Long Term Evolution Lte Ebook

EVOLUTION IN COMMUNICATION

LONG TERM EVOLUTION

Antonis Hontzeas

About :
Antonis Hontzeas has been In the forefront of the
Telecommunications industry for twenty years.
Tenure includes positions ranging from design and
technical management up to and including
executive positions dealing with solution
management and strategic marketing management.

The author’s current interest lies in designing and executing
strategies for engaging profitably new business opportunities in current
and emerging communications markets.

______________

Contact Info: edinpress@gmail.com
Linkedin Antonis Hontzeas
http://considerations.wordpress.com
 2009 Antonis Hontzeas for free public use

L O N G T E R M E V O L U T I O N

Long Term Evolution

LTE (Long Term Evolution) or 3G Long Term
Evolution is the evolution of mobile cellular
communications technology towards a full edge to
edge broadband ip network, and is introduced in 3rd
Generation Partnership Project (3GPP) Release 8.

The aim of this 3GPP project is to further develop the
Universal Mobile Telecommunications System
(UMTS) standard and provide an enhanced user
experience and simplified technology for next
generation mobile broadband. Scientists and design
engineers from more than 60 operators, vendors and
research institutes have teamed up to realise this
radio access standardization effort.

Much of the 3GPP Release 8 standard will be
oriented towards upgrading UMTS to 4G mobile
communications technology, and an all-IP flat
architecture system.

L O N G T E R M E V O LU T IO N

LTE targets requirements of next generation
networks including downlink peak rates of at least
100Mbit/s, uplink rates of 50 Mbit/s and RAN (Radio
Access Network) round-trip times of less than 10ms.
LTE supports flexible carrier bandwidths, from
1.4MHz up to 20MHz as well as both FDD
(Frequency Division Duplex) and TDD (Time Division
Duplex).

LTE further aspires to improve considerably spectral
efficiency, lowering costs, improving services,
making use of new spectrum and refarmed spectrum
opportunities, and better integration with other open
standards. The resulting architecture is referred to as
EPS (Evolved Packet System) and comprises the
E-UTRAN (Evolved UTRAN) on the access side and
EPC (Evolved Packet Core) via the System
Architecture Evolution concept (SAE), on the core
network side.

4


LTE advantages include high throughput, low
latency, plug and play from day one, FDD and TDD
in the same platform, superior end-user experience
and simple architecture resulting in low operating
expenditures (OPEX). LTE will also support
seamless connection to existing networks, such as
GSM, CDMA and WCDMA. However LTE requires a
completely new RAN and core network deployment
and is not backward compatible with existing UMTS
systems.

The standard includes:

Peak download rates of 326.4 Mbit/s for 4x4
antennas, 172.8 Mbit/s for 2x2 antennas for
every 20 MHz of spectrum.
Peak upload rates of 86.4 Mbit/s for every
20 MHz of spectrum.
5 different terminal classes ranging from a
voice centric class up to a high end terminal
that supports the peak data rates. All
terminals will be able to process 20 MHz
bandwidth.
At least 200 active users in every 5 MHz cell.
(i.e., 200 active data clients)
Sub-5ms latency for small IP packets.
Increased spectrum flexibility, with spectrum
slices as small as 1.5 MHz .and as large as
20 MHz. W-CDMA requires 5 MHz slices,
leading to some problems with roll-outs in

5


countries where the 5 MHz spectrum is
already allocated to 2 - 2.5G legacy GSM
and cdmaOne. The 5 MHz chunks also limit
the amount of bandwidth per handset.
Optimal cell size of 5 km, 30 km sizes with
reasonable performance, and up to 100 km
cell sizes supported with acceptable
performance.
Co-existence with legacy standards (users
can transparently start a call or transfer of
data in an area using an LTE standard, and
should coverage be unavailable, continue the
operation without any action on their part
using GSM/GPRS or W-CDMA-based UMTS
or even 3GPP2 networks such as cdmaOne
or CDMA2000) .
Support for MBSFN (Multicast Broadcast
Single Frequency Network). This feature can
deliver services such as MBMS using the LTE
infrastructure, and is a competitor to DVB-h.

A large amount of the work is aimed at simplifying
the architecture of the system, as it evolves from the
existing hybrid (packet and circuit switching) network,
to an all-IP flat architecture system.

6


Why LTE ?

Why is the cellular
industry
reconsidering the
overall architecture
of the GSM based
mobile
communication
system after only a
decade from the
introduction of the very first 3G/UMTS networks?

This is a common question and the chief answer has
to do with the fact that the world is very different
today that it was ten years ago. Fixed broadband
connectivity is now ubiquitous with multi-megabit
speeds available at reasonable cost to customers
and business users via DSL, fiber and cable
connections.
Broadband is part of today’s mobile customer
experience. This shift in user perception is
demonstrated by the rapid increase in the uptake of
WCDMA and HSPA networks worldwide. As of
January 2009, there are over 4 billion wireless
subscribers and over 254 operators in more than 110
countries supporting WCDMA.

7


In January 2009 237 operators had commercially
launched HSPA in 105 countries and over 70% of
HSDPA networks supported 3.6 Mbps (peak) or
higher, and over 34 % of HSDPA networks
supported 7.2 Mbps (peak) or higher. There were 66
commercial HSUPA systems commercially launched
in 47 countries.

