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3G LTE Tutorial - 3GPP Long TermEvolution- developed by 3GPP,
LTE, Long Term Evolution is the successor to 3G UMTSand HSPA
providing much higher data download speeds and setting
thefoundations for 4G LTE Advanced..LTE, Long Term Evolution, the
successor to UMTS and HSPA is now being deployed and is theway
forwards for high speed cellular services.In its first forms it is
a 3G or as some would call it a 3.99G technology, but with further
additionsthe technology can be migrated to a full 4G standard and
here it is known as LTE Advanced.There has been a rapid increase in
the use of data carried by cellular services, and this increasewill
only become larger in what has been termed the "data explosion". To
cater for this and theincreased demands for increased data
transmission speeds and lower latency, furtherdevelopment of
cellular technology have been required.The UMTS cellular technology
upgrade has been dubbed LTE - Long Term Evolution. The ideais that
3G LTE will enable much higher speeds to be achieved along with
much lower packetlatency (a growing requirement for many services
these days), and that 3GPP LTE will enablecellular communications
services to move forward to meet the needs for cellular technology
to2017 and well beyond.Many operators have not yet upgraded their
basic 3G networks, and 3GPP LTE is seen as thenext logical step for
many operators, who will leapfrog straight from basic 3G straight
to LTE asthis will avoid providing several stages of upgrade. The
use of LTE will also provide the datacapabilities that will be
required for many years and until the full launch of the full 4G
standardsknown as LTE Advanced.3G LTE evolutionAlthough there are
major step changes between LTE and its 3G predecessors, it is
neverthelesslooked upon as an evolution of the UMTS / 3GPP 3G
standards. Although it uses a differentform of radio interface,
using OFDMA / SC-FDMA instead of CDMA, there are manysimilarities
with the earlier forms of 3G architecture and there is scope for
much re-use.In determining what is LTE and how does it differ from
other cellular systems, a quick look atthe specifications for the
system can provide many answers. LTE can be seen for provide
afurther evolution of functionality, increased speeds and general
improved performance.
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In addition to this, LTE is an all IP based network, supporting
both IPv4 and IPv6. Originallythere was also no basic provision for
voice, although Voice over LTE, VoLTE was added waschosen by GSMA
as the standard for this. In the interim, techniques including
circuit switchedfallback, CSFB are expected to be usedWhat is LTE?
- specification overviewIt is worth summarizing the key parameters
of the 3G LTE specification. In view of the fact thatthere are a
number of differences between the operation of the uplink and
downlink, thesenaturally differ in the performance they can
offer.
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These highlight specifications give an overall view of the
performance that LTE will offer. Itmeets the requirements of
industry for high data download speeds as well as reduced latency -
afactor important for many applications from VoIP to gaming and
interactive use of data. It alsoprovides significant improvements
in the use of the available spectrum.What are the main LTE
technologies?LTE has introduced a number of new technologies when
compared to the previous cellularsystems. They enable LTE to be
able to operate more efficiently with respect to the use
ofspectrum, and also to provide the much higher data rates that are
being required.
OFDM (Orthogonal Frequency Division Multiplex): OFDM technology
has been incorporatedinto LTE because it enables high data
bandwidths to be transmitted efficiently while stillproviding a
high degree of resilience to reflections and interference. The
access schemes differbetween the uplink and downlink: OFDMA
(Orthogonal Frequency Division Multiple Access isused in the
downlink; while SC-FDMA(Single Carrier - Frequency Division
Multiple Access) is usedin the uplink. SC-FDMA is used in view of
the fact that its peak to average power ratio is smalland the more
constant power enables high RF power amplifier efficiency in the
mobile handsets
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- an important factor for battery power equipment. Read more
about LTE OFDM / OFDMA /SCFMDA
MIMO (Multiple Input Multiple Output): One of the main problems
that previoustelecommunications systems has encountered is that of
multiple signals arising from the manyreflections that are
encountered. By using MIMO, these additional signal paths can be
used toadvantage and are able to be used to increase the
throughput.
When using MIMO, it is necessary to use multiple antennas to
enable the different paths to bedistinguished. Accordingly schemes
using 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used.While it
is relatively easy to add further antennas to a base station, the
same is not true ofmobile handsets, where the dimensions of the
user equipment limit the number of antennaswhich should be place at
least a half wavelength apart. Read more about LTE MIMO
SAE (System Architecture Evolution): With the very high data
rate and low latencyrequirements for 3G LTE, it is necessary to
evolve the system architecture to enable theimproved performance to
be achieved. One change is that a number of the functions
previouslyhandled by the core network have been transferred out to
the periphery. Essentially thisprovides a much "flatter" form of
network architecture. In this way latency times can bereduced and
data can be routed more directly to its destination. Read more
about LTE SAE
A fuller description of what LTE is and the how the associated
technologies work is alladdressed in much greater detail in the
following pages of this tutorial.
LTE OFDM, OFDMA and SC-FDMA- overview, information, tutorial
about the basics of LTE OFDM, OFDMA andSC-FDMA including cyclic
prefix, CP.One of the key elements of LTE is the use of OFDM
(Orthogonal Frequency Division Multiplex)as the signal bearer and
the associated access schemes, OFDMA (Orthogonal FrequencyDivision
Multiplex) and SC-FDMA (Single Frequency Division Multiple
Access).OFDM is used in a number of other of systems from WLAN,
WiMAX to broadcast technologiesincluding DVB and DAB. OFDM has many
advantages including its robustness to multipathfading and
interference. In addition to this, even though, it may appear to be
a particularlycomplicated form of modulation, it lends itself to
digital signal processing techniques.In view of its advantages, the
use of ODFM and the associated access technologies, OFDMA
andSC-FDMA are natural choices for the new LTE cellular
standard.OFDM basicsThe use of OFDM is a natural choice for LTE.
While the basic concepts of OFDM are used, ithas naturally been
tailored to meet the exact requirements for LTE. However its use of
multiplecarrier each carrying a low data rate remains the same.
