A common challenge in designing a wireless system is to overcome
the effects of the wireless channel, such as multi-path propagation,
and Inter-symbol Interference. and the ability of OFDM to combat
the effects of multi-path propagation made it th
e modulation of
choice for third and fourth generation networks.
In OFDM system we transmit data symbols on a large number of
subcarriers, and these data symbols exposed to changes in
amplitude and phase, caused of noise and frequency selective
fading and Doppler shift .
To get the transmitted data at the receiver we must cope with these
changes, so we need to know the channel response at every
subcarrier and every symbol, and for that reason we use PILOTS
and we use many methods to estimate the channel response depend
on pilots, and the most important channel is LMMSE Method.
We will discuss in these issue the wiener filtering method
(LMMSE) which give best performance but it is very complicated,
so we will use Discrete Fourier Transform (DFT) to reduce the
complexity of these method and we will study the BER and MSE in
both case when we use QPSK or 16QAM Modulation .
This work aims to analyze the performance of Orthogonal Frequency Division
Multiplexing (OFDM) applied in the fourth generation mobile networks and WiFi. Fuzzy
logic technique is used in this study to analyze the problem of OFDM, taking into
consi
deration the modulation techniques applied in OFDM. Three input parameters in the
fuzzy logic system are mainly considered: signal-to-noise ratio, the modulation degree and
the number of sub-carriers. The output parameters are selected to be the bandwidth and bit
error rate. This requires an analytical study to determine the optimal values of the input
parameters used in this study. This means studying the membership of functions of each
input and output parameter using fuzzy logic.
Theoretical calculations using density functional theory (DFT) both on semi
empirical and Ab initio levels have been carried out for pyrromethene laser
dye and related compounds (PM-chromophore, PM-4m, PM 546, PM650 PM
567 and PM597). We carried o
ut theoretical calculations using DFT, AM1, TDDFT
and CIS on ground and excited states for the selected laser dye materials,
we obtained the optimized geometry of the molecules, UV, IR spectrum, and
the transition between the ground S0 and the first excited S1 states exclusively,
the HOMO and LUMO states and other properties.
In this work, theoretical calculation of the ground and excited state of
coumarin compounds are performed using DFT-B3LYP and CIS methods with
6-31G basis set. IR spectrum, UV/Vis spectrum, molecular orbitals and energy
gap are calculated. We use
different solvents ethanol, methanol, water,
acetonitrile (ACN), dimethyl sulfoxide (DMSO), acetone, and dichloromethane
to compare values of UV/Vis absorption spectra. Then the calculated results are
compared with the experimental values.
