Comparing with the existing incandescent, light-emitting diodes (LEDs) offer higher power efficiency, higher brightness, longer lifetime, and have a fast dynamic response in the order of a few megahertz. LEDs are recently expected to be utilised for the next generation indoor optical wireless communication (OWC) system. In this paper, we present a mathematical design model as well as a practical measurement for an indoor diffuse cellular visible light communication (VLC) system. It operates at a date rate of 5 Mb/s using the on-off keying non-return-to-zero (OOK-NRZ) modulation format. Using commercially available luminit holographic light shaping diffusers (LSD), we show that the achieved distributions of received power and the Q-factor are more uniform. The range and coverage area of the cellular link are therefore significantly extended

Ghassemlooy, Zabih

Kavian, Yousef

Le Minh, Hoa

Rajbhandari, Sujan

Wu, Dehao

English

Northumbria Research Link

Power Distribution and Q-factor Analysis of DiffuseCellular Indoor Visible Light CommunicationSystemsD. Wu*, Z. Ghassemlooy*, H. LeMinh*, S. Rajbhandari* and Y.S. Kavian***Optical Communication Research Group, School of CEIS, Northumbria University, Newcastle Upon Tyne, UK**Faculty of Engineering, Shahid Chamran University, Ahvaz, IranE-mail: dehao.wu@northumbria.ac.ukAbstract- Comparing with the existing incandescent, light-emitting diodes (LEDs) offer higher power efficiency, higherbrightness, longer lifetime, and have a fast dynamic response inthe order of a few megahertz. LEDs are recently expected to beutilised for the next generation indoor optical wirelesscommunication (OWC) system. In this paper, we present amathematical design model as well as a practical measurementfor an indoor diffuse cellular visible light communication (VLC)system. It operates at a date rate of 5 Mb/s using the on-offkeying non-return-to-zero (OOK-NRZ) modulation format.Using commercially available luminit holographic light shapingdiffusers (LSD), we show that the achieved distributions ofreceived power and the Q-factor are more uniform. The rangeand coverage area of the cellular link are therefore significantlyextended.Keywords- Visible light communication, LED, power distribution,BERI. INTRODUCTIONCompared with the traditional incandescent and fluorescentlamps, LEDs have a number of advantages such as a longerlife expectancy, a higher tolerance to humidity, a smaller sizeand lower power consumption. As the cost of manufacturingdecreases, LEDs become affordable and popular for colourdisplays, traffic signals, and for illumination applications. Inrecent years, LEDs have been used to transmit data at higherrates over a short-range OWC link [1-3].For dual purpose of illumination and data communications,white LEDs are ideal sources for future applications. Withavailability of highly efficient white LEDs (created bycombining the prime colours: red, green, and blue) or by usinga blue emitter in combination with a phosphor, we arewitnessing a surge in research and development in indoorVLC systems [4, 5]. In this paper, we use the commerciallypopular (Luxeon Star/O) royal blue LED type as thetransmitter.The most common link configurations for indoor OWCsystems are the line-of-sight (LOS) and the diffuse or a hybridLOS-diffuse. Normally, the diffuse system provides a lagercoverage area and an excellent mobility [6], but at the cost oflower data rates, higher path losses and multipath inducedintersymbol interference (ISI) caused by the signal reflectionsfrom