01 lte basics training fundamentals features october 2011 2 2

COPYRIGHT © 2011 ALCATEL-LUCENT. ALL RIGHTS RESERVED.

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LTE BASICS & FUNDAMENTAL RADIO FEATURES

Advanced Network RF Design Engineering

November 2011


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1. OFDM Fundamentals

2. Physical layer

3. Downlink Structure

4. Uplink Structure

5. Fractional Power Control

6. Scheduler

7. Fractional Frequency Re-use

8. LTE Link Adaptation

9. MIMO

10. Performances and capacities

AGENDA


4

OFDMMotivation

Based on the previous technologies used the main source of interference is coming from multi-path channel

It induces

Inter-Symbol Interference (ISI) in the time domain

Frequency-selectivity in the frequency domain

High data rates imply a short symbol duration:

For same multipath delays, short symbols encounter more ISI than longer ones

To reduce ISI:

Conventional time-domain equalizers

Discrete Fourier Transform (DFT) to have

frequency-domain equalization

OFDM

symbol #1symbol #1symbol #1

symbol #1symbol #1symbol #1t

symbol #1

symbol #2

symbol #1

symbol #2 t

ISI

ISI


5

OFDMMotivation

Single carrier vs. multi-carrier transmissions

=> How to remove guard bands between subcarriers?

B

Pulse length ~1/B

Guard bands

Channelization N carriers

B

Pulse length ~ N/B

• Flat fading per carrier

• Pulse length is N times longer

• ISI is much shorter

• Simpler equalization

• Need guard bands, which reduces the spectrum efficiency

channel

• Selective fading

• Short pulse length

• ISI is comparatively long

• Complex equalization

• Need guard band, which reduces the spectrum efficiency

• Data transmitted on 1 carrier • Data shared among MC and simultaneously transmitted


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OFDMMotivation

• Answer is OFDM!

• Characteristics:

Overlapping orthogonal subcarriers

Wideband BW divided into K subcarriers with spacing

Cyclic Prefix (CP): robustness to multipath

Easy implementation with IFFT/FFT at transmitter and receiver

K

BW=f


7

Basic of OFDMWaveform


8

Basic of OFDM


9

Basic of OFDMOrthogonality lost


10

Basic of OFDMDoppler & frequency offset effects


11

Basic of OFDMMulti-path effect


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Basic of OFDMMulti-path effect


13

Basic of OFDMCP length

• Extended CP length ~ 17µs


14

Basic of OFDMOFDM scalable

( 1.4MHz*, 1.6MHz**, 3MHz, 3.2MHz**, 5MHz, 10MHz, 15MHz, 20MHz)

* FDD only, **TDD only


15

OFDMPros and cons• Summary of advantages

Robust against Intersymbol interference (ISI) and multipath fading

High spectral efficiency

Efficient implementation using FFT – low complexity

Can easily adapt to severe channel conditions without complex equalization

Low sensitivity to time synchronization errors

Tuned sub-channel receiver filters are not required (unlike traditional FDM)

More favorable to MIMO techniques

Facilitates Single Frequency Networks

• Summary of disadvantages

Sensitive to Doppler shift and to frequency synchronization problems

Inter-Carrier Interference (subcarrier orthogonality not anymore respected)

High Peak to Average Power Ratio

due to linear power amplifier requirement

Loss of spectral efficiency due to the insertion of the CP


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


17

Requirements for E-UTRAN

Scalable bandwidth :

1.4/1.6, 3/3.2, 3, 5, 10, 15, 20MHz

Targeted Peak Throughputs

DL : >100Mbps for 20MHz spectrum allocation

UL : 50Mbps for 20MHz spectrum allocation

Scaling linearly with the spectrum allocation

Targeted increased of spectrum efficiency vs HSPA

DL : 3-4 times R6 HSDPA for LTE MIMO (2,2)

UL : 2-3 times R6 E-DCH (HSUPA) for LTE (1 Tx,2 Rx)

Ultra low latency

<10ms for round trip delay from UE to server

Reduced call set-up time

Transition time (Idle -> Active) < 100 msec

Transition time (Dormant -> Active) < 50 msec


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Requirements for E-UTRAN

High capacity per cell

200 users per cell for 5MHz,

400 users in larger spectrum allocations

Mobility

LTE is optimized for low speeds 0-15km/h, high performance for speeds up to 120km/h, and mobility maintained for speeds up to 350km/h

Efficient support of the various types of services in the PS domain

Co-existence and Inter-working with 3GPP RAT

Handover between 3G & LTE:

