Download A Dynamic Buffer Management Scheme for End-to

A Dynamic Buffer Management Scheme for End-to-end QoS
Enhancement of Multi-flow Services in HSDPA
Suleiman Y. Yerima, Khalid Al-Begain
Integrated Communications Research Centre
Faculty of Advanced Technology
University of Glamorgan
Outline

HSDPA overview

TSP queuing and BM schemes

Time-space priority BM

2
Dynamic Time-space priority BM

Simulation model

Results

Conclusions
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
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
External
Network
Core Network
User Equipments
Three interacting domains:

Core Network

Radio Access Network (RAN)

User Equipment (UE)
Iub interface
Node B
HSDPA CELL
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Radio Network
Controller
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)
External
Network
Core Network
User Equipments

L1 retransmissions (HARQ)

Shorter Transmission interval (2ms)
Iub interface
Node B
HSDPA CELL
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Radio Network
Controller
motivation:

Emergence of multiple flow traffic profile per user/connection

Existing HSDPA QoS mechanisms single flow based


Node B buffering

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E.g. MAC-hs Packet Scheduling (PS)
No BM schemes in standards- open issue
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
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
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
TSP queuing model
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 flow


RTC packets:

High priority delay

Low priority loss
Service
process
NRTC
flow
NRTC packets

High priority loss

low priority delay
Hence RTC => preferential transmission
NRTC =>preferential buffer admission
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TSP
threshold
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Transmission
to user
terminal

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

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Exploiting existing mechanisms in HSDPA specs.
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
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

UE1
N
H
Iub flow
control
algorithm to mitigate buffer overflow

UE1 MAC-hs buffer
RNC
L
UE2
Employs Discard Timer for RTC
R
Packet
Scheduling
Higher layer protocol (ARQ, TCP)
UE1 RT flow
performance improvement
UE1 NRT flow
TCP Source
UE3
UE
CN & EXTERNAL IP
Node B
RNC
Node B
Capacity Request {Priority, User Buffer Size (UBS)}
Capacity Allocation {Priority, Credits}
RNC
HARQ
HS-DSCH Frame {Priority, UBS, PDU size, #PDUs}
ARQ
Air interface
TCP
Iub interface
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
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 ,
N’T > H
0<β<1
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
10
is an EWMA of total queue size
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008

