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WIRELESS OPTICAL COMMUNICATION

Wireless OPTICAL COMMUNICATION is suitable for wireless home links because:
¢ Wide bandwidth is available for an optical carrier and is suitable for high speed transmission
¢ The optical devices are small and low in cost.Thus they can simplify the structure of transmitters and receivers
¢ The optical wireless network needs no license

There are certain scenarios in which RF signals are not suitable because:
¢ They produce and are affected by EM interferences
¢ As they require legal procedure to be installed they are confined to some frequencies and the bandwidth become a scarce recourse
¢ They can be intercepted by other users and communication can result non secure

WHAT DO WIRELESS INFRARED COMMUNICATION OFFER

¢ They neither produce,nor are affected by EM interferences,so they can be used in EM restricted scenarios and in others in which interferences are present now
¢ They do not require legal procedures to be installed so you have all the bandwidth you can manage
¢ There are well established commercial devices and standards offering good performance
¢ They can be intercepted but it is not easy to accessdata without detection and even without codification

UOWC
It is URBAN OPTICAL WIRELESS COMMUNICATION
The UOWC terminal includes an optical transmitter and a receiver positioned,several hundred meters

ADVANTAGES OF UOWC
RAPID DEVELOPMENT
LIGHT WEIGHT
HIGH CAPACITY COMMUNICATION WITHOUT LICENSING FEES AND TARIFFS

WHY INFRARED FOR MEDICAL APPLICATIONS
The standardisation of communication processes that has led to the explosion of tele communication products in the consumer area has yet to take hold in the world of clinical medicine
IT standards within the commercial application domain are inadequate to fully address the needs of the clinical IT domain especially in the patients bed side
RF system has got security and operation problems

ON BOARD APPLICATIONS
¢ ON BOARD systems for cable replacement on satellites
¢ Weight considerations
¢ Robustness on rocket launching

CONCLUSION
¢ UWB is to assume much of the nowadays applications of wireless optical systems
¢ MANY OF THE SCENARIOS are held by very conservative organisations such as hospitala,nuclear administrations and changes are delayed to the state of art in communications
¢ Optical system have an opportunity on cheap in house and ad-hoc sensor internet working

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wireless communication systems

INTRODUCTION
Traditional wireless communication systems use a single antenna for
transmission and a single antenna for reception. Such systems are
known as single input single output (SISO) systems (Fig.1). In
recent years, significant progress has been made in developing
systems that use multiple antennas at the transmitter and the receiver
to achieve better performance[3]. Such systems are known as
multiple input multiple output (MIMO) systems (Fig.2).
There are two types of benefits of using multiple antennas: link
budget / spatial diversity improvement and throughput improvement
from spatial multiplexing. Both are intrinsic to wireless channels,
where rich spatial variations or spatial dimensionality exist [3].
Spatial diversity refers to the fact that the probability of having
all antennas at bad locations is significantly lower as the number of
antennas increases. Link budget improvement refers to the fact that
the signals from the various antennas can be combined to form a
signal stronger than any of the individual signals. For receive
spatial diversity, signals received on multiple antennas are weighted
and combined, e.g. maximal ratio combining (MRC)[3]. There are
two types of transmit spatial diversity, open-loop and closed-loop.
Open-loop transmit diversity involves transmitting signals from
multiple antennas in some deterministic pattern, that does not
depend on the channel. Open-loop techniques include cyclic delay
diversity (CDD) and space-time block codes (STBC)[3]. Closedloop
transmit diversity techniques, in contrast, require channel
information to guide transmissions. An example is transmit
beamforming (TxBF), where proper magnitude and phase weights
computed from the channel estimation are re-applied across
antennas to aim the signal in a given desired direction[3]. MIMO
systems with spatial diversity achieve better performance, i.e. longer
range for a given data rate, or higher data rate than SISO systems at
a given same location.

