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Simu5G–An OMNeT++ Library for End-to-End Performance Evaluation of 5G Networks

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In this paper we introduce Simu5G, a new OMNeT++-based model library to simulate 5G networks. Si-mu5G allows users to simulate the data plane of 5G New Radio deployments, in an end-to-end perspective and including all protocol layers, making it a valuable tool for researchers and practitioners interested in the performance evaluation of 5G networks and services. We discuss the modelling of the protocol layers, net-work entities and functions, and validate our abstraction of the physical layer using 3GPP-based scenarios. Moreover, we show how Simu5G can be used to evaluate Multi-access Edge Computing (MEC) and Cellu-lar Vehicle-to-everything (C-V2X) services offered through a 5G network
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Received July 30, 2020, accepted September 23, 2020, date of publication October 2, 2020, date of current version October 14, 2020.
Digital Object Identifier 10.1109/ACCESS.2020.3028550
Simu5G–An OMNeT++ Library for End-to-End
Performance Evaluation of 5G Networks
GIOVANNI NARDINI 1, DARIO SABELLA2, GIOVANNI STEA 1, (Member, IEEE),
PURVI THAKKAR3, AND ANTONIO VIRDIS 1
1Dipartimento di Ingegneria dell’Informazione, University of Pisa, 56122 Pisa, Italy
2Intel GmbH, 85579 Neubiberg, Germany
3Intel Corporation, Santa Clara, CA 95054, USA
Corresponding author: Giovanni Stea (giovanni.stea@unipi.it)
This work was supported in part by the Italian Ministry of Education and Research (MIUR) in the framework of the CrossLab Project
(Departments of Excellence).
ABSTRACT In this article we introduce Simu5G, a new OMNeT++-based model library to simulate
5G networks. Simu5G allows users to simulate the data plane of 5G New Radio deployments, in an
end-to-end perspective and including all protocol layers, making it a valuable tool for researchers and
practitioners interested in the performance evaluation of 5G networks and services. We discuss the modelling
of the protocol layers, network entities and functions, and validate our abstraction of the physical layer
using 3GPP-based scenarios. Moreover, we show how Simu5G can be used to evaluate Multi-access Edge
Computing (MEC) and Cellular Vehicle-to-everything (C-V2X) services offered through a 5G network.
INDEX TERMS Computer simulation, object-oriented modeling, computer networks, 5G mobile commu-
nication.
I. INTRODUCTION
The two main pillars of the next technology revolution in
the field of mobile networks will be the deployment of 5G
access and Multi-access Edge Computing (MEC). The for-
mer will provide ultra-reliable, high-bandwidth and low-
latency connectivity, thus enabling new ICT services, such
as smart cities, autonomous vehicles, augmented reality and
Industry 4.0. The latter will endow mobile networks with
cloud-computing capabilities located at the edge, enabling
computation-intensive, context aware services for mobile
users, such as those based on artificial intelligence. The next
generation of mobile networks will therefore witness a tight
integration of computation and communication.
The 5G Radio Access Network (RAN) network, based on
the New Radio (NR) 3GPP standard, will be deployed pro-
gressively, and will coexist for a relatively long time with the
existing 4G (LTE/LTE-Advanced) infrastructure. To favor the
above transition, the data plane of the NR technology consists
of a stack of layered protocols, which closely resembles that
of 4G. NR User Equipments (UEs), e.g. handheld devices,
will need to be able to connect to either or both the 5G and
the 4G network.
The associate editor coordinating the review of this manuscript and
approving it for publication was Tiago Cruz .
5G networks will matter for both the communication
performance they offer, and the services that they enable.
This calls for credible tools to evaluate the performance of
both, in an end-to-end context. As far as communication
performance is concerned, most of the intelligence in 5G
networks will be realized in software: therefore, being able
to assess the Quality of Service offered by the NR RAN to
a user (e.g., the latency of a connection), as a function of
different network intelligence designs (e.g., admission con-
trol, packet scheduling), in a credible way, will help network
operators to maximize their network utilization. On the other
hand, service providers of next-generation services, such as
autonomous driving or factory automation, will need to assess
the performance of their services on different 5G network
configurations or deployments.
In this article, we present Simu5G, a novel 5G simula-
tion library for the OMNeT++ simulation framework [14].
Simu5G includes a collection of models with well-defined
interfaces, which can be instantiated and connected to build
arbitrarily complex simulation scenarios, and is fully com-
patible with the INET library [15], which allows one to
simulate end-to-end scenarios involving arbitrarily com-
plex TCP/IP networks including 5G NR layer-2 interfaces.
In particular, Simu5G models the data plane of the 5G
RAN (rel. 16) and core network. It allows simulation of
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G. Nardini et al.: Simu5G–An OMNeT++ Library for End-to-End Performance Evaluation of 5G networks
5G communications in both Frequency Division Duplexing
(FDD) and Time Division Duplexing (TDD) modes, with
heterogeneous gNBs (macro, micro, pico etc.), possibly com-
municating via the X2 interface to support handover and
inter-cell interference coordination. Dual connectivity with
an eNB (LTE base station) and a gNB (5G NR base station)
is also available, making it possible to simulate 4G/5G tran-
sitions scenarios. 3GPP-compliant protocol layers are mod-
eled, and physical transmission is modelled via a realistic,
customizable channel models. Resource scheduling in both
uplink and downlink directions is supported, with support for
Carrier Aggregation and multiple numerologies, as specified
by the 3GPP standard. Simu5G supports a large variety of
models for mobility of UEs, including vehicular mobility.
Simu5G allows one to code and test, for instance, resource
allocation and management schemes in 5G networks, e.g.
selecting which UEs to target, using which modulation
scheme, etc., taking into account inter-cell interference coor-
dination, carrier selection, energy efficiency and so on. As far
as services are concerned, it allows a user to instantiate
scenarios where a user application, running at the UE,
communicates with a MEC application residing at a MEC
host, to evaluate (e.g.) the round-trip latency of a new-
generation service, inclusive of the computation time at
the MEC host. Moreover, it models the Cellular Vehicle-
to-Everything (C-V2X) standard, which relies on network-
controlled resource allocation for device-to-device (D2D)
communications. Simu5G can also run in real-time emulation
mode [11], enabling interaction with real devices. A user can
thus run live networked applications through an emulated 5G
network, using the same codebase for both simulations and
live prototyping, which abates the developing time and makes
results more reliable and easier to demonstrate.
In this article, we present the modeling and the capabilities
of Simu5G, with the aim of helping researchers to understand
the level of detail and to get a clear idea of its function-
alities. We also discuss the provisions that were made to
make Simu5G scalable (e.g., able to simulate tens of cells
as required by 3GPP scenarios), and how it was validated.
To show the type of studies enabled by Simu5G, we report
two representative case studies involving the evaluation of
next-generation services running on a 5G network: the first
one compares MEC service migration policies, and the sec-
ond one compares the impact of communication modes on
platooning services in a C-V2X scenario.
To the best of our knowledge, few tools that simulate
the 5G NR data plane are available to the research commu-
nity. Leaving aside physical-level 5G simulators, such as the
Vienna 5G SL simulator [4], which model the physical layer
(and possibly the MAC), but nothing above that, hence are
not suitable for the kind of evaluations that we discussed
earlier, the only other end-to-end 5G simulators that we know
of are 5G-LENA [5] and the 5G-air-simulator [6]. However,
both lack several functionalities included in Simu5G, e.g.,
5G- LENA lacks FDD, and both lack network-controlled
FIGURE 1. OMNeT++ module connection.
D2D communications and do not model dual-connectivity
scenarios.
The rest of the paper is organized as follows: Section II
reports background on OMNeT++. Section III discusses
the related work on simulation of 5G networks in detail.
In Section IV we present the architecture of the 5G net-
work, the way Simu5G models it, and discuss its valida-
tion. Section V presents topical use cases, and Section VI
concludes the paper.
