A Dynamic Buffer Management Scheme for End-to-end QoS Enhancement of Multi-flow Services in HSDPA

A Dynamic Buffer Management Scheme for End-to-end QoS Enhancement of Multi-flow Services in HSDPA

Suleiman Y. Yerima, Khalid Al-BegainIntegrated Communications Research Centre

Faculty of Advanced TechnologyUniversity of Glamorgan

2 NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

Outline

HSDPA overview

TSP queuing and BM schemes

Time-space priority BM

Dynamic Time-space priority BM

Simulation model

Results

Conclusions


HSDPA Overview

High Speed Downlink Packet Access (HSDPA):

3GPP Enhancements to UMTS (3G) RAN

Higher Peak data rate: up to 14Mbps

Lower connection and response times

3-5 X capacity increase

Three interacting domains:

Core Network

Radio Access Network (RAN)

User Equipment (UE)

Radio Network Controller

Iub interface

User Equipments

Core Network

HSDPA CELL

Node B

External Network


HSDPA Overview

New PHY & MAC enhancements in Node B:

New MAC-hs layer in Node B

High-Speed downlink Shared Channel

Link adaptation (AMC)

Packet Scheduling (PS)

L1 retransmissions (HARQ)

Shorter Transmission interval (2ms)

Radio Network Controller

Iub interface

User Equipments

Core Network

HSDPA CELL

Node B

External Network


motivation:

Emergence of multiple flow traffic profile per user/connection

Existing HSDPA QoS mechanisms single flow based

E.g. MAC-hs Packet Scheduling (PS)

Node B buffering

No BM schemes in standards- open issue


motivation (contd.)

The most challenging multiple flow scenario is connections with RT and NRT

flows (conflicting QoS requirements) e.g. Voice + file download

RT flow -> delay, jitter sensitive & loss tolerance

NRT flow-> loss sensitivity & delay, jitter tolerance

Hence our proposed MAC-hs BM schemes based on Time-Space Priority

(TSP) queuing model


TSP queuing model

Transmission to user terminal

TSPthreshold

RTC flow

NRTC flow

Service process

Typical priority queuing models are either loss or delay differentiated

Our Time-space priority queuing model (TSP):

Single queue with hybrid differentiation

Loss differentiated

delay differentiated

RTC packets:

High priority delay

Low priority loss

NRTC packets

High priority loss

low priority delay

Hence RTC => preferential transmission

NRTC =>preferential buffer admission


TSP advantages

Efficient buffer utilization

Most viable for joint RTC and NRTC QoS control compared to

typical priority queuing approaches

Hence we designed an efficient TSP-based BM scheme for HSDPA

Exploiting existing mechanisms in HSDPA specs.


TSP-based Buffer Mgt. in HSDPA

Enhanced TSP with flow control thresholds

RNC sends MAC PDUs over Iub interface

Employs Iub signalling with credit allocation

algorithm to mitigate buffer overflow

Employs Discard Timer for RTC

Higher layer protocol (ARQ, TCP)

performance improvement

HARQ

ARQ

TCP

CN & EXTERNAL IP

TCP Source

RNC

Node B

UE

Iub interface

Air interface

UE3

UE2

UE1 RT flow

UE1UE1 MAC-hs buffer

Capacity Request {Priority, User Buffer Size (UBS)}

RNC

UE1 NRT flow

R

H

L

N

Iub flow control

Packet Scheduling

Capacity Allocation {Priority, Credits}

HS-DSCH Frame {Priority, UBS, PDU size, #PDUs}

RNC Node B


TSP-based BM in HSDPA

Credit based FC algorithm:

CTotal = CNRT + CRT

CRT = (λRT / PDU_size) ∙ TTI

CNRT = min { CNRTmax , RNCNRT }

CNRTmax = (λ’NRT /PDU_size) ∙ TTI , N’T < L

β ∙ (λ’NRT /PDU_size) ∙ TTI , L ≤ N’T ≤ H, 0 < β < 1

0 , N’T > H

Where λ'NRT = α ∙ λ'NRT-1 + (1- α) ∙ λNRT is EWMA of Scheduler NRT data rate

and N’T = θ ∙ NT-1 + θ ∙ NT is an EWMA of total queue size


Enhanced TSP improves e2e NRTC throughput without compromising RT QoS

Problem: TSP has static delay prioritization Potential NRTC bandwidth starvation Non optimal ARQ and TCP performance

A possible solution: Exploit possible RTC delay tolerance

Hence we extend the TSP BM with Dynamic Time priority switching


D-TSP

RNC UE1 MAC-hs buffer

NRT

R

H

L

N

Iub flow control

Packet Scheduling

Priority switching

RT

UE1

Incorporates delay Priority switching to TSP

DTSP priority switching algorithm:

IF RT packets < k AND RT HOL delay< MAX_delay AND NRT packets > 0Time Priority = NRT flowGenerate Transport Block from NRT PDUsELSETime Priority = RT flowGenerate Transport Block from RT PDUs

MAX_delay = Max e2e delay – other queuing and propagation delays

k= Delay budget / RTC inter-arrival time

Delay budget ≤ MAX_delay

Discard timer (DT) setting = MAX_delay


HSPDA modelling

Detailed custom modelling with OPNET:

