INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303
Free-Space Optical Networking Using the Spectrum of Visible Light Nitin Chacko1 1
2
Department of Electronics and Communication Engineering Rajagiri School of Engineering and Technology, Cochin nitinchacko7@gmail.com
Swapna Davies2 Department of Electronics and Communication Engineering Rajagiri School of Engineering and Technology, Cochin swapnadavies@gmail.com
Abstract— Radio frequency technology suffers from limited bandwidth and electromagnetic interference. The recent developments in solid-state Light Emitting Diode (LED) materials and devices are driving resurgence into the use of Free-Space Optical (FSO) wireless communication. LED-based network transceivers have a variety of competitive advantages over RF including high bandwidth density, security, energy consumption, and aesthetics. They also use a highly reusable unregulated part of the spectrum (visible light). Many opportunities exist to exploit low-cost nature of LEDs and lighting units for widespread deployment of optical communication. The prime focus is to reducing cost, and for that, we have to make appropriate selection of system’s components, e.g. modulation, coding, filtering. The objective is to describe the viability of an optical free-space visible light transceiver as a basis for indoor wireless networking and to achieve acceptable bit error rate (BER) performance for indoor use, with a low cost system. Index Terms— Free-space optics, Light Emitting Diode, Optical communication, Optical modulation techniques, Visible light spectrum, Wireless communication . —————————— ——————————
1 INTRODUCTION Optical wireless communication (OWC) refers to a free-space optical (FSO) link, where the transmitter and receiver are not necessarily aligned to each other. OWC in general addresses quite different applications, starting from chip-to-chip interconnects and ending in intra-satellite data links. OWC links can be realized with quite different optical sources and detectors. For low data rates, traditional light bulbs, liquid crystal displays (LCDs), or plasma display panels (PDPs) can be used. In the receiver end, low-cost digital cameras are used as they are currently featured in every mobile device. As societal dependence upon wireless systems continues to grow, wireless technology needs to expand to meet the demand. Phones, laptops, and global positioning systems are all devices that implement certain forms of wireless communication to send information to another location. However, the availability of current forms of wireless is very limited, and it is not necessarily safe to implement wireless radio, making it necessary to explore other alternatives to wireless communication to allow continued expansion upon communication systems and to ensure safe use. The radio spectrum is highly congested and the demand for wireless data communication is increasing day-by-day. The bandwidth required for the radio frequency communication is rapidly getting exhausted.[1,2] The introduction of multiple nodes and cell splitting can be done to overcome this, but it is expensive. Also, two nodes do not provide double the capacity of one due to the interference issue. Moreover, doubling the infrastructure will not double the revenue. Recent studies on the hazards of radio frequency have found that extreme radio frequency radiation causes adverse effect on the environment. Optical Wireless Communication (OWC) refers to a free-space optical (FSO) link, where both transmitter and receiver are not necessarily aligned to each other. OWC in general addresses quite different applications, starting from chip-to-chip interconnects and ending in intra-satellite data links. OWC links can be realized with
quite different optical sources and detectors. For low data rates, traditional light bulbs, liquid crystal displays (LCDs), or plasma display panels (PDPs) can be used. In the receiver end, low-cost digital cameras are used as they are currently featured in every mobile device. The new LED-based luminaries will be omnipresent a few years from now. Besides their original lighting function, their light can be modulated at high speed. In this way, we can realize significantly higher data rates over moderate distances.[3] When compared with the traditional incandescent and fluorescent lamps, LEDs have a number of advantages such as a longer life expectancy, a higher tolerance to humidity, a smaller size and lower power consumption. As the cost of manufacturing decreases, LEDs become affordable and popular for color displays, traffic signals, and for illumination applications.[4] In recent years, LEDs have been used to transmit data at higher rates over a short-range optical wireless communication link. For dual purpose of illumination and data communications, white LEDs are ideal sources for future applications. With the availability of highly efficient white LEDs or by using a blue emitter in combination with a phosphor, we are witnessing a surge in research and development in indoor visible light communication systems. Light Emitting Diode (LED) Visible Light Communication (VLC) system is creating a possible valuable addition to future generations of technology, which have the potential to utilize light for the purposes of advanced technological communication at ultra high speed surpassing that of current wireless systems.[5] The most common link configurations for indoor OWC systems are the line-of-sight (LOS) and the diffuse or a hybrid LOS-diffuse.
