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From 3GPP LTE to 5G: An Evolution
Oluwadamilola Oshin, Matthew Luka and Aderemi Atayero
Abstract All-IP network architecture is fast becoming a norm in mobile
telecommunications. The International Telecommunications Union—Radio com-
munication sector (ITU-R) recognizes a technology as 4G after haven met the
International Mobile Telecommunications Advanced (IMT-A) specification of a
minimum of 100 Mb/s downlink data rate for high mobility and 1 Gb/s for low
mobility. The Long Term Evolution specified by the 3GPP, provides a minimum
downlink data rate of 100 Mb/s and marks a new beginning in Radio Access
Technologies (RATs). It also notably implements an all-IP network architecture,
providing higher data rates, end-to-end Quality of Service (QoS) and reduced
latency. Since the first release of the LTE standard (3GPP release 8), there have
been a number of enhancements in subsequent releases. Significant improvements
to the standard that enabled LTE to meet the IMT-A specifications were attained in
release 10, otherwise known as LTE-Advanced. Some of the enhancements such as
the use of small cells (known as femtocells) are envisioned to be the basis of fifth
generation (5G) wireless networks. Thus, it is expedient to study the LTE tech-
nology and the various enhancements that will shape the migration towards 5G
wireless networks. This paper aims at providing a technical overview of 3GPP LTE.
With a brief overview of its architecture, this paper explores some key features of
LTE that places it at the forefront in achieving the goals of wireless access evo-
lution, enabling it to become a key element of the ongoing mobile internet growth.
The migration to 5G may be radical, thus some enabling technologies that will
shape the 5G cellular networks are also examined.
O. Oshin (&)A. Atayero
EIE Department, Covenant University, Km 10, Idiroko Road,
Ota, Ogun State, Nigeria
e-mail: damilola.adu@covenantuniversity.edu.ng
A. Atayero
e-mail: atayero@covenantuniversity.edu.ng
M. Luka
Department of Electrical and Electronics Engineering,
Modibbo Adama University of Technology, Yola, Nigeria
e-mail: matthewkl@mautech.edu.ng
©Springer Science+Business Media Singapore 2016
S.-I. Ao et al. (eds.), Transactions on Engineering Technologies,
DOI 10.1007/978-981-10-1088-0_36
485
Keywords 4G 5G E-UTRAN GSM IMT-A LTE LTE-A UMTS
1 Introduction
LTE is designed to meet the IMT-2000 requirements set out by International
Telecommunications Union—Radio communication sector (ITU-R). As at February
2014, the Global mobile Suppliers Association (GSA) confirmed a total of 274 LTE
networks launched in 101 countries thus far, with majority deployed on the
1800 MHz frequency band [1]. LTE is a phenomenal technology—it enables oper-
ation under a vast set of conditions and still delivers excellent performance. LTE
(Long Term Evolution) was developed and standardized by 3GPP as Release 8. It
builds on 3GPP GSM/UMTS cellular concept and uses E-UTRAN (Evolved-UMTS
Terrestrial Radio Access Network) as its radio access: it is therefore sometimes
referred to as E-UTRAN. Compared to previous 3GPP telecommunication standards,
LTE marks a departure from the normal circuit switched or a combination of circuit
and packet switched networks, to an all-IP/packet-based network. LTE is a wireless
access technology, which provides high quality experience. 3GPP LTE is a signifi-
cant advancement in cellular technologies. The motivations for LTE as outlined by
3GPP are: need to ensure the continuity of competitiveness of the 3G system for the
future, user demand for higher data rates and quality of service, packet-switched
optimized system, continued demand for cost reduction in terms of both capital and
operational expenditure (CAPEX and OPEX), low complexity and to avoid unnec-
essary fragmentation of technologies for paired and unpaired band operation [2]. The
spectrum bandwidth of LTE is scalable with subsets of 1.4, 3, 5, 10, 15 and 20 MHz
using the 20 MHz bandwidth, LTE is capable of achieving peak data rate of
100 Mbps in the downlink and up to 50 Mbps in the uplink for a 1 2 antenna
configuration. The spectrum efficiency and throughput are up to 3–4 times better for
the forward link and 2–3 times better for the reverse link than 3GPP release 6. Latency
is significantly reduced by using a flat architecture with reduced number of network
nodes. User plane and control latency are less than 30 and 100 ms respectively.
Internetworking with backend systems such as 3GPP GERAN/UTRAN and
non-3GPP systems such as WiMAX and Wi-Fi is supported via various interfaces.
The use of self-organizing network operations, specification of uniform interfaces for
multi-vendor interoperability and reduced terminal nodes are all envisioned to reduce
cost. LTE also supports operation in both unpaired spectrum (Time Division Duplex)
and paired spectrum (Frequency Division Duplex Modes). LTE supports Voice over
Internet Protocol (VoIP) with an end-to-end quality of service comparable to that of
UMTS circuit switched network [3]. Leveraging on these features LTE wireless
access technology provides rich experience and high performance, connectivity,
coverage and roaming, ecosystem richness, efficiency and cost effectiveness.
LTE-Advanced leverages on an increased bandwidth of up to 100 MHz to target
a peak data rate of up 1 Gbps in the downlink and up to 500 Mbps in the uplink for
low mobility scenarios. With support of up to 8 8 antenna configuration, LTE
486 O. Oshin et al.
advanced offers a peak spectral efficiency of up to 30 bps/Hz (approximately 2
times that of release 8) which translates into an improved user throughput.
