| Mobile to Mobile (Mobile to Mobile, M2M) communication system is a kind of peer to peer wireless communication. The Doppler shift is inevitable in the M2M channels. The Doppler frequency will become relativly high if both of the terminals move fast, and it will affect the symbol error rate of signal transmission. Thus, it is of great significance to study the doppler shift.The Doppler spectra for M2M communications are summarized for a ring, a disk and an elliptical geometry-based stochastic scattering models. The autocorrelation function (ACF) and power spectrum density (PSD) are derived and investigated for vehicle-to-vehicle (V2V) propagation scenarios where the local scatterers are moving in any direction with random velocity at the predefined geometries of the models. The velocity distributions of the scattterers are assumed to follow exponential and mixed Gaussian for low-and high-speed scatterers, respectively. Since the analytical expressions of V2V channel model are of general applicability, several communication scenarios such as V2V communications with low-and high-speed moving scatterers, fixed-to-fixed (F2F) communications withfixed scatterers can be derived. It is simulated by the integral function of Matlab in this paper.The scatterer distributions affect the ACFs and PSDs significantly when the transceiver vehicles move relatively fast compared to the mean velocity of the scatterers. However, the distribution of scatterers is not so critical when the mean velocity of the scatterers is relatively faster than the vehicle speed at transceiver in the V2V propagation scenarios. Moreover, different shape factors have little effect on the ACFs and PSDs in the disk model. As the shape factor is large enough, the UDSM tends to be as the one-ring model. In the disk model, the scatterers distributions except rayleigh distribution have the same effect on the ACF for low-speed scatterers.In the F2F propagation, The ACFs and PSDs of one-ring model and disk model for different scatterers distributions are same as [26] when the eccentricity of ellipse is 0.25. The ACFs and PSDs of one-ring, disk and UDSM are almost same either with low-or high-speed scatterers. However, the ACFs and PSDs will change when the eccentricity of ellipse changes. In the other models, the ACFs and PSDs have no change as the distance between Tx and Rx changes. Because the scatterers surround not only the Rx but the Tx in the elliptical model. |
