Browsing by Author "Mneney, Stanley Henry"

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    A narrowband dominant carrier SCPC satellite for rural information services
    (University of Dar es Salaam, 1987) Mneney, Stanley Henry
    New audio-visual, services and a new communication system for the distribution of information to the rural communities of Third-World countries have been defined and demonstrated. These services can be distributed over narrowband satellite channels at a low space segment rental cost. The baseband system for still picture transmission has been implemented. R dominant carrier in e single channel per carrier frequency division multiple access (SCPC/FDMA) system is selected as the option that can be employed using existing international satellites. The dominant carrier enables the use of low cost receive-only earth stations at the sacrifice of transponder capacity and increased intermodulation distortion. Intermodulation products thus formed result in baseband signal distortion. This thesis presents a theoretical analysis of intermodulation distortion for two types of systems; the equi-amplitude carrier case and a two-level SCPC/FDMA carrier system in the presence of a dominant carrier. Analytical models for the computation of the products at the output of a nonlinear transponder are developed. These models which are in the form of double integrals involving products of Bessel functions are solved to give the peak amplitude at the output of the amplifier, corresponding to the input carriers and the 3rd order intermodulation products. Intermodulation products are grouped according to their constituent frequency components and hence their individual magnitude. Techniques are developed to compute the number of third order products in e carrier slot thus saving computer time. This enables the computation of the resultant peak amplitude voltage. These results are used to determine a frequency assignment that gives a minimum number of inband intermodulation products and hence minimum baseband distortion. Input signal back off reduces the peek amplitude of the output products and hence the resultant peak amplitude of the intermodulation products. In this thesis an optimum back off point is obtained for two systems; the equi-amplitude carrier case and the two level SCPC system necessary with two types of standard earth stations. The system performance can therefore be computed. A practical audio-visual system for rural information services is designed employing the results developed in the theses.