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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 Normally, the diffuse system provides a larger coverage area and an excellent mobility, but at the cost of lower data rates, higher path losses and multipath induced inter-symbol interference (ISI) caused by the signal reflections from walls and other objects within the room. On the other hand, LOS links, where the beam is confined within a narrow field-of-view (FOV), offer a much higher channel capacity and a longer range. However, LOS links offer a limited coverage area as well as requiring alignment and tracking to maintain link availability. In order to protect the data integrity during transmission the input data should be framed, so as to detect lost signals and to ensure correct transmission and reception of the data. Computer network protocols like stop and wait algorithms are employed to solve this problem.
terminal, has a dedicated FOV of 30° to ensure seamless connectivity as well as alleviating the need for using pointing and tracking schemes. In addition, the suitable modulation scheme can also be adopted to improve the overall system capacity. The separation between the source and receiver will be a few meters. Each compartment or cell consists of an LED transmitter, a diffuser and an optical receiver.
2 VISIBLE LIGHT COMMUNICATION The radio spectrum is highly congested and the demand for wireless data communication is increasing day-by-day. Bandwidth required for the radio frequency communication is rapidly getting exhausted. Introduction of multiple nodes and cell splitting can be done to overcome this, but it is expensive. Also, two nodes do not provide double the capacity of one due to the interference issue. Moreover, doubling the infrastructure will not double the revenue. Recent studies on hazards of radio frequency have found that extreme radio frequency radiation causes adverse effect on environment.[2,3] Optical wireless communication (OWC) systems operating in the visible band (390–750 nm) are commonly referred to as visible light communication (VLC). The history of Visible Light Communications (VLC) dates back to the 1880s in Washington, D.C. when the Scottish-born scientist Alexander Graham Bell invented the photophone, which transmitted speech on modulated sunlight over several hundred meters. This pre-dates the transmission of speech by radio. Visible light communication is a subset of wireless optic technology. Specially designed electronic device containing a photodiode receives signals from light sources. The image sensor used in these devices is in fact an array of photodiodes and in some applications its use may be preferred over a single photodiode. Such a sensor may provide either multi-channel communication or a spatial awareness of multiple light sources.
3 SYSTEM DESCRIPTION Precise dimming appears to be challenging for incandescent and gasdischarge lamps, whereas in the LEDs it is quite convenient to accurately control the dimming level. This is because, the LED response time during on and off switch operation is very short. Therefore, by modulating the driver current at a relatively high frequency, it is thus possible to switch LEDs on and off without this being perceived by the human eyes.
Fig. 1. Indoor cellular visible light communication with four compartments (cells)
3.2 Transmitter End The network transmission elements and lighting are very often used in the same space, and thus combining the two devices into one would save on overall component and power cost. Similarly, light sources such as traffic lights can be retrofitted with VLC capabilities to enable vehicular communications, or at the very least, road-tovehicle communications, where traffic lights can be used to transmit information about upcoming traffic. All of these use cases rely on the implementation of a modulated light source for communication. Given the ease of modulating LEDs electrically, the extension of LED lighting towards communications seems a natural next step. Additionally, research has demonstrated that white LEDs are a viable low-cost next step with respect to power efficient lighting. The comparative assessment of the luminous efficacy of different light sources is shown in table I. LEDs with no shaping lenses can be essentially considered as the Lambertian source. A surface which obeys Lambert's law is said to be Lambertian, and exhibits Lambertian reflectance. Such a surface has the same radiance when viewed from any angle. This means that, to the human eye it has the same apparent brightness (or luminance). It has the same radiance because, although the emitted power from a given area element is reduced by the cosine of the emission angle, the apparent size (solid angle) of the observed area, as seen by a viewer, is decreased by a corresponding amount. Therefore, its radiance is the same.