II. THE OMNeT++ SIMULATION FRAMEWORK
OMNeT++1is a well-known discrete-event simulation
framework that can be used to model virtually any kind of
networks, such as wired, wireless, on-chip, sensors, photonic,
etc. Its main building blocks are modules, which can be either
simple or compound. Modules exchange messages through
connections linking their gates, which act as interfaces. A net-
work is a special compound module, with no gates to the out-
side world, which sits at the top of the hierarchy. Connections
must respect module hierarchy: with reference to Figure 1,
simple module 3 cannot connect to 2 directly, but must instead
pass through the compound module gate. Simple modules
implement model behavior via event handlers, called by the
simulation kernel on receipt of messages. For instance, a node
can schedule a timer by sending a message to itself. Simple
modules have an initialization and finalization function, that
can be called in user-defined order at the start and the end of
a simulation. OMNeT++ offers support for basic simulation
functionalities (e.g., event queueing, random number genera-
tion, etc.), allowing users to concentrate on writing their own
simulation models.
OMNeT++ separates a model’s behavior, description and
parameter values. The behavior is coded in object-oriented
C++. The description (i.e., gates, connections and parameter
definition) is expressed in separate files written in Network
Description (NED) language. Parameter values are written
in initialization (INI) files. NED is a declarative language,
which exploits inheritance and interfaces, and it is fully
convertible into XML. NED allows one to write parametric
simulation scenarios, e.g. rings or trees of variable size, via
both a GUI (for basic/novice editing) and textual editing
(for advanced/expert editing). INI files contain the parameter
values that will be used to initialize the model. Multiple
values or intervals can be specified for a parameter.
1http://omnetpp.org, last accessed May 2020
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The OMNeT++ software offers support to simulation
workflow automation [9], facilitating the steps of a simu-
lation study that are most time consuming and error prone
for a user. Its Eclipse-based Integrated Development Envi-
ronment (IDE) facilitates debugging by allowing a user to
inspect modules, turn on/off textual output during execution,
visualizing the message flow in an animation, and displaying
events on a time chart. OMNeT++ studies are generated
automatically from INI files, computing the Cartesian prod-
uct of all the parameter values and generating independent
replicas with different seeds for the random number genera-
tors. Multiple runs can be executed in parallel on a multicore
machine. Rule-based data analysis allows a user to construct
recipes to filter or aggregate data, which can then be applied
to selected data files or folders.
INET [15] is a model library for OMNeT++. It imple-
ments models of many components of a communication
network, such as communication protocols, network nodes,
connections, etc. INET contains models for the Internet stack
(TCP, UDP, IPv4, IPv6, OSPF, BGP, etc.), wired and wireless
link layer protocols (Ethernet, PPP, IEEE 802.11, etc.), and
provides support for developing custom mobility models,
QoS architectures, etc. Thanks to OMNeT++ modular struc-
ture, by incorporating the INET library a user can instantiate
and connect protocol layers (e.g., an entire TCP/IP stack at
a host, from the application to the MAC), and quickly setup
composite models, e.g., an IP router with an Ethernet card
and a PPP WAN connection.
An interesting feature of OMNeT++ is that it can slow
down the flow of simulation time to the pace of real time. This
is only possible if simulated time flows faster than real time,
which depends on the density of events, their processing, and
the hardware running the simulation. Since the INET library
allows one to attach a host’s network interface to a simulation
module, to inject real TCP/IP packets into a simulator, and
collect them from it, it is possible to run simulators based on
OMNeT++ and INET, such as Simu5G, as real-time network
emulators, carrying packets between real applications.
III. RELATED WORK
In this section we compare Simu5G with the related work.
In order to give the reader a fair and thorough comparison,
we first need to lay down some terminology.
As far as wireless network simulation is concerned,
a meaningful distinction is between physical-level and
end-to-end simulators. With the former, one is interested in
measuring physical-layer quantities, such as the Signal to
Interference to Noise Ratio (SINR) or spectral efficiency, as a
function of physical-layer designs, such as antenna layout,
transmission schemes, etc. With the latter, one is interested in
the performance of application-level quantities (e.g., the end-
to-end delay, the throughput of user transactions, etc.), as a
function of higher-layer designs (e.g., an admission control
scheme, or an airtime scheduling algorithm). Link-level sim-
ulators model physical links to a high level of fidelity, but
typically do not model layers above the MAC. What is above
the MAC is normally abstracted as a ‘‘traffic generator’’,
its only purpose being generating backlog for the physical
layer. Quite often, link-level simulators follow a Monte-Carlo
approach rather than a discrete-event one. On the other hand,
end-to-end simulators normally include models of applica-
tion logic, layer-4, layer-3 and layer-2 protocols, as well as
network equipment running those protocols, and they always
are discrete-event (typically, events include packet arrivals
and departures at some interface).
A recurring term in simulation parlance, which can how-
ever be misleading with respect to the above distinction,
is system-level simulator: the latter defines a simulator where
the interaction among composing models is more impor-
tant than the level of detail of each single model. End-
to-end simulators are certainly system-level ones (think, for
instance, of the interaction between protocol models), but
physical-level simulators can be too (e.g., a cellular network
simulator that account for the interaction among different
cells in order to compute the SINR of each UE).
Orthogonally, we distinguish standalone simulators from
model libraries for simulation frameworks. A standalone
simulator is a software designed to serve a specific pur-
pose. A simulation framework (e.g., OMNeT++ or ns3) is
a software that allows developers to write their own model
libraries. Model libraries, if correctly coded, are interop-
erable, which means that they get reused, hence validated,
by the users of the framework. The same users can thus setup
complex scenarios quickly and reliably, just collating exist-
ing validated models. On the contrary, adding a model to a
standalone simulator takes a considerable amount of time and
effort. Simulation frameworks often come with prebuilt func-
tionalities, such as event-handling routines, random number
generation, statistics collection, thus freeing developers from
the burden of writing them. Moreover, they often offer sup-
port to simulation workflow automation. This includes the
ability to define parametric scenarios, to manage multiple
repetitions with independent initial conditions, to efficiently
store, retrieve, parse, analyze and plot simulation results, etc.
The lack of workflow automation support forces users to
develop home-brewed, error-prone or however unstructured
solutions (e.g., one-shot scripts), which is a known cause
of delay and errors in simulation studies, especially when
considering large-scale ones, as shown in [9] and [10].
According to the above classifications, Simu5G is a model
library, written for the OMNeT++/INET framework, for
end-to-end simulation studies. A previous conference paper
of ours [1] first introduced it. With respect to [1], this article
reports a more comprehensive description of functionalities,
including device-to-device transmissions, and topical exam-
ples of case studies, namely modeling of C-V2X scenarios in
a 5G New Radio network. Paper [11] discusses the real-time
emulation capabilities of Simu5G, showing that a desktop
computer can run an emulation of a multicell 5G network
carrying application traffic up to several Mbps.
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To the best of our knowledge, few other tools to simu-
late 5G networks are available to the research community.
Hereafter, we review them according to the above
classifications.
A well-known physical-level simulator is the Vienna 5G
SL simulator [4]. It is a MATLAB-based simulator that allows
one to evaluate average PHY-layer performance by means
of Monte Carlo simulations. A system-level version of it,
called Vienna 5G System Level Simulator, allows one to trade
accuracy for scale, thus enabling the evaluation of larger-scale
networks in terms of average performance. This simulator
is well tailored for the evaluation of lower-layer procedures,
including signal-processing techniques. However, it cannot
be used to evaluate multi-layer, end-to-end scenarios.
The 5G K-Simulator [3] is a standalone simulator suite
for analyzing various aspects of 5G networks. The suite is
composed of three tools: K-SimLink simulates the PHY layer
of a single UE-gNB pair; K-SimSys allows the evaluation
of MAC-layer interactions of multiple UEs and gNBs; both
are physical-level simulators in the above classification. The
third tool, K-SimNet evaluates the RLC, RRC, PDCP layers.