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Note on OFDM:Orthogonal Frequency Division Multiplex (OFDM) is a
form of transmission that uses a largenumber of close spaced
carriers that are modulated with low rate data. Normally these
signalswould be expected to interfere with each other, but by
making the signals orthogonal to eachother there is no mutual
interference. The data to be transmitted is split across all the
carriers togive resilience against selective fading from multi-path
effects..Click on the link for an OFDM tutorialThe actual
implementation of the technology will be different between the
downlink (i.e. frombase station to mobile) and the uplink (i.e.
mobile to the base station) as a result of the
differentrequirements between the two directions and the equipment
at either end. However OFDM waschosen as the signal bearer format
because it is very resilient to interference. Also in recent yearsa
considerable level of experience has been gained in its use from
the various forms ofbroadcasting that use it along with Wi-Fi and
WiMAX. OFDM is also a modulation format thatis very suitable for
carrying high data rates - one of the key requirements for LTE.In
addition to this, OFDM can be used in both FDD and TDD formats.
This becomes anadditional advantage.LTE channel bandwidths and
characteristicsOne of the key parameters associated with the use of
OFDM within LTE is the choice ofbandwidth. The available bandwidth
influences a variety of decisions including the number ofcarriers
that can be accommodated in the OFDM signal and in turn this
influences elementsincluding the symbol length and so forth.LTE
defines a number of channel bandwidths. Obviously the greater the
bandwidth, the greaterthe channel capacity.The channel bandwidths
that have been chosen for LTE are:
1. 1.4 MHz2. 3 MHz3. 5 MHz4. 10 MHz5. 15 MHz6. 20 MHz
In addition to this the subcarriers are spaced 15 kHz apart from
each other. To maintainorthogonality, this gives a symbol rate of 1
/ 15 kHz = of 66.7 s.Each subcarrier is able to carry data at a
maximum rate of 15 ksps (kilosymbols per second).This gives a 20
MHz bandwidth system a raw symbol rate of 18 Msps. In turn this is
able toprovide a raw data rate of 108 Mbps as each symbol using
64QAM is able to represent six bits.
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It may appear that these rates do not align with the headline
figures given in the LTEspecifications. The reason for this is that
actual peak data rates are derived by first subtractingthe coding
and control overheads. Then there are gains arising from elements
such as the spatialmultiplexing, etc.LTE OFDM cyclic prefix, CPOne
of the primary reasons for using OFDM as a modulation format within
LTE (and manyother wireless systems for that matter) is its
resilience to multipath delays and spread. However itis still
necessary to implement methods of adding resilience to the system.
This helps overcomethe inter-symbol interference (ISI) that results
from this.In areas where inter-symbol interference is expected, it
can be avoided by inserting a guardperiod into the timing at the
beginning of each data symbol. It is then possible to copy a
sectionfrom the end of the symbol to the beginning. This is known
as the cyclic prefix, CP. The receivercan then sample the waveform
at the optimum time and avoid any inter-symbol interferencecaused
by reflections that are delayed by times up to the length of the
cyclic prefix, CP.The length of the cyclic prefix, CP is important.
If it is not long enough then it will notcounteract the multipath
reflection delay spread. If it is too long, then it will reduce the
datathroughput capacity. For LTE, the standard length of the cyclic
prefix has been chosen to be 4.69s. This enables the system to
accommodate path variations of up to 1.4 km. With the symbollength
in LTE set to 66.7 s.The symbol length is defined by the fact that
for OFDM systems the symbol length is equal tothe reciprocal of the
carrier spacing so that orthogonality is achieved. With a carrier
spacing of15 kHz, this gives the symbol length of 66.7 s.LTE OFDMA
in the downlinkThe OFDM signal used in LTE comprises a maximum of
2048 different sub-carriers having aspacing of 15 kHz. Although it
is mandatory for the mobiles to have capability to be able
toreceive all 2048 sub-carriers, not all need to be transmitted by
the base station which only needsto be able to support the
transmission of 72 sub-carriers. In this way all mobiles will be
able totalk to any base station.Within the OFDM signal it is
possible to choose between three types of modulation:
1. QPSK (= 4QAM) 2 bits per symbol2. 16QAM 4 bits per symbol3.
64QAM 6 bits per symbol
The exact format is chosen depending upon the prevailing
conditions. The lower forms ofmodulation, (QPSK) do not require
such a large signal to noise ratio but are not able to send thedata
as fast. Only when there is a sufficient signal to noise ratio can
the higher order modulationformat be used.
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Downlink carriers and resource blocksIn the downlink, the
subcarriers are split into resource blocks. This enables the system
to be ableto compartmentalise the data across standard numbers of
subcarriers.Resource blocks comprise 12 subcarriers, regardless of
the overall LTE signal bandwidth. Theyalso cover one slot in the
time frame. This means that different LTE signal bandwidths will
havedifferent numbers of resource blocks.
LTE SC-FDMA in the uplinkFor the LTE uplink, a different concept
is used for the access technique. Although still using aform of
OFDMA technology, the implementation is called Single Carrier
Frequency DivisionMultiple Access (SC-FDMA).One of the key
parameters that affects all mobiles is that of battery life. Even
though batteryperformance is improving all the time, it is still
necessary to ensure that the mobiles use as littlebattery power as
possible. With the RF power amplifier that transmits the radio
frequency signalvia the antenna to the base station being the
highest power item within the mobile, it is necessarythat it
operates in as efficient mode as possible. This can be
significantly affected by the form ofradio frequency modulation and
signal format. Signals that have a high peak to average ratio
andrequire linear amplification do not lend themselves to the use
of efficient RF power amplifiers.As a result it is necessary to
employ a mode of transmission that has as near a constant
powerlevel when operating. Unfortunately OFDM has a high peak to
average ratio. While this is not aproblem for the base station
where power is not a particular problem, it is unacceptable for
themobile. As a result, LTE uses a modulation scheme known as
SC-FDMA - Single CarrierFrequency Division Multiplex which is a
hybrid format. This combines the low peak to averageratio offered
by single-carrier systems with the multipath interference
resilience and flexiblesubcarrier frequency allocation that OFDM
provides.
LTE MIMO: Multiple Input Multiple OutputTutorial- MIMO is used
within LTE to provide better signal performance and / or higherdata
rates by the use of the radio path reflections that exist.
