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Adaptive Downlink and Uplink Channel Split Ratio Determination for TCP-Based Best Effort Traffic in TDD-Based WiMAX Networks. Chih-He Chiang, Wanjiun Liao, Tehuang Liu, Iam Kin Chan, and Hsi-Lu Chao National Taiwan University

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Chih he chiang wanjiun liao tehuang liu iam kin chan and hsi lu chao

Adaptive Downlink and Uplink Channel Split Ratio Determination for TCP-Based Best Effort Traffic in TDD-Based WiMAX Networks

Chih-He Chiang, Wanjiun Liao, Tehuang Liu, Iam Kin Chan, and Hsi-Lu Chao

National Taiwan University

IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 27, NO. 2, FEBRUARY 2009


Outline

Outline

  • Introduction

  • Adaptive bandwidth allocation for DL and UL

  • Simulation

  • Conclusion


Introduction

Introduction


Introduction1

Introduction

  • To determine the ratio of downlink to uplink bandwidth capacities between the BS and SSs is a challenge.

  • The last mile access for residential users tends to be asymmetric

    • more demands on downloading and less on uploading.

  • An equal split between the uplink and downlink channels may lead to inefficient bandwidth utilization.

    • Ex: TCP traffic


Introduction goal

BS

BS

Data

Ack

Data

Ack

SS

SS

Introduction_ Goal

?


Adaptive bandwidth allocation for dl and ul

Adaptive bandwidth allocation for DL and UL

  • Overview

  • Bandwidth Asymmetry Ratio for TCP over a Direct Link

  • Bandwidth Asymmetry Ratio for TCP over WiMAX

  • Adaptive Channel Split Ratio Adjustment Mechanism


Adaptive bandwidth allocation for dl and ul overview

Adaptive bandwidth allocation for DL and UL_ Overview

asymmetry ratio k for one-way TCP transfers

the average delay for an SS sending twoconsecutive packetsout from the queue

derive

the asymmetryratio for downloading users, denoted by ηd

derive

derive


Adaptive bandwidth allocation for dl and ul overview1

Adaptive bandwidth allocation for DL and UL_ Overview

derive

derive

Total number of time slots allocated for downlink channel

Total number of time slots allocated for uplink channel (do not contain contention slots)

Total number of time slots allocated for uplink channel (contain contention slots)

derive

Total number of time slots allocated for downlink channel


Adaptive bandwidth allocation for dl and ul1

Adaptive bandwidth allocation for DL and UL


Adaptive bandwidth allocation for dl and ul bandwidth asymmetry ratio for tcp over a direct link

Adaptive bandwidth allocation for DL and UL_ Bandwidth Asymmetry Ratio for TCP over a Direct Link

The downlink channel capacity in terms of bps

÷

The size of one TCP data packet in terms of bits

derive

asymmetry ratio k for one-way TCP transfers

K≧1, TCP operates normally


Adaptive bandwidth allocation for dl and ul bandwidth asymmetry ratio for tcp over wimax

Adaptive bandwidth allocation for DL and UL_ Bandwidth Asymmetry Ratio for TCP over WiMAX

asymmetry ratio k for one-way TCP transfers

d is the delayed ACK parameter (i.e., sending one

ACK packet per d data packets)

the average delay for an SS sending two consecutive packets

out from the queue

the asymmetryratio for downloading users, denoted by ηd

The number of downloading TCP transfers


Adaptive bandwidth allocation for dl and ul2

Adaptive bandwidth allocation for DL and UL

BS

BS

Data

Ack

Data

Ack

SS

SS


Adaptive bandwidth allocation for dl and ul bandwidth asymmetry ratio for tcp over wimax1

Adaptive bandwidth allocation for DL and UL _ Bandwidth Asymmetry Ratio for TCP over WiMAX

One slot time in terms of sec

Total number of time slots


Adaptive bandwidth allocation for dl and ul3

Adaptive bandwidth allocation for DL and UL

2

1

3

4

2+12

*

+2 +12

Ex:

2


Adaptive bandwidth allocation for dl and ul bandwidth asymmetry ratio for tcp over wimax2

Adaptive bandwidth allocation for DL and UL _ Bandwidth Asymmetry Ratio for TCP over WiMAX

The goal is to make ηd ≤ 1 and ηu ≤ 1.


Adaptive bandwidth allocation for dl and ul4

Adaptive bandwidth allocation for DL and UL

derive


Adaptive bandwidth allocation for dl and ul5

Adaptive bandwidth allocation for DL and UL

derive


Adaptive bandwidth allocation for dl and ul6

Adaptive bandwidth allocation for DL and UL


Adaptive channel split ratio adjustment mechanism

Adaptive Channel Split Ratio Adjustment Mechanism

BS

ndSS and nuSS

SS

SS

SS

SS

  • Step1:

    • BS retrieves the information about ndSS and nuSS

  • Step2:

    • Ensure that the bandwidth asymmetry ratios for both downloading and uploading TCP transfers are each equal to one

  • Step3:

    • After the ratio of n to m is determined at Step 2, we can adjust the split between uplink and downlink


Simulation

Simulation

  • NS2 simulator

  • Link capacity is 25.4 Mbps,

  • Time slot is 0.5 μs,

  • Nc = 650, and Nf = 10000 slots.

  • Each TCP packet has a fixed length of 1000 bytes

  • The size of ACK packet is 40 bytes.


Simulation scenario 1 downloading ftp

Simulation_ scenario 1(downloading FTP)


Simulation scenario 1 downloading ftp1

Simulation_ scenario 1(downloading FTP)


Simulation scenario 1 downloading ftp2

Simulation_ scenario 1(downloading FTP)


Simulation scenario 2 dl and ul ftp

Simulation_ scenario 2(DL and UL FTP)

To fix the total number of TCP transfers at 20


Simulation scenario 2 dl and ul ftp1

Simulation_ scenario 2(DL and UL FTP)


Simulation scenario 2 dl and ul ftp2

Simulation_ scenario 2(DL and UL FTP)


Conclusions

Conclusions

  • Adaptive Split Ratio (ASR) scheme is proposed to adjust the downlink to uplink capacity ratio adaptively

  • ASR can cooperate with the BS scheduler to throttle the TCP source when acknowledgements are transmitted infrequently


Chih he chiang wanjiun liao tehuang liu iam kin chan and hsi lu chao

Thank you~


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