Error probabilities of optical heterodyne OOK and FSK communications systems

An error probability analysis is performed for two types of optical communications systems employing spread-spectrum code-division multiple-access (CDMA) techniques. Spread-spectrum is specifically employed to overcome additive noise and increase system user capacity. The two types of systems considered are a coherent optical heterodyne on-off keying (OOK) system using optical orthogonal spreading code sequences (OOCs), and a coherent optical heterodyne frequency shift keying (FSK) system using random spreading codes. The OOK system spreads the signal optically, and the FSK system spreads the signal electromagnetically before converting it to an optical signal for transmission. System performance is degraded by laser phase noise, additive Gaussian multiuser interference, and additive Gaussian receiver noise