Huawei WCDMA Load Control

WCDMA Load Control www.huawei.com

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The WCDMA system is a self interference system. As the load of the WCDMA system increases, the interference rises. A relatively high interference may affect the coverage and Quality of Service (QoS) of established services. Therefore, capacity, coverage and QoS of the WCDMA system are mutually affected. The purpose of load control is to maximize the system capacity while ensuring coverage and QoS.

1

Objectives


Upon completion of this course, you will be able to: 

Know the load control principles



Know the load control realization methods in WCDMA system



Know The load control parameters in WCDMA system

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

2

Contents 1. Load Control Overview 2. Basic Load Control Algorithms

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

3

Contents 1. Load Control Overview 2. Basic Load Control Algorithms

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

4

Load Definition


Load: the occupancy of capacity




Two kinds of capacity in CDMA system 

Hard capacity 

Code channels



Hard ware resource: Transport resource, NodeB processing capability (CE)



Soft capacity 

Interference (UL)



Power (DL)

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

5

Uplink Load Definition


Cell Load Factor: ηUL = 1−

1 noise rise

noise rise =

RTWP PN

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

PN: Background noise In the uplink, the RTWP value can be measured easily. Therefore, the UL cell load factor (based on RTWP) can be used to describe UL load.

6

Downlink Load Definition Common Measurement in Node B

Scenario

Cell Load Factor (based on RTWP) UL Load

R99 load control RTWP (Received Total Wideband Power) Transmitted carrier power of all codes not used for HS-PDSCH or HS-SCCH

R99 load control

transmission DL Load

Total Carrier Power (TCP)

R99 and HSDPA load control

HS-DSCH Required Power

HSDPA load control

HS-DSCH Provided Bit Rate

HSDPA load control

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The definition of DL load is very different from the definition of UL load, the adjacent cell interference factor and the non-orthogonality factor in the downlink are very difficult to measure and calculate, therefore, the DL cell load factor can not be used to describe the DL cell load. Then, the transmission power is used to describe DL load.

7

The Objectives of Load Control


Keeping system stable




Maximizing system capacity while ensuring the coverage and QoS PUC

• LDR • OLC

• CAC • IAC

1. Before UE access 2. During UE access

3. After UE access Time

PUC: Potential User Control CAC: Call Admission Control

IAC: Intelligent Admission Control

LDR: Load Reshuffling

OLC: Overload Control

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Load control algorithm can be classified into three parts according to the different working states of UE. Before UE accesses, the PUC algorithms will function. RNC will monitor the cell load periodically. If the current cell load exceeds a specific threshold, RNC will modify the cell selection and re-selection parameters, in order that UE can select the low-load cell easily when UE will initiate some services and work at CELL-DCH state. This algorithm aims at UE which working at IDLE mode, CELL-FACH state, CELL-PCH state or URA-PCH state in this cell. During UE accesses, the CAC and IAC algorithms will function. RNC will judge whether the new access is admissible. After UE accesses, LDR and OLC algorithms will function. There are some practical algorithms to decrease the cell load. When a cell is in basic congestion, the RNC shall select some UEs for inter-frequency handover. When a cell is in overload congestion, the RNC shall select some UEs to release if failing to release the cell from overload congestion by BE service TF control.

8

Load Control Algorithms NodeB transmit power (noise) Icons for different load levels

Cell load OLC starts: to reduce the TFs of BE subscribers, and release some UEs forcibly

No Load control

CAC or IAC: to prevent new calls into cells with heavy load DRD starts: to enable rejected UEs to retry neighboring cells or GSM cells PUC starts: to enable UEs in idle mode to camp on cells with light load LDR starts: to check and release initial congestion in cells

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

In a cell, the higher the cell load, the higher the NodeB transmit power (noise). In this diagram, different icons indicates different load levels. And for different load levels, the different load control algorithm will function.

9

Load Measurement


The objectives of LDM (LoaD Measurement) 

Measure the system load



Filter the measured data according to the requirement of different load control algorithms




Major Measurement Quantities 

Uplink Received Total Wideband Power (RTWP)



Downlink Transmitted Carrier Power (TCP)



TCP of all codes not used for HSDPA transmission



Power Requirement for Guaranteed Bit Rate (GBR) on HS-DSCH



Provided Bit Rate (PBR) on HS-DSCH

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

For LDR and OLC algorithms, the LDM algorithm needs to decide whether the system works in basic congestion or overload congestion mode and to notify related algorithms for handling. Delay susceptibilities of PUC, CAC, LDR, and OLC to common measurement are different. When some or all the algorithms use the same common measurement, the LDM must apply different smoothed filter coefficients in order to get rippling and timely common measurement as required.

10

LDM procedure




Smooth Window Filtering on the RNC Side N −1





P ( n) =

∑P

n −i

i =0

N

N : the size of the smooth window

Pn : the reported measurement value

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

11

Parameters for LDM (1)


CHOICERPRTUNITFORULBASICMEAS /CHOICERPRTUNITFORDLBASICMEAS (Time unit for UL/DL basic meas rprt cycle) 

Value Range: TEN_MSEC, MIN



Recommended value: TEN_MSEC, means the time unit is 10ms

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the following parameters through SET LDM, query it through LST LDM.

12

Parameters for LDM (2)


TENMSECFORULBASICMEAS/TENMSECFORDLBASICMEA S (UL/DL basic meas rprt cycle, Unit:10ms)






Value Range: 1~6000



Recommended value: 20, namely 200ms

MINFORULBASICMEAS/MINFORDLBASICMEAS (UL/DL basic meas rprt cycle, Unit: min) 

Value Range: 1~60



Recommended value: none

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Notes: 1. [LDR period timer length] and [OLC period timer length] which are configured in the command SET LDCPERIOD must be twice greater than the UL basic common measurement report cycle. 2. [Intra-frequency LDB period timer length], [PUC period timer length], [LDR period timer length] and [OLC period timer length] which are configured in the command SET LDCPERIOD must be twice greater than the DL basic common measurement report cycle.

13

Parameters for LDM (3)


ULBASICCOMMMEASFILTERCOEFF / DLBASICCOMMMEASFILTERCOEFF (UL/DL basic common measure filter coeff) 

Value Range: D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D11, D13, D15, D17, D19



Recommended value: D6

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

ULBASICCOMMMEASFILTERCOEFF / DLBASICCOMMMEASFILTERCOEFF (UL/DL basic common measure filter coeff) This parameter specifies the L3 filtering coefficient of the measurement value on the NodeB side. The greater this parameter is, the greater the smoothing effect and the higher the anti slow fading capability, but the lower the signal change tracing capability. The change of this parameter has an effect on PUC, CAC, LDR algorithms.

14

Parameters for LDM (4)


The parameters for smoothing filter window Value Range

Recommend Value

PucAvgFilterLen

1–32

32

UL LDR moving average filter length

UlLdrAvgFilterLen

1–32

25

DL LDR moving average filter length

DlLdrAvgFilterLen

1–32

25

UL CAC moving average filter length UlCACAvgFilterLen

1–32

3

DL CAC moving average filter length DlCACAvgFilterLen

1–32

3

UL OLC moving average filter length UlOLCAvgFilterLen

1–32

25

DL OLC moving average filter length DlOLCAvgFilterLen

1–32

25

Parameter Name

Parameter ID

PUC moving average filter length

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

These parameters specify the length of smoothing filter window of the report measurement value on the RNC side. The greater these parameters are, the greater the smoothing effect, but the lower the signal change tracing capability.

15

Parameters for HSDPA LDM (1)


CHOICERPRTUNITFORHSDPAPWRMEAS (Time unit of HSDPA need pwr meas cycle)






Value Range: TEN_MSEC, MIN



Recommended value: TEN_MSEC, means the time unit is 10ms

CHOICERPRTUNITFORHSDPARATEMEAS (Time unit of HSDPA bit rate meas cycle) 

Value Range: TEN_MSEC, MIN



Recommended value: TEN_MSEC, means the time unit is 10ms

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

16

Parameters for HSDPA LDM (2)





TENMSECFORHSDPAPWRMEAS (HSDPA need pwr meas cycle,Unit:10ms) 

Value Range: 1~6000



Recommended value: 10, namely 100ms

TENMSECFORHSDPAPRVIDRATEMEAS (HSDPA bit rate meas cycle,Unit:10ms) 

Value Range: 1~6000



Recommended value: 10, namely 100ms

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

17

Parameters for HSDPA LDM (3)


MINFORHSDPAPWRMEAS (HSDPA need pwr meas cycle, Unit: min)






Value Range: 1~60



Recommended value: none

MINFORHSDPAPRVIDRATEMEAS (HSDPA bit rate meas cycle, Unit: min) 

Value Range: 1~60



Recommended value: none

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

18

Parameters for HSDPA LDM (4)






HSDPANEEDPWRFILTERLEN (HSDPA need power filter len) 

Value Range: 1~32



Recommended value: 1

HSDPAPRVIDBITRATEFILTERLEN (HSDPA bit rate filter len) Value Range: 1~32 

Recommended value: 1

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

These parameters specify the length of the smoothing filter window of HSDPA power and bit rate requirement.

19

Priority


The service of user with low priority will be affected by the load control algorithms first




Three kinds of priority 

User Priority



User Integrate Priority



RAB Integrate Priority

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

User Priority: mainly applying to provide different QoS for different users. Eg., setting different GBR according to the level of users for BE service. User Integrate Priority: defining different ARP (Allocation/Retention Priority) to the user with the same User Priority. RAB Integrate Priority: considering ARP, traffic class, THP (Traffic Handling Priority) synthetically.