walls and other objects within the room. On the otherhand, LOS links, where the beam is confined within a narrowfield of view (FOV), offer a much higher channel capacity anda longer range [6]. However, LOS links offer a limitedcoverage area as well as requiring alignment and/or tracking tomaintain link availability. To achieve higher data rates as wellas a wider coverage area, a cellular system would be thepreferred option.In this paper, a practical cellular indoor VLClink employing a blue LED as a transmitter is reported. Inorder to increase the cell coverage area with a uniform powerdistribution, holographic LSDs of different angles areemployed.The rest of the paper is organized as follow. In section II,characteristics of the transmitter, diffuser, channel andreceiver are described. In section III, the experiment work isoutlined followed by results and discussion. Finally, theconclusion is given in the last section IV.II. SYSTEM DESCRIPTIONA. System OverviewThe proposed indoor cellular VLC system is shown in Fig.1.LEDs are used both for lighting as well as communications.LED access points are connected to the backbone wirednetwork via the ceiling. Communications for the entire roomin the proposed system is covered by four optical cells, each ofwhich has a wide divergence angle LED source. At thereceiving end, the optical receivers, mounted on a mobileterminal, has a dedicated FOV of 300 to ensure seamlessconnectivity as well as alleviating the need for using pointingand tracking schemes. In addition the suitable modulationscheme can also be adopted to improve the overall systemcapacity.Fig. 2 shows the proposed practical cellular indoor VLClink. The metallic frame has a dimension of 1.8×1.5×1 m3,which is divided into four compartments (or cells). Each cellconsists of an LED transmitter, a diffuser and an opticalreceiver.Fig. 1. Proposed indoor cellular VLC systemFig. 2. Practical setup of indoor VLC systemFig. 3. A single cell VLC system diagramThe separation between the source and receiver is 1 m. In thispaper, we only show the practical results for one cell at a datarate of 5 Mb/s using the OOK-NRZ modulation scheme.B. TransmitterLEDs, with no shaping lenses, can be essentially consideredas the Lambertian source [3]. In many applications, however,there are requirements for specific radiation distributions toensure a full coverage and an optimum link performance. Insuch cases shaping lenses are used at the transmitter. Here thelight source position at the centre of a cell is composed of anLED and an optical lens. With the transmitter’s full width atthe half maximum angle (FWHM) of 7o [7], the cell radius is12.2 cm. This is equivalent to a coverage area of 474 cm2. Toachieve a wider coverage area with a uniform radiationdistribution pattern, a luminit holographic LSD (100, 200, and300) is employed. Fig. 3 depicts the system block diagram of asignal cell VLC system which includes a transmitter, adiffuser and a receiver.C. Model of Holographic LSDUsing holographic LSD, the effective divergence angle ofthe transmitter can be extended, which can be calculated as[6]:ߠ௢௨௧௣௨௧≈ ඥ(ߠிை௏)ଶ + (ߠ௅ௌ஽)ଶ (1)where θoutput is the effective output angle of the light, θFOV isthe light source FOV, and θLSD is the angle of LSD [7].The hologram is a two level surface relief diffractiveelement that affects only the phase of light passing through it[8]. The far-field radiation pattern passing through thehologram is approximately the Fourier transform of thesurface relief structure [9]. In order to