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LTE Training DocumentIndexIntroductionLTE Key featureLTE Network Elements(Architecture)LTE Network InterfacesLTE-Channel

3G LTE evolutionAlthough there are major step changes between LTE and its 3G predecessors, it is nevertheless looked upon as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different form of radio interface, using OFDMA / SC-FDMA instead of CDMA, there are many similarities 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 general improved performance.LTE Introduction WCDMA(UMTS)HSPAHSDPA / HSUPAHSPA+LTEMax downlink speedbps384 k14 M28 M100MMax uplink speedbps128 k5.7 M11 M50 MLatencyround trip timeapprox150 ms100 ms50ms (max)~10 ms3GPP releasesRel 99/4Rel 5 / 6Rel 7Rel 8Approx years of initial roll out2003 / 42005 / 6 HSDPA2007 / 8 HSUPA2008 / 92009 / 10Access methodologyCDMACDMACDMAOFDMA / SC-FDMAIn addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. There is also no 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 cellular systems. They enable LTE to be able to operate more efficiently with respect to the use of spectrum, 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.

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.

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.LTE specification overviewIt is worth summarizing the key parameters of the 3G LTE specification. In view of the fact that there are a number of differences between the operation of the uplink and downlink, these naturally differ in the performance they can offer.pARAMETERDETAILSPeak downlink speed64QAM(Mbps)100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO)Peak uplink speeds(Mbps)50 (QPSK), 57 (16QAM), 86 (64QAM)Data typeAll packet switched data (voice and data). No circuit switched.Channel bandwidths(MHz)1.4, 3, 5, 10, 15, 20Duplex schemesFDD and TDDMobility0 - 15 km/h (optimised),15 - 120 km/h (high performance)LatencyIdle to active less than 100msSmall packets ~10 msSpectral efficiencyDownlink: 3 - 4 times Rel 6 HSDPAUplink: 2 -3 x Rel 6 HSUPAAccess schemesOFDMA (Downlink)SC-FDMA (Uplink)Modulation types supportedQPSK, 16QAM, 64QAM (Uplink and downlink)LTE Key Features Evolved NodeB (eNB)No RNC is provided anymoreThe evolved Node Bs take over all radio management functionality.This will make radio management faster and hopefully the network architecture simpler

IP transport layerEUTRAN exclusively uses IP as transport layer

UL/DL resource schedulingIn UMTS physical resources are either shared or dedicatedEvolved Node B handles all physical resource via a scheduler and assigns them dynamically to users and channelsThis provides greater flexibility than the older system

LTE Network ArchitectureLTE-UEEvolved UTRAN (E-UTRAN)MMES10S6aServingGatewayS1-US11PDNGatewayEvolved Packet Core (EPC)S1-MMES5/S8EvolvedNode B(eNB)cellX2LTE-UuHSSMME: Mobility Management Entity

LTEGatewayInter-cell RRM: HO, load balancing between cellsRadio Bearer Control: setup, modifications and release of Radio ResourcesConnection Mgt. Control: UE State Mgmt. MME-UE ConnectionRadio Admission ControleNode B Measurements Collection and evaluationDynamic Resource Allocation (Scheduler)eNB FunctionsIP Header Compression/ de-compressionAccess Layer Security: ciphering and integrity protection on the radio interfaceMME Selection at Attach of the UEUser Data Routing to the LTE GW.Transmission of Paging Message coming from MMETransmission of Broadcast Info (System info, MBMS)

EvolvedNode B(eNB)cellLTE-Uu

LTE-UEIt is the only network element defined as part of EUTRAN. It replaces the old Node B / RNC combination from 3G.It terminates the complete radio interface including physical layer.It provides all radio management functionsAn eNB can handle several cells. To enable efficient inter-cell radio management for cells not attached to the same eNB, there is a inter-eNB interface X2 specified. It will allow to coordinate inter-eNB handovers without direct involvement of EPC during this process.Evolved Node B (eNB)