LTE-Advanced also supports higher mobility speeds of up to 350–500 km/h, which
is a significant improvement over the 10 km/h mobility speed for release 8. The use
of relay nodes (particularly layer 3 relay technology) significantly improves system
coverage at a reduced cost [4]. In order to meet up with mobile traffic explosion,
LTE-Advanced uses low cost small cells to improve system capacity. The use of
small cells also improves user experience by reducing transmit-receive distance.
The most obvious bottleneck for the currently deployed network to meet up with
increasing traffic is scarcity of frequency spectrum. This challenge can be sur-
mounted by using the vast spectrum in the millimetre band for 5G mobile network
to support multi-gigabit communications services. The evolution towards 5G can be
achieved by either continuous enhancements to the LTE radio access network or
developing a new radio access network technology that departs from the concepts
of LTE. Continuous enhancements to LTE will primarily focus on further
enhancements to small cells and other general cellular enhancements for beyond
release 13. For example in [5], MIMO-OFDM technology (on which LTE is based)
was enhanced using an 8 16 antenna configuration in the 11 GHz frequency
band to achieve a data rate of 10 Gbps. Defining a new Radio Access Technology
(RAT) should prioritize the achievement of more gains over backward compati-
bility with LTE [6]. 5G is expected to combine sub 6 GHz and the band beyond
6 GHz to support extreme services such as low data Internet of Things applications
to high data Ultra High Definition Video (UHDV) as illustrated in Fig. 1.
Rel-8/9
Rel-10/11
Rel-12/13
Rel-14/15/...
New RAT
Frequency
1 – 3
GHz
Below 6 GHz
(WRC 15)
Above 6 GHz
(WRC 19)
LTE
LTE-Advanced
5G Radio
Access
Continuous Evolution
Big Gain
Revolution
Fig. 1 Evolution paths from LTE to 5G
From 3GPP LTE to 5G: An Evolution 487
2 LTE Network Architecture
LTE network architecture is a generally simplified access network which marks a
total departure from previous standards, characterized by the absence of a
circuit-switched domain. It employs a non-hierarchical (distributed) structure.
The LTE network architecture incorporates new network elements. As shown in
Fig. 2, LTE network architecture can be sub-divided into three major groups: air
interface, radio access network and core network. Transmission of data and control
information between the user equipment (UE) and the evolved base stations (eNBs)
take place within the air interface. LTE uses various mechanisms (as discussed later
in this paper) within the air interface to provide highly reliable and efficient means
of carrying out these operations.
The RAN of LTE consists only of a network of fully interconnected eNBs; hence
the network is described as being flat or distributed. This RAN is called the
E-UTRAN i.e. the Evolved-UMTS Terrestrial Radio Access Network. It is an
evolved RAN from UTRAN, used by 3G networks but in LTE, all radio network
controller (RNC) functions are transferred to the eNBs. Some of the functions of the
eNB include:
•Radio Resource Management: This involves functions such as scheduling,
dynamic allocation of resources, radio bearer control and mobility control.
•IP Header Compression.
•Security.
•Connection of users to the core network.
HSS
MME
S-GW
PCRF
P-GW
ePDG
IP
Services
or Internet
Trusted
3GPP
Access
(GERAN/
UTRAN)
Trusted
non-
3GPP
Access
(WiMAX)
Un-
trusted
non-
3GPP
Access
(WiFi)
Core Network
X2
S6a
S11
S4
S5
S2a
S7
S2b
SGi
Rx+
Wn*
eNB
eNB
E-UTRAN
S1-U
S1-MME
X2
S1-MME
X2
S1-MME
X2
Fig. 2 LTE network architecture
488 O. Oshin et al.
The core network of LTE differed significantly from previous standards. All
others had their core networks either entirely circuit switched or split into circuit
switched domain and packet switched domain, but LTE core network is entirely
packet switched and it is called the Evolved Packet Core (EPC). The EPC in
conjunction with the E-UTRAN is called the Enhanced Packet System (EPS),
whose details have been defined by 3GPP’s study of System Architecture Evolution
(SAE).
A Summary of the functional elements of the EPC are outlined below [7]:
•Mobility Management Entity (MME): this handles user authentication, it tracks
and maintains the location of a user equipment, performs signalling operations,
MME selection for inter-MME handovers.
•Serving Gateway (S-GW): while the MME handles control distribution func-
tions, the S-GW handles data bearer functions where it handles user data
functionality, routes and forwards data packets to the P-GW, performs mobility
anchoring for inter-3GPP mobility and is responsible for lawful interceptions.
•Packet Data Network Gateway (P-GW or PDN-GW): It handles packet filtering
for every user, allocation of IP addresses to the UEs, supports service level
charging by collecting and forwarding call data records, handles DL data rate
enforcement to ensure that a user does not surpass his traffic rate subscription
level, provides interworking for the user plane, between some 3GPP access
systems and all non-3GPP access systems, supports QoS differentiation between
multiple IP flows. It is also capable of handling multiple lawful interceptions of
user traffic to promote government intelligence services fighting criminal
activities. The P-GW enforces PCRF policies.
