Delay diversity for correlated MIMO channel

Although uncorrelated channels are commonly assumed in cyclic delay diversity (CDD) based multiple input and multiple output (MIMO) orthogonal frequency division mutiplexing (OFDM) systems, correlated channels can evolve due to closeness of antennas or lack of scatterers in the environment. To mitigate the correlation effect, a random continuous phase offset is induced into the transmitting symbols. In a correlated channel the random phase offset scheme provides all the OFDM symbols the same average received power as offered by the uncorrelated channel. Our numerical results demonstrate that depending on the channel spatial correlation, the random phase offset scheme is capable of yielding a dramatic performance improvement of CDD based MIMO-OFDM systems. A modified scheme with random binary phase offset is also introduced that yields almost identical performance as the continuous phase offset scheme yet with a simpler implementation.