Coefficients separation MIMO-OFDM optical wireless communication system in diffuse fading channels

In indoor optical wireless communication systems with intensity modulation (IM) and direct detection (DD), diffuse links could be established through reflecting. For such a case, line-of-sight does not exist between the transmitter and receiver, and the channel delay spread will be large. The dispersion of the channel might cause inter-symbol interference. Also, the transmitted signal must be nonnegative. Thus most modulation schemes for radio communications cannot be used directly for such a system. This paper develops a new multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) IM/DD systems: real and imaginary coefficients separation (RIS) system. Two transmit data streams require only one inverse fast Fourier transform (IFFT) block, resulting in a low computational complexity. Compared with traditional OFDM based schemes, the RIS scheme achieves a better BER performance and requires fewer IFFT blocks at the transmitter. The transmitter architecture and receiver algorithm are analyzed in detail. BER performance and simulation results are provided.