SYNCHRONIZATION OF MULTI INPUT MULTI OUTPUT ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM

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.