International Journal of Scientific & Engineering Research, Volume 3, Issue 9, September-2012 1
ISSN 2229-5518
OPTICAL WIRELESS COMMUNICATION: A FUTURE PERSPEC- TIVE FOR NEXT GENERATION WIRELESS SYSTEMS
Shuchita Chaudhary
Index Terms— Hybrid wireless systems, Indoor infrared wireless communications, Infrared, wireless communication, local area networks, Optical wireless, Outdoor optical wireless communication.
—————————— ——————————
N optical wireless (OW) communication system relies on optical radiations to convey information in free space, with wavelengths ranging from infrared (IR) to ultravio-
let (UV) including the visible light spectrum. The transmit- ter/source converts the electrical signal to an optical signal, and the receiver/detector converts the optical power into elec- trical current. Light emitting diodes (LEDs) or laser diodes (LDs) can be used as optical sources and photodiodes (PDs) as detectors [1]. An optical wireless communication system is an attractive alternative to radio, primarily because of a virtually unlimited, unregulated bandwidth. The optical spectrum is a universally available resource without frequency and wave- length regulations. An optical wireless communication system has the advantage of requiring low cost and low power con- sumption, also. In 1990s, some practical applications using optical wireless communication become actual, and some products and their standards were completed. Optical wire- less systems are classified into two categories depending on where the system is utilized.
There is a growing interest in indoor wireless networks as a consequence of the large scale utilization of personal comput- ers and mobile communicators. Infrared is preferred as wave- length in these applications, originally. This is because essen- tially a large total transmission bandwidth is possible, facilitat- ing fast transmission system due to the very high frequency involved in optical carrier. The Infrared Data Association (Ir- DA) specifies three infrared communication standards: IrDA- Data, IrDA Control, and a new emerging standard called AIr. Since this document focuses on IrDA-Data and its relationship to Bluetooth, for the purpose of this document, IrDA refers to the IrDA-Data standard. In general, IrDA is used to provide wireless connectivity technologies for devices that would normally use cables for connectivity. IrDA is a point to- point, narrow angle (30° cone), ad-hoc data transmission stadard
designed to operate over a distance of 0 to 1 meter and at speeds of 9600 bps to 16 Mbps.
Characteristics include:
Proven worldwide universal cordless connection.
Installed base of over 50 million units.
Wide range of supported hardware and software
platforms.
Designed for point-to-point cable replacement.
Backward compatibility between successive stan-
dards.
Narrow angle (30 degree) cone, point-and shoot style
applications. (Non-interference with other electronics and low-level security for stationary devices.)
High data rates; 4 Mbps currently, 16 Mbps under
development.
IrDA is used to transmit data by the following devices:
Notebook, desktop, and handheld computers
Printers
Phones and pagers
Modems
Cameras
LAN access devices
Medical and industrial equipment
Watches etc.
With a worldwide installed base of over 150 million units and growing at 40% annually, IrDA is widely available on person- al computers, peripherals, embedded systems and devices of all types. In addition, the wide use and acceptance of IrDA standards and robust solutions have accelerated adoption of the IrDA specifications by other standards organizations. The universal adoption and worldwide implementation of IrDA specifications guarantees a universal hardware port, and ra-
IJSER © 2012
The research paper published by IJSER journal is about Optical Wireless Communication: A Future Perspective For Next Generation Wireless Systems 2
ISSN 2229-5518
pidly emerging software interoperability [2].
Optical wireless communication is rapidly becoming a famili- ar part of modern urban life. Over the last half decade, there has been a steady increase in the number of consumers using high capacity data transmissions, and their data-rate demands have risen from hundreds of megabits per second to tens of gigabits per second. These consumers include businesses, edu- cational and recreational establishments, government offices, and utilities. Capacity-hungry communication applications range from local area network (LAN) systems to Internet and company intranet. The high data rates needed can be attained with optic fiber, which has been distributed to connect cities and continents. However, often the “last mile” from the fiber backbone to the client premises presents a significant problem. It may not be possible or practical to lay down optic fibers, and it is invariably costly and time-consuming. Optical wire- less communication (UOWC) can bridge the gap (Fig. 1).