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MIMO, Multiple Input Multiple Output is another of the LTE major
technology innovations usedto improve the performance of the
system. This technology provides LTE with the ability tofurther
improve its data throughput and spectral efficiency above that
obtained by the use ofOFDM.Although MIMO adds complexity to the
system in terms of processing and the number ofantennas required,
it enables far high data rates to be achieved along with much
improvedspectral efficiency. As a result, MIMO has been included as
an integral part of LTE.LTE MIMO basicsThe basic concept of MIMO
utilises the multipath signal propagation that is present in
allterrestrial communications. Rather than providing interference,
these paths can be used toadvantage.Note on MIMO:Two major
limitations in communications channels can be multipath
interference, and the datathroughput limitations as a result of
Shannon's Law. MIMO provides a way of utilising themultiple signal
paths that exist between a transmitter and receiver to
significantly improve thedata throughput available on a given
channel with its defined bandwidth. By using multipleantennas at
the transmitter and receiver along with some complex digital signal
processing,MIMO technology enables the system to set up multiple
data streams on the same channel,thereby increasing the data
capacity of a channel.Click on the link for a MIMO tutorialMIMO is
being used increasingly in many high data rate technologies
including Wi-Fi and otherwireless and cellular technologies to
provide improved levels of efficiency. Essentially MIMOemploys
multiple antennas on the receiver and transmitter to utilise the
multi-path effects thatalways exist to transmit additional data,
rather than causing interference.The schemes employed in LTE again
vary slightly between the uplink and downlink. The reasonfor this
is to keep the terminal cost low as there are far more terminals
than base stations and as aresult terminal works cost price is far
more sensitive.For the downlink, a configuration of two transmit
antennas at the base station and two receiveantennas on the mobile
terminal is used as baseline, although configurations with four
antennasare also being considered.For the uplink from the mobile
terminal to the base station, a scheme called MU-MIMO (Multi-User
MIMO) is to be employed. Using this, even though the base station
requires multipleantennas, the mobiles only have one transmit
antenna and this considerably reduces the cost ofthe mobile. In
operation, multiple mobile terminals may transmit simultaneously on
the samechannel or channels, but they do not cause interference to
each other because mutually
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orthogonal pilot patterns are used. This techniques is also
referred to as spatial domain multipleaccess (SDMA).
LTE FDD, TDD, TD-LTE Duplex Schemes- information, overview, or
tutorial about the LTE TDD and LTE FDD duplexschemes used with LTE
and including TD-LTE.LTE has been defined to accommodate both
paired spectrum for Frequency Division Duplex,FDD and unpaired
spectrum for Time Division Duplex, TDD operation. It is anticipated
thatboth LTE TDD and LTE FDD will be widely deployed as each form
of the LTE standard has itsown advantages and disadvantages and
decisions can be made about which format to adoptdependent upon the
particular application.LTE FDD using the paired spectrum is
anticipated to form the migration path for the current 3Gservices
being used around the globe, most of which use FDD paired spectrum.
However therehas been an additional emphasis on including TDD LTE
using unpaired spectrum. TDD LTEwhich is also known as TD-LTE is
seen as providing the evolution or upgrade path for TD-SCDMA.In
view of the increased level of importance being placed upon LTE TDD
or TD-LTE, it isplanned that user equipments will be designed to
accommodate both FDD and TDD modes. WithTDD having an increased
level of importance placed upon it, it means that TDD operations
willbe able to benefit from the economies of scale that were
previously only open to FDDoperations.Duplex schemesIt is essential
that any cellular communications system must be able to transmit in
both directionssimultaneously. This enables conversations to be
made, with either end being able to talk andlisten as required.
Additionally when exchanging data it is necessary to be able to
undertakevirtually simultaneous or completely simultaneous
communications in both directions.It is necessary to be able to
specify the different direction of transmission so that it is
possible toeasily identify in which direction the transmission is
being made. There are a variety ofdifferences between the two links
ranging from the amount of data carried to the transmissionformat,
and the channels implemented. The two links are defined:
Uplink: the transmission from the UE or user equipment to the
eNodeB or base station. Downlink the transmission from the eNodeB
or base station to the UE or user equipment.
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Uplink and downlink transmission directions
In order to be able to be able to transmit in both directions, a
user equipment or base station musthave a duplex scheme. There are
two forms of duplex that are commonly used, namely FDD,frequency
division duplex and TDD time division duplex..Note on TDD and FDD
duplex schemes:In order for radio communications systems to be able
to communicate in both directions it isnecessary to have what is
termed a duplex scheme. A duplex scheme provides a way oforganizing
the transmitter and receiver so that they can transmit and receive.
There are severalmethods that can be adopted. For applications
including wireless and cellulartelecommunications, where it is
required that the transmitter and receiver are able to
operatesimultaneously, two schemes are in use. One known as FDD or
frequency division duplex usestwo channels, one for transmit and
the other for receiver. Another scheme known as TDD, timedivision
duplex uses one frequency, but allocates different time slots for
transmission andreception.Click on the link for more information on
TDD FDD duplex schemesBoth FDD and TDD have their own advantages
and disadvantages. Accordingly they may beused for different
applications, or where the bias of the communications is
different.
Advantages / disadvantages of LTE TDD and LTE FDD for
cellularcommunicationsThere are a number of the advantages and
disadvantages of TDD and FDD that are of particularinterest to
mobile or cellular telecommunications operators. These are
naturally reflected intoLTE.
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LTE TDD / TD-LTE and TD-SCDMAApart from the technical reasons
and advantages for using LTE TDD / TD-LTE, there are marketdrivers
as well. With TD-SCDMA now well established in China, there needs
to be a 3.9G andlater a 4G successor to the technology. With
unpaired spectrum allocated for TD-SCDMA aswell as UMTS TDD, it is
natural to see many operators wanting an upgrade path for
theirtechnologies to benefit from the vastly increased speeds and
improved facilities of LTE.Accordingly there is a considerable
interest in the development of LTE TDD, which is alsoknown in China
as TD-LTE.With the considerable interest from the supporters of
TD-SCDMA, a number of features to makethe mode of operation of
TD-LTE more of an upgrade path for TD-SCDMA have beenincorporated.
One example of this is the subframe structure that has been adopted
within LTETDD / TD-LTE.While both LTE TDD (TD-LTE) and LTE FDD will
be widely used, it is anticipated that LTEFDD will be the more
widespread, although LTE TDD has a number of significant
advantages,especially in terms of higher spectrum efficiency that
can be used by many operators. It is alsoanticipated that phones
will be able to operate using either the LTE FDD or LTE-TDD
(TD-LTE) modes. In this way the LTE UEs or user equipments will be
dual standard phones, and able
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to operate in countries regardless of the flavour of LTE that is
used - the main problem will thenbe the frequency bands that the
phone can cover.