•Home Subscriber Server (HSS): this is a major database, which houses all
subscription-related information, to perform call control activities and session
management functions.
•Policy and Charging Control Function (PCRF): The PCRF ensures QoS regu-
lation within the network based on definite policies. It is responsible for framing
policy rules from the technical details of Service Date Flows (SDFs) that will
apply to the users’services, and then forwarding these rules to the P-GW for
enforcement.
•Evolved Packet Data Gateway (ePDG): The ePDG provides interworking with
un-trusted non-3GPP IP access systems. It ensures security by having a secured
tunnel between the UE and the ePDG. It can also function as a local mobility
anchor within un-trusted non-3GPP access networks.
As observed in Fig. 2, LTE uses interfaces as indicated for communication
between its entities. In general, LTE network architecture implements a simplified,
flat all-IP architecture which leads to reduced latency, reduced CAPEX and OPEX,
increased scalability and efficiency among other benefits. Increased cost savings
and increase capacity can be realized by using LTE femtocells known as Home
eNodeB (HNB). Can be backhauled to the cellular operator network through a
From 3GPP LTE to 5G: An Evolution 489
broadband gateway such as fiber optic cable over the internet. The reference model
of the HNB is shown in Fig. 3.
The HNB gateway is an optional entity that serves as a concentrator for HNB
connections and as a Radio Network Controller (RNC) to the core network.
Alternatively, the HNB can connect directly to the core network when a Local
Gateway functionality is incorporated into it [8]. Enhancements to the HNB is very
critical to the continuous evolution of the 3GPP LTE standard.
3 Enabling Technologies
LTE leverages on several technologies such as use of Orthogonal Frequency
Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO)
antenna techniques to achieve the specified targets. Continuous improvements of
these enabling technologies is the basis for the evolution of the LTE technology.
3.1 Multiplexing/Multiple Access Mechanism
The aim of multiplexing/multiple access mechanisms is to share scarce resources in
order to achieve high capacity, by enabling simultaneous allocation of
bandwidth/channel to multiple users. Multiplexing is a method by which multiple
signals are transmitted at the same time in form of a single complex signal over a
shared medium and then recovering the individual signals at the receiving end while
Multiple access mechanisms define how the channel is shared in a finite frequency
bandwidth i.e. it controls how to use (share) the radio resources efficiently. These
operations take place within the air interface of the LTE network.
The OFDM is a data transmission multi-carrier modulation technique, which
divides a high bit-rate data signal into several parallel low bit-rate data signals
which are then modulated using an appropriate modulation scheme. OFDM is the
core of LTE downlink transmission system. Majority of the striking features of LTE
is made possible by its use of OFDM. The “low bit-rate multi-carrier”technique of
OFDM, with a cyclic prefix added to it, makes the transmission robust to time
luh
luh
Security Gateway
Gn/S5
Gn/S5
HNB
HNB-GW
Uu lurh
Core
Networ
k
Fig. 3 HNB access radio
access network reference
model
490 O. Oshin et al.
dispersion on the radio channel without the need for advanced and complex receiver
channel equalization. In the downlink, this leads to reduced cost of terminal
equipment and reduced power consumption as well. OFDM is also used due to its
resilience to multipath delays and spread, its capability for carrying high data rates
and its ability to support both FDD and TDD schemes. The concept of orthogo-
nality can be illustrated by considering two OFDM modulation symbols ai1and ai2
used to modulate time-limited complex signals (subcarriers):
Z
ðmþ1ÞTs
mTs
ai1a
i2ej2pk1Dftj2pk2Dftdt ¼08k16¼ k2ð1Þ
where Df¼1=Tsis the subcarrier spacing and k:Dfis the sampling frequency
which corresponds to the sampling frequency of the signal. In essence, OFDM
transmission is the modulation of a set of orthogonal functions given by [9]:
bðtÞ¼ ej2pkDft 0t\Ts
0otherwise
ð2Þ
In the downlink, the Base Station (BS) is the transmitter while the User
Equipment (UE) only receives, therefore it does not have multiple access problems
in terms of collisions. Fading is a natural characteristic of radio communication
channels (either in time, frequency or space domain), resulting in rapid variations in
radio channel quality. A derivative of OFDM—OFDMA is used in LTE downlink,
where it combines functionalities of FDMA and TDMA. With OFDMA, the UE
gets scheduled to a time slot and a frequency group (which makes the system
resilient to frequency-selective fading) among other features, in order to send
information. Using OFDMA, LTE can use channel-dependent scheduling to take
advantage of the variations resulting in more efficient use of available radio
resources. This creates a lot of flexibility and makes the system robust, as not all the
requirements for transmission can be bad at the same time.
In the uplink, the UEs transmit to the BSs. Due to the high peak-to-average ratio
(PAR) of OFDM (characterized by the high amount of power required by the RF
power amplifier to push out the RF signal from the UE antenna to the BS), 3GPP
was forced to adopt a different transmission scheme for LTE uplink. SC-FDMA, a
hybrid scheme, was the solution—it combines the low PAR feature (which allows
high RF power amplifier efficiency in the UEs, thereby reducing battery con-
sumption for the UE) of single-carrier schemes with the resilience of multipath
interference and the flexible subcarrier frequency allocation of OFDM technology
[10].