FIGURE 1. A schematic illustration of an optical wireless communi- cation network
In fact, all modalities of wireless communication can offer solutions to the last mile problem, affording flexible and rapid connectivity. However, radio frequencies carry heavy tariffs and licensing fees. Furthermore, the beaurocracy involved in obtaining permits can take months. This is particularly troub- lesome when a temporary solution is sought, or an unexpected redeployment of premises calls for the provision of instant communication links. There is also growing concern about the health hazards associated with extensive exposure to radio frequency radiation. On the other hand, if eye safety hazards are allayed, optical communication is not dangerous. After all, sunlight has been harmlessly endured since time immemoria [3].
In contrast to wireless links, existing infrastructures of elec-
trical cable can be used to bridge the last mile gap as is famili-
ar with asynchronous digital subscriber line (ADSL) or cable
television (CATV) connectivity. However, the broadband data
rates offered by optical communications would be relin-
quished and data flow may stall. This solution is also subject
to high leasing fees. In practice, the unique features offered by
what is alternatively termed free space optics (FSO) or laser-
com (a popular abbreviation for laser communications) have
been demonstrated in the urban environment. Numerous links between high-capacity fiber backbone and end users function satisfactorily in major cities all over the world. An optical wireless communication system can provide the transmission capacities of fiber links using lightweight and compact equipment that can be installed in less than a day — and no licensing fees are necessary [4]. When installing a link, the transmitters and receivers can be placed on rooftops, lamp- posts, billboards, bridges, and even inside office windows, and a system can be operative within hours. A tragic example of the deployment efficiency of lasercom was witnessed fol- lowing the September 11th terrorist attacks. Communication with the disaster area was operational within hours, aiding in the recovery work itself and regaining connectivity with many of the businesses and companies hit by the devastation. In some applications, the high security features of OWC is of paramount importance, as the extremely directional, narrow beam optical link makes eavesdropping and jamming nearly impossible. Even if a transient bird can momentarily block the path, unwanted interferers are thwarted. This characteristic has been exploited for many years in high security satellite- ground links, which prefer the optical communication modali- ty because of its small “footprint.” Health and safety regula- tions ensure that the potential threats of laser light such as eye damage are held in check. Strict adherence to these rules makes OWC a safe and secure solution for easily deployable high bandwidth communication. Furthermore, with the many advances witnessed in optical communication technology, OWC is considered to have great potential for future cost- effective data links. Much groundwork research has already been done in the field of lasercom in intersatellite links, where many of the benefits listed for UOWC are equally advanta- geous.
The different kinds of links for indoor optical wireless com- munication have been classified, depending on the existence of a line of sight (LOS) path between the transmitter and the receiver, and the degree of directionality (directed, non di- rected or hybrid). The six basic configurations are shown in figure 2.
Figure 2. Indoor optical wireless link configurations
LOS link systems improve power efficiency and minimize
IJSER © 2012
The research paper published by IJSER journal is about Optical Wireless Communication: A Future Perspective For Next Generation Wireless Systems 3
ISSN 2229-5518
multipath distortion. Non LOS links, on the other hand in- crease link robustness as they allow the system to operate even when obstacles are placed between the transmitter and receiver, and alignment is not required.
Directed links also improve as the path loss is minimized, but this kinds of system need alignment of the transmitter, the receiver, or both, making them less convenient to use for cer- tain applications.
Directed-LOS links also improve power efficiency because the transmitted power is concentrated into a narrow optical beam making possible the use of narrower field of view (FOV) re- ceivers, and an improved link budget. Also this kind of system does not suffer from multipath distortion, and a predeter- mined maximum transmission distance can always be assured for a given optical power, independently of the reflective properties or the shape of the room, as far as the line of sight is not interrupted. Thus, the drawback of this configuration is that it is susceptible to blocking, and it requires aiming of the transmitter or receiver. A special case of this topology is the tracked system. This configuration presents the advantages of maximum power efficiency, and high coverage.
Hybrid non-LOS systems do not present the blocking prob- lem, but suffer from multipath distortion that increases as the area is increased.
