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Dynamic Bandwidth Allocation for 802.16E-

2005 MACSpeaker：黃筱婷

Date： 2010/10/22

2

Outline

Introduction

Overview of the MAC Protocol

Bandwidth Allocation scheme

Two-Phase Proportionating

Simulation

Conclusion

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IEEE 802.16 Deployment

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GPC and GPSS

Grand Per Connection(GPC) Not flexible for SSs to be adaptive to connections of

real-time applications. Not supported by the standard.

Grand Per Subscriber Station(GPSS) BS grants requested bandwidth to each SS. SS can flexibly respond to different QoS

requirements of the connections.

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IEEE 802.16 Protocol Model

Sending entity(ex: SS)

SDU

PDU

Receiving entity(ex: BS)

SDU

PDU

Wireless channel

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TDD V.S. FDD

Time-Division Duplex(TDD)

Frequency-Division Duplex(FDD)

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Outline

Introduction

Overview of the MAC Protocol

Bandwidth Allocation scheme

Two-Phase Proportionating

Simulation

Conclusion

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QoS Architecture for IEEE 802.16 MAC Protocol

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Frame Structure for TDD System

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OFDMA

Orthogonal Frequency-Division Multiple Access (OFDMA) Multi-user version of the popular Orthogonal frequency-

division multiplexing (OFDM) digital modulation scheme. Advantage: highly suitable for broadband wireless networks,

scalability, MIMO-friendliness, and ability to take advantage of channel frequency selectivity.

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OFDMA Mapping

Subchannel allocation in the DL may be performed in the following ways: FUSC(Full Usage of Subchannels) PUSC(Partial Usage of Subchannels)

For DL/UL FUSC, one slot is one subchannel by one OFDMA symbol. For DL PUSC, one slot is one subchannel by two OFDMA symbols. For UL PUSC, one slot is one subchannel by three OFDMA symbols.

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QoS Classes

QoS Category Application QoS Specification

UGSUnsolicited Grant

ServiceT1/E1

Transport•Maximum Sustained Rate•Maximum Latency Tolerate•Jitter Tolerance

rtPSReal-Time Polling

ServiceVoIP

•Minimum Reserved Rate•Maximum Sustained Rate•Maximum Latency Tolerate•Traffic Priority

ErtPSExtended Real-Time

Polling ServiceMPEG Video

•Minimum Reserved Rate•Maximum Sustained Rate•Maximum Latency Tolerate•Jitter Tolerance•Traffic Priority

nrtPSNon-Real-Time Polling

ServiceFTP

•Minimum Reserved Rate•Maximum Sustained Rate•Traffic Priority

BEBest-Effort Service HTTP •Maximum Sustained Rate

•Traffic Priority

priority

高

低

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Outline

Introduction

Overview of the MAC Protocol

Bandwidth Allocation scheme

Two-Phase Proportionating

Simulation

Conclusion

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Deficit Round Robin(DRR)

每個 data flow 會有一初始值為零的 deficit counter 依序檢視並嘗試傳送封包前，先檢查該 data flow 最前面的封包大小是否小於等於 deficit counter 內的值

是 : 傳送出去，並將 deficit counter 扣掉此封包的大小，重覆執行此步驟直到該 data flow 最前面的封包大小已超過欠額計數器內的值再換下一個 data flow 被服務 否 : 不傳送，把該 deficit counter 累加上一個固定數值

(quantum) ，等待下一輪再被服務

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Deficit Fair Priority Queue(DFPQ)

結合 Deficit Round Robin(DRR) and priority ，限制某類資料流在一個 frame 中能夠傳送的資料量，與不同類資料流之間以 priority 方式進行頻寬配置。 在使用 DFPQ 前須對連線種類及方向做優先權分類，其區分規則為 rtPS>nrtPS>BE ， Downlink>Uplink 。

Quantum size ： rmax(i,j) 為 the Maximum Sustained traffic rate of the jth connection in the ith class of service flow

Ji

j

jiriQuantum0

max ,][

1 2 3 4 5 6DL-rtPS UL-rtPS DL-nrtPS UL-nrtPS DL-BE UL-BE

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DFPQ(cont.)

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Strict Priority(SP)

Packets in higher priority queues always transmit before packets in lower priority queues.

A lower priority queue has a chance to transmit packets only when there are no packets waiting in a higher priority queue.

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Outline

Introduction

Overview of the MAC Protocol

Bandwidth Allocation scheme

Two-Phase Proportionating

Simulation

Conclusion

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MAC Protocol

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Overview of the Algorithm

IEEE 802.16 頻寬配置的目標是確實填滿整個 TDD time frame ，但是 uplink 跟 downlink subframe 的比例是可以動態調整的。

此演算法分為兩個階段。第一個階段根據 SS 之 DL 與 UL的要求來決定 subframe sizes 的大小 第二個階段是根據的 QoS 參數 (ex: weight, 反映實際需求的調節因子 A-factor) 來分配頻寬給每個不同連線的

queue 。 Finally the TPP adheres to the GPSS by granting SSs

the allocated bandwidth of each queue.