Real-Time services < 300ms

Non- Real Time services < 500ms

Both FDD and TDD modes


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Requirements for E-UTRANAir Interface characteristics

Multiple Access Schemes:

Downlink: OFDMA

Uplink: Single Carrier FDMA (SC-FDMA)

Multiple Input Multiple Output (MIMO) with up to 4 antennas per base station

High Order Modulations:

Downlink: QPSK, 16QAM, 64QAM

Uplink: QPSK, 16QAM

Turbo coding

H-ARQ


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Frame structure

• Duration is 10ms; made up with 10 subframes of 1ms

• Each subframe contains Physical Resource Blocks (PRB), whose number depends on the total bandwidth available

• * TDD only, **FDD only

• A PRB spans over 12 subcarriers over a subframe duration.

Bandwidth occupancy is 180 kHz (=12*15kHz)

Several configuration of CP:

Normal CP: 4.7µs => 7 OFDM/SC-FDMA symbols per slot

Extended CP ~ 17µs => 6 OFDM/SC-FDMA symbols per slot

In 1 subframe, 14 symbols are transmitted (resp. 12 for extended CP)

BW 1.4MHz** 1.6 MHz* 3 MHz 3.2 MHz * 5 MHz 10 MHz 15 MHz 20 MHz

PRBs 6 7 15 16 25 50 75 100


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LTE Physical Channels Overview

eNode-BSlot/Frame

synchronization &

Cell Id identification

Random access

Traffic

HARQ feedback

Transport format

UL scheduling grant

Resource allocation

Traffic

HARQ feedback

CQI reporting

UL scheduling request

CQI reporting for MIMO

related feedback


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


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DL Channels Mapping


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LTE Downlink: Frame Format, ChannelStructure & Terminology


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LTE Downlink: Number of Resource Blocks & Numerology


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Downlink common Reference Signal structure

Reference signal symbol distribution sequence over 12 subcarriers x 14 OFDM symbols.

The Reference signal sequence is correlated to Cell ID.


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Downlink common Reference Signal structure per number of antenna port


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PBCH, SCH Time and frequency location


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Basic of cell search


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Primary BCH & Dynamic BCH

D-BCH:


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Primary BCH & Dynamic BCH


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P-BCH SINR achievable on the field

The targets specified below concern the frequency re-use 1 configuration.

These targets concern the channels transmitted in TXdiv mode so, P-BCH

For PBCH as all the cells transmit it all the time on the same spectrum allocation the conditions are always 100% load

The achievable targets below for zones essentially interference limited which represents 99% of the conditions in which a network is deployed.

95% of the field area should have SINR ≥ -5dB, with 100% DL load

95% of the field area should have a SINR ≥-2dB with 50% DL load

All the explanation concerning these targets will be detailed in slides “ RF design rules”


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PBCHTXDIV : BLER VERSUS SINR

Based on curves above PBCH can support SINR conditions lower than -5dB for 1% BLER.


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PCFICH & PHICH


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PDCCH


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PDCCH SINR achievable on the field

The targets specified below concern the frequency re-use 1 configuration.

These targets concerned the channels transmitted in TXdiv mode so, PDCCH,

For PDCCH ( like for PDSCH) the SINR targets value depends on the traffic load, but is not impacted by the number of Tx antennas until all the cells of a same cluster have the same number; which is highly recommended.

These targets are valid when there is no power control

The achievable targets below for zones essentially interference limited which represents 99% of the conditions in which a network is deployed.

95% of the field area should have SINR ≥ -5dB, with 100% DL load

95% of the field area should have a SINR ≥-2dB with 50% DL load

All the explanation concerning these targets will be detailed in slides “ RF design rules”


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PDCCH

Aggregation Level 2 is used for common transmission, and data transmission signaling

Aggregation Level 8 is used for HHO and constraining phase

Based on the curves above PDCCH BLER is extremely high for AL2 for –5dB SINR which measured at cell edge in 100% load conditions


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PDCCHPower control impact

The table below shows the impact of PDCCH power control on PDSCH BLER and transmission quality

These results have been obtained for ETU 5Hz profile; for a full loaded scenario considering 10 users/ cells

LA3.0 implemented power control is IS-PWCTL.