20

User Priority


There are three levels of user priority (1, 2, and 3) 

gold (high), silver (middle) and copper (low) user

User priority

Gold

Silver

Copper

Uplink

128kbps 64kbps 32kbps

Downlink

128kbps 64kbps 32kbps

gold user

Pay $100 for 3G services

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

In CN HLR, we can set this priority; CN send ARP and user priority to RNC

21

User Priority


The relationship between user priority and ARP is configurable 

ARP

The typical relationship as follow:

1

2

3

4

5

6

7

8

9

10 11 12 13 14

User Priority 1

1

1

1

1

2

2

2

2

2



3

3

3

3

The relationship can be configured through SET USERPRIORITY, and queried through LST USERPRIORITY

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

ARP 15 is always the lowest priority and it cannot be configured.

22

RAB Integrate Priority


The values of RAB Integrate Priority are set according to the following parameters 

PRIORITYREFERENCE (Integrated Priority Configured Reference)





Value range: ARP, TrafficClass



Recommended value: ARP

CARRIERTYPEPRIORIND (Indicator of Carrier Type Priority) 

Value range: DCH, HSDPA



Recommended value: DCH

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the parameter through SET USERPRIORITY, and query it through LST USERPRIORITY. If the value of the parameter is set to Traffic Class, the integrate priority abides by the following rules: •Classes of services: conversational -> streaming -> interactive -> background •Services of the same class: priority based on Allocation/Retention Priority (ARP) values •Only for the interactive service of the same ARP value: priority based on THP •Services of the same class and priority: HSDPA or DCH service preferred on the basis of the value of the Indicator of Carrier Type Priority parameter If the value of the parameter is set to ARP, the integrate priority abides by the following rules: •ARP1 -> ARP2 -> ARP3 … -> ARP14 •Same ARP value: conversational -> streaming -> interactive -> background •THP •Indicator of Carrier Type Priority parameter

23

Example for RAB Integrate Priority Based on ARP, HSDPA priority is higher Service ARP Traffic Class ID Services attribution in the cell Service ARP ID

Traffic Class

Bear type

B

1

Interactive

HSDPA

Bear type

A

1

Interactive

DCH

C

2

Conversational

DCH

D

2

Background

DCH

A

1

Interactive

DCH

B

1

Interactive

HSDPA

C

2

Conversational

DCH

D

2

Background

DCH

Based on Traffic Class, HSDPA priority is higher Service ID

Traffic Class

ARP

Bear type

C

Conversational

2

DCH

B

Interactive

1

HSDPA

A

Interactive

1

DCH

D

Background

2

DCH

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

When the user just has one RAB, User integrate priority is the same as the service of the RAB integrate priority; For multiple RAB users, the integrate priority of the user is based on the service of the highest priority.

24

User Integrate Priority


For multiple-RAB users, the integrate priority of the user is based on the service of the highest priority. User integrate priority is mainly used to select different users during LDR/OLC.

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

25

Contents 1. Load Control Overview 2. Basic Load Control Algorithms 2.1 PUC (Potential User Control) 2.2 CAC (Call Admission Control) 2.3 IAC (Intelligent Admission Control) 2.4 LDR (Load Reshuffling) 2.5 OLC (Overload Control)

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

26

Contents 1. Load Control Overview 2. Basic Load Control Algorithms 2.1 PUC (Potential User Control) 2.2 CAC (Call Admission Control) 2.3 IAC (Intelligent Admission Control) 2.4 LDR (Load Reshuffling) 2.5 OLC (Overload Control)

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

27

PUC Principles Light load Freq1

Modify System Info SIB3,11,12

1.Hard to trigger reselection 2.Easy to camp on the cell Increase the POTENTIAL load

Normal load Stay System Info SIB3,11,12

Heavy load

Freq2 1.Easy to trigger reselection

2.Easy to select light load Inter-freq neighbor Cell

Modify

Decrease the POTENTIAL load Idle state

System Info SIB3,11,12

CCH state

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The function of PUC is to balance traffic load among inter-frequency cells. By modifying cell selection and reselection parameters and broadcasting them through system information, PUC leads UEs to cell with light load. The UE may be in idle mode, Cell_FACH state, Cell _PCH state, URA_PCH state

28

PUC Realization


PUC can modify inter-frequency cell reselection parameters to control the user distribution between cells. 

Sintersearch: when the load of a cell is “Heavy”, PUC will increase this parameter; when the load of a cell is “Light”, PUC will decrease this parameter.



QOffset1sn and QOffset2sn: when the load of a cell is “Heavy”, PUC will decrease these parameters; when the load of a cell is “Light”, PUC will increase these parameters.

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

According to the load level of a cell, system will adjust the cell-reselection parameters in SIB3, 11 and 12: 1. Sintersearch: When the UE detects that the quality of the service cell (CPICH Ec/N0 measured by the UE) is lower than the sum of the minimum quality criterion of the service cell (Qqualmin) plus this threshold, it will start the inter-frequency cell reselection process. If this parameters are too high, cell reselection will probably start frequently, resulting in UE battery waste; If they are too low, cell reselection will probably start difficultly. 2. QOffset1sn and QOffset2sn: These parameters are offsets of CPICH measured values of neighboring cells. QOffset1sn is used for the RSCP measurement and the neighboring cell measurement value participates in cell reselection sequencing after this offset is deducted from it. QOffset2sn is used for the Ec/No measurement and the neighboring cell measurement value participates in cell reselection sequencing after this offset is deducted from it. The bigger these values are, the smaller the probability of selecting the neighboring cell will be; the smaller these values are, the bigger the probability of selecting the neighboring cell will be.

29

Parameters for PUC Algorithm Switch


NBMSWITCH (Cell algorithm switch) 

Value Range: 






PUC

Default status: OFF

PUCPERIODTIMERLEN (PUC period timer length) 

Value Range:6s~86400s



Default value: 1800, namely 1800 seconds, i.e. 30 minutes

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set PUC Algorithm Switch through ADD CELLALGOSWITCH, query it through LST CELLALGOSWITCH, and modify it through MOD CELLALGOSWITCH. Set PUC period timer through SET LDCPERIOD, query it through LST LDCPERIOD. Note: [PUC period timer length must be twice greater than the DL basic common measurement report cycle (default value is 200ms).

30

Parameters for PUC (1)








SPUCHEAVY (Load level division threshold 1) 

Value Range: 0 to 100%



Recommended value: 70, namely 70%

SPUCLIGHT (Load level division threshold 2) 

Value Range: 0 to 100%



Recommended value: 45, namely 45%

SPUCHYST (Load level division hysteresis) 

Value Range: 0 to 100%



Recommended value: 5, namely 5%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the following parameters through ADD CELLPUC, query it through LST CELLPUC, and modify it through MOD CELLPUC. SPUCHEAVY (Load level division threshold 1): It is used to decide whether the cell load level is "Heavy" or not. If the load of a cell is equal to or higher than this threshold, the load level of this cell is heavy. If the load level of a cell is heavy, the PUC algorithm will configure selection/reselection parameters for this cell to lead the UE camping on this cell to reselect another interfrequency neighboring cell with light load. SPUCLIGHT (Load level division threshold 2): It is used to decide whether the cell load level is "Light" or not. If the load of a cell is equal to or lower than this threshold, the load level of this cell is light. If the load level of a cell is light, the PUC algorithm will configure selection/reselection parameters for this cell to lead the UE to reselect this cell rather than the previous inter-frequency neighboring cell with heavy load. SPUCHYST (Load level division hysteresis): The hysteresis used while judging cell load level, it is used to avoid the unnecessary ping-pong of a cell between two load levels due to tiny load change.

31

Parameters for PUC (2)





OFFSINTERLIGHT (Sintersearch offset 1) 

Value Range: -10 to 10



Physical Value Range: -20 to 20dB, step 2dB



Recommended value: -2, namely -4dB

OFFSINTERHEAVY (Sintersearch offset 2) 

Value Range: -10 to 10



Physical Value Range: -20 to 20dB, step 2dB



Recommended value: 2, namely 4dB

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

OFFSINTERLIGHT (Sintersearch offset 1): The offset of Sintersearch when center cell load level is "Light“ (Note: Sintersearch is used to decide whether to start the inter-frequency cell reselection). OFFSINTERHEAVY (Sintersearch offset 2): The offset of Sintersearch when center cell load level is "Heavy“ (Note: Sintersearch is used to decide whether to start the inter-frequency cell reselection).

32

Parameters for PUC (3)





OFFQOFFSET1LIGHT (Qoffset1 offset 1) 

Value Range: -20 to 20



Physical Value Range: -20 to 20dB, step 1dB



Recommended value: -4, namely -4dB

OFFQOFFSET2LIGHT (Qoffset2 offset 1) 

Value Range: -20 to 20



Physical Value Range: -20 to 20dB, step 1dB



Recommended value: -4, namely -4dB

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

OFFQOFFSET1LIGHT (Qoffset1 offset 1): The offset of Qoffset1 when neighboring cell load is lighter than that of center cell (Note: Qoffset1 is used as a priority to decide which cell will be selected while cell selecting or reselecting). OFFQOFFSET2LIGHT (Qoffset2 offset 1): The offset of Qoffset2 when neighboring cell load is lighter than that of center cell (Note: Qoffset2 is used as a priority to decide which cell will be selected while cell selecting or reselecting).