The three tools are interoperable. However, they only interact
by passing average values from one to the other, and it is
not possible to perform end-to-end simulations. For instance,
one cannot observe a single packet traveling from a source
application to its destination and traversing all protocol lay-
ers. Application models are limited only to full buffer and
non-full buffer, no explicit mention is made of mobility mod-
els. Finally, the MAC layer is based on the ns3 mm-wave
module [8], which was developed at the earliest stages of
the 5G standardization process and is known to be non-fully
standard compliant [6]. Other physical-level simulators, with
fewer functionalities than the above, are [20]–[23].
Among end-to-end simulators of 5G networks, we find
5G-LENA [5] and the 5G-air-simulator [6], both recently
released. The 5G-LENA model library for the ns3 frame-
work evolves from the LENA 4G library [7] and includes an
upgraded, standard-compliant version of the ns3 mm-wave
module [8]. It is focused on the simulation of MAC and
PHY layer of NR and provides tools for the evaluation
of Bandwidth Parts management, which Simu5G lacks.
However, it lacks support for FDD mode [6], it does not
model dual-connectivity, and we have no indications that it
supports network-controlled D2D, MEC or C-V2X scenarios,
hence it would not be possible to perform the analysis
reported in Section 5 with it.
The 5G-air-simulator is an end-to-end standalone simula-
tor, developed as an extension of the preexisting LTE-Sim,
that simulates LTE and LTE-Advanced networks. As such,
it inherits most of LTE-Sim pros and cons. On the pros side,
it models a wide variety of standard 5G functionalities, some
of which are – to the best of our knowledge – exclusive to
it, such as Massive MIMO and broadcasting. On the cons
side, it lacks others, notably D2D and 4G/5G dual connectiv-
ity. Moreover - and more importantly - like its predecessor,
it lacks tools for simulation workflow automation, which
reduce its usability for large-scale simulations. For example,
scenario definitions are written as static C++ functions, and
are compiled together with the simulator. Mixing models,
scenarios and definition of experiments is a clear don’t in sim-
ulation practice [9]. Moreover, despite being designed to be
an application-level tool, it does not model layer-4 protocols
such as TCP and UDP (they are listed, but their behavior is not
defined), which makes it impossible to perform a full-stack
end-to-end analysis of (e.g.) TCP-based services, such as the
ones run in [11].
IV. 5G NETWORKS AND THE Simu5G LIBRARY
This section describes the main elements of the data plane
of a 5G cellular network, and the way Simu5G models these
elements and functionalities. Moreover, we describe how
Simu5G was validated.
A 5G cellular network consists of a Radio Access
Network (RAN) and a Core Network (CN), as shown in Fig-
ure 2. The RAN is composed of cells, under the control of a
single base station (BS). 5G base stations are called gNodeBs
(gNBs), and they represent an evolution of 4G base stations,
which are called eNodeBs (eNBs). UEs are attached to a BS
and can change the serving BS through a handover proce-
dure. BSs communicate with each other via the X2 interface,
a logical connection which normally runs on a wired network.
The data plane of the CN consists of one or more User Plane
Functions (UPFs) that provide the interconnection between
the RAN and the data network. Forwarding in the CN is
carried out using the GPRS tunneling protocol (GTP).
FIGURE 2. Architecture of the data plane of a 5G cellular network.
In the RAN, communications between the BS and the UE
occur at layer 2 of the OSI reference model. Layer 1 and 2
are implemented using a stack of four protocols, on both
the BS and the UE. From the top down, we first find the
Packet Data Convergence Protocol (PDCP), which receives
IP datagrams, performs cyphering and numbering, and sends
them to the Radio Link Control (RLC) layer. RLC Service
Data Units are stored in the RLC buffer, and they are fetched
by the underlying MAC (Media Access Control) layer when
the latter needs to compose a transmission. The MAC assem-
bles the RLC Protocol Data Units (PDUs) into Transport
Blocks, adds a MAC header, and sends everything through
the physical (PHY) layer for transmission.
Resource scheduling is done by the BS periodically, every
Transmission Time Interval (TTI). On each TTI the BS
allocates a vector of Resource Blocks (RBs) to backlogged
UEs, according to its scheduling policy. A Transport Block
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occupies a variable number of RBs, based on the Modulation
and Coding Scheme (MCS) chosen for transmission. The
MCS defines the number of bits that an RB can carry, and
is selected by the BS, based on the Channel Quality Indicator
(CQI) reported by the UE. The latter mirrors the SINR
perceived by the UE, quantized over a range going from 0
(i.e., very poor) to 15 (i.e., optimal).
In the downlink (DL), the BS transmits the TB to the
scheduled UEs on the allocated RBs. In the uplink (UL),
the BS sends transmission grants to UEs, specifying which
RBs and MCS to use. UEs signal to the BS that they have
UL backlog by sending Buffer Status Reports (BSRs) after
a scheduled transmission, or by starting a random access
procedure in order to obtain a scheduling grant by the BS,
if they are not scheduled. Scheduling and transmissions in
the UL and DL directions are independent. The partitioning
between UL and DL resources can be in frequency or time,
leading to FDD and TDD. In FDD, each direction uses a
separate spectrum. In TDD, instead, the DL and UL legs
share the same spectrum, and the two transmission directions
alternate over time.
MAC transmissions are protected by a Hybrid-Automatic
Repeat reQuests (H-ARQ). After a configurable number of
TTIs, the receiver sends an ACK/NACK to the sender, which
can then re-schedule a failed transmission.
A. THE Simu5G LIBRARY
Simu5G simulates the data plane of the 5G New Radio RAN
and CN. Signalling and management protocols are not imple-
mented in the current version (but they can easily be added
by the interested user). The main elements of the Simu5G
library are the NrUe and gNodeB compound modules, which
model a UE and a gNB with NR capabilities. Their internal
architecture is shown in Figure 3. All nodes are geolocated
on a three-dimensional cartesian plane, which allows one to
measure inter-node distances (e.g., to compute path loss).
A UE model includes all protocol layers, from the physi-
cal to the application layer. Notably, it also includes the IP
and TCP/UDP protocols, as well as vectors of TCP/UDP
applications. The UE’s NR functionalities are implemented
in its Network Interface Card (NIC), called NrNicUe. On the
FIGURE 3. Main modules of the Simu5G model library.
other hand, a gNB compound module includes protocols up to
layer 3 (IP) and has two network interfaces: a NR one, imple-
mented in the NrNicGnb module, and one running the Point-
to-Point Protocol, for wired connectivity towards the CN. The
internal structure of both NICs is shown in Figure 4, and will
be described in more detail later. For the time being, we just
need to observe that the NrNicUe module has a dual stack of
protocols (identified by the LTE and NR prefixes) to allow
the dual connectivity with both LTE and NR, as foreseen by
the deployment roadmap.
FIGURE 4. Structure of the NR NIC modules.
An arbitrary number of NrUe and gNodeB modules can
be instantiated in a simulation scenario. Conversely, there are
two modules, namely the binder and the carrierAggregation
modules, that exist in a single copy. Both maintain global
information and can be queried by the other modules. The
binder maintains data structures containing network-wide
information and can be accessed via method calls by every
node (both UEs and gNBs). Examples of information stored
in the binder are: membership of UEs to multicast groups;
which gNB used which frequency resources in the last
TTI, etc. This modeling choice has two advantages: first,
maintaining a centralized repository of relevant information
simplifies the handling of distributed tasks. Second, it allows
users to abstract control-plane functions and elements (e.g.,
servers or signaling protocols), substituting them with queries
to the binder for the relevant information. This last aspect
considerably speeds up the setup of a simulation scenario and
the implementation of new functionalities, making Simu5G
easier to use and evolvable. The alert reader will notice
that the architecture of Simu5G draws heavily from the
one of our previous SimuLTE library [12]. This is a design
choice, which allows us to incorporate into Simu5G all the
models and functionalities of SimuLTE at no cost. These
functionalities include, among others, UE handover and
network-controlled D2D communications, both one-to-one
and one-to-many [16].
