Long TermEvolution Beyond 3G
OVERVIEW • LTE targets • Network architecture • LTE Physicallayer • LTE Access tecniques • MIMO • Channels • LTE Advanced
LTE TARGETs • Packet-Domain-Services only (e.g. VoIP) upon LTE, TCP/IP- based layers • Higher peak data rate/ user throughput 100 Mbps DL/50 Mbps UL @20MHz bandwidth • Reduced delay/latency user-plane latency<5ms • Improved spectrum efficiency up to 200 active users in a cell @5MHz bandwidth • Mobility optimized for low-mobility (up to 15Km/h), supported with high performance for medium mobility (up to 120 Km/h), supported for high mobility (up to 500 Km/h) • Multimedia broadcast & multicast services • Spectrum flexibility • Multi-antennas configuration • Coverage up to 30 Km
Network Architecture – E-UTRAN • User Equipment • Evolved Node B (eNB)Functionalities: • resource management (allocation and HO) • admission control • application of negotiated UL QoS • cell information broadcast • ciphering/deciphering of user and control plane data
Network Architecture Evolved Packet Core • Mobility Management Entity key control-node for the LTE ac- cess-network. Functionalities: 1) idle mode UE tracking and paging procedure including retransmissions 2) bearer activation/deactivation process and choice of the SGW for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation 3) authentication of users : it checks the authorization of the UE to camp on the service provider’s Public Land Mobile Network (PLMN) 4) control plane function for mobility between LTE and 2G/3G access
Network Architecture Evolved Packet Core • Serving Gateway Functionalities: • routing and forwardinguser data packets • actsasmobilityanchorfor the userplaneduringinter-eNBhandovers and formobilitybetween LTE and other 3GPP • foridle state UEs, terminates the DL data pathand triggerspagingwhenDL data arrivesfor the UE • performsreplicationof the usertraffic in case oflawfulinterception.
Network Architecture Evolved Packet Core • Packet Data Network Gateway Functionalities: • providesconnectivityto the UE toexternalpacket data networks(IP adresses..). A UE mayhavesimultaneousconnectivitywith more thanone PDN GW foraccessing multiple PDNs • performs policy enforcement, packetfilteringforeachuser, chargingsupport, lawfulInterception and packet screening • acstas the anchorformobilitybetween 3GPP and non-3GPP technologies (WiMAX)
LTE PHY Layer + Includes methods for contrasting distortion due to multipath: • OFDM • MIMO + New access method scheme: • OFDMA • SC-FDMA
Multipath effects • ISI induced by multipath time-domain effect of multipath • Frequency selectivity frequency-domain effect of multipath
Spectrumflexibility • Possibility for using all cellular bands (45o MHz, 800 MHz, 900 MHz, 1700 MHz, 1900 MHz, 2100MHz, 2600MHz) • Differently-sized spectrum allocations - up to 20 MHz for high data rates - less than 5 MHz for migration from 2G technologies
Orthogonal Frequency Division Multiplexing Eliminates ISI problems simplification of channel equalization OFDM breaks the bandwidth into multiple narrower QAM-modulated subcarriers (parallel data transmissions) OFDM symbol is a linear combination of signals (each sub-carrier) VERY LONG SYMBOLS!!!
Orthogonal Frequency Division Multiplexing Cyclic prefix duration linked with highest degree of delay spread FTT PERIOD Possible interference within a CP of two symbols
OFDM Problems Zero ICI achieved if OFDM symbol is sampled exactly at its center f(14/45 KHz..) FFT is realized at baseband after down-conversion from RF
Orthogonal Frequency Division Multiple Access Multiplexing scheme for LTE DL more efficient in terms of LATENCY than classical packet oriented schemes (CSMA/CA) Certain number of sub-carriers assigned to each user for a specific time interval Physical Resource Block (time-frequency dimension) FRAME STRUCTURE:
Orthogonal Frequency Division Multiple Access PRB is the smallest element for resource allocation contains 12 consecutives subcarriers for 1 slot duration Resource element 1 subcarrier for each symbol period
Orthogonal Frequency Division Multiple Access CARRIER ESTIMATION PHY preamble not used for carrier set Use of reference signals transmitted in specific position (e.g. I and V OFDM symbols) every 6 sub-carriers INTERPOLATION is used for estimation of other sub-carriers
Multiple Input – Multiple Output • MIMO CHANNEL Definition of a time-varying channel response for each antenna:
Multiple Input – Multiple Output • In LTE each channel response is estimated thanks to pilot signals transmitted for each antenna When an antenna is transmitting her references, the others are idle. Once the channel matrix is known, data are transmitted simultaneously.
