3GPP LTE Principles.ppt
3GPP LTE Principles,2010,Agenda,1.LTE Market2.3GPP LTE-Evolved UTRA 2.1 Radio Interface Concepts2.2 LTE Radio Frame and Subframe Structure2.3 LTE Channels2.4 LTE Procedures3.TD-LTE&FDD LTE Comparison,TD-LTE Market,1,LTE Market,LTE FDD Commercial Deployments 2010Start in 2010 with major operators in Asia(NTT DoCoMo)and North America(Verizon)Initial deployments will focus on“Hot Zone”areas to maximise access to high data users2.6GHz,1800MHz and Digital Dividend spectrum will dominate Europe and Asia deployments.USA will focus on 700MHz and AWSTrials proving LTE performance prior to commercial launch,LTE TDD(TD-LTE)Commercial deployments 2011Key part of overall LTE standard to prevent repeat of 3G TDD failureTD-LTE led by CMCC,driving it to be next gen broadband network to replace GSM and TD-SCDMAUnique Global Alignment between Vodafone,CMCC to promote the success of TD-LTE ecosystemDriven across 2.3/2.5/3.5GHz Bands,LTE is a market reality,driven by 3GPP&3GPP operators,1000 operators worldwide)2 parts to the standard FDD and TDD(TD-LTE),ALU LTE FDD Trials,ALU LTE TDD Trials,3GPP LTE-Evolved UTRA,2,3GPP Reference Architecture,Generic 3GPP Network Architecture:flat IP architecture,UE to Operators IP services,3GPP LTE-Radio Interface Concepts,2.1,3GPP LTE-Evolved UTRA-Radio Interface Concepts 3G LTE Requirements,3GPP LTE-Evolved UTRA-Radio Interface Concepts DOWNLINK:OFDMA Transmission Scheme,The OFDMA systems break the available bandwidth into many narrower sub-carriers and transmit the data in parallel streams.Each sub-carrier is modulated using varying levels of QAM modulation,e.g.QPSK,QAM,64QAM or possibly higher orders depending on signal quality,3GPP LTE-Evolved UTRA-Radio Interface Concepts DOWNLINK:OFDMA Transmission Scheme,Conventional OFDMA with cyclic prefix Carrier Spacing 15KHz,Tcp=4.8s Extended cyclic prefix needed for broadcast/multicast and environments with extreme delay spread,TECP=16.7 s Channel dependent scheduling in time and frequency domain Scheduler assigns a number of(possibly non-contiguous)chunks to a user.Each user is assigned a chunk(colored blocks)in time and frequency plane.,3GPP LTE-Evolved UTRA-Radio Interface Concepts DOWNLINK:Why OFDMA in Downlink,Inter-Symbol Interference(ISI)Elimination:Since the signal is transmitted over many narrow subcarriers,the symbol time is enlarged and ISI can be easily eliminated.,Less Receiver Complexity:OFDMA modulation/Demodulation can be done using a simple FFT/IFFT technique,which simplifies the transmitter and receiver processing complexity.Frequency domain equalization is done at the receiver and has less implementation complexity.,Suitable for Multiple Antenna Techniques:Since the OFDM symbol is block-based,it is suitable for a multiple antenna operation.,Spectral Efficiency:Scheduling operation can be done in both the time and frequency domain.This property slightly improves the spectral efficiency by means of granular allocation of resources.,3GPP LTE-Evolved UTRA-Radio Interface Concepts Drawbacks of using OFDMA the Uplink,High PAPR:Since OFDMA is multicarrier based,The transmitted signal is a superposition of all the subcarriers with different carrier frequencies and high amplitude peaks occur because of the superposition.high Peak-to-Average power ratio in the modulated signal:Affecting the performance of power amplifier in the linear region,leads to less power efficiency in UE.This is the main issue which is considered for LTE uplink.,High Sensitivity to Frequency Offset:Multicarrier modulations are more sensitive to frequency offsets.Since LTE is aiming for high mobility applications,the occurrence of Inter-Carrier Interference(ICI)is possible in OFDMA-based transmission.,Sensitive to Spectral