The carrierAggregation module stores all the information
related to the carrier components (CC) deployed in the net-
work. CCs are disjoint portions of frequency, characterized by
a carrier frequency and a number of available RBs. NR com-
munication can occur on multiple CCs simultaneously, in the
so-called Carrier Aggregation (CA) mechanism. The carrier-
Aggregation module includes a vector of N componentCar-
rier submodules, whose parameters can be configured via
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NED/INI. The parameters associated to a CC are its carrier
frequency, the number of RBs, the numerology employed,
the selection of either FDD or TDD mode and the slot format
in case TDD is employed. Both the numerology and the TDD
slot format will be described later in more detail. A gNB or
a UE might not support all the CCs, due e.g. to deployment
choices or equipment limitations. A UE can only attach to a
gNB that supports at least one of the CCs supported by the UE
itself, and communication can only occur on CCs supported
by both.
As far as the CN is concerned, Simu5G provides an
implementation of the UPF element of the 5G Core. The
UPF module implements the GTP for routing IP datagrams
between the gNBs and the data network. A gNB can be
connected to the data network through the CN, as shown
in Figure 5 (left). This architecture is called StandAlone
(SA) deployment, and is expected to occur in new, 5G-only
deployments. However, in the next few years, it is expected
that 5G will be deployed alongside 4G and coexist with
the latter, allowing for a smoother transition. To favor this,
3GPP defines the E-UTRA/NR Dual Connectivity (ENDC)
deployment [27], shown in Figure 5 (right). In the latter, there
are both an eNB, working as a Master Node (MN) and a gNB,
working as a Secondary Node (SN). The eNB is connected to
the CN, which is composed by a model of the Packet Data
Network Gateway (PGW) of the LTE Evolved Packet Core
in this case. LTE traffic flows through the eNB only, while
NR traffic goes through the eNB first, and then reaches the
gNB via the X2 connection between the two nodes, as shown
in Figure 6. Three types of bearer are defined by 3GPP for an
ENDC deployment:
FIGURE 5. SA (left) and ENDC (right) deployment.
FIGURE 6. Interactions between eNB and gNB in an ENDC deployment.
- Master Cell Group bearer: the UE is served by the eNB,
and traffic traverses the LTE protocol stack at both;
- Secondary Cell Group bearer: the UE is served by the
gNB. Data destined to the UE gets into the NR PDCP
entity at the eNB and is transferred to its peering NR
RLC entity in the gNB via the X2 interface.
- Split Bearers: the UE is served by both the eNB and the
gNB. Data belonging to the same connection traverses
either the eNB or the gNB. The PDCP layer at the UE
side will then reorder PDUs coming from LTE/NR RLC
layers before presenting traffic to the upper layers.
Simu5G allows one to simulate both SA and ENDC
scenarios. The internal structure of the NRNicGnb module is
shown in Figure 4 (left). It is composed of one submodule
for each layer of the protocol stack, plus one Ip2Nic module
that acts as a bridge with the IP layer. Data packets can be
received from the UPF (through the Ip2Nic module) in SA
scenarios, or from the MN (through the X2Manager module)
in ENDC scenarios. Figure 4 (right) shows the NrNicUe mod-
ule, which is equipped with two sets of PHY, MAC and RLC
submodules to enable dual connectivity. The NR versions of
the layers are used for processing data coming from/going to
the gNB, whereas the LTE ones are used for processing data
coming from/going to the eNB, if any. As shown in the figure,
the PDCP layer is unique. This way, packets belonging to a
Split Bearer are handled by the same PDCP entity, ensuring
in-sequence delivery to upper layers.
B. MODELING OF NR PROTOCOL STACK
As Figure 4 shows, in Simu5G NICs are compound modules
which include one simple module per protocol of the NR
stack. We describe the main modeling choices and function-
alities of each sublayer.
1) PDCP LAYER
The NrPdcp module implements the PDCP protocol.
Assuming a SA deployment, on the transmission path it
performs Robust Header Compression and assigns/creates
a Connection Identifier (CID) to packets. The pair CID,
UE ID is unique in the whole network. A Logical Con-
nection Identifier (LCID) is kept for each 4-tuple in
the form <sourceAddr, destAddr, sourcePort,
destPort>. When an IP packet arrives at the NrPdcp
module, its LCID is attached to it (or created, if it does not
exist). A PDCP Protocol Data Unit (PDU) is then created and
sent to the RLC layer below. On the reception path, a PDCP
PDU coming from the RLC is decapsulated, its header is
decompressed and the resulting PDCP PDU is sent to the
upper layer.
Some extra functionalities are required to handle ENDC
settings. In this case, in fact, the NrPdcp module is also
instantiated in the NIC of an eNB acting as a MN, where
packets arriving from the upper layers need to be forwarded
to either the eNB’s RLC, or to the gNB acting as SN. This is
accomplished by marking each packet in the Ip2Nic module
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with the intended destination. The NrPdcp entity then redi-
rects packets towards the RLC layer of either the eNB or the
gNB via the X2 interface accordingly. The marking policy
within the Ip2Nic module works at the packet level (rather
than at the connection level). This allows finer granularity and
dynamic management of SB functionalities, and allows users
to design and evaluate, e.g., eNB/gNB load-balancing poli-
cies. On the reception path, the PDCP ensures in-sequence
delivery to the IP layer in all cases.
2) RLC LAYER
The NR RLC can be configured in Transparent Mode (TM),
Unacknowledged Mode (UM) and Acknowledged Mode
(AM). The TM has no buffering, and it forwards packets
transparently to the MAC layer. On the other hand, AM and
UM have their own set of transmission/reception buffers.
On the transmission path, RLC PDUs are buffered in the
transmission buffers, and are fetched by the underlying MAC
module on each TTI, as a result of the MAC scheduling
process. On the reception path, RLC PDUs are stored in
the reception buffer until reassembly of a PDCP PDU is
completed, and the latter is sent to the PDCP.
3) MAC LAYER
A NR radio frame is 10 ms long and consists of 10 subframes,
each having a duration of 1 ms. NR subframes can be fur-
ther divided into a variable number of time slots, which are
called TTIs. A numerology index µdefines the slot duration,
as shown in Table 1, and – accordingly – the number of
TTIs per subframe. UEs are scheduled in slots. In our model,
a different µcan be associated to each CC, and config-
ured via NED/INI. We allow for gNBs and UEs to support
only a subset of the available numerologies. The example in
Figure 7 shows a gNB supporting three CCs that employ
different carrier frequencies and numerologies. The gNB
serves UE 1 and UE 2, which have different capabilities in
terms of supported frequencies and numerologies, as shown
in the figure. For instance, UE 1 only supports µ < 3,
whereas UE 2 supports frequencies below 6GHz. According
to that configuration, UE1 can be served by the gNB using
CC 0 and CC 1, whereas UE 2 can be served by the gNB
using CC 0 and CC 2.
TABLE 1. NR numerologies.
Simu5G supports both FDD and TDD. In FDD, each
CC has separate portions of spectra for the UL and the
DL. In TDD, the same spectrum is used for both the DL
and the UL, which are instead separated in time. NR TDD
allows one to choose among 62 possible slot formats [28],
where individual symbols in a slot can be DL, UL or
flexible. Examples of slot formats are shown in Figure 8.
FIGURE 7. Example of UEs’ capabilities.
FIGURE 8. Examples of TDD slot formats.
