Optical 5G Fronthaul (Microwave Photonic)

This literature review discusses the concept of Optical 5G Fronthaul using Microwave Photonic technology. It explores the role of fiber optic in front haul networks and the challenges in producing mm-wave signals from the optical domain. The review also covers the available optical solutions for transporting CPRI data and the need for new technologies and standards in 5G transport networks.

OPTICAL 5G FRONTHAUL (MICROWAVE PHOTONIC)
By Name
Course
Instructor
Institution
Location
Date

Literature Review
Transport networks will form an n integral part of 5G networks development. A number of the
existing technologies will be used in the construction of the network including radio over fiber
transmission as well as millimeter wave technologies [1]. Radio over fiber technology includes
the fiver as well as the ratio wave communication. In the transmission wireless communication,
mobile fraunthall networks as well as transmission systems which link the central office and the
base station depended on wireless communication in in the bands of microwave frequency. The
current network make use of MW band found in the electromagnetic spectrum for the purposes
of transmission hence it is anticipated that 5G mobile networks are able to utilize MMW band in
a more efficient manner with interferences that are neglible with the current wireless networks.
The capacity of the transmission is limited by the microwave fraunthall owing to the available
bandwidths which are very narrow. With the opening at MMW bands, higher rates of data are
achievable. A new spectral window is opened by MMW technology that is to be used for
transmission in the next generation [2]. Still, the MMW carrier’s high frequencies allow them to
transmit data at relatively high date rates in comparison with the RF carriers that are found in the
MW band.
As a result of the rapid revolution being experienced and witnessed ion mobile technology,
wireless communication technology has managed to evolve from 1G t0 4G. The main focus of
the 4G technology was on the seamless integration of cellular network among them 3G, WLAN,
GSM and Bluetooth. Researchers and scholars are at the moment work on how to define the
wireless communication of the next generation. With emphasis put on small cell concepts,
enhancement of capacity, network speed as well as introduction of new technologies of
communication, 5G is on progress an improvement in the capacity as well as speed is need to

ensure the communication for the possibility billions of wireless devices is made more feasible
[3]. WAN at millimeter bands tends to have large bandwidth that provides an alternative for high
speed hotspot or indoor communication that is to be use by 5G.
In supporting the combination of mm-wave ratio as well as small cells for future access by 5G,
an important role is played by fiber optic both in the backhaul a front haul networks. Optical
access network should be scalable to support the anticipated deployment goals of 5G by 2020.
As is notable from the diagram above, making an end-to-end transport network requires a
connection of all the various types of WAN to the fiber optic. In on hand, the high speed as well
as convenient mm-wave alongside small cell WAN is used while on the other, OAN offer access
to very high speed internet for fiver to the x(FTTX) [4]. Numerous bands among them the local
multipoint distribution service at between 28 and 30 GHz, 92-95 GHz, the licence free band that

is at 60 GHz as well as the E-band which is at 81-86 GHz, 71-76 GHz of high speed WAN are
availed for 5G.
Using the conventional electronics in the generation of the high frequency mm-wave electrical
signals sis costly hence a concern regarding directly producing mm-wave signals from the
optical domain. This work hence provides a demonstration and presentation on photonic
generation, distribution of 60 GHz frequency band signals as well as modulation that are to be
used in 5G [5].
A photonics based mm-wave is a laser beam that is composed of longitudinal modes that are
coherent and have spacing of frequent that is equal to the needed mm-wave. The needed
electrical mm-wave may be produced as the longitudinal modes knock each other in the
photodiode.
Numerous techniques have been proved to be usable in the production of optically mm-waves.
Such techniques include those that are based on dual lasers having various wavelengths that are
locked using optical phase locking or even injection phase locking, dual-mode laser, optical
heterodyning methods, mode locked lasers, on optical external modulation or even on strategies
that depend on nonlinear features among them four wave mixing as well as stimulated Brillouin
scattering [6]. Still, there are methods that depend on the optical frequency combs q which is
produced by gain striking of a distributed feedback laser. The technique of comb generation
provided flexibility since the free spectral range of optical combs are tunable within a range of
20 GHz and offer ideal signal to noise ratio.
As the longitudinal modes produced by a dual mode laser or two different lasers are often
associated with low coherency, poor spectral purity is observed in the mm-wave that is produced

by their beating. In as much as the mode locked lasers are able to produce a frequency comb
having a very wide bandwidth, they have challenges of cavity complexity as well as invisibility
of tenability of the FSR as a result of fused length of the cavity. Still, the optical line width of
each of the comb lines can be significantly large and the coherence of the imperfect phase
between the optical tones may result in significant noise of the phase on the produced mm-wave
signal [7].
The longitudinal modes produced by the nonlinear impacts have greater efficiency even though
they require higher pump powers and the efficiencies of their conversion are very low.
Furthermore, owing to the fixed nature of Brillouin frequency shift in the fiber, the produced
optical mm-wave has limited frequent. For the case of EM, the modulators tend to have very
large insertion losses especially when cascaded. Combined with modulation efficiency as well as
the instability introduced by the bias drift, using EM technique may prove very challenging and
sophisticated.
One of the approaches of producing radio frequency, RF, signals at frequencies of mm as well as
terahertz sources is the dual wavelength fiber laser. Erbium doped fiber, EDF, is the gain
medium that is often used in the setup of fiber laser in regions that have 1.5 micron among them
multi-wavelength laser [8]. Nevertheless, the strong mode competition introduced by
homogenous broadening has turned out to be the major challenge in achieving stable oscillation
of multi-wavelength in room temperature.
The string mode competition as result of homogenous gain that broaden in the gain media
presents a challenge in the achievement of dual wavelength generation in 1.5 um region od
wavelength with EDFL. Different approaches for combating the challenge among the
polarization hole burning, FWM as well as cascaded stimulated Brillouin scattering have been

