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A PROFICIENT PILOT DESIGNING PATTERN FOR CHANNEL ESTIMATION IN MIMO-OFDM SYSTEMS

The high data transmission rates in the communication channel is a recent growing demand which is achieved by using the multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems because of their unique properties.. The OFDM systems that adopt the cyclic-delay diversity (CDD) scheme require only one inverse discrete Fourier transform (IDFT) operation at the transmitter. Hence, the CDD provides a low-complexity by means of increasing the transmission diversity in MIMO-OFDM systems. However, the optimal pilot sequences which minimize the mean square error (MSE) of the channel estimate in traditional MIMO-OFDM systems are inapplicable to CDD-OFDM systems. Thus this paper originates by deriving the criteria which yield the minimum MSE of both the least square (LS) channel estimate and the MMSE channel estimate in CDD-OFDM systems. The derived criteria are then used to develop a general methodology for determining the optimal pilot sequence. Significantly, the proposed design methodology enables the status of the channel to be estimated using single OFDM symbol. We have compared the performances of channel estimation algorithm by measuring bit error rate vs. SNR with BPSK, QPSK 16-PSK and 256-PSK modulation schemes.