Flexible symbols can be assigned dynamically to either DL or
UL transmissions, or kept idle as a guard interval to minimize
the DL/UL interference. Hence, the number of bytes that can
be transmitted to/by a UE in a slot varies with the TDD slot
format, as well as with the selected MCS. As we explain
later, this affects the computation of the Transport Block Size
(TBS) at the MAC level. We model the TDD slot format as a
property of the CC: this means that all gNBs using a given CC
will use the same slot format on it. Accordingly, we associate
the slot format to the componentCarrier submodules. This
greatly simplifies interference management, since it guar-
antees that DL and UL transmissions never interfere with
each other. Therefore, their exact arrangement within a slot
is immaterial, the only relevant information being their total
number. Accordingly, we model a slot format as a triplet
of integers hnDL ,nUL ,nFi, representing the number of DL,
UL and flexible symbols, respectively, whose sum is equal to
the total number of symbols available within a slot (i.e., 14).
Policies to assign flexible symbols to DL or UL dynamically
can be easily defined by a user, e.g. by implementing a
function to be invoked at every TTI before executing the
scheduling operations, which tells the scheduler to consider
the flexible symbols as either UL or DL symbols in that TTI.
The current default is that flexible symbols are used as guard
symbols.
At both the UE and the gNB, the MAC layer runs peri-
odically, on each TTI. Different CCs may employ differ-
ent numerologies, hence have different TTI durations. This
allows a gNB to run an independent scheduler per CC.
Figure 9 shows an example of a scheduling procedure, which
takes as input the set Qof backlogged UEs, then it allocates
one CC at a time, e.g. starting from CC 0. For each CC i,
the scheduler considers Ui, i.e. the set of UEs that can use
CC i, to obtain subset QiQ, including backlogged UEs
schedulable on CC i. Then, the scheduling routine sorts Qi
according to a given policy (e.g. MaxC/I or PF, both of which
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FIGURE 9. Pseudocode for the scheduling procedure.
are already implemented) and scans it to allocate RBs to UEs.
The scheduling routine produces a schedule list Si, including
the set of UEs allocated on CC i. UEs which clear their
backlog are removed from Q, so that subsequent CCs will
not consider them. In the above approach, CCs are scanned
in sequence. However cross-CC scheduling policies can also
be implemented in this framework.
After scheduling each CC, the scheduler obtains the global
schedule list S= ∪iSi. For each element of S, the MAC
layer builds a MAC Transport Block (TB) (in the DL) or
issues a scheduling grant (in the UL). The TBS depends on
both the number of allocated RBs and the MCS. The latter
is chosen following the CQI reported by the UE. The NrAmc
C++ class determines the TBS according to the procedure
defined in [29]. According to the formulas therein, the TBS is
also a function of the number of DL(UL) symbols in the slot.
When TDD is employed, the number of available symbols
is defined by the slot format. The NrAmc class supports the
extended MCS table with higher modulation orders, i.e. up to
the 256QAM modulation.
Simu5G supports flexible timing for the NR H-ARQ feed-
back, which is asynchronous: i.e., the timing of ACK/NACKs
is not fixed, and can be configured from the NED/INI file.
Following the standard [30], we model independent H-ARQ
processes for every CC.
4) PHY LAYER
At the physical layer, the effects of signal propagation and
interference on a whole MAC TB, rather than on the symbols
composing it, are simulated. Each MAC TB is encapsulated
within an AirFrame OMNeT++ message sent to the destina-
tion module. On receipt of the above message, the destination
entity performs the computations summarized in Figure 10,
namely:
- Starting from the transmitted power at the sender,
it applies a channel model to compute the received
power. A channel model can be configured to incor-
porate fading, shadowing, pathloss, etc., and can be
made arbitrarily complex. Simu5G comes with a default
channel model called Realistic Channel Model, which is
compliant with the 3D model described in [19].
- On each RB occupied by the TB, it computes the SINR
as SINR =PRX .PjPj
RX +R, where PRX is the
received signal power, Pj
RX is the power received from
the j-th interferer and Ris the Gaussian noise. The set of
indexes jis computed by querying the Binder to know
which other nodes were using the same RB. For each
interferer, the received power is computed by applying
the channel model, starting from the transmission power.
- Then, it uses Block Error Rate (BLER) curves to com-
pute the reception probability for each RB composing
the ongoing transmission. BLER curves can be obtained
from a link simulator or from 3GPP documents. This
makes it possible to translate a SINR and a transmission
format to a probability of correct reception of an RB.
More specifically, the error() function considers the
BLER curve related to the MCS used in transmission,
at the abscissa represented by the measured SINR, and
it obtains an error probability for that RB, call it Perr .
- Finally, a uniform random variable X[0;1] is sampled
and the AirFrame is assumed to be corrupted if X<
1Qi1Pi
err , and correct otherwise.
Note that a MAC TB is sent on a given CC, hence the corre-
sponding AirFrame is subjected to channel effects (e.g. path
loss, shadowing etc.) that depend on that CC. To account for
this, each gNB/UE is equipped with a vector of channelModel
modules, as shown in Figure 4, and each of them is associated
with one of the CCs available in the carrierAggregation
module. Figure 11 shows an example of such association,
where the carrierAggregation module implements two CCs,
whose indexes in the componentCarrier vector are 0 and 1,
respectively. The gNB and UE1 are configured to use both
FIGURE 10. Block diagram of the modelling of the physical layer within Simu5G.
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FIGURE 11. Example of CA configuration.
CCs, hence they have two channel models, associated with
the two CCs. UE2, instead, is configured with one channel
model only associated with CC 1. Each transmitted AirFrame
includes a control field specifying the CC it is transmitted
onto, thus enabling the receiver to process it via the relevant
channelModel module.
The PHY layer interacts with the channelModel modules
via getSinr() end error() functions, which compute
the SINR and check if the airframe is correctly decoded,
respectively. The latter are the functions that need to be
redefined when implementing a new channel model.
C. MODELING OF DEVICE-TO-DEVICE TRANSMISSIONS
D2D communication is a feature of LTE-A and NR since
release 12 [31] and it allows two UEs to communicate directly
when they are in proximity, hence without relaying their
traffic through the BS and the CN as in conventional cellular
communications. This makes D2D transmissions faster, since
they require a single hop (called the sidelink – SL) instead
of two (i.e., through the UL leg to the serving BS, and the
DL one to the receiving UE) and enables proximity services,
including those for IoT transmissions and Cellular Vehicle-
to-Everything (C-V2X, [36]). In network-controlled D2D,
data is sent on the SL, while the BS retains control over
resource allocation and takes care of contention and inter-
ference management. SL communications can be allocated
anywhere, in principle. A common policy (to which we stick
in our work) is to use resources in the UL spectrum, which
is normally less utilized than the DL one and less prone to
interference.
Both point-to-point (P2P) and point-to-multipoint (P2MP)
D2D communications are envisaged. With P2P D2D, a UE
sends a packet to one (and only one) receiving UE, whereas
with P2MP D2D a UE sends a packet to a set of neighboring
UEs belonging to a multicast group, identified by a multicast
group ID in the MAC Transport Block. P2P transmissions are
acknowledged by the receiver, whereas P2MP are not.
Data packets to be sent using D2D (either P2P or P2MP)
traverse all the layers of the NR/LTE protocol stack and
undergo the same processing as UL/DL packets, with few
modifications. This allowed us to reuse the modeling of the
protocol layers shown in the previous sections, adding to both
the UE and the gNB the required D2D-specific operations,
which we will explain in the following.
In addition to the LCID, at the sender UE’s PDCP layer
we assign a flow direction to each packet coming from the
IP layer, as shown in Figure 12. The direction can be UL,
P2P D2D or P2MP D2D. This way, packets having the same
LCID (i.e., same 4-tuple) but different flow directions will
be treated as belonging to different, independent data flows.
The flow direction of P2P flows can be either set statically
via the NED/INI file or changed dynamically via some mode
switching policy. In fact, mobile UEs may not always be in
communication range, hence the gNB may want to change
their communication mode dynamically [32]. In Simu5G,
mode-switching policies are user-definable.
