Abstract
M.Ing.
In general, error control coding is absolutely necessary for reliable data transmission.
However, the performance of error control codes depends on the statistical structure of the error process on the communication channel. The mobile radio channel, which has been investigated, is subject to path loss effects, a variety of noise effects and interferences and various types of scattering and multipath fading. All these effects contribute to the error processes on the radio channel when transmitting data over it. Any meaningful analytical description of the error process in terms of the characteristics of the individual physical causes of errors are difficult to undertake. Consequently, alternative ways of modelling real communication. channels are being presented. It is more convenient to include the above mentioned perturbations in a discrete inner communication channel consisting of the modem, radio equipment and the mobile radio medium, which are then modelled with a discrete partitioned Markov chain. The partitioned Markov chain inner channel models also give a more accurate description of a real communication channel than does a binary symmetric channel model. However, in order to model a communication channel, the complete statistical structure of the bit error sequence on the channel must be known. In the first instance the memory effective recording of the error sequence of discrete inner communications channels has been considered. This has led to an implementation, where a portable recording system has been developed for mobile .radio channels or any other communication channel with a data rate of up to 4800 bits per second. Programs have been developed to determine all the important statistical distributions which are necessary to be able to model the channel. A channel modelling system has been developed, which fits a channel model to the real channel and then determines the important statistical distributions of the channel model to enable comparison with the real channel. The channel modelling system is versatile and can be used with any future communication system. A number of different mobile VHF and UHF inner channels have been investigated experimentally and the associated discrete models have been developed. In addition to the above mentioned discrete inner communications channels, some "outer channels" have been developed. The "outer channels" comprise of an inner channel and the block error detection, correction and misdetection events, associated with the code words of an error control system. It has been shown that the underlying statistical structure of these events on a discrete renewal inner channel can be represented with outer channel models, i.e. simple partitioned Markov processes, similar to the inner channel models. Analytical procedures to determine the parameters of these outer channel models are being presented. The inner channel parameters and the characteristics of the error control event have been used to develop the outer channel models, i.e. the simple partitioned Markov chains, representing the underlying statistical structure of the block error detection, decoding error in error correction and misdetection (undetected error) events of a block code on the discrete renewal inner channel. Finally it is shown that these outer channel models can be used to evaluate error control codes and systems. Forward-error control and automatic-repeat-request systems have been evaluated and compared with each other.