From 3GPP LTE to 5G: An Evolution 491
3.2 Coding and Modulation
The reduced latency and high throughput of LTE is traceable to a number of
mechanisms implemented in it. The physical/MAC layer of LTE adopts two key
techniques: Hybrid Automatic Repeat reQuests (HARQ) and adaptive modulation
and coding (AMC). These two techniques work together to give a very adaptive
transport mechanism in LTE [11]. To handle re-transmission errors, LTE uses two
loops: a fast HARQ inner loop with soft combining to take care of most errors and a
robust selective-repeat ARQ outer loop to take care of residual errors [12,13].
HARQ is a technique for both error detection and correction by identifying when
transmission errors occur and facilitating retransmission from the source thereby
ensuring that data is transported reliably from one network node to another. LTE
uses Type-II HARQ protocols. LTE demonstrates dynamic resource allocation
through link adaptation. Link adaptation is achieved using the AMC mechanism,
with the aim of improving data throughput in a fading channel. AMC works by
varying the downlink modulation technique depending on the channel conditions of
each user. Given a good channel condition, the LTE system can use a higher order
modulation scheme (64-QAM with 6 bits per symbol) or reduced channel coding,
making the channel more spectrally efficient, and resulting in higher data rates. But
as the channel becomes noisy due to signal fading or interference, the system selects
a lower modulation technique (QPSK or 16-QAM with fewer bits per symbol) or
stronger channel coding.
3.3 Radio Access Modes (Duplex Schemes)
A duplex scheme organizes how radio communication systems communicate in the
two possible directions (uplink and downlink). 3GPP has specified LTE to operate
in either unpaired spectrum for Time Division Duplex (TDD) called TD-LTE or
paired spectrum for Frequency Division Duplex (FDD); where each has its pros and
cons, therefore selection is made depending on the intended application.
LTE specifications emphasize on TD-LTE, as it presents significant advantages
over LTE FDD. TD-LTE, asides many other advantages, provides an upgrade path
for TD-SCDMA, it does not require a paired spectrum since uplink and downlink
transmissions occur on the same channel making it highly spectrally efficient and
TD-LTE also reduces hardware cost. LTE operation in FDD which is the same
duplex method for GSM/UMTS, gives room for subscribers’migration to LTE.
LTE also supports half-duplex FDD at the UE. This mode allows the uplink and
downlink to share hardware since they are never used simultaneously. The half
duplex LTE FDD offers reduced complexity and therefore reduced cost [14].
492 O. Oshin et al.
3.4 Radio Channel Bandwidth
LTE is not only able to operate in different frequency bands, but can be imple-
mented using different spectrum sizes. This makes it possible to harness the global
wireless market and align with regional spectrum regulations and the obtainable
spectrum. LTE implements a scalable radio channel bandwidth from 1.4 to 20 MHz
with a subcarrier spacing of 15 kHz. The 20 MHz bandwidth will be required for
optimum performance and to cope with the growth of the mobile internet. 3GPP has
specified the LTE air interface to be “bandwidth agnostic”thereby allowing the
physical layer to adapt to different spectrum allocation without severe impact on
system operation.
LTE defines an enhanced mode of operation for broadcast/multicast services
called eMBMS (Enhanced- Multimedia Broadcast/Multicast Service), yielding
notable performance benefits compared to MBMS over WCDMA. LTE does this by
enabling the support of MBSFN (Multimedia Broadcast over Single Frequency
Network) yielding a possible subcarrier spacing of 7.5 kHz for standalone eMBMS
operation using a dedicated carrier [15].
3.5 Multiple Antenna Techniques
Every terrestrial radio communication channel has data throughput limitations as
defined by Shannon’s theorem, and multipath interference. LTE networks are
expected to provide high data rate in addition to high spectral efficiency; therefore,
3GPP included the use of multiple antenna techniques to provide additional
robustness to the radio link [16]. Multiple antenna techniques take advantage of the
effects of multipath interference to increase data throughput significantly within the
channel’s given bandwidth. The use of multiple antenna techniques introduces a
concept called precoding, which is essential for obtaining the best data reception
result at the receiver. It specifically maps the modulation symbols onto the different
antennas. The basic principle of MIMO is illustrated in Fig. 4.
MIMO Channel
Rx Antenna 1
Rx Antenna 2
Tx Antenna 1
Tx Antenna 2
h11
h
h
h
12
21
22
Fig. 4 Block diagram of a
22 MIMO system
From 3GPP LTE to 5G: An Evolution 493
The MIMO system for each subcarrier can be expressed as a system of linear
equations which gives the relationship between the transmit antennas and the
receive antennas. The relationship can be expressed in vector form as:
~
Y¼h11 h12
h21 h22
~
Xð3Þ
In order to correctly recover the transmitted data, the receiver must estimate the
channel response (channel state information) at each subcarrier for any pair of
transmitted and received symbol. In selecting the type of multiple antenna tech-
nique to use, transmission modes were defined. 3GPP’s Release 8 (LTE) specifies
seven transmission modes (named TM1, TM2 etc.) for the downlink and one
transmission mode for the uplink. These antenna techniques differ by the benefit
they provide and the conditions required for their operation. The transmission
modes differ in the number of layers or ranks and the number of antenna ports. The
uplink transmission mode is Closed-loop switched antenna diversity.
