lte by bruno melis

7/30/2019 LTE by Bruno Melis

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Telecom Italia Proprietary

Outline LTE Study Item

Rationale & Objectives

Requirements

LTE Key enabling Technologies

OFDM

MIMO

All IP Flat Architecture

LTE peak rates and UE categories

LTE radio interface and procedures

LTE Advanced overview

Requirements with respect to Release 8

Additional features


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LTE Study Item (2004): Rationale & objectivesFROM 3GPP TR 25.913:

to ensure competitiveness in an even longer time frame, i.e. for the next 10 years and

beyond, a long-term evolution of the 3GPP radio-access technology needs to be considered.

Important parts of such a long-term evolution include reduced latency, higher user data

rates, improved system capacity and coverage, and reduced cost for the operator. In order to

achieve this, an evolution of the radio interface as well as the radio network architecture should

be considered.

.Considering a desire for even higher data rates and also taking into account future

additional 3G spectrum allocations the long-term 3GPP evolution should include an evolution

towards support for wider transmission bandwidth than 5 MHz. At the same time, support for

transmission bandwidths of 5 MHz and less than 5 MHz should be investigated in order to allow

for more flexibility in whichever frequency bands the system may be deployed.


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FROM 3GPP TR 25.913

The objective of Evolved UTRA and UTRAN is to develop a framework for the

evolution of the 3GPP radio-access technology towards a high-data-rate, low-

latency and packet-optimized radio-access technology. Thus the study should focus

on supporting services provided from the PS-domain. In order to achieve this,

studies should be carried out in at least the following areas:

Related to the radio-interface physical layer (downlink and uplink): e.g. means to support flexible transmission bandwidth up to 20 MHz, introduction

of new transmission schemes and advanced multi-antenna technologies

Related to the radio interface layer 2 and 3: e.g. signalling optimization

Related to the UTRAN architecture: identify the most optimum UTRAN network architecture and functional split

between RAN network nodes, not precluding considerations on the functional

split between UTRAN and CN

LTE Study Item (2004): Rationale & objectives


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FROM 3GPP TR 25.913 The targets for the evolution of the radio-interface and radio-access network

architecture should be: Significantly increased peak data rate e.g. 100 Mbps (downlink) and 50 Mbps (uplink)

Increase "cell edge bitrate" whilst maintaining same site locations as deployed today

Significantly improved spectrum efficiency ( e.g. 2-4 times over UMTS/HSPA Release 6)

Possibility for a Radio-access network latency (user-plane UE RNC (or corresponding

node above Node B - UE) below 10 ms

Significantly reduced C-plane latency (e.g. including the possibility to exchange user-

plane data starting from camped-state with a transition time of less than 100 ms

(excluding downlink paging delay)

Scalable bandwidth

5, 10, 20 and possibly 15 MHz

allow flexibility in narrow spectral allocations where the system may be

deployed



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FROM 3GPP TR 25.913

The targets for the evolution of the radio-interface and radio-access networkarchitecture should be: Support for inter-working with existing 3G systems and non-3GPP specified systems

Reduced CAPEX and OPEX including backhaul

Cost effective migration from Release 6 UTRA radio interface and architecture

Reasonable system and terminal complexity, cost, and power consumption.

Support of further enhanced IMS and core network

Backwards compatibility is highly desirable, but the trade off versus performance and/orcapability enhancements should be carefully considered.

Efficient support of the various types of services, especially from the PS domain (e.g.Voice over IP, Video streaming, Gaming, etc.)

System should be optimized for low mobile speed but also support high mobile speed

Operation in paired and unpaired spectrum should not be precluded

Possibility for simplified co-existence between operators in adjacent bands as well ascross-border co-existence



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Requirements of LTE (1/3)

100 Mbit/s DL and 50 Mbit/s UL within a 20 MHz bandwidth

Peak data rate

Downlink: in a loaded network, target for spectrum efficiency (bits/sec/Hz/site)is 3 to 4 times Release 6 HSDPA.

Uplink: in a loaded network, target is 2 to 3 times Release 6 HSUPA

Spectral Efficiency

Optimized for low mobile speed from 0 to 15 km/h

Higher speeds between 15 and 120 km/h supported with high performance

Mobility shall be maintained at speeds from 120 km/h to 350 km/h (or even upto 500 km/h depending on the frequency band)

Mobility

* Details in 3GPP TR 25.913


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Performance should be met for 5 km cells, with slight degradation for 30 kmcells. Cells range up to 100 km should not be precluded

Coverage

At least 200 users per cell supported in the active state for spectrum allocationsup to 5 MHz

Control plane capacity

User plane : less than 5 ms in unload condition (i.e. single user with single datastream) for small IP packet

Control plane : transition time of less than 100 ms from a camped state to anactive state

Latency


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Support for spectrum allocations of different sizes (1.4 MHz - 20 MHz). Operation in paired (FDD) and unpaired (TDD) spectrum shall be supported

Spectrum flexibility

Provision of simultaneous dedicated voice and MBMS services to the user

MBMS (Multimedia Broadcast Multicast Service)

The E-UTRAN architecture shall be packet based, but should support real-timeand conversational class traffic

Enhanced support for end-to-end QoS

Architecture


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to summarise the main ones:

RANUE

Coverage:

5 km: full performance

30 km: some degradations

100 km: not prevented

DL

Peak data rate: 100Mbps

UL

Peak data rate: 50Mbps

UL

DL

Mobility:

0-15 km/h: optimized

15-120 km/h: high performance

120-500 km/h: supported

Scalable BW:

1.4 3 5 10 15 - 20 MHz

User Plane Latency: 5ms

Control Plane Latency:

50-100 ms
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Key enabling technologies for Long Term Evolution

x1

x2

x3

y1

y2

y3

MIMO Network Evolution

eNBeNB

eNB

MME/UPE MME/UPE

S1

X2

X2

X2

Evolved

Packet

Core

E-UTRAN

OFDMScalable Bandwidth

RECIPES


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Orthogonal Frequency Division Multiplexing (OFDM) is a particular form of multi-

carrier modulation (MCM).