LTE Frame and Subframe Structure- information, overview, or
tutorial about the LTE frame and subframe structureincluding LTE
Type 1 and LTE Type 2 frames.In order that the 3G LTE system can
maintain synchronisation and the system is able to managethe
different types of information that need to be carried between the
base-station or eNodeB andthe User Equipment, UE, 3G LTE system has
a defined LTE frame and subframe structure forthe E-UTRA or Evolved
UMTS Terrestrial Radio Access, i.e. the air interface for 3G
LTE.The frame structures for LTE differ between the Time Division
Duplex, TDD and the FrequencyDivision Duplex, FDD modes as there
are different requirements on segregating the transmitteddata.There
are two types of LTE frame structure:
1. Type 1: used for the LTE FDD mode systems.2. Type 2: used for
the LTE TDD systems.
Type 1 LTE Frame StructureThe basic type 1 LTE frame has an
overall length of 10 ms. This is then divided into a total of
20individual slots. LTE Subframes then consist of two slots - in
other words there are ten LTEsubframes within a frame.
Type 1 LTE Frame Structure
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Type 2 LTE Frame StructureThe frame structure for the type 2
frames used on LTE TDD is somewhat different. The 10 msframe
comprises two half frames, each 5 ms long. The LTE half-frames are
further split into fivesubframes, each 1ms long.
Type 2 LTE Frame Structure(shown for 5ms switch point
periodicity).
The subframes may be divided into standard subframes of special
subframes. The specialsubframes consist of three fields;
DwPTS - Downlink Pilot Time Slot GP - Guard Period UpPTS -
Uplink Pilot Time Stot.
These three fields are also used within TD-SCDMA and they have
been carried over into LTETDD (TD-LTE) and thereby help the upgrade
path. The fields are individually configurable interms of length,
although the total length of all three together must be 1ms.LTE TDD
/ TD-LTE subframe allocationsOne of the advantages of using LTE TDD
is that it is possible to dynamically change the up anddownlink
balance and characteristics to meet the load conditions. In order
that this can beachieved in an ordered fashion, a number of
standard configurations have been set within theLTE standards.A
total of seven up / downlink configurations have been set, and
these use either 5 ms or 10 msswitch periodicities. In the case of
the 5ms switch point periodicity, a special subframe exists inboth
half frames. In the case of the 10 ms periodicity, the special
subframe exists in the first halfframe only. It can be seen from
the table below that the subframes 0 and 5 as well as DwPTS
arealways reserved for the downlink. It can also be seen that UpPTS
and the subframe immediatelyfollowing the special subframe are
always reserved for the uplink transmission.
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Where:D is a subframe for downlink transmissionS is a "special"
subframe used for a guard timeU is a subframe for uplink
transmission
Uplink / Downlink subframe configurations for LTE TDD
(TD-LTE)
LTE Physical, Logical and TransportChannels- overview,
information, tutorial about the physical, logical, control
andtransport channels used within 3GPP, 3G LTE and the LTE channel
mapping.In order that data can be transported across the LTE radio
interface, various "channels" are used.These are used to segregate
the different types of data and allow them to be transported
acrossthe radio access network in an orderly fashion.Effectively
the different channels provide interfaces to the higher layers
within the LTE protocolstructure and enable an orderly and defined
segregation of the data.3G LTE channel typesThere are three
categories into which the various data channels may be grouped.
Physical channels: These are transmission channels that carry
user data and control messages. Transport channels: The physical
layer transport channels offer information transfer to
Medium Access Control (MAC) and higher layers. Logical channels:
Provide services for the Medium Access Control (MAC) layer within
the LTE
protocol structure.
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3G LTE physical channelsThe LTE physical channels vary between
the uplink and the downlink as each has differentrequirements and
operates in a different manner.
Downlink:o Physical Broadcast Channel (PBCH): This physical
channel carries system information
for UEs requiring to access the network. It only carries what is
termed MasterInformation Block, MIB, messages. The modulation
scheme is always QPSK and theinformation bits are coded and rate
matched - the bits are then scrambled using ascrambling sequence
specific to the cell to prevent confusion with data from other
cells.
The MIB message on the PBCH is mapped onto the central 72
subcarriers or six centralresource blocks regardless of the overall
system bandwidth. A PBCH message isrepeated every 40 ms, i.e. one
TTI of PBCH includes four radio frames.
The PBCH transmissions has 14 information bits, 10 spare bits,
and 16 CRC bits.o Physical Control Format Indicator Channel
(PCFICH) : As the name implies the PCFICH
informs the UE about the format of the signal being received. It
indicates the number ofOFDM symbols used for the PDCCHs, whether 1,
2, or 3. The information within thePCFICH is essential because the
UE does not have prior information about the size of thecontrol
region.
A PCFICH is transmitted on the first symbol of every sub-frame
and carries a ControlFormat Indicator, CFI, field. The CFI contains
a 32 bit code word that represents 1, 2, or3. CFI 4 is reserved for
possible future use.
The PCFICH uses 32,2 block coding which results in a 1/16 coding
rate, and it alwaysuses QPSK modulation to ensure robust
reception.
o Physical Downlink Control Channel (PDCCH) : The main purpose
of this physicalchannel is to carry mainly scheduling information
of different types:
Downlink resource scheduling Uplink power control instructions
Uplink resource grant Indication for paging or system
information
The PDCCH contains a message known as the Downlink Control
Information, DCI whichcarries the control information for a
particular UE or group of UEs. The DCI format hasseveral different
types which are defined with different sizes. The different format
typesinclude: Type 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A, and
4.
o Physical Hybrid ARQ Indicator Channel (PHICH) : As the name
implies, this channel isused to report the Hybrid ARQ status. It
carries the HARQ ACK/NACK signal indicatingwhether a transport
block has been correctly received. The HARQ indicator is 1 bit long
-"0" indicates ACK, and "1" indicates NACK.
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The PHICH is transmitted within the control region of the
subframe and is typically onlytransmitted within the first symbol.
If the radio link is poor, then the PHICH is extendedto a number
symbols for robustness.
Uplink:o Physical Uplink Control Channel (PUCCH) : The Physical
Uplink Control Channel, PUCCH
provides the various control signalling requirements. There are
a number of differentPUCCH formats defined to enable the channel to
carry the required information in themost efficient format for the
particular scenario encountered. It includes the ability tocarry
SRs, Scheduling Requests.
The basic formats are summarised below:
o Physical Uplink Shared Channel (PUSCH) : This physical channel
found on the LTE
uplink is the Uplink counterpart of PDSCHo Physical Random
Access Channel (PRACH) : This uplink physical channel is used
for
random access functions. This is the only non-synchronised
transmission that the UE canmake within LTE. The downlink and
uplink propagation delays are unknown whenPRACH is used and
therefore it cannot be synchronised.