The natural counterpart to HSDPA, HSUPA boosts
mobile uplink speeds as
high as 5.8 Mbit/s. This
provides a valuable
complement for
operators wishing to
introduce mobile
broadband services
demanding greater
capacity and speed on both uplink and downlink. An
example of this is Voice over IP (VoIP), where voice
calls are delivered over the Internet or other IP
networks in a packet-based session.
Furthermore, other technologies have matured since
UMTS was first commercialised in 2001.

Mobile WiMAX which was accepted by ITU as the
sixth radio access method for IMT-2000 (IMT-2000O
FDMA TDD WMAN) is being deployed by operators
in Asia-Pacific and the Americas.
Some European carriers have expressed interest in
deploying the technology as a complement to their
current 3G/UMTS operations. The acceptance of
mobile WiMAX as a part of IMT-2000 opens up the
possibility of operators deploying the technology in

8


their existing licensed 3G/UMTS spectrum
allocations.

Operators are thus presented with a choice of
technologies to provide their customers with wireless
broadband services. This will allow them either to
compete with fixed operators or to provide
broadband services in areas where the fixed
infrastructure does not exist and would be too
expensive to deploy.

Against this backdrop, LTE offers compelling
attractions for incumbent UMTS/HSPA operators
such as the ability to re-use significant portions of
their existing infrastructure, together with re-use
existing spectrum assets. While LTE looks firmly to
the future, it does so with a Return of Investment
(ROI) approach.

As a result, LTE will allow operators to generate
fresh sources of value from their existing network
investments while enjoying the significant economies
of scale that flow from participation in the world’s
biggest and most successful family of evolving
cellular systems that are specified by 3GPP.

9


Flat Architecture

A characteristic of next generation networks is that
all connectivity and session control relies on TCP/IP.
Since different functional domains can now
communicate and interact easily, the result is a richer
communications experience including enhanced
voice, video, messaging services and advanced
multimedia solutions.

In 2004, 3GPP proposed Transmission Control
Protocol/Internet Protocol (TCP/IP) as the future for
next generation networks and began feasibility
studies into All IP Networks (AIPN). Proposals
developed included recommendations for 3GPP
Release 7(2005), which acts as the foundation of


higher level protocols and applicatons which form the
LTE concept. These recommendations are part of
the 3GPP System Architecture Evolution (SAE).
Some aspects of All-IP networks, however, were
already defined as early as release 4.

3GPP is defining IP-based, flat network architecture
as part of the System Architecture Evolution (SAE)
effort. LTE–SAE architecture and concepts have
been designed for efficient support of mass-market
usage of any IP-based service. The architecture is
based on an evolution of the existing GSM/WCDMA
core network, with simplified operations and smooth,
cost-efficient deployment. The main component of
the SAE architecture is the Evolved Packet Core
(EPC), also known as SAE Core. The EPC will serve
as equivalent of GPRS networks (via the Mobility
Management Entity, Serving Gateway and PDN
Gateway subcomponents).

The subcomponents of the EPC are:

MME (Mobility Management Entity): The MME
is the key control node for the LTE access
network. It is responsible for idle mode UE
(User Equipment) tracking and paging
procedure including retransmissions. It is
involved in the bearer activation/deactivation
process and is also responsible for choosing
the SGW for a UE at the initial attach and at
time of intra-LTE handover involving Core
Network (CN) node relocation. It is
responsible for authenticating the user (by
interacting with the HSS). The Non-Access

11


Stratum (NAS) signaling terminates at the
MME and it is also responsible for generation
and allocation of temporary identities to UEs.
It checks the authorization of the UE to camp
on the service provider’s Public Land Mobile
Network (PLMN) and enforces UE roaming
restrictions. The MME is the termination point
in the network for ciphering/integrity protection
for NAS signaling and handles the security
key management. Lawful interception of
signaling is also supported by the MME. The
MME also provides the control plane function
for mobility between LTE and 2G/3G access
networks with the S3 interface terminating at
the MME from the SGSN. The MME also
terminates the S6a interface towards the
home HSS for roaming UEs.
S-GW (Serving Gateway): The SGW routes
and forwards user data packets, while also
acting as the mobility anchor for the user
plane during inter-eNB handovers and as the
anchor for mobility between LTE and other
3GPP technologies (terminating S4 interface
and relaying the traffic between 2G/3G
systems and PDN GW). For idle state UEs,
the SGW terminates the DL data path and
triggers paging when DL data arrives for the
UE. It manages and stores UE contexts, e.g.
parameters of the IP bearer service, network
internal routing information. It also performs
replication of the user traffic in case of lawful
interception.
P-GW (PDN gateway): The PDN GW provides
connectivity to the UE to external packet data

12


networks by being the point of exit and entry
of traffic for the UE. A UE may have
simultaneous connectivity with more than one
PDN GW for accessing multiple PDNs. The
PDN GW performs policy enforcement, packet
filtering for each user, charging support, lawful
interception and packet screening. Another
key role of the PDN GW is to act as the
anchor for mobility between 3GPP and non-
3GPP technologies such as WiMAX and
3GPP2 (CDMA 1X and EvDO).

Radio

The Release 8 air
interface, E-UTRA
(Evolved UTRA, the
E- prefix being
common to the
evolved equivalents
of older UMTS
components) would
be used by UMTS
operators deploying their own wireless networks. It's
important to note that Release 8 is intended for use
over any IP network, including WiMAX and WiFi, and
even wired networks.