3.1 VLC System Overview LEDs are used both for lighting as well as communications. LED access points are connected to the backbone wired network.[1] Communications for the entire room in the system is covered by four optical cells, each of which has a wide divergence angle LED source. At the receiving end, the optical receivers, mounted on a mobile
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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 TABLE 1 APPROXIMATE LUMINOUS EFFICACY OF DIFFERENT LIGHT SOURCES
Holographic Diffusers are used to control the diffuse area of illumination and increase transmission efficiency to greater than 90 percentage from filament lamps, LEDs, arc lamps, and other sources. Standard ground glass and opal glass will produce diffuse illumination, but the diffuse light area will often exceed the requirements of the system.[1] This over-illumination, associated with traditional diffusers, reduces efficiency and can often lead to added costs by requiring higher power illumination sources, lenses, and possibly filters. It is important to note that diffusing angles are given for a collimated input beam and angular divergence will vary for different incidence angles.
lm/W = Lumens per Watt, hrs = Hours
In many applications, there are requirements for specific radiation distributions to ensure a full coverage and an optimum link performance. In such cases shaping lenses are used at the transmitter.[3,4] The light source position at the center of a compartment or cell is composed of an LED and an optical lens. To achieve a wider coverage area with a uniform radiation distribution pattern, a luminit holographic LSD is employed at the transmitter end. Figure 2 depicts the system block diagram of a signal cell VLC system which includes a transmitter, a concentrator, filter and a detector.
Fig. 2. Block diagram representation of visible light communication system
Unlike many holographic elements, these specific polycarbonate components can be used throughout the visible and near-infrared. The hologram is a two level surface relief diffractive element that affects only the phase of light passing through it. The far-field radiation pattern passing through the hologram is approximately the Fourier transform of the surface relief structure. In order to simplify the calculation of the beam intensity through the holographic LSD, it is divided into an array of ``pixels,'' and the MATLAB platform is used to simulate the beam profile for every pixel. For a very tiny beam profile, the intensity of light can be considered as uniform after passing through the single pixel. Finally, the overall coverage area is could be the sum of individual foot prints per pixel.
3.4 Receiver End A typical indoor optical wireless communication receiver frontend usually consists of a concentrator, an optical filter, a photodetector, a pre-amplifier, a post-equalizer, and an electrical filter. A schematic diagram is shown in figure. The specifications for the receiver are given in Table II. TABLE 2 SPECIFICATION OF INDOOR VLC SYSTEM
3.3 Extension of Divergence Angle of Transmitter The holographic light shaping diffusers provide extended effective divergence angle. đ?œƒ đ?‘œđ?‘˘đ?‘Ąđ?‘?đ?‘˘đ?‘Ą =
đ?œƒ(đ??šđ?‘‚đ?‘‰)2 + đ?œƒ(đ??żđ?‘†đ??ˇ)2
(1) where, θ (output) is the effective output angle of the light, θ (FOV) is the light source field-of-view and θ (LSD) is the angle of holographic light shaping diffuser.