simplify calculation ofthe beam intensity through the holographic LSD, as Fig. 4shows, we have divided LSD into an array of ‘pixels’, andhave used Matlab to simulate the beam profile for every‘pixel’. For a very tiny beam profile, the intensity of light canbe considered as uniform after passing through the single‘pixel’. Finally, the overall coverage area is could be the sumof individual foot prints per pixel.Fig. 4. Multiple beam profiles after holographic LSDD. Optical Wireless ChannelFollowing the LOS link configuration adopted in [10], andassuming no optical filter and optical concentrator are used,the LOS channel DC gain is given by:ܪ(0) = ቊ(௠ ାଵ)஺ଶ஠ௗమ cos௠ (߶) cos(߮) , 0 ≤ ߮ ≤ φୡ0, 0 ≥ φୡ (2)where A is the photodetector surface area, ϕ is the incidenceangle, φ is irradiance angle, φୡ is the FOV (semiangle) at thereceiver and H is the distance between transmitter andreceiver. = − ୪୬ଶ୪୬(ୡ୭ୱ஦భ/మ) is the order of Lambertian radiantwhich is related to the transmitter semiangle φ1/2, (at halfpower). The order m of the LED which we used is 110. Thereceived power is given by:ோܲ௫ = ்ܲ ௫ ܪ(0) (3)where ்ܲ ௫ is the transmitted optical power of LED, ோܲ௫ isthe received optical power at the receiving plane.E. ReceiverThis receiver front-end consists of a commercial PINjunction photodetector and a trans-impedance amplifier. Thespecifications for the receiver are given in Table I.TABLE ISPECIFICATION FOR INDOOR VLC SYSTEMLED product number LXHL-NRR8LED bandwidth 3.8 MHzLED working wavelength 455 nmLED output power 40 mWLED field of view (FWHM) 14oDiffuser Luminit LSD 10o, 20o and 300Channel distance 1 mPhotodectector product number OSD-15TPhotodectector detection area 15 mm2Photodectector responsivity 0.21 A/W at (λ=436 nm)Photodectector rise time 12 nsPreamplifier product number AD8015Preamplifier 3-dB bandwidth 240 MHzIII. RESULTSThe system specifications and parameters are given in Table I.A. Simulated ResultsWe have used Matlab to simulate the optical powerdistribution of the indoor cellular OWC system. Using Eqs.(2) and (3), the normalized power distribution for a 4-cellstructure (see Fig. 1) is illustrated in Fig. 5. Fig. 5 (b) is thecontour of the power density at the receiving plane. It is can beseen that most of the power is concentrated near the centre ofeach cell decreasing sharply towards the cell edges. In a 4-cellconfiguration with a circular foot print, the area within dottedline circle, see Fig. 5(b), is defined as the 3-dB powerattenuation area from the centre of a cell. The rest of the areais defined as the no coverage area or the ‘dead zones’ with nooptical illumination. The over 3-dB coverage area ܣ஼௢௩ ,where power attenuation is less than 3-dB for four cells isaround 1800 cm2, is given by:ܣ஼௢௩ = ෍ ܣ௖௢௩೔ே௜ୀଵ(4)where, N is the number of cellsThe complete area of receiving plane is given by:ܣ்௢௧௔௟= ܣ஼௢௩ + ܣ஽௭ + ܣை௟ (5)where ܣ஽௭ and ܣை௟ shown in Fig. 5(b) are the ‘dead zones’and the overlapping areas, respectively.To achieve a uniform distribution within each cell, we haveused a 30o LSD. Figs. 6 (a) and (b) display predicted powerdistributions and power density contours for a 4-cellconfiguration. The over 3-dB coverage area is marked in Fig.6(b). Using Eq. (5), the total coverage area is around 8000cm2. Note the increase in the power distribution at theboundary regions because of cell overlapping.Fig. 5 (a). Predicted normalized power distribution at the receiving planewithout LSDFig. 5 (b). Predicted power contour plot at the receiving plane without LSDFig. 