13


The proposed E-UTRA system uses OFDMA for the
downlink (tower to handset) and Single Carrier
FDMA (SC-FDMA) for the uplink and employs MIMO
(Multiple Input – Multiple Output) with up to four
antennas per station. The channel coding scheme for
transport blocks is turbo coding couple with a
contention-free quadratic permutation polynomial
(QPP) turbo code internal interleaver.

Orthogonal Frequency-Division Multiple Access
(OFDMA) is a multi-user version of the popular
Orthogonal frequency-division multiplexing (OFDM)
digital modulation scheme. Multiple access is
achieved in OFDMA by assigning subsets of
subcarriers to individual users as shown in the
illustration below. This allows simultaneous low data
rate transmission from several users.

14


OFDMA Advantages:

Flexibility of deployment across various
frequency bands with little needed
modification to the air interface.
Averaging interferences from neighboring
cells, by using different basic carrier
permutations between users in different cells.
Interferences within the cell are averaged by
using allocation with cyclic permutations.
Orthogonality in the uplink by synchronizing
users in time and frequency.
Single Frequency Network coverage, where
coverage problem exists and gives excellent
coverage.
Adaptive carrier allocation in multiplication of
23 carriers = nX23 carriers up to 1587 carriers
(all data carriers).
Frequency diversity by spreading the carriers
all over the used spectrum.
Time diversity by optional interleaving of
carrier groups in time.
Optimal cell capacity through adaptivity to the
highest modulation a user can use. Less
carriers means higher gain per carrier (up to
18dB gain for 23 carrier allocation instead of
1587 carriers), and increase in overall cell
capacity.

15


Recognised disadvantages of OFDMA:

Higher sensitivity to frequency offsets and
phase noise.
Asynchronous data communication services
such as web access are characterized by
short communication bursts at high data rate.
The complex OFDM electronics, including the
FFT algorithm and forward error correction is
constantly active independent of the data rate.
This results in inefficient power consumption
even though the FFT algorithm may hibernate
during certain time intervals.
The OFDM diversity gain and resistance to
frequency-selective fading may partly be lost if
very few sub-carriers are assigned to each
user, and if the same carrier is used in every
OFDM symbol. Adaptive sub-carrier
assignment based on fast feedback
information about the channel, or sub-carrier
frequency hopping, is therefore desirable.
Co-channel interference processing from
neighbouring cells is more complex in OFDM
than in CDMA. It would require dynamic
channel allocation with advanced coordination
among adjacent base stations.
Fast channel feedback information and
adaptive sub-carrier assignment is more
complex than CDMA fast power control.

16


Characteristics and principles of operation

Adaptive user-to-subcarrier assignment is achieved
from received channel condition feedback. If the
assignment is done sufficiently fast, this further
improves the OFDM robustness to fast fading and
narrow-band cochannel interference, and makes it
possible to achieve even better system spectral
efficiency.

Different number of sub-carriers can be assigned to
different users, in view to support differentiated
Quality of Service (QoS), i.e. to control the data rate
and error probability individually for each user.

OFDMA resembles code division multiple access
(CDMA) spread spectrum, where users can achieve
different data rates by assigning a different code
spreading factor or a different number of spreading
codes to each user.

OFDMA can be seen as an alternative to combining
OFDM with time division multiple access (TDMA) or
time-domain statistical multiplexing, i.e. packet mode
communication. Low-data-rate users can send
continuously with low transmission power instead of
using a "pulsed" high-power carrier. Constant delay,
and shorter delay, can be achieved.

OFDMA can also be described as a combination of
frequency domain and time domain multiple
accesses, where the resources are partitioned in the

17


time-frequency space and slots are assigned along
the OFDM symbol index as well as OFDM sub-
carrier index.

OFDMA is considered as highly suitable for
broadband wireless networks, due to advantages
including scalability and MIMO-friendliness, and
ability to take advantage of channel frequency
selectivity.

In spectrum sensing cognitive radio, OFDMA is a
possible approach to filling free radio frequency
bands adaptively.

Single-carrier FDMA (SC-FDMA) is frequency-
division multiple access scheme. It is a multi-user
version of Single-carrier frequency domain
equalization (SC-FDE) modulation scheme. SC-FDE
can be viewed as a linearly precoded OFDM scheme
(LP-OFDMA) or as a single carrier multiple access
scheme. One prominent advantage over
conventional OFDM and OFDMA is that the SC-FDE
and LP-OFDMA/SC-FDMA signals have lower peak-
to-average power ratio (PAPR) because of its
inherent single carrier structure.

Just like in OFDM, guard intervals with cyclic
repetition are introduced between blocks of symbols
in view to efficiently eliminate time spreading (caused
by multi-path propagation) among the blocks. In
OFDM, fast Fourier transform (FFT) is applied on the
receiver side on each block of symbols, and inverse

18


FFT (IFFT) on the transmitter side. In SC-FDE, both
FFT and IFFT are applied on the receiver side, but
not on the transmitter side. In SC-FDMA, both FFT
and IFFT are applied on the transmitter side, and
also on the receiver side.

