liflb_dec2013

Prepared by Thierry Billon

december 2013,

INTER FREQ LOAD BALANCING IN LTE CONTEXT

Agenda

1. Scope/rational

2. MAIN ASSUMPTIONS

3. REFERENCE CASE :ALL SITES EQUIPED WITH ONLY ONE CARRIER

4. F2 CARRIER ONLY ON CENTER SITE

5. ALL SITES EQUIPPED WITH F1 and F2

1. Comparison equal loading from idle mode and unequal loading (70/30) without Load balancing

2. Comparison unequal loading from idle (70/30) with without load balance

Conclusion and further study

Copyright © 2009 Alcatel-Lucent, d.r.3 | Titre de la présentation | Mois 2009

Scope/rational

This document deals with load balancing between carrier in a LTE context

Previous documents have analyzed idle mode selection as root for establishing an initial balance between frequency layers, with different carrier priority ( priority to F2 layer, equal priority). Some solution with adaptive tuning of the idle mode threshold targeting equal %PRB load were tested.( Interfreq_loadbalance_FDD_SON_5 dec 2012)

Connected mode load balancing was studied , with as conclusion that its efficiency could be linked to the existence of relatively stable connection in demand and in time (e.g. GBR) , and traffic profile dependant. Short data session, dormancy timer, measurement gap… were seen to cause difficulties (IFLB_IDLE_CONNECTED_september 2013)

The previous traffic model was very short data session. Here we use an updated model , more heavy tail, with larger mean data volume

On previous version, most cases were done with all sites equipped with dual band. Here we also look at the case of dual band only in center site


MAIN ASSUMPTIONS

o NETWORK TOPOLOGY

o LOAD BALANCING

o RADIO PARAMETERS


NETWORK TOPOLOGY

We use a wrap round 7* 3*2 sector sites topology.

The two carriers are 780 Mhz and 2100 Mhz, with 5 Mhz bandwidth and look at two cases

The first case is with dual band only on the center site

The second case with where each site is equipped with 3 sectors on F1 and 3 sectors on F2 ( Collocated )

Copyright © 2009 Alcatel-Lucent, d.r.

LOAD BALANCING (1/2)

The load balancing algorithm is the load equalization one

If ( %PRB load cell > Threshold1 and delta%PRB load with other cell > Threshold2)

Offload up to N users to other cell

The user to be offloaded are selected by taking among all connected users those that have the highest average PRB consumption

In the simulation the filter time constant for the cell %PRB load is taken to 20s. The filter time constant for the per user PRB consumption is 2s, with one sample every 1 ms

N is set to 10 users maximum to be offloaded per second. Users are selected until their %PRB contribution is lower than half the delta%PRB or N=10

Threshold1 is set to 50%, threshold2 to 20%

Compared to november edition, we add in this december edition some cases, in particular a comparison between using actual prb load or using semi static prb

Copyright © 2009 Alcatel-Lucent, d.r.

LOAD BALANCING (2/2)

Once a user has been selected, it is configured in measurement Gap with 80 ms cycle, and offload if it fullfills an A4 event

The A4 event is set in the simulation to -104 dbm. In the simulation all users fulfills this criteria. Hand over failure are not simulated

All users are dual band

The simulation does not model the data transfert from one cell to the other ( assume immediat transfert)


RADIO PARAMETERS


TRAFIC MODEL


TRAFIC MODEL (1/3)

Along this document we use best effort traffic only, with a traffic profile that match about the statistic as provided by Omar Salvador the 24 of october about Mobile originated and mobile terminating user traffic from NY market lower Manhattan (see two next chart)

We use 70% connection Mobile originated

The dormancy timer is set to 5s

The traffic is generated as a Poisson process, and the average arrival rate is varied from 1 to 20 call attempt per cell per second.

For each arrival rate, each simulation corresponds to 500 second of observation

The maximum number of connected users par cell is set to 200. Arrival when the number of connected user is 200 are rejected


TRAFIC MODEL :Best effort short data packet session (2/3)

00.10.20.30.40.50.60.70.80.9

1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Pro

bab

ility

kbytes

Uplink Ue trafic volume distribution (kbytes)

Uplink MT

Uplink MO

00.10.20.30.40.50.60.70.80.9

1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Prob

abili

ty

kbyres

Downlink Ue trafic volume distribution (kbytes)

Downlink MT

Downlink MO


TRAFIC MODEL :Best effort short data packet session (3/3)

UL traffic (Kbytes) per connection for Mobile Terminated (MT)

Min. 1st Qu. Median Mean 3rd Qu. Max.