6(a). Predicted normalized power distribution at the receiving plane usinga 30o LSDFig. 6 (b). Predicted power contour plot at the receiving plane using a 30oLSDB. Practical MeasurementsFig. 7 outlines the measured optical power distributions withand without holographic LSDs for a single cell configuration.The power density is more uniform when larger angle LSDsare used. Comparing the power density profiles of a linkwithout a holographic LSD with a 30o holographic LSD (Figs.7(a) and (d), it can be seen that a 3-dB transmission boundaryhas increased from 8 cm to 20 cm (i.e. 625% increasing in thecoverage area).Next we measured the eye diagrams for links with andwithout the holographic LSD in order to determine the Q-factor performance. Fig. 8 shows the 3D spatial distribution ofthe Q-factor. For the case with no LSD, Fig. 8(a), for a Q-factor > 5 corresponding to a BER < 10-6 (using OOK-NRZmodulation format), the effective coverage area is ~625 cm2.The coverage area increases to ~ 1600 cm2 using 30o LSDs.As shown in Fig. 8 using wider angle LSDs, the Q-factordistribution is more uniform within a cell compared to the casewith no LSD where the Q-factor is the highest at the cellcentre.Fig. 7. Spatial distribution of received power: (a) without LSD, (b) with 10oLSD, (c) with 20o LSD, and (d) with 30o LSDFig. 8. Spatial distribution of Q factor: (a) without using LSD, (b) with 10oLSD, (c) with 20o LSD, and (d) with 30o LSDIV. CONCLUSIONIn this paper, we have modeled, simulated and measured thereceived power distributions for a practical indoor VLC linkemploying a holographic diffuser. The investigation showedthat, using holographic LSDs with suitable angles, a uniformpower distribution can be obtained thus increasing thecoverage area in indoor VLC environment. This is a stepforward to design a VLC cellular system.ACKNOWLEDGMENTI would like to acknowledge Dr David Johnston and MrAndrew Burton for their help.REFERENCES[1] J.K, Kim and E.F. Schubert, “Transcending the replacement paradigm ofsolid-state lighting,” Optics Express, vol. 16, no. 26, pp. 21835-21842,December 2008.[2] Y. Tanaka, S. Haruyama, and M. Nakagawa, “Wireless opticaltransmissions with white colored LED for wireless home links,” Proc.IEEE International Symposium on Personal, Indoor and Mobile RadioCommunications, vol. 2, pp. 1325-1329, 2000.[3] T. Komine and M. Nakagawa, “Fundamental analysis for visible lightcommunication system using LED lights,” IEEE Trans. on consumerElectronics, vol. 50, pp. 100-107, 2004.[4] T. Komine, J.H. Lee, S. Haruyama and M. Nakagawa, “Adaptiveequalization system for visible light wireless communication utilizingmultiple white LED lighting equipment,” IEEE Trans. on wirelesscommunications, vol. 8, no. 6, pp. 1536-1276, 2009.[5] H.L. Minh, et al, “100-Mb/s NRZ visible light communication using apost-equalized white LED,” IEEE Photonics Technology Letters, vol.21, no. 15, August 1, 2009.[6] D.R. Wisely, “A 1 Gbit/s Optical Wireless Tracked Architecture forATM Delivery,” IEE Colloquium on Optical Free SpaceCommunication Links, London, UK, 1996.[7] Luminit, “Light Shaping Diffusers,” Available at:http://www.luminitco.com/files/u1/Technical_Data_Sheet_rev_9-28-10.pdf (Accessed: 15 Jan 2011).[8] P.L. Eardley, D.R. Wisely, D. Wood and P. McKee, “Holograms forOptical Wireless LANs,” IEE Proc. Optoelectron., Vol. 143, No. 6,December 1996.[9] M.Born and E. Wolf, “Principles of optics,” Pergamon Press, 1986.[10] J.M. Kahn and J.R. Barry, “Wireless infrared communication,” Proc.IEEE, vol. 85, no. 2 pp. 265-298, 1997.