The PRACH instance is made up from two sequences: a cyclic
prefix and a guard period.The preamble sequence may be repeated to
enable the eNodeB to decode thepreamble when link conditions are
poor.
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LTE transport channelsThe LTE transport channels vary between
the uplink and the downlink as each has differentrequirements and
operates in a different manner. Physical layer transport channels
offerinformation transfer to medium access control (MAC) and higher
layers.
Downlink:o Broadcast Channel (BCH) : The LTE transport channel
maps to Broadcast Control
Channel (BCCH)o Downlink Shared Channel (DL-SCH) : This
transport channel is the main channel for
downlink data transfer. It is used by many logical channels.o
Paging Channel (PCH) : To convey the PCCHo Multicast Channel (MCH)
: This transport channel is used to transmit MCCH
information to set up multicast transmissions.
Uplink:o Uplink Shared Channel (UL-SCH) : This transport channel
is the main channel for uplink
data transfer. It is used by many logical channels.o Random
Access Channel (RACH) : This is used for random access
requirements.
LTE logical channelsThe logical channels cover the data carried
over the radio interface. The Service Access Point,SAP between MAC
sublayer and the RLC sublayer provides the logical channel.
Control channels: these LTE control channels carry the control
plane information:o Broadcast Control Channel (BCCH) : This control
channel provides system information
to all mobile terminals connected to the eNodeB.o Paging Control
Channel (PCCH) : This control channel is used for paging
information
when searching a unit on a network.o Common Control Channel
(CCCH) : This channel is used for random access information,
e.g. for actions including setting up a connection.o Multicast
Control Channel (MCCH) : This control channel is used for
Information
needed for multicast reception.o Dedicated Control Channel
(DCCH) : This control channel is used for carrying user-
specific control information, e.g. for controlling actions
including power control,handover, etc.
Traffic channels:These LTE traffic channels carry the user-plane
data:o Dedicated Traffic Channel (DTCH) : This traffic channel is
used for the transmission of
user data.
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o Multicast Traffic Channel (MTCH) : This channel is used for
the transmission ofmulticast data.
It will be seen that many of the LTE channels bear similarities
to those sued in previousgenerations of mobile
telecommunications.
LTE Frequency Bands & SpectrumAllocations- a summary and
tables of the LTE frequency band spectrum allocations for 3G&
4G LTE - TDD and FDD.There is a growing number of LTE frequency
bands that are being designated as possibilities for use withLTE.
Many of the LTE frequency bands are already in use for other
cellular systems, whereas other LTEbands are new and being
introduced as other users are re-allocated spectrum elsewhere.
FDD and TDD LTE frequency bandsFDD spectrum requires pair bands,
one of the uplink and one for the downlink, and TDDrequires a
single band as uplink and downlink are on the same frequency but
time separated. As aresult, there are different LTE band
allocations for TDD and FDD. In some cases these bandsmay overlap,
and it is therefore feasible, although unlikely that both TDD and
FDDtransmissions could be present on a particular LTE frequency
band.The greater likelihood is that a single UE or mobile will need
to detect whether a TDD or FDDtransmission should be made on a
given band. UEs that roam may encounter both types on thesame band.
They will therefore need to detect what type of transmission is
being made on thatparticular LTE band in its current location.The
different LTE frequency allocations or LTE frequency bands are
allocated numbers.Currently the LTE bands between 1 & 22 are
for paired spectrum, i.e. FDD, and LTE bandsbetween 33 & 41 are
for unpaired spectrum, i.e. TDD.
LTE frequency band definitions
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FDD LTE frequency band allocationsThere is a large number of
allocations or radio spectrum that has been reserved for
FDD,frequency division duplex, LTE use.The FDDLTE frequency bands
are paired to allow simultaneous transmission on twofrequencies.
The bands also have a sufficient separation to enable the
transmitted signals not tounduly impair the receiver performance.
If the signals are too close then the receiver may be"blocked" and
the sensitivity impaired. The separation must be sufficient to
enable the roll-off ofthe antenna filtering to give sufficient
attenuation of the transmitted signal within the receiveband.
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TDD LTE frequency band allocationsWith the interest in TDD LTE,
there are several unpaired frequency allocations that are
beingprepared for LTR TDD use. The TDD LTE allocations are unpaired
because the uplink anddownlink share the same frequency, being time
multiplexed.
There are regular additions to the LTE frequency bands / LTE
spectrum allocations as a result ofnegotiations at the ITU
regulatory meetings. These LTE allocations are resulting in part
from thedigital dividend, and also from the pressure caused by the
ever growing need for mobilecommunications. Many of the new LTE
spectrum allocations are relatively small, often 10 -20MHz in
bandwidth, and this is a cause for concern. With LTE-Advanced
needing bandwidthsof 100 MHz, channel aggregation over a wide set
of frequencies many be needed, and this hasbeen recognised as a
significant technological problem. . . . . . . . .Additional
information on LTE frequency bands.
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LTE UE Category and Class Definitions- LTE utilises UE or User
Equipment categories or classes to define theperformance
specifications an enable base stations to be able to
communicateeffectively with them knowing their performance
levels.In the same way that a variety of other systems adopted
different categories for the handsets oruser equipments, so too
there are 3G LTE UE categories. These LTE categories define
thestandards to which a particular handset, dongle or other
equipment will operate.LTE UE category rationaleThe LTE UE
categories or UE classes are needed to ensure that the base
station, or eNodeB,eNB can communicate correctly with the user
equipment. By relaying the LTE UE categoryinformation to the base
station, it is able to determine the performance of the UE
andcommunicate with it accordingly.As the LTE category defines the
overall performance and the capabilities of the UE, it is
possiblefor the eNB to communicate using capabilities that it knows
the UE possesses. Accordingly theeNB will not communicate beyond
the performance of the UE.LTE UE category definitionsthere are five
different LTE UE categories that are defined. As can be seen in the
table below, thedifferent LTE UE categories have a wide range in
the supported parameters and performance.LTE category 1, for
example does not support MIMO, but LTE UE category five supports
4x4MIMO.It is also worth noting that UE class 1 does not offer the
performance offered by that of thehighest performance HSPA
category. Additionally all LTE UE categories are capable
ofreceiving transmissions from up to four antenna ports.A summary
of the different LTE UE category parameters provided by the 3GPP
Rel 8 standard isgiven in the tables below.