0.00 0.09 0.25 6.97 2.00 74560.00

DL traffic (Kbytes) per connection for Mobile Terminated (MT)


0.00 0.22 0.44 40.70 2.00 210500.00

DL traffic (Kbytes) per connection for Mobile Originated (MO)


0.0 0.1 1.0 104.6 9.0 1375000.0

UL traffic (Kbytes) per connection for Mobile Originated (MO)


0.00 0.21 1.00 16.38 5.00 260100.00


RESULTS

For each cases, for each arrival rate, we provide as results

The % PRB consumption, the served traffic per cell, the mean and 5% worst case and the number of rejected or offloaded users.

We provide the results,– With the case were idle mode provide a good balance– Compare the case where idle mode provide unbalance w/o load balancing


REFERENCE CASE : ALL SITES EQUIPED WITH ONLY ONE CARRIER F1


REFERENCE CASE( 1 carrier 5Mhz)

0

1000000

2000000

3000000

4000000

5000000

1 2 3 4 5 6 7 8 9 10

bit/

s

Ue Arrival rate per cell per second

DL traffic demand and served traffic (bit/s) 1 carrier (5 Mhz)

Dl traffic demand bit/s

DL served traffic bit/s

0

200000

400000

600000

800000

1000000

1200000

1 2 3 4 5 6 7 8 9 10

bit/

s


UL traffic demand and served traffic (bit/s) 1 carrier (5 Mhz)

Ul traffic demand bits/s

Ul served traffic bits/s

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10


%PRB consumption 1 carrier (5 Mhz)

% PRB DL

% PRB UL

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10

Conn

ectio

n tim

e(in

100

ms u

nit)


Connection time 1 carrier 5Mhz

mean connection time

3rd quartile connection time

5% worst case connection time


REFERENCE CASE ( 1 carrier 5Mhz)

0

20

40

60

80

100

120

140

160

180

200

1 2 3 4 5 6 7 8 9 10Ue Arrival rate per cell per second

Av Connected Ue 1 carrier 5Mhz

Av Connected Ue

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1 2 3 4 5 6 7 8 9 10Ue Arrival rate per cell per second

Rejected Ue per second 1 carrier 5Mhz, 200 connected user max

Ue rejected per second

With one carrier 5 Mhz, the maximum number of users (200) is achieved with an average arrival rate of 10 call attemps per second. At this load, the served downlink traffic is about 4.3 Mbit/s , all resources consumed . The uplink traffic is much less


F2 carrier only on center site, F1 on all sites

1) For the simulation, we create an unbalance between F1 and F2 by having 70% of access on F1 and 30% on F2 .We compare results with without load balancing

2)Comparison on using actual PRB load and static PRB load, and Idle mode setting benchmark



1) Unbalance 70/30 and comparison results with without load balancing


PRB consumption w/o Load balancing: carrier 5Mhz unequal user repartition (70 /30) from idle mode, F2 only on center site, F1 on all sites.

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Ue Arrival rate per dual cell per second

%PRB consumption 2 carriers (5 Mhz) unequal user repartition (70/30) F2 only on center site,LB off

% PRB DL F1

% PRB UL F1

% PRB DL F2

% PRB UL F2

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Ue Arrival rate per dual cell per second

%PRB consumption 2 carriers (5 Mhz) unequal user repartition from idle, F2 only in center site, LB on

% PRB DL F1

% PRB UL F1

% PRB DL F2

% PRB UL F2


Served traffic on F1 and F2 w/o load balancing : carrier 5Mhz unequal user repartition (70 30) from idle mode, F2 only on center site, F1 on all sites.