In OFDM as well as SC-FDE and SC-FDMA,
equalization is achieved on the receiver side after the
FFT calculation, by multiplying each Fourier
coefficient by a complex number. This helps combat
frequency-selective fading and phase distortion.

In SC-FDMA, multiple access is made possible by
inserting silent fourier-coefficients on the transmitter
side before the IFFT, and removing them on the
receiver side before the IFFT. Different users are
assigned to different fourier-coefficients (sub-
carriers).

The use of OFDM, a system where the available
spectrum is divided into many thin carriers, each on
a different frequency, each carrying a part of the
signal, enables E-UTRA to be much more flexible in
its use of spectrum than the older CDMA based
systems that dominated 3G. CDMA networks require
large blocks of spectrum to be allocated to each
carrier, to maintain high chip rates, and thus
maximize efficiency. Building radios capable of
coping with different chip rates (and spectrum
bandwidths) is more complex than creating radios
that only send and receive one size of carrier, so
generally CDMA based systems standardize both.

19


Standardizing on a fixed spectrum slice has
consequences for the operators deploying the
system: too narrow a spectrum slice would mean the
efficiency and maximum bandwidth per handset
suffers; too wide a spectrum slice implies
deployment issues and spectrum cramming with
legacy systems. This became a major issue in the
US roll-out of UMTS over W-CDMA, where W-
CDMA's 5 MHz requirement often left no room in
some markets for operators to co-deploy it with
existing GSM standards.

LTE supports both FDD and TDD mode. Each mode
has its own frame structure within LTE and these are
aligned with each other meaning that similar
hardware can be used in the base stations and
terminals to allow for economy of scale. The TDD
mode in LTE is aligned with TD-SCDMA as well
allowing for coexistence. Ericsson demonstrated at
the MWC 2008 in Barcelona for the first time in the
world both LTE FDD and TDD mode on the same
base station platform.

Downlink

LTE uses OFDM for the downlink – that is, from the
base station to the terminal. OFDM meets the LTE
requirement for spectrum flexibility and enables cost-
efficient solutions for very wide carriers with high
peak rates. It is a well-established technology, for
example in standards such as IEEE 802.11a/b/g,
802.16, HIPERLAN-2, DVB and DAB.

20


In the time domain you have a radio frame that is 10
ms long and consists of 10 sub frames of 1 ms each.
Every sub frame consists of 2 slots where each slot
is 0.5 ms. The subcarrier spacing in the frequency
domain is 15 kHz. Twelve of these subcarriers
together (per slot) is called a resource block so one
resource block is 180 kHz. 6 Resource blocks fit in a
carrier of 1.4 MHz and 100 resource blocks fit in a
carrier of 20 MHz.

Supported modulation formats on the downlink data
channels are QPSK, 16QAM and 64QAM.

For MIMO
operation, a
distinction is made
between single user
MIMO, for
enhancing one
user's data
throughput, and multi user MIMO for enhancing the
cell throughput.

In MIMO systems, a transmitter sends multiple
streams by multiple transmit antennas. The transmit
streams go through a matrix channel which consists
of multiple paths between multiple transmit antennas
at the transmitter and multiple receive antennas at
the receiver. Then, the receiver gets the received
signal vectors by the multiple receive antennas and
decodes the received signal vectors into the original
information. Spatial multiplexing techniques makes
the receivers very complex, and therefore it is

21


typically combined with orthogonal frequency-division
multiplexing (OFDM) or with Orthogonal Frequency
Division Multiple Access (OFDMA) modulation,
where the problems created by multi-path channel
are handled efficiently.

Uplink

In the uplink, LTE uses a pre-coded version of
OFDM called Single Carrier Frequency Division
Multiple Access (SC-FDMA). This is to compensate
for a drawback with normal OFDM, which has a very
high Peak to Average Power Ratio (PAPR). High
PAPR requires expensive and inefficient power
amplifiers with high requirements on linearity, which
increases the cost of the terminal and drains the
battery faster. SC-FDMA solves this problem by
grouping together the resource blocks in such a way
that reduces the need for linearity, and so power
consumption, in the power amplifier. A low PAPR
also improves coverage and the cell-edge
performance.

Supported modulation formats on the uplink data
channels are QPSK, 16QAM and 64QAM.

If virtual MIMO / Spatial division multiple access
(SDMA) is introduced the data rate in the uplink
direction can be increased depending on the number
of antennas at the base station. With this technology
more than one mobile can reuse the same
resources.

22


Spectrum

LTE and WIMAX each have their own benefits and
are suited to address different target market
segments.WiMAX is primarily TDD (Time-Division-
Duplex) and will address operators that have
unpaired spectrum whereas LTE is FDD (Frequency-
Division-Duplex) and will address operators that
have paired spectrum. TDD allows the up-link and
down-link to share the same spectrum, whereas FDD
has the up-link and down-link transmit on different
frequencies.