MIMO is a generic term with several special cases and applications. When a
point-to-point MIMO link between an eNB (base station) and a single user is
involved, we have a case of single user MIMO (SU-MIMO). Multi-user MIMO
(MU-MIMO) refers to use cases where several user equipment (UE) communicate
with a single eNB using the same time and frequency—domain resources (David
et al. 2009). Special cases of MIMO configuration include:
Single-Input-Multiple-Output (SIMO), Multiple-Input-Single-Output (MISO). The
main aim of the various MIMO configuration revolves around achieving either
diversity gain, array gain or spatial multiplexing gain. Transmit/receive diversity
involves the transmission/reception of redundant information on different antennas
at each subcarrier. Diversity gain makes the link robust by mitigating the effect of
multipath fading. In order words, diversity gain is aimed at improving the statistics
of instantaneous Signal-to-Noise Ratio (SNR) in a fading channel. In LTE, transmit
diversity gain is achieved using Space Frequency Block Codes (SFBCs) and
Frequency Switched Transmit Diversity (FSTD). Beamforming is used to achieve
array beamforming gain, by using multiple antenna to control the direction of wave
front based on weighting the phase and magnitude of individual antenna signals
[17]. Spatial multiplexing is designed to boost a link by transmitting non-redundant
(independent) information on different antennas. The transmission modes for LTE
based on these configurations are summarized in Table 1[17].
3.6 Voice Over LTE/IP Multimedia Subsystem (IMS)
LTE implements an all-IP architecture; this implies that voice communication
cannot be “business as usual”i.e. voice communication cannot be circuit-switched
as it is with lower generation technologies. This problem also applies to SMS
494 O. Oshin et al.
communication as well; therefore, new solutions for supporting voice and SMS on
LTE network became an urgent need.
In order to provide these very crucial services, alliances were tasked to come up
with solutions to these shortcomings, which are listed below:
•Circuit-Switched Fall-Back (CSFB): This method involves the use of a 2G/3G
network alongside the LTE network. The LTE network is used for data services
but on a call initiation, the network falls back to a 2G/3G circuit-switched
connection while the LTE network (packet-switched) is suspended. For an SMS
transmission, the mobile equipment uses an interface known as SGs
(MME-MSC interface) which allows messages to be transmitted over an LTE
channel.
•Simultaneous Voice—LTE (SV-LTE): This is very similar to the CSFB but in
SV-LTE, the user device makes use of the 2G/3G network and the LTE network
concurrently. Thus, when a call is initiated, it is routed through the
circuit-switched 2G/3G connection while maintaining connection with the LTE
network. This option requires the use of two radios simultaneously by the
mobile device which causes a degrading impact on the battery life of the device.
•Over-the-top (OTT) VoIP: An example of an OTT VoIP solution is Skype. This
concept led to the widespread usage of VoIP as a voice communication service
and has advanced to an era of being pre-installed in smart phones. However,
OTT VoIP solutions cannot guarantee satisfactory user experience in the
absence of LTE coverage. OTT VoIP service providers do not have control over
QoS in the wireless network, therefore, cannot ensure a good quality of
Table 1 Transmission modes in LTE release 9
Transmission
modes
Description Remarks
1 Single transmit antenna Single antenna port; port 0
2 Transmit diversity 2 or 4 antennas
3 Closed loop spatial
multiplexing with cyclic delay
diversity
2 or 4 antennas
4 Closed loop spatial
multiplexing
2 or 4 antennas
5 Multi-user MIMO 2 or 4 antennas
6 Closed loop spatial
multiplexing using a single
transmission layer
1 layer (rank 1)
2 or 4 antennas
7 Beamforming Single antenna port, port 5 (virtual
antenna port, actual antenna configuration
depends on implementation)
8 Dual-layer beamforming Dual-layer transmission, antenna port 7
and 8
From 3GPP LTE to 5G: An Evolution 495
experience (QoE) under all load circumstances. It also lacks the capability of
handing over to a circuit-switched connection.
•Voice over LTE via Generic Access (VoLGA): This method relies on the
operating principles of 3GPP’s Generic Access Network (GAN). The aim of
GAN is to extend mobile services over a generic IP access network. For
example, using Wi-Fi as an access technology to a 2G/3G network. In the case
of LTE, VoLGA uses LTE as the access technology to a 2G/3G network.
A GAN gateway provides a secure connection from the user to the mobile
network operator’s infrastructure. This connection serves as the channel for
transmitting voice and other circuit-switched services such as SMS over the
intermediate LTE network.
•Voice over LTE (VoLTE): This method implements 3GPP’s IMS core network
by deploying Multimedia Telephony (MMTel) on the IMS core as the solution
for voice service delivery and other traditional circuit-switched services over the
LTE network. VoLTE eliminates the need for fall-backs to 2G/3G voice,
ensuring a truly flat all-IP LTE network. With VoLTE users are assured telecom
grade voice and all forms of rich communication services on LTE-enabled
devices. VoLTE defines three working interfaces:
–The User Network Interface (UNI): This is the interface between the user
device and the operator’s network.
–The Roaming Network Network Interface (R-NNI): This is the interface
between the Home and Visited Network, for use in a roaming situation.
–The Interconnect Network Network Interface (I-NNI): This is the interface
between the networks of the two users making a call.