FIGURE 12. Selection of flow direction at PDCP layer.
For P2MP D2D communications, we chose to map multi-
cast IP datagrams (i.e. those with a multicast IP destination
address) to the P2MP D2D flow direction. In this case, pack-
ets are also assigned a multicast group ID, as specified by the
NED/INI file. The information regarding the flow direction
will also be included in the BSR sent by the UE to the BS,
so that the latter can allocate resources on either the SL or the
UL, depending on the UE request.
At the receiver side, the main modifications involved the
H-ARQ mechanism of P2P communications. With reference
to Figure 13, the H-ARQ (N)ACK is sent directly to the
sender without going through the BS. However, the BS still
needs to know if a H-ARQ retransmission is due in a future
TTI, because it needs to allocate resources for that to occur.
FIGURE 13. H-ARQ mechanism of P2D D2D communications.
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In our model, this issue is solved by sending a copy of the
H-ARQ (N)ACK to the BS as well, so that it can keep trace of
the status of SL transmissions and schedule retransmissions
when needed.
As far as resource allocation is concerned, Simu5G models
dynamic scheduling of D2D transmissions (which is coherent
with C-V2X Mode 1, as we discuss in Section V): whenever
a UE has data to send using D2D, it sends a random access
request and a BSR to its serving BS, which schedules SL
resources accordingly and issues a SL grant to the UE, either
P2P or P2MP. With this scheme, the BS can schedule D2D
transmissions on exclusive resources, or enforce frequency
reuse. This consists in allocating the same set of RBs to
different D2D transmitters at the same TTI, provided that the
interference level is kept low (i.e., colliding D2D transmis-
sions happen sufficiently far from one another), and it allows
the BS to reduce the overall spectrum occupancy.
D. MODELLING FOR SCALABILITY
A common criticisms of end-to-end network simulators (see,
e.g., [4]) is that they are not scalable, because they model the
entire protocol stack of every node, instead of, e.g., abstract-
ing everything that lies above the MAC as a traffic generator.
Hereafter, we provide evidence of the mechanisms that were
employed to make Simu5G scalable.
It is often the case that a user is interested in the perfor-
mance of a single cell (e.g., its RB occupancy or throughput),
or of few neighboring cells (e.g., to account for handover).
However, the above performance cannot be correctly assessed
unless several other cells are simulated as well, for the correct
accounting of inter-cell interference. Simulating more cells
implies a higher computation load, which limits the scale of
the scenarios that can be simulated.
To solve this issue, Simu5G includes two models of a gNB.
Besides the ‘‘full’’ one described in the previous sections,
a gNB can be modeled as a light cell. A light cell does not
run the NR protocol stack. It is configured with a location,
a radiation pattern, a transmission power, and a distribution
of occupied RBs. On each TTI, it samples a value from that
distribution and occupies the resulting number of RBs in the
DL subframe, so as to produce inter-cell interference. This
allows one to produce a configurable level of interference
in the cell(s) of interest, without incurring the overhead of
simulating many full-stack gNBs and their served UEs. This
way, we can run credible simulations with tens of external
cells at a tolerable computation cost. This is also useful
when running Simu5G in emulation mode, where keeping
the computation load low is of paramount importance to
enable real-time emulation. Paper [11] shows that real-time
emulation of a multicell scenario is possible on a desktop PC,
exactly thanks to the usage of light cells.
E. VALIDATION AND CALI BRATION
A simulator should be properly validated, to ensure that the
results obtained with it are credible. The techniques used to
do so are several and should be used concurrently. Some of
the ones that were used with Simu5G are:
- Extensive parsing of event traces (leveraging the features
of the OMNeT++ IDE);
- Continuity, consistency and degeneracy tests [24];
- Backward compliance: for instance, running a 5G sce-
nario with FDD and µ=0, i.e. TTIs of 1 ms (as LTE’s),
and forcing all nodes to use MCS schemes which are
common to both LTE and NR, yields the same results as
SimuLTE does;
- Fingerprinting, to test that results and/or the sequence of
function calls does not change following code updates.
In this section we focus on a specific validation technique,
i.e. comparison with known analytical models. We simu-
late the Urban Macro scenario described in Table 4, config.
A of [25]. We compare the SINR that we obtain with the one
reported as an attachment of that document.
With reference to Figure 14, we simulated 57 cells
deployed according to a regular hexagonal tessellation, whose
inter-site distance is 500 m. Each site hosts three cells,
radiating outwards according to the horizontal and vertical
pattern described in [25]. We collect statistics only from the
central site (three central cells), whereas the other (light) cells
only produce interference occupying the whole spectrum.
We randomly deploy 30 UEs in the three central hexagons,
which attach to the cell from which they perceive the best
SINR. 80% of UEs are assumed to be indoor, 20% outdoor.
We assume DL traffic only and each UE receives a 240kbps
constant bit rate traffic. The values in the following charts
are obtained by averaging statistics from 50 independent
repetitions, with 95% confidence intervals. The main simula-
tion parameters are summarized in Table 2. Figure 15 shows
that the CDF of the SINR measured by UEs in the scenario
described above overlaps the 3GPP reference one.
FIGURE 14. 3GPP Urban Macro simulation scenario.
Having validated Simu5G’s channel model, we calibrate
the sensitivity of a receiver following the guidelines reported
in [25]. We employed the BLER curves taken from [6].
Such curves represent the error probability for a transmission
occupying one RB. Since 3GPP recommends a target TB
error rate of 10%, we carried out simulations with different
sensitivities of a 5G receiver, modeled by an offset 1
[3 db,7db] to shift the above BLER curves to the left,
in order to determine the sensitivity that allows us to meet
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TABLE 2. Main simulation parameters.
FIGURE 15. Measured SINR with Simu5G.
FIGURE 16. Average error rate after 1st TX attempt.
that target. Figure 16 reports the average error rate for the first
transmission attempt of Transport Blocks, i.e. the probability
that the first transmission of a MAC Transport Blocks is not
decoded correctly. The employed shift increases from left to
right. We observe that the rate is close to the target 10% error
rate when a shift of either 1=5db or 1=7db are used.
Figure 17 shows the CDF of the error rate for the first H-ARQ
transmission attempt, where we observe that the target 10%
error rate is around the median value, whereas only a small
fraction of UEs (i.e. 5%) gets an error rate larger than 20%
when 1=5db or 1=7db.
FIGURE 17. CDF of error rate after 1st TX attempt.
V. PERFORMANCE EVALUATION USE-CASES
In this section we show how Simu5G can enable mean-
ingful performance assessment of cutting-edge technolo-
gies. We concentrate on two use-cases, namely application
offloading with MEC and platooning with C-V2X.
A. APPLICATION OFFLOADING WITH MEC
Although orthogonal to the access technology itself, MEC is
expected to unleash its full power in conjunction with cellular
access, and specifically 5G. In a MEC environment, compu-
tation nodes called MEC Hosts are placed close to the RAN
and interact tightly with the latter to obtain information on the
status of the radio network and its users. MEC applications
run on behalf of the user on MEC hosts, in a virtualized
environment. Computational resources can be allocated on
demand to users requesting a service or task.
According to the ETSI architecture [33], MEC functions
are organized in two layers, namely the MEC System Level
and the MEC Host Level. The MEC System Level maintains
a global view of the status of all the MEC Hosts in the
system. It receives MEC Application Instantiation requests
from applications running at the user side and routes them
to the most suitable MEC Host, e.g. based on requirements
such as maximum communication latency, computational
resources and availability of MEC services. Within the MEC
Host, the MEC Platform provides MEC Services [33] that can
be exploited by MEC Apps, such as the Smart Relocation Ser-
vice, to handle migration of MEC Apps to other MEC Hosts;
the Radio Network Information Service (RNIS), to gather
information from the network elements (e.g. number of users
connected to a specific radio base station); the Bandwidth
Manager, which defines the priority of data traffic destined
to MEC Apps within the MEC Host; the Location Service,
which provides information on the users’ position. The
Virtualization Infrastructure runs MEC Apps as instances
of virtual machines and allows them to communicate both
within (e.g., with the services within the MEC Platform) and
outside the MEC Host (e.g., with users’ local application).