0

2000000

4000000

6000000

8000000

10000000

12000000


DL served traffic (bit/s) 2 carriers (5 Mhz) unequal user repartition,F2 only

on center site LB onDL served traffic F1 bit/s

DL served traffic F2 bit/s

DL served traffic F1+F2 bit/s

010000002000000300000040000005000000600000070000008000000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


DL served traffic (bit/s) 2 carriers (5 Mhz) unequal user repartition from idle ,F2 only on

center site LB offDL served traffic F1 bit/s




Rejected and offloaded users w/o Load balancing: carrier 5Mhz unequal user repartition (70 30) from idle mode, F2 only on center site, F1 on all sites:

0

1

2

3

4

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Rejected Ue per second 2 carrier 5Mhz unequal user repartition (70/30), F2 center site

only LB off

Ue rejected per second F1

012345678

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Rejected and offloaded Ue 2 carrier 5Mhz unequal user repartition (70/30), F2 center site

only LB on



Ue offload per second


0

0.5

1

1.5

2

2.5

3


Traffic ratio in F1 and F2 traffic 2 carriers (5 Mhz) unequal user repartition from idle, F2 only in center

site, LB on ratio DL traffic demand F1/F2

ratio DL traffic served F1/F2

ratio offload F1 DL traffic

0

0.5

1

1.5

2

2.5

3

3.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Ue Arrival rate per dual cell per seconde

Traffic ratio in F1 and F2 traffic 2 carriers (5 Mhz) unequal user repartition from idle, F2 only in

center site, LB off

ratio DL traffic demand F1/F2



Traffic repartition on F1 and F2 w/o load balancing : carrier 5Mhz unequal user repartition (70 30) from idle mode, F2 only on center site:


Connection time on F1 and F2 w/o load balancing 2 carrier 5Mhz unequal user repartition (70 30) from idle mode, F2 only on center site

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Conn

ectio

n tim

e(in

100

ms u

nit


Connection time 2 carriers 5Mhz unequal user repartition from idle (70/30) F2 only on centersite, LB

onmean connection time F1

5% worst case connection time F1

mean connection time F2


0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Co

nne

ction

tim

e(i

n 1

00m

s un

it


Connection time 2 carriers 5Mhz unequal user repartition from idle (70/30) F2 only on centersite, LB

off






Load balancing conclusion with dual band F1 F2 only on center site, all other sites on F1, with initial 70/30 users unbalance

With an initial unbalance of 70/30 for call attempts in F1 and F2, load balance allows to go up to 20 call attempts per second while without load balance, user start to be rejected ( more than 200 connected user in F1) at 13 call attempt per second.

The time of connection with load balance is minimized and the served traffic better ( 10 Mbit/s at 20 call attempts per second, rather than 7 Mbits without load balancing)

This asks, at this load, for 6 hand over per second.

When comparing the case of initial unbalance 70/30 plus load balance and the case of a good tuning of idle mode threshold ( either manually or by self adaptive mechanism, see next chart) we obtain almost the same results with the difference that idle mode tuning don’t need hand over ,is not trafic profile dependant, and has some trend to better equalize.


PRB and Served traffic on F1 and F2 : 2 carrier 5Mhz, F2 only on center site, with idle mode access tuning for equal %PRB

0102030405060708090


%PRB consumption 2 carriers (5 Mhz) F2 only on center site , idle mode

tuning for equal %PRB F1F2% PRB DL F1

% PRB UL F1

% PRB DL F2

% PRB UL F2

0

2000000

4000000

6000000

8000000

10000000

12000000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


DL served traffic (bit/s) 2 carriers (5 Mhz) F2 only on center site , idle mode tuning for equal %PRB F1F2






2)Comparison on using actual PRB load and static PRB load, and Idle mode setting benchmark


Comparison when using actual or static PRB as trigger, and idle mode setting benchmark

Here we compare Load balancing using either actual PRB consumption or static PRB consumption .For these simulation we assume that priority has been set badly set to F2 resulting to most of the user entering on the F2 carrier .For static PRB , we use a minBeBitRate of 60 kbit/s

For idle mode setting benchmark, we use priority on F2, with self tuned Threshold X high using PRB load from time 0. The SIB information is updated every 15 s

The simulation is conducted from time 0 ( no load on the network) to 1000 s

The load ( call attempts per second per dual cell) is increasing linearly with time, as follow

0

5

10

15

20

25

30

35

0 120 240 360 480 600 720 840 960

simulation time (s)

Ue arrival rate( per s) per dual band cell versus time

Ue arrival rate( per s) per dual band cell


2 carrier 5Mhz dual band on center site Idle mode Priority F2 badly set, LB with actual PRB

0

50

100

150

200

250

0 120 240 360 480 600 720 840 960time( s)

Nb Users per cell

NbUeconnectedF1

NbUeconnectedF2

AggregateConnected

NbRejectedUeF1/s

NbRejectedUeF2/s

-2000000

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

16000000

0 120 240 360 480 600 720 840 960

time( s)