One of the most attractive configurations is the non directed non-LOS, or diffuse. Systems working under this configura- tion do not require a direct line of sight, or alignment, between the optical transmitter and the receiver because the optical waves are spread as uniformly as possible in the room by making use of the reflective properties of the walls and ceiling. This kind of link has the advantages that it can operate even when barrier are placed between the transmitter and the re- ceiver. This makes it the most robust and flexible configura- tion. In spite of the advantages of the diffuse configuration, this kind of system suffers from multipath dispersion and higher optical losses than LOS and hybrid LOS. [1][5][12] Outdoor system configuration is changed from indoor system. As shown in fig 3 In outdoor system the transmitter telescope collimates the beam in the direction of the receiver and deter- mines the beam diameter. At the receiver, a telescope collects the incoming light and focuses it onto the photodetector, which then converts it to electric current.
Figure 3. Outdoor optical wireless link
The electrical signal is amplified and processed. A decision
making device determines the nature of the signal according
to its amplitude and arrival time. The quality of reception is
measured by the probability of error, expressed in terms of bit
error rate (BER). The transmitter and the receiver are sepa-
rated by the propagation channel, which, in the case of out-
door OWC the atmosphere. Even on an apparently clear day the atmosphere is pervaded by molecules and aerosols, which cause absorption and scattering of the light. Changes in tem- perature along the propagation path lead to scintillations in the received light due to the resultant due to the resultant tur- bulence. Line of sight is imperative for outdoor OWC, and may be maintained with the help of a tracking and pointing system. Tracking is performed in two stages, coarse tracking and fine pointing. Coarse tracking may use GPS or other a priori Knowledge. Fine pointing requires electro-optic me- chanisms such as a quadrature or a matrix detector. Pointing involves a beam-steering device which may be mechanical, such as a galvo-mirror, or non-mechanical, such as acousto- optic crystals, electro-optic devices or optical phased arrays (OPAs).
The individual link between transmitter and receiver can be extended to a network topology. This allows for greater flex- ibility and extends the effective transmission range.
3. APPLICATIONS AREA FOR OPTICAL WIRELESS
There is little doubt that radio solutions will remain dominant for most applications, but there are several areas where OW is attractive.
There is also a growing interest in optical communications between moving vehicles, and between vehicles and roadside hubs. These are being considered for telematic applications, such as road pricing and navigation, as indicated by the de- velopment of an ISO standard (ISO CALM 204) for such sys- tems. The German government has adopted an optical com- munications system for its tolling system for freight vehicles [6]. Several train-operating companies are investigating FSO for communications with trains, to provide broadband „to the seat‟.
There are a number of applications where OW can provide secure communications. The IRDA is promoting „Financial Messaging‟, where a secure transaction takes place between a handheld and a retail terminal, albeit at low data rates [7]. Such a concept might be extended to retailing of high band- width content such as DVDs and CDs to portable players. In the future this might require several Gb/s in order to achieve reasonable download times. Theft of content would be limited by the confined nature of the optical signal, and extremely high spatial bandwidth could be achieved within the retail environment. This is relatively straightforward to achieve with a directed OW link used in a „point and shoot‟ manner, or in a booth in which the link environment can be controlled.
There may also be other environments such as dealing rooms where secure wireless networks are required, and OW can easily provide this.
IJSER © 2012
The research paper published by IJSER journal is about Optical Wireless Communication: A Future Perspective For Next Generation Wireless Systems 4
ISSN 2229-5518
Applications such as virtual reality suites, and wireless TV studios require multi Gb/s wireless communications with very high spatial bandwidth density. The directivity available with optical links, combined with tracking makes this feasible. [11]
One of the major growth sectors in avionics is data and speech communications to aircraft. Satellite broadband is being added to aircraft, and many aircraft are equipped with telephone to the seat. The wireless link from the passenger to the data in- frastructure is currently not possible, and OW represents per- haps the only allowable alternative. A mobile phone or PDA containing a radio and optical terminal could allow seamless communications with a local optical base station part of the aircraft infrastructure. Hospitals offer similar opportunities, both in wireless instrumentation and transmission of data. In sensitive environments, the access point or network could au- tomatically disable the radio interface, enabling communica- tions through the optical link.