Nulls:In the presence of a null in the channel,there is no way to recover the data of the subcarriers that are affected by the null unless we use rate adaptation or a coding in the transmission scheme.,Per Subcarrier Equalization:Equalization in the frequency domain is done at each subcarrier in the OFDMA receiver.This increases the complexity of the receiver.,3GPP LTE-Evolved UTRA-Radio Interface Concepts UPLINK:Key Requirements,Less Equipment Complexity:The complexity of the equipment should be minimized,High Data Rate:The UE should support high rate applications.,Coverage at Cell Boundaries:Coverage of the UE should be large,which increases the quality of service at the cell boundaries.,Less Transmit Power Requirements:The maximum transmit power required by the equipment should be low(low PAPR),3GPP LTE-Evolved UTRA-Radio Interface Concepts UPLINK:SC-FDMA transmission Scheme,To facilitate efficient power amplifier design in the UE,3GPP chose single carrier frequency division multiple access(SC-FDMA)in favor of OFDMA for uplink multiple accessSC-FDMA improves the peak-to-average power ratio(PAPR)compared to OFDMA4 dB improvement for QPSK,2 dB improvement for 16-QAMReduced power amplifier cost for mobileReduced power amplifier back-off improved coverage,3GPP LTE-Evolved UTRA-Radio Interface Concepts UPLINK:SC-FDMA transmission Scheme,SC-FDMA signals have lower Peak-to-Average power Ratio(PAPR)because of its inherent single carrier structure.,LTE Radio Frame and Subframe Structure,2.2,3GPP LTE-Evolved UTRA-Radio Interface Concepts LTE Frame Structure Overview,Generic Frame Structure(FDD&TDD)applicable for both FDD-and TDD-based transmissions.radio frame duration is 10 ms,1 Frame(10 msec),1 Sub-Frame(1 msec),1 slot(0.5 msec),7 OFDM Symbols,(Short CP),Cyclic Prefix,Short CP:7 OFDM SymbolsLong CP:6 OFDM Symbols,3GPP LTE-Evolved UTRA-Radio Interface Concepts LTE Frame Structure Overview:FDD&TDD,Normal subframes have exactly the same structure in TDD and FDD.As consequences:They carry the same amount of data,They have similar link budgets/MAPL properties,Frame(10 ms),Sub-frame(1 ms),Time Division Duplex,Frequency Division Duplex,3GPP LTE-Evolved UTRA-Radio Interface Concepts LTE Frame Structure type 2(TDD),TDD uses a Special subframe used for the DL to UL switch.Special subframes carry DL user/control data,Frame(10 ms),Sub-frame(1 ms),Time Division Duplex,7 possible configurations allowing various DL/UL asymetry ratios,3GPP LTE-Evolved UTRA-Radio Interface Concepts LTE Frame Structure type 2(TDD)Zoom on S sub-frame,“S”denotes a special subframe 3 fieldsDownlink pilot time slot(DwPTS):used for downlink synchronization,it can be used to send PDSCH and scheduling grants on the PDCCHUplink pilot time slot(UpPTS)zone:used by node B to determine the received power level,it can be used to send PRACH and SRS on the uplink.Guard Period:it ensures the transmission of UE without interference between UL and DL,Frame(10 ms),Sub-frame(1 ms),Time Division Duplex,Special SF,3GPP LTE-Evolved UTRA-Radio Interface Concepts LTE Frame Structure type 2(TDD)Zoom on S sub-frame,9 configurations for S-Subframes with normal Cyclic prefix:,3GPP LTE-Evolved UTRA-Radio Interface Concepts Configuration of special subframe(lengths of DwPTS/GP/UpPTS).,Extract from 3GPP TS 36.211,Special subframe configurationTo avoid remote eNB interference(DL interference from remote base station to local UL Rx signal):Shorter DwPTS and longer DL to UL Guard Time.To provide high Data Rate:long DwPTS and short Guardtime,3GPP LTE-Evolved UTRA-Radio Interface Concepts Downlink:Channel Structure and Terminology,t,f,Physical Resource Block(PRB)=14 OFDM Symbols x 12 SubcarrierThis is the minimum unit of allocation in LTE,first 1.3 OFDM