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TWO-PHASE PROPORTIONATING

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Bandwidth Translation and Slot Dispatching

在 BS 從 backbone network 收到 data traffic 或收到uplink bandwidth request 後， TPP 就會先把所要求的頻寬 (bytes) 轉換成 OFDMA 的 slots ，因為 slot 是PHY 傳輸的基本單位。

這些 slot 被分配給相對應的 service queue ，包括了五種 uplink classes with/o latency guarantee 。 每個 queue 使用三個變數：

the bandwidth request slots (BRQ) ，用來計算 request slots 的個數

Rmax ，計算 Maximum sustained traffic rate (MSTR) Rmin ，計算 minimum reserved traffic rate (MRTR)

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First Phase

Goal : Dividing a Frame into Downlink and Uplink Subframes

UR and DR : the BRQ of the uplink and downlink. S : # of symbols in a frame.

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Second Phase

Goal : Allocating Subframes to Queues. Rmin of all queues are firstly satisfied for minimum

slots guarantee, followed by the proportionating of the remaining slots to queues except the UGS and ertPS whose requested slots are already served.

In order to avoid bandwidth waste and starvation, we use an adjustment factor(A-factor)=

The remaining slots are therefore allocated according to the following proportion

minmax

min

RRRBRQ

BEBEBE

BEBEnrtPS

nrtPSnrtPS

nrtPSnrtPSrtPS

rtPSrtPS

rtPSrtPS

RRRRBRQR

RRRBRQR

RRRBRQ

maxminmax

minmax

minmax

minmax

minmax

min ::

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Example

For Phase 1 ： UR = 60, DR = 40, S=26 　　 x = 3,

　 indicating 6x/3 = 6 slot columns for uplink while (26-6x)/2 = 4 slot columns for downlink. If we use direct proportion, however, the number of symbols for uplink is 26×[60 /(60 + 40)] 16, in ≅which only 15 symbols are effective.

For Phase 2 ：

xSx

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321

4060

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Outline

Introduction

Overview of the MAC Protocol

Bandwidth Allocation scheme

Two-Phase Proportionating

Simulation

Conclusion

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Simulation Setup

One BS serving 20SSs, and 2 remote stations including an FTP server and voice end point.

5 service classes are supported and each class involves 4 SSs.

UL and DL channel capacity is 10.24 Mbps and the frame duration is 5ms.

Rmax of rtPS, nrtPS and BE are 8,6, and 4, respectively, while Rmin are 4,2, and 1, respectively.

Subframe Allocation: Static vs. Dynamic

The FTP traffic load of the downlink is 3 times of the link.

By stealing the unused uplink slot columns for the downlink, TPP improves the overall link utilization from 75% to 96%.

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Effectiveness of the A-Factor

Grant Ratio = If Grant Ratio >1, resulting bandwidth waste. In BE, is not feasible because it tends to favor classes

with a small Rmin which oftentimes is BE, and therefore violates the spirit of service differentiation.

# #

slotsrequestedslotsallocated

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Service Differentiation

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Bandwidth Utilization

From the figure we can learn that the bandwidth utilizations of the three algorithms increase linearly but start to decrease when hitting a certain level: 85.5% for TPP, 80.6% for DFPQ and 68.4% for SP.

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Bandwidth Utilization(cont.)

Each class has an unused portion, which occurs during the translation from requested bytes to slots. Since the calculation, namely dividing the requested bytes by slot size, always rounds up, the resulted assignment is often larger than expected.

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Bandwidth Utilization(cont.)

Assuming that a slot contains 64 bytes, the # of requested slots is thus 4, causing 256 – 213 = 43 bytes waste.

TPP : breadth-firstly ; DFPQ : depth-firstly

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Outline

Introduction

Overview of the MAC Protocol

Bandwidth Allocation scheme

Two-Phase Proportionating

Simulation

Conclusion

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Conclusion

這個方法考慮了 IEEE 802.16 中會出現的頻寬配置問題，所提出的 TPP 頻寬配置演算法能更好的利用頻寬資源並且支援 service differentiation 。 同時考慮了 uplink 和 downlink 的頻寬配置所以能夠動態的調整頻寬配置的內容。 模擬的結果證明了此演算法在第一階段能夠增加 20%的頻寬利用率；並且在第二階段能夠適當的達到

service differentiation 。

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Future Work

對各種排程方法做更深入的研究在考量 802.16 網路有 QoS 效能並具有較佳的頻寬分配之下，找出合適的演算法。利用 Self-Similar 的特性，找出最合乎現實狀況的的 Traffic Model 來做演算法的模擬及驗證。

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Reference

[1] IEEE Std 802.16-2009[2] Y. N. Lin, S. H. Chien, Y. D. Lin, Y. C. Lai, and M. Liu, "Dynamic

Bandwidth Allocation for 802.16e-2005 MAC," in Current Technology Developments of WiMax Systems, edited by Maode Ma, Springer Netherlands, 2009, pp. 17-29.

[3] A. Ganz, Z.Ganz and K.Wongthavarawat ,Multimedia Wireless Networks: Technologies, Standards, and QoS, Prentice Hall PTR, 2003, ch.7

[4] L. Nuaymi, WiMAX: Technology for Broadband Wireless Access, Wiley, 2007, ch.11

[5] K. Etemad, Overview of Mobile WiMAX Technology and Evolution, IEEE Communications Magazine, pp. 31-40, October 2008 

[6] 林衣修 . “ 一種基於 QoS 與 Overhead 考量之二維 OFDMA 配置方法 ” , 中央大學通訊所 , July 2007

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