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Load Balancing in Downlink LTE Self- Optimizing Networks TD - - PowerPoint PPT Presentation

Jun 18, 2023 152 likes •421 views

FP7 ICT-SOCRATES Load Balancing in Downlink LTE Self- Optimizing Networks TD (10)10071 COST 2100, 10 th MCM Athens, Greece February 3 rd 5 th NSN, Wroclaw, Poland NSN, Munich, Germany TUBS, Braunschweig, Germany IBBT, Ghent, Belgium

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SLIDE 1

FP7 ICT-SOCRATES

Load Balancing in Downlink LTE Self- Optimizing Networks

TD (10)10071 COST 2100, 10th MCM Athens, Greece February 3rd – 5th NSN, Wroclaw, Poland NSN, Munich, Germany TUBS, Braunschweig, Germany IBBT, Ghent, Belgium

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WWW.FP7-SOCRATES.EU

Outline

Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

  • 1. Introduction
  • 2. Simulation metrics
  • 3. Load balancing algorithm
  • 4. Load estimation for the target eNodeB
  • 5. Simulation scenarios
  • 6. Simulation results
  • 7. Conclusion

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SLIDE 3

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Introduction

  • Problem

– Users concentrate in the area served by one

cell

– Unequal load distribution causes an overload – Users can not be served with required quality

level due to lack of resources

  • Main Idea

– Reallocate some users from the overloaded cell

to less loaded neighbour cell(s)

– Overloaded (SeNB) cell must find neighbour

cell(s) (TeNB) which may accommodate additional load

– SeNB adjusts the HO offset of the TeNB and

forces users to HO to the TeNB

  • Result

– TeNB increases the overlapping area and takes

  • ver some users previously served by SeNB

– LB operation sets free resources at SeNB – SeNB is able to serve remaining users with the

required QoS

SeNB TeNB SeNB TeNB

Hysteresis

LB HO offset

SeNB TeNB

Received signal strength Distance Overlaped area increase

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SLIDE 4

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Virtual load

Virtual cell load can be expressed as the sum of the required resources of all users u connected to cell c by connection function X(u) which gives the serving cell c for user u.

  • Du is the average data rate requirement per user u
  • R(SINRu) is the average throughput data rate per physical resource block

(PRB) for user u

  • MPRB is the number of available PRBs
  • All users in a cell are satisfied as long as . In a cell with we will

have a fraction of satisfied users

c u X u u u PRB c

SINR R D M

) ( |

) ( 1 ˆ

1 ˆ c 1 ˆ c

c

ˆ 1

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SLIDE 5

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Throughput mapping

  • Throughput mapping bases on the concept of a truncated Shannon-Gap mapping

curve

  • The necessary number of PRBs for the required throughput Du and the

transmission bandwidth of one PRB BW = 180 kHz can be obtained from the following equation

1 2 3 4 5

  • 6.5
  • 4.5
  • 2.5
  • 0.5

1.5 3.5 5.5 7.5 9.5 11.5 13.5 15.5 17.5 19.5 21.5 23.5

SINR [dB] Throughput bps/Hz

1 2 3 4 5 6 7 8 9

required PRBs

DL throughput DL PRBs for 512 kb/s

SINR SINR Thr 1 log ) (

2

BW SINR Thr D N

u PRB

) (

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SLIDE 6

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

LB performance evaluation z metric

  • Unsatisfied users due to resources limitation

– the total number of unsatisfied users in the whole network (which is the sum of

unsatisfied users per cell, where the number of users in cell c is represented by Mc)

  • Unsatisfied users due to power limitation (applies to UL transmission)

– Where Mmax,u denotes the maximum number of PRBs that

can be granted to user u

c c c load

M z ˆ 1 1 , max

c c u X u u u u u u u power

SINR R D M for SINR R D M for z ) ( 1 ) (

max, max,

load

z

power

z

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SLIDE 7

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

LB algorithm

  • The load level of all cells is permanently monitored
  • If the load level exceeds a certain threshold the load balancing is initiated
  • 1. Sort all users by their SINR
  • 2. Split the users in groups (according to the best suited target eNodeB)
  • 3. Decide on the users to be handed over to other cells (based on the

remaining cell load target for the source eNodeB)

  • 4. Assure that the target eNodeBs are not overloaded after the load

balancing activity

  • 5. Modify the HO thresholds of the target eNodeBs
  • 6. Send HO command to the selected users

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SLIDE 8

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

List of target eNodeBs for load balancing

  • The central entity provides guidelines on LB priorities

– cell 1 can obtain information about its neighbour cells over X2 – best target cells for cell #1 seem to be cells # 3 and # 7 – based on the overall load distribution available in the central

