Page 51 - ITU Journal Future and evolving technologies – Volume 2 (2021), Issue 2

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 2

modulator, single and multi-core optical fiber, of user terminals in a picocell, the requirements for
multichannel reflecting Bragg grating, and for cost-efficiency of the RU equipment, in fact,
some MWP devices using these models. The representing the interface between the optical and
development results are summarized in [23]. In RF sections of the transmission system come to the
addition, in order to show the effectiveness and forefront. The most obvious solution to this
reliability of the proposed approach, a comparative problem is the ultimate simplification of the RU
study was carried out using a direct comparison of scheme, which is carried out by removing all the
ME-CAD vs OE-CAD models when simulating both processing units (generation, modulation,
individual optoelectronic elements in a microwave demodulation, RF frequency conversion, etc.) to
bandwidth and some MWP devices based on them the CU or DU. That is, a package of modulated RF
[24]. The result clearly showed that the optimal carriers with frequencies corresponding to the
approach for this purpose was in using established operating frequencies of the wireless fronthaul is
microwave-electronic CAD tool Cadence AWRDE, inputted to the optical transmitters of the DU
especially during the modeling of MMW devices, as (downlink) and the RU (uplink). Therefore, the
it is needed for designing analog fronthaul RU of decisive influence on their characteristics effects
B5G. the scheme of transporting digitally modulated RF
signals through a fiber-optic cable between the DU
Nevertheless, this unit raises the question of
choosing the optimal principle for designing its and RU. Fig. 2 illustrates two possible options
noted in the Introduction to design NG-RAN
circuitry using an MWE or MWP approach. To
clarify this, in this paper we perform a comparative wireless fronthaul including RFoF (a), and IFoF (b).
simulation for a specific example of developing The following abbreviations are used in the figure:
such an obligatory RU’s node as a reference EA – electronic amplifier; EOM – electro-optic
oscillator with an output frequency of more than modulator; IFDM – IF demodulator; IFM – IF
100 GHz, which is typically implemented by means modulator; IF/RF – frequency up-converter; MIMO
of a circuit that includes a relatively low-frequency – multiple input/multiple output; MMW-RO –
RF oscillator followed by a high-order frequency millimeter-wave reference oscillator; MW-RO –
multiplier. Thus, the rest of the paper contains the microwave reference oscillator; PD –
following. Section 2 addresses the features of photodetector; RF/IF – frequency down-converter;
RFDM – RF demodulator; RFM – RF modulator; SLS
configuring an analog fronthaul network using the
above two options of RoF architecture. In addition, – semiconductor laser source.
the key principles of MWP-based hardware design Downlink
are explained in Section 3. Following the principles From CU PD Data RFM EOM PD EA
and approaches outlined, Section 4 proposes and
describes two alternative schemes for MMW-RO SLS SLS MIMO MMW
band
implementing a frequency multiplier from 4.25 to
102 GHz using MWE or MWP approach. Further, To CU EOM Data RFDM PD EOM EA
with the help of AWRDE software with an DU RU
additional introduction of the previously proposed Uplink
models of optoelectronic devices, their main (a) RFoF-based wireless fronthaul
characteristics are considered. To ensure the
practical orientation of the model experiments, the From CU Data Downlink
parameters of each of the models used are selected PD IFM EOM PD IF/RF
based on the the specifications of commercially MW-RO
MMW
available discrete components. Section 5 concludes SLS SLS MMW-RO MIMO band
the paper.
To CU Data
EOM IFDM PD EOM RF/IF
2. A-ROF-BASED ARCHITECTURE FOR DU Uplink RU
WIRELESS FRONTHAUL (b) IFoF-based wireless fronthaul

In general, a NG-RAN of A-RoF architecture Fig. 1 – Conceptual diagrams of NG-RAN’s A-RoF wireless
combined with a small-cell scenario is considered fronthauls (Optical connections are painted in red, electrical
as the reliable way for the further development of connections in black)
cellular communication networks beyond 5G. At
the same time, due to the relatively small number

© International Telecommunication Union, 2021 37