Influence of if narrow‐band filtering on bit error rates in coherent optical heterodyne CPFSK receiver using variable delay demodulation

Abstract

AbstractIn this article we discuss a coherent optical heterodyne CPFSK receiver using optimum variable delay demodulation considering the effect of narrow‐band IF filtering or intersymbol interference (ISI) caused by it. First we investigate the error probability at the normalized bandwidth of IF filter BT = 1 for a Gaussian IF filter. Numerical results show that the impact of narrow‐band IF filtering increases with an increase in normalized IF spectral linewidth ΔvT and a decrease in modulation index h. Second, in order to decrease the impact of ISI, the optimum BT values are determined, which can minimize the error probability for given SNR. If a Gaussian IF filter is used, the optimal BT values are 1.3 for ΔvT = 0.25%, 1.4 for ΔvT = 0.5% at h = 0.5, 1.2 for ΔvT = 0.25%, 1.4 for ΔvT = 0.5% at h = 0.7, and 1.2 for all ΔvT ≤ 0.5% at h = 1. Finally, the performance of an optimal receiver employing optimum Gaussian IF filter is studied. We know that h = 1 is optimum and ΔvT ≤ 0.5% is necessary for 1‐dB EB/N0 penalty per bit at BER of 10−9. © 1992 John Wiley & Sons, Inc.