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3G LTE Tutorial - 3GPP Long TermEvolution- information, overview, or tutorial about the basics of the 3GPP / 3G LTE, thelong term evolution plans for the next generation of cellular telecommunicationsservices3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE Advanced3G LTE is now being deployed and is the way forwards for high speed cellular services.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.LTE can be seen for provide a further evolution of functionality, increased speeds and generalimproved performance. HSPA WCDMA HSDPA / HSPA+ LTE (UMTS) HSUPAMax downlink speed 384 k 14 M 28 M 100MbpsMax uplink speed 128 k 5.7 M 11 M 50 MbpsLatency 50msround trip time 150 ms 100 ms ~10 ms (max)approx3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8Approx years of initial roll 2005 / 6 HSDPA 2003 / 4 2008 / 9 2009 / 10out 2007 / 8 HSUPA OFDMA / SC-Access methodology CDMA CDMA CDMA FDMAIn addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. There is alsono basic provision for voice, although this can be carried as VoIP.3GPP LTE technologiesLTE 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 incorporated into LTE because it enables high data bandwidths to be transmitted efficiently while still providing a high degree of resilience to reflections and interference. The access schemes differ between the uplink and downlink: OFDMA (Orthogonal Frequency Division Multiple Access is used in the downlink; while SC-FDMA(Single Carrier - Frequency Division Multiple Access) is used in the uplink. SC-FDMA is used in view of the fact that its peak to average power ratio is small and 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 previous telecommunications systems has encountered is that of multiple signals arising from the many reflections that are encountered. By using MIMO, these additional signal paths can be used to advantage 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 be distinguished. 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 of mobile handsets, where the dimensions of the user equipment limit the number of antennas which 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 latency requirements for 3G LTE, it is necessary to evolve the system architecture to enable the improved performance to be achieved. One change is that a number of the functions previously handled by the core network have been transferred out to the periphery. Essentially this provides a much "flatter" form of network architecture. In this way latency times can be reduced and data can be routed more directly to its destination. Read more about LTE SAEThese technologies are addressed in much greater detail in the following pages of this tutorial.3G 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. Parameter DetailsPeak downlink speed64QAM 100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO)(Mbps)Peak uplink speeds 50 (QPSK), 57 (16QAM), 86 (64QAM)(Mbps) All packet switched data (voice and data). NoData type circuit switched.Channel bandwidths 1.4, 3, 5, 10, 15, 20(MHz)Duplex schemes FDD and TDD 0 - 15 km/h (optimised),Mobility 15 - 120 km/h (high performance) Idle to active less than 100msLatency Small packets ~10 ms
Parameter Details Downlink: 3 - 4 times Rel 6 HSDPASpectral efficiency Uplink: 2 -3 x Rel 6 HSUPA OFDMA (Downlink)Access schemes SC-FDMA (Uplink)Modulation types QPSK, 16QAM, 64QAM (Uplink and downlink)supportedThese 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.LTE OFDM, OFDMA and SC-FDMA- overview, information, tutorial about the basics of LTE OFDM, OFDMA andSC-FDMA including cyclic prefix, CP.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedOne 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 eachanother there is no mutual interference. This is achieved by having the carrier spacing equal tothe reciprocal of the symbol period. This means that when the signals are demodulated they willhave a whole number of cycles in the symbol period and their contribution will sum to zero - inother words there is no interference contribution. The data to be transmitted is split across all thecarriers and this means that by using error correction techniques, if some of the carriers are lostdue to multi-path effects, then the data can be reconstructed. Additionally having data carried ata low rate across all the carriers means that the effects of reflections and inter-symbolinterference can be overcome. It also means that single frequency networks, where alltransmitters can transmit on the same channel can be implemented.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 MHz 2. 3 MHz 3. 5 MHz 4. 10 MHz 5. 15 MHz 6. 20 MHzIn 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 µs.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 4.69µs. This enables the system to accommodate path variations of up to 1.4 km. With the symbollength in LTE set to 66.7 µs.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 µs.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 symbol 2. 16QAM 4 bits per symbol 3. 64QAM 6 bits per symbolThe 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.Channel bandwidth 1.4 3 5 10 15 20(MHz)
Number of resource blocks 6 15 25 50 75 100LTE 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- overview, information, tutorial about the basics of how MIMO is used within3G LTE.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions
• SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedMIMO, 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 Shannons 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 mutuallyorthogonal 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.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedLTE 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 there
has 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 directionsIn 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 forcellular communicationsThere 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. Parameter LTE-TDD LTE-FDD Does not require paired Requires paired spectrum withPaired spectrum as both transmit and sufficient frequency separation tospectrum receive occur on the same allow simultaneous transmission channel and reception Lower cost as no diplexer is needed to isolate the transmitter and receiver. As Diplexer is needed and cost isHardware cost cost of the UEs is of major higher. importance because of the vast numbers that are produced, this is a key aspect. Channel propagation is the Channel characteristics differentChannel same in both directions which in both directions as a result ofreciprocity enables transmit and receive to the use of different frequencies use on set of parametersUL / DL It is possible to dynamically UL / DL capacity determined byasymmetry change the UL and DL frequency allocation set out by
Parameter LTE-TDD LTE-FDD capacity ratio to match the regulatory authorities. It is demand therefore not possible to make dynamic changes to match capacity. Regulatory changes would normally be required and capacity is normally allocated so that it is the same in either direction. Guard period required to ensure uplink and downlink Guard band required to provide transmissions do not clash. sufficient isolation betweenGuard period / Large guard period will limit uplink and downlink. Largeguard band capacity. Larger guard period guard band does not impact normally required if distances capacity. are increased to accommodate larger propagation times. Discontinuous transmission is required to allow both uplinkDiscontinuous and downlink transmissions. Continuous transmission istransmission This can degrade the required. performance of the RF power amplifier in the transmitter. Base stations need to be synchronised with respect to the uplink and downlink transmission times. IfCross slot neighbouring base stations use Not applicableinterference different uplink and downlink assignments and share the same channel, then interference may occur between cells.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 ableto 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.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedIn 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 StructureType 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. Uplink- Downlink to downlink uplink switch Subframe number configuration periodicity 0 1 2 3 4 5 6 7 8 9
Uplink- Downlink to downlink uplink switch Subframe number configuration periodicity 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U DWhere: D is a subframe for downlink transmission S is a "special" subframe used for a guard time U 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.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE
• SecuritySee also: 4G LTE AdvancedIn 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. o Physical Control Format Indicator Channel (PCFICH) : o Physical Downlink Control Channel (PDCCH) : The main purpose of this physical channel is to carry mainly scheduling information. o Physical Hybrid ARQ Indicator Channel (PHICH) : As the name implies, this channel is used to report the Hybrid ARQ status. o Physical Downlink Shared Channel (PDSCH) : This channel is used for unicast and paging functions. o Physical Multicast Channel (PMCH) : This physical channel carries system information for multicast purposes. o Physical Control Format Indicator Channel (PCFICH) : This provides information to enable the UEs to decode the PDSCH. • Uplink:
o Physical Uplink Control Channel (PUCCH) : Sends Hybrid ARQ acknowledgement o Physical Uplink Shared Channel (PUSCH) : This physical channel found on the LTE uplink is the Uplink counterpart of PDSCH o Physical Random Access Channel (PRACH) : This uplink physical channel is used for random access functions.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 PCCH o 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 channels • Control channels: 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: 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 of multicast data.LTE Frequency Bands & SpectrumAllocations- a summary and tables of the LTE frequency band spectrum allocations for 3G& 4G LTE - TDD and FDD.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedThere is a growing number of LTE frequency bands that are being designated as possibilities foruse with LTE. Many of the LTE frequency bands are already in use for other cellular systems,whereas other LTE bands are new and being introduced as other users are re-allocated spectrumelsewhere.
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 definitionsFDD 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.
