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Fiber Optic Radio: Overview, Principles and Applications
D Ropero-Torres1,2, K-Port1,2 and D Guevara-Ibarra1,2
1
Research and Development Group in Electronics and Telecommunications - GIDET.
2
Francisco de Paula Santander University, Cúcuta - Colombia.
Francisco de Paula Santander University, Cúcuta - Colombia.
E-mail: dionelrt@ufps.edu.co, karlaceciliapl@ufps.edu.co and dinaelgi@ufps.edu.co.
Abstract. This paper presents documentary type descriptive research through the comparison
and analysis of electronic documents from international, national and regional databases with
the purpose of knowing generalities, principles and applications of radio systems on optical
fiber (RoF). In RoF systems, the optical signal is modulated by a radio frequency carrier, then
transmitted by optical fibre; one of the most important advantages is to concentrate the costs of
high-frequency equipment in a central office. RoF applications include the inclusion of Hybrid
Fiber-Coaxial solutions, use of femtocells to improve coverage and increase bit rate,
transmission to 10 GbE via RoF with 96GHZ wireless bridge. This system uses different types
of digital modulation and division multiplexing of: orthogonal frequency (OFDM), time
(TDM), wavelength (WDM) and coarse wavelength (DWDM). When comparing the state of
the art of proposed RoF systems with 4G technology, it was determined that because of the
projection of connected users in future generations it is necessary to bring RoF to areas of easy
access due to its flexibility and robust bandwidth.
1. Introduction
Over time, there has been a significant evolution in the way of transmitting information, from the
transmission by means of electrical pulses such as the telegraph, to the discovery of the
electromagnetic and radioelectric spectrum. Initially, studies were carried out on transmission media,
such as guided media, such as coaxial cable or fiber optic and non-guided media such as air through
the radio spectrum. In 1952, it was discovered scientifically how to transmit signals outside the radio
spectrum through a guided medium outside the common, these signals were transmitted in the range of
visible spectrum through what is now known as fiber optic. [1]. This is called as a guided transmission
medium, in which information is sent about an optical carrier or a beam of light, this technology of
rapid progress and development, seeks to improve the quality of life of man, allowing communications
to be achieved quickly, safely and effectively. [2]
The commercial offer and the great demand of users in new services for information transmission,
has led the companies to implement digital communication systems, in this way the radio systems on
fiber (RoF) emerge, which uses as transmission medium the optical fiber and wireless systems, whose
main characteristic is to send information to long distances, with a great bandwidth and little
attenuation that this medium presents. [3]
It is expected that by 2022 the number of devices connected to IP networks will be more than three
times the world population, with 3.6 devices in the capita network, compared to 2.4 devices in the
network per capita in 2017, with this it is estimated that there will be 28.5 billion devices in the
network by 2022, compared to 18 billion in 2017. [4]. At the end of the first quarter of 2018 in
Colombia, the penetration rate of broadband internet connections increased 3.4 percentage points
compared to 2017, reaching an index of 61%, as shown in Figure 1. [5] Because of this massive
growth, the systems are not able to meet the needs of users; therefore, the great demand for bit rate
leads to the migration of new technologies such as systems based on Radio on Fiber (RoF), Fiber to
the Home (FTTH) and solutions Hybrid Fiber and Coaxial (HFC), for some years by network
operators. [6]
The increase in the number of users and mobile devices, as well as an increase in traffic in
telecommunications networks in recent years, has led to the development of solutions to improve the
capacity of the communications infrastructure. Today, the traffic of wirelessly transmitted data
continues to grow. In this sense, it is expected that by 2019 there will be 11.5 billion mobile devices
connected to the network and it is expected that data traffic will increase from 20% to 2019 with
respect to 2014, where more than half of this traffic will be transported by 4G networks. [7] Wireless
communications technology uses a base station requires a modulator/demodulator that receives a
digital baseband signal and must modulate it to the respective RF carrier. RoF reduces the complexity
and cost of each base station, since the signal that propagates through the optical fiber is the RF signal
at the appropriate carrier frequency to be sent directly to the antenna. RoF integrates the high capacity,
high coverage and low power consumption of fiber optics with the possibility of always being
connected that offers wireless communication. [8]
Figure 1. Broadband internet connections and penetration index in Colombia 1T, 4Q 2017- 1Q 2018.
