H.A. Mansour (France), A. Albagul, and A. Diyah (Libya)
Maximum of six words. e.g.. Modelling, simulation, artificial intelligence, and neural networks
This paper presents the results obtained by computer simulations of QPSK modulation in multi-channel systems. The constant envelope property and the relatively high power efficiency of QPSK modulation technique make it suitable for satellite and mobile communications. But when QPSK signal is filtered before a Non-linear device the signal no longer has property of the constant envelope and becomes sensitive to non-linear distortion. When a non-linear device with AM/AM and AM/PM conversions is shared by several channels, the output power of the device is backed-off from saturation to reduce the non-linear distortion. When the transponder TWTA is loaded by multi-carrier signal with up-link noise the characteristic of TWTA will change due to the noise loading. In this paper the net effect of the up-link noise is addressed with a linearization technique for linearizing the TWTA is described and simulated results are presented. This results show that in multi-carrier system good improvement was gained when the system is linearized lower channel spacing and less input back-off.
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