csma.m

csma模型的仿真

function out=csma_depart(lambda,beta,q_r)
%***********************************************************************************
% lambda: total arrival rate of all stations
% beta: normalized duration of an idle slot
 %***********************************************************************************



i=1;
g=i*q_r+lambda*beta;


while g<2,    % i is the number of backlogged nodes
 
 a=g*exp(-g);
 b=exp(-g);
 Departure_csma(i)=a/(beta+1-b);
 Departure_csma_cd(i)=a/(beta + a + beta*(1 - b - a));
 arrival_rate(i)=lambda;
 i=i+1;
 g=i*q_r+lambda*beta;   % Expected number of attempted transmissions
                % Note: impact of retransmission rate q_r and the number of backlogged node
                %      are captured in  
 
end


figure;
plot([1:i-1],Departure_csma,'k-');
hold on;
plot([1:i-1],Departure_csma_cd,'k-o');
hold on;
plot([1:i-1],arrival_rate,'k--');
hold off;


set(gca,'FontSize',18);

%Title('Departure rate, in packets per unit time');
xlabel('N, the number of backlogged nodes');
legend('Departure rate of slotted CSMA','Departure rate of slotted CSMA/CD','Arrival rate',0);