Long Term Evolution Beyond 3G

OVERVIEW LTE targets Network architecture LTE Physical layer 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

LTE TARGETs

Network Architecture

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 forwarding user data packets acts as mobility anchor for the user plane during inter-eNB handovers and for mobility between LTE and other 3GPP for idle state UEs, terminates the DL data path and triggers paging when DL data arrives for the UE performs replication of the user traffic in case of lawful interception.

Network Architecture Evolved Packet Core Packet Data Network Gateway  Functionalities: provides connectivity to the UE to external packet data networks (IP adresses..). A UE may have simultaneous connectivity with more than one PDN GW for accessing multiple PDNs performs policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening acst as the anchor for mobility between 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

Spectrum flexibility 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: LTE FRAME DURATION 10ms diviso per 10 sub-frame Ogni sub-frame è spezzato in 2 time slot Ogni slot contiene 6/7 OFMD symbol a seconda del CP

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 Transmit diversity Closed loop rank 1 MU- MIMO Beamforming

Single User MIMO Two way to work: Closed Loop Open Loop CLOSED LOOP SU-MIMO eNodeB applies a pre-codification on the transmitted signal, according to the UE channel perception. Tx Rx X Y=WX RI, PMI, CQI RI: rank indicator PMI: Precoding Matrix Indicator CQI: Channel Quality Indicator

Single User MIMO OPEN LOOP SU-MIMO Used when the feedback rate is too low and/or the feedback overhead is too heavy. eNodeB applies a pre-coded cycling scheme to all the transmitted subcarriers . Tx Rx X Y=WX

Other MIMO Techniques Transmit diversity Many different antennas transmit the same signal. At the receiver, the spatial diversity is exploited by using combining techniques. Closed Loop 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 eNodeB uses the antenna beams as well as an antenna array.

Single Carrier FDMA Access scheme for UL  different requirements for power consumption!! OFDMA is affected by a high PAPR (Peak to Average Power Ratio). This fact has a negative influence on the power amplifier development.

Single Carrier FDMA

Single Carrier FDMA 2 ways for mapping sub-carriers Assigning group of frequencies with good propagation conditions for UL UE The subcarrier bandwidth is related to the Doppler effect when the mobile velocity is about 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