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
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
D-TSP
Incorporates delay Priority switching to TSP
RNC
UE1 MAC-hs buffer
UE1
DTSP priority switching algorithm:
N
IF RT packets < k AND RT HOL delay<
MAX_delay AND NRT packets > 0
Time Priority = NRT flow
Generate Transport Block from NRT PDUs
ELSE
Time Priority = RT flow
Generate Transport Block from RT PDUs
MAX_delay = Max e2e delay – other queuing and
propagation delays
H
Iub flow
control
L
RT
R
NRT
Priority
switching
k= Delay budget / RTC inter-arrival time
Delay budget ≤ MAX_delay
Discard timer (DT) setting = MAX_delay
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Packet
Scheduling
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
voice + data
connection
HSDPA
CELL
Node B
2ms
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RNC
20ms
Core Network
External Network
70ms
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
simulation set up
HSDPA Simulation Parameters
Concurrent VoIP + FTP for 180s
• MAX_delay = 250 –( 70 – 20) = 160ms
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
Performance metrics in test UE:
HARQ feedback delay
5ms
• End-to-end NRTC throughput
Test UE position from
Node B
0.2 km
• Voice PDU discard ratio (Discard timer)
Packet Scheduling
Round Robin
• % HSDPA channel utilization
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
• 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
RNC
Node B
14
2ms
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
20ms
70ms
Results: UE1 Data download throughput (1 user)
220000
200000
180000
160000
Throughput at UE1
Throughput (bps)
140000
• DTSP and TSP show similar
performance
120000
• Increased DB settings has
marginal effect on throughput
100000
80000
• very low HS-DSCH load hence no
DTSP gain
60000
40000
20000
0
0
18
36
54
72
90
108
126
144
162
180
Time (s)
TSP
15
D-TSP (k = 2)
D-TSP (k = 4)
D-TSP (k = 6)
D-TSP (k = 8)
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Results: UE1 Data download throughput (5 users)
160000
150000
140000
130000
120000
Throughput at UE1
Throughput (bps)
110000
100000
• More load on HSDPA channel
90000
• Increased DB settings show
noticeable improvement
80000
70000
• DTSP performs better than TSP
60000
50000
40000
30000
20000
10000
0
0
18
54
36
72
90
108
126
144
162
180
Time (s)
TSP
16
D-TSP (k = 2)
D-TSP (k = 4)
D-TSP (k = 6)
D-TSP (k = 8)
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Results: UE1 Data download throughput (10 users)
120000
110000
100000
90000
Throughput at UE1
Throughput (bps)
80000
• Higher load on HSDPA channel
70000
50000
• Increased DB settings show
noticeable improvement
40000
• DTSP performs better than TSP
60000
30000
20000
10000
0
0
18
36
54
72
90
108
126
144
162
180
Time (s)
TSP
17
D-TSP (k = 2)
D-TSP (k =4)
D-TSP (k = 6)
D-TSP (k = 8)
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Results: UE1 Data download throughput (20 users)
80000
75000
70000
65000
60000
Throughput at UE1
Throughput (bps)
55000
50000
• Higher load on HSDPA channel
45000
• Increased DB settings show
noticeable improvement
40000
35000
30000
• DTSP performs better than TSP
25000
20000
15000
10000
5000
0
0
18
36
54
72
90
108
126
144
162
180
Time (s)
TSP
18
D-TSP (k =2)
D-TSP (k = 4)
D-TSP (k = 6)
D-TSP (k = 8)
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Results: UE1 Data download throughput (30 users)
55000
50000
45000
40000
Throughput (bps)
35000
Throughput at UE1
30000
• Higher load on HSDPA channel
25000
• Increased DB settings show
noticeable improvement
20000
15000
• DTSP performs better than TSP
10000
5000
0
0
18
36
54
72
90
108
126
144
162
180
Time (s)
TSP
19
D-TSP (k = 2)
D-TSP (k = 4)
D-TSP (k =6)
D-TSP (k = 8)
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Results: UE1 Data download throughput (50 users)
34000
32000
30000
28000
26000
24000
Throughput at UE1
Throughput (bps)
22000
20000
• Higher load on HSDPA channel
18000
• Increased DB settings show
noticeable improvement
16000
14000
12000
• DTSP performs better than TSP
10000
8000
• performance peaks at k = 6
6000
4000
2000
0
0
18
54
36
72
90
108
126
144
162
180
Time (s)
TSP
20
D-TSP ( k =2)
D-TSP (k =4)
D-TSP (k = 6)
D-TSP (k = 8)
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Results: Voice pdu discard ratio vs DB settings
0.28
0.26
Voice pdu discard loss
0.24
• assuming max DR= 2%
% of VoIP PDUs dropped by Discard Timer
0.22
0.18
•In 1, 5, and 10 user
scenarios VoIP QoS satisfied
0.16
•Optimum k for 20 users = 6
0.14
• optimum k for 30 users = 4
0.12
•Optimum k for 50 users = 2
0.2
0.1
0.08
0.06
0.04
0.02
0
TSP
D-TSP (k=2)
1 user
21
5 users
D-TSP (k=4)
10 users
20 users
D-TSP (k=6)
30 users
D-TSP (k=8)
50 users
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Results: HSDPA channel utilization vs DB settings
0.68
0.66
UE 1 HSDPA Channel Utilization
0.64
UE1 HSDPA channel
utilization
0.62
0.6
•Utilization constant in DTSP
regardless of DB setting in 1
user scenario
0.58
0.56
• channel utilization
improves with higher load
due to pdu bundling
0.54
0.52
0.5
0.48
TSP
D-TSP (k =2)
1 user
22
5 users
D-TSP (k=4)
10 users
20 users
D-TSP (k=6)
30 users
D-TSP (k=8)
• DTSP has better channel
utilization than TSP except at
very low load ( e.g. 1 user
scenario)
50 users
NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
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
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008
Thank You!!!
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NGMAST ’08 International Conference, University of Glamorgan, Cardiff, Wales, Sept19th 2008