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WIRELESS LAN TECHNOLOGY

A new trend in Wireless Networking
A
TECHNICAL PAPER SUBMITTED
AS PART OF

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Presented BY


D.SWATHI 02671A1282
M.MADHAVI 02671A1222


J.B.INSTITUTE OF ENGG & TECH Affiliated to JNTU, Yenkapally, Moinabad mandal, Himayat Nagar Post ,Hyderabad-75.

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ABSTRACT



Wireless networking is one of the ways of establishing connectivity and creating a network by using radio frequency signal between the computers to share information. There are several ways of creating a wireless network viz., blue tooth technology, IrDA , Wireless LAN and Home- RF. Though all the technologies operate in the same frequency there is a slight difference among them in the data speeds, range ,band width and some other factors which makes them usable world-wide.

T h e present paper touches upon latest communication techniques of data transmission through wireless LAN. It also discusses the pros and cons of utilizing the spread spectrum technology used for data communication. Also the security issues which play a prominent role in a wireless LAN are highlighted.


The present paper is not an exhaustive study of the technology under focus but it is an honest endeavor to peep into the amazing world of wireless LAN which is making rapid strides in the world of computer networking.

INTRODUCTION TO METHODS OF WIRELESS
NETWORKING

NETWORKING

Over the last decade advances in communication and information technology is tremendous. Networking technology has become an explosive area of growth in the computer industry. The demand for larger , faster , higher capacity networks has increased as businesses have realized the value of networking their computing systems . Initially there were wired networks where every user can connect to every other user in the network directly . As the technology advanced wireless networks came into picture .

The main reason behind developing these wireless networks is to extend the wired network using electro magnetic waves
For example, if an organization has several departments and the connectivity between these departments centralized hub is achieved by means of a wireless network .
Wireless vs wired
> Wired networks are capable of sharing information with any remote computer located in a specific network. But extending wires to every nook and corner of the network becomes extremely expensive.To avoid this wireless networking came into picture.
> Wireless networks extend the existing wired network and adds coverage to wired network's range.
> Wireless networks minimizes the cost of wiring as it requires wired connectivity only to connect the access points from the centralized hub.
> Though we find difference in the modes of operation , basic functionality of both remain same.
WIRELESS NETWORKING
Wireless networking is a way of establishing a network by sending radio-frequency signals between the computing devices to share information.
Wireless Networking is one of the emerging technologies in the field of computer networking and has reached a level where it can be used for reliable communication over a network. The way it's set up will depend upon the specific requirements of an organization, but the general topologies remain the same. Moreover, the technology used for data transmission allows wireless throughput of up to 11 Mbps.
There are four types of wireless networks, ranging from slow and inexpensive to fast and expensive:
¦ Bluetooth
¦ IrDA (Infrared Data Association) -Infrared
¦ Wireless Local Area Network (WLAN)
Though all the techniques operate in the same frequency range , the effective data transfer - rate and range of each technology differs . This lead to the development of new technologies whose data transfer rate is comparatively increasing up to a maximum of 11Mbps.

BLUETOOTH - A LEADING TECHNOLOGY

Blue tooth refers to an open specification technology that enables short - range wireless voice and data communication globally. It was begun to produce low power and low cost radio interface between mobile phones and their accessories

When two blue tooth equipped devices come within 10 meters of each other .they can establish a connection.The connectivity can be extended up to 100 meters with an optional amplifier

Blue tooth is best described as a multipoint piconet structure .It uses the Frequency Hopping spread spectrum communication method and employs 1600 hops per second.. In this method of communication the data transmission is in the form of radio signals following a pre¬defined hopping sequence.
¢ Blue tooth is designed to carry voice , data and video information at up to 1Mbps.
¢ Blue tooth facilitates real - time transmissions, which makes it possible to connect any portable and stationary communication device easily.
¢ Blue tooth' s radio frequency technology does not require a direct " line - of - sight" between transmitter and receiver as in the case of infrared technology.

Disadvantage
Bluetooth is not expected to replace the need for high-speed data networks between computers.

INFRARED-ANOTHER TECHNOLOGY IN THE OFFING
IrDA(Infrared Data Association) is a standard for devices to communicate using infrared light pulses. This was an experiment by IrDA which proved that a network can be established not only by radio waves but also by infrared light pulses, a faster wave frequency that is closer to visible light
¢ Since IrDA devices use infrared light, they depend on being in direct line of sight with each other.
¢ An IrDA-based network is capable of transmitting data at speeds up to 4 Mbps, and up to a short transmission range of 15 feet , and is used mainly for Personal Area Networks.
Disadvantages
¢ IrDA technologies did not develop with interoperability and industry standardization as a primary goal, as did Bluetooth.
¢ Many proprietary implementations make IR more difficult to use.
For example, consider a computer lab in a university where the computer system of the Head lecturer is considered as the central hub and those of the students form the clients of the network .