EvolvedNode B(eNB)MMEServingGatewayS1-US1-MMES11HSSS6aMME FunctionsNon-Access-Stratum (NAS)SignallingIdle State Mobility HandlingTracking Area updatesSecurity (Authentication, Ciphering, Integrity protection)Trigger and distribution of Paging Messages to eNBRoaming Control (S6a interface to HSS)Inter-CN Node Signaling (S10 interface), allows efficient inter-MME tracking area updatesand attachesSignaling coordination for LTE Bearer Setup/Release & HOSubscriber attach/detachControl plane NE in EPCMobility Management Entity (MME) It is a pure signaling entity inside the EPC. LTE uses tracking areas to track the position of idle UEs. The basic principle is identical to location or routing areas from 2G/3G. MME handles attaches and detaches to the LTE system, as well as tracking area updates Therefore it possesses an interface towards the HSS (home subscriber server) which stores the subscription relevant information and the currently assigned MME in its permanent data base. A second functionality of the MME is the signaling coordination to setup transport bearers (LTE bearers) through the EPC for a UE. MMEs can be interconnected via the S10 interface It generates and allocates temporary ids for UEs

EvolvedNode B(eNB)MMEServing GatewayS1-US1-MMES5/S8PDNGatewayS11S6aServing Gateway The serving gateway is a network element that manages the user data path ( bearers) within EPC. It therefore connects via the S1-U interface towards eNB and receives uplink packet data from here and transmits downlink packet data on it. Thus the serving gateway is some kind of distribution and packet data anchoring function within EPC. It relays the packet data within EPC via the S5/S8 interface to or from the PDN gateway. A serving gateway is controlled by one or more MMEs via S11 interface.At a given time, the UE is connected to the EPC via a single Serving-GWPacket Buffering and notification toMME for UEs in Idle ModePacket Routing/Forwarding between eNB, PDN GW and SGSNLawful Interception supportServing Gateway FunctionsMobility anchoring for inter-3GPP mobility. This is sometimes referredto as the 3GPP Anchor functionLocal Mobility Anchor Point: Switching the User plane to a new eNB in case of HandoverPacket Data Network (PDN) Gateway The PDN gateway provides the connection between EPC and a number of external data networks. Thus it is comparable to GGSN in 2G/3G networks. A major functionality provided by a PDN gateway is the QoS coordination between the external PDN and EPC. Therefore the PDN gateway can be connected via S7 to a PCRF (Policy and Charging Rule Function). If a UE is connected simultaneously to several PDNs this may involved connections to more than one PDN-GW MMEServingGatewayS5/S8PDN LTEGatewayS11S6aPolicy Enforcement (PCEF)Per User based Packet Filtering (i.e. deep packet inspection)Charging SupportPDN Gateway FunctionsIP Address Allocation for UEPacket Routing/Forwarding between Serving GW and external Data NetworkMobility anchor for mobility between 3GPP access systems and non-3GPP access systems. This is sometimes referred to as the LTE Anchor function Packet screening (firewall functionality)Lawful Interception supportHome Subscriber Server (HSS) The HSS is already introduced by UMTS release 5. With LTE/LTE the HSS will get additionally data per subscriber for LTE mobility and service handling. Some changes in the database as well as in the HSS protocol (DIAMETER) will be necessary to enable HSS for LTE/LTE. The HSS can be accessed by the MME via S6a interface. Permanent and central subscriber databaseHSS FunctionsStores mobility and service data for every subscriberMMEHSSS6aContains the Authentication Center(AuC) functionality.LTE UE CategoriesQualcomm first chipset has 50 Mbps downlink and 25 Mbps uplinkAll categories support 20 MHz64QAM mandatory in downlink, but not in uplink (except Class 5)2x2 MIMO mandatory in other classes except Class 1Class 1Class 2Class 3Class 4Class 510/5 Mbps50/25 Mbps100/50 Mbps150/50 Mbps300/75 MbpsPeak rate DL/UL20 MHzRF bandwidth20 MHz20 MHz20 MHz20 MHz64QAMModulation DL64QAM64QAM64QAM64QAM16QAMModulation UL16QAM64QAM 16QAM16QAMYesRx diversityYesYesYesYes1-4 txBTS tx diversityOptionalMIMO DL2x24x42x22x21-4 tx1-4 tx1-4 tx1-4 txLTE-ChannelUpper LayersRLCMACPHYLogical channelsTransport channelsBCCHCCCHPCCHMTCHMCCHBCHPCHDL-SCHRACHUL-SCHPBCHPDSCHPHICHPDCCHPCFICHPMCHPUCCHPRACHPUSCHMCHCCCHDCCHDTCHULDLAir interfaceDCCHDTCHThe radio interface is composed of different layers in order to set up, reconfigure and release the radio bearer services.

