Download Review Of Literature

(Light Fidelity): An Innovative Approach to Optical Wireless
Communications
Review Of Literature
Navaneeth Atluri
Telecommunications, George Mason University
Email: [email protected]
Introduction
The main aim of communications is to increase the data rate, which is transferring the
data in a smaller bandwidth. There are two types of networking in Telecommunications, the one
which we use for our phones from the satellite, which uses Radio Frequency (RF) and is known
as radio communications, similar to this is Wireless Fidelity (Wi-Fi) which also uses RF and is
used in our homes. The other type of networking is Light Fidelity (Li-Fi). This uses light as a
medium to transfer data. My research explores the advancements of this existing technology,
which uses 2.4 megahertz bandwidth and this limits the data rate. This is when optical wireless
communications or Li-Fi is considered. With the increasing use of energy efficient lighting such
as Light Emitting Diodes (LEDs), Visible Light Communication (VLC) is emerging as a
promising technique for high speed indoor wireless communications. Unlike conventional light
sources, these LEDs have a modulation bandwidth of several megahertz [1]. Using LED bulbs
for Light Fidelity (Li-Fi) it can transfer at high speeds as much as Terabytes (TB) which is 1024
Gigabytes. Despite intense study, previous research do not consider combining multiplexing and
modulation and in this paper both are combined and this increases data rates at less costs which
makes the access to network cheaper.
Previous research suggests that compact prism array receivers which combine both good
performance and large Field Of View (FOV) can be designed [2]. But these researchers do not
consider the use of array in the reverse manner using a single LED bulb to scatter the rays and
increase the Field Of View.
The purpose of this research is to thoroughly evaluate these older ways of working with
technology, approach and suggests an innovative way of looking at Light Fidelity (Li-Fi) and
suggests a new way of approach to make this network efficient and cheaper for people to use.
Now LED’s are used for indoor and outdoor purposes. Light Fidelity is a process where a LED
bulb is used with an amplifier to amplify the internet signals into Light waves which transfer data
at high speeds of around 10 Tera Bytes per Second (GBPS).
Although there are drawbacks to use Li-Fi such as Dimming where dimmed light provides less
speed than with high intensity, we also have problems with direct sunlight as it corrupts light
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intensity. With these draw backs we also have advantages with Li-Fi which are high data rates
and secure internet connections. As we know that light cannot pass through solid objects, it
cannot pass through our walls, which can increase the security as it cannot be accessed by wrong
doers. This literature review explains the working of Multiple Input Multiple Output (MIMO)
techniques and explain multiplexing and modulation and suggest a new way of approach to solve
existing challenges.
Working of Multiple Input Multiple Output (MIMO):
In Multiple Input Multiple Output (MIMO) process light is emitted from LED arrays and light
from each of the LED arrays is received by all the separate receivers, but with different strengths
[3]. This source explains the faults in the approach of using these techniques where the signal
strength varies with each different receiver which is a drawback. This simple matrix inversion
and multiplication is used to obtain an estimate of the transmitted data which is susceptible to
noise and computationally inefficient compared with many of the advanced Radio Frequency
(RF) techniques in use [4]. Due to this inefficiency, we can look into the Vertical Cavity Surface
Emitting Laser diodes (VCSEL). Recently, VCSEL arrays have been employed at the transmitter
in Line of Sight (LoS) cellular and tracked optical wireless architectures. [5-7]. These VCSEL
emit light in a circular emission and due to this, these are considered much more efficient
compared to other light emitting diodes such as simple matrix inversion and multiplication, these
emit light in oval shape. These emitters are efficient while providing light but not so efficient
while using in the Light Fidelity (Li-Fi) network as light is emitted in oval shape.
Due to these drawbacks, we consider the newer approaches such as orthogonal frequency
division multiplexing, where they use different kinds of networks such as orthogonal frequency
multiplexing and precoder matrix modulation, where in these two schemes, most of the
concentration is done to increase the efficiency of multiplexing and modulation which helps
increase the efficiency of Li-Fi network.
