The migration to the use of optical fiber has required several developments, because nowadays it is the most widely used transmission medium in vast fields, particularly video transmission. The work carried out made it possible to study, evaluate and analyze the implementation of this transmission system. We examined the characteristics of the operating techniques of each channel of the video transmission chain and found several problems, one of which is the performance of error-correcting codes based on coding and decoding algorithms, optical fiber and these several criteria for which we have the rate, propagation distance and good transmission quality, which implies that there is always research and improvements in this area.
The last decade has been marked by the rapid evolution of
the information and communication technology (ICT)
sector, including telecommunications and the Internet.
Solutions have been developed by allowing devices to
connect to the Internet from an access point without the
need for a cable connection [
The first section is devoted to the theoretical study of optical fiber. In the second we studied the video transmission by optical fiber and the different treatments that video undergoes. Finally, the third section was devoted to the simulation of video transmission by optical fiber taking into account: compression, decompression, attenuation and length. And will conclude with a conclusion.
II. OPTICAL FIBER, ITS EVOLUTION AND USE
With the advent of the Internet, bandwidth requirements
have become increasingly important in order to convey the
growing mass of information on the various networks,
with reliability and while maintaining a good quality of
service. Indeed, this has required the development of
communication systems that are efficient and reliable
enough to interconnect a constantly growing number of
users around the globe. Researchers and industrialists were
able to propagate a deformation-free pulse at the speed of
light over very long distances and with a wide bandwidth.
The door to the transport of information in optical and
binary form was broken and this was the starting point of
the race for speed, which led to pharaonic progress in just
20 years [
The fiber is nothing more than fused silica glass
filament[
To understand the applications of optical fiber, it is necessary to understand each type and its characteristics. Optical fibers can be classified into two categories according to their diameters and wavelength propagation. The dispersion phenomenon results in a widening of the pulses at the heart of their propagation; this widening limits the bandwidth of the optical fiber channel. The (Table 1.) provides a comparative summary of the advantages, disadvantages and practical application between the different types of optical fibers
At present the most efficient and widespread technology is
based on the fiber optic transmission system. These offer a
low attenuation physical support that is virtually
insensitive to electromagnetic noise, easy to install and has
a high transmission capacity. The optical fiber as we
currently use it is the result of intensive research on new
low-dissipative waveguides. Like all other transmission
media, optical fiber has disadvantages but also offers many
advantages for telecommunications [
The telecommunications network is a set of connected equipment that can be defined as an extensible web of interconnected nodes by physical lines: optical fibers in some places and, in others, by copper electrical wires; so we talk about afixed network.
Data Processing Terminal Equipment or any other source (Transmitter) of digital data is called DTE. They communicate with each other through a data circuit that consists of Data Circuit Termination Equipment (DCTE). All the functions necessary for the management of the data circuit by each DTE constitute the physical layer of the latter or it is carried out by joins or interfaces DTE/DCT. A DTE is characterized by its rate (bits/s), the transmission mode (synchronous or asynchronous), and the type of transmission line, the operating mode of the circuit (simplex, duplex... etc.), the coding method, the modulation speed and the type of interface with the DTE (Fig.3).
An optical fiber telecommunications network can be
divided into three categories according to their size (in
terms of number of machines), data transfer speed and
extent [
The access network - LAN (local area network) or local network, covering dimensions ranging from a few kilometers to a few tens, the metropolitan area network (MAN), with dimensions of the order of one hundred kilometers, The wide area network (WAN) or broadband network, the best known WAN is the Internet, extending over several hundred kilometers. It includes terrestrial or underwater systems.
Although these networks have deployment advantages
and user mobility, real-time video transmission over these
networks for various applications such as Telemedicine,
videoconferencing and video streaming is a challenging
task[
Source encoding/decoding: Source encoding consists of
transforming the source message into a sequence of
information. By reducing the redundancy (lossy or
lossless) contained in the message and thus minimizing the
amount of information useful for its representation. The
source decoding performs the dual operation; the
information message is decompressed in order to find its
equivalent from the substitution sequence before
transmission. It should be noted that the theoretical limits
of source coding are set by Shannon's first
theorem[
Channel encoding/decoding: Channel encoding is an operation that reduces errors and protects transmitted information from transmission channel interference. To combat these transmission errors, it is necessary to add redundancy in order to detect and possibly correct errors during reception. It is therefore possible to improve the signal-to-noise ratio (SNR), which defines the difference between the power of the transmitted signal and the noise of the propagation channel. This is expressed in decibels (dB).
The signal strength is derived from the energy required to emit an Es modulation symbol.
The noise power depends on the density of the noise spectrum N0, so the SNR is defined according to the relationship (1.1). = (1)
0 = . ( )(2) Modulation/demodulation: Digital modulation allows the coded information to be adapted to the transmission medium. The transmitter is in charge of the modulation operation which associates one or more binary elements with a symbol characterized by its amplitude and phase. Modulation acts on the parameters of a carrier signal to transmit the encoded data. There are several types of modulations that can be applied to optical channels [18], (Fig.6) The demodulator plays the dual role of the modulator and thus transforms the received signal into a bitstream.
The transmission channel: It represents the link between the transmitter and the receiver and can be of different natures depending on the type of quantity it allows to convey. The transmission channel is characterized by its capacity and bandwidth.
Note that the input of the transmission channel processes binary elements, while the output produces probabilistic information associated with the binary elements. There are several theoretical models of the transmission channel depending on the most frequent types of errors.