[9]
2. Experimental Process
In this section, we will mention the essential steps that were carried out in order to carry out this
work. As an initial part, research was carried out on primary sources such as databases: Association
for Computing Machinery (ACM) and data from International and National Universities, secondary
sources such as scientific journals from universities, congress documents and organizations focused on
fiber optic communications, these data were taken from studies conducted in the last 5 years with the
purpose of having information on the most recent techniques and technologies used.
The topology and architecture of communication systems using Radio on Fiber (RoF) technology
were investigated, for which a previous study or state of the art was carried out; in the process some of
the most important applications were determined, such as the inclusion of Fiber-Coaxial Hybrid
solutions for network interconnection, the use of femtocells to improve coverage and increase the bit
rate or the transmission of GbE by means of RoF links with a 96 GHz wireless bridge. [10]among
other applications.
As a final part it was possible to compare the state of the art of proposed RoF systems with 4G
technology, determining that because of the projection of connected users in future generations it is
necessary to bring RoF technology to areas of difficult access due to its flexibility and robust
bandwidth.
3. Results and Discussions
The massive growth of modern societies in the demand for telecommunication networks has reached
such a point that by 2021 the number of devices connected to IP networks will be 3 times greater than
the world population, thus leaving an estimate of 3.5 devices connected to the network per inhabitant,
compared to 2.3 devices connected in 2016. [6]
This indicates that the increase in the number of users and mobile devices as well as increased
traffic in telecommunications networks in recent years leads researchers to work on improving the
capacity of the communications infrastructure, Radio over Fiber (RoF) technology is an economically
viable and technologically stable option because it can transmit large volumes of information over a
single fiber optic link, this technology has the advantage of transmitting radio signals with low Bit
error rates and low latency. [8]
The next generation of mobile communications, promises provision of hybrid wireless and optical
technologies, especially systems known as RoF, in 5G are provided as broadband wireless services;
RoF architecture conventionally proposes a central office (CO - Central Office) in which are
concentrated the most robust processing equipment and high frequency modulation. [11]as can be seen
in figure 3.
Figure 2. Radio System on Fiber (RoF) [12]
Sebastián Molina, Rubio Jiménez and Andrés Guillermo Rodríguez conducted a national study at the
Francisco José de Caldas University in 2016, which reflected Colombia's commitment, analyzing
information transport alternatives through infrastructure for 4G services through RoF systems, in
which a study was conducted in order to reach areas where there was no access to the network,
because the infrastructure is focused only on a part of the country, taking into account that by 2016
there was only 29% of broadband services, where fiber optic technologies are used; 3G technology
with a transmission rate of 2Mbps was compared to 4G technology with a transmission rate of up to
100Mbps, in order to reach different urban and rural areas promoting the highest bandwidth as the
demands over the years have increased due to the quality of the applications.[13]
Dalma Novak, B. Waterhouse, Nirmalathas, Christina Lim, A. Gamage Prasanna, R. Thomas Clark,
L. Michael Dennis and A. Jeffrey Nanzer, conducted international research published in the IEEE
Journal of Quantum Electronics, conducted a publication describing that fiber optic radio transmission
has been widely studied as a means of realizing a wireless fiber optic distribution network that allows
seamless integration of optical and wireless network infrastructures. These networks are compatible
with the new broadband services, thus providing greater opportunities for photonic technologies to
play a leading role in the next generations where it is expected to make integrated networks between
optical and wireless. [14] In their research they presented some recent developments in fiber radio
technologies, which can support the distribution of broadband wireless signals in an optical/wireless
network. It also describes some challenges for the applications of Fibre Radio technologies in future
wireless systems, such as 5G and 60 GHz networks.
