AM/OFDM versus AM/QAM for mixed analog/digital subcarrier multiplexed lightwave transmission

Hybrid multichannel AM/QAM subcarrier multiplexed (SCM) lightwave systems are attractive for mixed analog/digital video-data transport over hybrid fiber/coax (HFC) networks. In this paper we show that significant bit-error-rate (BER) improvements can be obtained using AM/OFDM (orthogonal frequency division multiplexing) vis-a-vis AM/QAM, when corrupted by both clipping-impulse and Gaussian noise. It is shown that the clipping effect on the BER of an OFDM signal can be negligible for a large range of laser optical modulation depths, and therefore, virtually no limit is imposed on the channel capacity. It is further shown that OFDM introduces little effect on the analog AM channels, as opposed to use of QAM systems.