Advanced Wireless Services (AWS)

In September 2006 the FCC completed an auction of
AWS licenses (“Auction No. 66”) in which the winning
bidders won a total of 1,087 licenses. In the spirit of
the U.S. government’s free-market policies, the FCC
does not usually mandate that specific technologies
be used in specific bands. Therefore, owners of AWS
spectrum are free to use it for just about any 2G, 3G
or 4G, technology. This is the foundation of the tech
neutrality concept.
This spectrum uses 1.710-1.755 GHz for the uplink
and 2.110-2.155 GHz for the downlink. The 90 MHz
of spectrum is divided into six frequency blocks
labeled A through F. Blocks A, B, and F are 20
23


megahertz each and blocks C, D, and E, are 10
megahertz each. The FCC wanted to harmonize its
“new” AWS spectrum as closely as possible with
Europe’s UMTS 2100 band. However, the lower half
of Europe’s UMTS 2100 band almost completely
overlaps with the U.S PCS band, so complete
harmonization wasn’t an option. Given this
constraint, the FCC harmonized AWS as much as
possible with the rest of the world. The upper AWS
band aligns with Europe’s UMTS 2100 base transmit
band, and the lower AWS band aligns with Europe’s
GSM 1800 mobile transmit band.

700 MHz

In the U.S. this includes 62 MHz of spectrum broken
into 4 blocks; Lower A (12 MHz), Lower B (12 MHz),
Lower E (6 MHz unpaired), Upper C (22 MHz),
Upper D (10 MHz). These bands are highly prized
chunks of spectrum and a tremendous resource: the
low frequency is efficient and will allow for a network
that doesn’t require a dense buildout and provides
better in-building penetration than higher frequency
bands.
In 2005, the President of the U.S. signed the Digital
Television Transition and Public Safety Act of 2005
into law, designating February 17, 2009 as the date
that all U.S. TV stations must complete the transition
from analog to digital broadcasts, vacating the 700
MHz radio frequency spectrum, and thereby making
it fully available for new services. The upper C block
will have “open access” rules. In the FCC’s context
“open access” means that there will be “no locking
and no blocking” by the network operator. That is,

24


the licensee must allow any device to be connected
to the network as long as the device is compatible
with, and will not harm the network
(i.e., no “locking”), and the licensee cannot impose
restrictions against content, applications, or services
that may be accessed over the network (i.e., no
“blocking”).
The upper D block will include a Public/Private
Partnership obligation. As part of the 700 MHz FCC
decision, the commercial license owner will
combine this asset with an additional 10 MHz of
adjacent spectrum licensed to a national Public
Safety Broadband Licensee (PSBL), creating a
public-private partnership. In exchange for
constructing and operating the shared network to
Public Safety specifications, the D Block commercial
licensee will gain access to spectrum, on a
secondary basis, held by the PSBL to provide it with
additional capacity to furnish non-priority
communications services to commercial subscribers.
Indications are strong that in Europe and much of the
rest of the world, the so-called digital dividend – the
freeing up of spectrum brought about by the switch
from analog to digital TV- will also allow a significant
amount of spectrum to be carved out for wireless
broadband in the UHF band. While the details of the
digital dividend outside of the U.S are still being
debated, the expectation is that allocations will align
with, or as closely as possible with the U.S.
allocations in order to facilitate Global Roaming.

25


Refarming GSM 900 MHz

The 900 MHz band is the most ubiquitous and the
most harmonized worldwide wireless
telecommunication spectrum band available today. It
also has the benefit of increased coverage and
subsequent reduction in network deployment costs
compared to deployments at higher frequencies,
making it a highly strategic spectrum band.
Furthermore, 900MHz offers improved building
penetration and is particularly well suited to
supporting those regions that have a predominantly
rural population. The ongoing subscriber migration
from GSM to UMTS taking place in over 150
countries worldwide is relieving pressure on the
GSM900 networks and is starting to free up some
spectrum capacity in that band. Consequently, many
operators are evaluating the potential for deploying
UMTS (HSPA/HSPA+) in this GSM900 band. On the
other hand a number of operators are considering
keeping that freed-up GSM spectrum until LTE
becomes available in the beginning of 2010.From a
planning perspective, UMTS deployments require a
full 5 MHz of spectrum to be freed up before being
deployed in that band. Additionally, the availability of
mobile devices able to support 900 MHz is not
planned until 2010 and counting. In contrast, LTE will
be able to be deployed in spectrum bands as small
as 1.25MHz and it provides good initial deployment
scalability as it can be literally “squeezed” in as the
GSM spectrum is freed-up, and grow as more
spectrum becomes available. These factors reduce
the time advantage of deploying UMTS
(HSPA/HSPA+) in the 900 MHz band.In addition,

26


with the improved spectrum efficiency, LTE
deployment in the 900 MHz band would bring the
highest capacity benefit and also provide operators
the ability to deploy an LTE network with greater
coverage at a much reduced cost compared to
higher frequency spectrum hence provide a good
mobile broadband data countrywide layer. Finally,
deploying LTE in 900MHz can also bring the
additional cost and logistic benefits of being able to
deploy LTE at existing GSM sites as the coverage of
GSM/LTE in 900MHz should be very similar.It is
unlikely that operators in Europe would shut down
their GSM networks as GSM still provides the
backbone of voice communication and global
roaming. GSM networks with EDGE or future E-
EDGE upgrades do provide a good data sub-layer to
hand over to, when, initially, LTE coverage will not
available. The most likely scenario is that LTE at 900
MHz could run alongside GSM900 for a 5-10 year
period after which time a GSM shutdown might be
considered. The willingness of operators to commit
to refarming 900 MHz will in many cases hinge on
discussions at the EU level on the continuing legal
applicability of the GSM Directives. Based on recent
development, it now looks like the EU Parliament has
endorsed the refarming of GSM spectrum paving the
way for potential deployments of LTE into 900MHz.