MCM is a parallel transmission method which divides a high bandwidth signal intoseveral narrower bandwidth subcarriers and transmits data simultaneously on each

subcarrier.

Orthogonal Frequency Division Multiplexing


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It is possible to demonstrate that the signal sent on the channel is the reverse FFT

(or IFFT, Inverse Fast Fourier Transform) of the source signal. A reverse FFT is then

carried out within the transmitter from the N input parallel flows. High spectral efficiency is guaranteed being the sub-carrier orthogonal to each

other.

Orthogonal Frequency Division Multiplexing

OFDM is well suited for high data rate systems

which operate in multi-path environmentsbecause of its robustness to delay spread.

0

1

2

1

2

0

1

2

0

1

2

1

2

0

1

2

1

2

0

1

2

0

1

2


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OFDM: Orthogonal Frequency Division ModulationOFDM as modulation

Spectrum is divided in several orthogonal sub-carriers : f=1/Ts

Information flow is divided over the sub-carriers

Mo-demodulation by FFT/iFFT

OFDM as mulitple access (OFDMA)

A group of sub-carriers can be allocated to different users inside the available

bandwidth

ffsingle-carrier mod.

fconventional multi-

carrier modulation

OFDM


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OFDM: Characteristics

Sub-carriers

FFT

Time

Symbols

N subcarriers in W

Bandwidth

Guard Intervals

Frequency

f=1/Ts


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High resistance to multipath propagation

Low implementation complexity (IFFT/FFT)

Sharp power spectrum decrease at the band edges

Inter-Symbol Interference (ISI) is eliminated at the receiver by removing the cyclic prefix

(i.e. no need for channel equalizers or Rake receivers)

Space-time processing operations performed independently for each sub-carrier (lower

receiver complexity that single carrier transmission)

High Peak to Average Power Ratio (PAPR)

Power amplifiers with high linearity are required (critical issue on the terminal side)

Sensitivity to frequency offset and phase noise

Advantages

Disadvantages

Orthogonal Frequency Division Multiplexing (OFDM)

frequency

sub-carriers

f

Power spectrum)( fX


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In 3GPP Long Term Evolution:

Orthogonal Frequency Division Multiple Access (OFDMA) is used in downlink direction

Single Carrier Frequency Division Multiple Access (SC-FDMA) is used in the uplinkdirection

OFDM in 3GPP Long Term Evolution

Downlink Multiple access is achieved in OFDMA by assigning subsets of subcarriers to

individual users. The subcarrier spacing in the OFDM downlink is 15 kHz and there is

a maximum of 2048 subcarriers available. The transmission is divided in time into

time slots of duration 0.5 ms and subframes of duration 1.0 ms. A radio frame is 10

ms long. Supported modulation formats on the downlink data channels are QPSK,

16-QAM and 64-QAM.

Uplink SC-FDMA was chosen in order to reduce Peak to Average Ratio (PAR), which has been

identified as a critical issue for use of OFDMA in the uplink where power efficient

user-terminal amplifiers are required. Another important requirement was to

maximize the coverage. For each time interval, the base station scheduler assigns aunique time-frequency interval to a terminal for the transmission of user data,

thereby ensuring intra-cell orthogonality.


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Multi-Antenna techniques

x1

x2

x3

y1

y2

y3

Multiple input multiple output (MIMO) antenna techniques are required to achieve the

higher LTE bit-rate targets.

MIMO is simpler to implement with OFDMA than with CDMA, and it is more effective,

since OFDMA is more robust to multipath and MIMO can exploit rich scattering

environment without being negatively affected by multipath.

For this reason, MIMO schemes up to 4x4 are defined in the LTE Release 8 standard.

MIMO can be used to provide both spatial multiplexing and space-time coding.

Spatial Multiplexing Space Time Coding


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E-UTRAN architecture

The E-UTRAN consists of eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and

control plane (RRC) protocol terminations towards the UE.

