paloha.m

系统分别对无线通信中的几种重要的多址接入协议进行了仿真

% Program 6-6
% paloha.m
%
% Pure ALOHA System
%
% Input argument
% now_time :now time but,now_time<0 initializes
% the access terminals
%
% Output argument
% next_time :next state change time
%
function [next_time]=paloha(now_time);
global STANDBY TRANSMIT COLLISION     % definition of the global variable
global Srate Plen
global Mnum Mplen Mstate
global Tint Rint
global Spnum Splen Tplen Wtime
persistent mgtime mtime               % definition of the static variable
if now_time<0                         % initialize access terminals
    rand('state',sum(100*clock));     % resetting of the random table
    mgtime    =-Tint*log(1-rand(1,Mnum));% packet generation time
    mtime     =mgtime;                % packet transmitting time
    Mstate    =zeros(1,Mnum);
    Mplen(1:Mnum)=Plen;               % packet length
    next_time =min(mtime);
    return
end
idx=find(mtime==now_time & Mstate==TRANSMIT);
                                      % finding of the terminal which
                                      % transmission succeeded
if length(idx)>0
    Spnum      =Spnum+1;
    Splen      =Splen+Mplen(idx);
    Wtime      =Wtime+now_time-mgtime(idx);
    Mstate(idx)=STANDBY;
    mgtime(idx)=now_time-Tint*log(1-rand);% next packet generation time
    mtime(idx)=mgtime(idx);            % next packet transmitting time
end
idx=find(mtime==now_time & Mstate==COLLISION);
                                       % finding of the terminal which
                                       % transmission failed
if length(idx)>0
    Mstate(idx)=STANDBY;
    mtime(idx)=now_time-Rint*log(1-rand(1,length(idx)));% resending time
end
idx=find(mtime==now_time);             % finding of the terminal which
                                       % transmission start
if length(idx)>0
    Mstate(idx) =TRANSMIT;
    mtime(idx)  =now_time+Mplen(idx)/Srate;
                                       % end time of transmitting
    Tplen       =Tplen+sum(Mplen(idx));
end
next_time=min(mtime);                  % next state change time

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