snpisma.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 6-10
% snpisma.m
%
% Slotted non-persistent ISMA 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]=snpisma(now_time)
global STANDBY TRANSMIT COLLISION PERMIT  % definition of the global variable
global Srate Plen Dtime
global Mnum Mplen Mstime Mstate
global Tint Rint
global Spnum Splen Tplen Wtime

persistent mgtime mtime slot          % definition of the static variable
if now_time <0                        % initialize access terminal
    rand('state',sum(100*clock));     % resetting of the random table
    mgtime=-Tint*log(1-rand(1,Mnum)); % packet generation time
    Mstime=zeros(1,Mnum)-inf;         % packet transmitting time 
    mtime=mgtime;                     % inhibit sensing time
    Mstate=zeros(1,Mnum);
    Mplen(1:Mnum)=Plen;               % packet length
    next_time=min(mtime);             % state change time
    slot=Plen/Srate*Dtime;            % idle slot length
    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 & Mstate==STANDBY);
                                      % finding of the terminal which
                                      % inhibit sensing
if length(idx)>0
    Tplen =Tplen+sum(Mplen(idx));
    for ii=1:length(idx)
        jj=idx(ii);
        if inhibitsense(jj,now_time)==0% channel is idle
            Mstate(jj) =PERMIT;        % packet transmitting
            [temp1 kk] =max(Mstime);   % calculation of the transmitting start time slot
            if temp1 <0
                mtime(jj) =ceil(now_time/slot)*slot;
            else
                temp1 =temp1+Mplen(kk)/Srate;
                temp2 =now_time-temp1;
                if temp2<0
                    mtime(jj)=temp1+slot;
                else
                    mtime(jj)=temp1+ceil(temp2/slot)*slot;
                end
            end
        else                                      % channel is busy
            mtime(jj)=now_time-Rint*log(1-rand);  % waiting time
        end
    end
end

idx=find(mtime==now_time & Mstate==PERMIT);
                                      % finding of the terminal which
                                      % carrier sensing
if length(idx)>0
    Mstate(idx) =TRANSMIT;
    Mstime(idx) =now_time;
    mtime(idx)  =now_time+Mplen(idx)/Srate;
                                      % end time of transmitting
end
next_time =min(mtime);                 % next state change time