100-Mb/s NRZ visible light communication using a post-equalized white LED,”

Adaptive equalization system for visible light wireless communication utilizing multiple white LED lighting equipment,”

Fundamental analysis for visible light communication system using

Holograms for Optical Wireless LANs,”

Light Shaping Diffusers,” Available at: http://www.luminitco.com/files/u1/Technical_Data_Sheet_rev_9-28-10.pdf (Accessed: 15

Principles of optics,”

Transcending the replacement paradigm of solid-state lighting,”

Wireless infrared communication,”

Wireless optical transmissions with white colored LED for wireless home links,”

Power distribution and Q-factor analysis of diffuse cellular indoor visible light communication systems

Northumbria Research Link
Citation: Wu, Dehao, Ghassemlooy, Zabih, Le Minh, Hoa, Rajbhandari,  Sujan and Kavian, Yousef 
(2011) Power distribution and Q-factor analysis of diffuse cellular indoor visible light communication 
systems. In: 16th European Conference on Networks and Optical Communications (NOC), 20 July - 
22 July 2011, Northumbria University, Newcastle-upon-Tyne. 
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Power Distribution and Q-factor Analysis of Diffuse
Cellular Indoor Visible Light Communication
Systems
D. Wu*, Z. Ghassemlooy*, H. LeMinh*, S. Rajbhandari* and Y.S. Kavian**
*Optical Communication Research Group, School of CEIS, Northumbria University, Newcastle Upon Tyne, UK
**Faculty of Engineering, Shahid Chamran University, Ahvaz, Iran
E-mail: dehao.wu@northumbria.ac.uk
Abstract- Comparing with the existing incandescent, light-
emitting diodes (LEDs) offer higher power efficiency, higher
brightness, longer lifetime, and have a fast dynamic response in
the order of a few megahertz. LEDs are recently expected to be
utilised for the next generation indoor optical wireless
communication (OWC) system. In this paper, we present a
mathematical design model as well as a practical measurement
for an indoor diffuse cellular visible light communication (VLC)
system. It operates at a date rate of 5 Mb/s using the on-off
keying non-return-to-zero (OOK-NRZ) modulation format.
Using commercially available luminit holographic light shaping
diffusers (LSD), we show that the achieved distributions of
received power and the Q-factor are more uniform. The range
and coverage area of the cellular link are therefore significantly
extended.
Keywords- Visible light communication, LED, power distribution,
BER
I. INTRODUCTION
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 colour
displays, traffic signals, and for illumination applications. In
recent years, LEDs have been used to transmit data at higher
rates over a short-range OWC link [1-3].
For dual purpose of illumination and data communications,
white LEDs are ideal sources for future applications. With
availability of highly efficient white LEDs (created by
combining the prime colours: red, green, and blue) or by using
a blue emitter in combination with a phosphor, we are
witnessing a surge in research and development in indoor
VLC systems [4, 5]. In this paper, we use the commercially
popular (Luxeon Star/O) royal blue LED type as the
transmitter.
The most common link configurations for indoor OWC
systems are the line-of-sight (LOS) and the diffuse or a hybrid
LOS-diffuse. Normally, the diffuse system provides a lager
coverage area and an excellent mobility [6], but at the cost of
lower data rates, higher path losses and multipath induced
intersymbol 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 [6]. However, LOS links offer a limited
coverage area as well as requiring alignment and/or tracking to
maintain link availability. To achieve higher data rates as well
as a wider coverage area, a cellular system would be the
preferred option.In this paper, a practical cellular indoor VLC
link employing a blue LED as a transmitter is reported. In
order to increase the cell coverage area with a uniform power
distribution, holographic LSDs of different angles are
employed.
The rest of the paper is organized as follow. In section II,
characteristics of the transmitter, diffuser, channel and
receiver are described. In section III, the experiment work is
outlined followed by results and discussion. Finally, the
conclusion is given in the last section IV.
II. SYSTEM DESCRIPTION
A. System Overview
The proposed indoor cellular VLC system is shown in Fig.1.
LEDs are used both for lighting as well as communications.
LED access points are connected to the backbone wired