33

Parameters for PUC (4)





OFFQOFFSET1HEAVY (Qoffset1 offset 2) 

Value Range: -20 to 20



Physical Value Range: -20 to 20dB, step 1dB



Recommended value: 4, namely 4dB

OFFQOFFSET2HEAVY (Qoffset2 offset 2) 

Value Range: -20 to 20



Physical Value Range: -20 to 20dB, step 1dB



Recommended value: 4, namely 4dB

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

OFFQOFFSET1HEAVY (Qoffset1 offset 2): The offset of Qoffset1 when neighboring cell load is heavier than that of center cell OFFQOFFSET2HEAVY (Qoffset2 offset 2): The offset of Qoffset2 when neighboring cell load is heavier than that of center cell

34

Contents 1. Load Control Overview 2. Basic Load Control Algorithms 2.1 PUC (Potential User Control) 2.2 CAC (Call Admission Control) 2.3 IAC (Intelligent Admission Control) 2.4 LDR (Load Reshuffling) 2.5 OLC (Overload Control)

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

35

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

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

CAC is needed under such scenarios: 1. New call 2. New RAB(s) for ongoing call 3. Handover 4. Bandwidth increasing reconfiguration (AMRC, DCCC)

36

Flow chart of CAC

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The admission decision is based on: •

Cell available code resource: managed in RNC

•

Cell available power resource: DL/UL load measured in Node B

•

NodeB resource state, that is, NodeB credits : Reported by Node B

•

Available Iub transport layer resource, that is, Iub transmission bandwidth: managed in RNC

•

HSDPA user number (only for HSDPA service)

•

HSUPA user number (only for HSUPA service) Only when all of these resources are available can a call be admitted.

37

CAC Code Resource Admission


For handover services 

The current remaining code resource should be enough for the service




For other R99 services 

RNC shall ensure the remaining code does not exceed the configurable thresholds after admission of the new service




For HSDPA services 

The code resource admission is not needed

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

For handover services, the code resource admission is successful if the current remaining code resource is enough for the service. For other R99 services, RNC shall ensure the remaining code does not exceed the configurable O thresholds after admission of the new service. For HSDPA services, the reserved codes are shared by all HSDPA services; so the code resource admission is not needed. The RNC adjusts the reserved HS-PDSCH codes according to the real-time usage status of the codes.

38

Parameters for Code Resource Admission


DLHOCECODERESVSF (DL HandOver Credit and Code Reserved SF) 

Value Range:0, 1, 2, 3, 4, 5, 6, 7



Physical value Range: SF4, SF8, SF16, SF32, SF128, SF256, SFOFF



Recommended value: SF32



Configuration Rule and Restriction: 

[Dl HandOver Credit and Code Reserved SF] >= max ([Dl LDR Credit SF reserved threshold], [Cell LDR SF reserved threshold])

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set this parameter through ADD CELLCAC, query it through LST CELLCAC, and modify it through MOD CELLCAC. DLHOCECODERESVSF (Dl HandOver Credit and Code Reserved SF): This parameter is the Downlink Credit and Code Reserved by Spread Factor for Handover service. SFOFF means that none of them are reserved for Handover. If the DL spare resource can not satisfy the reserved resource after the access of a new service, the service will be rejected. The parameter of [Dl HandOver Credit and Code Reserved SF] must be not less than the either of [Dl LDR Credit SF reserved threshold] and [Cell LDR SF reserved threshold]. The parameters of [Dl LDR Credit SF reserved threshold] and [Cell LDR SF reserved threshold] are set in ADD CELLLDR and MOD CELLLDR, and they can be listed by LST CELLLDR.

39

CAC Power Resource Admission


Algorithm 1: based on UL/DL load measurement and load prediction (RTWP and TCP) 

The algorithm is easy to implement, but it is affected by the result of RTWP and TCP measurement




Algorithm 2: based on Element Number of User (ENU) 

The algorithm is no need to measure RTWP and TCP, but the calculation is more complex




Algorithm 3: loose call admission control algorithm 

Similar to algorithm 1, but the prediction of needed power of a new call will be set to zero

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

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. 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.

40

Uplink CAC Algorithm 1 - Load Prediction Admission request

ηUL = 1 −

Get current RTWP, and calculate the current load factor

∆η

Get the traffic characteristic, and estimate the increment of load factor

ηUL _ predicted = ηUL + ∆η

Calculate the predicted load factor

Y

Smaller than the threshold?

admitted

PN RTWP

N

rejected

End of UL CAC Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Pn is uplink receive background noise. The procedure for uplink power resource decision is as follows: 1. The RNC obtains the uplink RTWP of the cell, and calculate the current uplink load factor. 2. The RNC calculates the uplink load increment ΔηUL based on the service request. 3. The RNC uses the formula ηUL,predicted=ηUL + ΔηUL to forecast the uplink load factor. 4. By comparing the forecasted uplink load factor ηUL,predicted with the corresponding threshold (UL threshold of Conv AMR service, UL threshold of Conv non_AMR service, UL threshold of other services, UL Handover access threshold), the RNC decides whether to accept the access request or not.

41

Downlink CAC Algorithm 1 - Load Prediction Admission request

P(N )

Get current TCP Get the traffic characteristic, and estimate the increment of TCP

∆P

P( N ) + ∆P

Calculate the predicted TCP

Y

Smaller than the threshold?

admitted

N

rejected

End of DL CAC Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The procedure for downlink power resource decision is as follows: 1. The RNC obtains the cell downlink TCP, and calculates the downlink load factor by multiplying the maximum downlink transmit power by this TCP. 2. The RNC calculates the downlink load increment ΔP based on the service request and the current load. 3. The RNC forecasts the downlink load factor. 4. By comparing the downlink load factor with the corresponding threshold (DL threshold of Conv AMR service, DL threshold of Conv non_AMR service, DL threshold of other services, DL Handover access threshold), the RNC decides whether to accept the access request or not.

42

Uplink and Downlink CAC Algorithm 2 - ENU Admission request

ENU

Get current total ENU Get the traffic characteristic, and estimate the increment of ENU

Smaller than the threshold?

admitted

N

∑ ENU i =1

i

ENU new

ENU total ( N + 1) = ENU total ( N ) + ENU new

Calculate the predicted ENU

Y

total

(N ) =

N

ENULoad = ENU total ( N + 1) / ENU max

rejected

End of UL/DL CAC Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The ENUmax of DL is very different from the ENUmax of UL. The UL ENUmax is calculated by the system automatically. The DL ENUmax can be configured through parameter: DL total Non-HSDPA equivalent user number The procedure for ENU resource decision is as follows: 1. The RNC obtains the total ENU of all exist users ENUtotal. 2. The RNC get the ENU of the new incoming user ENUnew. 3. The RNC forecast the ENU load. 4. By comparing the forecasted ENU load with the corresponding threshold (the same threshold as power resource), the RNC decides whether to accept the access request or not.

43

Typical equivalent number of users Service

Equivalent Number of User (ENU) For Already Existing Users

For New Incoming Call

3.4 kbit/s SIG

0.2669

0.4569

13.6 kbit/s SIG

0.4531

1.2131

3.4 + 12.2 kbit/s

0.7662

1.3210

3.4 + 8 kbit/s (PS)

0.5106

0.6325

3.4 + 16 kbit/s (PS)

0.9215

1.0472

3.4 + 32 kbit/s (PS)

2.1319

2.2680

3.4 + 64 kbit/s (PS)

3.2479

3.4188

3.4 + 128 kbit/s (PS)

6.2219

6.4143

3.4 + 144 kbit/s (PS)

6.9731

7.1888

3.4 + 256 kbit/s (PS)

11.2941

11.5245

3.4 + 384 kbit/s (PS)

17.0178

17.1897

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

44

Parameters for Power Resource Admission Algorithm Switch


NBMULCACALGOSELSWITCH (Uplink CAC algorithm switch) 

Value Range: 

ALGORITHM_OFF, ALGORITHM_FIRST, ALGORITHM_SECOND, and ALGORITHM_THIRD




NBMDLCACALGOSELSWITCH (Downlink CAC algorithm switch) 

Value Range: 

ALGORITHM_OFF, ALGORITHM_FIRST, ALGORITHM_SECOND, and ALGORITHM_THIRD

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set CAC Algorithm Switch through ADD CELLALGOSWITCH, query it through LST CELLALGOSWITCH, and modify it through MOD CELLALGOSWITCH. The algorithms the above values represent are as follow: ALGORITHM_OFF: Disable uplink (or downlink) call admission control algorithm. ALGORITHM_FIRST: The load factor prediction algorithm will be used in uplink (or downlink) CAC. ALGORITHM_SECOND: The equivalent user number algorithm will be used in uplink (or downlink) CAC. ALGORITHM_THIRD: The loose call admission control algorithm will be used in uplink (or downlink) CAC.

45

Parameters for Load Prediction (1)


CELLENVTYPE (Cell environment type) 

Value Range: 






TU: typical urban district

RA: rural area HT: hill terrain

Default value: TU

BACKGROUNDNOISE (Background noise) 

Value Range: 0 to 621



Physical Range: -112 to -50dBm, step: 0.1



Recommended value: 71, namely -105dBm

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the following CAC parameters through ADD CELLCAC, query it through LST CELLCAC, and modify it through MOD CELLCAC. CELLENVTYPE (Cell environment type): This parameter is used for Eb/No calculation. you can get the corresponding curves of BLER-Eb/No according the coding mode index and cell environment type index. The curves of BLER-Eb/No with different coding modes and cell environment types are different from each other. BACKGROUNDNOISE (Background noise): This parameter specifies the background noise received in the uplink.

46

Parameters for Load Prediction (2)





ULINTERFACTOR (UL neighbor interference factor ) 

Value Range: 0 to 200



Physical Range: 0 to 2, step: 0.01



Recommended value: 60, namely 0.6

NONORTHOFACTOR (DL Nonorthogonality factor) 

Value Range: 0 to 1000



Physical Range: 0 to 1, step: 0.001



Recommended value: 400, namely 0.4

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

ULINTERFACTOR (UL neighbor interference factor ) This parameter specifies the ratio of UL neighboring cells' interference to this cell's interference. NONORTHOFACTOR (Nonorthogonality factor): This parameter is used to predict the transmit power. Zero represents that channels are completely orthogonal and no interference exists between users in DL load factor prediction.

