LTE optimisation

8/13/2019 LTE optimisation

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1 Copyright 2010 AIRCOM International

LTE Optimization

GRAHAM WHYLEY


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Scheduler


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Scheduler

It is the task of the scheduler to assign resource

blocks to physical channels belonging to differentusers or for general system tasks. The job of the

MAC layer


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Scheduler

It is the task of the scheduler to

assign resource blocks to physical

channels belonging to different

users or for general system tasks

If resources are still available afterthe GBR demands then different

schedulers are available

There are 4 main schedulers

Max SINR Proportional Demand Proportional Fair Round Robin


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Scheduler

Round Robin The aim of this scheduler is to share the

available/unused resources equally among the RT

terminals (i.e. the terminals requesting RT services) in

order to satisfy their RT-MBR demand.

Proportional Fair

The aim of this Scheduler is to allocate theavailable/unused resources as fairly as possible in such

a way that, on average, each terminal gets the highestpossible throughput achievable under the channel

conditions.


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eNodeB

MAC Scheduler

DL

Physical Uplink Shared

Channel(PUSCH) Buffer Status

Report

Physical Downlink ControlChannel (PDCCH) -

Additional UL GRANT

FDD | TDD - Layer 1

( DL: OFDMA, UL: SC-FDMA )

Medium Access Control (MAC)

Transport Channels

RLC

(Radio Link

Control)

RLC

(Radio Link

Control)

RLC

(Radio Link

Control)

PDCP

(Packet Data

Convergence

Protocol)

RLC

(Radio Link

Control)

PDCP

(Packet Data

Convergence

Protocol)

RLC

(Radio Link

Control)

PDCP

(Packet Data

Convergence

Protocol)

Logical Channel

(E-)RRC

(Radio Resource Control)

IP / TCP | UDP |

Application LayerNAS Protocol(s)

(Attach/TA Update/)

Scheduling /

Priority Handling

HARQ

Scheduler

Proportional Demand

The aim of this scheduler is to allocate the remaining unused resources to RTterminals in proportion to their additional resource demands


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64QAM

16 QAM

QPSK

2 BITS

4 BITS

6 BITS

Scheduler

Max SINR

Terminals with higher bearer rates (and consequently higher SINR) arepreferred over terminals with lower bearer rates (and consequently

lower SINR). This means that resources are allocated first to those

terminals with better SINR/channel conditions, thereby maximising the

throughput.


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Scheduler


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Sub-band CQI, can be created by

splitting the channel into several sub-bands

The number of sub-bands depends on

the channel bandwidth

WidebandCQI

Frequency-selective Scheduler


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ASSET LTE

There are 4 schedulers

Max SINR

Proportional Demand Proportional Fair

Round Robin


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Using MU-MIMO


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Cell throughput.

MU-MIMO is used to increase the cellsthroughput.

This is achieved by co-schedulingterminals on the same Resource Blocks.

Applying MU-MIMO will make no obvious

changes to a network unless it

is overloaded.

What is CSSR?


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Are there any disadvantages of MU-MIMO?


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MU-MIMO

RSRQ changes when MU-MIMO is deployed because the number

of served terminals changes.

We can observe that when MU-MIMO is deployed everywhere, it provides small

improvements close to the cell, large improvements close to the cell edge


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MU-MIMODL Cell throughput per carrier

Cell Throughout (per carrier) increases when MUMIMOis enabled. This

is an effect of the eNodeB now being capable to serve a higher number

of usersby scheduling them on the same resources.

These users would be otherwise failing to connect.


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Strategy will be to use SM close to the eNodeBs to increase data rates

Diversity further away from the eNodeB to increase coverage

MU-MIMO for heavily loaded cells

MU-MIMO for heavily

loaded cells switches

to Diversity

Switch Over is based on DLRS SNR What happens if the load increases

SM close to the eNodeBs

to increase data ratesswitches to Diversity


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LOAD INCREASES- What happens to celledge?

Load increases DLRS

reduces


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DL Data Rate Improvement w ith Diversi ty


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TTI bundling can repeat the same data in multiple (up to four) TTIs

TTI bundling effectively increases the TTI length allowing the UE to transmit for alonger time.

A single transport block is coded and transmitted in a set of consecutive TTIs

The same hybrid ARQ process number is used in each of the bundled TTIs..

TTI bundling


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TTI bundling can repeat the same data in multiple (up to four) TTIs

TTI bundling effectively increases the TTI length allowing the UE to transmit for alonger time.

A single transport block is coded and transmitted in a set of consecutive TTIs

The same hybrid ARQ process number is used in each of the bundled TTIs..