The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core),

more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to

the Serving Gateway (S-GW) by means of the S1-U.

internet

eNB

RB Control

Connection Mobility Cont.

eNB MeasurementConfiguration & Provision

Dynamic ResourceAllocation (Scheduler)

PDCP

PHY

MME

Serving Gateway

S1

MAC

Inter Cell RRM

Radio Admission Control

RLC

E-UTRAN EPC

RRC

Mobility Anchoring

SAE Bearer Control

Idle State MobilityHandling

NAS Security

Logical Nodes

Radio Protocol Layers

Functional Entities of Control Plane


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eNB functionalities

The eNB hosts the following functions:

Functions for RRM: Radio Bearer Control, Radio Admission Control, ConnectionMobility Control, Dynamic allocation of resources to UEs in both uplink and

downlink (scheduling)

IP header compression and encryption of user data stream

Selection of an MME at UE attachment

Routing of User Plane data towards S-GW Scheduling and transmission of paging messages (originated from the MME)

Scheduling and transmission of broadcast information (originated from the MME orO&M)

Measurement and measurement reporting configuration for mobility and scheduling


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MME and S-GW functionalities

The MME hosts the following functions:

Distribution of paging messages to the eNBs Security control

Idle state mobility control

SAE bearer control

Ciphering and integrity protection of NAS signalling

The Serving Gateway hosts the following functions:

Termination of U-plane packets for paging reasons

Switching of U-plane for support of UE mobility

NAS = Non-Access Stratum

SAE = System Architecture Evolution


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Radio protocol architecture

User plane: the protocol stack comprises PDCP, RLC, MAC

and PHY sublayers (terminated in eNB on the network side)The PDCP, RLC and MAC perform the functions of header

compression, ciphering, ARQ, scheduling and HARQ.

Control plane: the protocol stack comprises NAS,

(terminated in MME), RRC, PDCP, RLC, MAC and PHY

sublayers (terminated in eNB).

eNB

PHY

UE

PHY

MAC

RLC

MAC

PDCPPDCP

RLC

eNB

PHY

UE

PHY

MAC

RLC

MAC

MME

RLC

NAS NAS

RRC RRC

PDCP PDCP

* Details in 3GPP TS 36.300


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Layer 3 radio protocol

Layer 3 is composed by the RRC (Radio Resource Control) that is terminated in the eNB on

the network side

Broadcast of System Information related to the non-access stratum (NAS) and tothe the access stratum (AS)

Paging Establishment, maintenance and release of an RRC connections

Security functions including key management Establishment, configuration, maintenance and release of point to point Radio

Bearers (RB)

Mobility functions including: Inter-cell handover, UE cell selection and reselection QoS management functions

UE measurement reporting and control of the reporting

The main layer 3 functions are:


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Layer 2 radio protocol

Layer 2 is split into Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data

Convergence Protocol (PDCP).

The multiplexing of several logical channels (i.e. radio bearers) on the same transportchannel (i.e. transport block) is performed by the MAC sublayer.

In uplink and downlink, only one transport block is generated per TTI in the non-MIMO case.

Layer 2 Structure for DL(user plane)

Segm.

ARQ

Multiplexing UE1

Segm.

ARQ...

HARQ

Multiplexing UEn

HARQ

BCCH PCCH

Scheduling / Priority Handling

Logical Channels

Transport Channels

MAC

RLCSegm.

ARQ

Segm.

ARQ

PDCP

ROHC ROHC ROHC ROHC

Radio Bearers

Security Security Security Security

...

ROHC = robust header compression

Ciphering


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LTE numerology

An Orthogonal Frequency Division Multiple Access (OFDMA) scheme is employed for

downlink (DL) transmission.

Scalable-OFDM (S-OFDM) technology is employed: the sub-carrier spacing f is fixed andequal to 15 KHz, independently from the transmission bandwidth so that the number

NFFT of subcarriers is proportional to the transmission bandwidth (BW).

The clock frequency can be derived from the W-CDMA chip-rate (3.84 MHz)

Channel Bandwidth (BW) 1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz

Subframe duration 1.0 ms

Sub-carrier spacing (f) 15 kHz

Sampling frequency1.92 MHz

(1/2 3.84 MHz)3.84 MHz

7.68 MHz

(2 3.84 MHz)

15.36 MHz

(4 3.84 MHz)

23.04 MHz

(6 3.84 MHz)

30.72 MHz

(8 3.84 MHz)

FFT size (NFFT) 128 256 512 1024 1536 2048

Number of used

sub-carriers72 180 300 600 900 1200

Number of

OFDM symbols

per sub frame

(Normal/Extended CP)

7/6

CP length

(s/samples)

Normal(4.69/9) 6,

(5.21/10) 1*

(4.69/18) 6,

(5.21/20) 1

(4.69/36) 6,

(5.21/40) 1

(4.69/72) 6,

(5.21/80) 1

(4.69/108) 6,

(5.21/120) 1

(4.69/144) 6,

(5.21/160) 1

Extended (16.67/32) (16.67/64) (16.67/128) (16.67/256) (16.67/384) (16.67/512)

LTE peak data rates (theoretical calculation)


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LTE peak data rates (theoretical calculation)

Downlink (20 MHz, code rate 0.95, 64-QAM) 150 Mbit/s with 22 MIMO 300 Mbit/s with 44 MIMO

Uplink (20 MHz, code rate 0.95, Single transmit antenna) 50 Mbit/s with 16-QAM 75 Mbit/s with 64-QAM