IMT Extension Band

WRC-2000 identified three additional bands for
terrestrial IMT-2000 including 2500-2690 MHz. As a
result, starting in 2008, as much as 140 MHz of
IMT2000 FDD expansion spectrum will be allocated

27


in Europe; 2500-2570 MHz for uplink and 2620- 2690
MHz for downlink. Additionally up to 50 MHz (2570
MHz-2620 MHz) will be allocated as an unpaired
TDD band. As a globally common band plan, this
spectrum band will also enable economies of scale
and global roaming. It is likely that LTE will be
deployed in the FDD portion of this band due to its
benefits as compared to HSPA/ HSPA+. In addition,
this band is the only one of 2 bands that offers the
unique opportunity for the deploymentof LTE in
maximum spectrum bandwidth by providing channels
of up to 20 MHz. In that sense, it is largely expected
that current mobile operators will try and secure the
maximum 20 MHz allocation to provide themwith the
ability to support future mobile broadband capacity
requirement.

Other Candidate Bands

GSM 1800: Interest from Americas, Asia Pac and
some countries in EMEA, especially for the refarming
of existing GSM spectrum.

UMTS Core Band 2.1 GHz: This is the core 3-3.5G
band for EMEA, AsiaPac & LAC with deployments of
networks in over 150 countries. Most operators were
awarded 2, 3 and in some limited instances 4 x 5
MHz carriers in this spectrum band. Most operators
have so far only used one band, but with mobile data
growth and subscriber migration to UMTS/HSPA, it is
yet unclear if and how many carriers will be available
in that band for LTE services in 2010 - 2012.

28


PCS 1900: Alternative to core band, which is not
available in EMEA. Service providers may refarm this
spectrum after the new 700 MHz and AWS spectrum
is consumed.

Cellular 850: Refarm this spectrum after the new 700
MHz and AWS spectrum is consumed. Very popular
alternative in former Warsaw pact countries that
have joined NATO.

Future Spectrum Requirements

ITU (ITU-R M.2078) projects overall spectrum
requirements for the future development of IMT-2000
and for IMT-Advanced. The results assert that
additional spectrum demand of between 500 MHz
and 1 GHz will be needed in all ITU Regions by
2020. This report expresses traffic growth factors of
2 to 3 by 2010 for Europe compared to today. It is
clear that existing bands will not be enough for IMT
services approximately after the year 2015 and
additional bands are needed. In order to deliver a
true broadband experience, large blocks of spectrum
will need to be identified and allocated. One of the
goals of WRC-07 was to identify additional,
harmonized, worldwide spectrum, to enable global
roaming services while bringing economies of scale
to vendors. In this regard, WRC-07 identified the
450-470 MHz and 2300-2400 MHz bands for IMT
(which includes both IMT-2000 and IMT-Advanced)
on a global basis. In addition, WRC-07 identified
portions or all of 698-862 MHz and 3400-3600 MHz.
The identification and use of these bands varies from
region-to-region and country-to-country as detailed in

29


below. The Final Acts from WRC-07 provide full
details on these identifications. WC-07 made positive
steps towards making spectrum available for future
LTE deployments. In particular, WRC-07 began the
process of migrating broadcast spectrum in the 698-
806 MHz band to mobile applications. The next steps
will be working with individual countries to ensure
spectrum is recovered and licensed for mobile
systems at a national or regional level around the
world. In addition, achieving an internationally
harmonized band plan for use of the spectrum is also
important.

30


NETWORK EVOLUTION

In parallel with its
advanced new radio
interface, realising the
full potential of LTE
requires an evolution from today’s hybrid
packet/circuit switched networks to a simplified, all-IP
(Internet Protocol) environment. From an operator’s
point of view, the pay-off is reduced delivery costs for
rich, blended applications combining voice, video
and data services plus simplified interworking with
other fixed and wireless networks.
By creating new value-added service possibilities,
LTE promises
long-term
revenue stability
and growth for
around two
hundred mobile
operators that
are already
firmly committed
to the
UMTS/HSPA family of 3G systems. Just as

31


importantly, it provides a powerful tool to attract
customers who are provided with an increasing
number of technology options for broadband
connectivity on the move.
Based on the UMTS/HSPA family of standards, LTE
will enhance the capabilities of current cellular
network technologies to satisfy the needs of a highly
demanding customer accustomed to fixed broadband
services. As such, it unifies the voice-oriented
environment of today’s mobile networks with the
data-centric service possibilities of the fixed Internet.
Another key goal of the project is the harmonious
coexistence of LTE systems alongside legacy circuit
switched networks. This will allow operators to
introduce LTE’s all-IP concept progressively,
retaining the value and preserving the ROI of their
existing voice-based service platforms while
benefiting from the performance boost that LTE
delivers for data services. 3GPP proposed migrating
towards an all-IP core network as early as Release
4, hinting at what would become a prominent feature
of later UMTS/HSPA releases
and ultimately LTE.
The concept
of ‘Long Term
Evolution’ for
today’s
3G/UMTS
standard was
discussed in
detail in 2004,
when a RAN
(Radio Access
Network)

