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[CreaPhase.git] / octave_packages / communications-1.1.1 / prbs_iterator.m

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+## Copyright (C) 2006 Muthiah Annamalai <muthiah.annamalai@uta.edu>
+##
+## This program is free software; you can redistribute it and/or modify it under
+## the terms of the GNU General Public License as published by the Free Software
+## Foundation; either version 3 of the License, or (at your option) any later
+## version.
+##
+## This program is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+## details.
+##
+## You should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## This function generates the output bits from the PRBS
+## state, for the number of iterations specified.
+##
+## First argument is the PRBS structure obtained from prbs_generator.
+## PRBS iterations is specified in the second argument.
+## PRBS start state is taken from the prbs.sregs.
+##
+## Second argument of the output is PRBS structure with a new
+## state. This allows usage like: 
+## 
+## [ seq, prbs ] =  prbs_iterator( prbs, niterations );
+## 
+## while the state of the PRBS is updated.
+## 
+## Example: If you had a PRBS shift register like the diagram
+## below with 4 registers we use representation by polynomial
+## of [ 1 2 3 4], and feedback connections between [ 1 3 4 ].
+## The output PRBS sequence is taken from the position 4.
+## 
+##  +---+    +----+   +---+   +---+
+##  | D |----| D  |---| D |---| D |
+##  +---+    +----+   +---+   +---+
+##    |                 |       |
+##    \                 /      /
+##    [+]---------------+------+
+##   1   +    0.D   + 1.D^2 + 1.D^3
+##
+## The code to implement this PRBS will be 
+## prbs=prbs_generator([1 3 4],{[1 3 4]},[1 0 1 1]);
+## x = prbs_iterator(prbs,15)
+## 
+## See Also: This function is to be used along with functions 
+## prbs_iterator, prbs_generator and prbs_sequence.
+
+function [outputseq, prbs] = prbs_iterator (prbs, iterations = 2^(prbs.reglen)-1)
+
+  if ( nargin < 1 || nargin > 2 )
+    print_usage;
+  endif
+  outputseq=zeros(1,iterations);
+  nstate=zeros(1,prbs.reglen);
+  
+  ## For each iteration, shift the output bit. Then compute the xor pattern of connections. 
+  ## Finally apply feedback the stuff. Insert the computed pattern.
+  for itr=1:iterations
+    ## save output.
+    outputseq(itr)=prbs.sregs(prbs.reglen);
+    
+    ## compute the feedback.
+    for itr2=1:prbs.conlen
+      val=0;
+      L=length(prbs.connections{itr2});
+      for itr3=2:L
+        val=bitxor(val,prbs.sregs(prbs.connections{itr2}(itr3)));
+      endfor
+      nstate(prbs.connections{itr2}(1))=val;
+    endfor
+    
+    ## rotate the output discarding the last output.
+    prbs.sregs=[0 prbs.sregs(1:prbs.reglen-1)];
+
+    ## insert the feedback.
+    for itr2=1:prbs.conlen
+      prbs.sregs(itr2)=nstate(itr2);
+      nstate(itr2)=0; # reset.
+    endfor
+    
+  endfor
+endfunction
+
+##
+##  TEST CASES FOR PRBS.
+##
+##
+##  2^31 -1 : D31 + D28 + 1 =0  inverted 
+##  2^23 -1 : D23 + D18 + 1 = 0 ,
+##  2^15 -1 : D15 + D14 + 1 = 0,
+##  2^10 -1 : D10 + D7 + 1 = 0,
+##  2^7  -1 : D7 + D6 + 1 = 0,
+##  2^4  -1 : D3 + D2 + 1 = 0,
+##
+##  +---+    +----+   +---+   +---+
+##  | D |----| D  |---| D |---| D |
+##  +---+    +----+   +---+   +---+
+##    |                 |       |
+##    \                 /      /
+##    [+]---------------+------+
+##   1   +    0.D   + 1.D^2 + 1.D^3
+##
+##
+## prbs=prbs_generator([1 3 4],{[1 3 4]},[1 0 1 1]);
+## x = prbs_iterator(prbs,15)
+## y = prbs_iterator(prbs,30)(16:end)
+## z = prbs_sequence(prbs)
+## exit
+## break
+
+##
+## Multiple Tap, Simple Sequence Generator.
+##
+## n=10;
+## k=8;
+## inits=round(abs(rand(1,n)*1.0))
+## prbs=prbs_generator([n 1],{[1 2 k n-1 n]},inits);
+## prbs_iterator(prbs,1023)
+## prbs_seqlength(prbs,inits)
+
+##prbs=prbs_generator([1 2 3],{[1 2 3]},[1 1 1]);
+##prbs_iterator(prbs,7)
+
+##
+##  2^4  -1 : D4 + D1 + 1 = 0,
+##
+##  +---+    +----+   +---+   +---+
+##  | D |----| D  |---| D |---| D |
+##  +---+    +----+   +---+   +---+
+##    |        |                |
+##    \        /                /
+##    [+]---------------+------+
+##   1   +    0.D   + 1.D^2 + 1.D^3
+##
+##prbs=prbs_generator([1 3 4],{[1 2 4]},[1 0 1 1]);
+##prbs_iterator(prbs,16)
+##prbs_iterator(prbs,32)
+
+
+##prbs=prbs_generator([7],{[1 7 6]},[1 0 0 1 0 0 0]);
+##y=prbs_iterator(prbs,128);
+##x=prbs_iterator(prbs,256);