BUT with 2x2 MIMO in the 5 MHz bandwidth the DL

peak throughput would be similar to HSPA+

LTE bandwidth [MHz] 1.4 3 5 10 15 20

Number of PRB 6 15 25 50 75 100

Number of OFDM symbols for PDCCH 2 2 2 2 2 2

Number of data subcarriers per TTI 132 132 132 132 132 132

Modulation 6 6 6 6 6 6

Number of TX antennas 2 2 2 2 2 2

Maximum Code Rate 0.95 0.95 0.95 0.95 0.95 0.95

DL Peak Throughut [Mbit/s] 9.0 22.6 37.6 75.2 112.9 150.5

LTE bandwidth [MHz] 1.4 3 5 10 15 20

Number of PRB 6 15 25 50 75 100

Number of PRBs used for UL control CH 2 2 4 6 8 8

Number of OFDM symbols for RS 2 2 2 2 2 2

Number of data subcarriers per TTI 144 144 144 144 144 144

Modulation 6 6 6 6 6 6

Number of TX antennas 1 1 1 1 1 1

Maximum Code Rate 0.95 0.95 0.95 0.95 0.95 0.95

UL Peak Throughut [Mbit/s] 3.3 10.7 17.2 36.1 55.0 75.5


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UE categories


Downlink capabilities

Uplink capabilities

16-QAM only

Support of 64-QAM

4 Rx antennas

UE Category Maximum number of

DL-SCH transportblock bits received

within a TTI

Peak Throughput

supported by theUE [Mbit/s]

Maximum number

of supportedlayers for spatial

multiplexing in DL

Category 1 10296 10.296 1

Category 2 51024 51.024 2

Category 3 102048 102.048 2

Category 4 150752 150.752 2

Category 5 299552 299.552 4

UE Category Maximum number of

bits of an UL-SCH

transport block

transmitted within a

TTI

Peak Throughput

supported by the

UE [Mbit/s]

Support for

64QAM in UL

Category 1 5160 5.16 No

Category 2 25456 25.456 NoCategory 3 51024 51.024 No

Category 4 51024 51.024 No

Category 5 75376 75.376 Yes

LTE f


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LTE frame structures

Downlink and uplink transmission are organized into radio frames with duration Tf = 10 ms.

Two radio frames structures are supported

Type 1 frame structure Applicable to FDD and HD-FDD duplexing

Type 2 frame structure Applicable to TDD duplexing

Type 1 frame structureType 2 frame structure

The alternative frame structure has been defined to facilitate the coexistence with the 1.28

Mchip/s UTRA TDD system (i.e. the TD-SCDMA standard primarily adopted in China).

#0 #1 #18 #19#2

Sub-frame

slot

One radio frame = 10ms

0.5 msOne radio frame = 10 ms

Half-frame = 5 ms

Subframe = 1 ms

#0 #2 #3 #4

DwPTS

GP

UpPTS* Details in 3GPP TS 36.211

T 1 f t t


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Each radio frame consists of 20 slots each of length Tslot = 0.5 ms.

A subframe is defined as two consecutive slots where subframe j consists of slots 2j and 2j+1

For FDD duplexing, downlink and uplink transmission are separated in the frequency domain

and both the downlink and uplink frame is composed by 10 subframes of 1 ms each.

Type 1 frame structure

2048

1

2048

f

TT

symb

s

sampling time = 32.6 ns

f = subcarrier spacing = 15 KHz

symbT = OFDM symbol duration = 66.6 s

sT

#0 #1 #2 #3 #19#18

One radio frame, Tf= 307200Ts = 10 ms

One slot, Tslot = 15360Ts = 0.5 ms

One subframe


Sl t t t


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Slot structure

Slot period equal to 0.5 ms and TTI= 1ms

Two cyclic prefix lengths : normal and extended

Number of OFDM symbols per slot : 7 (normal CP) or 6 (extended CP)

Normal cyclic prefix: TCP = 160Ts (OFDM symbol #0) , TCP = 144Ts (OFDM symbol #1 to #6)

Extended cyclic prefix: TCP-e = 512Ts (OFDM symbol #0 to OFDM symbol #5)

Symb 0 Symb 1 Symb 2 Symb 3 Symb 4 Symb 5

Tslot = 0.5 ms

Tsymb = 66.7 sTCP = 16.6 s

Extended CP

Symb 6 Normal CPymb 5ymb 4ymb 3ymb 2ymb 1ymb 0

TCP = 4.69 sTCP = 5.21 s

Ph i l R bl k (PRB) (1/2)


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Physical Resource block (PRB) (1/2)

Physical Resource Block : is the smallest unit of bandwidth assigned by the scheduler at

physical level. One PRB is composed by a set of 12 adjacent subcarriers allocated on a slot-

by-slot basis. Resource element : each subcarrier in the resource grid

Physical Resource Block (PRB)Resource Element (k,l)

RB

SCN subcarriers

RB

SC

DL

RB NN subcarriers

DL

symbN

OFDM

symbols

l=0

l = 1D L

sy m bN

k=0 k= 1RB

SC

DL

RB NN

Slot

freq

time




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Channel bandwidth

BW [MHz]1.4 3 5 10 15 20

Number of active PRBs

per slot (NRB)6 15 25 50 75 100

The following symbols are introduced in the 3GPP standard (TS 36.211)

DL

RBN = downlink bandwidth configuration, expressed in number of resource blocks

RB

SCN = resource block size in the frequency domain, expressed as a number of subcarriers

The quantity depends on the downlink transmission bandwidth configured in the cellDLRBN

The quantities and depend on the frame structure and on the cyclic prefix typeRBSCN

DL

symbN

DL

symbN = number of OFDM symbols in a downlink slot


ConfigurationRBscN

DLsymbN

Normal cyclic prefix kHz15f 7

kHz15f 12

6Extended cyclic prefix

kHz5.7f 24 3

LTE Physical Channels (DL) (1/2)