Rudy Paola Báez Parada, Ángel David Torres Palencia, Karla Cecilia Puerto López, Dinael Guevara
Ibarra and Francisco Moreno García; under the framework of the IV International Week and XII week
of science, technology and innovation at the University Francisco de Paula Santander, an investigation
was carried out on the non-linear effects in a RoF system since these are characterized by taking
advantage of optical fiber to transport radio signals directly to the base station, for this research, the
initial stage of RoF and the technique of coarse wave division multiplexing (DWDM) with 50GHz
spread were implemented by means of specialized software, resulting in the signal degradation effects
being provided at the established fiber optic distance and the input power used being optimal for the
fiber optic to behave as a non-linear medium. [15]
María Camila Palacios Garzón and Gustavo Adolfo Puerto Leguizamón; conducted research at the
Francisco José de Caldas District University on the design of a radio frequency signal transmission
system over optical fiber using spectral partitioning; From the spectral partitioning of a very high
bandwidth light signal by means of AWGs, several carriers of different wavelengths at different
frequencies are obtained; the aim is to use each carrier cost-effectively for the transmission of
millimetre-wave radio over optical fibre, which is the physical link between the base station and the
network's central station for information processing. In its research, it makes a proposal that addresses
the problem of transport and distribution in the millimetre band, given the low coverage that this band
presents, due to propagation losses in the medium. [16]
Balseca, Carlos Alfredo Vargas Quinzo and Deysi Vilma Inca, conducted research in Riobamba,
Ecuador on the non-linear effects of optical fiber are highly important to study, but there are other
important characteristics in which some investigations are derived as the effects of the relation signal
to noise (SNR) or the rate of error of bits (BER), based on this in the city of Riobamba, Ecuador a
study on the demonstration of the nonlinear effect (FWM) was carried out, a WDM network was
designed and simulated, in the software OptiSystem, With this study we studied the performance
parameters of the physical network applying WDM, for the evaluation of the systems there are
different techniques such as the eye diagram or the constellation map, reflecting in these according to
their behavior the required parameters, the generation of the FWM effect in a single mode fiber
depends largely on whether the spacing between the channels is the same or different, since, as there is
an equal distribution between channels, the frequencies generated FWM agglomerate on the
communication signals, decreasing the signal to noise level of the communication and the transmission
rate. [17]
Another important application of RoF systems is presented by Atsushi Kanno and Naokatsu
Yamamoto at the SPIE OPTO event where they explained according to their publications that the
millimeter-wave band technology of the 96 GHz frequency band promises to detect small ones due to
the high range resolution due to its short wavelength distance and the amplitude of the available
bandwidths of 8 GHz; but the transmission in the millimeter-wave bands is limited by the high
atmospheric attenuation. Implementing RoF technology for transporting these millimeter-wave signals
to remote radar heads over a fiber optic network will provide higher performance due to the qualities
of this form of signal transmission with this technology. [18]
Dewra, Anjali Koundal and Sanjeev; at the Shaheed Bhagat Singh state technical campus, India
conducted research on the performance analysis of the 4*10 GBPS OFDM-PON system via RoF,
these researchers analyzed the Orthogonal Frequency Division Multiplexing (OFDM) system for
transmission of radio signals over optical fiber (RoF) in a passive optical network at different input
powers, implemented a speed of 10 Gbits/s to simulate the system. They were able to observe that the
performance of the system gave an acceptable quality factor and a bit error rate with a low signal input
power in the presence of non-linearity of the fiber, in addition, the system did not use any amplifier
and the work was done at higher bit rates. It was analyzed that as the input power increases, the quality
factor also increases and the bit error rate decreases. [19]
4. Conclusions
Currently, technological development is growing exponentially, such as the number of devices
connected to telecommunications networks; the data taken as a reference from different studies
proposed in this article, reflect the need to cover lines of research in the areas of telecommunications
in order to be at the forefront with the technological evolution required by the world.
The RoF system is generally used in the areas of telecommunications, but, it is not tied to such
applications, since its utility can cover different spaces where it is necessary, not only to reach a large
bandwidth, but also where there is the obligation that the transmission of data is done quickly and
effectively, because these technologies are applicable in electronics in general, as in the transmission
of data acquired by sensors, among other applications, since the reduction of costs in this technology is
notorious with respect to the transmission of wireless networks commonly used in the market.
Evidently it is not possible to stop researching development in the area of telecommunications in
view of the fact that as days go by more users are accessing the information network; it is necessary to
enlarge and supply the systems in order to meet the needs of users. On the other hand, in 4G mobile
telephony different techniques were implemented over time, one of these was RoF for effective data
transmission, but RoF in its different applications is not only for 4G but also applicable and promising
in the different areas of 5G soon; it is expected that over time can be applied in the 5G and possibly in
future generations, thanks to the way you adapt these technologies.
Finally, RoF applications either in industry or in bringing it to homes as FTTH technology does, is
an important need in the development and advancement worldwide, making necessary the
combination of multiplexing techniques such as OFDM, WDM and DWDM, this in turn demonstrates
that the connections of different technological links provide and will provide greater support in the
advancement of telecommunications and electronics in general.
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