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Wireless LAN 802.11 - PowerPoint PPT Presentation

Wireless LAN 802.11. Haithem AL-Balawi. Outline. Background Design Consideration and Assumptions Results and Findings Questions. Background. IEEE 802.11  Defines the Medium Access Control (MAC) and Physical Layer (PHY) specified for wireless connection. Background.

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Wireless LAN802.11

Haithem AL-Balawi

• Background

• Design Consideration and Assumptions

• Results and Findings

• Questions

• IEEE 802.11  Defines the Medium Access Control (MAC) and Physical Layer (PHY) specified for wireless connection

• Components of the IEEE 802.11

PCF

MAC

DCF

PHY

Background

• MAC Overview

• Distributed Coordination Function (DCF) is the Media Access Function of 802.11 MAC and used for contention services

• Point Coordination Function (PCF) is used for contention free services

• DCF Operation

• STAs are transmitting randomly through a Bernoulli distribution

• Hidden STAs are ignored

• CW is randomly and equally likely selected between [0 CW]

• STA will transmit whenever it’s P_STA >P_Tx

if (Time_Access(1,i)==0)

N_Colision=N_Colision+1;

randint(1,1,[1 2^randint(1,1,CW-1)]);

end

end

clear all

STA=50; %Number of Terminals

P_Tx=0.5;

for N=1:STA

data_Tx=10; %Transmitted data size

IFS=2; %Interframe Space size

%N_Success=zeros(1,N); % Number of successful trials

CW=5; %Contention Wendow

Time_Access=zeros(1,100000);

N_Backoff=zeros(1,N); %Backoff Counter for each STA

N_Count=zeros(1,N);

IFS_Count=0;

Idle=0;

N_Colision=0;

• Algorithm

[min_N,indx_N]=min(N_Backoff);

y=1;

if (min_N ==0) %Backoff timer is "0" if not non of the

for a=1:N

if (N_Backoff(1,a) ==0)

if (P_STA(1,a) >= P_Tx)

y=y+1;

end

end

end

Time_Access(1,i:i+data_Tx-1)=indx_N;

N_Backoff(1,indx_N)=randint(1,1,[1 2^randint(1,1,CW-1)]);

Time_Access(1,i+data_Tx:i+data_Tx+IFS-1)=-1;

else

N_Backoff=N_Backoff-1;

end

• System Behavior for Random Access

• the throughput is high for large number of STAs (65% for 50 STA)

• the number of collided attempts is almost negligible

• by using longer data packet size throughput improves