TTI bundling

Number of TTIs

bundled

1 4

Transmission

bandwidth

360 kHz 360 kHz

Required SNR

(dB)

-4 -8


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Reducing other cell interference


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SINR

SINR ave = SI + N

I = Iown + Iother

SNR = S

N

What is N?


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Interference Own Cell

The LTE uplink is orthogonal, which is to say there is,at least in the ideal case, no interference between

users in the same cell.

Closer a terminal isto a neighbouring cell

the stronger the

interference


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Cell-edge performance

LTE supporting

Cell

Not supporting

LTE

Reduced coverage

may arise due to

interference

SINR ave = SI + N

I = Iown + Iother

Most trial networks only contain a few base

stations.

Some people believe that the out-of-cell

interference is not important if it originates

from cells that are physically far away from

the centre cell


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Soft Frequency Reuse in LTE

Frequency Reuse is a well known

concept that has been applied to

wireless systems over the past two

decades e.g. in GSM systems.

Frequency Reuse implies using the

same frequencies over different

geographical areas.


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Different Carrier /Different Frequency


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DLRS SINR= 10.32 dB DLRS SNR = 13.3 db

SNR = S/N


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Cell Loads

Load (%) Interference

Margin (dB)

35 1

40 1.3

50 1.8

60 2.4

70 2.9

80 3.3

90 3.7

100 4.2


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inter-cell interference control (ICIC).

ICIC can allocate

different RB

frequencies to

cell-edge users in

different cells


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inter-cell interference control (ICIC).Proactive schemes: Here an eNodeB informs its

neighboring eNodeBs how it plans to schedule its users inthe future (i.e. sending announcements), so that the

neighboring eNodeB can take this information into account.

eNB

eNB

X2

Proactive schemes are

supported via standardizedsignaling between eNodeBs

over the X2 interface.

ICIC schemes are primarily

designed for improving the

performance of the uplink and

downlink shared data channel

(PDSCH and PUSCH

PDSCH

PDSCH


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The following ICIC schemes are supported in ASSET:

Reuse 1 (Prioritisation) Soft Frequency Reuse

Reuse PartitioningFundamental to each of

these methods is a

division of the network

into two areas in relation

to the cell coverage, i.e.

Cell Centre Users

(CCUs) and Cell

Edge Users (CEUs).

Cell Edge Thresholds defined per cell in the Site Database


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The available thresholds

are RSRP and

Relative RSRP.RSRP is self explanatory

while the latter is defined

in dBs and can be

expressed as

the difference between

the RSRPs of theserving and the

strongest interfering cell


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RSRPs of the serving and the strongest

interfering cell


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Defining cell centre


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CarriersThe following ICIC schemes are

supported in ASSET:

Reuse 1 (Prioritisation)

Soft Frequency Reuse Reuse Partitioning


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Coordination factor

The improvement of Traffic &

Control SINR with the

deployment of Prioritisation is

dependent on the Cell Loading

and on the coordination factor.

coordination factor of 0

assumes nocoordination at all. No dB

improvement. No ICI

coordination factor of 1 means

perfect coordination.

Recommended 0.7


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REUSE 1(PRIORITISATION)

A h i bl DL b i h d i h


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Ach ievable DL bearer w ithou t and w ith

ICIC (Reuse-1, Prio rit i sation)

DL D t R t i th t d i th ICIC


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DL Data Rate withou t and w ith ICIC

(Reuse-1, Prio ri t isat ion )


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S ft F R i LTE


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Soft Frequency Reuse in LTE

. The lack of spectrum at

the cell edge may result

in much reducedShannon Capacity for

that region.

This is overcome by

allocating high power

carriers to the users inthis region thus

improving the SINR

and the Shannon

Capacity.

Note:1. The Signal to Interference and Noise Ratio is given as:

SINR=Signal Power/(Intercell Interference+Intracell Interference+AWGN

Noise)


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Soft Frequency Reuse

Soft Frequency Reuse Scheme (Power Ratio 50%, Bandwidth

Ratio 50%)


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Soft Frequency Reuse

Soft Frequency Reuse Scheme (Power Ratio 50%, Bandwidth Ratio

50%)


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Reuse Part it ion ing

Multiple partitions.

Two dedicated zones, one for CCUs, theother for CEUs.

Each sector can only consume CE

resources from its own dedicated CE partition


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Comparison


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Questions

3. What is the aim of ICIC?


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Questions

4. What is meant by:

Reuse Partitioning

LTE optimisation

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