Coding performance on satellite channels using AX.25 protocol

Abstract

A form of data transmission which is increasing in popularity is satellite communication. In order to insure that data is received correctly, certain error control strategies are employed. In packetized transmission, automatic-repeat-request (ARQ) schemes and error correcting codes have been employed. Currently a combination of both is not employed by the AX.25 protocol. The purpose of this project is to determine which error correcting code should be combined with ARQ to provide the optimum performance.

This project investigates the performance of the (7,4) Hamming code, (23,12) Golay code, Reed-Solomon, RS , codes over the Galois fields of 16, GF(16), and 256, GF(256), elements, and common rate convolutional codes of various constraint lengths. The codes are evaluated on three primary criteria, which include: throughput vs. input bit error rate, coding complexity, and burst error performance.

The class of Reed-Solomon codes over GF(256) was chosen to be superior due to the throughput and burst error performance. The encoding complexity is small, but the decoding is more complicated. The conclusion is that error correcting codes should be employed in ARQ satellite systems. However, the error correcting strength of the code must be determined by observing the channel characteristics.