MHz = Mega Hertz, nm = Nanometer, mW =Milli Watt, m = meter, mm = millimeter, A/W = Ampere/Watt, ns=nanosecond
Fig. 3. Visible light communication using holographic light shaping diffuser
For Non-LOS channel or non-directed channel such as a diffuse channel, using non-imaging hemispherical or compound parabolic concentrator (CPC) and corresponding optical filter could effectively enlarge the active receiving area and broaden the FOV to increase the received optical power. However, for the directed LOS channel, the FOV should be designed to be small to reduce the received ambient light noise power because the ambient light noise is usually
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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 diffused inside the whole room as background light. Generally there are two kinds of photodetectors that can be adopted in an indoor LOS VLC system design - the photodiode (PD) and the image sensor. The photodiode has been widely adopted in optical communication systems with relatively large received optical power. The advantages of the photodiode include its low price and possible high reception bandwidth. The bandwidth of the photodiode is usually inversely proportional to its active receiving area due to the internal capacitance along with the receiving area.[5,6]
Among all modulation techniques based on intensity modulation with direct detection, on-off keying (OOK) is the most used scheme for digital optical transmission due to its simplicity. A bit one is simply represented by an optical pulse that occupies the entire or part of the bit duration while a bit zero is represented by the absence of an optical pulse. Both return-to-zero and non-return-tozero schemes can be applied. In the NRZ scheme, a pulse with duration equal to the bit duration is transmitted to represent 1 while in the RZ scheme, the pulse occupies only the partial duration of bit. The electrical power spectral densities of OOK-NRZ and OOK-RZ (Duty cycle = 0.5) assuming independently and identically distributed (IID) ones and zeros are given by sin đ?œ‹đ?‘“ đ?‘‡đ?‘? đ?œ‹đ?‘“ đ?‘‡đ?‘?
đ?‘ đ?‘‚đ?‘‚đ??žâˆ’đ?‘ đ?‘…đ?‘? đ?‘“ = (đ?‘ƒđ?‘&#x; đ?‘…)2 đ?‘‡đ?‘?
2
1+
� (�)
(2)
đ?‘‡đ?‘?
Fig. 3. Receiver front-end for the VLC system
Compared with the photodiode, the image sensor is able to provide receiver spatial diversity to enhance detection performance and additional source location information for location-aware services. For application scenarios where multiple LED arrays in a room send different signals to multiple users, using a large FOV PD detector may lead to large interference that degrades received SNR. In this case an image sensor would better serve as a photodetector that could effectively discriminate different LED arrays and reduce inter-array interference. Besides, using an image sensor to realize high data rate MIMO optical wireless communication has also been proved to be feasible. The major noise sources present in an indoor VLC system include ambient light noise (background solar radiation through windows, incandescent radiation, and fluorescent radiation), signal and ambient light induced shot noise in the photodetector, and the electrical preamplifier noise. The ambient light noise induced by background solar radiation and incandescent lamps represents essentially a DC interference that could be easily eliminated using an electrical high pass filter. The noise induced by fluorescent lamps needs to be determined in different application scenarios based on what kind of driving circuit is used.
4 MODULATION TECHNIQUES The eye safety introduces a limitation on the amount of optical power being transmitted For indoor applications, the eye safety limit on transmit optical power is even more stringent. The optical channel differs significantly from the RF channels. Unlike RF systems where the amplitude, frequency and phase of the carrier signal are modulated, in optical systems, it is the intensity of the optical carrier that is modulated in most systems operating below 2.5 Gbps data rates. For data rates greater than 2.5 Gbps, external modulation is normally adopted. Additionally, the use of photodetectors with a surface area many times larger than the optical wavelength facilitates the averaging of thousands of wavelength of the incident wave.[3]
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= (đ?‘ƒđ?‘&#x; đ?‘…)2 đ?‘‡đ?‘?
∞
2
đ?›ż(đ?‘“ −
1+ đ?‘›=−∞
đ?‘› ) đ?‘‡đ?‘?
đ?‘‡đ?‘?
(3)
where, � � is the Dirac delta function, f = Frequency, Tb = Bit duration, Rb = Bit rate, Pr = Average optical power, R = Responsivity
Pulse Position Modulation (PPM) In PPM, each symbol interval of duration T = log2 L/Rb is partitioned into L subintervals, or chips, each of duration T/L, and the transmitter sends an optical pulse during one and only one of these chips. For any L greater than 2, PPM requires less optical power than OOK. In principle, the optical power requirement can be made arbitrarily small by making L suitably large, at the expense of increased bandwidth. The bandwidth required by PPM to achieve a bit rate of Rb is approximately the inverse of one chip duration, B = L/T. In addition to the increased bandwidth requirement, PPM needs (compared to OOK) more transmitter peak power and both chip- and symbol-level synchronization.