Multiple Input – Multiple Output • Advantages: • Higher data rate more than one flow simultaneously • Spatial diversity taking advantage from multiple paths multipath as a resource - Disadvantages: • Complexity LTE admitted configurations: - UL: 1x1 ,1x2 -DL: 1x1, 1x2, 2x2, 4x2
Multiple Input – Multiple Output MIMO techniques in LTE: • SU-MIMO • Transmitdiversity • Closedlooprank1 • MU- MIMO • Beamforming
Single User MIMO Two way to work: • ClosedLoop • Open Loop • CLOSED LOOP SU-MIMO eNodeBapplies a pre-codification on the transmittedsignal, accordingto the UE channelperception. X Y=WX Tx • RI: rankindicator • PMI: Precoding Matrix Indicator • CQI: Channel QualityIndicator Rx RI, PMI, CQI
Single User MIMO • OPEN LOOP SU-MIMO Usedwhen the feedback rate istoo low and/or the feedback overheadistooheavy. • eNodeBapplies a pre-coded cycling schemetoall the transmittedsubcarriers . X Y=WX Tx Rx
Other MIMO Techniques Transmit diversity Manydifferentantennastransmit the samesignal. At the receiver, the spatialdiversityisexploitedbyusingcombiningtechniques. ClosedLoop Rank-1 The same as the closed loop with RI=1 this assumption reduces the riTx overhead. Multi User MIMO, MU-MIMO The eNodeB can Tx and Rx from more than one user by using the same time-frequency resource Need of orthogonal reference signals. BEAMFORMING The eNodeBuses the antenna beamsaswellasan antenna array.
Single Carrier FDMA Access scheme for UL different requirements for power consumption!! OFDMA isaffectedby a high PAPR (PeaktoAveragePowerRatio). Thisfacthas a negative influence on the poweramplifierdevelopment.
Single Carrier FDMA • 2 ways for mapping sub-carriers Assigning group of frequencies with good propagation conditions for UL UE The subcarrierbandwidthisrelatedto the Doppler effectwhen the mobile velocityisabout 250 Km/h
DL CHANNELS and SIGNALS • Physical channels: convey info from higher layers ° Physical Downlink Shared Channel (PDSCH) - data and multimedia transport - very high data rates supported - BPSK, 16 QAM, 64 QAM ° Physical Downlink Control Channel (PDCCH) • Specific UE information • Only available modulation (QPSK) robustness preferred
DL CHANNELS and SIGNALS ° Common Control Physical Channel (CCPCH) • Cell wide control information • Only QPSK available • Transmitted as closed as the center frequency as possible • Physical signals: convey information used only in PHY layer • Reference signals for channel response estimation (CIR) • Synchronization signals for network timing
TRANSPORT CHANNELS • Broadcast channel (BCH) • Downlink Shared channel (DL-SCH) - Link adaptation - Suitable for using beamforming - Discontinuous receiving/ power saving • Paging channel (PGH) • Multicast channel (MCH)
UL CHANNELS ° Physical Uplink Shared Channel (PUSCH) • BPSK, 16 QAM, 64 QAM ° Physical Uplink Control Channel (PUCCH) • Convey channel quality information • ACK • Scheduling request ° Uplink Shared channel (UL-SCH) ° Random Access Channel (RACH)
UL SIGNALS • Random Access Preamble transmitted by UE when cell searching starts • Reference signal
CHANNEL MAPPING DOWNLINK UPLINK
Beyond the future: LTE Advanced • Relay NodesUE • Dual TX antenna solutions for SU-MIMO and diversity MIMO • Scalable system bandwidth exceeding 20 MHz, Potentially up to 100 MHz • Local area optimization of air interfaceNomadic / Local Area network and mobility solutions • Flexible Spectrum Usage / Cognitive radio • Automatic and autonomous network configuration and operation • Enhanced precoding and forward error correction • Interference management and suppression • Asymmetric bandwidth assignment for FDD • Hybrid OFDMA and SC-FDMA in uplinkUL/DL inter eNB coordinated MIMO