owj103104 wcdma load control issue1.1

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ISSUEISSUE

OWJ103104 WCDMA Load OWJ103104 WCDMA Load Control Control

OWJ103104 WCDMA Load OWJ103104 WCDMA Load Control Control

1.11.1

Confidential Information of Huawei. No Spreading without Permission. Security Level: Internal

2

The ContentThe Content

The Load Concept

The Load Control Measures

Admission Control

Load Balance

Congestion Control


3

Load MeasurementLoad Measurement

Load Concept

Uplink Load

Downlink Load


4

Load ConceptLoad Concept

Load:

The occupancy of capacity

TDMA and FDMA system: the capacity is hard

limited.

Example: In GSM, the cell capacity (channel

number) is fixed.

CDMA system:

soft capacity

Hard capacity


5

Load ConceptLoad Concept

Time

Frequency

FDMA

User#1

User#2

User#3

User#1User#2

User#3Frequency

TimeTDMA

Frequency

Time

CodeCDMA

User#1User#2

User#3


6

Capacity of CDMA systemCapacity of CDMA system

Soft capacity:

Interference (UL)

Power (DL)

Hard capacity

Code

Hard ware resource

Transport resource, NodeB processing capability.


7

System loadSystem load

Uplink : RTWP (Received Total Wide band Power)

Downlink : TCP (Transmitted Carrier Power)

RTWP

noiseBackgroudUL 1

The RTWP has an unique corresponding with the uplink load

The TCP has no unique corresponding with the actual downlink load factor. And because the actual downlink load factor is difficult to measure, we use the TCP instead.


8

Activity factor : The percentage of time that the data

transmission is active.

The UL and DL activity factor may be different for dedicated

channel.

Different service type has different activity factor.

Activity factorActivity factor


9

Eb/No

j

j

b

PRTWP

P

R

W

powerceInterferen

powerSignalgaingprocesNE

sin/ 0

RTWP

NE

RWP

b

j

0/

)/(1

1

0/

)/(1

1

NE

RWL

b

j

celltheinuserallj

jUL Lf )1(

Received power Pj

Define load factor for user j

UL load factor

Definition of UL load factorDefinition of UL load factor


10

Noise rise : defined as the ratio of RTWP and background

noise.

NP

RTWPrisenoise

UL

risenoise

1

1

Relationship between UL load factor and the noise rise.

risenoise

risenoiseUL

1

and

Noise rise & UL load factorNoise rise & UL load factor


11

Pj can be written as

erferencebase

ULNjjj

P

PLRTWPLP

int

1

1

Received power if there is no interference.

Increment due to the interference.

Meaning of the UL load factor

Meaning of UL load factorMeaning of UL load factor


12

Stability and noise riseStability and noise rise


13

Eb/No

N

miiN

ji

itotal

jm

total

jm

j

ob

PL

P

LP

L

p

R

WNE

,1 ,

,

,

,/

is the non-orthogonal factor

is the interference of own celljm

total

L

P

,

is the interference of neighbor cells

N

mii ji

itotal

L

P

,1 ,

,

is the pathlossL

Definition of DL load factorDefinition of DL load factor


14

Let’s suppose for simply, and base on , we can getitotaltotal PP ,

j

jtotal PP

)()/(

)/(1

)/(

)/(

,1 ,

,

,

N

mii ji

jm

j j

job

jmj j

jobN

total

L

L

RW

NE

LRW

NEP

P

Defined as the DL load factor DL

Base power due to the pass loss.

Increment due to the interference.

Definition of DL load factorDefinition of DL load factor


15

Non-orthogonal factor and interference from other cells

are various with position, and are difficult to measure.

N

mii ji

jm

L

L

,1 ,

,

The same DL load factor may correspond to different transmitted

carrier power due to the different pass loss (cell radius).

This is why the TCP will not correspond uniquely with the DL

load factor, and why we use TCP in the DL CAC instead.

Transmitted power & DL load factorTransmitted power & DL load factor


16

The Load controlsThe Load controls

CAC: Call Admission Control Used to admit/reject the resource request to keep

the system work in stable state.Load Balance:

To balance load between cells to maximize the system capacity

Congestion Control: To make the system come back from congestion

state to the stable state.


17

The ContentThe Content

The Load Concept

The Load Control Measures

Admission Control

Load Balance

Congestion Control


18

Load control - CACLoad control - CAC

Admission Control


19

Call Admission Control (CAC)Call Admission Control (CAC)

What is CAC?

Why we need CAC?

How the CAC been implemented.