32


Evolution Workshop in Toronto accepted
contributions from more than 40 operators,
manufacturers and research institutes (including
3GPP members as well as non-member
organisations). Contributors offered a range of views
and proposals on the evolution of the UTRAN
(Universal Terrestrial Radio Access Network).
Following the
Toronto workshop,
in December 2004,
3GPP launched a
feasibility study in
order “to develop a
framework for the
evolution of the 3GPP radioaccess technology
towards a high-data-rate, low-latency and packet-
optimised radio -access technology”. In other words,
the study would map out specifications for a radio
access network (RAN) capable of supporting the
broadband Internet user experience we already
enjoy in today’s fixed networks – with the addition of
full mobility to enable exciting new service
possibilities.
Today, specifications for LTE are encapsulated in
3GPP Release 8, the newest set of standards that
defines the technical evolution of 3GPP mobile
network systems.
Release 8 succeeds the previous iteration of 3G
standards – Release 7 – that includes specifications
for HSPA+, the ‘missing link’ between HSPA and
LTE. Defined in 3GPP Releases 7 and 8, HSPA+
allows the introduction of a simpler, ‘flat’, IP-oriented
network architecture while bypassing many of the
legacy equipment requirements of UMTS/HSPA.

33


Peak data rates with HSPA+ are 28 Mbit/s on the
downlink and 11.5 Mbit/s on the uplink using 2x2
MIMO (Multiple-Input Multiple-Output) antenna
techniques and 16QAM (Quadrature Amplitude
Modulation). However, HSPA+ can further boost
data rates up to 42 Mbit/s on the downlink and 23
Mbit/s on the uplink using 2x2MIMO and 64QAM, a
combination that is part of Release 8.
As such, HSPA+ slots neatly between the already
impressive performance of HSPA (with its theoretical
downlink performance of up to 14.4 Mbit/s) and LTE
that promises rates of 300 Mbit/s in the downlink and
75 Mbit/s in the uplink forevery 20 MHz of paired
spectrum.

34


SERVICES

Through a
combination of
very high downlink
(and uplink)
transmission
speeds, more
flexible, efficient
use of spectrum
and reduced
packet latency, LTE promises to enhance the
delivery of mobile broadband services while adding
exciting new value-added service possibilities.
But what does this mean in terms of operator
revenues and subscriber growth in a market where
broadband connectivity is rapidly becoming
commoditised?
An overarching objective for LTE is the stabilisation
and reversal of steadily declining ARPU (Average
Revenue per User) that is characteristic of many
mobile markets.
A study conducted in 2007 for the UMTS Forum,
compared the services supported by today’s mobile
network technologies with the richer service
possibilities that LTE enables through higher
downlink speeds and reduced latency for packet-
based services.

35


For consumers, this
enriched user
experience will be
typified by the large-
scale streaming,
downloading and
sharing of video,
music and rich
multimedia content.
All these services will
need significantly
greater throughput to provide adequate quality of
service, particularly as users’ future expectations will
be increased by the growing popularity of other high-
bandwidth platforms like High Definition TV
transmission. For business customers it will mean
high-speed transfer of large files, high-quality
videoconferencing and secure nomadic access to
corporate networks.
Similarly, LTE brings the
characteristics of today’s ‘Web
2.0’ into the mobile space for
the first time. Alongside secure
e-commerce, this will span real-
time peer-topeer applications
like multiplayer gaming and file
sharing.

In addition, the study considered a distinct set of
services that do not have clear analogies in today’s
fixed network environment. These include ‘machine
to machine’ (M2M) applications and the large-scale
exchange of community based projects.

36


37


LTE ADVANCED

Being defined as a 3G technology LTE does not
meet the requirements for 4G also called IMT
Advanced as defined by the International
Telecommunication Union such as peak data rates
up to 1 Gbit/s. The ITU has invited the submission of
candidate Radio Interface Technologies (RITs)
following their requirements as mentioned in a
circular letter.

The mobile communication industry and
standardisation organisations have therefore started
to work on 4G access technologies such as LTE
Advanced. At a workshop in April 2008 in China
3GPP agreed the plans for future work on Long Term
Evolution (LTE) a first set of 3GPP requirements on
LTE Advanced has been approved in June 2008.
Besides the peak data rate 1 Gbit/s that fully
supports the 4G requirements as defined by the ITU-
R, it also targets faster switching between power
states and improved performance at the cell edge.
Detailed proposals are being studied within the
working groups.

38


Proposed Features:

Backward compatibility with LTE and 3gpp
legacy systems.
Peak data rate 1 Gbps DL and 500 Mbps UL.
BW about 70 MHz in DL and 40 MHz in UL.
C plane latency from Idle with IP address to
Connected less than 50 ms and U plane
latency shorter than 5 ms towards RAN,
taking into account 30% retransmissions
(FFS).
Cell edge throughput twice that of LTE.
3 times higher average user throughput than
LTE.
3 times more spectral efficient than LTE.
Support of scalable BW and spectrum
aggregation.
Peak spectrum efficiency 30 bps/Hz in DS and
15 bps/Hz in UL.