Bad performances for fixed PDCCH power mode at cell edge : 48% residual PDCCH BLER with mcs0 and AL2


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PDCCH: DCI formats carried

DCI includes resource assignments and other control information


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Downlink Shared Channel (DL-SCH)


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


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LTE UplinkOverview

• Uplink employs Single-carrier OFDMA (SC-FDMA)

UL physical channel

Shared channel PUSCH

Control channel PUCCH

Carry the ACK/NACK to support the DL

Never transmitted with the PUSCH (to keep the Single-Carrier property)

• UL physical signals

Reference Signal (RS) => narrowband information

Sounding RS => broadband: used for UL resource scheduling

• Available modulation for data

QPSK, 16QAM, (64QAM)

• MIMO

MU-MIMO

Collaboration between UEs to transmit on the same PRBs

SU-MIMO will be addressed in the future


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LTE UplinkMultiple Access Scheme

To facilitate efficient power amplifier design in the UE, 3GPP chose single carrier frequency domain multiple access (SC-FDMA) in favor of OFDMA for uplink multiple access

SC-FDMA improves the peak-to-average power ratio (PAPR) compared to OFDMA

~4 dB improvement for QPSK, ~2 dB improvement for 16-QAM

Reduced power amplifier cost for mobile

Reduced power amplifier back-off improved coverage

High PAPR in OFDMA

OFDMA:

• amplitude of combined subcarriers

depends widely on the symbol data

transmitted

• peak when identical symbols are

transmitted

• waveform becomes Gaussian

• practical RF amplifiers have a

certain range => non-linear distortion


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LTE UplinkMultiple Access Scheme

Node B

UE C

UE B

UE A

UE A Transmit Timing

UE B Transmit Timing

UE C Transmit Timing

a

b

g

SC-FDMA is still an orthogonal multiple access scheme (DFT-precoded OFDMA)

Single carrier leads to ISI => need for equalization

1 tap equalization with the use of CP

Synchronous in the time domain through the use of timing advance (TA) signaling

Only need to be synchronous within a fraction of the CP length

TA command sent as a MAC control element with 0.52 ms timing resolution

frequency

SC-FDMA


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LTE Uplink: Number of Resource Blocks & Numerology


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UL Physical Channels


48

UL Channels Mapping


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Demodulation Reference Signal & Sounding Reference Signal


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Demodulation Reference Signal & Sounding Reference Signal


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PUCCH


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PUCCH


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PUCCH


54

PRACH


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RACH Cell Range Limitations – LTE

LTE Systems can be limited by the time duration allocated to an RA Slot during RACH.

3GPP standards define four RACH Formats that will support different maximum cell

ranges.

In LA1.x ALU supports RACH format 0 (15km)

In LA5.0 time frame ALU will support RACH format 2 (30 km)

In LA6.0 time frame ALU will support RACH format 3 (100km) (to be confirmed).

RACH Format RA Slot Tcp Tseq TgapMax Cell

Range

Format 0 1 msec 0.10 msec 0.80 msec 0.10 msec 15 km





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Radom Access procedures


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


58

LTE UplinkPower control

• Open-loop power control:

To constrain the dynamic range between signals received from different UEs

Unlike CDMA there is no intra-cell interference exploit fading by means of link

adaptation and scheduling

• Classical PC:

all users achieve the same target SINR

Interior users transmit at reduced power spectral density

• Fractional PC (more flexible):

Trade-off between spectral efficiency and cell edge rates

Target SINR increases with decreasing path loss

Others, e.g. aperiodic fast power control

Fractional PC

Interference over Thermal noise (IoT) is a key performance criterion: open-loop PC

params can be adjusted to reach a target IoT

crucial in reuse-1 deployment to guarantee coverage and stability


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Fractional Power Control

While using the same target SINR for each user results in very good fairness (as far as power allocation is concerned), it also results in poor spectral efficiency

An improved power control scheme called Fractional Power Controladjusts the target SINR in relation to the UE’s path loss to its serving sector

UE_TxPSD_dBm = a x PL_dB + Nominal_Target_SINR_dB + UL_Interference_dBm

a is called the fractional compensation factor, and is sent via cell broadcast; 0 < a< 1

Target SINR

Target_SINR_dB = Nominal_Target_SINR_dB- (1-a) x PL_dB

Target SINR increases with decreasing path loss

Flexible trade-off between cell edge rate and average spectral efficiency


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IoT Control Mechanism (Inter-cell Power Control)

Setting of Target_SINR_dB determines the IoT operating point

Especially in a reuse-1 deployment, it is critical to manage the uplink interference level

In LTE, e-NBs can send uplink overload indications to neighbor e-NBs via the X2 interface

Power control parameters (i.e. Target SINR) can be adapted based on overload indicators