20

What is CAC?


21

call arrive

Get the service characteristic and the current load

Suppose the user is accepted, and calculate the predictedUL load factor. And then compared with the threshold.

admitted?

Suppose the user is accepted, andcalculate the predicted DL load factor.And then compared with the threshold.

admitted?

call admitted call rejected

end

n

y

y

n

Flow chart of CACFlow chart of CAC


22

Principle of the CACPrinciple of the CAC


23

Why we need CAC?


24

Why we need CAC?Why we need CAC?

WCDMA is an interference limited system, after a new call

is admitted, the system load will be increased.

If a cell is high loaded, a new call will cause ongoing user

dropped.

We must keep the coverage planed by the Radio Network

Planning.


25

Admission control scenariosAdmission control scenarios

CAC is needed under such scenarios

New call

Handover

New RAB(s) for ongoing call

Bandwidth increasing reconfiguration


26

How the CAC been implemented.


27

Only for dedicated channels, and reserve a certain resource for the

common channels.

UL and DL CAC algorithms are independently.

In principle, a request will be admitted only when UL and DL are

both admitted. But if UL or DL CAC switch is closed, only one

direction CAC also can be realized.

StrategiesStrategies


28

Handover threshold, conversational threshold and other

services threshold are used to keep the priority of the handover

higher than the conversational, conversational than the Best

Effort services.

UL CAC is not need for intra-frequency handover because the

interference is already included in the target cell.

StrategiesStrategies


29

Admission request

Smaller than thethreshold?

admitted

y

end of UL CAC

rejected

n

Get current RTWP, and calculate thecurrent load factor. RTWP

PNUL 1

Get the traffic characteristic, andestimate the increment of load factor.

RNEW

b

0

1

1

Calculate the predicted load factor.

0_ ULpredictedUL

UL Algorithm1UL Algorithm1


30

Admission request


admitted

y

end of DL CAC

rejected

n

Get current TCP. )(NP

Get the traffic characteristic, andestimate the increment of tcp. P

Calculate the predicted tcp. commPPNP )(

DL Algorithm1DL Algorithm1


31

Reference service : 12.2k AMR with activity factor = 1.

Normalized traffic factor of user i :

dardsc

ici NE

NEk

tan0

0

Normalized traffic factor(NTF) has the meaning of equivalent nu

mber of user i relatives to the 12.2k AMR.

UL and DL may have different normalized traffic factor.

No resource is reserved for common channels.

Normalized traffic factorNormalized traffic factor


32

Admission request


admitted

y

end of UL/DL CAC

rejected

n

Get current total NTF.

N

iikNK

1

)(

Get the traffic characteristic, andestimate the increment of NTF.

dardsc

NcN NE

NEk

tan0

101

Calculate the predicted NTF. 1)()1( NkNKNK

UL & DL Algorithm2UL & DL Algorithm2


33

Selected by algorithm switch

Auto switch from algorithm 1 to algorithm 2 when algorithm1 is

selected for UL/DL.

When RTWP and/or TCP measurement value are/is

invalid/unavailable, the CAC will change from algorithm 1 to 2

automatically.

When measurement are/is valid/available, the CAC will

change back to algorithm 1 automatically.

UL and DL are independently.

Switch between algorithm 1 &2Switch between algorithm 1 &2


34

Load control - LBLoad control - LB

Load Balance


35

Load Balancing (LDB)Load Balancing (LDB)

What is LDB?

Why do we need LDB?

How is the LDB implemented?


36

What is LDB?


37

Load decrease, and cell expand.

Load increase, and cell shrink.

Original

Intra-frequency LDB ( Cell Breathing)Intra-frequency LDB ( Cell Breathing)


38

f1

Load level indication

For cells have different frequencies, and the same coverage.

f2f1 & f2

Result

Inter-frequency LDBInter-frequency LDB


39

Why we need LDB?


40

Why we need LDB?Why we need LDB?

Intra-frequency LDB

Inter-frequency LDB

To move calls from a heavily loaded cell to neighboring

cells.

To relieve calls in surrounding cells when lightly loaded.

To distribute calls from a heavily loaded cell to the

lightest loaded carrier co-located.


41

How the LDB been implemented.