47

Parameters for Power Resource Admission (1)





ULCCHLOADFACTOR (UL common channel load factor) 

Value range: 0 to 100%



Recommended value: 0, namely 0%

DLCCHLOADRSRVCOEFF (DL common channel load reserved coefficient) 

Value range: 0 to 100%



Recommended value: 0, namely 0%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

ULCCHLOADFACTOR (UL common channel load factor): The CAC is only used for dedicated channels, and for common channels, some resource is reserved. In UL, according to the current load factor and the characteristics of the new call, the UL CAC algorithm predicts the new traffic channels load factor with the assumption of admitting the new call, then plus with the premeditated common channel UL load factor to get the predicted UL load factor. Then, compare it with UL admission threshold. If it is not higher than the threshold, the call is admitted; otherwise, rejected. DLCCHLOADRSRVCOEFF (DL common channel load reserved coefficient): This patameter is used for downlink common channel, the effect of this parameter on the network performance is similar with ULCCHLOADFACTOR.

48

Parameters for Power Resource Admission (2)





ULCONVAMRTHD (UL threshold of Conv AMR service) 

Value range: 0 to 100%



Recommended value: 75, namely 75%

ULCONVNONAMRTHD (UL threshold of Conv non_AMR service) 

Value range: 0 to 100%



Recommended value: 75, namely 75%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The UL load factor thresholds include this parameter, [UL threshold of Conv AMR service], [UL handover access threshold], and [UL threshold of other services]. The four parameters can be used to limit the proportion between conversational service, handover user and other services in a specific cell, and to guarantee the access priority of conversational service. ULCONVAMRTHD (UL threshold of Conv AMR service): This parameter is shared by algorithm 1 and algorithm 2. If this parameter is too high, the system load after admission will probably be too high, which will affect the system stability and result in system congestion; If it is too low, there will be a bigger probability that users will be rejected, and some resources will be idled and wasted. ULCONVNONAMRTHD (UL threshold of Conv non_AMR service): This parameter is also shared by algorithm 1 and algorithm 2. The effect of this parameter on the network performance is similar with ULCONVAMRTHD.

49

Parameters for Power Resource Admission (3)





ULOTHERTHD (UL threshold of other services) 

Value range: 0 to 100%



Recommended value: 60, namely 60%

ULHOTHD (UL handover access threshold) 

Value range: 0 to 100%



Recommended value: 80, namely 80%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

ULOTHERTHD (UL threshold of other services): This parameter is also shared by algorithm 1 and algorithm 2. The effect of this parameter on the network performance is similar with ULCONVAMRTHD. ULHOTHD (UL handover access threshold): This parameter is also shared by algorithm 1 and algorithm 2. The effect of this parameter on the network performance is similar with ULCONVAMRTHD. Notes: 1. This parameter only applies to inter-frequency handover. 2. This parameter is to reserve resources for handover and to ensure the handover performance; so the value of this parameter must be bigger than uplink threshold for conversation services and smaller than uplink OLC trigger threshold. Usually, UL handover access threshold>UL threshold of Conversational services>[UL threshold of other services].

50

Parameters for Power Resource Admission (4)





DLCONVAMRTHD (DL threshold of Conv AMR service) 

Value range: 0 to 100%



Recommended value: 80, namely 80%

DLCONVNONAMRTHD (DL threshold of Conv non_AMR service) 

Value range: 0 to 100%



Recommended value: 80, namely 80%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The DL load factor thresholds include this parameter, [DL threshold of Conv non_AMR service], [DL handover access threshold], and [DL threshold of other services]. The four parameters can be used to limit the proportion between conversational service, handover user and other services in a specific cell, and to guarantee the access priority of conversational AMR service. DLCONVAMRTHD (DL threshold of Conv AMR service): This parameter is shared by algorithm 1 and algorithm 2. If it is too high, the downlink coverage of the cell will be reduced, the neighboring cells will be interfered seriously, and system stability will be affected when cell coverage is very small; l If it is too low, the system resources will be idled, and the target capacity of the network planning cannot be satisfied. DLCONVNONAMRTHD (DL threshold of Conv non_AMR service): This parameter is also shared by algorithm 1 and algorithm 2. The effect of this parameter on the network performance is similar with DLCONVAMRTHD.

51

Parameters for Power Resource Admission (5)





DLOTHERTHD (DL threshold of other services) 

Value range: 0 to 100%



Recommended value: 75, namely 75%

DLHOTHD (DL handover access threshold) 

Value range: 0 to 10%



Recommended value: 85, namely 85%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

DLOTHERTHD (DL threshold of other services): This parameter is also shared by algorithm 1 and algorithm 2. The effect of this parameter on the network performance is similar with DLCONVAMRTHD. DLHOTHD (DL handover access threshold): This parameter is also shared by algorithm 1 and algorithm 2. The effect of this parameter on the network performance is similar with DLCONVAMRTHD. Notes: 1. This parameter only applies to inter-frequency handover. 2. This parameter is to reserve resources for handover and to ensure the handover performance; so the value of this parameter must be bigger than downlink threshold for conversation services and smaller than downlink OLC trigger threshold. Usually, DL handover access threshold>DL threshold of Conversational services>[DL threshold of other services].

52

Parameters for Power Resource Admission (6)





ULTOTALEQUSERNUM (UL total equivalent user number) 

Value range: 1 to 200



Recommended value: 80, namely UL ENUmax = 80

DLTOTALEQUSERNUM (DL total nonhsdpa equivalent user number) 

Value range: 1 to 200



Recommended value: 80, namely DL ENUmax = 80

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

ULTOTALEQUSERNUM (UL total equivalent user number): When algorithm 2 is used, this parameter defines the total equivalent user number corresponding to the 100% uplink load. DLTOTALEQUSERNUM (DL total nonhsdpa equivalent user number): When the algorithm 2 is used, this parameter defines the total equivalent user number corresponding to the 100% downlink load.

53

CAC Credit Resource Admission


Credit resource admission is similar with code resource admission




For handover services 

The current remaining credit resource should be enough for the service




For other R99 services 

RNC shall ensure the remaining code does not exceed the configurable thresholds after admission of the new service

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

For handover service, the credit resource admission is successful if the current remaining credit resource is enough for the service. For other R99 and HSUPA service, RNC shall ensure the remaining credit of the local cell, local cell group (if any), NodeB does not exceed the configurable O&M thresholds (Ul HandOver Credit Reserved SF/ Dl HandOver Credit and Code Reserved SF) after admission of the new service. For HSDPA service, no credit resource needed.

54

Parameters for Credit Resource Admission (1)


DLHOCECODERESVSF (DL HandOver Credit and Code Reserved SF) 

Value Range:0, 1, 2, 3, 4, 5, 6, 7



Physical value Range: SF4, SF8, SF16, SF32, SF128, SF256, SFOFF



Recommended value: SF32



Configuration Rule and Restriction: 

[Dl HandOver Credit and Code Reserved SF] >= max ([Dl LDR Credit SF reserved threshold], [Cell LDR SF reserved threshold])

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set this parameter through ADD CELLCAC, query it through LST CELLCAC, and modify it through MOD CELLCAC. DLHOCECODERESVSF (Dl HandOver Credit and Code Reserved SF): This parameter is the Downlink Credit and Code Reserved by Spread Factor for Handover service. SFOFF means that none of them are reserved for Handover. If the DL spare resource can not satisfy the reserved resource after the access of a new service, the service will be rejected. The parameter of [Dl HandOver Credit and Code Reserved SF] must be not less than the either of [Dl LDR Credit SF reserved threshold] and [Cell LDR SF reserved threshold]. The parameters of [Dl LDR Credit SF reserved threshold] and [Cell LDR SF reserved threshold] are set in ADD CELLLDR and MOD CELLLDR, and they can be listed by LST CELLLDR.

55

Parameters for Credit Resource Admission (2)


ULHOCERESVSF (Ul HandOver Credit Reserved SF) 

Value Range:0, 1, 2, 3, 4, 5, 6, 7



Physical value Range: SF4, SF8, SF16, SF32, SF128, SF256, SFOFF



Recommended value: SF16



Configuration Rule and Restriction: 

[Ul HandOver Credit Reserved SF] >= Ul LDR Credit SF reserved threshold

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set this parameter through ADD CELLCAC, query it through LST CELLCAC, and modify it through MOD CELLCAC. ULHOCERESVSF (Ul HandOver Credit Reserved SF): This parameter is the Uplink Credit Reserved by Spread Factor for Handover service. SFOFF means that none of them are reserved for Handover. If the UL spare resource cant safisfy the reserved resource after the acess of a new service, the service will be rejected. The parameter of [Ul HandOver Credit Reserved SF] must be not less than the [Ul LDR Credit SF reserved threshold]. The parameter of [Ul LDR Credit SF reserved threshold] is set in ADD CELLLDR and MOD CELLLDR, and they can be listed by LST CELLLDR.

56

Contents 1. Load Control Overview 2. Basic Load Control Algorithms 2.1 PUC (Potential User Control) 2.2 CAC (Call Admission Control) 2.3 IAC (Intelligent Admission Control) 2.4 LDR (Load Reshuffling) 2.5 OLC (Overload Control)

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

57

Why we need IAC?





The disadvantage of CAC: 

For PS NRT (Non-Real Time) services, CAC is not flexible



No consideration about the priority of different users



No consideration about Directed Retry after CAC rejection

“Intelligent” means the algorithm can increase admission successful rate

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

IAC can increase admission successful rate through the following methods: 1. The data rate of PS service is not fixed, so maybe the cell can admit the UE after the data rate is decreased. 2. Since the service is non-real time, the users can wait a short time, then access to the cell. 3. The user with high priority can preempt the resource of users with low priority. 4. If the load of neighboring cell is not “Heavy”, UE may be admitted to the neighboring cell directly.

58

Flow chart of IAC

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The IAC procedure includes rate negotiation, DRD, preemption and queuing.

