M.Sc.

Speech security is an important aim for users of many speech communication systems. Speech scramblers are gaining widespread acceptance as a means of enhancing protection in both military and civilian applications. Therefore, there is an increasing interest in speech scramblers due to the desire for secure speech communication over existing telephone channels with standard telephone bandwidth at acceptable speech quality and reasonable cost. In this thesis, different types of scrambling systems in different domains are presented.

This thesis is concerned with the data transmission over a mobile radio channel, which is characterized a by multipath propagation with a Rayleigh fading at 900 MHz, for different Doppler frequencies. The work introduces software radio receiver design and simulation. It then attempts to develop the software radio receiver over a mobile radio channel. Many techniques were used to improve the performance of the data transmission like equalization and diversity. An adaptive equalizer is used in this work to reduce the effect of intersymbol interference (ISI).

In this work the electrical properties of the locally produced MOS devices are investigated. For this purpose, simple MOS capacitor is used. The oxide in this structure was prepared by the thermal oxidation technique. MOS capacitors are used for its simple fabrication and analysis. The important parameters which affect the MOS device performance and stability are mobile impurities, oxide charge and interface states density which are described in details in the present work.