Allows control of the IoT level to ensure coverage and system stability

PC params PC params

Measure Interference, emit overload indicator

Based on overload indicator from neighbor cell,

adapt PC paramsinterference

Overload indicator (X-2 interface)


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Improved Power Control Based on Neighbor Cell Path Loss

Path loss to the serving cell is not indicative of the amount of interference a user will generate to neighboring sectors

An improved power control scheme adjusts the target SINR in relation to PL_dB = PL_strongestNeighborCell_dB – PL_servingCell_dB

UE_TxPSD_dBm = PL_dB + Nominal_Target_SINR_dB + (1-b) x PL_dB + UL_Interference_dBm

(1-b) x PL_dB is sent to each UE via higher layer (RRC) signaling

Target SINRTarget_SINR_dB = Nominal_Target_SINR_dB

+ (1-b) x PL_dB

Target SINR increases with increasing “radio position”


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


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Scheduler


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Scheduler weighted proportional fair


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Scheduler proportional fair principles


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Frequency Non-Selective Scheme

The SRS SYNC SINR is a scalar quantity per user that is formed by averaging the SRS SINR across

PRBs and then filtered in time; used to form a single priority metric, which is replicated and used for

all PRBs

To support a large number of UEs, the SRS period needs to be reduced given the multiplexing capabilities (max of 8 UEs per SRS transmission per frequency comb)

The regular MPE algorithm as in the FSS algorithm is then utilized, which minimizes

testing/verification to just the new code introduced

Single priority metric formed and used in the first stage of the MPE algorithm

Then MPE algorithm continues as in FSS scheme

12

34

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78

9

UE 1

UE 2

UE 30

1

2

3

4

5

6

Priority

Metric

Resource Unit Index

UE 1

UE 2

UE 3


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


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ICIC

In a reuse-1 deployment it is critical to manage the UL & DL interference level

Interference measured by UE and reported to eNB

• Implemented to improve interference-limitations

Also improves UE throughput at cell edge

• Inter Cell Interference Coordination

Uplink – Fractional Frequency Reuse and Soft Fractional Frequency Reuse

• Improvements in later releases

Downlink - Power limitation on frequency blocks

Semi-static interference coordination

Antenna parameter optimisation e.g. tilt

interference

Part of SON functionality


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ICICUplink

• Virtual 1/3 Frequency Reuse

static subcarrier restriction in each sector

=> Inefficient use of BW

0 1 2 3 4 5 6 7 8 9 10 11

Sector a Sector b Sector g

5 MHz

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

1.67 MHz 1.67 MHz 1.67 MHz

F1 F2 F3

-5 0 5 10 15 20 250

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Scheduled User Symbol SINR (dB)

CDF

reuse-1

reuse-1/3

0 1 2 3 4 5 6 7 8 9 10 11

Sector a Sector b Sector g

5 MHz

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

1.67 MHz 1.67 MHz 1.67 MHz

F1 F2 F3

UL Sector Throughput

5% CDF UL User Throughput

Reuse-1 3.33 Mbps 135 kbps

Reuse-1/3 2.32 Mbps 160 kbps

• Simulation results:

Increased user SINR due to lower interference

Increased cell-edge user throughput (~18%)

But... reduced sector throughput


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ICICUplink

• Soft Fractional Frequency Reuse

Mobiles at the cell border cause most of the interference to adjacent cells

• inner cell, reuse 1 => better spectral efficiency

• cell borders, reuse 1 but the transmit power for the cell edge user is reduced in non-preferred frequency zones

Designate a portion of BW in each cell which bears the interference from neighboring cells (call this the “trash heap”)

Through the usual handoff measurements, the serving cell knows the identity of the strongest neighboring cell for each mobile

For cell border mobiles, the uplink scheduler prefers to assign resources in the trash heap of the mobile’s strongest neighboring cell

If the scheduler needs to assign the mobile outside the trash heap, it does so with a reduced transmit PSD level

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

0 1 2 3

4 5 6 7 8 9 10 11

Sector a

Sector b

Sector g

IoT

0 1 2 3

4 5 6 7

8 9 10 11

0 1 2 3 4 5 6 7

8 9 10 11

IoT

IoT

Try to concentrate interference

in these “trash heaps”


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Pros: Coordination of the interference between cells concentrates interference into known portions of the system bandwidth in each cell

Interference level is reduced over a large part of the operating bandwidth

Cons: Reduction in uplink interference level is done by placing restrictions on how the scheduler can allocate resources to cell border mobiles