59

IAC – Rate negotiation


Iu QoS Negotiation: based on the UE capability

Maximum allowed bit rate •384kbps



Physical layer capability



Transport channel capability



RLC capability

•256kbps •128kbps


Initial / Target data rate •64kbps

RAB Downsizing: based on system load 

Channelization codes



Iub transmission resources



Radio resources

•32kbps

Scenarios: RAB setup， ，RAB modify, SRNSR request, reconfiguration Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Iu QoS Negotiation (Maximum expected rate negotiation): In PS domain, CN will negotiate with UE about the access rate. For every service, CN will send a QoS( includes the required data rate) to UTRAN, and UE will report its capability ( the maximum supported rate) to UTRAN. After negotiation, the maximum supported rate of UE will be the maximum negotiation rate. RAB Downsizing (Initial/target rate negotiation): To save system resources and improve the admission success rate, BE services does not require access at the maximum expected rate at setup. In stead, a proper rate is adopted for initial access, the rate is smaller than or equal to the maximum expected rate and bigger than or equal to the lowest guarantee rate (usually 8kbps) according to the cell load information. After access, the rate is adjusted higher when the traffic requires and system resources allow it to do so. The negotiation is based on cell load information, including: •Uplink and downlink radio bearer states of the cell •Iub resource state •Minimum spreading factor supported •HSDPA capability

60

IAC – Direct Retry based on service


Data service can be retry to HSDPA cells for better QoS

Data service Frequency A

CELL2 R99

CELL 1

R99

Frequency B CELL A

HSDPA

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

61

IAC – Preemption


The user with high priority can preempt the resource of users with low priority




Triggering resource for Preemption 

Power (or ENU), SF (spreading factor), Iub transmission resource, NodeB CE High priority Preempting resource

Low priority Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

In the service setup, modification, hard handover and transition-in scenarios, if service request supports preempting capability (core network configuration) when application for cell resources fails, preempting will be executed, and the resource of lower-priority user supporting preempting is released to set up the service request. The preemption procedure is as follows: 1.The preemption algorithm determines which radio link sets can be preempted according to the following preemption rules: - High priority user preempt the resource of low priority users - Preempting the resource of users with low priority first - Preempting single service user first - Preempting UEs as few as possible, that is, choose the UEs that can release the most resources - Preempting should follow this sequence: channelization codes first, then Iub transmission resources, radio resources last 2.Release resources occupied by candidate UEs. 3.The requested service uses the released resources to access the network directly without further admission decision.

62

IAC – Queuing


After CAC rejection, UE can wait a moment and queue, then try to admit again




Queuing priority: Pqueue = Tmax – Telapsed 

Tmax is the maximum time in the queue, default value is 5s



Telapsed is the time has queued

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The queuing algorithm is triggered by poll timer. The specific processing is as follows: 1. Reject this request if the actual wait time of each of the other requests is longer than the maximum queuing time of this request. 2. Calculate the weights of all requests in the queue. The weight: W = (Tmax – Telapsed) / Tmax * Priority Level of the service. 3.

Choose the request with the smallest weight to attempt resource allocation.

4. Put it back into the queue with the time stamp unchanged if this request is rejected. 5.

Choose the request with the smallest weight from the rest and performs another attempt until admitting a request or rejecting all requests.

63

IAC – Directed Retry based on Load Balance


Service will be set up to the cell with lightest load




The advantages 

Keeping the load of the network balanced



Supporting higher data rate for the user Cell 1

Cell 2 RRC Connection

Cell 1

Cell 2 RAB

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

If the load of neighboring cell is lighter than current cell, UE may be admitted to the neighboring cell directly. The RAB DRD procedure is as follows: 1. The RNC determines the admission of the inter-frequency target cell for blind handover. 2. If the admission is accepted, DRD procedure is performed for the interfrequency target cell for blind handover. 3. The RNC starts the RL setup procedure to complete the inter-frequency hard handover. 4. The RNC starts the RB setup procedure to complete the inter-frequency hard handover on the Uu interface and the service setup.

64

Parameters for IAC Algorithm Switch (1)





IU_QOS_NEG_SWITCH (Switcher for IU QoS Negotiation) 

Value range: 0 (close), 1 (open)



Default value: 0

RAB_DOWNSIZING_SWITCH (RAB Downsizing Switch) 

Value range: 0 (close), 1 (open)



Default value: 1

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set IU_QOS_NEG_SWITCH and RAB_DOWNSIZING_SWITCH through SET CORRMALGOSWITCH, and query them through LST CORRMALGOSWITCH

65

Parameters for IAC Algorithm Switch (2)





PREEMPTALGOSWITCH (Preempt algorithm switch) 

Value range: On, Off



Default value: Off

QUEUEALGOSWITCH (Queue algorithm switch) 

Value range: On, Off



Default value: Off

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set QUEUEALGOSWITCH and PREEMPTALGOSWITC through SET QUEUEPREEMPT, and query them through LST QUEUEPREEMPT.

66

Parameters for RAB Downsizing


ULBETRAFFINITBITRATE (Uplink initial access rates) & DLBETRAFFINITBITRATE (Downlink initial access rates) 

Value range: D8, D16, D32, D64, D128, D144, D256, D384, D768, D1024, D1536, D2048



Physical Value range: 8, 16, 32, 64, 128, 144, 256, 384, 768, 1024, 1536, 2048, Unit: kbps



Default value: D64, namely 64kbps

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the parameter through SET FRC, and query it through LST FRC. When the initial rate selection (RAB Downsizing) function is enabled, this value is the uplink/downlink initial access rate when the BE service is set up. If this rate access fails to satisfy the current load condition, then the actual initial access rate is the negotiated rate based on this rate. When the RAB Downsizing function is disabled, this parameter is the uplink/downlink initial access rate when the BE service is set up. The higher this parameter set, the shorter the time fro the BE service to reach the maximum rate but the easier for adjustment downward through negotiation when the system is congested, so it makes no sense to set it too high. The smaller this parameter, the easier for the BE service to access as per this rate, but, if it is set too low, it will take a longer time to adjust to the required rate when there is a service requirement.

67

Parameters for Queuing (1)





QUEUELEN (Queue length) 

Value range: 5 to 20



Recommended value: 10

POLLTIMERLEN (Poll timer length) 

Value range: 1 to 6000



Physical value range: 10 to 60000 ms step: 10ms



Recommended value: 50, namely 500 ms

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the parameters through SET QUEUEPREEMPT, and query them through LST QUEUEPREEMPT.

68

Parameters for Queuing (2)


MAXQUEUETIMELENx (Max queuing time length 1~12) 

Value range: 1 to 60s



Recommended value: 5, namely 5 seconds

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the parameters through SET QUEUEPREEMPT, and query them through LST QUEUEPREEMPT.

69

Parameters for DRD (1)


DRMAXUMTSNUM (Max inter-frequency direct retry number) 

Value range: 0 to 5



Recommended value: 2

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the parameter through SET DRD.

70

Parameters for DRD (2)





R99CSSEPIND (R99 CS separation indicator) 

Value range: FALSE (no separation), TRUE (separation)



Recommended value: FALSE

R99PSSEPIND (R99 PS separation indicator) 

Value range: FALSE (no separation), TRUE (separation)



Recommended value: FALSE

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the parameter through MOD CELLINETSTRATEGY. According to the cell type (R99 or R99+HSDPA), an HSDPA user accessing the R99 cell can be DRDed to a R99+HSDPA cell. According to these two parameters, a R99 user accessing the R99+HSDPA cell can be DRDed to a R99 cell.

71

Contents 1. Load Control Overview 2. Basic Load Control Algorithms 2.1 PUC (Potential User Control) 2.2 CAC (Call Admission Control) 2.3 IAC (Intelligent Admission Control) 2.4 LDR (Load Reshuffling) 2.5 OLC (Overload Control)

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

72

Load%

LCC (Load Congestion Control) 100%

Overload state: OLC will be

section A

THOLC

used 1

2

section B

THLDR

Basic congestion state: LDR will be used

section C

Normal state: Permit entry

Times Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

LCC (Load Congestion Control) consist of LDR (Load Reshuffling) and OLC (OverLoad Control). In basic congestion state, LDR will be used to optimize resource distribution, the main rules is not to affect the feeling of users as possible as we can. In overload state, OLC will be used to release overload state quickly, keep system stability and the service of high priority users.

73

LDR (Load Reshuffling)


Reasons 

When the cell is in basic congestion state, new coming calls could be easily rejected by system







Purpose 

Optimizing cell resource distribution



Decreasing load level, increasing admission successful rate

Triggering of LDR 

Power resources, code resource, Iub resources or Iub bandwidth, NodeB Credit resource

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The resources that can trigger the basic congestion of the cell are: Power resources If the current UL/DL load of the R99 cell is not lower than UL/DL LDR Trigger threshold (basic congestion control threshold in UL/DL), the cell works in basic congestion state and the related load reshuffling actions are taken. Code resource If the current remaining code of the cell is higher than Cell SF reserve threshold, code congestion is triggered and related load reshuffling actions are taken. Iub resources or Iub bandwidth Iub congestion control in both the uplink and downlink is NodeB-oriented. Load trigger threshold and load release threshold are set for the uplink and the downlink separately. Iub congestion control is implemented in a separate process module, so its functionality does not controlled by LDR switchers. NodeB Credit resource If the UL/DL current remaining credit resource is higher than Ul Credit SF reserved threshold/ Dl Credit SF reserved threshold, credit congestion is triggered and related load reshuffling actions are taken.

74

LDR procedure Turn on LDR algorithm switch Mark "current LDR state = uncongested" Start LDM congestion indication report

Mark "current action = first LDR action" Clear "selected" mark of all UE LDR actions Congestion state indication

Wait for congestion indication

Current LDR state = congested?

Inter-freq load handover

Succeed?

N

Y

N Code reshuffling

Succeed?