In broad terms optical wireless provides high bandwidth, and providing coverage is problematic, whilst for RF approaches the opposite is the case. Perhaps the key advantage of OW (in a general environment where security is unimportant) is the ease with which high bandwidth LOS channels can be pro- vided, and the potential these have to decrease the load on the infrastructure. Hybrid systems that can allow this are there- fore attractive, and fit well within the 4G vision of heterogene- ous wireless systems working together to provide a seamless infrastructure. Very simple hybrid approaches combining opt- ical and radio frequency links have been proposed recently for short-range (indoor) communications [8, 9]. Reference [10] describes protocols that use RF signalling and reallocate the optical sources under blocking conditions. Future research in this area is discussed in later sections.
The Optical Mobile
In modern smart phones 3 communication channels available (RF, Mobile, Giga Speed). It Provide optical mobile communication within a RF free environment and fastest data transfer method of a mobile device. It can be Communicates optical "on the move" at
100 Mbit/s and GigaSpeed data transfer and reception 10 Gbit/s.
The Optical Memory
Optical memory is the most basic version of a wireless optical data network. Optical memory stick consist GigaSpeed mobility transceiver. It can be used for data storage and connects equipment to each other within a range of 1 m. memory stick uploads and downloads files with GigaSpeed tech- nology and communicates with mobile device within a range of 2 m.
IRDA has formed The Travel Mobility Special Interest Group (IrTM) in order to develop a specification for toll payment. A standard also exists for longer-range communications (ISO TC
204 CALM). A major commercial amount of activity is by Ef- kon, who have won large contracts for payment systems worldwide, notably a German project for truck traffic tolling.
Much more commercial optical system being investi- gated that are not discussed in this paper are optical router, GigaSpeed Technology , The Optical Room Connector , Ultra- high bandwidth wireless etc.
This paper reviews OW communication technology; over- views research activities, and state the perspective for next generation wireless network. It is anticipated that further ex-
IJSER © 2012
The research paper published by IJSER journal is about Optical Wireless Communication: A Future Perspective For Next Generation Wireless Systems 5
ISSN 2229-5518
perimental and theoretical studies will provide enhanced foundations for important new developments in this very ra- pidly growing area. Future wireless standards offer a good opportunity for the wider adoption of OW. In particular, as
4G networks will be highly heterogeneous, OW based air
interfaces can be incorporated to terminals in addition to
the conventional RF based ones. Considerable work is still
needed to fully exploit the clear advantages of the optical
solutions, as well as developing low-cost subsystems and
components to implement them.
[1]. Indoor Optical Wireless Communication: Potential and State-of-the- Art. IEEE Communications Magazine • September 2011
[2]. IrDA and Bluetooth: A Complementary Comparison ©Copyright 2000,
Extended Systems, Inc. Author: Dave Suvak
[3] I. Kim et al., “Wireless Optical Transmission of Fast Ethernet, FDDI, ATM, and ESCON Protocol Data using the TerraLink Laser Communica- tion System,” Opt. Eng., vol. 37, no. 12, 1998, pp. 3143–55.
[4] E. J. McCartney, Optics of the Atmosphere, Wiley,
[5] STEVE HRANILOVIC Springer eBook ISBN: 0-387-22785-7 “Wireless
Optical Communication Systems” [6] http://www.efkon.com. 2004. [7] www.irda.org.
[8]. Miyamoto, S., Y. Hirayama, and N. Morinaga. Indoor wireless local area network system using infrared and radio communications. in Proceedings of APCC/OECC'99 5th Asia Pacific Conference on Communications/4th Optoelec- tronics and Communications Conference. vol.1 18 22 Oct. 1999 Beijing, China.
1999: Beijing Univ. Posts & Telecommun, Beijing, China.
[9]. Sakurai, Y., et al. A study of seamless communication method with the ade- quate switching between optical and RF wireless LAN . in 2003 Digest of Tech- nical Papers. International Conference on Consumer Electronics. 17 19 June 2003
Los Angeles, CA, USA. 2003: IEEE, Piscataway, NJ, USA.
[10]. Hou, J., D.C. O'Brien, and D.J. Edwards, Polling scheme for indoor LOS
optical wireless LAN. Electronics Letters, 2003.
[11]. Foerster, J., et al., Ultra-Wideband technology for short- or medium-range wireless communications. Intel Technology Journal. 2001.
[12]. Kahn, J.M. and J.R. Barry, Wireless infrared communications. Proceed- ings of the IEEE, 1997. 85(2): p. 265-298.
IJSER © 2012