Served trafic(bit/s) per cell

ServedTraficDLF1_bit/s


AggregateServedTraficDL_bit/s

0

10

20

30

40

50

60

70

80

90

100

0 120 240 360 480 600 720 840 960time( s)

%PRB per cell

%PRBDLF1

%PRBDLF2

0

20

40

60

80

100

120

140

0 120 240 360 480 600 720 840 960time( s)

Mean time to serve (ms) a "PDCP" segment

TTGpF1

TTGpF2


2 carrier 5Mhz dual band on center site Idle mode Priority F2 badly set, LB with static PRB

0

50

100

150

200

250

300

0 120 240 360 480 600 720 840 960time( s)

Nb Users per cell

NbUeconnectedF1

NbUeconnectedF2

AggregateConnected

NbRejectedUeF1/s

NbRejectedUeF2/s

-2000000

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

16000000

18000000

0 120 240 360 480 600 720 840 960

time( s)



0

10

20

30

40

50

60

70

80

90

100

0 120 240 360 480 600 720 840 960time( s)

%PRB per cell

%PRBDLF1

%PRBDLF2

0

50

100

150

200

250

0 120 240 360 480 600 720 840 960time( s)


TTGpF1

TTGpF2


2 carrier 5Mhz dual band on center site Idle mode Priority F2, self learnt ThreshXhigh, no LB

0

50

100

150

200

250

300

350

400

450

0 120 240 360 480 600 720 840 960time( s)

Nb Users per cellNbUeconnectedF1

NbUeconnectedF2

AggregateConnectedNbRejectedUeF1/s

NbRejectedUeF2/s

-2000000

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

0 120 240 360 480 600 720 840 960

time( s)




AggregateServedTraficDL_bit/s

0

10

20

30

40

50

60

70

80

90

100

0 120 240 360 480 600 720 840 960time( s)

%PRB per cell

%PRBDLF1

%PRBDLF2

0

100

200

300

400

500

600

700

800

0 120 240 360 480 600 720 840 960time( s)


TTGpF1

TTGpF2


Conclusion for single site dual band

Offloading with PRB load as trigger fails to recover large user unbalance that could exist due to idle mode setting. The trend is to offload the more PRB demanding users, that will fullfill rapidly the PRB of the other layer, which will preclude further offloading.

For this case of dual band in the center site only , loading first F1 ( case with 70% in F1 and 30% in F2) leads to different Load balancing behavior than loading first F2. F2 having no interference , the PRB consumption to trig load balancing from F2 to F1 is obtain latter than in F1

Using static PRB as trigger rather than actual PRB load gives better performance ( In term of user balance). The reason is that the static PRB mechanism include a weighting with the number of connected users and a minimum bit rate .

If large user unbalance between frequencies exist due too idle mode setting, load balancing using PRB either actual or static fails to recover the unbalance, and the hard limit on maximum number of users is hit on one frequency, well before this limit is hit with a good idle tuning


F1 and F2 carrier on all sites

1) Comparison equal loading from idle mode and unequal loading (70/30) without Load balancing

2) Comparison unequal loading from idle (70/30) with without load balance

3) Comparison on using actual PRB load and static PRB load and idle mode setting benchmark



1) Comparison equal loading from idle mode and unequal loading (70/30) without Load balancing


2 carrier 5Mhz all sites equal and unequal user repartition (70 30) from idle mode no load balance

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


%PRB consumption 2 carriers (5 Mhz) unequal user repartition (70/30)

% PRB DL F1

% PRB UL F1

% PRB DL F2

% PRB UL F2

0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


%PRB consumption 2 carriers (5 Mhz) equal user repartition

% PRB DL F1

% PRB UL F1

% PRB DL F2

% PRB UL F2


Served traffic 2 carriers 5Mhz all sites equal and unequal user repartition from idle mode no load balance

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

bit

/s


DL served traffic (bit/s) 2 carriers (5 Mhz) equal user repartition




0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


DL served traffic (bit/s) 2 carriers (5 Mhz) unequal user repartition (70/30) LB off





Connection time 2 carrier 5Mhz all sites equal and unequal user repartition from idle mode no load balance

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Conn

ecti

on ti

me(

in 1

00m

s un

it


Connection time 2 carriers 5Mhz unequal user repartition (70/30)


