This paper presents a novel generalized Doppler power spectrum. The expression is useful especially when the scattering propagation is three-dimensional and non-isotropically distributed, which is almost always the case in urban macrocell environments. The generalized Doppler power spectrum includes the well-known U-shaped power spectrum as a special case. This generalized expression helps further investigations on the characteristics of wireless channels. It also assists the research on mobility management for next generation networks.