FOUR WEEKS PROJECT TOPIC: ERROR DETECTION AND CORRECTION GROUP MEMBERS: ALEX NYARKO ANTHONY TSETSE BENJAMIN BOATENG SUPERVISOR: ZOLTAN SAFAR DATE: JUNE 28, 2004

Summary of Project objective Investigation of various error detection and correction mechanisms. Design and implementation of elements of a typical error detection mechanism (CRC) Concepts of message Segmentation of Message data (blocks) Each block has K fixed bits Conversion of K bits to K+N codewords by encoder (sender) Parity bits (N-K) with code rate given by K/N Medium of message transfer is the channel Original message is obtained by decoding at receiver end

Causes of message transfer errors Noise sources: Spurious noise that corrupt messages/signals (e.g. Thermal noise, cross talk, background noise etc.) Attenuation: reduction in message signals over distances in channel ( due to energy dissipation). Mechanisms for error detection and correction Error detection/correction makes use of basic idea from message transfer concept (processes for encoding and decoding, i.e. parity check codes). Parity check codes –Single parity codes (1 Dimensional) One bit is appended to message bit (K) to form K+1 codewords by encoder Appended bit is the linear summation of message bit (even or odd)

Limitations of Single parity checks –Dectects odd number of bits errors not even ones –Cannot correct any detected errors 2D (Retangular) parity codes –Improvement over 1-D parity check –Resorted to help correct some(1 bit) detected errors –Message transformed in M row *N columns

Strengths of 2D parity codes –Single bit error can be identified and corrected –Bits error up to 3 can be detected Limitation of 2D parity codes –Parity check provides little protection when errors occur in groups. –Reliable mechanisms like CRC under linear codes takes care of the above limitation