||Although linear modulation schemes can achieve high spectrum|
efficiency,the nonlinearity of the transmitter power amplifier
tends to spread the spectrum. Thus, it eliminates any spectrum
efficiency advantage gained throughthe use of linear modulation
schemes. This thesis discusses the systemperformance degradation
resulting from using a nonlinear transmitter power amplifier.
Three modulation schemes (pi/4-DQPSK, DQPSK, and GMSK)
areconsidered and simulated. The closed expression (AM-to-AM and
AM-to-PMconversions) of TWTA is used to model the transmitter
power amplifier. Thespectral regrowth due to nonlinearity of
power amplifier is discussed. Simulation results are represented
for AWGN, Rayleigh flat fading, and Rayleigh frequency selective
fading environments. After knowing how the effectsof
nonlinearity affect systems, we can design the compensation
circuits to reducethe impairment in the future.