Performance of CPFSK systems with tight IF filtering and optimised delay time

The possibility of using larger delay time values in CPFSK systems with tight IF filtering to improve the bit error rate performance is investigated. The analysis uses a previously developed rigorous model for CPFSK systems with tight IF filtering. It is shown theoretically that a resulting system sensitivity of 36.2 photoelectrons per bit time for a 10^-9 bit error rate can be obtained for a modulation index of 0.8 and that the optimum system can be operated with a laser linewidth that is 0.87 times the linewidth tolerated by a DPSK system with tight IF filtering