Simu5G includes a model of the above infrastructure,
as well as functions that allow a UE to dynamically
request the initialization and the termination of one or more
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applications within a MEC Host and to communicate with
such applications so that a specific task is accomplished. The
above architecture allows a user to develop its own MEC
App and plug it seamlessly within Simu5G. The main build-
ing block of our model is the MecHost, shown in Figure 18.
The latter hosts MEC Apps created on demand on reception
of a request from UEs. The MEC Host includes a GTP
module, so that it can be placed anywhere in the CN of the 5G
network, and a Virtualization Infrastructure module that han-
dles the data traffic. The Virtualization Manager submodule
manages the life cycle of MEC Apps, handling requests for
instantiation and termination of MEC Apps from the UEs and
forwarding data packets to the correct MEC App. Moreover,
it interacts with the Resource Manager, which keeps track
of the computational resources (RAM, storage and CPU)
currently in use within the MEC Host. In fact, each MEC Host
has a configurable maximum amount of resources, and MEC
App creation requests come with an indication of how much
of each they are going to use. When a new request reaches
the Virtualization Manager, the latter queries the Resource
Manager, where admission control is checked. For instance,
this allows a user to model the computation delay at the
MEC Host based on the amount of occupied resources (e.g.,
using queueing network models). Finally, the MEC Platform
submodule contains MEC services. The number and the type
of each MEC Service can be configured. Our implementation
comes with a simplified version of the Radio Network Infor-
mation Service.
FIGURE 18. Modeling of a MecHost module.
A UE local application exchanges signalling messages
with MEC hosts, e.g. to request, respectively, initialization
and termination of a MEC App. The initialization message
includes a list of its computational requirements. Once the
MEC App is instantiated on the MEC Host, data packets
can flow through. If necessary, the MEC App can request
the services of the MEC Platform to carry out (part of) its
operations. For example, it can contact the Radio Network
Information Service to collect information about the radio
network.
We consider the scenario of Figure 19, where five servers
representing MEC hosts are respectively co-located with five
gNBs. The inter-gNB distance is 500m. One UE is linearly
moving from the service area of gNB1 to that of gNB2, gNB3
and so on, at a constant speed of 30 km/h. The UE offloads
tasks to the MEC Host periodically, with period T=1 s. For
each offloaded task, the UE transfers the context to an MEC
App running on the MEC Host, which performs computations
and sends the context back to the UE. We let liU(8,12)
be the context size for task i(hence, the size of the i-th packet
to be transmitted), measured in kbits. Moreover, we model
the processing time at the MEC Host as Tproc =(liβi)F,
where βiU(100,300)are the cycles per bit necessary
for processing task iand F=9 Gcycles/s is the processing
capacity at the MEC [34].
FIGURE 19. Simulation scenario with ME app migration.
We assume that at the beginning of the simulation the UE
offloads its tasks to MEC Host 1. When the UE performs
the handover to the other gNBs, we consider the two fol-
lowing scenarios: a) the UE keeps offloading its tasks to
MEC Host 1, and b) the UE offloads its tasks to the MEC
Host co-located with the serving gNB, i.e. the MEC App
migrates according to the UE mobility. In the first scenario,
data needs to be routed through the UPF, hence the additional
latency is uniformly distributed between 15 and 35 ms [34].
In the second scenario, we assume that the migration needs
a time in the range (20s,30s), which is compatible with
the results in [35]. More advanced migration algorithms and
models can be easily implemented and tested within Simu5G.
Figure 20 shows the latency required for obtaining the
result of the task offloading over time. The UE performs
the handover at 64s, 124s, 184s and 224s, where the latency
increases due to need of rerouting the traffic through the UPF.
Without service migration, the latency always stays above
35ms. When the application migrates, the latency goes back
to about 20ms after the transient. Figure 21 shows the same
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FIGURE 20. Latency of task offloading, µ=0.
FIGURE 21. Latency of task offloading, µ=3.
metric when µ=3 is employed. As expected, the latency
has the same evolution, except for scaled-down values due to
shorter TTIs.
B. PLATOONING WITH C-V2X
C-V2X has been part of the 3GPP specifications since
release 14. With the development of the 5G, the NR standard
evolves C-V2X to support ultra-reliable and ultra-low-latency
services for vehicular applications like autonomous driving,
platooning, infotainment, and so on.
C-V2X communications are realized in two ways: between
a vehicle and the network infrastructure, i.e. using the
UL/DL path, and between vehicles, i.e. using D2D com-
munications on the SL. In the latter case, we refer to
Vehicle-to-vehicle (V2V) communications. While earlier
specifications (release 12) for the SL were mostly designed
for energy efficiency at the cost of higher latency, the more
stringent requirements for V2X services motivated the design
of enhanced resource allocation schemes for NR-based
C-V2X. In NR, V2V communications can be scheduled
according to two resource allocation policies, namely Mode 1
and Mode 2 [36]. With Mode 1, the BS selects the resources to
be assigned to vehicles, either dynamically (same as with the
UL’s) or using Semi-persistent Scheduling (SPS). According
to Mode 2, instead, vehicles autonomously select a set of
RBs from a V2X resource pool, indicated by the BS. V2V
communications can be either P2P or P2MP.
As explained in Section IV.C, a resource allocation method
compliant with Mode 1 of C-V2X is already available in
Simu5G, as well as P2P and P2MP D2D communications
and different numerologies. Moreover, Simu5G can be easily
integrated with OMNeT++ vehicular mobility libraries such
as Veins [37] and Artery [38].
We now report an example of performance study of a
C-V2X application with Simu5G. In particular, we consider
the platooning use case, in which vehicles are instructed to
travel in a train-like fashion, i.e. keeping the same speed and
a small, constant distance to the vehicle ahead. We consider
the scenario of Figure 22, where three gNBs are connected
to a single MEC host in the CN. Five vehicles move along
a straight road and are equipped with a NR NIC, so that
they can exploit 5G connectivity and the services offered
by the MEC Host to form a platoon. In particular, the first
vehicle is the platoon leader (PL) whereas the other ones are
the platoon members (PMs). At the beginning of the simu-
lation, vehicles have different speed and distance from their
respective predecessor. Each vehicle runs one application that
sends the information about the vehicle’s position and speed
to its corresponding MEC application at the MEC host every
TUE =50ms. In the meantime, the MEC Host executes two
MEC services, running at period TMEC =250ms: a platoon
formation service (PFS) that groups vehicles into platoons
based on the information gathered from MEC applications,
and a platoon control service (PCS) that takes as input the
platoon(s) formed by the PFS and computes new acceleration
values that vehicles must use in order to converge towards
a target speed vtarget =13.89m/s=50km/h. To do so,
the PCS employs the control algorithm in [26], which aims
at maintaining safe inter-vehicle distances given the target
speed. Then, the output of the PCS, i.e. the acceleration
values, are sent to the vehicles which adjust their course
accordingly.
FIGURE 22. Simulation scenario with C-V2X-based platooning.
