Evaluation of different 4x4 Coded MIMO System

Thuraya Mahmood Qaradaghi1 & Diana Hayder Hussein1

1College of Engineering/ Electrical Engineering Department , Salahaddin University/ Hawler (Arbil), Kurdistan Region – Iraq

In this paper 4x4 coded MIMO-OFDM systems with two different code rate OSTBC
(1/2 and 3/4) and different types of QAM as a baseband modulation have been studied,
and compared with a 4x2 coded MIMO system. The system has been evaluated over a
multipath flat-fading and frequency-selective fading, assuming channels with non line of
sight (NLOS). Three different Doppler frequencies (5, 50 and 100 Hz) have been used to
study the systems in different channel situations. The results shows that increasing the
number of antennas at the receiver side reduce the effect of the Doppler shift, because
increasing the number of antennas means increasing the number of channels, and
transmitting the symbols through these channels in different times. OSTBC with two
different code rate (R=1/2 and 3/4) have been used with 4 transmitting antennas, and
OSTBC with R= 1/2 gives a better results than the one with R= 3/4, because when R=3/4
three symbols are send during 4 time slots, but when R=1/2 just two symbols are send
during four time slots. That is beside sending multi-copies of each symbol in different
time and different space

Key Words: MIMO, OFDM, OSTBC, Rayleigh Channel 

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