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Physical broadcast channel (PBCH)

Mapped to four subframes within a 40 ms interval

Each subframe is self-decodable

Timing is blindly detected (i.e. no explicit signalling indicating 40 ms timing)

Physical control format indicator channel (PCFICH)

Informs the UE about the number of OFDM symbols used for the PDCCHs

Transmitted in every subframe

Physical downlink control channel (PDCCH)

Informs the UE about the resource allocation and H-ARQ information related to

DL-SCH and PCH

Carries the uplink scheduling grant.

eNB

UE

PBCH

PCFICH

PDCCH



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Physical downlink shared channel (PDSCH)

Carries the DL-SCH

Physical multicast channel (PMCH)

Carries the MCH

Physical Hybrid ARQ Indicator Channel (PHICH)

Carriers ACK/NAKs in response to uplink transmissions

eNB

UE

PDSCH

PMCH

PHICH

LTE Physical Channels (UL)


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LTE Physical Channels (UL)

Physical uplink shared channel (PUSCH)

Carries the UL-SCH

Physical uplink control channel (PUCCH)

Carries ACK/NAKs in response to downlink transmission

Carries Scheduling Request (SR)

Carries CQI reports

Physical random access channel (PRACH)

Carries the random access preamble

eNB

UE

PUSCH

PUCCH

PRACH

DL Reference Signals


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DL Reference Signals

The Reference Signal (RS) consist of known reference symbols inserted in the first and third

last OFDM symbol of each slot (in case of normal CP)

Cell-specific reference signals are transmitted on one or several of antenna ports from 0 to 3

Cell-specific reference signals are defined for f=15 kHz only

The reference-signal sequence is defined by

There are 504 unique cell IDs

Code Division Multiplexing (CDM) is used for distinguishing RSs of sectors belonging to the

same eNB

Frequency Division Multiplexing (FDM) is used for distinguishing RSs of each antenna in case

of MIMO


12,...,1,0,)12(212

1)2(21

2

1)( DLmax,RB, s Nmmcjmcmr nl

)(s,mr nl

where nS is the slot number within a radio frame and l is the OFDM symbol number within the

slot. The pseudo-random sequence c(i) is initialised at the start of each OFDM symbol with a

function that depends on nS , l and the cell ID

DL Reference Signals (SISO)


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DL Reference Signals (SISO)

pR reference signal transmitted on antenna port p

Time

Frequency

1 ms

180

kHz

Normal CP Extended CP

1 ms

Pilot pattern for a SISO system

DL Reference Signals (MIMO)


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DL Reference Signals (MIMO)

Pilot pattern for a MIMO system (normal CP)

1 ms

180

kHz

Antenna port 0 Antenna port 1

MIMO 22

MIMO 44

DL Control Channels (1/2)


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DL control signalling is located in the first n OFDM symbols (n 3) of a subframe and

consists of:

Downlink control channels and data are transmitted on different OFDM symbols

Number n of control OFDM symbols per subframe (PCFICH)

Transport format, resource allocation, and hybrid-ARQ information (PDCCH)

Uplink scheduling grant (PDCCH)

ACK/NAK in response to uplink transmission (PHICH)

Time

Frequency

180

kHz

Control Data



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Multiple physical downlink control channels are supported and a UE monitors a set of

control channels.

Control channels are formed by aggregation of control channel elements (CCE), each

control channel element consisting of a set of resource elements

QPSK modulation is used for all control channels

Control information is decodable without using the 2nd RS symbol (UE micro-sleep)

H-ARQ


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H ARQ

UL/DL H-ARQ characteristics:

N-process Stop-And-Wait

H-ARQ transmits and retransmits Transport Blocks (TBs) H-ARQ retransmissions have lower priority than measurement gaps

UL H-ARQ principles:

Synchronous adaptive / non adaptive HARQ

Adaptive retransmissions are scheduled through PDCCH

Non-adaptive retransmissions are triggered by a NACK on PHICH only DL ACK / NACK in response to UL (re)transmissions are sent on PHICH

Maximum number of retransmissions configured per UE

DL H-ARQ principles:

Asynchronous adaptive H-ARQ

UL ACK/NAKs in response to DL (re)transmissions are sent on PUCCH or PUSCH

PDCCH signals the H-ARQ process number and if it is a transmission or retransmission

Retransmissions are always scheduled through PDCCH

Modulation


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Modulation

For each code word q, the block of scrambled bits is modulated resulting in a block of

complex-valued modulation symbols

Modulation schemes for DL physical channels

Modulation schemes for UL physical channels


Physical

channel

Definition Modulation scheme

PDSCH Physical Downlink Shared Channel QPSK, 16-QAM, 64-QAM

PBCH Physical Broadcast Channel QPSK

PMCH Physical Multicast Channel QPSK, 16-QAM, 64-QAM

PCFICH Physical Control Format Indicator Channel QPSK

PDCCH Physical Downlink Control Channel QPSKPHICH Physical Hybrid ARQ Control Channel BPSK

Physical

channel

Definition Modulation scheme

PUSCH Physical Uplink Shared Channel QPSK, 16-QAM, 64-QAM

PUCCH Physical Uplink Control Channel BPSK, QPSK, BPSK + QPSK

PRACH Physical Random Access Channel Specific Zadoff-Chu sequences

Single Carrier FDMA


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Single Carrier FDMA

Single carrier FDMA (SC-FDMA) accommodates multiple-user access

Also known as DFT-precoded OFDMA

Similarities with OFDMA:

Block-based modulation

Divides the transmission bandwidth into smaller subcarriers

Channel equalization done in the frequency domain

CP added to overcome ISI (Inter Symbol Interference) and to convert

linear convolution of the channel impulse response to circular one

Advantages over OFDMA:

Lower PAPR than OFDMA (efficient UE transmitter, improved cell-edge performance)

DFT

Sub-

carrierMapping

IFFT CPinsertion

(size M) (size NM)

Uplink Transmission Scheme


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Based on single-carrier FDMA

Uplink sub-carrier spacing f = 15 kHz. The sub-carriers are grouped into sets of 12

adjacent sub-carriers

One PRB corresponds to 12 adjacent sub-carriers during one slot period (0.5 ms). The

number of resource blocks can range from 6 (1.25 MHz) to 100 (20 MHz)

There are two cyclic-prefix lengths defined: normal cyclic prefix and extended cyclic

prefix corresponding to seven and six SC-FDMA symbols per slot respectively

Normal cyclic prefix: TCP = 160Ts (OFDM symbol #0) , TCP = 144Ts (OFDM symbol #1 to #6)

Extended cyclic prefix: TCP-e = 512Ts (OFDM symbol #0 to OFDM symbol #5)

Uplink reference signals (for channel estimation and coherent demodulation) are

transmitted in the 4-th symbol of the slot


Subcarrier mapping


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Subcarrier mapping

Two subcarrier mapping schemes analyzed during the standardization

Distributed: inherent frequency diversity, lower PAPR in case of IFDMA

Localized: better performance with frequency domain scheduling and H-ARQ,

higher PAPR than the case of IFDMA

3GPP decided to use only the localized mapping for LTE uplink with support for inter-TTI

FH and intra-TTI FH (RAN1 #46bis - R1-063613)

Distributed Mapping Localized Mapping



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Based on single-carrier FDMA, UL sub-carrier spacing f = 15 kHz.

While the maximum transmission bandwidth is up to 20 MHz, the minimum transmission

bandwidth is down to 180 kHz, equal to the 12 x 15 kHz sub-carriers in the downlink

direction or, rather, one resource block.

One PRB corresponds to 12 adjacent sub-carriers during one slot period (0.5 ms). The

number of resource blocks can range from 6 (1.4 MHz) to 100 (20 MHz)


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LTE Physical Layer procedures

Transmission Time Adjustment


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j

Upon reception of a timing advance command, the UE shall adjust its uplink

transmission timing

The timing advance command is expressed in multiples of 16Ts ( 521 ns) and is relative

to the current uplink timing

For a timing advance command received on subframe n, then corresponding adjustment

occurs at the beginning of subframe n+x


CyclicPrefixUser A

User B

User C

TD max

Selected sampling window

for users A, B and CT

CyclicPrefix

CyclicPrefix

eNB

UE C

UE A

UE B

S1

S-GW

Random Access Channel (RACH)


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( )

RACH is an uplink common transport channel

Two random access procedures : contention based and non-contention based (for HO)

The PRACH preamble consists of a CP of length TCP and a sequence part of length TSEQ

In the frequency domain the PRACH occupies a bandwidth corresponding to 6 PRB

RACH preambles are generated from Zadoff-Chu sequences with zero correlation zone.

The network configures the set of preamble sequences the UE is allowed to use

Normal cells

Extended format : large cells

Repeated format : very large cells (up to 30 km)

Repeated format : very large cells (up to 100 km)

sampling time = 32.6 nssT


Random Access Channel (RACH)


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( )

CQI definition


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The CQI table is defined in terms of channel coding rate and modulation scheme

A UE reports a CQI index corresponding to a transport format with 10% BLER target at

the first H-ARQ transmission, over the set of PRBs corresponding to the CQI value.

CQI index modulation code rate x 1024 efficiency

0 out of range

1 QPSK 78 0.1523

2 QPSK 120 0.2344

3 QPSK 193 0.3770

4 QPSK 308 0.6016

5 QPSK 449 0.87706 QPSK 602 1.1758

7 16QAM 378 1.4766

8 16QAM 490 1.9141

9 16QAM 616 2.4063

10 64QAM 466 2.7305

11 64QAM 567 3.3223

12 64QAM 666 3.9023

13 64QAM 772 4.523414 64QAM 873 5.1152

15 64QAM 948 5.5547

CQI reporting


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CQI reporting is periodic or aperiodic

UE transmits CQI reporting on the PUCCH for subframes with no PUSCH transmission and

on the PUSCH for those subframes with scheduled PUSCH transmissions

Three reporting methods:


Wideband CQI

Higher Layer-configured subband feedback

UE-selected subband feedback (best-M algorithm)

A subband is a set of k contiguous PRBs, where k is semi-statically configured by higher

layersSystem Bandwidth Subband Size

DLRBN

(k)

6 - 7 (wideband CQI only)

8 - 10 411 - 26 4

27 - 64 6

64 - 110 4, 8

Downlink Power Allocation


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Downlink power allocation determines the Energy Per Resource Element (EPRE)

The EPRE denotes the energy prior to CP insertion and averaged over all constellation

points

A UE assumes downlink RS EPRE is constant across the downlink system bandwidth and

constant across all subframes until different RS boosting information is received