WHAT IS WIRELESS LOCAL AREA NETWORK

Wireless Local Area Network (WLAN) is a flexible data communication system which uses electro magnetic waves for transmission of data and does not require a physical connection (phone lines or fiber optic cables) between individual nodes and the hub . A wireless local area network communications system is implemented as an extension to, or as an alternative for, a wired LAN. Using radio frequency (RF) technology, wireless LANs minimizes the need for wired connections. Thus, wireless LANs combine data connectivity with user mobility.




THE TOPOLOGIES
Wireless networks can be formed in two basic ways: Ad-hoc and Infrastructure.
Ad - hoc
¢ Ad - hoc is purely a wireless network.
¢ In this the computing devices communicate with each other directly over wireless without using any access points in the network.
¢ Even if it uses any access points they generally vary in features and cost depending on the requirement.
¢ All wireless cards in ad - hoc form a peer -to -peer network.
¢ Ad hoc wireless setups are usually suitable for temporary arrangements, such as in meetings, etc.
Disadvantage As the devices are directly connected the network cannot communicate with the wired network
Infrastructure
¢ Infrastructure basically augments the existing wired network with a wireless LAN and extends the network .
¢ In this, there would be access points connecting to the network' s backbone.
¢ All wireless cards connect to a central access point that provides them connectivity with each other as well as the wired.
¢ The position of the access point should be such that the access point ranges overlap so as to provide roaming to mobile users. This way the user will get seamless connectivity as he passes from one access point to another. [ diagram]
DATA TRANSMISSION TECHNIQUES
Data transmission over wireless using Radio frequency is similar to the techniques used in an ordinary radio, AM and FM.
Basic principle
A constant carrier signal that is generated, is superimposed by another signal containing the data to be transmitted. The carrier frequency' s amplitude could be modulated by a signal (Direct Sequence), or its Frequency could be modulated (called Frequency Hopping). After modulation, the carrier signal no longer remains a single frequency, or fixed amplitude, depending upon the modulation technique.
There are two RF techniques used for data transmission in wireless LANs,
¦ Low power Narrowband
¦ Spread spectrum
Spread Spectrum is further divided into two more techniques, ¢ Frequency Hopping Spread Spectrum and
¢ Direct Sequence Spread Spectrum.





LOW-POWER NARROW BAND
> This was the first wireless transmission system that uses radio-transmission systems to transmit and receive user information on one specific radio frequency.
> The radio signal frequency is kept as narrow as possible to minimize cost through simple radio design.
> Every wireless node communicates using a different frequency, so that there' s no cross talk with other nodes. This prevents one node from listening to others.
> So while receiving, a node will filter out all other frequencies but for the one that' s meant for it.
Disadvantage
Narrowband technology has limited range, reliability, and security.


SPREAD SPECTRUM Introduction to Spread Spectrum
Spread spectrum is the art of secure digital communications that is now being exploited for commercial and industrial purposes. This group of modulation techniques is characterized by its wide frequency spectra. The transmitted signal bandwidth should be much greater than the information bandwidth.Then modulated output signals occupy a much greater bandwidth than the signal's baseband information bandwidth.
Inside the Spread Spectrum
Spread Spectrum signals use fast codes that run many times the information bandwidth or data rate. These special "Spreading" codes are called "Pseudo Random" or "Pseudo Noise" codes. They are called "Pseudo" because they are not real gaussian noise.

Some Important terms: Correlator
A SS correlator is a very special matched filter which responds only to signals that are encoded with a pseudo noise code that matches its own code
Generally ,an SS receiver uses a locally generated replica pseudo noise code and a receiver correlator to separate only the desired coded information from all possible signals.
An SS correlator can be "tuned" to different codes simply by changing its local code. This correlator does not respond to man made, natural or artificial noise or interference
The correlator then "spreads" out a narrow band interferer over the receiver's total detection bandwidth.
The total integrated signal density at the correlator's input determines whether there will be interference or not.
Threshold level
All SS systems have a threshold or tolerance level of interference beyond which useful communication ceases. This tolerance or threshold is related to the SS processing gain.
Processing gain
Processing gain is essentially the ratio of the RF bandwidth to the information bandwidth.
Characteristics of SS signals
SS signals are noise-like and appear wide-band which makes them possess the quality of Low Probability of Intercept