SON entity we generate a priority list for the load balancing event: – 4 – 5, 6 – 3

– Cell # 7 is not on the list (LB to this cell is not allowed) – Cell #3 has the lowest priority due to the load situation in cell

# 2

  • The central entity has been presented by NSN in the SA5

meeting in Vancouver (pseudo CR for TS 32.521)

1 2 3 60% 4 85% 5 75% 6 65% 7 60% 1 2 3 60% 4 85% 5 75% 6 65% 7 60%

  • We propose a decentralised load balancing solution

– all neighbouring eNodeBs are potential targets for load balancing – the decision depends on the reported load situation from all eNodeBs

  • An decision made by one individual eNodeB cannot take the larger network

environment into account (e.g. the neighbour of the neighbouring eNodeB of the

  • verloaded cell may be also be overloaded)

– the central load balancing entity can report the cell load of the 2nd neighbours

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SLIDE 9

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Load estimation in the downlink

  • Load estimation error measured for moving

hotspot

  • Accuracy of load estimation could be higheer

if users are fixed

S1 S2 I – interference from other eNB S1 S2 a) b) SeNB TeNB SeNB TeNB I – interference from other eNB

2 1 1 2

S S SINR S S SINR

SeNB TeNB

10 20 30 40 50 60 70 80 90 100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 [%] cdf load estimation error

  • The load estimation at the TeNB has to be computed before the LB
  • It is based on a SINR estimation for the time after the LB

– Required UE measurements RSRP – We assume that the UE does not change its position during the LB operation

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Load estimation in the uplink

  • Load estimation error measured for a

moving hotspot

  • Accuracy of the load estimation could be

higher if users would be static

  • IoT cannot be predicted, we assumed

small changes during the LB

S1 S2 I – interference from UEs from other cells S1 S2 a) b) SeNB TeNB SeNB TeNB I – interference from UEs from other cells

IoT S SINR SINR

SeNB TeNB

5 10 15 20 25 30 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

load estimation error [%] cdf load estimation error in UL

This equation is valid for users not limited in power

10/24

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SLIDE 11

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Scenarios for evaluation studies

Study 1: Impact of environment

Scenario proposal: In a network setting with multiple cells consider different site to-site distances and cell types

–

Hexagonal network grid ISD 500m

–

Hexagonal network grid ISD 1700m

–

Nonregular network grid

Study 2: Impact of service type

Scenario proposal: Consider scenarios with a high and/or low rate of broadband service users. The load situation in the surrounding cells should also be varied for this study for the sake of service type or link direction.

–

Like VoIP service, UL/DL 30 kbps

–

Like video service, DL 512kbps, UL 256 kbps

Study 3: Impact of user mobility

Scenario proposal: The speed of the users should be varied to create scenarios with high/low user mobility

–

User mobility speed 3 km/h

–

User mobility speed 30 km/h

Study 4: Impact of traffic load

Scenario proposal: The amount of traffic load, load balance, size and shape of the overloaded area and location of the overloaded area should be varied in the scenarios.

–

Users move through cells

–

Users move along the cell borders

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Network layouts and hotspot routes

3) Non regular network layout, hotspot moving through the cells

  • 1000
  • 500

500 1000

  • 1000
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  • 600
  • 400
  • 200

200 400 600 800 1000 X [m] Y [m]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

ISD = 500m; hotspot is moving from cell 10 to 20 Base Station shotspot route

  • 4000
  • 3000
  • 2000
  • 1000

1000 2000 3000 4000

  • 3000
  • 2000
  • 1000

1000 2000 3000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

X [m] Y [m] ISD = 1700m; hotspot is moving along the cell borders Base Station shotspot route

  • 2000
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500 1000 1500

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500 1000 1500 2000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

X [m] Y [m] non-regular network; hotspot is moving from cell 27 to 13 Base Station shotspot route

1) Regular network layout, hotspot moving through the cells 2) Regular network layout, hotspot moving along the cell borders

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Realistic SOCRATES scenario – Bus scenario

  • Background users: static users in buildings and dynamic users moving along

the streets

  • Bus is moving with variable speed of 0 – 50 km/h (Red line – bus route)
  • Grey lines indicate the theoretical cell borders (without shadowing)

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Simulation tool

  • Matlab based simulator
  • Almost real time

simulations 

  • Modular structure
  • Dynamic simulations
  • DL and UL implemented
  • Different network layouts