For each UE, the PDSCH-to-RS EPRE ratio in all the OFDM symbols containing RS is equal

to P_A, whereas in the OFDM symbols not containing RS is equal to P_B

The cell-specific ratio between P_A and P_B is determined by eNB based on the cell-

specific RS boosting value

P_A(EPRE)RS

(EPRE)PDSCH P_B

(EPRE)RS

(EPRE)PDSCH

OFDM symbols with RS OFDM symbols without RS

Uplink Power Control (1/2)


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Uplink power control determines the average power over a DFT-SOFDM symbol in which

the physical channel is transmitted

The setting of the UE Transmit power for the physical uplink shared channel (PUSCH)

transmission in subframe i is defined by

)}())(()())((log10,min{)( MCSO_PUSCHPUSCH10MAXPUSCH ifiMCSPLjPiMPiP

where:

= maximum allowed power that depends on the UE power class

= bandwidth of the PUSCH transmission expressed in number of PRB

= parameter with 1 dB resolution signalled by higher layers

MAXP

)(PUSCH iM

)(O_PUSCH jP

Uplink Power Control (2/2)


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= 3-bit cell specific parameter signalled by HL

= downlink pathloss estimate calculated in the UE

= cell specific values function of MCS and signalled by RRC

= UE specific correction value

1,9.0,8.0,7.0,6.0,5.0,4.0,0

PL

))((MCS iMCS

)( if

)()1()( P U S C HP U S C H Kiifif

= is a UE specific correction value, also referred to as a TPC command and

transmitted on PDCCH

P U S C H


Static ICIC: Fractional Frequency Reuse


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f

P

f

P

f

P

P

P

PbN N

bN N

bN N

b

Static ICIC: Soft Frequency Reuse


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f

P

P

f

P

P

f

P

P

Semi static ICIC


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eNB

eNB

eNB

Reactive ICIC

Reactive ICIC

Release 8Proactive ICIC messages over X2:UL: HII (High Interference Indicator)DL: RNTP (Relative Narrow band Transmit Power)Reactive ICIC messages over X2:UL: OI (Overload Indicator)

LTE Standard Specifications


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Physical layer specifications: TS 36.201: Physical layer General description

TS 36.211: Physical channels and modulation

TS 36.212: Multiplexing and channel coding

TS 36.213: Physical layer procedures

TS 36.214: Physical layer Measurements

36.211Physical Channels and

Modulation

36.212Multiplexing and channel

coding

36.213Physical layer procedures

36.214Physical layer

Measurements

To/From Higher Layers

Stage 2 specification:

TS 36.300: E-UTRA and E-UTRAN Overall description

LTE Standard Specifications


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Layer 2 specifications:

TS 36.304: User Equipment (UE) procedures in idle mode

TS 36.306: User Equipment (UE) radio access capabilities

TS 36.321: Medium Access Control (MAC) protocol specification

TS 36.322: Radio Link Control (RLC) protocol specification

TS 36.323: Packet Data Convergence Protocol (PDCP)

Radio Resource Control (RRC)

Medium Access Control

Transport channels

Physical layerControl/Measurements

Layer 3

Logical channels

Layer 2

Layer 1

Radio interface protocol

architecture around physical layer

Layer 3 specifications:

TS 36.331: Radio Resource Control (RRC) protocol specification


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LTE Advanced overview

LTE-A requirements: R8 and beyond


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The Table summarizes some requirements of the Release 8 LTE system and of the LTE-Advanced (LTE-A)(1)

(1)3GPP TR 36.913 , Requirements for LTE-Advanced

(2) Achievable by means of Carrier Aggregation

(3) R1-072444, Summary of Downlink Performance Evaluation. Ericsson, TSG-RAN WG1 #49

(4) R1-072261, LTE Performance Evaluation - Uplink Summary. Vodafone, TSG-RAN WG1 #49

Release 8 LTE Next Releases LTE-A (3GPP targets in TR 36.913)

Downlink Uplink Downlink Uplink

Peak data rate300 Mbps (4x4 MIMO)

150 Mbps (2x2 MIMO)

75 Mbps (1x2 SIMO)

150 Mbps (Virtual MIMO)

3 Gbps (8x8 MIMO, low

mobility)

1.5 Gbps (4x4 MIMO, low

mobility)

Bandwidth Up to 20 MHz Up to 20 MHz Up to 100 MHz (2) Up to 100 MHz (2)

Peak Spectrum

efficiency 16.3 bit/s/Hz

4.3 bit/s/Hz (1x2 SIMO)

8.6 bit/s/Hz (Virtual MIMO)

30 bit/s/Hz 15 bit/s/Hz

Average

Spectrum

efficiency

[bit/s/Hz/cell]

1.69 (2x2 MIMO) (3)

1.87 (4x2 MIMO)

2.67 (4x4 MIMO)

0.74 (1x2 SIMO) (4)

2.4 (2x2 MIMO) (1)

2.6 (4x2 MIMO)

3.7 (4x4 MIMO)

1.2 (1x2 SIMO) (1)

2.0 (2x4 MIMO)

LatencyData plane : 10 ms (round trip delay)

Control plane : 100 ms (idle to active state)

Data plane :


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Carrier Aggregation

Carrier aggregation, where two or more component carriers, each with a bandwidth up to 20 MHz, are

aggregated, is considered for LTE-Advanced in order to support downlink transmission bandwidths larger than

20 MHz

Extended Multi-Antenna configurations

Extension of LTE downlink spatial multiplexing to up to eight layers is considered. For the uplink spatial

multipexing with up to four layers is considered.