Asymmetrically clipped optical orthogonal frequency division multiplexing:
If asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) is
considered as a modulation scheme, we use six to eight prisms in asymmetrically clipped
position such that the receiver can refract the light ray to its signal modulator, such that it
improves the efficiency while using this array. ACO-OFDM is currently attracting widespread
interest because it has the flexibility of a multicarrier system while also being very power
efficient for small and medium sizes of constellations. [8-10].
The discussion is about the flexibility of multi carrier system which is power efficient for small
and medium sizes of constellations. However these articles did not consider large size
constellations which is necessary for Light Fidelity (Li-Fi) to take over existing Wireless Fidelity
(Wi-Fi), Which is considered as small and medium size constellation as the new technology
should be better and convince people that it is the best to take over the existing technology. After
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intense research conclusions have been made that the channel matrices of these receivers are
analyzed for a typical indoor scenario, demonstrating that as long as the number of REs is greater
than the number of Transmitting LEDs, matrices with full rank can be achieved at every possible
receiver position for the scenario we have considered. [11]. This implies that using channeled
matrices Li-Fi technology can achieve full efficiency due to the fact that there are Radio
Frequency emitters in the used system and Radio Frequency emitters should be more in number
than LEDs in the system to provide balance in the network, which is a draw back and this can be
fixed if a different approach such as Precoder Matrix Modulation is considered.
Precoder Matrix Modulation:
When Precoder Amplitude Modulation (PAM) is considered, the best option would be to
use 2-PAM over one of the two spatial channels and 4-PAM over the other spatial channel [12],
where in amplitude modulation we modulate amplitude to the required channel so that the
channel can transmit the data in its own bandwidth and at high data rates. This is similar to
another approach, where a new modulation scheme 2x2 arranging , 2,4,8 Precoder Matrix
Modulation(PMM) that is appropriate for MIMO optical wireless systems with Intensity
Modulation/Direct Detection (IM/DD), is proposed in this paper. The proposed PMM scheme
exploits the spatial dimension in MIMO systems to realize higher-order modulations while
guaranteeing a nonnegative transmitted signal, as required by IM/DD optical wireless
communications. We use a 2 × 2 optical wireless system and explain how this is better [11].
Here the channels are used in such a way that if one matrix is arranged in a manner which we can
consider it an X arrangement, where intensity modulation is accounted for, the intensity
decreases the data rate decreases hence we use these type of modulations or channels to increase
the efficiency of the network. We also account for Direct Detection (DD), where intensity
modulation directly affects the detection capability of the receiver. Hence Precoder Matrix
Modulation considers the increase of efficiency but this modulation needs unusual schemes,
which also increases the cost of the MIMO systems. This is a draw back. In this constellation
they do not consider the lower order modulation, even they achieved efficiency lower order
modulation is something that questions the credibility of the existing research processes.
Limitations and Future scope:
All the articles help the research in their own way, yet what this existing research fails to
do is combine the sources. In the first key concept, Asymmetrically Clipped Orthogonal
Frequency Division Multiplexing (ACO-FDM) is about the usage of multiplexing but the
research’s authors fail to consider matrix modulation although they use an array. Array reduces
costs but modulation needs to be done separately and that on the whole, increases the cost of the
network and the first theory might not be useful for all types of modulations. When the intensity
decreases we might not find the array of prism useful and it is a fault in the technology.
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In the second key concept, they considered different types of modulation but they did not
consider multiplexing as the modulation schemes need to multiplexed as multiplexing helps
constellations function efficiently, if multiplexing and modulation are considered separately like
these kinds of research are solely based on one aspect of communications, which might be useful
for publishing, but cannot be used for the betterment of technology.
Hence I suggest future research to consider the constellation sizes, every modulation
schemes and using the concept of prism in the reverse way. Where a Multi Wavelength Emitting
High Intensity light bulb is used and prisms are used in an array to scatter rays such that it
illuminates the whole room as it saves costs to fit an array such that the data can be accessed
from every part of the room. Specifications are made for the light bulb because every light bulb
does not emit multi-wavelengths so that it can be scattered through a prism. For a future scope,
we can also consider the use of Wi-Fi and Li-Fi in a single system such that light can produce
high data rate and greater speed and where light cannot pass such as corners. We can use Radio
Frequency (RF) from Wi-Fi and this might be useful in large firms. While using Wi-Fi and Li-Fi
simultaneously, we can consider combining multiplexing and modulation which increases the
efficiency of the network and considerably reduce usage cost of the network.