39


Technology proposals

The proposals could roughly be categorized into:

UE Dual TX antenna solutions for SU-MIMO
and diversity MIMO scalable system
bandwidth exceeding 20 MHz, potentially up
to 100MHz.
Local area optimization of air interface.
Nomadic / Local Area network and mobility
solutions.
Flexible Spectrum Usage.
Cognitive Radio.
Various concepts for Relay Nodes.
Automatic and autonomous network
configuration and operation.
Enhanced precoding and forward error
correction.
Interference management and suppression.
Asymmetric bandwidth assignment for FDD.
Hybrid OFDMA and SC-FDMA in uplink.
UL/DL inter eNB coordinated MIMO.

As can be seen most of the proposals address the
PHY layer.

40


Support of larger bandwidth in LTE Advanced

In 4G, bandwidths up to 100MHz are foreseen to
provide peak data rates up to 1 Gbps. In general
OFDM provides simple means to increase bandwidth
by adding additional subcarrier. Since Release 8
UE capabilities only support 20MHz bandwidth, the
scheduler must consider a mix of terminals. Due to a
fragmented spectrum the available bandwidth might
also be not contiguous. To ensure backward
compatibility to current LTE the control channels
such as synchronisation, broadcast or
PDCCH/PUCCH might be needed per 20MHz. Some
of the main challenges for 100 MHz terminals are:

Availability of RF filter for such an large
bandwidth and bandwidths of variable range
Availability of Analog Digital Converter with
such a high sampling rate and quantization
resolution
Increased decoding complexity e.g. for
channel decoding and increased soft buffer
size

Minimum changes to the specifications will be
required if Resource Allocation, MIMO, Link
Adaptation, HARQ etc are done per 20MHz. The
scheduler must operate across the bandwidth and
there will be a larger number of transport blocks per
transmission time interval. Currently the Frequency
Division Duplex (FDD) schemes as defined for LTE
in Release 8 are limited to operate in a fully
symmetric allocation of paired spectrum. This makes
it difficult to find suitable FDD spectrum allocations

41


and also cannot efficiently support asymmetric traffic.
For LTE Advanced more flexible bandwidth
allocations are currently being considered.

LTE Advanced will be standardised in the 3GPP
specification Release 10 and will be designed to
meet the 4G requirements as defined by ITU.
Amongst others 4G technologies must support
various bandwidth allocations up to 100MHz and
shall support peak data rates up to 1 Gbps for
stationary terminals. LTE Advanced, which is likely to
be the first true 4G technology, will be a smooth
evolution of the LTE standard will be based on same
principles. Work on the requirements is already
progressing in 3GPP while work on technology
proposals is expected to go on for some time within
the working groups. Several changes on the physical
layer can be expected to support larger bandwidths
with more flexible allocations and to make use of
further enhanced antenna technologies. Coordinated
base stations with coordinated scheduling,
coordinated MIMO or interference management and
suppression will also require changes on the network
architecture.

42


Strategic Marketing Perspective

Long Term Evolution has been, directly or
indirectly, about 14 years in the making when the
cellular industry decided to slowly, but surely,
abandon the circuit switched global title/ISDN/SS7
network (which had been around in one way or
another since the beginning of the 1940s) and
migrate to an all ip framework (GSM- GPRS-3G (incl.
HSPA)-SAE/LTE - 4G LTE Advanced).

A number of LTE promotional materials state that
LTE gives equivalent fixed line and better voice
service. This kind of positioning does injustice to
mobile communication technologies and generates
unrealistic expectations.

Mobile throughput
and quality will
never be able to
compete with
state of the art
fixed and should
not be positioned
to. Fixed
technology
propagates within
a controlled environment (ex. a wire) while mobile
technology (propagation based) is always challenged
by nature (propagation effects etc…). If LTE boasts
100 Mbps downlink and 50 Mbps uplink, fixed can
43


deliver via fiber 100Gbps symmetrical. If mobile
reaches 100 Gbps (which will require a good portion
of spectrum), then fixed will top 100 Tbps.

Mobile technologies should be marketed for the
benefit that they add, i.e. that they offer mobility with
an adequate infrastructure to accommodate the
required services with resilience and certainty.
Mobility is the key word and not Compare.

LTE goes a long way in offering mobility based
broadband services. In addition, the flattened
network will make it more manageable and less
expensive to maintain. The fact that it rests (finally)
on a common architecture/protocol (ip) implies that it
can eventually align its roadmaps with other ip based
systems, including an ip based fixed network
(implying an eventual technical convergence to a
common core network for fixed/mobile systems).

LTE does not go a long way in opening up the
network to accommodate third party initiatives, even
though the IMS subsystem will indeed provide APIs
to independent approved software developers. LTE
is still very much a telecom network and not an open
network as many from the other side of the fence
would’ve hoped. The fact that LTE is an IMS based
network (implying SIP based central core network
control) implies limited accommodation of peer
advancements and surrogate based technologies
which are emerging rapidly and accelerating the
evolution at the edge of the network.

44


Summary

Most operators will upgrade their packet core
network (SGSN, GGSN etc…) towards the
Evolved Packet Core functionality (initially this will
be a pure software upgrade but eventually, once
the CS functionality is totally removed, this will be
replaced by high capacity routing mechanisms).
These boxes will then be replaced by high
capacity high speed dumb ip routers and the
mobility intelligence will reside in servers. This
means that voice call handling (which will be ip
based) will be nothing more than another
software application and pcm based
communication will be, at least for mobile
technology, a thing of the past.

45

Long Term Evolution Lte Ebook

Related slideshows

More Related Content

Long Term Evolution Lte Ebook