VoLTE has been accepted globally by a significant number of telecom industries
as the standard for carrying voice, SMS and other related services over the LTE
network [18].
3.7 Self-organizing Networks (SON)
The impact or functionality of a network is not just in its deployment and usage but
in its ability to achieve operational excellence. This involves continuous end-to-end
network management of the system i.e. seamless operation and consistent perfor-
mance. Due to the increasingly expanding and evolving wireless network, there is a
crucial need to automate this management process [19,20]. In order to achieve this,
LTE adopts SON techniques which enables the network to configure itself and
manage the radio resources to achieve optimum performance at all times with
minimal human supervision. SON techniques cover three main areas:
•Self Configuring: As a network expands and more eNBs are deployed, self
configuring networks eliminate the need to go around configuring each one;
rather, they are configured using automatic installation procedures.
496 O. Oshin et al.
•Self Optimizing: After configuration, self optimizing techniques adjust the
network’s operational characteristics based on measurement information col-
lected from the UEs and eNBs, and use them to auto-tune the network to best
meet its needs.
•Self Healing: In any system, faults are very likely to occur; however, the self
healing capability of a network enables automatic detection and fault masking
by changing relevant network characteristics. For example, edges of adjacent
cells can be increased by raising power levels and changing antenna elevations.
4 LTE Technological Advancements
There are two groups of technological advancements on LTE Release 8, namely
LTE Release 9 and LTE Release 10 [21]. Transmission Mode 8 (TM8), Dual Layer
Beamforming, was added in LTE Release 9. LTE Release 9 also focuses on features
that enhance the core network of LTE Release 8. These enhancements centre on:
•Location, broadcast and IMS emergency services using GPRS and EPS.
•Support of circuit switching services over the EPS of LTE.
•Home NB or eNB architecture considerations focusing on security, QoS,
charging and access restrictions.
•IMS evolution.
LTE Release 10: This is the evolution of LTE to meet the IMT-A requirements
defined by ITU. It is known as LTE-Advanced (LTE-A), and its focus is on higher
capacity as outlined:
•Downlink peak data rate of 3 Gb/s and Uplink peak data rate of 1.5 Gb/s.
•Higher spectral efficiency on the downlink, from an upper limit of 16 bps/Hz in
Release 8–30 bps/Hz in Release 10.
•Increased number of simultaneously active subscribers.
•Improved performance at cell edges.
LTE-A centres on three new techniques that enable it achieve the
above-mentioned feats [22]:
•Carrier Aggregation (CA): The most basic method of increasing capacity is by
adding more bandwidth. LTE-A is increased in bandwidth through aggregation
of up to five component carriers of different bandwidths to form a maximum
bandwidth of 100 MHz. This also provides LTE-A backward compatibility with
Release 8 and Release 9 mobiles. Carrier aggregation can be used in both FDD
and TDD schemes.
•Enhanced multiple antenna techniques: It adds a ninth transmission mode to the
downlink called Eight Layer Spatial Multiplexing (8 8 MIMO), and adds a
second transmission mode to the uplink (4 4 MIMO).
From 3GPP LTE to 5G: An Evolution 497
•Relay Nodes (RN): Relay nodes bring about the possibility of efficient hetero-
geneous network planning in LTE-A. The Relay Nodes are low power base
stations that provide enhanced coverage and capacity at cell edges and can also
provide connectivity to remote areas without the need for optical fibre cables.
•Coordinated Multipoint (CoMP) Transmission/Reception: This feature was
finalized in Release 11. In this technique, multiple transmit and receive points
provide coordinated transmission/reception. This transmission/reception is car-
ried out jointly and dynamically across multiple cell sites, same site or within
same or different eNBs. The primary purpose of CoMP is to improve the per-
formance at cell edge.
The on-going enhancements in release 13 include additional enhancements for
LTE to operate in the unlicensed spectrum and expansion of the carrier aggregation
framework to support more than 5 component carriers. Other enhancements
described in [23,24] include:
•Enhancements for Machine-Type Communications (MTC) involves defining a
new low complexity UE type that supports reduced support for downlink
transmission modes, reduced bandwidth, reduced transmit power and very long
battery life to support Internet of Things (IoT) markets.
•Improving multi-user transmission techniques using superposition coding for
increasing spectral efficiency of the LTE system.
•Use of full dimension MIMO/Elevation Beamforming for improved spectral
efficiency by the use of higher dimension MIMO of up to 64 antennas at the
eNB and utilizing the vertical dimension for MIMO and beamforming
operations.
•Improved indoor positioning accuracy and support for Single-cell
Point-to-Multipoint (SC-PTM).
Table 2gives a summary of the key characteristics of LTE at its inception and
the current features of LTE as at today, LTE-A. However, recall that there are
Table 2 LTE—LTE-A comparison
Parameter LTE LTE-A
Frequency band Country-dependent Country-dependent
Downlink peak
data rate
100–326 Mbps 1–3 Gbps
Uplink peak data
rate
50–86 Mbps 500 Mbps–1.5 Gbps
Channel
bandwidth (MHz)
1.4, 3, 5, 10, 15, 20 Up to 100 MHz
Peak spectral
efficiency
16 bps/Hz downlink 30 bps/Hz downlink
Latency *10 ms Less than 5 ms
(continued)
498 O. Oshin et al.
improvements on the first release of LTE as already discussed in this sub-section,
before the LTE Release 10 (LTE-A).
