Performance Limits of Multicarrier Based Systems over Fading Channels with Optical Detection

We investigate the performance limits of optical detection of multicarrier modulation over time-variant frequency selective fading channels. We consider general multicarrier architectures where parallel information signals are transmitted through sub-channels that are shaped with the deployment of sub-channel transmit filters. The discrete-time implementation is generally referred to as filtered multitone (FMT) modulation. We first describe the optimum multicarrier detector. Then, we evaluate its performance limits as a function of the design of the sub-channel spacing, the sub-channel transmit filters, the time-variant frequency selective channel impulse response. The optimal detector is applicable to discrete multitone modulation (DMT or OFDM). In such a case, the analysis allows illustrating that conventional detection of OFDM signals, i.e., FFT followed by one-tap equalization, is sub-optimal and that performance gains are available with the proposed optical detector.