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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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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
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 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 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 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 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 2 dl and ul ftp
Simulation_ scenario 2(DL and UL FTP)

To fix the total number of TCP transfers at 20

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
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