Y

N BE rate reduction

Succeed?

Y

N Sequence of actions can be configured (current action is taken firstly)

Inter-system handover in CS domain Inter-system handover in CS domain

AMR rate reduction

Succeed?

Y

N Succeed?

Y

Mark "current action = successful action"

Wait time for LDR action duration

N Succeed?

Y

N

QoS renogiation on Iu interface

Succeed?

Y

N MBMS power reduction

Succeed?

Y

N No related action can be found

Mark "current action = first LDR action"

75

Resource UL/DL

LDR Actions

Power UL

DL

Inter-Frequency Load Handover

√

√

BE Rate Reduction

√

Inter-system Handover in CS Domain

Iub

Code

Credit

UL

DL

DL

UL

DL

√

√

√

√

√

√

√

√

√

√

√

√

Inter-System Handover in PS Domain

√

√

√

√

√

√

AMR Rate Reduction

√

√

√

√

Iu QoS Negotiation

√

√

√

√

√

√

√

Code Reshuffling MBMS Power Reduction

√

Different reason will trigger different actions

76

LDR Actions - Inter-frequency Load Handover


Target cells 

Load difference between current load and the basic congestion trigger threshold of target cell is larger than “UL/DL Inter-freq cell load handover load space threshold”




Target users 




Based on user priority and the current service rate

Result 

The load of two cells is lower than the basic congestion trigger threshold



The user with low priority hand over to the “Light load” cells

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

It is implemented as follows: 1. The LDR check whether the existing cell has a target cell of inter-frequency blind handover. If there is no such a target cell, the action fails, and the LDR performs the next action. 2. The LDR checks whether the load difference between the current load and the basic congestion trigger threshold of each target cell for blink handover is larger than UL/DL Inter-freq cell load handover load space threshold (Both uplink and downlink condition must be all fulfilled). If the basic congestion trigger threshold is not set, the admission threshold of the cell is used. If the difference is not larger than the threshold, the action fails. The LDR performs the next action. 3. If the LDR finds out a target cell that meets the specified blind handover conditions, the LDR selects one UE to make an inter-frequency blind handover, depending on the UE’s integrate priority and occupied bandwidth. The selected UE has lower integrate priority and its bandwidth is less than and has the least difference between the UL/DL Inter-freq cell load handover maximum bandwidth parameter. If the LDR cannot find such a UE, the action fails. The LDR performs the next action.

77

LDR Actions - BE Rate Reduction


Candidate RABs 




The data rate of BE service is larger than GBR

Target RABs 

Rank the candidate RABs by the integrate priority, the low priority RABs reduce BE rate first




Result 

Cell load is decreased under basic congestion trigger threshold



The BE service rate of low priority RABs is limited in GBR

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

BE rate reduction is implemented by reconfiguring the bandwidth. Bandwidth reconfiguration requires signaling interaction on the Uu interface. This procedure is relatively long. The LDR algorithm is implemented as follows: 1. Based on the integrate priority, the LDR sorts the RABs in descending order. The top RABs related to the BE services whose rates are higher than a threshold (target rate of Uplink/Downlink BE guarantee bit rate on DCH) are selected. The target rate is ULPSBEGUARRATE/DLPSBEGUARRATE which is configured DCCC algorithm (ADD CELLDCCC). 2. The bandwidth of the selected services is reduced to the specified rate. The number of selected RABs is determined by UL/DL LDR-BE rate reduction RAB number. 3. If services can be selected, the action is successful. If services cannot be selected, the action fails. The LDR performs the next action. 4. The BE rate reduction algorithm is controlled by the DCCC algorithm switch. BE rate reduction can be performed only when the DCCC algorithm switch is turned on.

78

LDR Actions - Uncontrolled Real-time QoS Renegotiation


Target RABs 

Rank the candidate RABs by the integrate priority, the service with lowest priority and current data rate higher than GBR will be selected




Result 

Cell load is decreased under basic congestion trigger threshold



The data rate of low priority service is reduced to GBR

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The load is reduced by adjusting the rate of the real-time services through uncontrolled real-time OoS renegotiation. Upon receipt of the message, the CN sends the RAB ASSIGNMENT REQUEST message to the RNC for RAB parameter reconfiguration. Based on this function, the RNC can adjust the rate of real-time services to reduce the load. The LDR algorithm is implemented as follows: 1. Based on the integrate priority, the LDR sorts the real-time services in the PS domain in descending order. The top services are selected for QoS renegotiation. 2. The LDR performs QoS renegotiation for the selected services. The GBR during service setup is the maximum rate of the service after QoS renegotiation. 3. The RNC initiates the RAB Modification Request message to the CN for QoS renegotiation. 4. If the RNC cannot find a proper service for QoS renegotiation, the action fails. The LDR performs the next action.

79

LDR Actions - Inter-system Handover In the CS/PS Domain


Target user 

Based on the integrate priority, sorting the UEs in descending order. The top CS/PS services are selected GSM cell WCDMA cell




Result 

Cell load is decreased under basic congestion trigger threshold

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The 2G and 3G systems have different cell sizes and coverage modes. Therefore, blind handover across systems is not taken into account. The LDR is implemented in the downlink (e.g.) as follows: 1. Based on the integrate priority, the LDR sorts the UEs in descending order. The top CS/PS services are selected. 2. For the selected UEs, the LDR sends the load handover command to the intersystem handover module to ask the UEs to hand over to the 2G system. 3. The handover module decides to trigger inter-system handover, depending on the capability of the UE and the capability of the algorithm switch to support the compression mode. 4. This action is successful if any load handover UE is found. Otherwise, this action fails.

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LDR Actions - AMR Rate Reduction


Target user (downlink e.g.) 

Candidate RABs: users accessing the AMR services (conversational) and with the bit rate higher than the GBR



Rank the candidate RABs by the integrate priority, the AMR service with lowest priority will be selected




Result 

Cell load is decreased under basic congestion trigger threshold



The AMR user with low priority is reduced to low voice rate mode

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

In the WCDMA system, voice services work in eight AMR modes. Each mode has its own rate. Therefore, mode control is functionally equal to rate control. The LDR algorithm is implemented as follows: 1. Based on the integrate priority, the LDR sorts the RABs in the descending order. The top UEs accessing the AMR services (conversational) and with the bit rate higher than the GBR are selected. 2. In downlink, the RNC sends the “Rate Control request” message through the IuUP to the CN to adjust the AMR rate to the GBR. 3. In uplink, The RNC sends the TFC CONTROL command to the UE to adjust the AMR rate to the assured rate. 4. If the RNC cannot find a proper service for AMR rate reduction, the action fails. The LDR performs the next action.

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LDR Actions - Code Reshuffling


Purpose 

Cell load is decreased under basic congestion trigger threshold



Sufficient code resources can be reserved for subsequent service SF=4 SF=8

SF=16

7

SF=32 SF=64

C

3 1

2

4

A

5 6

B

SF=128

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

When code resources are in basic congestion state, sufficient code resources can be reserved for subsequent service access through code reshuffling. The LDR algorithm is implemented as follows: 1. Select a subtree. Ensure that the number of users in the subtree is not higher than Max user number of code adjust. 2. Treat each user in the subtree as a new user and allocate code resources to each user. 3. Initiate the reconfiguration procedure for each user in the subtree and reconfigure the channel codes of the users to the newly-allocated code resources. 4. The reconfiguration procedure on the air interface is implemented through the PHYSICAL CHANNEL RECONFIGURATION message and that on the Iub interface through the RL RECONFIGURATION message.

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LDR Actions - MBMS Power Reduction


Purpose 

The downlink power load can be reduced by lowering power on MBMS traffic channels

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The LDR algorithm is implemented as follows: 1. Select all RABs with low priorities. 2. The RNC initiates the reconfiguration procedure and resets the transmit power of MTCH (FACH) to the minimum value. The transmit power corresponds to the MBMS service. 3. The reconfiguration procedure on the Iub interface is implemented through the COMMON TRANSPORT CHANNEL RECONFIGURATION REQUEST message.

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Parameters for LDR Algorithm Switch


NBMLdcAlgoSwitch (Cell algorithm switch) 

Value Range: 



ULLDR, DLLDR, CELL_CODE_LDR, CELL_CREDIT_LDR

Default status: OFF 

Most of the LDR actions (except inter-frequency load handover) affect QoS

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set LDR Algorithm Switch through ADD CELLALGOSWITCH, query it through LST CELLALGOSWITCH, and modify it through MOD CELLALGOSWITCH.

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Parameters for LDR Algorithm Priority


Priority for load reshuffling 

Value Range: 

IUBLDR(Iub load reshuffling), CREDITLDR(Credit load reshuffling), CODELDR (Code load reshuffling), UULDR (Uu load reshuffling)



Default status: 

LdrFirstPri = IUBLDR



LdrSecondPri = CREDITLDR



LdrThirdPri = CODELDR



LdrFourthPri = UULDR

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set LDR Algorithm Switch through SET LDCALGOPARA, query it through LST LDCALGOPARA, and modify it through MOD LDCALGOPARA.

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Parameters for Triggering of Power Resource (1)





ULLDRTRIGTHD (UL LDR trigger threshold) 

Value range: 0 to 100%



Recommended value: 55, namely 55%

ULLDRRELTHD (UL LDR release threshold) 

Value range: 0 to 100%



Recommended value: 45, namely 45%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the following parameters through ADD CELLLDM, query it through LST CELLLDM, and modify it through MOD CELLLDM. When uplink basic congestion status is triggered, the uplink LDR action will be started. LDR control objective is to preserve space for admission to increase the success rate. Therefore under the current policy, the LDR trigger threshold shall be so set that the congestion is less than or close to the concerned admission threshold index. The smaller the LDR trigger threshold and release threshold, the easier the system is in preliminary congestion status, the harder it is released from this status, the easier the LDR action happens, and the more likely the users are affected. However, since the resources are preserved, the admission success rate becomes higher. The carrier shall make tradeoff between these factors. The uplink LDR trigger thresholds must be greater than uplink LDR release thresholds, and the recommended difference between the two thresholds is larger than 10%, otherwise maybe the basic congestion state is “Ping-Pong”.