The most commonly used channels in information theory are the Symmetric Binary Channel (CBS) and the Gaussian White Additive Noise
CHAIN WITH THE MATLAB /
SIMULINK SOFTWARE
In this section, we describe the motivation to better choose the components of an optical telecommunication chain; we need to calculate the optical link balance [20] which is summarized in the calculation of the energy balance and the bandwidth balance of the link. Two effects limit the transmission capacity: attenuation and dispersion. First of all, this paper provides an overview of the transmission chain and program architecture, each of the above blocks is used in the code as a subprogram. The script used for the simulation will therefore only pass the variables from one subprogram to another and calculate it.
Or loss of transmitted power, during propagation in the fiber, the power decreases as a function of the length of the fiber at a defined wavelength ʎ, according to the law: = 0 (− )
( / ) = 10 (4) A: AttenuationP0: Power of light at the entrance of the fiber
PL: Power of light at the fiber output : 0 absorption factor in Neper/m.
= −4,34 (5)
The simulation is carried out for reference values for the attenuation: 0.17, 0.22, 0.50 associated with the single mode fiber F: (λ = 1550nm) for lengths ranging from 40km to 110km.In this part we tried to implement a Matlab code that allowed us to get as close as possible to the theoretical results. First we created a video file and saved it (the video must be in the same path as the Matlab code backup), then we started processing the video to send it correctly on the fiber. We will study the influence of transport with optical fiber, indeed we will see the influence of the attenuation on the quality of the video and the losses it will cause. The results obtained are summarized in table Ⅱ:
ATTENUATION ACCORDING TO
LENGTH 0.17 Fig.10.
Absorption factor by attenuation value Fig.11.
Absorption coefficient by length
The optical signal is propagated along the fiber as well as in the different components of a transmission chain, the latter will be assigned to the various types of noise so attenuation is not the only disadvantage there is also the influence of noise that distorts the video signal, such as the Gaussian additive noise channel. We present: the Gaussian model which is the most common in the literature for optical fibers. It is a rather simplistic model, it is the reference channel to study error-correcting codes and their decoding algorithms. The AWGN assumes that a noise element Bn is added to the emitted element: Hence: Yn :received signal Bn : noisy signalXn : emitted signal = + (6) Fig.12.
Video noisy for Att= 0.17: [1- L=40km, 2- L=50km, 3 Fig.13.
Video noisy for Att= 0.22: [1- L=40km, 2- L=50km, 3 L=60km, 4 - L=70km, 5-L=80km, 6-L=90km, 7- L=100km, 8L=110km] Fig.14.
Video noisy for Att= 0.50: [1- L=40km, 2- L=50km, 3 L=60km, 4 - L=70km, 5-L=80km, 6-L=90km, 7- L=100km, 8L=110km]
The signal-to-noise ratio is often used as a measure of quality between the original image and a compressed image. For this fact, the square error (MSE) and the peak signal-to-noise ratio (PSNR) are the two error measures used to compare the quality of image compression. The MSE represents the cumulative squared error between the compressed image and the original image, while the PSNR represents a measure of the maximum error.It is calculated using two equations: = ( ( _
é − )2(7) = 10 ∗ 10(2552 ⁄ (8) The results obtained are summarized in (table Ⅲ)
IV.SIMULATIONRESULTS According to (Table Ⅱ) and the plot of the curves, we notice that indeed the attenuation has an influence on the video, but whenever the attenuation increases the quality of the video becomes more and more mediocre more precisely to a distance of 80 km (According to Algeria Telecom) it is the maximum theoretical distance of sending the signal without amplifiers. Beyond 110km in cannot send. The length of the optical link affects the quality of the video transmitted, in addition it is long the attenuation increases and the quality of the video is degraded [22]. The attenuation of the fiber must be compensated periodically by optical amplifiers (AOSC, EDFA), the chromatic dispersion must also be compensated by (Bragg grating, fiber with two concentric cores) as well as the nonlinear effects [23].Other techniques, such as multiplexing are implemented to increase the flow in an optical link and improve service quality, and the design of new fibers for compensating polarization dispersion. For further details on attenuation and its causes, the interested reader may refer to references [21].
The PSNR is the most commonly used evaluation, which allowed us to conclude that: The higher the PSNR is, the better the quality of the compressed or reconstructed image. The lower the MSE value, the lower the error.
V.
CONCLUSION The progress made in the field of telecommunications systems is much important and rapid in terms of transmission capacity. This is why it seemed interesting to us to start this work with a simulation of the video transmission chain under Matlab. This simulation is important to determine the performance of this chain. A study that allowed us to visualize the video and also measure the quality of its transmission, and allowed us to give similar results of reality. Thus, in the rest of our work we are looking for other more efficient coding/decoding algorithms, and test various architectures with implementations. [18] optical wireless communications :system and channel modelling with MATLAB/Z.Ghassemlooy,W.Popoola,S.Rajbhandari.
ISBN978-1-4398-5188-3 [19] Erwan Piriou, “Contribution of high-level modelling and synthesis in the design of flexible architecture dedicated to block turbocodes,” Doctoral thesis: Engineering sciences: Institut TELECOM/ TELECOM Bretagne, University of South Brittany: 2007 [21] W. Daum, J. Krauser, P. E. Zamzow et O. Ziemann. POF Handbook - Optical Short Range Transmission Systems, Springer, deuxième édition, 2008. [22] I. Azusa,Y. Koike, “Unconventional plastic optical fiber design for very short multimode fiber link,” Optics express vol 27,N 9 ,pp 12061-12069,2019. [23] P. A. FALL, M.FALL, “Experimental investigation of intensity modulator/direct detection (IM/DD) optical OFDM system with fiber bragg grating (FBG),”. Journal of Optical Communications, 2018.