5% worst case connection time F1mean connection time F2


050

100150200250300350400450

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Co

nn

ecti

on

tim

e(i

n 1

00

ms

un

it)


Connection time 2 carriers 5Mhz equal user repartition





Traffic volume ratio 2 carriers 5Mhz all sites equal and unequal user repartition from idle mode no load balance

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Traffic ratio between 2 carriers 5Mhz with equal user repartition



0

0.5

1

1.5

2

2.5

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Traffic ratio between 2 carriers 5Mhz with unequal user repartition (70/30)




Rejected users (limit=200 connected per cell) 2 carrier 5Mhz equal and unequal users repartition (70 30) from idle mode no load balance

00.5

11.5

22.5

33.5

44.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Av rejected Ue per cell 2 carrier 5Mhz unequal user repartition (70/30)



0

0.1

0.2

0.3

0.4

0.5

0.6


Av rejected Ue per cell 2 carrier 5Mhz equal user repartition




Conclusion for 2 carriers 5Mhz all sites ,equal and unequal user repartition from idle mode no load balance

For all sites equipped with 2 carriers, when each carriers have sufficient coverage ( small ISD makes that 2100 can cover the cell edge of 780 Mhz) equal user repartition from idle mode allows to go up to 20 call attempts per second with equal load on each layer

When there is unbalance from idle mode( 70/30), the maximum number of connected user is hit at an arrival rate of 13 call attempts per second



2) Comparison unequal loading from idle (70/30) with without load balance using actual %PRB load as trigger


2 carrier 5Mhz all sites unequal user repartition (70 30) from idle mode W/o load balance, selecting more PRB consuming users for offload

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


%PRB consumption 2 carriers (5 Mhz) unequal user repartition (70/30)

% PRB DL F1

% PRB UL F1

% PRB DL F2

% PRB UL F2

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Ue Arrival rate per dual cell per second

%PRB consumption 2 carriers (5 Mhz F1 F2 on all sites, LB on

% PRB DL F1

% PRB UL F1

% PRB DL F2

% PRB UL F2


Served traffic 2 carriers 5Mhz all sites unequal user repartition from idle mode W/0 load balance

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


DL served traffic (bit/s) 2 carriers (5 Mhz) unequal user repartition (70/30) LB off




0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000


DL served traffic (bit/s) 2 carriers (5 Mhz) F1 F2 on all sites, LB on





Connection time 2 carrier 5Mhz all sites unequal user repartition from idle mode w/O load balance

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Conn

ecti

on ti

me(

in 1

00m

s un

it


Connection time 2 carriers 5Mhz unequal user repartition (70/30)




0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19


Connection time 2 carriers 5Mhz F1 and F2 on all sites, LB on






Traffic volume ratio 2 carriers 5Mhz all sites unequal user repartition from idle mode w/o load balance

0

0.5

1

1.5

2

2.5

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Traffic ratio between 2 carriers 5Mhz with unequal user repartition (70/30)



0

0.5

1

1.5

2

2.5

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19


Traffic ratio in F1 and F2 traffic 2 carriers (5 Mhz) F1 and F2 on all sites, LB

onratio DL traffic served F1/F2



Rejected users (limit=200 connected per cell) 2 carrier 5Mhz equal and unequal users repartition (70 30) from idle mode no load balance

00.5

11.5

22.5

33.5

44.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Av rejected Ue per cell 2 carrier 5Mhz unequal user repartition (70/30)



0

0.5

1

1.5

2

2.5

3

3.5


Rejected and offloaded Ue 2 carrier 5Mhz unequal, F1 F2 on all sites, LB on


Ue offload per second


Load balancing conclusion with dual band F1 F2 on all sites

When all sites are equipped with dual band and with an initial unbalance of 70/30 for call attempts in F1 and F2, load balance with actual % PRB load is not efficient. We do not obtain at all equivalent performance or trends as when idle mode ensure equal user repartition.

While the % PRB load tends to be equalized between each band, the offload traffic (number of offloaded users ) is low, and the limit of 200 maximum connected users in F1 is not pushed far away than without load balancing

This is due to the algorithm that offload the more consuming PRB users. With the trafic profile we use (chart 10, 11 and 12), a large proportion of users have small payload, while 15% have large demand. Since we offload the users with largest PRB consumption, the trend is to select the largest payload users, and probably also the worst in SNR, and after offloading , they will occupied all the bandwidth they get, making the PRB load of F2 going high ( see chart 34), precluding further offloading from F1 .