The size of the trash heap zone is small, which limits the number of resource blocks that can be assigned to a cell border mobile

Cannot assign resources across the trash heap zone and the normal zone, because cannot have the same mobile transmit at different transmit PSD levels on different resource blocks

Restriction on cell edge mobiles reduces the frequency selective scheduling (FSS) gains, when FSS is utilized as there are less resource blocks available

Pros and Cons of Interference Coordination

Interference Coordination is beneficial providing it is not used in conjunction with Frequency Selective Scheduling


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


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DL MCS table


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UL MCS table


78


2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


79

MIMO Reminder

Reminder on some definitions

SU-MIMO (Single User MIMO)

Spatial Multiplexing (SM): increase peak rate by 2 in MIMO 2x2

Transmit Diversity (TxDiv): improve reliability of a single data stream

Closed-loop implementation: use channel state information at the transmitter (BF/precoding)

MU-MIMO (Multiuser MIMO)

Multiple data streams from/to different users sent on the same resource

Works even with single antenna/PA mobile

In the subsequent slides, the focus is on the downlink as uplink does not support SU-MIMO (i.e. 1 single PA/UE to have a low cost UE)

note that uplink MU-MIMO has an impact essentially on the scheduler algorithm

SIMO channel, i.e.

RxDivMIMO channel

SISO channel

user 1

user 2

MU-MIMO channel


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MIMOTerminology• The relationship between codewords, rank and layers is not unique and depends on

the MIMO scheme to be considered.

Codeword: an independently encoded data block, corresponding to a single transport block

with one CRC

a codeword is directly related to the channel coding operation

#codewords ≤ #layers

Rank: number of non-redundant data streams that can be transmitted (related to the spatial multiplexing gain)

coded data streams may be split into different layers and how the data stream is split depends on the antenna scheme and the rank of the channel:

if rank = 1, only one codeword can be transmitted – if multiple coded data streams, they carry the same information

if rank = 2, either one or two codewords can be transmitted while offering a spatial multiplexing gain of 2 2

unique coded data streams

if rank = k, up to k codewords while offering a SM gain of k k unique coded data streams

Layer: number of streams (including redundant ones) to be transmitted

#layers ≤ #antennas

a layer containing data symbols is mapped onto the transmit antenna ports:

TxDiv: #layers = #antennas

SM (including rank-1 precoding): #layers = rank of transmission


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WiMAX

1 codeword

3GPP LTE

2 codewords

MIMOExamples

Spatial multiplexing can be achieved with either 1 or multiple codewords transmission

SU-MIMO 2x2 offers 2 possibilities: 1 or 2 codewords for rank-2 transmission

Advantage: save signaling overhead as the

HARQ associated signaling is rather expensive

Advantage: permit Successive Interference

Cancellation decoding at the receiver


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MIMOExamples

Spatial multiplexing can be achieved with either 1 or multiple codewords transmission

SU-MIMO 2x2 offers 2 possibilities: 1 or 2 codewords for rank-2 transmission

x1

x’1

x2 precoder

x’2

Layer

mapping

1 codeword 2 layers

x1

x’1

x2

precoder

x’2

Layer

mapping

2 codewords 2 layers

s1s2 s’1s’2

x3x4

x’3x’4

Advantage: save signaling overhead as the

HARQ associated signaling is rather expensive

Advantage: permit Successive Interference

Cancellation decoding at the receiver

=> SIC allows significant gains


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MIMO in LTEDL Transmission modes

Beamforming solutions (1 or 2 beams)

Relying on long-term precoders e.g. AoA (Angle of Arrival) algorithm

Good performances maintained at

high UE speed

DL MU-MIMO

Relying on CSIT (Channel State Information at Transmitter)

Require accurate feedback (as interference rejection is here

also done at the transmitter side)

based on PMI – Rel’8 codebook designed for SU-MIMO

• Different transmission modes available for PDSCH (Rel’8 & Rel’9)

TM1: Single transmit from eNB

TM2: Transmit diversity (SFBC)

TM3: Open-loop Spatial Multiplexing (SM)

TM4: Closed-loop SM

TM5: MU-MIMO

TM6: Closed-loop rank-1 precoding

TM7: Single-layer beamforming (BF)

TM8 (3GPP Rel’9): Dual-layer BF


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MIMO in LTEDownlink Overview

• Improve reliability of a single data stream with SFBC. Useful to common channels