181188 VOLUME 8, 2020
G. Nardini et al.: Simu5G–An OMNeT++ Library for End-to-End Performance Evaluation of 5G networks
We run the above service in a RAN whose gNBs operate
on a single carrier with 10 RBs, employing numerology index
µ=2. While moving, vehicles perform handover to the
gNB they receive the highest SINR from. Since the distance
between gNBs is 500m and vehicles’ target speed is 50km/h,
vehicles remain in the area covered by the gNBs during the
100s of simulated time. We compare two different strategies
to deliver PCS commands: in the first mode, each vehicle
gets its new acceleration value via one DL transmission from
its serving gNB, as shown in Figure 22(a); in the second
mode, shown in Figure 22(b), one message including the
acceleration of all the vehicles is sent to the PL with a DL
transmission, then the PL forwards the message to its follower
PM1 using a D2D transmission, which in turn relays it to
PM2, and so on. In this last case, it is worth noting that
our D2D modeling allows P2P D2D communication between
UEs in the same cell only. This means that when the pla-
toon traverses a cell border due to mobility, the P2P D2D
connection is temporarily switched to the traditional UL-DL
path. Figure 23 reports the average end-to-end latency of
PCS commands. When only DL transmissions are used, all
vehicles obtain the message with minimum delay, whereas
with D2D the latency increases with the vehicle’s relative
position in the platoon, since the message traverses multiple
hops through its predecessors. However, since D2D exploits
the UL spectrum, using D2D allows one to save 73% of DL
frequency resources, which results in less energy consumed
by the gNBs. Despite the above differences at the radio level,
the two delivery modes produce the same results from the pla-
tooning perspective, as shown in Figure 24 and Figure 25. The
former shows each vehicle’s distance from its predecessor,
whereas the latter shows how the speed of vehicles changed
over time to obtain the result. In both cases, the platoon
reaches stability in less than one minute.
FIGURE 23. Average end-to-end latency of the PCS’ commands.
FIGURE 24. Vehicles’ distance from their predecessor over time.
FIGURE 25. Vehicles’ speed over time.
VI. CONCLUSION AND FUTURE WORK
This article presented Simu5G, a new model library for 5G
NR for the OMNeT++ simulation framework. To the best
of our knowledge, this is one of two libraries allowing end-
to-end application-level communications in complex, hetero-
geneous scenario (the other one being 5G-LENA [5]), but
the only one modelling ENDC deployments, FDD access,
D2D communications, MEC and C-V2X. We have described
Simu5G’s resource management and protocol layers, to allow
prospective users to understand its modeling philosophy,
aimed at research on 5G services and 5G resource man-
agement. We have presented validation results that show
near-perfect compliance with 3GPP requirements. We have
shown that Simu5G can be used to evaluate technologies
currently at the cutting edge of research, namely MEC and
platooning with C-V2X, with little setup effort on the user.
Future work on this topic includes thoroughly investigating
Simu5G’s capabilities as a real-time emulator. Some prelim-
inary results of this line of research have been presented
in [11], and show that Simu5G can be used by application
programmers to test their applications and services in a con-
trollable, yet lifelike environment, possibly in conjunction
with rapid-prototyping tools, such as the Intel OpenNESS
framework for MEC hosting [39], with which Simu5G is
perfectly integrated.
ACKNOWLEDGMENT
A preliminary version of this article was presented at the
INSTICC SIMULTECH 2020, Paris, France, 8–10 July 2020.
The subject matter of this article includes description of
results of a joint research project carried out by Intel Corpo-
ration and the University of Pisa. Intel Corporation reserves
all proprietary rights in any process, procedure, algorithm,
article of manufacture, or other results of said project herein
described.
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GIOVANNI NARDINI received the M.Sc. degree
in computer systems engineering (summa cum
laude) and the Ph.D. degree in information engi-
neering from the University of Pisa, in 2013 and
2017, respectively. He is currently an Assistant
Professor with the Department of Information
Engineering, University of Pisa. His research
interests include resource allocation algorithms
for Quality of Service in 4G and 5G networks,
multi-access edge computing, simulation, and per-
formance evaluation of computer networks. In these fields, he has coauthored
six patents and more than 30 peer-reviewed articles. He has been involved in
EU-funded and industrial research projects.
DARIO SABELLA is currently working with
INTEL as a Senior Manager Standards and
Research, driving new technologies and edge
cloud innovation for advanced systems, involved
in ecosystem engagement and coordinating inter-
nal alignment on edge computing across standards
and industry groups. In 2019, he was appointed
as the Vice-Chairman of ETSI Multi-access Edge
Computing (MEC), previously Lead of Indus-
try Groups, and since 2015, he has been the
Vice-Chair of IEG WG. Since 2017, he has been delegate of 5G Automotive
Association (5GAA). Before 2017, he worked with the Telecom Italia Group
(TIM), as responsible in various research, experimental and operational
activities on OFDMA technologies (WiMAX, LTE, 5G). He is the author
of several publications more than 40 and patents more than 20 in the field
of wireless communications, energy efficiency, and edge computing. He has
also organized several international workshops and conferences.
181190 VOLUME 8, 2020
G. Nardini et al.: Simu5G–An OMNeT++ Library for End-to-End Performance Evaluation of 5G networks
GIOVANNI STEA (Member, IEEE) received the
Ph.D. degree from the University of Pisa, Italy,
in 2003. He is currently an Associate Professor
with the Department of Information Engineering,
University of Pisa. His current research interests
include quality of service and resource allocation
in wireline and wireless networks, performance
evaluation through simulation, and analytical tech-
niques, traffic engineering. In these fields, he has
coauthored more than 100 peer-reviewed articles
and 16 patents. He has been involved in national and European research
projects, and he has led joint research projects with industrial partners. He has
served as a member of the technical and/or organization committees for
several international conferences, including SIGCOMM, WoWMoM, and
VALUETOOLS, and he is serving on the editorial board of the Wireless
Networks Journal. He is a Fellow of the European Alliance for Innovation.
PURVI THAKKAR received the Computer
Engineering degree. She is currently a Product
Manager with Intel and is part of the Edge
Computing and Ecosystem Enablement Team.
She manages developer outreach activities of
OpenNESS–a MEC solution and an enabler of
edge services on Intel Architecture (IA). She
also leads the partner and customer enablement
activities for accelerating the provisioning of edge
services on IA with OpenNESS. She is also a
management professional trained through executive program in business
management. She has a versatile experience across verticals and functions
gathered through 20 years of experience.
ANTONIO VIRDIS received the M.Sc. degree
in computer system engineering and the Ph.D.
degree in information engineering from the Uni-
versity of Pisa, in 2011 and 2015, respectively.
He is currently an Assistant Professor with the
University of Pisa. His research interests include
quality of service, scheduling and resource alloca-
tion in wireless networks, network simulation, and
performance evaluation. He has been involved in
national, EU-funded and industry-funded research
projects. He has coauthored seven patents and more than 40 peer-reviewed
articles.
VOLUME 8, 2020 181191
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We describe Veins, an open-source model library for (and a toolbox around) OMNeT++, which supports researchers conducting simulations involving communicating road vehicles—either as the main focus of a study or as a component. Veins already includes a full stack of simulation models for investigating cars and infrastructure communicating via IEEE 802.11 based technologies in simulations of Vehicular Ad Hoc Networks (VANETs) and Intelligent Transportation Systems (ITS). Thanks to its modularity, though, it can equally well be used as the basis for modeling other mobile nodes (like bikes or pedestrians) and communication technologies (from mobile broadband to visible light). Serving as the basis for hundreds of publications and university courses since its beginnings in the year 2006, today Veins is both one of the most mature and established tools in this domain.
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Abstract The investigation and prediction of new trends and technologies for mobile cellular networks is of utmost importance for researchers and network providers to quickly identify promising developments. With the verge of the fifth generation of mobile communications (5G), networks become more and more heterogeneous and dynamic while the amount of active users within a cell keeps ever increasing. Therefore, the search for more efficient network layouts and configurations attracts massive attention while on the other hand becomes more and more complex. In this contribution, we present the Vienna 5G system level simulator, which allows to perform numerical performance evaluation of large-scale multi-tier networks, with numerous types of network nodes. The simulator is based on Matlab and is implemented in a modular fashion, to conveniently investigate arbitrary network and parameter constellations, which can be enhanced effortlessly. We first discuss the distinguishing aspects of our simulator platform, describe its structure, and then showcase its functionality by demonstrating the key aspects in more detail.
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