3) Comparison on using actual PRB load and static PRB load, and Idle mode setting benchmark


Comparison when using actual or static PRB as trigger, and idle mode setting benchmark

Here we compare Load balancing using either actual PRB consumption or static PRB consumption .For these simulation we assume that priority has been set to F1 resulting to all the users entering on the same carrier .For static PRB , we use a minBeBitRate of 60 kbit/s

For idle mode setting benchmark, we use priority on F2, with self tuned Threshold X high using PRB load from time 0. The SIB information is updated every 15 s

The simulation is conducted from time 0 ( no load on the network) to 1000 s

The load ( call attempts per second per dual cell) is increasing linearly with time, as follow

0

5

10

15

20

25

30

35

0 120 240 360 480 600 720 840 960

simulation time (s)

Ue arrival rate( per s) per dual band cell versus time

Ue arrival rate( per s) per dual band cell


2 carrier 5Mhz all sites Idle mode Priority F1, LB with actual PRB load

0

50

100

150

200

250

0 120 240 360 480 600 720 840 960time( s)

Nb Users per cell

NbUeconnectedF1

NbUeconnectedF2

AggregateConnected

NbRejectedUeF1/s

NbRejectedUeF2/s

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

0 120 240 360 480 600 720 840 960time( s)


ServedTraficDLF1_bit/sServedTraficDLF2_bit/sAggregateServedTraficDL_bit/s

0

10

20

30

40

50

60

70

80

90

100

0 120 240 360 480 600 720 840 960time( s)

%PRB per cell

%PRBDLF1

%PRBDLF2

0

50

100

150

200

250

300

350

400

0 120 240 360 480 600 720 840 960time( s)


TTGpF1

TTGpF2


2 carrier 5Mhz all sites, Idle mode Priority F1, LB with static PRB load

0

50

100

150

200

250

300

0 120 240 360 480 600 720 840 960time( s)

Nb Users per cell

NbUeconnectedF1

NbUeconnectedF2

AggregateConnected

NbRejectedUeF1/s

NbRejectedUeF2/s0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

9000000

0 120 240 360 480 600 720 840 960time( s)



0

10

20

30

40

50

60

70

80

90

100

0 120 240 360 480 600 720 840 960time( s)

%PRB per cell

%PRBDLF1

%PRBDLF2

0

50

100

150

200

250

300

350

400

0 120 240 360 480 600 720 840 960time( s)


TTGpF1

TTGpF2


2 carrier 5Mhz all sites Idle mode Priority on F2, self learnt ThreshXhigh, no LB

0

50

100

150

200

250

300

350

400

450

0 120 240 360 480 600 720 840 960time( s)

Nb Users per cell

NbUeconnectedF1

NbUeconnectedF2

AggregateConnected

NbRejectedUeF1/s

NbRejectedUeF2/s

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

9000000

0 120 240 360 480 600 720 840 960time( s)



0

10

20

30

40

50

60

70

80

90

100

0 120 240 360 480 600 720 840 960time( s)

%PRB per cell

%PRBDLF1

%PRBDLF2

0

100

200

300

400

500

600

700

800

0 120 240 360 480 600 720 840 960time( s)


TTGpF1

TTGpF2


Conclusion

Offloading with PRB load as trigger fails to recover large user unbalance that could exist due to idle mode setting. The trend is to offload the more PRB demanding users, that will fullfill rapidly the PRB of the other layer, which will preclude further offloading.

Using static PRB as trigger rather than actual PRB load gives better performance ( In term of user balance). The reason is that the static PRB mechanism include a weighting with the number of connected users and a minimum bit rate .

If large user unbalance between frequency exist due too idle mode setting, load balancing using PRB either actual or static fails to correct the unbalance, and the hard limit on maximum number of users is hit on one frequency, well before this limit is hit with a good idle tuning.

In the simulation, when the hard limit of maximum connected users is hit, new arrival are rejected. We do not redirect them . Would we redirect them on the other frequency, this will probably reestablish some balance


www.alcatel-lucent.comwww.alcatel-lucent.com

liflb_dec2013

Documents

actual prb load

load balanceconclusion

freq load balancing

load balancing algorithm

prb load cell threshold1

connected mode load

load equalization oneif

static prb copyright