GMSK WITH DIFFERENTIAL PHASE DETECTION IN THE SATELLITE MOBILE CHANNEL - COMMENTS

The error probability results shown in this paper 1 indicate that the error floor is higher for systems with decision feedback (DF). It was concluded there that DF gives a lower error probability only for smaller values of the normalized bandwidth B(t)T of the premodulation Gaussian filter, higher values of the ratio of powers in the direct and diffuse signal components K, and a lower range of signal-to-noise ratio. In this letter we show that this conclusion is not correct by theoretically analyzing the case of the land mobile channel where K = O (or -infinity dB) and deriving a simple closed form expression for the error probability for one-bit differential detection with DF. We show that DF reduces the error probability for all values of B(t)T and signal-to-noise ratios. The derived formula can be easily evaluated not only for Gaussian minimum shift keying (GMSK) but for all partial-response continuous-phase-modulation (PRCPM) signals.