symbols*reserved for L1/L2 control signaling(PCFICH,PDCCH,PHICH),one OFDM symbol,Subcarrier,Resource Element is a single subcarrier in an OFDM symbol,Slot(0.5 ms),Subframe(1 ms),Slot(0.5 ms),15 kHz,PRB,subframe,*2.4 symbols for 1.4 MHz bandwidth only,3GPP LTE-Evolved UTRA-Radio Interface Concepts Resource Grid 3GPP TS 36.211,Total number of available subcarriers depends on the overall transmission bandwidth of the system.,A PRB is the smallest element of resource allocation assigned by eNB scheduler.A PRB is defined as consisting of 12 consecutive subcarriers for one slot(0.5 msec)in duration.,The transmitted DL signal consists of NBW subcarriers for a duration of Nsymb OFDM symbols.,Time Slot,Subframe,3GPP LTE-Evolved UTRA-Radio Interface Concepts Reference signals,Reference signals are transmitted during the first and fifth OFDM symbols of each slot when the shortCP is used And during the first and fourth OFDM symbols when the long CP is used.,Physical Resource Block(PRB)=14 OFDM Symbols x 12 Subcarrier,f,Subframe(1 ms),Slot(0.5 ms),12 Subcarriers,3GPP LTE-Evolved UTRA-Radio Interface Concepts Reference Signals,In DL,one reference signal is transmitted per antenna port to estimate the channel response for each antenna.,In UL,two types of reference signals are supported:,The estimated channel response is used for channel equalization,to estimate channel quality,3GPP LTE-Evolved UTRA-Radio Interface Concepts LTE-Antenna port configurations(1/2),LTE specifications define several transmission mode with specifics DL reference signalsSingle antenna,2 or 4 antennasAntenna port 0 up to antenna port 3:SISO,Diversity,CL and OL MIMO,3GPP LTE-Evolved UTRA-Radio Interface Concepts LTE-Antenna port configurations(2/2),Single virtual antenna port 5(can be used for BF in TDD)MBMS using virtual antenna port 4Physical Mulicast channels(PMCH)iso PDSCHPMCH shall not be transmitted in SF 0 and 5 on carrier supporting mix of dataSpecific RS pattern,3GPP LTE-Evolved UTRA-Radio Interface Concepts Transmission Mode,TS36 36.213 Rel 8 defined 7 DL transmit modeTM1:Single-antenna port;port 0TM2:Transmit diversity,based on space-frequency block coding(SFBC)TM3:Open-loop spatial multiplexingTM4:Closed-loop spatial multiplexingTM5:Multi-user MIMOTM6:Closed-loop Rank=1 precodingTM7:Single-antenna port;port 5UE is semi-statically configured by eNB via RRC signaling to operate in any of the above 7 modes.,TLA2.0,3GPP LTE-Evolved UTRA-Radio Interface Concepts MIMO and MRC,The LTE PHY can optionally exploit multiple transceivers at both the eNB and UE in order to enhance link robustness and increase data rates for the LTE downlink.In particular,maximal ratio combining(MRC)is used to enhance link reliability in challenging propagating conditions when signal strength is low and multipath conditions are challenging.MIMO is a related technique that is used to increase system data rates.,Conventional Single Channel Receiver w/Antenna Diversity,MRC/MIMO Receiver Configuration(2-ch),3GPP LTE-Evolved UTRA-Radio Interface Concepts MIMO and MRC,With MRC,a signal is received via two(or more)separate antenna/transceiver pairs.Note that the antennas are physically separated,and therefore have distinct channel impulse responses.Channel compensation is applied to each received signal within the baseband processor before being linearly combined to create a single composite received signal.Received signals add coherently within the baseband processor,Increasing in SNR of 3 dB on average for a two-channel MRC receiver in a noise limited environment.,3GPP LTE-Evolved UTRA-Radio Interface Concepts Reference signals from each transmitting antenna for MIMO,In order to successfully receive a MIMO transmission,the receiver must determine the channel