# Coding theory question

• Oct 8th 2008, 06:23 PM
wik_chick88
Coding theory question
an error correction encoding/decoding system for storing 4 digit binary sequences is set up using a 5-frame delay cross-interleave of two codes \$\displaystyle C_{1}\$ and \$\displaystyle C_{2}\$. The code \$\displaystyle C_{1}\$ has length 7, distance 3 and has the 4 digit binary strings as the message words for the code. The code \$\displaystyle C_{2}\$ is the first-order Reed-Muller code \$\displaystyle R(6)\$. The data is stored as a sequence of binary digits on the tape with no alteration (eg modulation) other than the error correction encoding.

(a) The system must be designed so that for some interger r, received words which are distance r or greater from a \$\displaystyle C_{2}\$ codeword have all their symbls marked as erasures. Received words at distance less than r must be corrected by the \$\displaystyle C_{2}\$decoder and the number of errors which the \$\displaystyle C_{2}\$decoder corrects must be maximised. However, it is also required that the chance of a random received word (which is a random sequence of 64 binary digits as a result of a burst error) being
undetected by the
\$\displaystyle R(6)\$ decoder is less than 1 × \$\displaystyle 10^-11\$. Find r.

(b)
Determine the smallest integer t such that there is a burst error of length t that the system cannot correct (in the presence of no other errors).

• Oct 8th 2008, 06:25 PM
wik_chick88
sorry the last part of (a) should read:

being undetected by the \$\displaystyle R(6)\$ decoder is less than 1 x \$\displaystyle 10^-11\$. Find r.
• Oct 8th 2008, 06:26 PM
wik_chick88
Quote:

Originally Posted by wik_chick88
sorry the last part of (a) should read:

being undetected by the \$\displaystyle R(6)\$ decoder is less than 1 x \$\displaystyle 10^-11\$. Find r.

grrr its 1 x \$\displaystyle 10^(-11)\$
• Oct 8th 2008, 06:26 PM
wik_chick88
Quote:

Originally Posted by wik_chick88
grrr its 1 x \$\displaystyle 10^(-11)\$

nope its \$\displaystyle 10^{-11}\$