Coordinated Multiple Point transmission and reception

This feature is considered as a tool to improve the coverage of high data rates, the cell-edge throughput and/or

to increase system throughput

Relaying functionality

Relaying is considered for LTE-Advanced as a tool to improve e.g. the coverage of high data rates, temporarynetwork deployment, cell-edge throughput and/or to provide coverage in new areas.

Carrier Aggregation

Carrier aggregation, where two or more component carriers are aggregated, is considered for LTE-Advanced in


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gg g , p gg g ,

order to support wider transmission bandwidths (e.g. up to 100 MHz) and for spectrum aggregation.

A terminal may simultaneously receive or transmit one or multiple component carriers depending on its

capabilities:

An LTE-Advanced terminal with reception and/or transmission capabilities for carrier aggregation can

simultaneously receive and/or transmit on multiple component carriers.

An LTE Rel-8 terminal can receive and transmit on a single component carrier only, provided that the structure

of the component carrier follows the Rel-8 specifications.

The L1 specification shall support carrier aggregation for both contiguous and non-contiguous component carriers

with each component carrier limited to a maximum of 100 RBs (using the Release 8 numerology)

It will be possible to configure a UE to aggregate a different number of component carriers of possibly different

bandwidths in the UL and the DL.

frequency

Case A : Contiguous components Case B : Non-Contiguous components

MIMO techniques for LTE (downlink)


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The Release 8 LTE downlink standard supports both SU-MIMO (where the data are transmitted to a single UE)

and MU-MIMO (where the data are transmitted to multiple UEs that are co-scheduled in the same resources).

Release 8 Release 10 and beyond

Max. Num. of codewords 2 2

Max. Num. of layers 4 8

MIMO Configurations Up to 4x4 Up to 8x8

Support of SU-MIMO Yes Yes

SU-MIMO Techniques

Spatial Multiplexing

Space Frequency Block Coding (SFBC)

Closed Loop Precoding

Cyclic Delay Diversity (CDD)

Single Layer Beamforming

All the Release 8 techniques plus double

layer beamforming and 8 layer

transmission

Support of MU-MIMO Yes Yes

MU-MIMO features

Codebook based precoding

Maximum two co-scheduled UEs

Single layer for each UE

Non-codebook based precoding

Maximum of four co-scheduled UEs

Multiple layers for each UE

MIMO techniques for LTE (uplink)


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The Release 8 LTE uplink standard supports the receive antenna diversity at the eNode B.

The antenna selection at the UE is an optional feature for all UE categories.

The standard also supports the so-called Virtual MIMO that is the equivalent of the downlink MU-

MIMO where two UEs can be simultaneously scheduled in the same uplink resources.

Release 8 Release 10 and beyond

Multiple access method SC-FDMA (contiguous RB mapping) SC-FDMA (clustered RB mapping)

Max. Num. of codewords 1 2

Max. Num. of layers 1 4

MIMO Configurations Up to 1 x 4 Up to 4 x 4

Support of Spattial Multiplexing No Yes

SU-MIMO Techniques Only Rx diversity supported at the eNB

UE antenna selection is optional

Spatial Multiplexing

Precoding for data channels

TX diversity for control channels

Support of MU-MIMO Yes Yes

Coordinated Multipoint Transmission (CoMP)

Coordinated multipoint (CoMP) transmission/reception is considered for LTE-Advanced as a tool to improve the


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Coordinated multipoint (CoMP) transmission/reception is considered for LTE Advanced as a tool to improve the

coverage of high data rates, the cell-edge throughput and/or to increase system throughput.

Downlink coordinated multi-point transmission implies dynamic coordination among multiple geographically

separated transmission points.

3GPP currently considers two types of downlink CoMP:

Joint Processing (JP): data is available at each point in CoMP cooperating set.

Joint Transmission: transmission from multiple points at a time to a single UE to

improve the received signal quality and/or cancel actively interference for other

UEs.

Dynamic cell selection: transmission from one point at a time (within CoMP

cooperating set).

Coordinated Scheduling/Beamforming (CS/CB): data is only available at serving cell

(data transmission from that point) but user scheduling/beamforming decisions are made

with coordination among cells corresponding to the CoMP cooperating set. controldata

MME/S-GWMME/S-GW

Relaying functionality


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Relaying is considered for LTE-Advanced as a tool to improve e.g. the coverage of high data rates, temporary

network deployment, cell-edge throughput and/or to provide coverage in new areas.

The Relay Node (RN) is wirelessly connected to radio-access network via a donor cell. There are two bi-

directional radio links/interfaces:

the RN / UE interface access link

the eNB / RN interface backhaul link eNB

RN

UE

Access linkBackhaul link

Donor cellDirect link

eNB

RN

UE

Access linkBackhaul link

Donor cellDirect link

eNodeB

Relay

Node

Relay

Node

UEUE

UE

UE

UE

LOS/NLOS link

NLOS link

eNodeB

Relay

Node

Relay

Node

UEUE

UE

UE

UE

LOS/NLOS link

NLOS link

Backhaul links may employ

directional antennas.

Source: R1-090593, 3GPP RAN1#56

lte by bruno melis

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