Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / communications-1.1.1 / prbs_generator.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/>.
+
+## Implement book keeping for a Pseudo-Random Binary Sequence ( PRBS )
+## also called as a Linear Feedback Shift Register.
+## 
+## Given a polynomial create a PRBS structure for that polynomial.
+## Now all we need is to just create this polynomial and make it work.
+## polynomial must be a vector containing the powers of x and an optional
+## value 1. eg: x^3 + x^2 + x + 1 must be written as [3 2 1 0]
+## all the coefficients are either 1 or 0. It generates only a Binary \
+## sequence, and the generator polynomial need to be only a binary
+## polynomial in GF(2).
+## 
+## connections, contains a struct of vectors where each vector is the
+## connection list mapping its vec(2:end) elements to the vec(1) output.
+## 
+## 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 with a start state of [1 0 1 1]
+## will be:
+## 
+## prbs=prbs_generator([1 3 4],{[1 3 4]},[1 0 1 1]);
+## x = prbs_sequence(prbs) #gives 15
+## 
+## prbs_iterator( prbs, 15 ) #15 binary digits seen
+## [ 1   1   0   1   0   1   1   1   1   0   0   0   1   0   0 ]
+## 
+## See Also: This function is to be used along with functions 
+## prbs_iterator, and prbs_sequence.
+
+function prbs=prbs_generator(polynomial,connections,initstate)
+  prbs.reglen=max(polynomial);
+  prbs.polynomial=polynomial;
+  prbs.sregs=initstate;
+  prbs.connections=connections;
+  prbs.conlen=length(connections);
+end