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2
+ [đ?‘ đ??ś,đ?‘ƒđ?‘ƒđ?‘€ đ?‘“ + đ?‘ đ??ˇ,đ?‘ƒđ?‘ƒđ?‘€ đ?‘“ ] (4)
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đ?‘ đ??ś,đ??ˇđ?‘ƒđ??źđ?‘€ đ?‘“ =
đ?‘ đ??ˇ,đ??ˇđ?‘ƒđ??źđ?‘€ đ?‘“ =
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Rk −
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1 L2
e−j2đ?œ‹đ?‘˜đ?‘“ đ?‘‡đ?‘ đ?‘Śđ?‘š _đ??ˇđ?‘ƒđ??źđ?‘€
∞ đ?‘˜ =−∞
δ f−
2đ?œ‹k đ?‘‡đ?‘ đ?‘Śđ?‘š _đ??ˇđ?‘ƒđ??źđ?‘€
(5)
(6)
f = Frequency, L = Symbol length, Tsym = Symbol duration, Sc = Continuous component, Sd = Discrete component, P(f) = Fourier transform of pulse shape
On-Off Keying (OOK)
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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 Digital Pulse Interval Modulation In DPIM, the information is encoded by inserting empty slots between two pulses. The DPIM offers a reduced complexity compared to PPM due to its built-in symbol synchronization. Guard slots can also be inserted. đ?‘ đ??ˇđ?‘ƒđ??źđ?‘€ đ?‘“ =
1 đ?‘‡đ?‘ đ?‘Śđ?‘š _đ??ˇđ?‘ƒđ??źđ?‘€
P f
2
+ [đ?‘ đ??ś,đ??ˇđ?‘ƒđ??źđ?‘€ đ?‘“ + đ?‘ đ??ˇ,đ??ˇđ?‘ƒđ??źđ?‘€ đ?‘“ ] (7)
5đ??ż
đ?‘ đ??ś,đ??ˇđ?‘ƒđ??źđ?‘€ đ?‘“ = đ?‘ đ??ˇ,đ??ˇđ?‘ƒđ??źđ?‘€ đ?‘“ =
đ?‘˜ =−5đ??ż
Rk −
2đ?œ‹ đ?‘‡đ?‘ đ?‘Śđ?‘š _đ??ˇđ?‘ƒđ??źđ?‘€ 2 L 2
1 L2
e−j2đ?œ‹đ?‘˜đ?‘“ đ?‘‡đ?‘ đ?‘Śđ?‘š _đ??ˇđ?‘ƒđ??źđ?‘€
∞ đ?‘˜ =−∞
δ f−
2đ?œ‹k đ?‘‡đ?‘ đ?‘Śđ?‘š _đ??ˇđ?‘ƒđ??źđ?‘€
(8) (9)
f = Frequency, L = Symbol length, Tsym_DPIM = Symbol duration, Sc = Continuous component, Sd = Discrete component, P(f) = Fourier transform of pulse shape
Fig.5. Power contour plot at the receiving plane
5 IMPLEMENTATION AND SIMULATION RESULTS The simulation is done using MATLAB software. MATLAB (MATrix LABoratory) is a numerical computing environment and fourth-generation programming language. The software is developed by MathWorks Incorporated. The matrix manipulations, plotting of functions and data and implementation of algorithms can be done using this platform. These are often used in physical and mathematical problems and are most useful when it is difficult or impossible to obtain a closed-form expression, or infeasible to apply a deterministic algorithm. The goal of conducting simulations is to verify and validate the selection of parameters as well as to visualize the intermediate results not obtainable from experimental results.