5 5G Enabling Technologies
The most obvious paths of evolution towards 5G radio access are improved
spectrum efficiency, network densification and spectrum extension. As earlier noted
[25], currently deployed networks are deployed in 1–3 GHz frequency band which
eventually fall short of meeting the multi-gigabit requirements of future commu-
nication services such as Ultra-High Definition Video (UHDV) [26]. The millimeter
wave (mmWave) frequency band from 30 to 300 GHz offers a huge bandwidth and
consequently spectrum extension for mobile networks. Millimeter communications
particularly in the 28, 38, 60 GHz and the E-band (71–76 and 81–86 GHz) bands
will play a critical role in 5G applications such as small cell access, cellular access
and wireless backhaul [27,28]. Some of the key radio access technologies that will
pave the way for 5G mobile communications include:
•Further enhancements to low power small cells to provide network
densification.
•The use of massive MIMO and large number of miniaturized antennas at high
(mmWave) frequencies to provide significant increase in spectrum efficiency
and user throughput.
•Use of new access techniques such as Filtered OFDM and Sparse Code Multiple
Access (SCMA) to improve system efficiency, support energy saving, reduced
latency and massive connectivity [29,30].
•Use of more efficient coding schemes such as Polar codes, which can achieve
Shannon capacity using a simple encoder and a successive cancellation decoder
for a large code block size. Another perspective to coding in 5G is to use
Table 2 (continued)
Parameter LTE LTE-A
Duplex method FDD and TDD
(TD-LTE)
FDD and TDD (TD-LTE)
Multiplexing OFDM OFDM
Multiple access
method
Downlink—
OFDMA
Uplink—SC-FDMA
Downlink—OFDMA
Uplink—SC-FDMA
Modulation
scheme
QPSK, 16-QAM,
64-QAM
QPSK, 16-QAM, 64-QAM
Multiple antenna
technique
Up to 4 4 MIMO
downlink
Higher order MIMO (8 8 MIMO downlink;
44 MIMO uplink)
From 3GPP LTE to 5G: An Evolution 499
network coding for interference management, which can improve security,
throughput and robustness for routing of information through the network.
•Use of Full Duplex to support bi-directional communications without the use of
time or frequency duplex is expected to double system capacity and reduce
latency.
•Use of self-organizing network operation for a cost effective management of the
massive network densification. The concept of Device-to-Device communica-
tion which allows direct communication between nearby device will depend
relies on self-organizing network operations.
6 Conclusion
It is most evident that LTE gives sustainable and significant advantages over
existing 3G technologies and also offers the most efficient and feasible evolution
path as user/operator network demands mature. The LTE technology has undergone
a significant evolution from its first release, which was aimed at meeting the
IMT-2000 requirements to achieving and even exceeding the IMT-Advanced (4G)
requirements. These technologies will continue to play a critical role in the new
frequency spectrum below 6 GHz expected to be allocated for mobile communi-
cations at the World Radio Conference (WRC) 2015. However, for the spectrum
band above 6 GHz which is expected to be allocated at WRC in 2019, a new radio
access technology may be necessary. Thus 5G which is the next frontier of a
broader ICT ecosystem that will enhance mobile internet and empower
Internet-of-Things (IoT) will be heterogeneous across frequency spectrum. The
lower frequency bands (below 6 GHz) can be used as the primary band of 5G
spectrum for wide area network coverage. The high frequency bands can be used
for Ultra Dense Networking and flexible backhauling. The high frequency bands
are also expected to use enhanced smalls cells due to high attenuation associated
with these frequencies.
References
1. GSA confirms 1800 MHz as the most popular LTE band; LTE1800 used in over 37 % of
networks (Online). Available: http://www.gsacom.com/news/gsa_367.php. Accessed 11 Nov
2014
2. Oni OO, Atayero AA, Idachaba FE, Alatishe AS (2014) LTE networks: benchmarks,
prospects and deployment limitation. In: Lecture notes in engineering and computer science:
proceedings of the world congress on engineering 2014, WCE 2014, pp 422–427. London,
UK, 2–4 July 2015
3. Gessner C, Roessler A, Kottkamp M (2012) UMTS long term evolution (LTE)—technology
introduction. In: Application note, 2012 (Online). Available: cdn.rhode-schwarz.com/pws/dl_
500 O. Oshin et al.
downloads/dl_application/application_notes/1ma111/1MA111_4E_LTE_technology_
introduction.pdf. Accessed 14 Nov 2015
4. Iwamura M, Takahashi H, Nagata S (2010) Relay technology in LTE-advanced. NTT Docomo
Tech J 12(2):29–36
5. Suyama S, Shen J, Oda Y (2014) 10 Gbps outdoor transmission for super high bit rate mobile
communications. NTT Docomo Tech J 15(4):22–28
6. 5G radio access: requirements, concept and technologies. In: DOCOMO 5G white paper, 2014
(Online). Available: https://www.nttdocomo.co.jp/english/corporate/technology/whitepaper_
5g/. Accessed 11 Nov 2015
7. Flore D (2009) LTE RAN architecture aspects I. In: IMT advanced evaluation, 2009 (Online).
Available: ftp://www.3gpp.org/workshp/2009-12-17_ITU_R_IMT-Adv_eval/docs/pdf/REV-
090005 LTE RAN architecture aspects.pdf. Accessed 13 Nov 2015
8. ETSI TS 125 467 (2013) Universal mobile telecommunications systems (UMTS); UTRAN
architecture for 3G home node B (HNB). ETSI, 2013
9. Erik D, Stefan P, Johan S (2011) 4G LTE/LTE-advanced for mobile broadband. Elsevier,
Oxford
10. Poole I (2015) LTE OFDM, OFDMA SC-FDMA and modulation. In: Radio electronics
(Online). Available: www.radio-electronics.com/cellulartelecomms/long-term-evolution.