network via the ceiling. Communications for the entire room
in the proposed 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
terminal, has a dedicated FOV of 300 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.
Fig. 2 shows the proposed practical cellular indoor VLC
link. The metallic frame has a dimension of 1.8×1.5×1 m3,
which is divided into four compartments (or cells). Each cell
consists of an LED transmitter, a diffuser and an optical
receiver.
Fig. 1. Proposed indoor cellular VLC system
Fig. 2. Practical setup of indoor VLC system
Fig. 3. A single cell VLC system diagram
The separation between the source and receiver is 1 m. In this
paper, we only show the practical results for one cell at a data
rate of 5 Mb/s using the OOK-NRZ modulation scheme.
B. Transmitter
LEDs, with no shaping lenses, can be essentially considered
as the Lambertian source [3]. In many applications, however,
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. Here the
light source position at the centre of a cell is composed of an
LED and an optical lens. With the transmitter’s full width at
the half maximum angle (FWHM) of 7o [7], the cell radius is
12.2 cm. This is equivalent to a coverage area of 474 cm2. To
achieve a wider coverage area with a uniform radiation
distribution pattern, a luminit holographic LSD (100, 200, and
300) is employed. Fig. 3 depicts the system block diagram of a
signal cell VLC system which includes a transmitter, a
diffuser and a receiver.
C. Model of Holographic LSD
Using holographic LSD, the effective divergence angle of
the transmitter can be extended, which can be calculated as
[6]:
≈௢௨௧௣௨௧ߠ ඥ(ߠிை௏)
ଶ + (௅ௌ஽ߠ)
ଶ (1)
where θoutput is the effective output angle of the light, θFOV is
the light source FOV, and θLSD is the angle of LSD [7].
The hologram is a two level surface relief diffractive
element that affects only the phase of light passing through it
[8]. The far-field radiation pattern passing through the
hologram is approximately the Fourier transform of the
surface relief structure [9]. In order to simplify calculation of
the beam intensity through the holographic LSD, as Fig. 4
shows, we have divided LSD into an array of ‘pixels’, and
have used Matlab 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.
Fig. 4. Multiple beam profiles after holographic LSD
D. Optical Wireless Channel
Following the LOS link configuration adopted in [10], and
assuming no optical filter and optical concentrator are used,
the LOS channel DC gain is given by:
(0)ܪ = ቊ
(௠ ାଵ)஺
ଶ஠ௗమ
cos௠ (߶) cos(߮) , 0 ≤ ߮ ≤ φୡ
0, 0 ≥ φୡ
(2)
where A is the photodetector surface area, ϕ is the incidence
angle, φ is irradiance angle, φୡ is the FOV (semiangle) at the
receiver and H is the distance between transmitter and
receiver. = −
୪୬ଶ
୪୬(ୡ୭ୱ஦భ/మ)
is the order of Lambertian radiant
which is related to the transmitter semiangle φ1/2, (at half
power). The order m of the LED which we used is 110. The
received power is given by:
ோܲ௫ = ்ܲ ௫ (0)ܪ (3)
where ்ܲ ௫ is the transmitted optical power of LED, ோܲ௫ is
the received optical power at the receiving plane.
E. Receiver
This receiver front-end consists of a commercial PIN
junction photodetector and a trans-impedance amplifier. The
specifications for the receiver are given in Table I.
TABLE I
SPECIFICATION FOR INDOOR VLC SYSTEM
LED product number LXHL-NRR8
LED bandwidth 3.8 MHz
LED working wavelength 455 nm
LED output power 40 mW
LED field of view (FWHM) 14o
Diffuser Luminit LSD 10o, 20o and 300
Channel distance 1 m
Photodectector product number OSD-15T
Photodectector detection area 15 mm2
Photodectector responsivity 0.21 A/W at (λ=436 nm)
Photodectector rise time 12 ns
Preamplifier product number AD8015
Preamplifier 3-dB bandwidth 240 MHz
III. RESULTS
The system specifications and parameters are given in Table I.
A. Simulated Results
We have used Matlab to simulate the optical power
distribution of the indoor cellular OWC system. Using Eqs.
(2) and (3), the normalized power distribution for a 4-cell
structure (see Fig. 1) is illustrated in Fig. 5. Fig. 5 (b) is the
contour of the power density at the receiving plane. 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 4-cell
configuration with a circular foot print, the area within dotted
line circle, see Fig. 5(b), 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. The over 3-dB coverage area ஼௢௩ܣ ,
where power attenuation is less than 3-dB for four cells is
around 1800 cm2, is given by:
஼௢௩ܣ = ෍ ௖௢௩೔ܣ
ே
௜ୀଵ
(4)
where, N is the number of cells
The complete area of receiving plane is given by:
=௢௧௔௟்ܣ ஼௢௩ܣ + ஽௭ܣ + ை௟ܣ (5)
where ஽௭ܣ and ை௟ܣ shown in Fig. 5(b) are the ‘dead zones’
and the overlapping areas, respectively.
To achieve a uniform distribution within each cell, we have
used a 30o LSD. Figs. 6 (a) and (b) display predicted power
distributions and power density contours for a 4-cell
configuration. The over 3-dB coverage area is marked in Fig.
6(b). Using Eq. (5), the total coverage area is around 8000
cm2. Note the increase in the power distribution at the
boundary regions because of cell overlapping.
Fig. 5 (a). Predicted normalized power distribution at the receiving plane
without LSD
Fig. 5 (b). Predicted power contour plot at the receiving plane without LSD
Fig. 6(a). Predicted normalized power distribution at the receiving plane using
a 30o LSD
Fig. 6 (b). Predicted power contour plot at the receiving plane using a 30o
LSD
B. Practical Measurements
Fig. 7 outlines the measured optical power distributions with
and without holographic LSDs for a single cell configuration.
The power density is more uniform when larger angle LSDs
are used. Comparing the power density profiles of a link
without a holographic LSD with a 30o holographic LSD (Figs.
7(a) and (d), it can be seen that a 3-dB transmission boundary
has increased from 8 cm to 20 cm (i.e. 625% increasing in the
coverage area).
Next we measured the eye diagrams for links with and
without the holographic LSD in order to determine the Q-
factor performance. Fig. 8 shows the 3D spatial distribution of
the Q-factor. For the case with no LSD, Fig. 8(a), for a Q-
factor > 5 corresponding to a BER < 10-6 (using OOK-NRZ
modulation format), the effective coverage area is ~625 cm2.
The coverage area increases to ~ 1600 cm2 using 30o LSDs.
As shown in Fig. 8 using wider angle LSDs, the Q-factor
distribution is more uniform within a cell compared to the case
with no LSD where the Q-factor is the highest at the cell
centre.
Fig. 7. Spatial distribution of received power: (a) without LSD, (b) with 10o
LSD, (c) with 20o LSD, and (d) with 30o LSD
Fig. 8. Spatial distribution of Q factor: (a) without using LSD, (b) with 10o
LSD, (c) with 20o LSD, and (d) with 30o LSD
IV. CONCLUSION
In this paper, we have modeled, simulated and measured the
received power distributions for a practical indoor VLC link
employing a holographic diffuser. The investigation showed
that, using holographic LSDs with suitable angles, a uniform
power distribution can be obtained thus increasing the
coverage area in indoor VLC environment. This is a step
forward to design a VLC cellular system.
ACKNOWLEDGMENT
I would like to acknowledge Dr David Johnston and Mr
Andrew Burton for their help.
REFERENCES
[1] J.K, Kim and E.F. Schubert, “Transcending the replacement paradigm of
solid-state lighting,” Optics Express, vol. 16, no. 26, pp. 21835-21842,
December 2008.
[2] Y. Tanaka, S. Haruyama, and M. Nakagawa, “Wireless optical
transmissions with white colored LED for wireless home links,” Proc.
IEEE International Symposium on Personal, Indoor and Mobile Radio
Communications, vol. 2, pp. 1325-1329, 2000.
[3] T. Komine and M. Nakagawa, “Fundamental analysis for visible light
communication system using LED lights,” IEEE Trans. on consumer
Electronics, vol. 50, pp. 100-107, 2004.
[4] T. Komine, J.H. Lee, S. Haruyama and M. Nakagawa, “Adaptive
equalization system for visible light wireless communication utilizing
multiple white LED lighting equipment,” IEEE Trans. on wireless
communications, vol. 8, no. 6, pp. 1536-1276, 2009.
[5] H.L. Minh, et al, “100-Mb/s NRZ visible light communication using a
post-equalized white LED,” IEEE Photonics Technology Letters, vol.
21, no. 15, August 1, 2009.
[6] D.R. Wisely, “A 1 Gbit/s Optical Wireless Tracked Architecture for
ATM Delivery,” IEE Colloquium on Optical Free Space
Communication Links, London, UK, 1996.
[7] Luminit, “Light Shaping Diffusers,” Available at:
http://www.luminitco.com/files/u1/Technical_Data_Sheet_rev_9-28-
10.pdf (Accessed: 15 Jan 2011).
[8] P.L. Eardley, D.R. Wisely, D. Wood and P. McKee, “Holograms for
Optical Wireless LANs,” IEE Proc. Optoelectron., Vol. 143, No. 6,
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[9] M.Born and E. Wolf, “Principles of optics,” Pergamon Press, 1986.
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http://nrl.northumbria.ac.uk/id/eprint/820/1/wu_power%20distribution%20and%20Q-factor%20analysis.pdf

Power distribution and Q-factor analysis of diffuse cellular indoor visible light communication systems

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