Abstract:
Orthogonal frequency division multiplexing (OFDM) has been the most widely
used multicarrier in recent mobile communication system due to its multiple ad vantages like high spectral efficiency, high data rate transmission over a multipath
fading channel, simple implementation, and low receiver complexity. Currently,
multiple-input multiple-output (MIMO) is combined with OFDM to boost spectral
efficiency, work in a frequency selective environment, and enhance link reliability.
Besides those crucial advantages, MIMO-OFDM system suffers from a high peak to-average power ratio (PAPR) that originates from the superimposition of the
number of sub-carriers with random amplitudes and phases. This high PAPR re sults in high power consumption by the power amplifier and high complexity in
the design of analog to digital converter.
In this thesis work, modified clipping based PAPR reduction technique has been
designed for MIMO-OFDM system and it is integrated with turbo channel coding
scheme. In modified clipping method the MIMO-OFDM signal in each transmitter
antenna has been clipped into different threshold values using a settle quantiza tion levels, step size value and number of clipped high peak envelope signals as
parameters. A powerful turbo channel coding enables to reduce the clipping and
channel fading distortion with the aids of iterative decoding using space-time block
code (STBC) bit-wise soft detection values as input. This allows to achieve better
bit error rate (BER) performance. The PAPR and BER of the turbo code based
modified clipping STBC MIMO-OFDM have been verified using Matlab software
for the selected numerical values of modified clipping parameters. In addition, the
designed modified clipping performance has been compared to the conventional
clipping performance using PAPR and BER metrics.
The simulation result demonstrated that the modified clipping having compa rable PAPR performance to that of the conventional clipping has better BER
performance. Using modified clipping method having 25% of clipped high peak
envelopes, 5 quantization levels, and 0.05 step size with 1/3 rate turbo code the
PAPR performance can improve by 69.09%, 71.05%, and 72.65% for a sequential
sub-carrier length of 128, 256, and 512 over its respective original PAPR perfor mances. Under those modified clipping parameters value with different turbo code
iteration the remarkable bit energy to noise power spectral density ratio Eb/N0
gain has been obtained at a given BER value
