Abstract
In this thesis the system performances of M-ary differential phase shift keying (DPSK)
with limiter discriminator detector (LDD) and differential phase detector (DPD) are
investigated. The average error probability for DPSK-LDD and DPSK-DPD is evaluated in
the additive white Gaussian noise (AWGN) channel and fading channels which include the
satellite mobile channel (Rician) and the land mobile channel (Rayleigh).
The systems analysed in this thesis are narrow-band systems which use Nyquist filters
as the system filters. The time domain representation of the signal is derived for the system.
Non-coherent detection methods; limiter discrimination detection and differential phase
detection are analysed. In the DPSK-LDD system there is intersymbol interference (ISI) at
the optimum sampling time. We can use the roll-off (3 of the Nyquist filter to reduce the
effect of ISI by increasing the value of (3.
Expressions for the error probability of DPSK-LDD and DPSK-DPD are derived. The
average error probability for binary, quaternary and octal symbols is computed as a function
of various parameters such as energy to noise ratio, time delay, Doppler frequency shift and
roll-off (3 of the Nyquist filters.
In the DPSK-LDD system the best sampling time has a shift of T/2 (T is the symbol
duration) from the point at which DPSK-DPD samples are optimal. The error probability
for DPSK-LDD fluctuates against time delay for small value of the time delay while for
DPSK-DPD it increases with time delay. In the presence of Doppler frequency shift the
DPSK-LDD system performs better than the DPSK-DPD system. In the absence of Doppler
frequency shift the DPSK-DPD system gives a lower error probability than the DPSK-LDD
system. The error probability for both DPSK-LDD and DPSK-DPD decreases with
increasing K (the ratio of energy in specular and diffuse components), energy to noise ratio
and (3 and the error probability increases with increasing Doppler frequency shift and the
number of symbols.