Data communication in the presence of atomospheric noise bursts

Abstract

At tropical latitudes, atmospheric noise bursts constitute an important interference to digital communication. The characteristics of these noise bursts have been extensively studied in the LF, MF and HF bands. Satisfactory information on the time statistics of such bursts is now available in the form of numerical data on level versus time distributions of the 揳ctive� functions - the burst duration and the burst repetition period . An examination of these data indicated the insufficiency of communication techniques such as burst correction coding, and motivated the study of two modes of data transmission for the burst noise channel:

(i) Multiple Transmission Logic The first scheme is based on a multiple transmission logic. The messages are in the form of error detection codes, and every code is transmitted a fixed number of times R. The duration and spacing of these transmissions are designed to maximise the probability that at least one of the R transmissions is unaffected by noise bursts.

(ii) Erasure Logic Using a Null Zone Receiver The second mode of transmission is based on an erasure logic. The technique is to employ a non linear, null zone receiver that restricts decoding failures in the presence of noise bursts essentially to erasures, whose decoding represents a relatively simpler problem.

Techniques under (i) and (ii) are not optimal in that their maximum information rates fall short of the estimated capacity of the channel. However, the proposed schemes are simple, readily implementable, and can be employed on channels without feedback. In view of the current state of the art in communication through channels with memory, these schemes constitute useful modes or bases of binary transmissions, particularly if the burst occupancy / is greater than about 0.1. The multiple transmission logic (i) has the additional advantage of adaptability to a wide range of noise burst statistics.