  This paper investigates the theoretical performance analysis for a subcarrier
multiplexed (SCM) wavelength division multiplexing (WDM) optical transmission
system in presence of optical beat interference (OBI) which occurs during the
photo detection process. We have presented a comparison for improving the
performance of SCM-WDM system in presence of OBI. Non-return-to zero (NRZ),
Manchester and Miller code (MC) line coding are used for performance
investigation of SCM-WDM system. A suitable signal bandwidth is selected and
200 KHz is considered as channel bandwidth. Power spectrum of signal and cross
component for those line coding are analyzed. Comparison results are evaluated
in terms of signal to OBI ratio for the three linecoding schemes which is
called signal to interference ratio (SIR). It is found that there is a
significant increase in the SIR by employing Miller code compared to NRZ and
Manchester for the same data rate. For example, for a number of subcarriers of
10, the achievable SIR is about -24 dB for Miller coded system compared to -46
dB for NRZ coded system and -49 dB for Manchester coded system. The results are
found to be satisfactorily agreed with the expected results.
