LTE optimisation

LTE Optimization GRAHAM WHYLEY 1

Copyright 2010 AIRCOM International

Scheduler

2

Copyright 2010 AIRCOM International

Scheduler It is the task of the scheduler to assign resource blocks to physical channels belonging to different users or for general system tasks. The job of the MAC layer

3

Copyright 2010 AIRCOM International

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 after the GBR demands then different schedulers are available

• There are 4 main schedulers • Max SINR • Proportional Demand • Proportional Fair • Round Robin 4

Copyright 2010 AIRCOM International

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 the available/unused resources as fairly as possible in such a way that, on average, each terminal gets the highest possible throughput achievable under the channel conditions.

5

Copyright 2010 AIRCOM International

Scheduler Proportional Demand

• The aim of this scheduler is to allocate the remaining unused resources to RT terminals in proportion to their additional resource demands Application Layer

NAS Protocol(s) (Attach/TA Update/…)

Physical Uplink Shared Channel(PUSCH) Buffer Status Report

IP / TCP | UDP | … (E-)RRC (Radio Resource Control)

PDCP (Packet Data Convergence Protocol)

RLC (Radio Link Control)

RLC (Radio Link Control)

RLC (Radio Link Control)

…

…

Logical Channel

Medium Access Control (MAC)

Transport Channels

PDCP (Packet Data Convergence Protocol)

PDCP (Packet Data Convergence Protocol)

RLC (Radio Link Control)

RLC (Radio Link Control)

eNodeB

MAC Scheduler DL Physical Downlink Control Channel (PDCCH) Additional UL GRANT

Scheduling / Priority Handling HARQ

FDD | TDD - Layer 1 ( DL: OFDMA, UL: SC-FDMA )

6

Copyright 2010 AIRCOM International

Scheduler Max SINR

• Terminals with higher bearer rates (and consequently higher SINR) are preferred 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. 6 BITS 2 BITS

64QAM

4 BITS 16 QAM QPSK

7

Copyright 2010 AIRCOM International

Scheduler

8

Copyright 2010 AIRCOM International

Frequency-selective Scheduler

Wideband CQI

Sub-band CQI, can be created by splitting the channel into several subbands

9

The number of sub-bands depends on the channel bandwidth

Copyright 2010 AIRCOM International

ASSET – LTE

There are 4 schedulers • Max SINR • Proportional Demand • Proportional Fair • Round Robin

10

Copyright 2010 AIRCOM International

Using MU-MIMO

11

Copyright 2010 AIRCOM International

Cell throughput. •MU-MIMO is used to increase the cells’ throughput. •This is achieved by co-scheduling terminals on the same Resource Blocks. •Applying MU-MIMO will make no obvious changes to a network unless it is overloaded. 12

What is CSSR?

Copyright 2010 AIRCOM International

Are there any disadvantages of MUMIMO?

13

Copyright 2010 AIRCOM International

MU-MIMO 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

RSRQ changes when MU-MIMO is deployed because the number of served terminals changes. 14

Copyright 2010 AIRCOM International

MU-MIMO DL 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. 15

Copyright 2010 AIRCOM International

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

SM close to the eNodeBs to increase data rates switches to Diversity

MU-MIMO for heavily loaded cells switches to Diversity

Switch Over is based on DLRS SNR – What happens if the load increases 16

Copyright 2010 AIRCOM International

LOAD INCREASES- What happens to cell edge? Load increases – DLRS reduces

17

Copyright 2010 AIRCOM International

Achievable DL Bearer without and with Diversity

18

Copyright 2010 AIRCOM International

DL Data Rate Improvement with Diversity

19

Copyright 2010 AIRCOM International

TTI bundling •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 a longer 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..

20

Copyright 2010 AIRCOM International

TTI bundling •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 a longer 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..

21

Number of TTIs bundled

1

4

Transmission bandwidth

360 kHz

360 kHz

Required SNR (dB)

-4

-8

Copyright 2010 AIRCOM International

Reducing other cell interference

22

Copyright 2010 AIRCOM International

SINR SINR ave =

S I+N

I = Iown + Iother

What is N? SNR =

23

S N

Copyright 2010 AIRCOM International

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 is to a neighbouring cell the stronger the interference

24

Copyright 2010 AIRCOM International

Cell-edge performance SINR ave =

S I+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 LTE supporting Cell Not supporting LTE

Reduced coverage may arise due to interference

25

Copyright 2010 AIRCOM International

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.