Conclusion:
In this review of literature I have thoroughly considered ACO-OFDM and PMM where
both the concepts are efficient but combining them might result in a more efficient and cheaper
constellation in networking which is definitely an aspect to look into which previous research has
failed to do. Combining both Wi-Fi and Li-Fi and make the networking more efficient might be a
help for the future. This suggestion is made because replacing the existing technology we need to
change routers, modulators and amplifiers. This process is expensive, so we can use them
simultaneously. Furthermore, this idea can revolutionize the existing telecommunications market
to provide faster data rates at high speeds.
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References:
[1] J. Grubor, S. Randel, K. D. Langer, and J. W. Walewski, “Broadband information
broadcasting using LED-based interior lighting,” IEEE/OSA J. Lightw. Technol., vol. 26, no. 4,
pp. 3883–3892, Dec. 2008.
[2] Thomas Q. Wang, Roger J. Green and Jean Armstrong, MIMO Optical Wireless
Communications Using ACO-OFDM and a Prism-Array Receiver. IEEE Journal on Selected
Areas in Communications, Vol.33, No.9, September 2015.
[3] Lubin Zeng, Dominic C. O’Brien, Hoa Le Minh, Grahame E. Faulkner,2009,
High Data Rate Multiple Input Multiple Output (MIMO) Optical Wireless Communications
Using White LED Lighting, IEEE journal on selected areas in communications, VOL. 27, NO. 9,
DECEMBER 2009
[4] D. Gesbert, M. Shafi, Da-shan-Shiu, P. J. Smith, and A. Naguib, “From theory to practice: an
overview of MIMO space-time coded wireless systems,” in IEEE J. Sel. Areas Commun., vol.
21, pp. 281-302, Apr.2003.
[5] J. Bellon, M. J. N. Sibley, D. R. Wisely, and S. D. Greaves, “HUB architecture
for infrared wireless networks in office environments,” Proc.
Inst. Elect. Eng. Optoelectron., vol. 146, no. 2, pp. 78–82, 1999.
[6] F. Parand, G. Faulkner, D. O’Brien, and D. Edwards, “A cellular optical
wireless system demonstrator,” in Inst. Elect. Eng. Colloq. OpticalWireless
Communications (Ref. 1999/128), 1999, pp. 12/1–12/6.
[7] V. Jungnickel, A. Forck, T. Haustein, U. Krueger, V. Pohl, and C. von Helmolt, “Electronic
tracking for wireless infrared communications,” IEEE Trans. Wireless Commun., vol. 2, pp.
2145–2153, May 2001.
[8] J. Armstrong and A. J. Lowery, “Power efficient optical OFDM,” Electron. Lett., vol. 42, no.
6, pp. 370–2, Mar. 2006.
[9] J. Armstrong, B. J. C. Schmidt, D. Kalra, H. A. Suraweera, and A. J. Lowery, “Performance
of asymmetrically clipped optical OFDM in AWGN for an intensity modulated direct detection
system,” in Proc. IEEE GLOBECOM, San Francisco, CA, USA, 2006, pp. 1–5.
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[10] J. Armstrong and B. J. C. Schmidt, “Comparison of asymmetrically clipped optical OFDM
and DC-biased optical OFDM in AWGN.” IEEE Commun. Lett., vol. 12, no. 5, pp. 343–345,
May 2008.
[11] Thomas Q. Wang, Roger J. Green and Jean Armstrong, MIMO Optical Wireless
Communications Using ACO-OFDM and a Prism-Array Receiver. IEEE Journal On Selected
Areas In Communications, Vol.33, No.9, September 2015.
[12] Liang Wu, Zaichen Zhang and Huaping Liu, Modulation Scheme Based on Precoder Matrix
for MIMO Optical Wireless Communication Systems, IEEE communication letters, vol. 16,
No.9, September 2012.
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