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

LTE TARGETs

Network Architecture

Network Architecture – E-UTRAN

User Equipment

Evolved Node B (eNB)Functionalities:

1) resource management (allocation and HO)

2) admission control

3) application of negotiated UL QoS

4) cell information broadcast

5) 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:

1) routing and forwardinguser data packets

2) actsasmobilityanchorfor the userplaneduringinter-eNBhandovers and formobilitybetween LTE and other 3GPP

3) foridle state UEs, terminates the DL data pathand triggerspagingwhenDL data arrivesfor the UE

4) performsreplicationof the usertraffic in case oflawfulinterception.

Network Architecture Evolved Packet Core

Packet Data Network Gateway Functionalities:

1) providesconnectivityto the UE toexternalpacket data networks(IP adresses..). A UE mayhavesimultaneousconnectivitywith more thanone PDN GW foraccessing multiple PDNs

2) performs policy enforcement, packetfilteringforeachuser, chargingsupport, lawfulInterception and packet screening

3) acstas the anchorformobilitybetween 3GPP and non-3GPP technologies (WiMAX)

LTE PHY Layer

+ Includes methods for contrasting distortion due to multipath:

a) OFDM

b) MIMO

+ New access method scheme:

a) OFDMA

b) 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

Possible interference within a CP of two symbols

FTT PERIOD

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

Resource element 1 subcarrier for each symbol period

PRB is the smallest element for resource allocation contains 12 consecutives subcarriers for 1 slot duration

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:

1) Higher data rate more than one flow simultaneously

2) Spatial diversity taking advantage from multiple paths multipath as a resource

- Disadvantages:

1) Complexity

LTE admitted configurations:

- UL: 1x1 ,1x2

-DL: 1x1, 1x2, 2x2, 4x2

Multiple Input – Multiple Output

MIMO techniques in LTE:

1) SU-MIMO

2) Transmitdiversity

3) Closedlooprank1

4) MU- MIMO

5) 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.

Tx Rx- RI: rankindicator- PMI: Precoding Matrix

Indicator- CQI: Channel

QualityIndicator

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 .

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 FDMAAccess scheme for UL different requirements for power consumption!!

OFDMA isaffectedby a high PAPR (PeaktoAveragePowerRatio). Thisfacthas a negative influence on the poweramplifierdevelopment.

Single Carrier FDMA

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

1) Reference signals for channel response estimation (CIR)

2) Synchronization signals for network timing

TRANSPORT CHANNELS

1) Broadcast channel (BCH)

2) Downlink Shared channel (DL-SCH)

- Link adaptation

- Suitable for using beamforming

- Discontinuous receiving/ power saving

1) Paging channel (PGH)

2) 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