86

Parameters for Triggering of Power Resource (2)





DLLDRTRIGTHD (DL LDR trigger threshold) 

Value range: 0 to 100%



Recommended value: 70, namely 70%

DLLDRRELTHD (DL LDR release threshold) 

Value range: 0 to 100%



Recommended value: 60, namely 60%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

When downlink basic congestion status is triggered, the downlink LDR action will be started. LDR control objective is to preserve space for admission to increase the success rate. Therefore under the current policy, the LDR trigger threshold shall be so set that the congestion is less than or close to the concerned admission threshold index. The smaller the LDR trigger threshold and release threshold, the easier the system is in preliminary congestion status, the harder it is released from this status, the easier the LDR action happens, and the more likely the users are affected. However, since the resources are preserved, the admission success rate becomes higher. The carrier shall make tradeoff between these factors. The downlink LDR trigger thresholds must be greater than downlink LDR release thresholds, and the recommended difference between the two thresholds is larger than 10%, otherwise maybe the basic congestion state is “Ping-Pong”.

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Parameters for Triggering of Code Resource and Credit Resource





CELLLDRSFRESTHD (Cell LDR SF reserved threshold) 

Value Range:0, 1, 2, 3, 4, 5, 6, 7



Physical value Range: SF4, SF8, SF16, SF32, SF128, SF256



Recommended value: SF8

UL (DL) LDRCREDITSFRESTHD (UL/DL LDR Credit SF reserved threshold ) 

Value Range:0, 1, 2, 3, 4, 5, 6, 7



Physical value Range: SF4, SF8, SF16, SF32, SF128, SF256



Recommended value: SF8

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the following parameters through ADD CELLLDR, query it through LST CELLLDR, and modify it through MOD CELLLDR. CELLLDRSFRESTHD (Cell LDR SF reserved threshold): The code adjusting could be done only when the minimum available SF of a cell is larger than this threshold. The parameter of [Dl HandOver Credit and Code Reserved SF] must be not less than the one of [Cell LDR SF reserved threshold]. The parameter of [Dl HandOver Credit and Code Reserved SF] is set in ADD CELLCAC and MOD CELLCAC, and they can be listed by LST CELLCAC. UL (DL) LDRCREDITSFRESTHD (UL/DL LDR Credit SF reserved threshold ): The UL/DL Credit LDR could be done only when the UL/DL Credit SF Reserve larger than this threshold. The parameter of [UL/DL HandOver Credit and Code Reserved SF] must be not less than the one of [UL/DL LDR Credit SF reserved threshold]. The parameter of [UL/DL HandOver Credit and Code Reserved SF] is set in ADD CELLCAC and MOD CELLCAC, and they can be listed by LST CELLCAC.

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Parameters for LDR Period


LDRPERIODTIMERLEN (LDR period timer length) 

Value range: 1 to 86400 unit: second



Recommended value: 10, namely 10s 

Not less than 8s

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set this parameters through SET LDCPERIOD, query it through LST LDCPERIOD. When preliminary congestion happens, the LDM (Load Measurement) module sends period of preliminary congestion instruction (i.e., LDR execution period) to LDR. Unlike OLC control mechanism, LDR itself has no action timer and relies on LDM’s sending congestion instruction periodically to trigger. This mechanism originates from the initial algorithm that tends to use period report control for LDR and time report control for OLC. The smaller the parameter value is, the more frequently LDR action is executed, in which case the load can be decreased quickly. However, if the value is too low, an LDR action may overlap the previous one before the result of the previous one is displayed in LDM. The larger the value, the more likely this problem can be prevented. If the value is set too large, the LDR action may be executed very rarely, failing to reach the expected purpose of lowering the load timely.

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Parameters for LDR Action Sequence


UL (DL) LDRFIRSTACTION (UL/DL LDR First action) ~

UL (DL) LDRSIXTHACTION (UL/DL LDR Sixth action) 

Value range: NOACT, INTERFREQLDHO, BERATERED, QOSRENEGO, CSINTERRATLDHO, PSINTERRATLDHO, AMRRATERED, MBMSDECPOWER, CODEADJ



Default value: UlLdrFirstAction or DlLdrFirstAction is CODEADJ, UlLdrSecondAction or DlLdrSecondAction is INTERFREQLDHO UlLdrThirdAction or DlLdrThirdAction is BERATERED，the other is NOACT

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the following parameters through ADD CELLLDR, query it through LST CELLLDR, and modify it through MOD CELLLDR. This set of parameters determines the action sequence for the uplink/downlink LDR. •NOACT: NO ACTION •INTERFREQLDHO: INTER-FREQ LOAD HANDOVER •BERATERED: BE TRAFF RATE REDUCTION •QOSRENEGO: UNCONTROLLED REAL-TIME TRAFF QOS RE-NEGOTIATION •CSINTERRATLDHO: CS DOMAIN INTER-RAT LOAD HANDOVER •PSINTERRATLDHO: PS DOMAIN INTER-RAT LOAD HANDOVER •AMRRATERED: AMR TRAFF RATE REDUCTION

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Parameters for LDR Code Reshuffling


MAXUSERNUMCODEADJ (Max user number of code adjust) 

Value range: 1 to 3



Recommended value: 1

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

MAXUSERNUMCODEADJ (Max user number of code adjust): Number of users selected in a code adjust. LDRCODEPRIUSEIND (LDR code priority indicator): "FALSE" denotes not considering the priority of code when code adjust; "TRUE" denotes considering the priority of code when code adjust.

91

Parameters for LDR Inter-Frequency Load Handover (1)


ULINTERFREQHOCELLLOADSPACETHD (UL Inter-freq cell load handover load space threshold)






Value range: 0 to 100%



Recommended value: 20, namely 20%

DLINTERFREQHOCELLLOADSPACETHD (DL Inter-freq cell load handover load space threshold) 

Value range: 0 to 100%



Recommended value: 20, namely 20%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Inter-frequency load handover happens only when the current load space of the target cell is higher than this parameter setting. This parameter value is relative to target cell LDR threshold. The smaller this parameter value is, the easier it is to find qualified target cell for blind handover. However, too low value easily makes the target cell enter congestion status. The larger the value, the more difficult for the inter–frequency blind handover to happen and the easier to guarantee the stability of the target cell.

92

Parameters for LDR Inter-Frequency Load Handover (2)


ULINTERFREQHOBWTHD (UL Inter-freq cell load handover maximum bandwidth)






Value range: 0 to 400000bps



Recommended value: 200000, namely 200kbps

DLINTERFREQHOBWTHD (DL Inter-freq cell load handover maximum bandwidth) 

Value range: 0 to 400000bps



Recommended value: 200000, namely 200kbps

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

During inter–frequency load handover, the UE is selected as the target of inter– frequency load handover from the UE set where the bandwidth is less than this threshold. The larger the parameter value is, the higher the service rate of the user who is handover and the more obviously the cell load is decreased. But large value gives rise to fluctuation and congestion of the target cell’s load. The smaller the parameter value is, the smaller the amplitude of the load decreased as a result of the inter–frequency load handover and the easier to maintain the stability of the target cell’s load.

93

Parameters for LDR Other Actions


UL (DL) LDRBERATEREDUCTIONRABNUM, UL (DL) LDRPSRTQOSRENEGRABNUM, UL (DL) LDRCSINTERRATHOUSERNUM, UL (DL) LDRPSINTERRATHOUSERNUM, ULLDRAMRRATEREDUCTIONRABNUM 

Value range: 1 to 10



Default value 

UL (DL) LDRBERATEREDUCTIONRABNUM:

1



UL (DL) LDRPSRTQOSRENEGRABNUM:

1



UL (DL) LDRCSINTERRATHOUSERNUM:

3



UL (DL) LDRPSINTERRATHOUSERNUM:

1



UL (DL) LDRAMRRATEREDUCTIONRABNUM:

3

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

This set of parameters determines the action sequence for the uplink/downlink LDR. UL (DL) LDRBERATEREDUCTIONRABNUM: UL/DL LDR-BE rate reduction RAB number UL (DL) LDRPSRTQOSRENEGRABNUM: UL/DL LDR un-ctrl RT Qos re-nego RAB number UL (DL) LDRCSINTERRATHOUSERNUM: UL/DL LDR CS inter-rat ho user number UL (DL) LDRPSINTERRATHOUSERNUM: UL/DL LDR PS inter-rat ho user number UL (DL) LDRAMRRATEREDUCTIONRABNUM: UL/DL LDR-AMR rate reduction RAB number The larger these parameters are, the more obviously the current cell’s load is reduced. Its cost is that user feelings are affected and that it gives rise to congestion of the target cell. The smaller these parameters are, the smaller the amplitude of the load adjusted by LDR. Its benefit is that the QoS is guaranteed and the target cell load is stable.

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Contents 1. Load Control Overview 2. Basic Load Control Algorithms 2.1 PUC (Potential User Control) 2.2 CAC (Call Admission Control) 2.3 IAC (Intelligent Admission Control) 2.4 LDR (Load Reshuffling) 2.5 OLC (Overload Control)

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

95

OLC (Over Load Control)


Reasons 




In overload state, system is not stable

Purpose 

Ensuring the system stability and making the system back to the normal state as soon as possible




Triggering of OLC 

Power resources only

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

After the UE access is granted, the power consumed by a single link is adjusted by the single link power control algorithm. The power varies with the mobility of the UE and the changes in the environment and the source rate. In some situations, the total power load of the cell may be higher than the target load. To ensure system stability, overload congestion must be handled. The OLC includes: •Restricting the TF (Transmission Format) of the BE service •Choosing and releasing some UEs Only power resources could result in overload congestion. Hard resources such as equivalent user number, Iub bandwidth, and credit resources do not cause overload congestion.

