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Evaluation of Dynamic Block error(BLER)

target Selection in HSUPA

20th November, 2014Tejas Subramanya

Supervisor: Prof. Riku JanttiInstructor: Rua Philippe

Conducted in: Nokia Networks

20-11-2014

Outline

• Introduction

• Objectives of the thesis

• Power control procedures

• ‘Dynamic BLER’ feature

• Simulation procedures

• Simulation results

• Problems and solutions when the feature is active

• Conclusion

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Introduction (1)

• Why WCDMA/HSPA ?

• HSPA -> High Speed Downlink/Uplink Packet Access

• Shared resources -> DL : Channelization codes; UL : Interference

• HSUPA – Dynamic HSUPA BLER target selection in outer loop power control to reduce interference

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Introduction (2)

• Uplink channels

Physical channels:

E-DPDCH -> Carries data over air interfaceE-DPCCH -> Carries control information related to E-DPDCHDPCCH -> Carries transmit power control commandsHS-DPCCH -> Carries acknowledgements and CQI information

Traffic channels:

E-DCH -> Carries HSUPA related dataDCH -> Carries WCDMA related data

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Objectives of the thesis

• Understand the importance of ‘Dynamic HSUPA BLER’ feature

• Simulate the feature based on system test logs

• Study the problems under low traffic and high traffic within the cell

• Discuss the solutions to each of the problems with simple simulations

• Analyze the gain achieved in terms of cell throughput based on simulation results

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Power Control Procedures (1)

Power control – Immediate response for fast changes in signal and interference levels.

Inner loop power control (ILPC)- Control uplink transmission powers of UE to

reach target SIR

Outer loop power control (OLPC) - Calculate minimum target SIR required for

sufficient quality of connection (Ideal BLER target fixed to 10% )

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Power Control Procedures (2)

Outer Loop Power Control

- OLPC entities (1 per traffic channel)- OLPC controller (1 per call connection)- OLFTOR

• OLPC entity:- Measures BLER- Reports it to OLPC controller

• OLPC controller:- Controls the state of OLPC entities (active, semi-active or inactive)**- Adjusts target SIR

• OLFTOR: - Forwards this information to Layer 3(Handover control in case of quality deterioration)

UL outer loop PC Entity #N

UL outer loop PC Entity #1

UL outer Loop PC Controller

RNC

BS 1

UL fast closed loop PC

BS 2

UL fast closed loop PC

L1/FP

L1/FP L1/FP L1/FP

OLFTOR (only in CDSP-C)

PQ II

DSP

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Dynamic BLER feature (1)Classification of users into different traffic types in OLPC

- Inputs: Frame rate, FP bit rate, Number of HARQ retransmissions

• Peak traffic type (Low BLER target)- Condition: Percentage of UE packets in FP frame > 90%

- Ideal BLER target: 8%

• Bursty traffic type (Moderate BLER target)- Condition: FP frames per second <= 10 (10ms TTI); FP

frames per second <= 50 (2ms TTI)- Ideal BLER target: 10% for 0 HARQ retransmissions

• Continuous traffic type (High BLER target)- Condition: FP frames per second > 10 (10ms TTI); FP

frames per second > 50 (2ms TTI)- Ideal BLER target: 10% for 1 HARQ/31.6% for 0 HARQ

retransmissions

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Dynamic BLER feature (2)

Algorithm 1: Mixture of DCH and E-DCH traffic channels in UE

• Determine dynamic BLER target using below equations

DCH:

E-DCH:

• Determine the change in SIR required

DCH:

E-DCH:

• Calculate the target SIR

- If all transport blocks of the frame are ok, ∆SIR = sir_down_step_size- If any transport block is CRC erroneous, ∆SIR = sir_up_step_size

BLER_EDCH)R_target(ideal_BLEveof_the_curDCH_solpe_

H_target_DCideal_BLERDCHER_target_dynamic_BL

*

BLER_DCH)R_target(ideal_BLErve_of_the_cuEDCH_solpe

CH_target_EDideal_BLEREDCHER_target_dynamic_BL

*

BLERstepizeDCHt_DCHBLER_Targetep_sizesir_down_s

HBLERstepsizeDCDCH)ER_Target_dynamic_BL(p_sizesir_up_ste

*

*1

HBLERstepizeEDCEDCHTargetBLERsizestepdownsir

CHBLERstepsizeEDEDCHTargetBLERdynamicsizestepupsir

*_____

*)___1(___

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1

2

Dynamic BLER feature (3)

Algorithm 2: Only E-DCH traffic channels in UE

• Determine the change in SIR required.