MIMO

Open LoopRI, CQI

Closed LoopRI, CQI, PMI

Single StreamRank 1

Multi-StreamRank 2-4

Transmit Diversity

(TM2)

Well-suited forhigh speed

Well-suited for low speed

Low SINR or low scattering

Open Loop SM (TM3)

Adapt To: OL TD

High SINR and rich scattering

Single StreamRank 1

Multi-StreamRank 2-4

CL Rank-1 Precoding

(TM6) Adapt To: OL TD

Low SINR or low scattering

High SINR and rich scattering

Closed Loop SM (TM4)

Adapt To: CL1 & OL TD

SM = Spatial Multiplexing

RI = Rank Indication

CQI = Channel Quality Indication

PMI = Pre-coding Matrix Indication

RS = Reference Symbol

OL = Open Loop

CL= Closed Loop

TD = Transmit Diversity

• Allow multiple data streams to be sent on the

same frequency-time RB. • Improve coverage and throughput with a channel-dependent precoding (PMI reporting)

• Limited channel knowledge at Tx (RI, CQI)


85

Codeword to layer mapping2 Transmit Antennas

• TM2 – OL TxDiv – SFBC is implemented which is a frequency-domain version of the Alamouti code.

The transmitted diversity streams are orthogonal

SFBC/Alamouti code (2x2):

1 single possibility:

transmission relies on 1 single codeword

the codeword is duplicated on 2 layers (redundancy)

rank = #symbols / #subcarriers

the single codeword is sent twice over 2 subcarriers (sc)

=> 2 unique symbols on 2 subcarriers = rank-1 transmission

x1

x1

x2

x2*

2 sc

SFBC

precoder

x2

-x1*

Modulation

+ codingb1b2bK ... Layer

mapping

1 codeword 2 layers


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Codeword to layer mapping2 Transmit Antennas

• TM3 or TM4 – LTE spatial multiplexing uses 2 codewords (see Fig. 2)

1 codeword corresponds to 1 Transport Block Size (TBS)

Rank-1 transmission (TM6) is often seen as a special case of SU-MIMO spatial multiplexing. In this case, 1 codeword is used

• The codeword to layer mapping is trivial: the codeword n is mapped to the layer n.

#codewords = #layers

#layers = rank of transmission

• The mapping between codewords and layers is shown below:

Precoding

(2x2)

CW#1

Rank-2layer #1

CW#2

Precoding

(1x2)

CW#1

Rank-1

layer 1

layer #2

Fig. 2: Rank-2 transmissionFig. 1: Rank-1 transmission


89

• MIMO 2x2 is supported on the RF hardware products as soon as modules have 2 RF transmit paths (2 PAs)

the product name should end with 2x such as RRH2x, TRDU2x.

MC-RRH is MIMO ready with a single module

however, 2 MC-TRX are required to support MIMO 2x2

MIMO in LTERF Hardware

CPRIRRH2xLTE Baseband Unit

LTE 2x2 MIMO

MC-RRH

supporting

LTE 2x2 MIMO

LTE BBU module


90

MIMO in LTEAntenna Design

Xpol

2 uncorrelated outputs: good diversity gains

algorithms supported

TxDiv/SFBC

CL & OL SM up to 2 streams

UL MU-MIMO with 2 users

XXpol closely spaced

correlation between elements with equal polarisation: array and diversity gains

algorithms supported:

TxDiv/SFBC



UL performance +++

DL performance +

Suitable radio environments: large/outdoor cell/cell border, LOS environments

X X

X X

X X

X X

X X

X X

~ 30 cm

~16 cm

X

X

X

X

X

X

~16 cm

recommended for balanced UL & DL performances


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XXpol widely spaced

4 uncorrelated outputs: good diversity gains

algorithms supported:

TxDiv/SFBC



UL performance +++

DL performance ++

Suitable radio environments: picoCell/indoor, high SNR, rich scattering environment

X

X

X

X

X

X

~16 cm

>1.m

X

X

X

X

X

X

best UL performances


92


10 λ

DIV-2X CLA-2X

λ/2

CLA-4X

λ/2 λ/2λ/2

ULA-4V

λ/2

4 uncorrelated outputs

8 outputs

Used in single-layer BF with 8Tx

4 outputs:

2 uncorrelated (different polar.)2 correlated (same polar.)