Fig. 6. Analytical power spectral density of OOK modulation
Fig. 7. Bit error probability curve for OOK modulation
Fig. 4. Normalized power distribution at the receiving plane
Fig. 8. Analytical power spectral density of pulse position modulation
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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 the transmitter beam divergence, receiver size and separation distance. However, a non-LOS configuration, also known as diffuse systems uses reflection from the room surfaces and furniture. These reflections could be seen as unwanted signals or multipath distortions which make the prediction of the path loss more complex. The delay spread is a measure of the multipath richness of a communications channel. In general, it can be interpreted as the difference between the time of arrival of the earliest significant multipath component (line-of-sight component) and the time of arrival of the latest multipath components.[2,3]
Fig. 9. Symbol error probability curve pulse position modulation
LOS Communication Link Line-of-Sight propagation is the characteristic of light waves traveling in a straight line. The fundamental equation for finding the DC gain of a line-of-sight optical wireless system is given by, ′
G=
A m+1 cosᵐ Φ cos(ψ) 2πd2 0
0 ≤ ψ ≤ ψₐ 0 ≥ ψₐ (10)
where G is the channel gain, A is the photodetector surface area, m is order of Lambertian emission, d is the distance vector, Φ is the incidence angle, ψ is the irradiance angle and ψa is the field-of-view (semiangle) at the receiver.
Fig. 10. Analytical power spectral density of digital pulse interval modulation
The received power is the product of transmitted power and the channel gain. P received = P transmitted X Channel gain (G) (11)
Fig. 11. Symbol error probability curve for digital pulse interval modulation
The normalized power distribution graph for a four-cell structure is shown in the figure 4.. It is can be seen that most of the power is concentrated near the centre of each cell decreasing sharply towards the cell edges. In a four-cell configuration with a circular foot print, the area within dotted line circle, see figure 5, is defined as the 3-dB power attenuation area from the centre of a cell. The rest of the area is defined as the no coverage area or the ―dead zones‖ with no optical illumination.[1,2]. To design, implement and operate efficient optical communication systems, it is imperative that the characteristics of the channel are well understood. The characterization of a communication channel is performed by its channel impulse response, which is then used to analyse and combat the effects of channel distortions. Two types of configurations are considered in VLC channel. They are LOS (Lineof-Sight) and non-LOS channels. For directed LOS and tracked configurations, reflections do not need to be taken into consideration. Consequently, the path loss is easily calculated from knowledge of
Diffuse (Non-LOS) Communication Link For non-directed LOS and diffuse links, the optical path loss is more complex to predict since it is dependent on a multitude of factors, such as room dimensions, the reflectivity of the ceiling, walls and objects within the room, and the position and orientation of the transmitter and receiver, window size and place and other physical matters within a room. The reflection characteristics of object surfaces within a room depend on several factors including, the transmission wavelength, surface material, the angle of incidence and roughness of the surface relative to the wavelength. The latter mainly determines the shape of the optical reflection pattern. The three digital modulation schemes popular in optical wireless communication systems (OOK, PPM and DPIM) are compared based on bandwidth requirement, power efficiency and transmission capacity. In OOK, the bandwidth requirement is roughly equivalent to the data rate. PPM achieves higher average power efficiency than OOK at the expense of an increased bandwidth compared to OOK. Besides, the use of PPM imposes more system complexity compared to OOK at the receiver. Unlike PPM, DPIM does not require symbol synchronization since each symbol is initiated with a pulse. Furthermore, DPIM displays a higher transmission capacity by eliminating all the unused
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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 time slots from within each symbol. The mean delay spread and RMS delay spread for a diffuse link is shown in the figure 12 a and b.
An indoor visible light communication is mathematically modeled and the system is simulated with the help of MATLAB software. The received power distributions and power contour plots for a practical indoor VLC link is obtained. By employing a holographic light shaping diffuser, the power distribution is made uniform. Thus the coverage area is extended further in indoor VLC environment. Visible light communication system provides advantages including ubiquitous computing, highly secure data transmission, very high data, dual functionality of illumination and communication, low cost of maintenance, low power consumption, safety and reliability. The visible light communication systems can serve either as a disruptive technology, as optical fiber was to the traditional all-copper long distance backbone, or as a system to be used in tandem with the existing wireless infrastructure to provide additional bandwidth.
