Automotive FM Diversity Systems, Part I: Propagation Channel Modeling and Multipath Review

This paper represents Part I of a three part series on automotive FM diversity systems. Part I focuses on a review of multipath fading. Part II (2007-01-1732) deals with analog diversity systems which have been developed to combat the effects of this fading in an FM broadcast and Part III (2007-01-1734) discusses new digital implementations of FM diversity systems that have been implemented in DSP algorithms.

This paper reviews propagation channel modeling and multipath. Three cases are studied: Additive white Gaussian noise channel, the Rician channel and the Rayleigh channel. It is further noted that the Rician and Rayleigh channels can be either flat or frequency selective based on the values of the time delays in the reflected signal paths. When the delays are relatively short the channel acts like a wide filter and the fading acts on all spectral components of the signal equally. When the time delays are long the channel acts like a narrow band filter resulting in frequency selective fading.