Signaling Technique for Free Space Optics on the Basis of Bit Error Rate
A new efficient method to implement Orthogonal Frequency Division Multiplexing (OFDM) on Intensity Modulated Direct Detection (IM/DD) channels is presented and termed auto-correlated optical OFDM. It is shown that a necessary and sufficient condition for a band limited periodic signal to be positive for all time is that the frequency coefficients form an autocorrelation sequence. Instead of sending data directly on the subcarriers, the autocorrelation of the complex data sequence is performed before transmission to guarantee non-negativity. In contrast to previous approaches, auto-correlated optical OFDM is able to use the entire bandwidth for data transmission and does not require reserved subcarriers.