CMPUT 640Resource Allocation In Networks

Final Project Presentation

TopicDynamic Tuning of RTS Threshold in IEEE802.11 based on

Packet Distribution of Network

Presented ByMohammad Saiful Islam

Student # 1270123

Outline

IEEE 802.11 IEEE 802.11 MAC A Balanced Intermix Previous Work Relatively Small Dynamic RTS Threshold Calculation Simulation Discussion

IEEE 802.11

Standard for Medium Access Control (MAC) & Physical Layer in wireless LAN

Ad-Hoc (DCF) & Infrastructure (PCF) Mode in MAC layer

Distributed Co-ordination Function (DCF)○ Basic & RTS/CTS based scheme

Basic Scheme○ Physical Carrier Sensing○ DATA – ACK○ Hidden Node Problem

IEEE 802.11 MAC Request to send (RTS)/Clear to send (CTS)

○ RTS - CTS - DATA - ACK○ Virtual Carrier Sensing○ Solves Hidden & Exposed Node Problems○ Problems [1]

— Virtual Jamming— Inhibiting non-interfering parallel transmission— False blocking

RTS Threshold (RT) value decides which scheme to use for each packet

Packet size >= RT → use RTS/CTS scheme else use Basic scheme

IEEE 802.11 MAC cont..

Basic scheme

RTS/CTS scheme

A Balanced Intermix Continue with both schemes in a balanced way Small packets => Low collision probability => Basic

scheme Large packets => High collison probability =>

RTS/CTS scheme

So smaller η% with Basic & larger (1-η)% with RTS/CTS

Problems with fixed RT○ Packet size can not be predicted before○ All packets may be smaller than the value○ Opposite can be also true

Previous Works

Author Basis of Tuning Assumptions

Shaohu et al. [2] Minimizing average time spent in successful and unsuccessful transmission

Homogenous traffic, negligible channel noise, no hidden node problem, static nodes

Liu et al. [3] Minimizing time overhead of packet transmission

No hidden node problem, static nodes

Zhang et al. [4] Minimizing time between two successful transmissions

Single-hop network, no hiddennode problem, fixed number ofnodes, static nodes

Mjidi et al. [5] Packet Delivery Ratio Static nodes

Huei-Jiun et al. [6] Use ”Waiting for CTS timeout” asthreshold

Ideal channel, linear network, static nodes

Ahsan et al. [7] Exploiting packet distribution toensure certain amount of packetsuse Basic Scheme

Static Nodes

Relatively Small Proposal

○ Use Basic scheme for relatively small sized packets and RTS/CTS scheme for relatively large packets

○ Set RT dynamically so that η% packet is lower than this value

Implementation○ Node has generated or received packet of size

○ Increase frequency count for that size

○ Do this in each interval of size δ○ After the end of each interval

— Adjust RT based on frequency count of the previous interval

— Reset frequency counter

sif i

Dynamic RTS Threshold Calculation

α is the memory factor

is the greatest probability less than or equal to η

is the packet size at

is the least probability greater than η

is the packet size at

RT current=[P s−P r∗C s−P s

C r−Pr]

RT average=[∗RT prev1−∗RT current ]

Pr

P s

C rC s

C r

Pr

Pi=Pr {Ssi}=∑j=1

i

f j

∑k=1

n

f k

Queuing Analysis

The average arrival rate is 13.58 packet/s with a confidence interval of 0.000327.

The average throughput is 13.024 with a confidence interval of 0.00028.

Simulation

NS-3 Simulator

Area 1000 * 1000 unit

Random Walk 2d Mobility Model

○ Speed 0.1 m/s

○ Nodes change direction in every 50 sec IEEE 802.11b in Ad-Hoc mode

Multi-hop network

1 source – destination pair for each 10 nodes

○ Source generates UDP packets

○ Packet inter arrival time and size exponentially distributed Routing Protocol – AODV and Static

Simulation Cont...

Independent variables

○ η = 0 to 100 in step of 10

○ Number of nodes 30, 50, 70

○ Packet Generation Rate 1, 2, 3 packet/sec Performance Metric

○ System Throughput

○ Total bytes received in all destination application layer

Simulation Cont...

Simulation Cont...

Simulation Cont...

References

[1] Ashikur Rahman and Pawel Gburzynski. Hidden problems with the hidden node problem. In 23rd Biennial Symposium on Communications- QBSC 2006, pages 270–273, 2006.

[2] Shiqi Wu-Wei Guo Shaohu Yan, Yongning Zhuo. Adaptive RTS threshold for maximum networkthroughput in IEEE 802.11 DCF. volume 5284, pages 332–343, 2004.

[3] Bai long Xiao Fei Huang Jun Liu, Wei Guo. RTSthreshold adjustment algorithm for IEEE 802.11 DCF.In 6th International Conference on ITS Telecommunications, pages 654–658, 2006.

[4] Liang Zhang and Yantai Shu. Rts threshold self-tuning algorithm based on delay analysis on 802.11 dcf. volume 1, pages 627 – 630, sep. 2005.

[5] Naoki Nakamura Kazuhide Koide Atushi Takeda Norio Shiratori Mostafa Mjidi, Debasish Chakraborty. Anew dynamic scheme for effcient RTS threshold handling in wireless networks. In 22nd International Conference on Advanced Information Networking and Applications, pages 734–740, 2008.

Reference cont...

[6] Yen-Cheng Kuan Huei-Jiun Ju, Izhak Rubin. An adaptive RTS/CTS control mechanism for IEEE 802.11 MAC protocol. Vehicular Technology Conference, 2003. VTC 2003-Spring. The 57th IEEE Semiannual, 2:1469– 1473, 2003

[7] S.M.R. Ahsan, M.S. Islam, N. Hassan, and A. Rahman. Exploiting packet distribution for tuning rtsthreshold in ieee 802.11. pages 369 –372, may. 2010.