Abstract:
Multi input multi output (MIMO) technology is being vastly applied in wireless
communication systems to enhance the rate of data transmission without increasing the
occupied bandwidth. The multipath fading phenomenon is an inevitable source of losses
in wireless communication. Orthogonal frequency division multiplexing (OFDM) is a
multicarrier communication method that has an inherent capability to defy distortions
caused by the fading channel. OFDM therefore is preferred over other single carrier
transmission techniques. The attraction towards MIMO OFDM is ever increasing due to
its efficient communication capabilities.
OFDM is much more sensitive to synchronization errors than single carrier systems.
Mismatch in the carrier frequencies of the transmitter and receiver introduces a frequency
offset which destroys the orthogonality of carriers. Correction of this synchronization
error is necessary otherwise inter carrier interference (ICI) will lead to great losses.
MIMO OFDM suffers in a similar way from this problem. This work proposes a method
for frequency synchronization of MIMO OFDM systems.
The proposed method is an extension of the scheme proposed by Minn. A
synchronization scheme for OFDM has been proposed by Minn. We propose to extend
this method to MIMO OFDM systems. Orthogonal training symbols are required to
achieve this goal. The training symbol used by Minn is spread by orthogonal sequences
obtained from Walsh-Hadamard matrices. This spreading results in a set of orthogonal
training symbols which are simultaneously transmitted. At the receiver the same
orthogonal sequences are used to decode the training symbols. Once the training symbol
has been retrieved the frequency offset is estimated separately at each antenna. The
estimation is completed in two stages. Channel estimation has also been incorporated in
the scheme.