42

Measure transmittedcarrier power Ptx

Ptx < Pexpand

&PCPICH < PCPICH,max

Increase the PCPICH

one step

y

Wait for next period

Ptx > Pshrink

&PCPICH > PCPICH,min

n

Decrease the PCPICH

one step

y

n

Intra-frequency LDBIntra-frequency LDB


43

Measure transmittedcarrier power

Ptx(m),m=1,2,...M

Get Ptx,max and Ptx,min fromPtx(m)

Ptx,max > Padjust

&Ptx,max - Ptx,min >

Pdifference

y

Initialize the hardhandover attempt counter

i=0

i < N?

Select one suitable userin the highest loaded

cell, and attempt to behandover to the lowest

loaded cell.

y

Successful?

i + 1

n

Wait for next period

y

n

Inter-frequency LDBInter-frequency LDB


44

Compute the normalized traffic factor (NTF) for each of the UEs

belongs to the Maximum Transmitted Carrier Power carrier.

Rank the UEs by their NTF in descending order, and remove those

UEs whose NTF larger than a pre-set threshold. And mark all the

UEs in the list unselected.

Select the UE has the largest NTF and marked with unselected. At

the same time, mark it with selected.

W

RNE

W

RNE

ireference

referenceob

iiiob

)/(

)/(NTF

How to select user?How to select user?


45

Load control - LCCLoad control - LCC

Congestion Control


46

Why We Need Congestion Control ?Why We Need Congestion Control ?

To receive information correctly, signal in receiver

must be above certain S/I (Signal/Interference )

threshold.

In CDMA system, all users in a cell use the same

frequency, so one customer’s signal will be an

interference to others.


47


To overcome the interference, transmitter must

increase signal power, that is, it need more MS or

BTS power.

MS or BTS power is limited. If interference keeps

rising, S/I requirement can not be achieved at a

certain degree, quality of services will deteriorate

and some users will drop.

Congestion occurs.


48


To guarantee the network’s stability and custo

mers’ QoS (Quality of Service), we should try

our best to avoid congestion.

I.e., some actions should be taken to keep the

whole system away from congestion or quickly

recover from congestion!


49

Congestion Control GeneralCongestion Control General

Abbr. LCC (Load Congestion Control)

Object: All BE (Best Effort) services.

Range: Downlink only. (Optimization is ongoing.)

Abstract: When congestion occurs, MAC limits the

valid max TF number, which pulls down the bandwidth

of all BE services, resulting in the reduction of load.

Once congestion relieves, MAC automatically recovers

the bandwidth of all BE services step by step slowly.


50

Congestion Control DescriptionCongestion Control Description

Monitor Cell Carrier PowerPeriodically or by event

If Carrier Power >Congestion threshold, or

receive a event

Congestion Detectedand inform MAC

Congestion Relievedand infrom MAC

MAC decrease themax TF number

Start a Adjust Timer

expi res

Kill the Adjust Timer

MAC increase themax TF number

Start a Recover Timer

expi res


51

Congestion Control DescriptionCongestion Control Description

LCC will monitor the cell’s downlink transmission carrier power

periodically or by event. When LCC finds the cell’s downlink load

rises above a certain threshold or receives a event claiming

congestion, it will inform MAC layer to limit the maximum

Transport Format(TF) of the BE service to a small value in order

to quickly pull down the bit-rate.

Congestion is not a long-term status, so after a certain moment,

congestion will relieve. Then MAC will recover the maximum TF

slowly. But if the first reduction of the maximum TF can’t control

congestion effectively, LCC will continue reduction until all BE

services’ bit-rate are reduced to a non-zero minimum value.


52

Congestion Control ExampleCongestion Control Example

For a 144kbps background user: TB size is 336bits, max valid

TF number is 9.

When congestion is detected, MAC will compute: 9*50%≈4, so

the adjusted max valid TF number is 4. The bandwidth halves.

Note: 50% is a parameter named Adjust Coefficient.

MAC starts a Adjust Timer, and then computes at the timer’s

expiry: 4*50%≈2, so the adjusted max valid TF number is 2.

If MAC get informed that the congestion is relieved before the

Adjust Timer’s expiry, MAC begin the recovering process.

Otherwise, the user’s max valid TF number will be reduced to 1

finally.


53

Congestion Control ExampleCongestion Control Example

When congestion relieves, MAC will be informed. So

MAC will begin recovering process.

Recovering Process: Assumed that the user’s max valid

TF number has been reduced to 1 during the congestion.

MAC first computes: 1+1=2. So the recovered max valid

TF number is 2. Note: 2 should be in the TFS which MAC

can use.

Then MAC starts a recovery timer, if it expires, MAC

increase the max valid TF number from 2 to 3……

Until the user’s max valid TF number is recovered to 9.

owj103104 wcdma load control issue1.1

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