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LTE UE category summaryIn the same way that category information
is used for virtually all cellular systems from GPRSonwards, so the
LTE UE category information is of great importance. While users may
not beparticularly aware of the category of their UE, it will match
the performance an allow the eNB tocommunicate effectively with all
the UEs that are connected to it.
LTE SAE System Architecture Evolution- information, overview, or
tutorial about the basics of the 3G LTE SAE, systemarchitecture
evolution and the LTE Network
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Along with 3G LTE - Long Term Evolution that applies more to the
radio access technology ofthe cellular telecommunications system,
there is also an evolution of the core network. Known asSAE -
System Architecture Evolution. This new architecture has been
developed to provide aconsiderably higher level of performance that
is in line with the requirements of LTE.As a result it is
anticipated that operators will commence introducing hardware
conforming to thenew System Architecture Evolution standards so
that the anticipated data levels can be handledwhen 3G LTE is
introduced.The new SAE, System Architecture Evolution has also been
developed so that it is fullycompatible with LTE Advanced, the new
4G technology. Therefore when LTE Advanced isintroduced, the
network will be able to handle the further data increases with
little change.Reason for SAE System Architecture EvolutionThe SAE
System Architecture Evolution offers many advantages over previous
topologies andsystems used for cellular core networks. As a result
it is anticipated that it will be wide adoptedby the cellular
operators.SAE System Architecture Evolution will offer a number of
key advantages:
1. Improved data capacity: With 3G LTE offering data download
rates of 100 Mbps, and the focusof the system being on mobile
broadband, it will be necessary for the network to be able tohandle
much greater levels of data. To achieve this it is necessary to
adopt a system architecturethat lends itself to much grater levels
of data transfer.
2. All IP architecture: When 3G was first developed, voice was
still carried as circuit switcheddata. Since then there has been a
relentless move to IP data. Accordingly the new SAE,
SystemArchitecture Evolution schemes have adopted an all IP network
configuration.
3. Reduced latency: With increased levels of interaction being
required and much fasterresponses, the new SAE concepts have been
evolved to ensure that the levels of latency havebeen reduced to
around 10 ms. This will ensure that applications using 3G LTE will
be sufficientlyresponsive.
4. Reduced OPEX and CAPEX: A key element for any operator is to
reduce costs. It is thereforeessential that any new design reduces
both the capital expenditure (CAPEX)and the operationalexpenditure
(OPEX). The new flat architecture used for SAE System Architecture
Evolutionmeans that only two node types are used. In addition to
this a high level of automaticconfiguration is introduced and this
reduces the set-up and commissioning time.
SAE System Architecture Evolution basicsThe new SAE network is
based upon the GSM / WCDMA core networks to enable
simplifiedoperations and easy deployment. Despite this, the SAE
network brings in some major changes,and allows far more efficient
and effect transfer of data.There are several common principles
used in the development of the LTE SAE network:
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a common gateway node and anchor point for all technologies. an
optimised architecture for the user plane with only two node types.
an all IP based system with IP based protocols used on all
interfaces. a split in the control / user plane between the MME,
mobility management entity and the
gateway. a radio access network / core network functional split
similar to that used on WCDMA / HSPA. integration of non-3GPP
access technologies (e.g. cdma2000, WiMAX, etc) using client as
well as
network based mobile-IP.
The main element of the LTE SAE network is what is termed the
Evolved Packet Core or EPC.This connects to the eNodeBs as shown in
the diagram below.
LTE SAE Evolved Packet Core
As seen within the diagram, the LTE SAE Evolved Packet Core, EPC
consists of four mainelements as listed below:
Mobility Management Entity, MME: The MME is the main control
node for the LTE SAE accessnetwork, handling a number of
features:
o Idle mode UE trackingo Bearer activation / de-activationo
Choice of SGW for a UEo Intra-LTE handover involving core network
node locationo Interacting with HSS to authenticate user on
attachment and implements roaming
restrictionso It acts as a termination for the Non-Access
Stratum (NAS)o Provides temporary identities for UEso The SAE MME
acts the termination point for ciphering protection for NAS
signaling. As
part of this it also handles the security key management.
Accordingly the MME is thepoint at which lawful interception of
signalling may be made.
o Paging procedureo The S3 interface terminates in the MME
thereby providing the control plane function for
mobility between LTE and 2G/3G access networks.o The SAE MME
also terminates the S6a interface for the home HSS for roaming
UEs.
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It can therefore be seen that the SAE MME provides a
considerable level of overall controlfunctionality.
Serving Gateway, SGW: The Serving Gateway, SGW, is a data plane
element within the LTESAE. Its main purpose is to manage the user
plane mobility and it also acts as the main borderbetween the Radio
Access Network, RAN and the core network. The SGW also maintains
thedata paths between the eNodeBs and the PDN Gateways. In this way
the SGW forms a interfacefor the data packet network at the
E-UTRAN.
Also when UEs move across areas served by different eNodeBs, the
SGW serves as a mobilityanchor ensuring that the data path is
maintained.
PDN Gateway, PGW: The LTE SAE PDN gateway provides connectivity
for the UE to externalpacket data networks, fulfilling the function
of entry and exit point for UE data. The UE mayhave connectivity
with more than one PGW for accessing multiple PDNs.
Policy and Charging Rules Function, PCRF: This is the generic
name for the entity within theLTE SAE EPC which detects the service
flow, enforces charging policy. For applications thatrequire
dynamic policy or charging control, a network element entitled the
ApplicationsFunction, AF is used.
LTE SAE PCRF Interfaces
LTE SAE Distributed intelligenceIn order that requirements for
increased data capacity and reduced latency can be met, along
withthe move to an all-IP network, it is necessary to adopt a new
approach to the network structure.For 3G UMTS / WCDMA the UTRAN
(UMTS Terrestrial Radio Access Network, comprisingthe Node B's or
basestations and Radio Network Controllers) employed low levels of
autonomy.
