The design of an HF band direct sequence point-to-point link for rural telecommunications.
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Date
2000
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Abstract
The following work documents the design of an HF band direct sequence point-to-point
link as used in a rural environment. The dissertation begins with a description of
the overall document layout. An introduction into the problems associated with
providing rural access is then given, with special emphasis on wireless technologies.
It is argued that the attributes of HF band radio make it a good candidate for providing
wireless communications links for under serviced rural areas in South Africa. The
pitfalls and disadvantages of using an ionospheric-based medium in which to
propagate an electromagnetic wave are discussed and several solutions are put
forward. One of these solutions is Direct Sequence Code Division Multiple Access
(DS-CDMA). A thorough analysis of the principles of DS-CDMA is given with
emphasis on its abilities to combat the negating effects of the HF channel. A CDMA
HF system is then proposed, outlining the various practical and theoretical aspects.
Next, an HF channel model is designed and simulated, first with no spreading or
coding, then with just spreading and finally with spreading and coding. It is found that
although the extra diversity of the spreading and coding aid in reducing the bit error
probability, more detailed local measurements and refinement in the design of the
channel model and simulated system are needed to increase performance. Various
aspects of a practical system that was built are then discussed, highlighting issues
such as hardware interfacing and the software design of a man-machine-interface.
Field measurements are also given with estimates on an upper limit on expected
performance of a practical system. Finally conclusions are given, detailing the
achievements and shortcomings of the research.
Description
Thesis (M.Sc.Eng.)-University of Durban-Westville, 2000.
Keywords
Telecommunications--South Africa., Theses--Electrical engineering.