for configuring the router and connecting to the particular network. In the case of additional users wireless network is best as no extra work is needed, but in wired again the process should be done.
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Mobility: Wired networks are immobile as the user should be at a stationary point to use the network, but in wireless networks users can move around in the network access area.
Cost: Wired networks are expensive covering large areas while wireless networks don't involve this cost.
Speed: Wired network is faster than wireless and never face performance problem.
Security: Wireless network is not secure as unauthorized users can access network which causes many problems like crashing networks, illegal usage of the data etc. Whereas in wired networks unless the user connects through the plug-in point they cannot access.
Reliability: When installing or moving wired networks lot of care should be taken to check the cable connections. Loose connections lead to failure of wired network no such problem in wireless networks.
Working of WLAN:
Wireless LANs use electromagnetic radio or infrared waves to communicate from one point to another point without depending on any physical connection. Radio waves are also called as radio carriers as they deliver energy to a remote receiver. The transmitted data is modulated on to the radio carrier. If the radio waves are transmitted properly on different frequencies, multiple carriers do not interfere even if they are in same space and at the same time. If the radio receiver has to extract data it tunes to one frequency and rejects all other frequencies. In a wireless configuration a device called as access point is used. This is used to receive, buffer and to transmit data between the wired network and wireless network infrastructure. Access point can function within a small range of area less than hundred feet to several hundred feet, which supports only a small group of users. Wireless LAN is accessed by end users through wireless LAN adapters.
Configuration of Wireless LAN:
Wireless network can operate in two modes:
Ad-hoc mode network:
Wireless network interface cards should be placed in PCs to install an ad-hoc network in small areas like home or small offices. PC cards are also available for notebook computers and laptops.
Ad-hoc mode is completely wire-less. Ad-hoc networks are easy to fix and are affordable. Peer-to-peer basis is used to connect workstations with each other. If a wireless broadband router is added to ad-hoc network, computers can be given internet access to that specific network.
Fig: Ad-hoc wireless network
Infrastructure- mode network:
For a larger network installation in infrastructure mode, both NICs and access points must be installed and configured. Access points should be configured carefully depending up on the signal strength and quality. After the installation, NIC s and access points should be configured. In this network access points are used to connect workstations. Workstations communicate access point without communicating workstations directly. For small and medium sized networks infrastructure is best.
Fig: Infrastructure wireless network
Wireless LAN Technologies:
Spread Spectrum Technology:
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Spread spectrum technology was originally developed for the military which uses more bandwidth than narrowband technology. Spread spectrum is more reliable, secure than narrowband. This is possible because the spread spectrum allows for more bandwidth as it continuously changes the frequency of the transmitted signal. High spectrum utilization and resistance to multipath are the main advantages which made spread spectrum technology so interesting. In satellite communication, telemetry systems spread spectrum technology is in use. Transmission capability of the wireless channel can be maximized in spread spectrum. In this technique the data rate can be modified or changed according to the need which maintains the link during adverse conditions. Spread spectrum is classified into two types:
Direct Sequence Spread Spectrum (DSSS):
DSSS generates redundant bit pattern for each transmitted bit which is known as chipping code. Length of the chip code and transmission of data are directly related like if the chip code is long, transmission of the data will be properly received but uses more bandwidth. Because of the chipping code, damage of bits and retransmitted data can be recovered.
One data bit
Zero data bit
Word for every
One data bit
Same chip code word but
Inverted for zero data bit
Fig: Direct Sequence Spread Spectrum technology
Frequency Hopping Spread Spectrum:
In frequency hopping spread spectrum data which is modulated with narrowband carrier signal hops from frequency to frequency as a function of time.
Fig: Frequency Hopping Spread Spectrum Technology
This is done by spreading the signal in time domain whereas DSSS is done by chopping each bit in frequency domain. If the transmitter and receiver travel at same time and same frequency a single logical can be maintained.
Narrowband system uses a specific radio frequency to transmit and receive data. It uses a narrow radio signal frequency for passing the information. By coordinating different channel frequencies for different users this technique avoids undesirable crosstalk between communication channels. One drawback is that end user must obtain FCC license for each site.
Types of WLAN:
Peer to Peer network:
In a basic wireless network, considering two computers with wireless adapter cards can transfer files, emails etc to each other directly in that network. Each computer acts as a sender and receiver depending up on the requirement. Peer to Peer network is best way for exchanging small amount of data and is also less expensive. This is not efficient for large data exchange.
Client and Access point:
Ad-hoc network range can be increased by installing access points. Each client should have access to server resources and to other clients as the access point is connected to the wired network. Number of clients each access point can accommodate depends on the nature of the transmission involved.
Multiple access point and extension point:
Access points can serve only small regions, if we have to use for large area like college many access points should be used. Access pints should be places in such an order that whole college can be connected to the network without any problem.
Directional Antenna Network:
This is the last item in wireless LAN network. Suppose wireless LAN should be extended from one building to another with certain distance, directional antennas are used. These are placed on the buildings facing each other. Antenna on one building is connected to the wired network via access point of that building and another building antenna is connected to that particular wired network with the help of access point because of which connection is enabled.
Advantages of Wireless LAN:
Convenience: Wireless LAN is convenient to use as there is no need to find a plug in point for the network access and to be in a particular place. Because of this technology use of laptops, cell phones and many handheld devices increased.
Mobility: This technology gives users the mobility to move around within the limited area of the network to access the network. This became helpful for business people where they can use internet in coffee shops, shopping malls etc.
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Installation Speed: It is very easy to install as there is no need to pull wires and connect.
Installation flexibility: It is flexible to install network even in places where wired access cannot be given.
Cost: First time installation cost is more than wired, but overall cost is low. Benefits are greater during frequent changing or moving.
Expandability: This can support the increase of the client as this doesn't need any wiring for increased users.
Disadvantages of Wireless LAN:
Security: Unauthorized users can access wireless LAN. Such users can capture data and cause problems like crashing a network, etc. This is a challenging task for business people and professionals to protect their data from such illegal users.
Signal interference: Walls, buildings and physical structures can reduce the strength of the signal, which results in limiting wireless LAN range and connection quality. Other wireless technologies using same network can also impact the signal strength.
Speed: The speed of wireless LAN is less compared to wire LAN. Performance issues are also caused by TCP and its built-in congestion avoidance.
Energy: Power consumption is high, battery life is low and heat is also problems for wireless LAN.
Applications of Wireless LAN:
In hospitals to send patients details from point to point (doctor to nurse or doctor to doctor).
It is helpful for members who are in meeting so that they can make a decision based upon other team member's opinion and also by seeing few practical things from the Internet.
It is a good application for training in companies, schools, and universities etc, where exchange of data can be done with the help of network access.