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optical communication


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INTRODUCTION

When we talk about optical communication, most people think about optical-fiber. But optical communication is also possible without optical-fiber. We know that light travels through air for a lot less money. This makes possible the optical communication without optical-fiber. Optical communication without fiber is known as Free Space Optics. It is used due to economic advantages. Since the introduction of internet the backbone traffic is increasing at the rate greater than 100%, hence the owner of the backbone infrastructure (which is entirely based on fiber optics) are eagerly embracing technologies that add of the capacity of the fiber optics without adding mountains of optical cables.
FSO is not a new idea. 30-years back optical-fiber cables are used for high-speed communication. In those days FSO are used for high-speed connectivity over short distances. Today’s FSO can carry full-duplex data at gigabit-per-second rates over metropolitan distances.


What is Free Space Optics (FSO)?
Free Space Optics (FSO) is a line-of-sight technology that uses lasers to provide optical bandwidth connections. Currently, Free Space Optics are capable of up to 2.5 Gbps of data, voice and video communications through the air, allowing optical connectivity without requiring fiber-optic cable or securing spectrum licenses. Free Space Optics require light, which can be focused by using either light emitting diodes (LEDs) or lasers (light amplification by stimulated emission of radiation). The use of lasers is a simple concept similar to optical transmissions using fiber-optic cables; the only difference is the medium. Light travels through air faster than it does through glass, so it is fair to classify Free Space Optics as optical communications at the speed of light.



HOW FREE SPACE OPTICS (FSO) WORKS

Free Space Optics (FSO) transmits invisible, eye-safe light beams from one "telescope" to another using low power infrared lasers in the teraHertz spectrum. The beams of light in Free Space Optics (FSO) systems are transmitted by laser light focused on highly sensitive photon detector receivers. These receivers are telescopic lenses able to collect the photon stream and transmit digital data containing a mix of Internet messages, video images, radio signals or computer files. Commercially available systems offer capacities in the range of 100 Mbps to 2.5 Gbps, and demonstration systems report data rates as high as 160 Gbps.


FSO: WIRELESS, AT THE SPEED OF LIGHT

Unlike radio and microwave systems, Free Space Optics (FSO) is an optical technology and no spectrum licensing or frequency coordination with other users is required, interference from or to other systems or equipment is not a concern, and the point-to-point laser signal is extremely difficult to intercept, and therefore secure. Data rates comparable to optical fiber transmission can be carried by Free Space Optics (FSO) systems with very low error rates, while the extremely narrow laser beam widths ensure that there is almost no practical limit to the number of separate Free Space Optics (FSO) links that can be installed in a given location.

WIRELESS OPTICAL COMMUNICATION

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ABSTRACT

This paper deals with the Wireless Optical Communication (WOC). In this paper we mainly discuss the problems with the conventional methods of communication such as Permissions, License fees, Lack of International standardization, Wastage of power and Security and how this new technology of WOC can be used to overcome these problems, along with its own set of advantages. We also discuss about the competitions it is facing and how it stands apart, and finally how low cost user friendly devices built using this technology can be used in the Rural Indian Scenario.

INTRODUCTION

As the term wireless optical communications (WOC) suggests, this is a group of technologies that use light to communicate through the air, and require clear line of sight between units. Modern systems typically use lasers or light-emitting diodes to produce the light at one end, while photo diodes at the receiver sense the incoming light, and send an appropriate signal to a connected computer.
In the telecommunications space, WOC systems are in use in niche applications, mostly for high-bandwidth applications needing to transfer hundreds of megabits per second, over distances typically less than a kilometer. Recent developments promise to bring WOC into the realm of inexpensive consumer products.

