Mercurial > forge
view main/comm/inst/prbs_sequence.m @ 9662:7e364201a793 octave-forge
prbs_generator, prbs_iterator, prbs_sequence: added copyright notice
author | carandraug |
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date | Tue, 13 Mar 2012 03:43:28 +0000 |
parents | a675f568ec92 |
children | 44714082301e |
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## Copyright (C) 2006 Muthiah Annamalai <muthuspost@gmail.com> ## ## 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/>. ## Implement book keeping for a Pseudo-Random Binary Sequence ( PRBS ) ## also called as a Linear Feedback Shift Register. ## ## For the given PRBS in a intial state, compute the PRBS sequence length. ## Length is period of output when the PRBS state is same as ## the start state of PRBS. ## ## 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_sequence(prbs) #gives 15 ## ## ## See Also: This function is to be used along with functions ## prbs_generator. function [itrs,seq]=prbs_sequence(prbs) if nargin < 1 error("usage: prbs_sequence(prbs struct ); \ create the prbs sequence using prbs_generator() function. \ This function generates the ML length sequence of 1 period\ and returns to the user.") end nstate=zeros(1,prbs.reglen); itrs=0; seq = []; inits = prbs.sregs; ## For each iteration, shift the output bit. Then compute the xor pattern of connections. ## Finally apply feedback the stuff. Insert the computed pattern. while( true ) itrs = itrs + 1; ## 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))); end nstate(prbs.connections{itr2}(1))=val; end ## rotate the output discarding the last output. seq = [seq, prbs.sregs(end)]; 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. end if(isequal(prbs.sregs,inits)) break; end end end