Load default parameters Create network layer, and drop users UL DL Create connection function regarding to LB HO_map and RSRP_map Calculate SINRs in DL Calculate load in DL

Connection / SINR / Load calculations Simulation preparation Load Balancing algorithm/ HO procedure

exit Last iteration? Print results No Yes

Results

Calculate load in UL UL switch on ? Calculate SINRs in UL Calculate IoTs Yes Save results No Chose algorithm for LB Standard HO procedure LB switch on? Yes No Find overloaded cells in DL Prepare TeNB list and group users Main DL LB algorithm, calculate LB HO

  • ffsets for DL

LB HO procedure Find overloaded cells in UL Prepare TeNB list and group users Main UL LB algorithm, calculate LB HO

  • ffsets for UL

LB HO procedure Calculate signal strength between users and eNBs, create RSRP_map Update users position

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

First results without load estimation

5 10 15 20 25 30 35 20 40 60 80 100 120 140 160 Virtual load in network [%] before LB HO after LB HO

  • LB algorithm base on HO offset
  • During LB operations TeNB can be
  • verloaded ( lack of admission

control mechanism)

  • Important load estimation at TeNB

after LB HO

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  • 1500
  • 1000
  • 500

500 1000 1500

  • 2000
  • 1500
  • 1000
  • 500

500 1000 1500 2000 After LB HO (HO offset modification)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

15 30 45 61 76 91 107 122 137 153 Base Station antenna orientation users

  • 2000
  • 1500
  • 1000
  • 500

500 1000 1500

  • 2000
  • 1500
  • 1000
  • 500

500 1000 1500 2000 Before LB HO (HO offset modification)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

15 30 45 61 76 91 107 122 137 153 Base Station antenna orientation users

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WWW.FP7-SOCRATES.EU

Downlink simulation results

Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

200 400 600 800 1000 1200 1400 1600 1800 10 20 30 40 50 60 70 80 90 40.2 1.89 scenario 1 t [s] n unsatisfied users in network reference with load balancing

1) Regular network ISD = 500m

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WWW.FP7-SOCRATES.EU

Downlink simulation results

Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

200 400 600 800 1000 1200 1400 1600 1800 2 4 6 8 10 12 0.895 0.113 scenario 2 t [s] n unsatisfied users in network reference with load balancing

2) Regular network ISD = 1700m

17/24

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Downlink simulation results

200 400 600 800 1000 1200 1400 1600 1800 20 40 60 80 100 120 140 160 180 200 104 35 scenario 3 t [s] n unsatisfied users in network reference with load balancing

3) Non regular network

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WWW.FP7-SOCRATES.EU

Uplink simulation results

Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

200 400 600 800 1000 1200 1400 1600 1800 10 20 30 40 50 60 70 80 90 100 32.6 0.0175 scenario 1 t [s] n unsatisfied users in network reference with load balancing

1) Regular network ISD = 500m

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WWW.FP7-SOCRATES.EU

Uplink simulation results

Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

200 400 600 800 1000 1200 1400 1600 1800 20 40 60 80 100 120 140 160 180 150 68.4 scenario 2 t [s] n unsatisfied users in network reference with load balancing

2) Regular network ISD = 1700m

20/24

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SLIDE 21

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Uplink simulation results

200 400 600 800 1000 1200 1400 1600 1800 20 40 60 80 100 120 140 160 180 46.6 5.49 scenario 3 t [s] n unsatisfied users in network reference with load balancing

3) Non regular network

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 100 200 300 400 500 600 40 50 60 70 80 90 100

time [s] unsatisfied users z Load Balancing performance over time

with Load Balancing reference

Simulation results using the realistic SOCRATES scenario

  • Simulation time 10 min
  • 100 static background

users

  • 100 dynamic background

users

  • 40 users in the bus
  • Reference case

– 75.7 unsatisfied users

  • Load Balancing

– 67.3 unsatisfied users

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SLIDE 23

WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Uplink simulation results

200 400 600 800 1000 1200 1400 1600 1800 20 40 60 80 100 120 140 160 180 200 178 176 scenario 5 t [s] n unsatisfied users in network reference with load balancing

3) Regular network ISD = 500m

23/24

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WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik

Conclusions

  • The proposed algorithm reduces the overload significantly of the cells and

increases the number of satisfied users

  • Several simulation scenarios have been considered
  • In almost every case the algorithm increased the system performance
  • The algorithm works on the measurements, information elements and

control parameters defined in 3GPP for LTE Release9

  • UL power limitation is the most limiting factor for load balancing activities

24/24

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SLIDE 25

FP7 ICT-SOCRATES

Thank you very much for your attention