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The Node Bs were connected in a star formation to the Radio
Network Controllers (RNCs)which carried out the majority of the
management of the radio resource. In turn the RNCsconnected to the
core network and connect in turn to the Core Network.To provide the
required functionality within LTE SAE, the basic system
architecture sees theremoval of a layer of management. The RNC is
removed and the radio resource management isdevolved to the
base-stations. The new style base-stations are called eNodeBs or
eNBs.The eNBs are connected directly to the core network gateway
via a newly defined "S1 interface".In addition to this the new eNBs
also connect to adjacent eNBs in a mesh via an "X2 interface".This
provides a much greater level of direct interconnectivity. It also
enables many calls to berouted very directly as a large number of
calls and connections are to other mobiles in the sameor adjacent
cells. The new structure allows many calls to be routed far more
directly and withonly minimum interaction with the core network.In
addition to the new Layer 1 and Layer 2 functionality, eNBs handle
several other functions.This includes the radio resource control
including admission control, load balancing and radiomobility
control including handover decisions for the mobile or user
equipment (UE).The additional levels of flexibility and
functionality given to the new eNBs mean that they aremore complex
than the UMTS and previous generations of base-station. However the
new 3GLTE SAE network structure enables far higher levels of
performance. In addition to this theirflexibility enables them to
be updated to handle new upgrades to the system including
thetransition from 3G LTE to 4G LTE Advanced.The new System
Architecture Evolution, SAE for LTE provides a new approach for the
corenetwork, enabling far higher levels of data to be transported
to enable it to support the muchhigher data rates that will be
possible with LTE. In addition to this, other features that enable
theCAPEX and OPEX to be reduced when compared to existing systems,
thereby enabling higherlevels of efficiency to be achieved.
LTE SON Self Organizing Networks- LTE, Long Term Evolution and
the requirements for LTE SON, SelfOrganising NetworksWith LTE
requiring smaller cell sizes to enable the much greater levels of
data traffic to behandled, there networks have become considerably
more complicated and trying to plan andmanage the network centrally
is not as viable. Coupled with the need to reduce costs by
reducingmanual input, there has been a growing impetus to implement
self organising networks.Accordingly LTE can be seen as one of the
major drivers behind the self-organising network,SON
philosophy.
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Accordingly 3GPP developed many of the requirements for LTE SON
to sit alongside the basicfunctionality of LTE. As a result the
standards for LTE SON are embedded within the 3GPPstandards.LTE SON
developmentThe term SON came into frequent use after the term was
adopted by the Next Generation MobileNetworks, NGMN alliance. The
idea came about as result of the need within LTE to be able
todeploy many more cells. Femtocells and other microcells are an
integral part of the LTEdeployment strategy. With revenue per bit
falling, costs for deployment must be kept to aminimum as well as
ensuring the network is operating to its greatest efficiency.3GPP,
the Third Generation Partnership Programme has created the
standards for SON and asthey are generally first to be deployed
with LTE, they are often referred to as LTE SON.While 3GPP has
generated the standards, they have been based upon long term
objectives for a'SON-enabled broadband mobile network' set out by
the NGMN.NGMN has defined the necessary use cases, measurements,
procedures and open interfaces toensure that multivendor offerings
are available. 3GPP has incorporated these aspirations intouseable
standards.Major elements of LTE SONAlthough LTE SON self-optimising
networks is one of the major drivers for the generic SONtechnology,
the basic requirements remain the same whatever the technology to
which it will beapplied.The main elements of SON include:
Self configuration: The aim for the self configuration aspects
of LTE SON is to enable new basestations to become essentially
"Plug and Play" items. They should need as little
manualintervention in the configuration process as possible. Not
only will they be able to organise theRF aspects, but also
configure the backhaul as well.
Self optimisation: Once the system has been set up, LTE SON
capabilities will enable the basestation to optimise the
operational characteristics to best meet the needs of the
overallnetwork.
Self-healing: Another major feature of LTE SON is to enable the
network to self-heal. It will dothis by changing the
characteristics of the network to mask the problem until it is
fixed. Forexample, the boundaries of adjacent cells can be
increased by changing antenna directions andincreasing power
levels, etc..
Typically an LTE SON system is a software package with relevant
options that is incorporatedinto an operator's network.
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Note on SON, Self Organizing Networks:SON mainly came out of the
requirements of LTE and the more complicated networks that
willarise. However the concepts behind SON can be applied at any
network enabling its efficiency tobe increased while keeping costs
low. Accordingly, it is being used increasingly to
reduceoperational and capital expenditure by adding software to the
network to enable it to organiseand run itself.Click on the link
for further information about Self Organising Networks, SONLTE SON
and 3GPP standardsLTE Son has been standardised in the various 3GPP
standards. It was first incorporated into3GPP release 8, and
further functionality has been progressively added in the further
releases ofthe standards.One of the major aims of the 3GPP
standardization is the support of SON features is to ensurethat
multi-vendor network environments operate correctly with LTE SON.
As a result, 3GPP hasdefined a set of LTE SON use cases and the
associated SON functions.As the functionality of LTE advances, the
LTE SON standardisation effectively track the LTEnetwork evolution
stages. In this way SON will be applicable to the LTE networks.
Voice over LTE - VoLTE- operation of Voice over LTE VoLTE system
for providing a unified format ofvoice traffic on LTE, and other
systems including CSFB, and SV-LTE.The Voice over LTE, VoLTE scheme
was devised as a result of operators seeking a standardisedsystem
for transferring voice traffic over LTE. Originally LTE was seen as
a completely IPcellular system just for carrying data, and
operators would be able to carry voice either byreverting to 2G /
3G systems or by using VoIP.Operators, however saw the fact that a
voice format was not defined as a major omission for thesystem. It
was seen that the lack of standardisation may provide problems with
scenariosincluding roaming. In addition to this, SMS is a key
requirement. It is not often realised, thatSMS is used to set-up
many mobile broadband connections, and a lack of SMS is seen as
ashow-stopper by many.As mobile operators receive over 80% of their
revenues from voice and SMS traffic, it isnecessary to have a
viable and standardized scheme to provide these services and
protect thisrevenue.
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Options for Voice over LTEWhen looking at the options for ways
of carrying voice over LTE, a number of possible solutionswere
investigated. A number of alliances were set up to promote
different ways of providing theservice. A number of systems were
prosed as outlined below:
CSFB, Circuit Switched Fall Back: The circuit switched fallback,
CSFB option for providing voiceover LTE has been standardised under
3GPP specification 23.272. Essentially LTE CSFB uses avariety of
processes and network elements to enable the circuit to fall back
to the 2G or 3Gconnection (GSM, UMTS, CDMA2000 1x) before a circuit
switched call is initiated.
The specification also allows for SMS to be carried as this is
essential for very many set-upprocedures for cellular
telecommunications. To achieve this the handset uses an
interfaceknown as SGs which allows messages to be sent over an LTE
channel.