The protocol layer is composed of physical layer (layer 1), data link layer (layer2), and the network layer (layer3).

In the E-UTRAN layer 2 is divided into two sub-layers: Medium Access Control (MAC) and Radio Link Control (RLC) protocol.

Layer 3 consists of two protocols, called Radio Resource Control (RRC) and Packet Data Convergence Protocol (PDCP).

The top to down arrows represent downlink (DL) channels from eNB to UE..

Down to top arrows are uplink channel (UL) from UE to eNB.

Most of common and dedicated channels transmitted from RLC to the physical layer share the same transport channel. There are no dedicated channels in transport and physical layer. Some physical channels are existing solely in the physical layer itself, such as PHICH, PCFICH and PDCCH.

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.Logical channelsBCCH Broadcast Control CHSystem information sent to all UEsPCCH Paging Control CHPaging information when addressing UECCCH Common Control CHAccess information during call establishmentDCCH Dedicated Control CHUser specific signaling and controlDTCH Dedicated Traffic CHUser dataMCCH Multicast Control CHSignaling for multi-cast MTCH Multicast Traffic CHMulticast data

LTE ChannelsTransport channelsBCH Broadcast CHTransport for BCCHPCH Paging CHTransport for PCHDL-SCH Downlink Shared CHTransport of user data and signaling. Used by many logical channelsMCH Multicast channelUsed for multicast transmissionUL-SCH Uplink Shared CHTransport for user data and signalingRACH Random Access CHUsed for UEs accessing the network

LTE ChannelsPhysical ChannelPDSCH Physical DL Shared CHUni-cast transmission and pagingPBCH Physical Broadcast CHBroadcast information necessary for accessing the networkPMCH Physical Multicast ChannelData and signaling for multicastPDCCH Physical Downlink Control CHCarries mainly scheduling informationPHICH Physical Hybrid ARQ Indicator Reports status of Hybrid ARQPCIFIC Physical Control Format IndicatorInformation required by UE so that PDSCH can be demodulated (format of PDSCH)PUSCH Physical Uplink Shared ChannelUplink user data and signalingPUCCH Physical Uplink Control ChannelReports Hybrid ARQ acknowledgementsPRACH Physical Random Access ChannelUsed for random access

LTE Channels Radio Resource Control (RRC) States From a mobility perspective, the UE can be in one of three states. LTE_DETACHED LTE_IDLE LTE_ACTIVE

LTE_DETACHEDLTE_ACTIVELTE_IDLEOFFPower UpRegistrationDe-registrationInactivityNew TrafficTimeout ofTracking AreaUpdate/PLMNChangeUE StatesLTE_DETACHEDPower OnRegistration (Attach)LTE_ACTIVE Allocate C-RNTI, S_TMSI Allocate IP addresses Authentication Establish security context Release RRC connection Release C-RNTI Configure DRX for pagingLTE_IDLERelease due to InactivityEstablish RRC ConnectionAllocate C-RNTI

New TrafficDeregistration (Detach)Change PLMN Release C-RNTI, S-TMSI Release IP addressesTimeout of Periodic TA Update Release S-TMSI Release IP addressesLTE_DETACHED state is typically a transitory state in which the UE is powered-on but is in the process of searching and registering with the network.

LTE_ACTIVE state, the UE is registered with the network and has an RRC connection with the eNB. In LTE_ACTIVE state, the network knows the cell to which the UE belongs and can transmit/receive data from the UE.

LTE_IDLE state is a power-conservation state for the UE, where typically the UE is not transmitting or receiving packets. In LTE_IDLE state, no context about the UE is stored in the eNB. In this state, the location of the UE is only known at the MME and only at the granularity of a tracking area (TA) that consists of multiple eNBs. The MME knows the TA in which the UE last registered and paging is necessary to locate the UE to a cell. Thanks