96

OLC Procedure

97

OLC Actions - TF Control


Target user 

Rank the candidate users by the integrate priority, the low priority user will be selected




Execution 

Send the control message to UE (downlink: TF control indication, uplink: Transport format combination control) to restricts the TFC selection



After the congestion is released, the BE service rate will be recovered

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The OLC algorithm for TF control is implemented as follows: 1. Based on the integrate priority, the OLC sorts the RABs in the descending order. The RABs with the BE services and its bit rate is higher than DCCC rate reduction threshold and with the lowest integrate priority are selected. The selected RAB number is UL/DL OLC fast TF restrict RAB number. 2. The RNC sends the control message to the MAC, during the continuous time (till congestion is released and traffic volume upsizing), MAC will restricts the TFC selection of these BE services to reduce data rate step by step. 3. Each time, RNC will select a certain number of RABs (which is determined by “UL/DL OLC fast TF restrict RAB number” ) to perform TF control, the times to perform TF control is determined by the UL/DLOLCFTFRSTRCTTimes parameter. 4. If the RNC cannot find a proper service for TF control, the action fails. The OLC performs the next action. 5. If the congestion is released, the RNC sends the congestion release indication to the MAC. 6. If the congestion is released and 4A report is received, and if rate recover timer (which length is RateRecoverTimerLen) is started and when this timer is expired, MAC will increase data rate step by step.

98

OLC Actions - Release of Some UEs


Target user (downlink e.g.) 

Rank the candidate users by the integrate priority, the low priority user will be selected




Execution 

Releasing the service of the selected user

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The OLC algorithm for release of some UEs is implemented as follows: 1. Based on the integrate priority, the OLC sorts all RABs in the descending order. 2. The top RABs selected. The number of selected UEs is equal to UL/DL OLC traff release RAB number. 3. The selected RABs are released directly.

99

Parameters for OLC Algorithm Switch


NBMSWITCH (Cell algorithm switch) 

Value Range: 



ULOLC, DLOLC

Default status: OFF 

OLC actions affect QoS heavily

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set OLC Algorithm Switch through ADD CELLALGOSWITCH, query it through LST CELLALGOSWITCH, and modify it through MOD CELLALGOSWITCH. Cell overload is an emergent status, OLC algorithm can quickly relieve uplink/downlink load by TF restriction or user release but may also cause oscillation of the cell load and affect the call drop rate. For the uplink, overload means the cell’s uplink interference is close to or reaches the limit and may give rise to difficulty in BTS uplink reception and decoding, resulting in call drop; For the downlink, overload means the downlink transmit power is close to or reaches the limit and the user’s downlink inner loop power control cannot be increased as needed because of the BTS power restriction, resulting in call drop.

100

Parameters for Triggering of Overload (1)





ULOLCTRIGTHD (UL OLC trigger threshold) 

Value range: 0 to 100%



Recommended value: 95, namely 95%

ULOLCRELTHD (UL OLC release threshold) 

Value range: 0 to 100%



Recommended value: 85, namely 85%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set these parameters through ADD CELLLDM, query it through LST CELLLDM, and modify it through MOD CELLLDM. The uplink OLC trigger threshold judges whether the system uplink is in overload status. If the cell load is consecutively higher than the threshold for pre-determined times, it means the system is in overload status for a long time. Under this circumstance, if the cell’s OLC switch is open, the system will perform OLC algorithm, including fast TF restriction or even user release. The smaller the OLC trigger threshold is, the easier the system will be in overload status. Since OLC will ultimately use extreme method like user release to lower the load, too low value will be very detrimental to the system performance. The smaller the OLC release threshold is, the harder for the system to release the overload. Since the consequence of overload is not as severe as expected, it is desirable to set the two parameters a bit higher given that the difference between OLC trigger threshold and OLC release threshold is fixed. The uplink OLC trigger thresholds must be greater than up OLC release thresholds, and the recommended difference between the two thresholds is larger than 10%, otherwise maybe the basic congestion state is “Ping-Pong”.

101

Parameters for Triggering of Overload (2)





DLOLCTRIGTHD (DL OLC trigger threshold) 

Value range: 0 to 100%



Recommended value: 95, namely 95%

DLOLCRELTHD (DL OLC release threshold) 

Value range: 0 to 100%



Recommended value: 85, namely 85%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set these parameters through ADD CELLLDM, query it through LST CELLLDM, and modify it through MOD CELLLDM. The downlink OLC trigger threshold judges whether the system downlink is in overload status. If the cell load is consecutively higher than the threshold for predetermined times, it means the system is in overload status for a long time. Under this circumstance, if the cell’s OLC switch is open, the system will perform OLC algorithm, including fast TF restriction or even user release. The smaller the OLC trigger threshold is, the easier the system will be in overload status. Since OLC will ultimately use extreme method like user release to lower the load, too low value will be very detrimental to the system performance. The smaller the OLC release threshold is, the harder for the system to release the overload. Since the consequence of overload is not as severe as expected, it is desirable to set the two parameters a bit higher given that the difference between OLC trigger threshold and OLC release threshold is fixed. The downlink OLC trigger thresholds must be greater than down OLC release thresholds, and the recommended difference between the two thresholds is larger than 10%, otherwise maybe the basic congestion state is “Ping-Pong”.

102

Parameters for OLC (1)


OLCPERIODTIMERLEN (OLC period timer length) 

Value range: 100 to 86400000, unit: ms



Recommended value: 3000, namely 3s

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set this parameters through SET LDCPERIOD, query it through LST LDCPERIOD. This parameter is the period of the OLC timer. When this period is up, OLC executes once and then restarts automatically. The period of the timer is the period of the OLC action. The uplink OLC and downlink OLC share the same timer. If the OLC action period is set too long, the system may respond very slowly to overload; If the OLC action period is set too short, unnecessary adjustment may occur before the previous OLC action has taken effect, thus affecting the system performance.

103

Parameters for OLC (2)





ULOLCFTFRSTRCTTIMES (UL OLC fast TF restrict times) 

Value range: 0 to 100



Recommended value: 3

DLOLCFTFRSTRCTTIMES (DL OLC fast TF restrict times) 

Value range: 0 to 100



Recommended value: 3

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Set the following parameters through ADD CELLOLC, query it through LST CELLOLC, and modify it through MOD CELLOLC. When uplink/downlink overload is triggered, the RNC will immediately execute OLC action by first executing uplink/downlink fast TF restriction. The internal counter is incremented by 1 with each execution. If the number of overloads does not exceed the OLC action threshold, the system lowers the BE service rate by lowering TF to try to relieve the overload. Exceeding OLC action threshold means that the previous operation has no obvious effect on alleviating the overload and the system has to release users to solve the overload problem. The lower the parameter value, the more likely the users are released, resulting in negative effect on the system performance. If the parameter value is set too high, the overload status is released slowly.

104

Parameters for OLC (3)


ULOLCFTFRSTRCTRABNUM (UL OLC fast TF restrict RAB number)






Value range: 1 to 100



Recommended value: 3

DLOLCFTFRSTRCTRABNUM (DL OLC fast TF restrict RAB number) 

Value range: 1 to 100



Recommended value: 3

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The higher the parameter value, the more users involved in fast TF restriction under identical conditions, the quicker the cell load decreases, and the more users’ QoS affected.

105

Parameters for OLC (4)


RATERSTRCTCOEF (DL OLC fast TF restrict data rate restrict coefficient) 

Value range: 1 to 99%



Recommended value: 68, namely 68%

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

OLC fast TF restriction rate coefficient means the degree of the rate restriction. The smaller the parameter value, the more severe the rate is restricted. Too low value may affect the BE transmission delay. Large value means loose restriction, which may be ineffective in alleviating the overload.

106

Parameters for OLC (5)


RATERSTRCTTIMERLEN (DL OLC fast TF restrict data rate restrict timer length)






Value range: 1 to 65535, unit: ms



Recommended value: 3000, namely 3s

RATERECOVERTIMERLEN (DL OLC fast TF restrict data rate recover timer length) 

Value range: 1 to 65535, unit: ms



Recommended value: 5000, namely 5s

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

RateRstrctTimerLen specifies the period for MAC to apply TF restriction on BE users in a downlink fast TF restriction. RateRecoverTimerLen specifies the period for MAC to apply TF recovery on BE users when the downlink overload is released. Once the MAC layer receives instruction to perform fast TF restriction on a user, it periodically uses rate restriction coefficient to restrict the maximum available TF of the user until it receives overload release instruction. Therefore every period specified by RateRstrctTimerLen, apart from the new OLC-selected users who are TF restricted, the previously selected users are also fast-TF restricted in an effort to release the overload more quickly. In order to timely adjust the BE service rate according to the load, the value of RateRstrctTimerLen shall be slightly larger than the system load response time after rate adjustment and the period of overload detection. The larger RateRstrctTimerLen value is, the slower the BE service rate decreases. The smaller RateRstrctTimerLen value is, the harder to receive the overload release instruction. Large RateRecoverTimerLen value leads to slow BE service recovery rate but can prevent overload from triggering again in short time. Small RateRecoverTimerLen value leads to quick BE service recovery rate but gives rise to yet more overloads.

107

Parameters for OLC (6)


ULOLCTRAFFRELRABNUM (UL OLC traff release RAB number)






Value range: 0 to 10



Default value: 0

DLOLCTRAFFRELRABNUM (DL OLC traff release RAB number) 

Value range: 0 to 10



Default value: 0

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

The higher the parameter value, the more obvious the cell load decreases at the cost of negatively affecting user feelings.

108

Thank You www.huawei.com

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

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