SS signals are hard to detect on narrow band equipment because the signal's energy is spread over a bandwidth of maybe 100 times the information bandwidth.
Common spread spectrum systems are of the "direct sequence" or "frequency hopping" type, or else some combination of these two types
(called a "hybrid")



Frequency Hopping Spread Spectrum
Frequency hopping is the easiest spread spectrum modulation to use.
A frequency hopped system can use analog or digital carrier modulation and can be designed using conventional narrow band radio techniques.
In Frequency Hopping, there' s a narrowband carrier signal that hops from one frequency to another in a pre-defined fashion.
It "hops" from frequency to frequency over a wide band.Both the transmitter and receiver know this hopping sequence or code sequence and therefore have to remain in synchronization in order to send and receive accurate data. and the rate of hopping from one frequency to another is a function of the information rate
Since the method hops over multiple frequencies, it forms a single logical channel used and maintained by the transmitter and receiver. To those who are not supposed to receive this signal, it appears to be wideband noise. the frequency hopper's output is flat over the band of frequencies used.
Between the two spread-spectrum technologies, DSSS (Direct Sequencing Spread Spectrum) and FHSS (Frequency Hopping Spread Spectrum), DSSS is more popular.
Direct Sequence Spread Spectrum.
A direct sequence system uses a locally generated pseudo noise code to encode digital data to be transmitted. The local code runs at much higher rate than the data rate.
Direct sequence spread spectrum systems are so called because they employ a high speed code sequence, along with the basic information being sent, to modulate their RF carrier.
The high speed code sequence is used directly to modulate the carrier, thereby directly setting the transmitted RF bandwidth.
Binary code sequences as short as 11 bits have been employed for this purpose, at code rates from under a bit per second to several hundred megabits per second.
In Direct Sequence Spread Spectrum technique, every binary ' 1' bit that' s transmitted is in the form of a sequence of ones and zeros. Every binary ' 0' transmitted uses the inverse sequence of this ' 1' bit. This redundant pattern for every bit that' s transmitted is called a
Chip.
A wider chip increases the chances of data recovery by the receiver.To unintended receivers, this appears as low-power wideband noise.


A Comparative study between SS and low power narrow band
> Spread Spectrum transmitters use similar transmit power levels to narrow band transmitters
> Because Spread Spectrum signals are so wide, they transmit at a much lower spectral power density, measured in Watts per Hertz, than narrowband transmitters. This lower transmitted power density characteristic gives spread signals a big plus.
> The spread of energy over a wide band, or lower spectral power density, makes SS signals less likely to interfere with narrowband communications.
> Narrow band communications, conversely, cause little to no interference to SS systems because the correlation receiver effectively integrates over a very wide bandwidth to recover an SS signal

ADVANTAGES OF SPREAD SPECTRUM

Most commercial part spread spectrum systems transmit an RF signal bandwidth as wide as 20 to 254 times the bandwidth of the information being sent. Some spread spectrum systems have employed RF bandwidths 1000 times their information bandwidth
Besides being hard to intercept and jam, spread spectrum signals are hard to exploit or spoof messages to a network.
SS signals also are naturally more secure than narrowband radio communications. Thus SS signals can be made to have any degree of message privacy that is desired
Spread Spectrum uses wide band, noise-like signals. Because Spread Spectrum signals are noise-like, they are hard to detect


APPLICATIONS
The Low Probability of Intercept (LPI) and anti-jam (AJ) features made Spread Spectrum use in milirary applications for so many years.
Applications for commercial spread spectrum range from "wireless" LAN's (computer to computer local area networks), to integrated bar code scanner/palmtop computer/radio modem devices for warehousing, to digital dispatch, to digital cellular telephone communications, to "information society" city/area/state or country wide networks for passing faxes, computer data, email, or multimedia data.
These spread spectrum signals are widely used in radar systems

