Abstract: In this paper, based on the joint theoretical and experimental research on indoor device-to-device (D2D) radio channels, the signal amplitude and Doppler spectra distributions in D2D indoor radio channels are investigated. The results show that the signal amplitude follows single, double, and multiple Rayleigh distributions at different indoor scenarios. Different distributions of the angle-of-arrivals (AoAs) in the azimuth and elevation planes can result in different Doppler spectrum distributions in 2D and 3D scattering environments. The correctness of the theoretical results is tested with the experimental results.