Abstract
M.Ing.
The transmission of digital data at higher data rates and greater reliabilities is
becoming increasingly more important in the society of today. The usage of,
especially wireless digital data, is increasing at an alarming rate, and the need
arises for more bandwidth to be made available for this purpose. Hence, the
need arises to optimise and expand the usage of bandwidth currently under
use. Existing wireless channels, such as the commercial FM service, need to
be re-evaluated and unused bandwidth needs to be developed and used as
close to capacity as possible.
In this dissertation, a study was launched to develop the FM SST
(Supplementary Signal Transmission) commercial analog service as a simplex
digital channel that can commercially be used to transmit a myriad of digital
data.
With the help of a commercial FM radio channel, digital data was transmitted
using a number of different modulation schemes to obtain channel
measurements for the FM SST channel. The modulation scheme that
performed the best, given certain criteria, was GMSK. This raw information
was then used to extract first and higher order statistical information from the
channel, in order to parameterise discrete channel models, based on a
Markov process. The channel models that were used were the Gilbert, GilbertElliott
and Fritchman channel models.
These channel models were then tested according to their iirst and higher
order statistical data to evaluate their effectiveness in modelling the error
process on the FM SST channel. It was found that the channel model best
approximating the real channels was the Gilbert channel. Once satisfactory
results were obtained, these discrete channel models were then used to
evaluate various error correction schemes for their ability to correct burst
errors on the FM SST channel. From the various schemes evaluated, a
(63,39) BCH with an interleaver of index 4 was found to perform the best. The
purpose of which is to transmit digital data at the highest data rate possible
and at the same time having a bit error rate less than lxl0-6.