Accessed 10 Nov 2015
11. 3GPP long term evolution system overview, product development and test challenges. In:
Agilent technologies application note, 2009 (Online). Available: www.ccontrol.ch/cms/
upload/applikationem/LTE/5989-8139EN.pdf. Accessed 13 Nov 2015
12. Anders F, Jonsson T, Lundevall M (2008) The LTE radio interface—key characteristics and
performance. In: IEEE Symposium on PIMRC, 2008, pp 1–5
13. Astely D, Dahlman E, Fursuskar A, Jading Y, Lindstrom M, Parkvall S (2009) LTE: the
evolution of mobile broadband. IEEE Commun Mag 44(4):44–51
14. Yonis AZ, Abdullah MFL, Ghanim MF (2012) LTE-FDD and LTE-TDD for cellular
communications. In: Progress in electromagnetics research symposium proceedings, 2012
15. 3G Americas (2007) UMTS evolution from Rel-7 to Rel-8—HSPA and SAE/LTE. In: White
paper, 2007 (Online). Available: www.3g4g.co.uk/Lte/LT_WP_0707_3GAmericas.pdf.
Accessed 13 Nov 2015
16. Shapira Y (2013) LTE multiple antenna techniques, 2013 (Online). Available: www.
exploregate.com/video.aspx?video_id=4
17. Schulz B (2011) LTE transmission modes and beamforming. In: Rhode and Schwarz white
paper, 2011 (Online). Available at: http://www.rohde-schwarz.cz/file_17063/1ma186.
Accessed 15 Nov 2015
18. Warren D (2010) Roaming in LTE and voice over LTE. In: GSM association, 2010 (Online).
Available: www.3gpp.org. Accessed 16 Nov 2015
19. Atayero AA, Adu IO, Alatishe AA (2014) Self organizing networks for 3GPP LTE. In:
Murgante B, Misra S, Rocha AMAC, Torre C, Rocha JG, Falcao MI, Taniar D, Apduhan BO,
Gervasi O (eds) Computational science and its applications-ICCSA. Springer, pp 242–254
20. Feng S, Seidel E (2008) Self-organizing networks (SON) in 3GPP long term evolution, Nomor
research, Munich, Germany, May 2008. In: White paper, 2008 (Online). Available: www.
nomor.de/home/technology/white-papers/self-organizing-networks-in-long-term-evolution.
Accessed 10 Nov 2014
21. 3G Americas (2009) The mobile broadband evolution: 3GPP release 8 and beyond HSPA+,
SAE/LTE and LTE-advanced. In: White paper, 2009
22. Atayero AA, Luka MK, Orya MK, Iruemi JO (2011) 3GPP long term evolution: architecture,
protocols and interfaces. Int J Inf Commun Technol Res 1(7):306–310
23. Nokia Network (2015) LTE release 12 and beyond. In: Nokia networks white paper (Online).
Available: networks.nokia.com/system/files/document/nokia_lte_a_evolution_white_paper.
pdf. Accessed 16 Nov 2015
24. Flore D (2015) Evolution of LTE in release 13 (Online). Available: www.3gpp.org. Accessed
16 Nov 2015
From 3GPP LTE to 5G: An Evolution 501
25. Adu OI, Atayero AA (2015) 3GPP LTE: an overview. In: Lecture notes in engineering and
computer science: proceedings of the world congress on engineering 2015, WCE 2015,
pp 616–621. London, UK, 1–3 July 2015
26. Elkashlan M, Duong TQ, Chen H-H (2015) Millemeter-wave communications for 5G-part 2:
applications. IEEE Commun Mag 53(1):166–167
27. Niu Y, Li Y, Jin D, Su L, Vasilakos AV (2015) A survey of millimeter wave (mmWave)
communications for 5G: opportunities and challenges. Springer Wirel Netw 21(8):2657–2676
28. Oshin OI, Oni O, Atayero A, Oshin B (2014) Leveraging Mmwave technology for mobile
broadband/internet of things. In: IAENG transactions on engineering technologies, lecture
notes in electrical engineering. Springer International Publishing, 2014
29. 5G: new air interface and radio virtualization. In: Huawei white paper, 2015 (Online).
Available: www.huawei.com/minisite/has2015/img/5g_radio_whitepaper.pdf. Accessed 15
Nov 2015
30. Nikopour H, Yi E, Bayesteh A, Au K, Hawryluck M, Baligh H, Ma J (2014) SCMA for
downlink multiple access of 5G wireless networks. Globecom 2014:3940–3945
502 O. Oshin et al.
