An eight-channel FDM system using Mach-Zehnder filters with cosine roll-off band-limiting characteristics

An eight-channel FDM system using Mach- Zehnder filters is equalized in order to be band-limited in cosine roll-off characteristics for no inter-symbol interference as an example of a multi-channel FDM system. The linearly equalization method is applied and the channel compensation is split equally between the transmitter and receiver filters. The equalizers consist of adaptively designed finite impulse response filters. The tap coefficients are obtained so as to satisfy the design objective transfer functions originated from both of the cosine roll-off characteristics and the Mach-Zehnder filter characteristics. As a result, the eye is fully open even when the neighboring channel spacing becomes narrow. The inter-symbol interference results in almost zero and the inter-channel interference powers decrease. Thus, the signal to inter-channel interference ratio increases more than 24 dB for the roll-off factor of 0.2.