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.

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.

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

- 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.

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.

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.

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.

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

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.

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.

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

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

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.

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.

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.

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.

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.

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

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.

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.

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.

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

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:

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.

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.

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.

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.

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.

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.

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.

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.

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.