Spectral characteristics of multilevel digital pulse interval modulation in optical wireless communication

To investigate spectral characteristics of multilevel digital pulse interval modulation (MDPIM) signal, a detailed derivation of it's power spectral density is presented. This mathematical model showed that the spectral profile contains a DC component, nulls at even multiples of the slot frequency, and a distinct slot component with its harmonics, which offers a simpler implementation with slot-synchronization. The DC component of MDPIM does not approach zero, so it is susceptible to the effects of baseline wander, but for certain bit resolution, a desirable DC level is achievable. The presented work offers considerations when designing pre-filter, synchronizer, and equalizer in receiver.