Interchannel interference considerations in angle-modulated systems

This paper considers the deterioration in performance of angle-modulated systems resulting from interchannel interference. We show that with band-limited white gaussian noise modulation (simulating modulation by a frequency division multiplex signal), we can derive an explicit expression for the spectral density of the baseband interchannel interference when two or more PM waves interfere with each other. We show that, if the interference is co-channel, maximum interference occurs at the lowest baseband frequency present in the system and we can derive upper and lower bounds to this minimum baseband signal-to-interference ratio. For high enough modulation index, we show that this minimum signal-to-interference ratio is proportional to the cube of the modulation index and that phase modulation can be used with advantage in interference limited systems. We do not consider the effects of linear filters on angle-modulated systems, but give some results about the effect of adjacent channel interference when the interference is in the passband of the receiver.