In the future
There are also "Time Hopped" and "Chirp" systems in existence. Time hopped spread spectrum systems have found no commercial application to date. However, the arrival of cheap random access memory (RAM) and fast micro-controller chips make time hopping a viable alternative spread

spectrum technique for the future. "Chirp" signals are often employed in radar systems and only rarely used in commercial spread spectrum systems.
Many newer commercial satellite systems are now converting to SS to increase channel capacity and reduce costs.
Basic components of a wireless LAN
The basic components of building a wireless LAN includes
Wireless cards
Access Points
Client Adapters
Wireless cards
This is perhaps the most essential component of a wireless LAN. These perform the same functions as Ethernet cards in a wired network.
NICs (Network Interface Cards) ,PCI cards, PCMCIA are different wireless cards that connect the computer to the WLAN. Each card has it' s own advantage.
The network-management software configures wireless connections, checks their performance and allows the network manager to change them when required.
The wireless cards can be run in either one of two modes: ad hoc or infrastructure. In ad hoc mode wireless cards are able to communicate with each other without using an access point, and form a kind of Peer to Peer network. In infrastructure mode these cards communicate with an access point


Access points
Accesspoints are considered to be the most important component of the network
Access points serve as transmitters / receivers connecting the wireless clients to the wired network by bridging both the wired and wireless protocols.
The number of clients an access point can serve can vary. They extend the range of peer-to-peer WLAN by working as a repeater, doubling the distance between wireless clients
All PCs that are equipped with a wireless NIC and within the microsell of the access point get connected to the wired network without the use of cable thus creating a WLAN.
A number of access points can be connected to the wired network to allow clients to roam through the network.ensuring unbroken connectivity as long as roaming users stay in range of at least one access point.
An access point can transmit data upto 300 feet (100 meters approx.) depending on the obstacles in the environment.
Directional antennas are used when the distance between two WLANs is a mile or more.
Three kinds of Access points are currently available.
Point to point.: These are used to connect two LAN segments together.
Point to multi-point: Here all bridged units communicate with each other wirelessly.
Repeater:.In the first two modes, bridging units talk only to each other, and do not connect to wireless clients. These are also usually the most expensive.
Access points control traffic as they buffer , transmit and receive the data flowing between sender and receiver .
Client Adapters
WLAN adapters acts as interface between the client network operating system and the data arriving from access points.
The network operating system recognize wireless data as it would recognize Ethernet data.
Basic functionality of these adapters remain the same both in wired and wireless LAN.
In the future
Some other based products have also started appearing in the market. These include wireless Internet cameras, presentation gateways, and print servers.
With more such devices coming into the market, networks will become even more flexible.


HOW WIRELESS NETWORK WORKS
+ WLAN configurations can be simple or complex. At the most basic level, two PCs with wireless adapter cards can set up an independent network, peer-to-peer wireless LAN, whenever they are in range of one another.
+ An access point's radius is called as microcell. The best way to extend the radius of a wireless LAN is to install several access points.
+ Overlapping microcells create seamless access as we roam from one microcell to another.
+ In a setting with overlapping microcells , mobile devices and access points frequently check the strength and quality of transmission and wireless LAN system hands-off roaming users to the access points with strongest and highest quality signal.
+ Adapters and access points work together and follow a series of steps to determine which access point should accept a hand -off between cell sites. This exchange is based on available bandwidth , traffic ,signal strength and quality.
+ When an adapter detects one signal getting weaker and another getting stronger , it requests a switch , and the new access point accepts a hand- off from the previous access point.
+ More users can cause air-wave congestion which can lead to slower throughput.
+ Throughput improves when ever there is less interference, whether from internal user or external sources and when mobile users are closer to the access points, hence range is also important.The type of WLAN systems determines the type of throughput.
+ Thus effective high speed data transmission is achieved through Wireless Local Area Network technology.
SECURITY
WLAN provide enormous flexibility, but they also can be a potential open door into the network..
Unauthorized access to networks by way of a wireless access point can be all too easy if you don't employ measures to protect your data. The security technologies offer increasing levels of protection for wireless businesses.
WLANs have their roots in military technology, so, from their inception, security has been an important priority
A WLAN solution can support multiple layers of security.
To gain access to the network, you must know the network ID of an access point. Once a user is associated with an access point, they have the same security as provided on the wired network: authentication with login ID and password, and so on.
In addition, WEP (Wired Equivalent Privacy), a standards-based security protocol for wireless networks, may be enabled, providing further security.
Some WLAN products offer multiple layers of security, like access point locking, user authentication, domain identification and option to scramble wireless data transmissions using encryption.
ADVANTAGES
WLAN is highly reliable, and maintains its integrity which depend on a variety of factors like number of users.
> While WLANs provide installation and configuration flexibility and the freedom inherent in network mobility, customers may have some concerns when considering WLAN systems, including: throughput, security, ease of use, and power source issues.
> It is highly secure and thus it could find in various applications.
> It's range can be increased by increasing the access points which is not possible with other wireless technologies.
DISADVANTAGES
> It is highly expensive yet used in various fields of applications.
> Systems using different frequency bands do not interoperate, even if they both employ the same technology and systems from different vendors may not interoperate even if they both employ the same technology and the same frequency band, because of differences in implementation by each vendor.
> To counter these issues, an interoperability alliance organization, WECA (Wireless Ethernet Compatibility Alliance), is formed by WLAN providers. WECA' s mission is to certify interoperability of High Rate products and promote that standard for the enterprises, small businesses and homes.
> Products bearing the WECA logo will interoperate with products from other manufacturers also bearing the WECA logo



