Error performance of two decision schemes for frequency‐detector gaussian minimum shift keying (gmsk) on a frequency‐selective fading channel

Abstract

AbstractIn high‐speed digital mobile communication systems, one of the most spectrally efficient modulation methods is Gaussian‐filtered minimum shift keying (GMSK). In this paper, two decision schemes of frequency‐detected GMSK under frequency‐selective fading are compared theoretically from the viewpoint of bit error rate (BER) performances.The GMSK signal which is encoded differentially has an eye pattern with three levels; and, by using the characteristic, the offset decision is made. The BER performances of the offset decision method are compared with those of the conventional one which is based on the eye pattern with two levels.Under the frequency‐selective fading, which is characterized by a two‐ray model, the BER performances for BbT = 0.20 with the offset‐type decision are superior to those with the conventional one when normalized rms delay spread (τ/2T for two‐ray model, τ: delay spread) is less than 0.10.By using the post‐detection selection diversity with two diversity branches, we can reduce the degradation of signal energy per bit to noise power spectral density ratio with the offset decision greater than that with the conventional one for τ/2T < 0.20.