ACKNOWLEDGMENT
Fig. 12. Channel delay spread for a diffuse communication link a) Mean delay spread b) RMS delay spread
6
I express my sincere gratitude to The Almighty who empowered me to successfully complete the M.Tech. project work, by showering his abundant grace and mercy. I would like to add heartfelt words for the people who helped me a lot in the completion of my project. I express my honor, respect, deep gratitude and regards to my guide Mrs. Swapna Davies for her kind guidance and constant supervision as well as for providing necessary information regarding the seminar. I am highly indebted to Mr. Jaison Jacob, Head of Department Electronics and Communication Engineering, for guiding me all throughout the process. I would like to express my heartfelt gratitude to Mr. Walter Joseph and Dr. Deepti Das Krishna for their valuable advice and timely help. I would like to acknowledge Mrs. Anu Mathew for the inspiration and warm encouragement. I would like to express the deepest appreciation to my family and friends for their abiding love and prayers. Their unconditional support is invaluable.
REFERENCES
CONCLUSION
[1]
The development of wireless communications technology over the last few decades has brought with it an explosion of new applications for consumers. Convenience of access to the internet is unprecedented, with indoor wireless local area network (WLAN). Large-area, high-speed network coverage through metropolitan access networks (MANs) is now being realized, and indeed, such networks are the current state-of-the-art with respect to developing standards, enabling next generation mobile applications and highspeed wireless municipal access networks. Moving forward, the natural inclination is towards faster, more reliable wireless communications. As a result, development of complex schemes that allow for high symbol rate and high signal-to-noise ratio is an open research topic in both academia and industry, complicated not just by the difficulties of transmitting in multipath fading channels, but also by interference from other users of the same frequency band. The latter is of increasing concern, especially as more and more wireless applications are refined. Visible light communication offers a real alternative to radio based communications. The spectrum is free, plentiful, and the cost of implementation is actually less than equivalent radio technology. This technology also saves a lot of energy.
I. Lee, M. Sim, and F. Kung, “A dual-receiving visible-light communication system under time-variant non-clear sky channel for intelligent transportation system,” in Networks and Optical Communications (NOC), 2011 16th European Conference, pp. 153 –156, July 2011.
[2] D. Wu, Z. Ghassemlooy, H. LeMinh, S. Rajbhandari and Y.S. Kavian, ―Power Distribution and Q-factor Analysis of Diffuse Cellular Indoor Visible Light Communication Systems‖, in Networks and Optical Communications (NOC),16th European Conference, 2011. [3]
Kavehrad, M.,“Sustainable energy-efficient wireless applications using light”, IEEE Communications Magazine, Volume 48, Issue 12, pp. 66 - 73, December 2010
[4]
H.Q.Nguyen, J.H.Choi, ‖A MATLAB-based simulation program for indoor visible light communication system‖, Communication Systems, Networks and Digital Signal Processing, Optical Wireless Communication Conference (OWC-5, CSNDSP),IEEE, 2010.
[5] Miya, Y. Kajikawa, ―Base station layout support system for indoor visible light communication‖, International Symposium on Communications and Information Technologies (ISCIT), Conference, pp. 661-666 IEEE, 2010.
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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 Author Profile: Nitin Chacko is currently pursuing M.Tech. degree in Electronics and Communication Engineering (Specialization in Communication Engineering) at Rajagiri School of Engineering and Technology, Cochin. Phone: +919995975963 E-mail: nitinchacko7@gmail.com Swapna Davies is currently Assistant Professor in the Department of Electronics and Communication Engineering at Rajagiri School of Engineering and Technology, Cochin. E-mail: swapnadavies@gmail.com
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