CURRENT SCHEMES OF WIRELESS COMMUNICATIONS

In the last decades, the use of wireless has grown at a furious pace. The advantages of wireless are rapid deployment, without the need to dig trenches for cables, and seek permissions for right of way. A big advantage of wireless is in allowing people to communicate while they are mobile. The systems in common use are:

Satellite

While satellites in low-earth orbit are sometimes used for communication, the most common are geostationary satellites, which are stationed approximately 34000 km away. These are particularly useful to bring communications to remote areas, and are also well suited to situations where the same content has to be delivered to a large number of people, as in the case of radio (Worldspace) and TV. Satellites, of course, are expensive to make and to maintain.

Radio

Over the years, a plethora of systems for radio communication have been developed. These use a variety of frequencies, as well as protocols for modulating the carrier frequency with data, and cover ranges from a few to thousands of kilometers. Perhaps the best recognized examples of such communication are the microwave towers scattered around the countryside.

WHY OPTICAL WIRELESS

Optical communication is, as a rule, a completely unregulated market, except to the extent required to protect the human eye from a strong beam. Under the IEC 8025 standard, to be unconditionally safe, devices must conform to a CLASS 1 designation This permits viewing at any range over any duration even using optical aids such as binoculars. The miliwatts of power typically used by modern optical communication systems are well below such limits. Since the frequencies used are unregulated, they attract no license fees, while the same frequencies can be used all over the world, eliminating the need for different models for different countries. A solution for South Asia could therefore easily be exported.
Laser beams can easily be focused very narrowly. "Laser pointers are cheap examples demonstrating mill radian collimation from a millimeter aperture. To get similar collimation for a 1 GHz RF signal would require an antenna 100 meters across, due to the difference in wavelength of the two transmissions. A similar advantage is seen at the receiver, where compact lenses can be used for optical beams, while radio signals need large and unwieldly antennae at the receiver end as well, to obtain significant improvement in efficiency. Because laser beams are tightly focused, it is nearly impossible for anyone to intercept them, or even to detect their use. Beams of light effortlessly pass through each other, without interfering. These considerations make it unlikely that optical communication will be regulated even in the future.

WOC PRODUCTS IN THE INTERNATIONAL MARKET

While most products allow only point-to-point communication, companies such as AirFiber and Terabeam have brought out products that easily allow a mesh of links between nodes to be set up. Prices are in the thousands, if not tens of thousands of dollars.

INDUSTRY PROBLEMS

The narrow beams used in wireless optical communications need to stay focused, even through wind and vibration. This requires special hardware for automatic alignment. Then again, weather and flying birds can interfere with quality reception. Consequently, the difficulties faced by the industry include:

High-speed, high cost niche

The products available in the market provide orders of bandwidth more than what the consumer needs, at a price she cannot afford. They are used when other methods are infeasible, or when a large amount of bandwidth needs to be provided at short notice, for instance during a conference.

Competition

Telecommunications is an industry with a high rate of innovation, with a variety of systems in use, which WOC must compete with. These include systems both, in the wired and wireless space. Only those that offer broadband connectivity are discussed here.

Optic Fiber

Much investment has taken place all over the world in this technology, which for long-distance high-bandwidth traffic has no equal. However, there are limitations: Almost 90 percent of all office buildings in the United States have no fiber connection. To link a building with fiber costs between $100,000 and $200,000 and often involves a provisioning delay of four to 12 months. Given the cost and time required, it is not realistic to expect optic fiber to reach all our villages any time soon.

CONCLUSION

Wireless optical communication has advanced far enough, that it encompasses all the benefits of conventional wireless - quick deployment and mobile communication, while delivering a million times more bandwidth than a GSM phone, providing much higher security and consuming far less power. Since, unlike conventional wireless, optical devices operate in globally unregulated frequency bands, they have an unrestricted global market. To make this technology marketable in rural South Asia, an end-user device costing under $10 is needed. A telephone handset that communicates optically with the base station would fit the bill.Our electrical industry has an understanding of the manufacturing processes of Opto-electronic equipment. Moving in a hi-tech direction such as this is becoming imperative for companies threatened by competition from across the Chinese border.