4 correlated outputs:

DL OL & CL with SM up to 2 streams (depending on correlation)

DL & UL MU-MIMO up to 4 users


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Antennas Configuration


94

ROADMAP OVERVIEWFDD mode

2011 2012 2013Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3

LTE FDDLA4.0

LA5.0LA6.0

LA4.0

Uplink:

4RxDiv (5MHz)

Downlink:

SISO & SIMO (as

back-up schemes)

LA5.0

Uplink:

4RxDiv (15MHz)

1 Rx

LA6.0

Uplink:

eNB IRC Rx

LA7.0

Uplink:

MU-MIMO with SIC

Downlink:

SU-MIMO & MU-MIMO

as in Rel’10 (LTE-a)

FDD

May’11

LA7.0

INTERNAL

• Note: All LTE UEs shall support the 2-way RxDiv

Supported configurations from Day-1:

UL: 2RxDiv

DL: OL TxDiv (SFBC) & MIMO 2x2


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UPLINK – 4RxDivBenefits

Peak user throughput no impact

Coverage

better SINR performances which depend upon the antenna correlation – 2.5dB are accounted in the link budget tool (high correlation case)

IoT reduction – 1dB IoT reduction is accounted for in ALU link budget

coverage enhancement of 3.5dB corresponding to a site count reduction of ~36%

Avg. Cell Throughput

Large spectral efficiency gain with 4RxDiv compared to 2RxDiv

Coverage Feature

Correlation Low Medium High

Rx Combining Gain 3dB (4RxDiv)

Spatial Diversity Gain Large Medium Small

4RxDiv Gain (QPSK) 4.2 dB 4.1 dB 3 dB

Spectral Efficiency Case 1 Case 3 WP

2RxDiv 0.74 bps/Hz 0.62 bps/Hz 0.60 bps/Hz


Delta +36% +29% +40%


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UPLINK – 4RxDiv Hardware

• Hardware requirements

RRH2x with an expander module which allows to combine the 4 radio branches in the uplink

4 feeders

4 antenna connectors with either 2 Xpol antennas widely spaced or XXpol

Coverage Feature

XXpol

10 λ

2 Xpol antennas

• 4 uncorrelated outputs best diversity gains• Rx Combining gain

• 2 correlated outputs reduced diversity gains• Rx Combining gain

λ/2


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UPLINK – 1RxDivBenefits

Peak user throughput no impact

Coverage

better SINR performances which depend upon the antenna correlation – 2.5dB are accounted in the link budget tool

IoT increased by 1 dB

coverage degradation of 3.5dB corresponding to a site count increase by ~57%


Large spectral efficiency loss

RxDiv scheme SINR IoT

1RxDiv -2.5 dB +1 dB

2RxDiv 0 dB 0 dB

Spectral Efficiency Case 1 Case 3 WP



Delta -27% -23% -29%

Fallback Feature


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DOWNLINK – Single TransmitBenefits

Peak user throughput

peak user trhoughput reduction as no spatial multiplexing is allowed

see the Peak Throughput training for more details


Expected throughput reduction due to the deactivation of 1 transmit antenna

1dB estimated in the link budget tool

< 10% cell spectral efficiency reduction

Note: with a single transmit & receive path (i.e. no RxDiv), the second antenna connector is not used and should be terminated by a load

Vpol antenna

RRH

Main Tx/Rx load

Spectral Efficiency

Case 1 Case 3 WP

SIMO 1.48 bps/Hz 1.36 bps/Hz 1.10 bps/Hz

MIMO 2x2 1.61 bps/Hz 1.48 bps/Hz 1.20 bps/Hz-8%

Fallback Feature


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DOWNLINK – MIMO 4x2Benefits


MIMO 4x2 same peak user rate as MIMO 2x2 (due to a maximum SM gain of 2)


Constant total power assumed wrt. MIMO 2x2

Received signal strength increased by enhanced 4 antenna pre-coding

Reduced interference due to more directional emission

Expected performances dependent upon the deployed antenna solution

DIV-2X: 2 Xpol antennas widely spaced

Capacity Feature

INTERNAL: Gains under discussions

Spectral Efficiency

Case 1 Case 3

MIMO 2x2 1.61 bps/Hz 1.48 bps/Hz


Today~7%

10 λ

λ/2

CLA-2X: XXpol closely spaced


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DOWNLINK – MIMO 4x4Benefits


MIMO 4x4 double the peak user rate wrt. MIMO 2x2 as the Spatial Multiplexing (SM)

gain is up to 4 spatial layers

UE Category 5 required – expected in > 2013 timeframe


Constant total power assumed

Good gains exhibited with MIMO 4x4 wrt. MIMO 2x2 – today 20% gain is considered (which seems quite low!)

