A novel signal modulation technique, termed optical OFDM-based carrierless amplitude and phase (CAP) modulation (OOFDM-CAP) is proposed, analyzed and evaluated, for the first time, in which multiple real-valued OFDM channels are multiplexed/demultiplexed using digital orthogonal filters embedded in DSP logic. An OOFDM-CAP theoretical model is established, based on which the dependence of the required minimum oversampling factor upon the total number of OFDM channels simultaneously transmitted is identified in simple SSMF systems utilizing intensity modulation and direct detection. In such a system consisting of two OFDM channels, detailed numerical explorations are also undertaken of the impacts of major transceiver design aspects on the OOFDM-CAP transmission performance. These aspects include digital orthogonal filter characteristics, oversampling factors and OOFDM adaptability. It is shown that OOFDM-CAP not only allows the utilization of a minimum oversampling factor as low as 2, but also overcomes all fundamental limitations associated with conventional CAP modulation.
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