APPLICATIONS
To date, wireless LANs have been primarily implemented in vertical applications such as manufacturing facilities, warehouses, and retail stores and the future will see business segments like healthcare facilities, educational institutions, and corporate enterprise office spaces benefit with the growth of WLANs.
As wireless networking is also being used in home networking Home RF is considered as one of the best emerging technologies in Home networking.


HOME RF AND SWAP
The HomeRF Working Group (RF stands for radio frequency) was an alliance of businesses that developed a standard called Shared Wireless Access Protocol (SWAP). SWAP supports both voice and data communication .SWAP transmits and receives data at a rate of 1 or 2Mbps .
SWAP is inexpensive and easy to install. It requires no additional wires, no access point. It has good power management and allows up to 127 devices per network, also allows multiple networks in the same location. Security is also robust.
SWAP has a limited range (75 to 125 ft / 23 to 38 m). It's not compatible with FHSS devices. Physical obstructions (walls, large metal objects) can interfere with communication and is difficult to integrate into existing wired networks
Because of this lack of an access point, HomeRF networks are significantly cheaper than the other viable wireless network, WECA's Wi-Fi. However, to send large amounts of data (like video) back and forth, SWAP speed is probably adequate for most home use, and the freedom of no wires can be quite appealing.
WECA and Wi-Fi
The Wireless Ethernet Compatibility Alliance (WECA) has gone in a completely different direction from HomeRF. Targeted more at office use than home networks, Wi-Fi (for "wireless fidelity", like Hi-Fi for "high fidelity" in audio equipment).This specification drops FHSS and focuses on DSSS because of the higher data rate it can attain. Though it may occasionally slow down, this keeps the network stable and very reliable.
¢ It has a long range (1,000 ft / 305 m in open areas, 250 to 400 ft / 76 to 122 m in closed areas)
¢ It's easily integrated into existing wired-Ethernet networks.

¢ It's compatible with original 802.11 DSSS devices. Here are the disadvantages:
¢ It's expensive.
¢ It can be difficult to set up.
¢ Speed can fluctuate significantly.

TECHNOLOGY COMPARISON

Blue tooth Wireless LAN Home- RF Infrared
Frequency 2.4GHz 2.4GHz 2.4GHz IR band
Data rate 1Mbps 11Mbps 1.6Mbps 4Mbps
Range 10m 150m 45m 5m
Standard Blue tooth IEEE Shared Wired Access Protocol IrDA
Communication technique FHSS DSSS FHSS -
Usage - model Cable
replacement High - speed
network
access Low- speed , low cost voice and data
networking Point- to-point data transmission

The future
With the recent adoption of new standards for high-rate WLANs, mobile users can realize levels of performance, throughput, and availability comparable to those of traditional wired Ethernet. As a result, WLANs are on the verge of becoming a mainstream connectivity solution for a broad range of business customers.


There' s ongoing development in the area of wireless LANs. New standards are being developed by the IEEE to improve the performance and throughput. For instance, the latest draft standard, the 802.11g, is trying to take the throughput in wireless LANs to 20+ Mbps, and that too in the 2.4 GHz band. Given such a development, wireless LANs seem to be a promising technology for the future.
Conclusion
Our world is rapidly changing -- computers have gone from mainframes to palmtops. Radio communications has gone from lunchbox sized (or trunk mounted/remote handset car phone) to cigarette-pack-sized micro-cellular telephone technology. The technical challenges of this progress are significant. The new opportunities created by this new technology are also significant. We've talked here about some of the very basic principles in spread spectrum and talked about evolving career opportunities -- isn't it time somebody did something about moving forward in the new millennium



Contents
Abstract.
Introduction to Methods of Wireless networking.
What is Wireless LAN
Data Transmission techniques
Spread Spectrum technologies.
FHSS ( Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum).
Basic components of a wireless LAN.
How wireless LAN works
Security.
Applications.
Conclusion.