4RxDiv instead of 2RxDiv

DL transmission mode up to rank-4 (potentially doubling the peak user rate)

Future evolution of spectral efficiencies may account for larger gains as shown in some Bell Labs simulations – this would be more consistent with the 4RxDiv gain (wrt 2RxDiv) observed in the uplink (~40%)

Capacity Feature

Spectral Efficiency

Case 1 Case 3



Today~20%

INTERNAL: Gains under discussions


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Future MIMO Evolutions towards LTE-advancedOutlook

• Radio Requirements

Bandwidth: up to 20 MHz

High peak rates:

DL: 100 Mbps with MIMO 2x2

UL: 50 Mbps with SIMO 1x2

Improved Cell Spectral Efficiency wrt.

HSPA Rel’6

Improved cell-edge performances

up to 100 MHz

LTE-advanced

1 Gbps

500 Mbps

3GPP Case 1 perf. targetsDL: 2.6 bps/Hz with MIMO 4x2UL: 2.0 bps/Hz with MIMO 2x4

LTE

3GPP Case 1 perf. targetsDL: 0.09 bps/Hz with MIMO 4x2UL: 0.07 bps/Hz with MIMO 2x4

40% to 60%

• CAPACITY INCREASE


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Future MIMO Evolutions towards LTE-advancedOutlook• Starting from Rel’10, LTE-advanced introduces some new MIMO capabilities

Uplink

SU-MIMO up to 4x4

Downlink

SU-MIMO up to 8x8

CoMP (collaborative Multi-Point) – joint scheduling / processing at the eNBs

Relays

• New UE categories defined (in 36.306):

UE category

Downlink Uplink

Maximum TBS bits within a TTI

Maximum # layersMaximum TBS bits

within a TTIIs 64QAM supported?

Cat. 1 10296 1 5160 No

Cat. 2 51024 2 25456 No

Cat. 3 102048 2 51024 No

Cat. 4 150752 2 51024 No

Cat. 5 299552 4 75376 Yes

Cat. 6 301504 2 or 4 51024 No

Cat. 7 301504 2 or 4 102048 No

Cat. 8 2998560 8 1497760 Yes


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Glossary

RxDiv: Receive Diversity

TxDiv: Transmit Diversity

SM: Spatial Multiplexing

MIMO: Multiple Input Multiple Output

SISO: Single Input Single Output

SIMO: Single Input Multiple Output

SU-MIMO: Single User MIMO

OL: Open-Loop, i.e. no channel knowledge at Transmitter side

CL: Closed-Loop, i.e. channel knowledge at Transmitter side

MU-MIMO: MultiUser MIMO

SDMA: Space Division Multiple Access (equivalent to MU-MIMO)

MCS: Modulation and Coding Scheme

TBS: Transport Block Size


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2. Physical layer


4. Uplink Structure


6. Scheduler



9. MIMO


AGENDA


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LTE Air Interface Capacity PerformancesHow to Quantify?

• As of today air interface capacity is quantified by two key metrics:

VoIP Capacity (typically expressed in Erlangs)

Data Capacity (typically expressed in bps/Hz or Mbps for a given BW)

• This is the current approach – doesn’t mean that we continue to take this approach going forward …

• Such capacity figures are notoriously dependent upon the underlying assumptions

Comparing like for like either between technologies internally with ALU let alone between vendors is always quite a challenge ….


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LTE Air Interface Capacity Performances


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LTE Air Interface Capacity Performances


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LTE Air Interface Capacity PerformancesWhat Most Impacts Air Interface Capacity Performances?

• Key assumptions impacting air interface capacities:

Carrier Bandwidth – big impact (roughly proportional to the bandwidth)

Antenna configuration - although this has less impact than you might expect

UE mobility assumptions, i.e. the channel modeling – significant impact

Traffic modeling (full buffer, number of UEs, “real” traffic model, etc) – significant

impact

Voice Codec Selected (for VoIP services)

Channel estimation and implementation margin assumptions

Scheduler, Overheads, Receiver modeling

• Marginal Impact:

Operating frequency, DL power


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Basis for ALU Capacity FiguresOverview

• ALU capacity figures are based on an extensive set of system simulations results with wide ranging simulation assumptions

• There are three key sets of results used for dimensioning today:

Next Generation Mobile Networks (NGMN) Alliance

NGMN Case3 large coverage limited cells

NGMN Case1 small interference limited cells

Multi-Techno White Paper

Reference for KPI contractual capacity commitments


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01 lte basics training fundamentals features october 2011 2 2

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