Abstract:
Space Time Coding is a communication technique for wireless systems that employs multiple
transmit antennas in addition to multiple receiver antennas. This is becoming a compulsory
technology to reduce the operating region of signal to noise ratios. With the ever increasing
demand for high data rate, these systems need to be implemented under frequency selective
fading conditions, sometimes subject to severe Inter Symbol Interference (ISI). Therefore
finding a means to use the existing Space Time Codes which were originally designed for
frequency nonselective channels is essential. The real usage of these codes depends on the
channel state information available at the receiver side for the decoding. Therefore channel
estimation plays a vital role and finding a better method for channel estimation is an important
problem.
The use of Orthogonal Frequency Division Multiplexing (OFDM) together with Space Time
Codes makes the frequency selective channels frequency nonselective due to the increased
symbol duration of the OFDM symbols. Channel estimation could be done using several
methods. Least Square (LS) Error based channel estimation and Minimum Mean square Error
(MMSE) based channel estimation are some of the available channel estimation methods for
Space Time Coded OFDM systems. MMSE estimation is more complex than LS but superior in
performance.
In this thesis we evaluate the performance and complexity of LS and MMSE channel estimation
methods for Space Time Coded OFDM systems. This also considers the application of MMSE
based channel estimation method to different Space Time Codes with different modulation
schemes. The performance of this channel estimation method and the state of system complexity
in the above mentioned situations were also evaluated. We have also considered a low
complexity Eigen Vector Decomposition based channel estimation method. The performance of
the system was simulated with two transmit and two receive antennas. It has been clearly shown
that the MMSE channel estimation method performs better with higher number of states in the
Space Time Codes and with higher modulation schemes. The Eigen Vector Decomposition base
channel estimation brings a low complexity solution.