impulse response from each transmitting antenna.In LTE,channel impulse responses are determined by sequentially transmitting known reference signals from each transmitting antenna,3GPP LTE-Evolved UTRA-Radio Interface Concepts MIMO Operation(1/2),Note that while one transmitter antenna is sending the reference signal,the other antenna is idle.Referring to the MIMO2x2 system,there are a total of four channel impulse responses(C1,C2,C3 and C4),3GPP LTE-Evolved UTRA-Radio Interface Concepts MIMO Operation(2/2),Once the channel impulse responses are known,data can be transmitted from both antennas simultaneously.,3GPP LTE Channels,2.3,3GPP LTE-Evolved UTRA Protocol Architecture,Logical Channels,Transport Channels,Physical Channels,Layer 3,Layer 2,Layer 1,Control/Measurements,3GPP LTE-Evolved UTRA LTE Downlink:Mapping of Logical,Transport,Physical Channels,LTE makes heavy use of shared channels common control,paging,and part of broadcast information carried on PDSCH,PCCH:paging control channelBCCH:broadcast control channelCCCH:common control channelDCCH:dedicated control channelDTCH:dedicated traffic channelPCH:paging channelBCH:broadcast channelDL-SCH:DL shared channel,3GPP LTE-Evolved UTRA LTE Uplink:Mapping of Logical,Transport,Physical Channels,CCCH:common control channelDCCH:dedicated control channelDTCH:dedicated traffic channelRACH:random access channelUL-SCH:UL shared channelPUSCH:physical UL shared channelPUCCH:physical UL control channelPRACH:physical random access channel,Procedures,2.4,3GPP LTE-Evolved UTRA Cell Search(FDD&TDD),UE acquires time and frequency synchronization with a cell and detects the cell ID of that cell.Based on BCH(Broadcast Channel)signal and hierarchical SCH(Synchronization Channel)signals.P-SCH(Primary-SCH)and S-SCH(Secondary-SCH)are transmitted twice per radio frame.Cell search procedure5 ms timing identified using P-SCH.Radio timing and group ID found from S-SCH.Full cell ID found from DL RS.Decode BCH.,3GPP LTE-Evolved UTRA Random Access Channel(FDD&TDD),The random access channel(RACH)is used during initial access,handoff,or when uplink synchronization is lostUE sends a RACH preamble on physical random access preamble(PRACH)UE first obtains downlink timing from SCH,then sends RACH preamble(non-synchronized)eNB detects timing preamble and sends a timing advance command to time synchronize UE,Gap time reflects the timing uncertainty due to round trip propagation delay CP is used to allow frequency domain processing,and must cover the round trip propagation delay as well as the delay spreadFormats#2 and#3 offer a 2 x 0.8ms preamble repetition to improve detection performance in poor channel conditionsDfRA=1/0.8ms=1.25 kHz sensitivity to doppler shift from high speed UEs(greater than 120 km/hr)Root sequence length=839;different signatures are generated by first using different cyclic shifts of a single root sequence(orthogonal),and then using additional root sequences as needed(low cross-correlation),CP,Zadoff-Chu(ZC)Sequence,Tcp,Tseq,Tgap,RA slot,Max cell size(m)=3E8*Tgap/2,3GPP LTE-Evolved UTRA Contention Based Random Access Procedure(FDD&TDD),PRACH preamble:6 bits(64 signatures)consisting of 5 bits random ID+1 bit infoRA response generated by MAC on DL-SCH using RA-RNTI on associated PDCCHRA-RNTI tied to time/freq resource of PRACHSemi-synchronous,no HARQContains RA preamble identifier,timing alignment info,initial uplink grantFirst scheduled UL transmission on UL-SCHUses HARQFor initial access,contains RRC connection request carried on CCCH,NAS UE identifier but no NAS messageContention resolution on DL-SCHGenerated by RRC and carried on CCCH,3GPP LTE-Evolved UTRA Non-Contention Based Random Access Procedure(FDD&TDD),0.eNB assigns non-contention RA preamb