26

Copyright 2010 AIRCOM International

Different Carrier /Different Frequency

27

Copyright 2010 AIRCOM International

DLRS SINR= 10.32 dB

DLRS SNR = 13.3 db SNR = S/N

28

Copyright 2010 AIRCOM International

Cell Loads

29

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

Copyright 2010 AIRCOM International

inter-cell interference control (ICIC).

ICIC can allocate different RB frequencies to cell-edge users in different cells

30

Copyright 2010 AIRCOM International

inter-cell interference control (ICIC). Proactive schemes: Here an eNodeB informs its neighboring eNodeBs how it plans to schedule its users in the future (i.e. sending announcements), so that the neighboring eNodeB can take this information into account. Proactive schemes are supported via standardized signaling 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 31

PDSCH

eNB

X2 PDSCH eNB

Copyright 2010 AIRCOM International

inter-cell interference control (ICIC). The following ICIC schemes are supported in ASSET: • Reuse 1 (Prioritisation) • Soft Frequency Reuse • Reuse Partitioning Fundamental 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 32

Copyright 2010 AIRCOM International

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 the serving and the strongest interfering cell

33

Copyright 2010 AIRCOM International

inter-cell interference control (ICIC).

RSRPs of the serving and the strongest interfering cell

34

Copyright 2010 AIRCOM International

Defining cell centre

35

Copyright 2010 AIRCOM International

Global Editor

36

Copyright 2010 AIRCOM International

Carriers

37

The following ICIC schemes are supported in ASSET: • Reuse 1 (Prioritisation) • Soft Frequency Reuse • Reuse Partitioning

Copyright 2010 AIRCOM International

REUSE 1(PRIORITISATION) 15 Mhz Carrier 1 A 1 A 1 5 Mh z

Number of Partitions = 3

A 3

A Carrier 1 3

38

A 2 Carrier 1

A 2

The simplest way to minimize ICI within a Frequency Reuse 1 (FR 1) scenario is by prioritisation of resources. Reuse 1 (Prioritisation) scheme prioritises certain portions of the carrier bandwidth (i.e., number of RBs) in each cell according to a set plan. The whole bandwidth is still available for transmission in all cells, but the concept is that each cell uses its prioritised RBs more often than its non-prioritised RBs, so that it minimises the interference that it may cause to other cells.

Copyright 2010 AIRCOM International

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 no coordination at all. No dB improvement. No ICI coordination factor of 1 means perfect coordination. Recommended 0.7

39

Copyright 2010 AIRCOM International

REUSE 1(PRIORITISATION)

40

Copyright 2010 AIRCOM International

Achievable DL bearer without and with ICIC (Reuse-1, Prioritisation)

41

Copyright 2010 AIRCOM International

DL Data Rate without and with ICIC (Reuse-1, Prioritisation)

42

Copyright 2010 AIRCOM International

Soft Frequency Reuse in LTE .

In Soft Frequency Reuse (SFR) the cell area is divided into two regions; a central region where all of the frequency band is available and a cell edge area where only a small fraction of the spectrum is available.

The spectrum dedicated for the cell edge may also be used in the central region if it is not being used at the cell edge.

43

Copyright 2010 AIRCOM International

Soft Frequency Reuse in LTE .

The lack of spectrum at the cell edge may result in much reduced Shannon Capacity for that region. This is overcome by allocating high power carriers to the users in this 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)

44

Copyright 2010 AIRCOM International

Soft Frequency Reuse

Soft Frequency Reuse Scheme (Power Ratio 50%, Bandwidth Ratio 50%) 45

Copyright 2010 AIRCOM International

Soft Frequency Reuse

Soft Frequency Reuse Scheme (Power Ratio 50%, Bandwidth Ratio 50%) 46

Copyright 2010 AIRCOM International

Reuse Partitioning •Multiple partitions. •Two dedicated zones, one for CCUs, the other for CEUs. •Each sector can only consume CE resources from its own dedicated CE partition

47

Copyright 2010 AIRCOM International

48

Copyright 2010 AIRCOM International

Comparison

49

Copyright 2010 AIRCOM International

50

Copyright 2010 AIRCOM International

Questions 1. What does a coordination factor of 0 mean?

2. What does a coordination factor of 1 mean?

51

Copyright 2010 AIRCOM International

Questions 3. What is the aim of ICIC?

52

Copyright 2010 AIRCOM International

Questions 4. What is meant by: • Reuse Partitioning

53

Copyright 2010 AIRCOM International