In addition to this CSFB requires modification to elements
within the network, in particular theMSCs as well as support,
obviously on new devices. MSC modifications are also required for
theSMS over SGs facilities. For CSFB, this is required from the
initial launch of CSFB in view of thecriticality of SMS for many
procedures.
SV-LTE - simultaneous voice LTE: SV-LTE allows to run packet
switched LTE servicessimultaneously with a circuit switched voice
service. SV-LTE facility provides the facilities of CSFBat the same
time as running a packet switched data service. This is an option
that manyoperators will opt for. However it has the disadvantage
that it requires two radios to run at thesame time within the
handset. This has a serious impact on battery life.
VoLGA, Voice over LTE via GAN: The VoLGA standard was based on
the existing 3GPP GenericAccess Network (GAN) standard, and the aim
was to enable LTE users to receive a consistent setof voice, SMS
(and other circuit-switched) services as they transition between
GSM, UMTS andLTE access networks.
For mobile operators, the aim of VoLGA was to provide a low-cost
and low-risk approach forbringing their primary revenue generating
services (voice and SMS) onto the new LTE networkdeployments.
One Voice / later called Voice over LTE, VoLTE: The Voice over
LTE, VoLTE schem for providingvoice over an LTE system utilises IMS
enabling it to become part of a rich media solution.
Issues for Voice services over LTEUnlike previous cellular
telecommunications standards including GSM, LTE does not
havededicated channels for circuit switched telephony. Instead LTE
is an all-IP system providing anend-to-end IP connection from the
mobile equipment to the core network and out again.In order to
provide some form of voice connection over a standard LTE bearer,
some form ofVoice over IP, VoIP must be used.The aim for any voice
service is to utilise the low latency and QoS features available
within LTEto ensure that any voice service offers an improvement
over the standards available on the 2Gand 3G networks.
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However to achieve a full VoIP offering on LTE poses some
significant problems which willtake time to resolve. With the first
deployments having taken place in 2010, it is necessary that
asolution for voice is available within a short timescale.Voice
over LTE, VoLTE basicsThe One Voice profile for Voice over LTE was
developed by a collaboration between over fortyoperators including:
AT&T, Verizon Wireless, Nokia and Alcatel-Lucent.At the 2010
GSMA Mobile World Congress, GSMA announced that they were
supporting theOne Voice solution to provide Voice over LTE.VoLTE,
Voice over LTE is an IMS-based specification. Adopting this
approach, it enables thesystem to be integrated with the suite of
applications that will become available on LTE.Note on IMS:The IP
Multimedia Subsystem or IP Multimedia Core Network Subsystem, IMS
is anarchitectural framework for delivering Internet Protocol, IP
multimedia services. It enables avariety of services to be run
seemlessly rather than having several disparate
applicationsoperating concurrently.Click for a IMS tutorial
To provide the VoLTE service, three interfaces are being
defined: User Network interface, UNI: This interface is located
between the user's equipment and the
operators network. Roaming Network Network Interface, R-NNI: The
R-NNI is an interface located between the
Home and Visited Network. This is used for a user that is not
attached to their Home network,i.e. roaming.
Interconnect Network Network Interface, I-NNI: The I-NNI is the
interface located between thenetworks of the two parties making a
call.
Work on the definition of VoLTE, Voice over LTE is ongoing. It
will include a variety ofelements including some of the
following:
It will be necessary to ensure the continuity of Voice calls
when a user moves from an LTEcoverage area to another where a
fallback to another technology is required. This form ofhandover
will be achieved using Single Radio Voice Call Continuity, or
SR-VCC).
It will be important to provide the optimal routing of bearers
for voice calls when customers areroaming.
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Another area of importance will be to establish commercial
frameworks for roaming andinterconnect for services implemented
using VoLTE definitions. This will enable roamingagreements to be
set up.
Provision of capabilities associated with the model of roaming
hubbing. For any services, including LTE, it is necessary to
undertake a thorough security and fraud threat
audit to prevent hacking and un-authorised entry into any area
within the network..
In many ways the implementation of VoLTE at a high level is
straightforward. The handset orphone needs to have software loaded
to provide the VoLTE functionality. This can be in theform of an
App.The network then requires to be IMS compatible.While this may
appear straightforward, there are many issues for this to be made
operational,especially via the vagaries of the radio access network
where time delays and propagationanomalies add considerably to the
complexity.
LTE Security- overview, about the basics of LTE security
including the techniques used forLTE authentication, ciphering,
encryption, and identity protection.LTE security is an issue that
is of paramount importance. It is necessary to ensure that
LTEsecurity measures provide the level of security required without
impacting the user as this coulddrive users away.Nevertheless with
the level of sophistication of security attacks growing, it is
necessary to ensurethat LTE security allows users to operate freely
and without fear of attack from hackers.Additionally the network
must also be organised in such a way that it is secure against a
varietyof attacks.
LTE security basicsWhen developing the LTE security elements
there were several main requirements that wereborne in mind:
LTE security had to provide at least the same level of security
that was provided by 3G services. The LTE security measures should
not affect user convenience. The LTE security measures taken should
provide defence from attacks from the Internet. The security
functions provided by LTE should not affect the transition from
existing 3G services
to LTE. The USIM currently used for 3G services should still be
used.
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To ensure these requirements for LTE security are met, it has
been necessary to add furthermeasures into all areas of the system
from the UE through to the core network.The main changes that have
been required to implement the required level of LTE security
aresummarised below:
A new hierarchical key system has been introduced in which keys
can be changed for differentpurposes.
The LTE security functions for the Non-Access Stratum, NAS, and
Access Stratum, AS have beenseparated. The NAS functions are those
functions for which the processing is accomplishedbetween the core
network and the mobile terminal or UE. The AS functions encompass
thecommunications between the network edge, i.e. the Evolved Node
B, eNB and the UE.
The concept of forward security has been introduced for LTE
security. LTE security functions have been introduced between the
existing 3G network and the LTE
network.
LTE USIMOne of the key elements within the security of GSM, UMTS
and now LTE was the concept ofthe subscriber identity module, SIM.
This card carried the identity of the subscriber in anencrypted
fashion and this could allow the subscriber to keep their identity
while transferring orupgrading phones.With the transition form 2G -
GSM to 3G - UMTS, the idea of the SIM was upgraded and aUSIM - UMTS
Subscriber Identity Module, was used. This gave more functionality,
had a largermemory, etc.For LTE, only the USIM may be used - the
older SIM cards are not compatible and may not beused.