33 1900 - 1920 2034 2010 - 2025 1535 1850 - 1910 6036 1930 - 1990 6037 1910 - 1930 2038 2570 - 2620 5039 1880 - 1920 4040 2300 - 2400 10041 2496 - 2690 19442 3400 - 3600 20043 3600 - 3800 200There 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- summary and overview of the 3G LTE UE or User Equipment categories andthe performance specifications of these LTE categories.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE
• SecuritySee also: 4G LTE AdvancedIn 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. Category 1 2 3 4 5Downlink 10 50 100 150 300Uplink 5 25 50 50 75 LTE UE category data rates Category 1 2 3 4 5
Category 1 2 3 4 5Downlink QPSK, 16QAM, 64QAM QPSK,Uplink QPSK, 16QAM 16QAM, 64QAM LTE UE category modulation formats supported Category 1 2 3 4 52 Rx Assumed in performance requirements across all LTE UEdiversity categories Not2 x 2 MIMO Mandatory supported4 x 4 MIMO Not supported Mandatory LTE UE category MIMO antenna configurationsNote: Bandwidth for all categories is 20 MHz.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 Network3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels
• Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedAlong 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 focus of the system being on mobile broadband, it will be necessary for the network to be able to handle much greater levels of data. To achieve this it is necessary to adopt a system architecture that lends itself to much grater levels of data transfer. 2. All IP architecture: When 3G was first developed, voice was still carried as circuit switched data. Since then there has been a relentless move to IP data. Accordingly the new SAE, System Architecture Evolution schemes have adopted an all IP network configuration. 3. Reduced latency: With increased levels of interaction being required and much faster responses, the new SAE concepts have been evolved to ensure that the levels of latency have been reduced to around 10 ms. This will ensure that applications using 3G LTE will be sufficiently responsive. 4. Reduced OPEX and CAPEX: A key element for any operator is to reduce costs. It is therefore essential that any new design reduces both the capital expenditure (CAPEX)and the operational expenditure (OPEX). The new flat architecture used for SAE System Architecture Evolution means that only two node types are used. In addition to this a high
level of automatic configuration 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 CoreAs 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 access network, handling a number of features: o Idle mode UE tracking o Bearer activation / de-activation o Choice of SGW for a UE
o Intra-LTE handover involving core network node location o Interacting with HSS to authenticate user on attachment and implements roaming restrictions o It acts as a termination for the Non-Access Stratum (NAS) o Provides temporary identities for UEs o 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 the point at which lawful interception of signalling may be made. o Paging procedure o 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 control functionality.• Serving Gateway, SGW: The Serving Gateway, SGW, is a data plane element within the LTE SAE. Its main purpose is to manage the user plane mobility and it also acts as the main border between the Radio Access Network, RAN and the core network. The SGW also maintains the data paths between the eNodeBs and the PDN Gateways. In this way the SGW forms a interface for the data packet network at the E-UTRAN. Also when UEs move across areas served by different eNodeBs, the SGW serves as a mobility anchor ensuring that the data path is maintained.• PDN Gateway, PGW: The LTE SAE PDN gateway provides connectivity for the UE to external packet data networks, fulfilling the function of entry and exit point for UE data. The UE may have 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 the LTE SAE EPC which detects the service flow, enforces charging policy. For applications that require dynamic policy or charging control, a network element entitled the Applications Function, AF is used.
LTE SAE PCRF InterfacesLTE 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 Bs 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 �G 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.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.3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedThe 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, that
SMS 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 voice over LTE has been standardised under 3GPP specification 23.272. Essentially LTE CSFB uses a variety of processes and network elements to enable the circuit to fall back to the 2G or 3G connection (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- up procedures for cellular telecommunications. To achieve this the handset uses an interface known 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 the MSCs as well as support, obviously on new devices. MSC modifications are also required for the SMS over SGs facilities. For CSFB, this is required from the initial launch of CSFB in view of the criticality of SMS for many procedures. • SV-LTE - simultaneous voice LTE: SV-LTE allows to run packet switched LTE services simultaneously with a circuit switched voice service. SV-LTE facility provides the facilities of CSFB at the same time as running a packet switched data service. This is an option that many operators will opt for. However it has the disadvantage that it requires two radios to run at the same 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 Generic Access Network (GAN) standard, and the aim was to enable LTE users to receive a consistent set of voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks. For mobile operators, the aim of VoLGA was to provide a low-cost and low-risk approach for bringing their primary revenue generating services (voice and SMS) onto the new LTE network deployments. • One Voice / later called Voice over LTE, VoLTE: The Voice over LTE, VoLTE schem for providing voice 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 users 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 the networks 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 LTE coverage area to another where a fallback to another technology is required. This form of handover 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 are roaming. • Another area of importance will be to establish commercial frameworks for roaming and interconnect for services implemented using VoLTE definitions. This will enable roaming agreements 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.
3G LTE technology tutorial includes: • Tutorial Introduction • OFDM and OFDMA / SC-FDMA • MIMO • TDD and FDD duplex schemes • Frame and subframe structure • Physical logical & transport channels • Frequency bands and spectrum • UE category definitions • SAE system architecture evolution • Voice over LTE, VoLTE • SecuritySee also: 4G LTE AdvancedLTE 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 different purposes. • The LTE security functions for the Non-Access Stratum, NAS, and Access Stratum, AS have been separated. The NAS functions are those functions for which the processing is accomplished between the core network and the mobile terminal or UE. The AS functions encompass the communications 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.