indicted for Ytterbium-doped fiber, Thulium-doped fiber laser as well as EDFL. Realization of
the operation multi-wavelength at room temperature has been proposed to be possible through
different methods through a reduction of the cross-gain saturation as well as suppressing the
mode competition. Such are among them four wave mixing, polarization hole burning effect,
cascaded stimulated Brillouin scattering as well as frequency shifted feedback [9].
The DWFL indicated high power stability when a very narrow line width is used. Using photonic
crystal fiber is associated with advantages of flexibility as well as characteristics that depend on
the wavelength which render the material almost an ideal option as a selective filter for
wavelength for EDF.
Optical networks for the front haul
The available optical solutions in the achievement of transportation of the common public radio
interference, CPRI, data include:
OTN which is a solution pegged on ITU-T G.709 that enables time multiplexing of numerous
tributaries on one wavelength or Dense WDM network. Protection as well as service level
agreement may be provided at the demarcation points. The OTN tools and equipment should be
supplied with adequate power.
PON offers one of the most common as well as low cost option to the implementation of fiber to
the various home networks. However, gigabit cable PON tends to be least attractive for use for
the front haul owing to the high bandwidth that is need for every sector. XG for 10 Gbits/s will
as well suffice as since the upstream bandwidth is restricted to 2.5 Gbits/s. An option might be
provided by newer standardization including the ITU-T G.987 which enables XG for 10 Gbits/s
with XG-PON2 symmetrical traffic [10].

Otherwise one is expected to wait for the completion of the Next Generation-PON2 that is based
on wavelengths that range between 4 and 8 stacking of XG-PON1 system. The equipment of
PON just is the case with those of OTN should be subjected to adequate supply of power at the
antenna as well as the site of the central office. The time division multiple access calling for a
window of ranging time is yet another challenge with PON interfaces especially in case where a
new optical network unit is to be linked and concerns with jitter introduced for the alternative
traffic.

References
[1] Alavi SE, Soltanian MR, Amiri IS, Khalily M, Supa’At AS, Ahmad H. Towards 5G: A
photonic based millimeter wave signal generation for applying in 5G access fronthaul. Scientific
reports. 2016 Jan 27;6:19891
[2] Chang GK, Cheng L, Xu M, Guidotti D. Integrated fiber-wireless access architecture for
mobile backhaul and fronthaul in 5G wireless data networks. In2014 IEEE Avionics, Fiber-
Optics and Photonics Technology Conference (AVFOP) 2014 Nov 11 (pp. 49-50). IEEE
[3] Chang GK, Liu C. 1–100GHz microwave photonics link technologies for next-generation
WiFi and 5G wireless communications. In2013 IEEE International Topical Meeting on
Microwave Photonics (MWP) 2013 Oct 28 (pp. 5-8). IEEE
[4] Chung HS, Cho SH, Han CG, Lee S, Lee JC, Lee JH. Design of RoF based mobile fronthaul
link with multi-IF carrier for LTE/LTE-A signal transmission. InMicrowave Photonics (MWP)
and the 2014 9th Asia-Pacific Microwave Photonics Conference (APMP) 2014 International
Topical Meeting on 2014 Oct 20 (pp. 303-306). IEEE
[5] Dat PT, Kanno A, Yamamoto N, Kawanishi T. 5G transport networks: the need for new
technologies and standards. IEEE Communications Magazine. 2016 Sep;54(9):18-26
[6] Kawanishi T, Kanno A, Freire HS. Wired and wireless links to bridge networks: Seamlessly
connecting radio and optical technologies for 5G networks. IEEE Microwave Magazine. 2018
May;19(3):102-11

[7] Liu C, Wang J, Cheng L, Zhu M, Chang GK. Key microwave-photonics technologies for
next-generation cloud-based radio access networks. Journal of Lightwave technology. 2014 Oct
15;32(20):3452-60
[8] Routray SK, Sharmila KP. Green initiatives in 5G. In2016 2nd International Conference on
Advances in Electrical, Electronics, Information, Communication and Bio-Informatics
(AEEICB) 2016 Feb 27 (pp. 617-621). IEEE
[9] Tian Y, Song S, Powell K, Lee KL, Lim C, Nirmalathas A, Yi X. A 60-GHz Radio-Over-
Fiber Fronthaul Using Integrated Microwave Photonics Filters. IEEE Photonics Technology
Letters. 2017 Oct 1;29(19):1663-6
[10] Waterhouse R, Novack D. Realizing 5G: Microwave photonics for 5G mobile wireless
systems. IEEE Microwave Magazine. 2015 Sep;16(8):84-92