BLER estimation = 0, if frame is ok;BLER estimation = 1, if frame failed;

)_(_ tBLER_targeestimationBLERsizestepSIR

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Simulation Procedure (1)

‘Noise rise’ gives the total uplink load factor (capacity of the cell).

Load factor per user= Sum(DPCCH,HS-DPCCH,E-DPCCH,E-DPDCH) load factors * activity factor of the user

Determine traffic type and ideal BLER target

Frame rate(Input)

FP bit rate (Input)

HARQ Rx number (Input)

Calculate SIR target

Measured BLER(Input)

DPCCH load

factor

HS-DPCCH load

factor

E-DPCCH load

factor

E-DPDCH load

factor

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Simulation Procedure (2)

Load factor DPCCH:

LDPCCH = 10^ ((SIR – 10log10 (SF))/10) , where

‘SF ‘ is the spreading factor of DPCCH.‘SIR’ is the signal to interference ratio of the user.

Load factor HS-DPCCH:

LHS DPCCH = 10^ ((10log10 (PO) + 10log10 (LDPCCH))/10) , where

‘(βhs/βc)’ is given by quantized amplitude ratio table for HS-DPCCH based on the signalled values.

2

c

hs

2

c

hs +-1sho

shosho

nonsho

nonshoshocqiHSDPCCH PPPPO

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Simulation Procedure (3)

Load factor E-DPCCH:

LE-DPCCH = LDPCCH * Aec2 , where

‘Aec’ is the gain factor for E-DPCCH (βec)/ gain factor for DPCCH (βc ).

‘Aec’ is obtained by quantized amplitude ratio table for E-DPCCH based on the signalled values.

Load factor E-DPDCH:

LE-DPDCH = LDPCCH * Absolute grant value

Absolute grant value = Aed*Number of codes‘Aed’ is the ’Gain factor for E-DPDCH (βed)/ gain factor for DPCCH (βc ).‘Absolute grant values’ are obtained by scheduling grant tables based on E-DCH transport block size used in uplink transmission.

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Simulation Procedure (4)

Average user throughput and cell throughput are calculated based on the activity factor, bearer bit rate and number of users in the cell.

Average user throughput (number of users) = (Sum (Activity factors of all the users)*Bit rate of radio bearer)/number of users

Cell throughput (number of users) = Average throughput (number of users) * number of users

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Simulation Results (1)

10 HSUPA users within the cell (10ms TTI)

Feature inactive:

841 Kbps

Feature active:

1.24Kbps

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Simulation Results (2)

10 HSUPA users within the cell (2ms TTI)

Feature inactive:1.7 Mbps

Feature active:

2.4 Mbps

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Problems and Solutions when the Feature is active (1)

1. HSUPA users within the cell < 3

Problem: End to end TCP downlink throughput reduces if the traffic type of the user is continuous.

Reason: If user is continuous, high BLER target is used which results in low SIR target, which in turn results in the increase of uplink HARQ Retransmissions.

Increase in HARQ retransmissions leads to increase in RLC retransmissions and thus increases TCP round trip time. Thus, TCP ACK’s in uplink are delayed and TCP downlink throughput reduces significantly.

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Problems and Solutions when the Feature is active (2)

1. HSUPA users within the cell < 3

Simulation proof:

The graph shows the behaviour Of TCP round trip time andTCP downlink throughputw.r.t BLER.

Solution: Feature is deactivated when the number of users within the cell is less than 3.

TCP RTT

TCP throughput

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Problems and Solutions when the Feature is active (3)

2. HSUPA users within the cell > 35

Problem: All the users tend to behave more like bursty traffic type even though the users are transmitting continuously. This results in the use of moderate BLER targets of bursty traffic type even for continuous users and thus reduces the gain achieved in cell throughput.

Solution: Users are not differentiated into continuous and bursty traffic type above 35 users and only BLER targets of continuous users are used. This improves the gain achieved in cell throughput.

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Problems and Solutions when the Feature is active (4)

2. HSUPA users within the cell > 35

Before the problem is

solved:200 Kbps

After the problem is solved:450 Kbps

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Conclusion

• ‘Dynamic HSUPA BLER’ is a feature which reduces the uplink interference and thus increases the cell capacity.

• Two shortcomings of the feature are addressed and the solutions are provided to overcome them.

- In low HSUPA traffic case, TCP downlink throughput decreases and thus feature is not activated.

- In high HSUPA traffic case, continuous users are treated as bursty and moderate BLER targets are used and thus user type differentiation is not done above 35 users. All the users are treated as continuous.

20-11-2014