Multi-flow connection: VoIP source, NRT source with TCP

Fixed external and Core Network delay assumed

RNC: Packet segmentation, RLC modes

Node B: AMC Link adaptation, HARQ, MAC-hs buffers, Packet scheduler

Receiver: SINR, HARQ, RLC modes, re-assembly queues, TCP

User Equipments

HSDPA CELL

Node B RNC Core Network

voice + data connection

External Network

70ms20ms2ms


simulation set up

Performance metrics in test UE:

• End-to-end NRTC throughput

• Voice PDU discard ratio (Discard timer)

• % HSDPA channel utilization

HSDPA Simulation Parameters

HS-DSCH TTI 2ms

Path loss Model 148 + 40 log (R) dB

Shadow fading Log-normal: σ = 8 dB

Number of HSDSCH codes

5

CQI delay 3 TTIs (6ms)

HARQ processes 4

HARQ feedback delay 5ms

Test UE position from Node B

0.2 km

Packet Scheduling Round Robin

RLC PDU size 320 bits

RNC-Node B delay 20ms

External + CN delays 70ms

TCP config MSS= 536 bytes, RWIND = 64

Flow control settings β = 0.5, α = 0.7, θ = 0.7 20ms2ms 70ms

Node B

RNC

Concurrent VoIP + FTP for 180s

• MAX_delay = 250 –( 70 – 20) = 160ms

• BM config: R = 10, L =100, H= 150, N= 200 PDUs

• DTSP params: k = 2, 4, 6, 8

• channel load: 1, 5, 10, 20, 30, 50 users


Results: UE1 Data download throughput (1 user)

Throughput at UE1

• DTSP and TSP show similar performance

• Increased DB settings has marginal effect on throughput

• very low HS-DSCH load hence no DTSP gain

0

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0 18 36 54 72 90 108 126 144 162 180

Time (s)

Thro

ughp

ut (b

ps)

TSP D-TSP (k = 2) D-TSP (k = 4) D-TSP (k = 6) D-TSP (k = 8)


Results: UE1 Data download throughput (5 users)

0

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0 18 36 54 72 90 108 126 144 162 180

Time (s)

Thro

ughp

ut (b

ps)

TSP D-TSP (k = 2) D-TSP (k = 4) D-TSP (k = 6) D-TSP (k = 8)

Throughput at UE1

• More load on HSDPA channel

• Increased DB settings show noticeable improvement

• DTSP performs better than TSP



0

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0 18 36 54 72 90 108 126 144 162 180

Time (s)

Thro

ughp

ut (b

ps)

TSP D-TSP (k = 2) D-TSP (k =4) D-TSP (k = 6) D-TSP (k = 8)

Throughput at UE1

• Higher load on HSDPA channel





0

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0 18 36 54 72 90 108 126 144 162 180

Time (s)

Thro

ughp

ut (b

ps)

TSP D-TSP (k =2) D-TSP (k = 4) D-TSP (k = 6) D-TSP (k = 8)

Throughput at UE1






0

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0 18 36 54 72 90 108 126 144 162 180

Time (s)

Thro

ughp

ut (b

ps)

TSP D-TSP (k = 2) D-TSP (k = 4) D-TSP (k =6) D-TSP (k = 8)

Throughput at UE1






0

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0 18 36 54 72 90 108 126 144 162 180

Time (s)

Thro

ughp

ut (b

ps)

TSP D-TSP ( k =2) D-TSP (k =4) D-TSP (k = 6) D-TSP (k = 8)

Throughput at UE1




• performance peaks at k = 6


Results: Voice pdu discard ratio vs DB settings

Voice pdu discard loss

• assuming max DR= 2%

•In 1, 5, and 10 user scenarios VoIP QoS satisfied

•Optimum k for 20 users = 6

• optimum k for 30 users = 4

•Optimum k for 50 users = 2

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

TSP D-TSP (k=2) D-TSP (k=4) D-TSP (k=6) D-TSP (k=8)

% o

f VoI

P PD

Us d

ropp

ed b

y Di

scar

d Ti

mer

1 user 5 users 10 users 20 users 30 users 50 users


Results: HSDPA channel utilization vs DB settings

UE1 HSDPA channel utilization

•Utilization constant in DTSP regardless of DB setting in 1 user scenario

• channel utilization improves with higher load due to pdu bundling

• DTSP has better channel utilization than TSP except at very low load ( e.g. 1 user scenario)

0.48

0.5

0.52

0.54

0.56

0.58

0.6

0.62

0.64

0.66

0.68

TSP D-TSP (k =2) D-TSP (k=4) D-TSP (k=6) D-TSP (k=8)

UE

1 H

SDPA

Cha

nnel

Util

izat

ion

1 user 5 users 10 users 20 users 30 users 50 users


Conclusions and Summary

Conclusions:

DTSP achieves e-2-e throughput improvement for the multi-flow

NRTC traffic

Better channel utilization is achieved with DTS P over TSP

Acceptable VoIP performance within QoS constraints

Further work Investigate with other Packet Scheduling Investigate other possible multi-flow scenarios


Thank You!!!

Documents

A Dynamic Buffer Management Scheme for End-to-end QoS Enhancement of Multi-flow Services in HSDPA