Constrained coded modulation in the time domain

We describe the application of constrained coded FSK-modulation in the time domain. We combine error correcting codes and Run Length Limited RLL-codes before FSK modulation to obtain a system where we have almost no change in the Power Spectral Density function but a net positive coding gain as for coded modulation invented by Ungerböck. The RLL-code is designed in such a way, that the minimum spacing between two transitions is the same as for the uncoded symbol duration. Furthermore, the RLL-codes have a minimum distance larger than 1 to also allow for soft decision RLL decoding. We give the performance for a Reed-Solomon error correcting code of length 255 symbols of 8 bits. The overall coding gain obtained is about 4 dB.