lte optimisation
TRANSCRIPT
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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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inter-cell interference control (ICIC).
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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inter-cell interference control (ICIC).
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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inter-cell interference control (ICIC).
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