Walter, M., D. Shutin, M. Schmidhammer, D. W. Matolak, and A. Zajic. 2020. “Geometric Analysis of the Doppler Frequency for General Non-Stationary 3D Mobile-to-Mobile Channels Based on Prolate Spheroidal Coordinates”. IEEE Trans. Vehicular Tech. vol 69 (no. 10): 10419-34.