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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 lan 802 11

Wireless LAN802.11

Haithem AL-Balawi

outline
Outline
  • Background
  • Design Consideration and Assumptions
  • Results and Findings
  • Questions
background
Background
  • IEEE 802.11  Defines the Medium Access Control (MAC) and Physical Layer (PHY) specified for wireless connection
background1
Background
  • Components of the IEEE 802.11
background2
Network

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
background3
Background
  • DCF Operation
design consideration and assumptions
Design Consideration and Assumptions
  • 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
slide8
for i=1:length(Time_Access)

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

elseif (Ready_Tx >1)

N_Colision=N_Colision+1;

for z=1:length(Ready_STA)

N_Backoff(1,Ready_STA(z))=

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;

Ready_STA=0;

  • Algorithm

[min_N,indx_N]=min(N_Backoff);

Ready_Tx=0;

y=1;

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

STAs are ready to transmit

for a=1:N

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

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

Ready_STA(y)=a;

y=y+1;

Ready_Tx=Ready_Tx+1;

end

end

end

if (Ready_Tx ==1)

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

results and findings
Results and Findings
  • 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
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